Dissertations / Theses on the topic 'Flexural behaviour'

This report presents the results of a laboratory investigation of the influence of the corrosion process on the flexural capacity such as strength, deflection and steel and concrete strains in reinforced concrete beams. Examination of the behaviour of crack development was also examined.<br>Fourteen simply supported concrete beams were cast and subjected to two third point concentrated loads, increased monotonically until failure. The strength, strain and crack development data were recorded to assess the corrosion rate and its effect on the steel bars.<br>An electrochemical system was used to achieve the different corrosion levels. The specimens were immersed in a 5 percent of sodium chloride by weight of water for a period of one to thirty weeks. An initial voltage of 1 volt was impressed through the beams to initiate and to accelerate the corrosion process. A steel plate was immersed in the solution to act as a cathode and force the steel reinforced concrete beam to act as an anode.<br>The report discusses the defects and environmental factors influencing the corrosion process. (Abstract shortened by UMI.)

The design of fibre reinforced polymer (FRP) reinforced concrete (RC) can often be governed by the serviceability limit state of deflection. Currently, the evaluation of short-term deflection of FRP RC is undertaken using radically different approaches, in both research and codes of practice. This study investigates the short-term deflection behaviour of FRP RC, both experimentally and analytically, and examines the merits of those different approaches. Experimentally, 28 RC beams and slabs with glass, carbon or steel rebars are tested under four-point loading. The main variables considered are the reinforcement ratio, modulus of elasticity and bond. In addition to measuring deflections, closely-spaced strain gauges are used to measure rebar strains between one forced crack at midspan and two naturally-occurring cracks on either side. This setup enables the investigation of rebar strains, tension stiffening and bond between flexural cracks. Furthermore, in connection with concrete strains at the extreme compressive concrete fibre, the flexural load-curvature relationship is evaluated experimentally and used to decompose the total deflection into flexural and shear-induced deflections. Analytically two numerical analysis methods are used to provide further insight into the experimental results. Finite element analysis with smeared modelling of cracks is used to predict and examine the stress-displacement response in detail. Cracked section analysis is used to provide upper-bound deflections and strains. This study also deals with the ACI and Eurocode 2 approaches for prediction of short- term deflection. The deflection prediction and tension stiffening expressions of these codes are evaluated against the experimental results of this and other studies. The main conclusion is that deflection of FRP RC is essentially due to flexural curvatures, and can be reasonably evaluated by the tension stiffening model of Eurocode 2. However, with reinforcement of relatively low axial stiffness, and depending on the reinforcement bond characteristics, shear-induced deformations become significant and may need to be evaluated.

This thesis has investigated the application of CFRP and GFRP bars as longitudinal reinforcement for continuously supported concrete beams. Two series of simply and continuously supported CFRP and GFRP reinforced concrete beams were tested in flexure. In addition, a continuously supported steel reinforced concrete beam was tested for comparison purposes. The FRP reinforced concrete continuous beams were reinforced in a way to accomplish three possible reinforcement combinations at the top and bottom layers of such continuous beams. The experimental results revealed that over-reinforcing the bottom layer of either the simply or continuously supported FRP beams is a key factor in controlling the width and propagation of cracks, enhancing the load capacity, and reducing the deflection of such beams. However, continuous concrete beams reinforced with CFRP bars exhibited a remarkable wide crack over the middle support that significantly influenced their behaviour. The ACI 440.1R-06 equations have been validated against experimental results of beams tested. Comparisons between experimental results and those obtained from simplified methods proposed by the ACI 440 Committee show that ACI 440.1R-06 equations can reasonably predict the load capacity and deflection of the simply and continuously supported GFRP reinforced concrete beams tested. However, The potential capabilities of these equations for predicting the load capacity and deflection of continuous CFRP reinforced concrete beams have, however, been adversely affected by the de-bonding of top CFRP bars from concrete. An analytical technique, which presents an iterative procedure based on satisfying force equilibrium and deformation compatibility conditions, has been introduced in this research. This technique developed a computer program to investigate flexural behaviour in particular the flexural strength and deflection of simple and continuously supported FRP reinforced concrete beams. The analytical modelling program has been compared against different prediction methods, namely ACI 440, the bilinear method, mean moment inertia method and Benmokrane's method. This comparison revealed the reliability of this programme in producing more enhanced results in predicting the behaviour of the FRP reinforced beams more than the above stated methods.

The flexural capacity of the new hollow flange steel section known as LiteSteel beam (LSB) is limited by lateral distortional buckling for intermediate spans, which is characterised by simultaneous lateral deflection, twist and web distortion. Recent research based on finite element analysis and testing has developed design rules for the member capacity of LiteSteel beams subject to this unique lateral distortional buckling. These design rules are limited to a uniform bending moment distribution. However, uniform bending moment conditions rarely exist in practice despite being considered as the worst case due to uniform yielding across the span. Loading position or load height is also known to have significant effects on the lateral buckling strength of beams. Therefore it is important to include the effects of these loading conditions in the assessment of LSB member capacities. Many steel design codes have adopted equivalent uniform moment distribution and load height factors for this purpose. But they were derived mostly based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. In contrast LSBs are made of high strength steel and have a unique crosssection with specific residual stresses and geometrical imperfections along with a unique lateral distortional buckling mode. The moment distribution and load height effects for LSBs, and the suitability of the current steel design code methods to accommodate these effects for LSBs are not yet known. The research study presented in this thesis was therefore undertaken to investigate the effects of nonuniform moment distribution and load height on the lateral buckling strength of simply supported and cantilever LSBs. Finite element analyses of LSBs subject to lateral buckling formed the main component of this study. As the first step the original finite element model used to develop the current LSB design rules for uniform moment was improved to eliminate some of the modelling inaccuracies. The modified finite element model was validated using the elastic buckling analysis results from well established finite strip analysis programs. It was used to review the current LSB design curve for uniform moment distribution, based on which appropriate recommendations were made. The modified finite element model was further modified to simulate various loading and support configurations and used to investigate the effects of many commonly used moment distributions and load height for both simply supported and cantilever LSBs. The results were compared with the predictions based on the current steel code design rules. Based on these comparisons, appropriate recommendations were made on the suitability of the current steel code design methods. New design recommendations were made for LSBs subjected to non-uniform moment distributions and varying load positions. A number of LSB experiments was also undertaken to confirm the results of finite element analysis study. In summary the research reported in this thesis has developed an improved finite element model that can be used to investigate the buckling behaviour of LSBs for the purpose of developing design rules. It has increased the understanding and knowledge of simply supported and cantilever LSBs subject to non-uniform moment distributions and load height effects. Finally it has proposed suitable design rules for LSBs in the form of equations and factors within the current steel code design provisions. All of these advances have thus further enhanced the economical and safe design of LSBs.

The flexural capacity of the new hollow flange steel section known as LiteSteel beam (LSB) is limited by lateral distortional buckling for intermediate spans, which is characterised by simultaneous lateral deflection, twist and web distortion. Recent research based on finite element analysis and testing has developed design rules for the member capacity of LiteSteel beams subject to this unique lateral distortional buckling. These design rules are limited to a uniform bending moment distribution. However, uniform bending moment conditions rarely exist in practice despite being considered as the worst case due to uniform yielding across the span. Loading position or load height is also known to have significant effects on the lateral buckling strength of beams. Therefore it is important to include the effects of these loading conditions in the assessment of LSB member capacities. Many steel design codes have adopted equivalent uniform moment distribution and load height factors for this purpose. But they were derived mostly based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. In contrast LSBs are made of high strength steel and have a unique crosssection with specific residual stresses and geometrical imperfections along with a unique lateral distortional buckling mode. The moment distribution and load height effects for LSBs, and the suitability of the current steel design code methods to accommodate these effects for LSBs are not yet known. The research study presented in this thesis was therefore undertaken to investigate the effects of nonuniform moment distribution and load height on the lateral buckling strength of simply supported and cantilever LSBs. Finite element analyses of LSBs subject to lateral buckling formed the main component of this study. As the first step the original finite element model used to develop the current LSB design rules for uniform moment was improved to eliminate some of the modelling inaccuracies. The modified finite element model was validated using the elastic buckling analysis results from well established finite strip analysis programs. It was used to review the current LSB design curve for uniform moment distribution, based on which appropriate recommendations were made. The modified finite element model was further modified to simulate various loading and support configurations and used to investigate the effects of many commonly used moment distributions and load height for both simply supported and cantilever LSBs. The results were compared with the predictions based on the current steel code design rules. Based on these comparisons, appropriate recommendations were made on the suitability of the current steel code design methods. New design recommendations were made for LSBs subjected to non-uniform moment distributions and varying load positions. A number of LSB experiments was also undertaken to confirm the results of finite element analysis study. In summary the research reported in this thesis has developed an improved finite element model that can be used to investigate the buckling behaviour of LSBs for the purpose of developing design rules. It has increased the understanding and knowledge of simply supported and cantilever LSBs subject to non-uniform moment distributions and load height effects. Finally it has proposed suitable design rules for LSBs in the form of equations and factors within the current steel code design provisions. All of these advances have thus further enhanced the economical and safe design of LSBs.

Sandwich panels m Australia commonly consist of steel faces and expanded polystyrene cores. The use of sandwich panels in buildings became popular in Europe and the USA in the 1970s, however, their use has been mainly confined to coldstorage buildings in Australia due to the relatively low demand for the product. The utilisation of sandwich panels however has been increasing in recent times, particularly as roof and wall cladding systems in buildings. This has led to this collaborative project with the leading Australian manufacturer of sandwich panels, James Hardie Building Systems. The European Recommendations for Sandwich Panels is one of the few documents (i.e., standards) available for the design and testing of sandwich panels. It reflects the interests of members of the working group that produced the document and therefore is predominantly concerned with panels with metal faces and polyurethane or polyisocyanurate core materials. In these panels the core is foamed in-situ. In this process of production the faces adhere naturally to the core without the need for any additional layer of adhesive. In Australia, expanded polystyrene is commonly used as the core material introducing several new considerations. These are the adhesive bond, and the presence of transverse joints in the foam core. The main objectives of this research project were to investigate sandwich panels which contain transverse joints and the increase in wrinkling capacity of lightly profiled panels over flat panels. An extensive experimental and finite element investigation has been carried out to determine the effects which transverse joints of the foam core and lightly profiled faces have on the wrinkling capacity of sandwich panels. It has been found that transverse joints are a source of weakness in a sandwich panel and that lightly profiled panels have the potential to provide an increase in wrinkling capacity compared with flat panels.

The LiteSteel Beam (LSB) is a new hollow flange channel section developed by OneSteel Australian Tube Mills using a patented Dual Electric Resistance Welding technique. The LSB has a unique geometry consisting of torsionally rigid rectangular hollow flanges and a relatively slender web. It is commonly used as rafters, floor joists and bearers and roof beams in residential, industrial and commercial buildings. It is on average 40% lighter than traditional hot-rolled steel beams of equivalent performance. The LSB flexural members are subjected to a relatively new Lateral Distortional Buckling mode, which reduces the member moment capacity. Unlike the commonly observed lateral torsional buckling of steel beams, lateral distortional buckling of LSBs is characterised by simultaneous lateral deflection, twist and web distortion. Current member moment capacity design rules for lateral distortional buckling in AS/NZS 4600 (SA, 2005) do not include the effect of section geometry of hollow flange beams although its effect is considered to be important. Therefore detailed experimental and finite element analyses (FEA) were carried out to investigate the lateral distortional buckling behaviour of LSBs including the effect of section geometry. The results showed that the current design rules in AS/NZS 4600 (SA, 2005) are over-conservative in the inelastic lateral buckling region. New improved design rules were therefore developed for LSBs based on both FEA and experimental results. A geometrical parameter (K) defined as the ratio of the flange torsional rigidity to the major axis flexural rigidity of the web (GJf/EIxweb) was identified as the critical parameter affecting the lateral distortional buckling of hollow flange beams. The effect of section geometry was then included in the new design rules using the new parameter (K). The new design rule developed by including this parameter was found to be accurate in calculating the member moment capacities of not only LSBs, but also other types of hollow flange steel beams such as Hollow Flange Beams (HFBs), Monosymmetric Hollow Flange Beams (MHFBs) and Rectangular Hollow Flange Beams (RHFBs). The inelastic reserve bending capacity of LSBs has not been investigated yet although the section moment capacity tests of LSBs in the past revealed that inelastic reserve bending capacity is present in LSBs. However, the Australian and American cold-formed steel design codes limit them to the first yield moment. Therefore both experimental and FEA were carried out to investigate the section moment capacity behaviour of LSBs. A comparison of the section moment capacity results from FEA, experiments and current cold-formed steel design codes showed that compact and non-compact LSB sections classified based on AS 4100 (SA, 1998) have some inelastic reserve capacity while slender LSBs do not have any inelastic reserve capacity beyond their first yield moment. It was found that Shifferaw and Schafer’s (2008) proposed equations and Eurocode 3 Part 1.3 (ECS, 2006) design equations can be used to include the inelastic bending capacities of compact and non-compact LSBs in design. As a simple design approach, the section moment capacity of compact LSB sections can be taken as 1.10 times their first yield moment while it is the first yield moment for non-compact sections. For slender LSB sections, current cold-formed steel codes can be used to predict their section moment capacities. It was believed that the use of transverse web stiffeners could improve the lateral distortional buckling moment capacities of LSBs. However, currently there are no design equations to predict the elastic lateral distortional buckling and member moment capacities of LSBs with web stiffeners under uniform moment conditions. Therefore, a detailed study was conducted using FEA to simulate both experimental and ideal conditions of LSB flexural members. It was shown that the use of 3 to 5 mm steel plate stiffeners welded or screwed to the inner faces of the top and bottom flanges of LSBs at third span points and supports provided an optimum web stiffener arrangement. Suitable design rules were developed to calculate the improved elastic buckling and ultimate moment capacities of LSBs with these optimum web stiffeners. A design rule using the geometrical parameter K was also developed to improve the accuracy of ultimate moment capacity predictions. This thesis presents the details and results of the experimental and numerical studies of the section and member moment capacities of LSBs conducted in this research. It includes the recommendations made regarding the accuracy of current design rules as well as the new design rules for lateral distortional buckling. The new design rules include the effects of section geometry of hollow flange steel beams. This thesis also developed a method of using web stiffeners to reduce the lateral distortional buckling effects, and associated design rules to calculate the improved moment capacities.

Aluminium foam has a range of properties that are desirable in many applications. These properties include good stiffness and strength to weight ratios, impact energy absorption, sound damping, thermal insulation and non combustibility. Many of these characteristics are particularly attractive for core materials within sandwich structures. The combination of aluminium foam cores with thermoplastic composite skins is easily manufactured and has good potential as a multifunctional sandwich structure useful in a range of applications. This thesis has investigated the flexural behaviour of such structures using a combination of experimental and modelling techniques. The development of these structures towards commercial use requires a thorough understanding of the deformation and strain mechanisms of the structure, and this will, in turn, allow predictions of their structural behaviour in a variety of loading conditions. ¶ The experimental research involved the use of an advanced 3D optical measuring technique that produces realtime, full-field strain evolution during loading. This experimental characterisation of strain evolution in this class of sandwich structure under flexural loading is the first of its kind in the world. The experimental work studied the sandwich structure undergoing four-point bend testing. Initial studies compared the behaviour of the aluminium foam structure with a more traditional polymer foam sandwich structure. The aluminium foam structure was found to have equivalent or improved mechanical properties including more ductile deformation and an enhanced energy absorption. An investigation was conducted on the effect of core and skin thickness on the metal structure and a range of flexural behaviours were observed. Analysis of the strain distribution showed a complex development including localised effects from the non-uniform cellular structure of the material. An understanding of the variation with size is important in establishing design methods for utilising these structures. In particular, it is desirable that finite element simulations can be used to predict behaviour of these structures in a diverse range of loading conditions. This aspect was considered in the second half of this study. An existing constitutive model for aluminium foam, developed for use in compression energy absorption studies, was used to investigate finite element simulations of the flexural behaviour of the sandwich structure. The FE model was able to predict the general deformation behaviour of the thinner skinned structures although the magnitude of the load-displacement response was underestimated. It is suggested this may be related to the size effect on the input parameter characterisation. The strain distribution corresponded well with the experimental strain measurements. It was found a simple increase in the material model input parameters was able to more closely match the magnitude of the load-displacement response while maintaining the appropriate strain distribution. The general deformation shape of the model with the thicker skin corresponded reasonably well with the experimental observations. However, further work is necessary on the element failure criterion to capture the shear cracking observed. The strain distributions of the model predicted this failure with high strain concentrations matching those of the experimental contours. The last part of the thesis describes a parametric study on the effect of the foam material model input parameters on the flexural behaviour of the sandwich structure model. An important conclusion of this work is that this material model for aluminium foam can, with some development, be utilized to provide a viable method for simulating aluminium foam composite sandwich structures in flexural loading situations.

Design of fibreglass composite sheet pile seawalls is traditionally based on the flexural rigidity (EI) of the piling system. To compare with commonly used steel or wood sheet piling, there is a strong need to properly characterise the flexural behaviour of composite piling systems. Directed by this industrial need, the research reported herein is focused on the flexural response of a pultruded sheet pile seawall panel consisting of E-glass fibre-reinforced polyester. The analysis consists of an experimental investigation, analytical modelling, and finite element simulation to determine the flexural and shear rigidities of the seawall panel for use in computing the deflections of the piling system.<br>A novel testing method was developed to simultaneously determine the flexural rigidity (EI) and shear rigidity (kAG) of the panel using Timoshenko's beam theory. Three- and four-point bending tests were performed on six different span lengths and the results were self-consistent from the two different tests. (Abstract shortened by UMI.)

The flexural behaviour of three different hybrid fibre-reinforced polymer (FRP) matrix composites, i.e. S2-glass/E-glass/epoxy, TR50S carbon/IM7 carbon/epoxy, and E-glass/TR50S carbon/epoxy hybrid FRP composites, has been investigated. The main objectives of this study were to: (i) improve the flexural properties of the parent composite materials, i.e. E-glass/epoxy and TR50S carbon fibre/epoxy composites, through substitution of stronger fibres, i.e. S2-glass and IM7 carbon fibres, for the fibres of the parent composite materials, and (ii) determine the optimum stacking configurations that produced the maximum increase in flexural properties of the resulting hybrid composites. In addition to these, two secondary objectives related to the preliminary investigation of determining the optimum stacking configurations have also been established. The two secondary objectives were to: (i) determine the optimum values of the processing parameters of the composites under investigation, and (ii) determine the compressive strength and compressive modulus of the parent materials.The investigation was carried out experimentally, thus data presented and analysed were obtained from laboratory work. Optimum values of five processing parameters, i.e. (i) the concentration of matrix precursor within the solvent solution utilised to wet the fibres, (ii) the compressive pressure applied during hotpress curing, (iii) the vacuum pressure of the atmosphere inside the curing chamber, (iv) the dwell time during hot-press curing, and (v) the holding temperature during hot-press curing, have been established. The criteria for determining the optimum values of these parameters were optimum fibre content, minimum void content, and optimum flexural properties. Compressive strength and compressive modulus of the parent composite materials have also been determined.Specimens were cut from flat composite plates using a diamond-tipped circular blade saw. The longitudinal edges of the specimens were carefully polished to remove any possible edge damage due to cutting. The composite plates were produced from preforms comprised of a number of glass fibre/epoxy prepregs, carbon fibre/epoxy prepregs or a combination of these. All the fabrication procedures were carried out using manual techniques. Whilst the compressive tests were conducted in accordance with the ASTM D3410-03 standard, flexural tests were carried out according to Procedure A of the ASTM D790-07 standard. Span-to depth ratios, S/d, of 16, 32, and 64 were selected for flexural testing in order to determine the minimum value of S/d required to ensure flexural failure rather than shear failure. Fibre and void contents were evaluated from optical micrograph images of the slices perpendicular to the fibre direction of the samples.It was concluded that the optimum values of the five processing parameters under investigations were: (i) epoxy concentration, C[subscript]e ~ 50 wt%, (ii) compressive pressure, p[subscript]c ~ 1.00 MPa, (iii) vacuum pressure, p[subscript]v ~ 0.035 MPa, (iv) dwell time, t ~ 30 minutes, and (v) holding temperature, T ~ 120 °C. Compressive tests revealed that the order of compressive strength for the parent composite materials were arranged as follows: S2-glass fibre/epoxy (476 MPa), E-glass fibre/epoxy (430 MPa), IM7 carbon fibre/epoxy (426 MPa), and TR50S carbon fibre/epoxy (384 MPa). The compressive modulus of these parent composite materials were found to be ordered as follows: IM7 carbon fibre/epoxy (67.9 GPa), TR50S carbon fibre/epoxy (61.8 GPa), S2-glass fibre/epoxy (45.1 GPa), and E-glass fibre/epoxy (32.9 GPa). After considering these compressive properties, three different hybrid combinations, as mentioned earlier, were manufactured and evaluated with the prepreg layers of the fibre composites possessing higher compressive strength being placed at the compressively loaded side of the flexural specimens.Shorter beam specimens (S/d = 16) of the three hybrid systems exhibited increased flexural strength as the amount of stronger fibre content was increased, but no hybrid effect was noted. The increase appeared to follow the rule of mixtures and this was attributed to their failure mode being shear failure. For beams tested at S/d = 32 and S/d = 64, the three hybrid systems demonstrated three different trends. The S2-glass fibre/E-glass fibre/epoxy hybrid system, where the S2-glass fibre (substituted at the compressive loading face) was slightly stronger and stiffer compared to the E-glass fibre at the tensile side, demonstrated increases in flexural strength together with the presence of a hybrid effect following partial substitution of the S2-glass fibre for E-glass fibres at the compressive side. The IM7 carbon fibre/TR50S carbon fibre/epoxy hybrid system, where the IM7 carbon fibre (substituted at the compressive side) was slightly stronger but significantly stiffer in compression compared to the TR50S fibre at the tensile side, exhibited a slight increase in flexural strength that appeared to obey the rule of mixtures.This result was attributed to the strength increase in the compressive side introduced by the substituted fibres not being sufficient to suppress the increase of internal compressive stress due to the increase in compressive modulus of the substituted fibres. The E-glass fibre/TR50S carbon fibre/epoxy hybrid system, where the E-glass fibre (substituted at the compressive side) was found to be slightly stronger but significantly less stiff in compression compared to the TR50S fibre at the tensile side, demonstrated a significant increase in flexural modulus and also exhibited a significant hybrid effect. The decrease in internal compressive stresses generated at the compressive side due to the decreased compressive modulus of the substituted fibre, when combined with the increase in compressive strength of the substituted fibre, was thought to led to the significant increase of flexural strength for this hybrid system.General trends observed in flexural modulus for the three hybrid systems were reasonably similar with any change in flexural modulus appearing to obey the rule of mixtures. Whilst an increase in flexural modulus was noted for higher contents of stronger fibre in the case of the S2-glass fibre/E-glass fibre/epoxy hybrid system and IM7 carbon fibre/TR50S carbon fibre/epoxy hybrid system, a decrease in flexural modulus with increased quantities of stronger fibre was exhibited by the E-glass fibre/TR50S carbon fibre/epoxy hybrid system. The increase or decrease in flexural modulus was attributed to the relative stiffness in compression of the substituted fibre when compared to that of the respective parent composite materials.Unlike the S2-glass fibre/E-glass fibre/epoxy hybrid system and IM7 carbon fibre/TR50S carbon fibre/epoxy hybrid system that did not exhibit any significant trend with regards the effect of the substitution of stronger fibre at the compressive side, the E-glass fibre/TR50S carbon fibre hybrid system demonstrated a significant increase in the energy stored to maximum stress with increasing content of the stronger fibre. This increase was mainly attributed to the increased strain–to-maximum stress of the hybrid system with respect to that of the parent composite material.In addition, for the three hybrid systems under investigation, the most significant change in flexural properties was noticed following substitution of the first layer at the compressive face. The relative position with respect to the neutral plane of the substituted layer was thought to be the reason for this phenomenon. It was also noted that flexural properties increased with the increase in S/d. A change in failure morphology was noted with the change of S/d from 16 to 32. It was thus determined that a S/d ratio of at least 32 was required in order to promote flexural failure (as opposed to shear failure). For the S2-glass fibre/E-glass fibre/epoxy hybrid system, this change appeared more obvious in comparison with that the other two hybrid systems with this change being accompanied by a significant increase in flexural strength.The main general conclusions that could be drawn from this investigation were that, although the flexural modulus appeared to obey the rule of mixture, an increase in flexural strength together with the presence of a hybrid effect, would most probably be observed when the fibre substituted at the compressive side possessed a significantly lower modulus combined with significantly higher compressive strength as demonstrated by the hybrid TR50S carbon - E-glass FRP composites. The most significant change in properties was exhibited by the first layer substitution whilst increasing the value of S/d resulted in an increase of flexural strength, with S/d = 32 being determined to be sufficient in order to promote flexural failure as opposed to shear failure.

Yes<br>This paper presents test results of six full scale reinforced concrete continuous T beams. One beam was reinforced with glass fibre reinforced polymer (GFRP) bars while the other five beams were reinforced with a different combination of GFRP and steel bars. The ratio of GFRP to steel reinforcement at both mid-span and middle-support sections was the main parameter investigated. The results showed that adding steel reinforcement to GFRP reinforced concrete T-beams improves the flexural stiffness, ductility and serviceability in terms of crack width and deflection control. However, the moment redistribution at failure was limited because of the early yielding of steel reinforcement at a beam section that does not reach its moment capacity and could still carry more loads due to the presence of FRP reinforcement. The experimental results were compared with the ultimate moment prediction of ACI 440.2R-17, and with the existing theoretical equations for deflection prediction. It was found that the ACI 440.2R-17 reasonably estimated the moment capacity of both mid-span and middle support sections. Conversely, the available theoretical deflection models underestimated the deflection of hybrid reinforced concrete T-beams at all load stages.<br>The full-text of this article will be released for public view after the publisher embargo on 10 Aug 2021.

LiteSteel Beam (LSB) is a new cold-formed steel beam produced by OneSteel Australian Tube Mills. The new beam is effectively a channel section with two rectangular hollow flanges and a slender web, and is manufactured using a combined cold-forming and electric resistance welding process. OneSteel Australian Tube Mills is promoting the use of LSBs as flexural members in a range of applications, such as floor bearers. When LSBs are used as back to back built-up sections, they are likely to improve their moment capacity and thus extend their applications further. However, the structural behaviour of built-up beams is not well understood. Many steel design codes include guidelines for connecting two channels to form a built-up I-section including the required longitudinal spacing of connections. But these rules were found to be inadequate in some applications. Currently the safe spans of builtup beams are determined based on twice the moment capacity of a single section. Research has shown that these guidelines are conservative. Therefore large scale lateral buckling tests and advanced numerical analyses were undertaken to investigate the flexural behaviour of back to back LSBs connected by fasteners (bolts) at various longitudinal spacings under uniform moment conditions. In this research an experimental investigation was first undertaken to study the flexural behaviour of back to back LSBs including its buckling characteristics. This experimental study included tensile coupon tests, initial geometric imperfection measurements and lateral buckling tests. The initial geometric imperfection measurements taken on several back to back LSB specimens showed that the back to back bolting process is not likely to alter the imperfections, and the measured imperfections are well below the fabrication tolerance limits. Twelve large scale lateral buckling tests were conducted to investigate the behaviour of back to back built-up LSBs with various longitudinal fastener spacings under uniform moment conditions. Tests also included two single LSB specimens. Test results showed that the back to back LSBs gave higher moment capacities in comparison with single LSBs, and the fastener spacing influenced the ultimate moment capacities. As the fastener spacing was reduced the ultimate moment capacities of back to back LSBs increased. Finite element models of back to back LSBs with varying fastener spacings were then developed to conduct a detailed parametric study on the flexural behaviour of back to back built-up LSBs. Two finite element models were developed, namely experimental and ideal finite element models. The models included the complex contact behaviour between LSB web elements and intermittently fastened bolted connections along the web elements. They were validated by comparing their results with experimental results and numerical results obtained from an established buckling analysis program called THIN-WALL. These comparisons showed that the developed models could accurately predict both the elastic lateral distortional buckling moments and the non-linear ultimate moment capacities of back to back LSBs. Therefore the ideal finite element models incorporating ideal simply supported boundary conditions and uniform moment conditions were used in a detailed parametric study on the flexural behaviour of back to back LSB members. In the detailed parametric study, both elastic buckling and nonlinear analyses of back to back LSBs were conducted for 13 LSB sections with varying spans and fastener spacings. Finite element analysis results confirmed that the current design rules in AS/NZS 4600 (SA, 2005) are very conservative while the new design rules developed by Anapayan and Mahendran (2009a) for single LSB members were also found to be conservative. Thus new member capacity design rules were developed for back to back LSB members as a function of non-dimensional member slenderness. New empirical equations were also developed to aid in the calculation of elastic lateral distortional buckling moments of intermittently fastened back to back LSBs. Design guidelines were developed for the maximum fastener spacing of back to back LSBs in order to optimise the use of fasteners. A closer fastener spacing of span/6 was recommended for intermediate spans and some long spans where the influence of fastener spacing was found to be high. In the last phase of this research, a detailed investigation was conducted to investigate the potential use of different types of connections and stiffeners in improving the flexural strength of back to back LSB members. It was found that using transverse web stiffeners was the most cost-effective and simple strengthening method. It is recommended that web stiffeners are used at the supports and every third points within the span, and their thickness is in the range of 3 to 5 mm depending on the size of LSB section. The use of web stiffeners eliminated most of the lateral distortional buckling effects and hence improved the ultimate moment capacities. A suitable design equation was developed to calculate the elastic lateral buckling moments of back to back LSBs with the above recommended web stiffener configuration while the same design rules developed for unstiffened back to back LSBs were recommended to calculate the ultimate moment capacities.

Steel hollow section members filled with concrete have been frequently used in recent construction industry as columns and beams and beam-columns because of their superior performance and constructability. Previous research demonstrated that such system has large energy absorption capacity which is critical in the event of an earthquake. By filling steel RHS with concrete, the failure of the steel shell due to local buckling can be delayed and the ductility of the concrete core can be improved as a result of the confinement of the steel shell. This type of composite section may be used in various structures including frames of high rise buildings, bridges, offshore structures, cast-in-situ piles in foundation etc. Design methods for concrete-filled steel tubular sections are recommended in a number of code of practices. Due to the significant differences in the material properties between normal strength concrete and high strength concrete, there is a need to study the behaviour of composite sections with higher strength concretes. The study emphasises ultimate strength, ductility, post-failure strength reserve and interface bond. It also emphasises ductility and post-failure strength of the composite beams due to the brittle behaviour of higher strength concretes when compared to normal strength concrete. Spreadsheet graph were used to present the results such as load versus strains, load versus deflections etc. In this thesis analytical study is presented on the calculation of ultimate moment of resistance of the concrete-filled RHS beams. Among the main considerations of the derivation, the steel portion was assumed either elastic-perfectly plastic or perfectly plastic and concrete carries no strength in the tensile zone. At the interface both full bond and partial bond were assumed for comparison. Efforts were also made to calculate the midspan deflections of the composite beams. Simple analytical expressions derived from this study can be coded to a prgrammable calculator or in a small spreadsheet program for design use. Finite element studies were carried out by using a proprietorship software package ANSYS. In the analysis of concrete-filled, three types of elements with large deformation and nonlinear capabilities were used. A plastic shell element, a solid concrete element with cracking and crushing capabilities, and a nonlinear spring contact element were used to model the steel shell, the concrete core and the interface respectively.<br>Doctor of Philosophy (PhD)

Steel hollow section members filled with concrete have been frequently used in recent construction industry as columns and beams and beam-columns because of their superior performance and constructability. Previous research demonstrated that such system has large energy absorption capacity which is critical in the event of an earthquake. By filling steel RHS with concrete, the failure of the steel shell due to local buckling can be delayed and the ductility of the concrete core can be improved as a result of the confinement of the steel shell. This type of composite section may be used in various structures including frames of high rise buildings, bridges, offshore structures, cast-in-situ piles in foundation etc. Design methods for concrete-filled steel tubular sections are recommended in a number of code of practices. Due to the significant differences in the material properties between normal strength concrete and high strength concrete, there is a need to study the behaviour of composite sections with higher strength concretes. The study emphasises ultimate strength, ductility, post-failure strength reserve and interface bond. It also emphasises ductility and post-failure strength of the composite beams due to the brittle behaviour of higher strength concretes when compared to normal strength concrete. Spreadsheet graph were used to present the results such as load versus strains, load versus deflections etc. In this thesis analytical study is presented on the calculation of ultimate moment of resistance of the concrete-filled RHS beams. Among the main considerations of the derivation, the steel portion was assumed either elastic-perfectly plastic or perfectly plastic and concrete carries no strength in the tensile zone. At the interface both full bond and partial bond were assumed for comparison. Efforts were also made to calculate the midspan deflections of the composite beams. Simple analytical expressions derived from this study can be coded to a prgrammable calculator or in a small spreadsheet program for design use. Finite element studies were carried out by using a proprietorship software package ANSYS. In the analysis of concrete-filled, three types of elements with large deformation and nonlinear capabilities were used. A plastic shell element, a solid concrete element with cracking and crushing capabilities, and a nonlinear spring contact element were used to model the steel shell, the concrete core and the interface respectively.

Thesis (Ph. D.)--University of Western Sydney, Hawkesbury.<br>"Thesis presented for the Degree of Doctor of Philosophy, School of Construction and Building Sciences, Faculty of Science, Technology and Agriculture, University of Western Sydney, Hawkesbury, December 1997.

Pultruded, fibre reinforced, polymeric composites are now being used in a wide range of structural engineering applications, due to their high strength to weight ratios and resistance to environmental conditions. However, such materials posses a relatively low shear modulus in relation to their axial and flexural moduli. This can result in shear deformation constituting a significant proportion of the total deformation and a reduction in buckling loads for various modes of instability. An experimental and theoretical study of the influence of shear deformation on the flexural and torsional stiffnesses and various modes of instability of pultruded polymeric bars of open cross-section is therefore presented. Theories for the bending and warping torsional response of pultruded, fibre reinforced polymeric bars of open cross-section, excluding and including the influence of shear deformation, are presented. Full section bending mechanical properties of several pultruded beams are determined using a static testing apparatus and a wide variety of span configurations. Full section warping torsional mechanical properties of several pultruded bars are determined using a new testing apparatus, capable of applying a torque to any cross-section along a bar, whilst maintaining the bars lateral position. Theories for the flexural, torsional and lateral instability of pultruded, fibre reinforced polymeric bars of open cross-section, excluding and including the influence of shear deformation, are developed and presented. Parametric studies of the influence of shear deformation in the flexural, torsional and lateral instability of various pultruded bars of open cross-section are also presented. The experimental and theoretical studies indicate that shear deformation reduces significantly the non-uniform bending stiffness of pultruded polymeric bars, but that its influence on the non-uniform and restrained warping torsional stiffness is practically negligible. Shear deformation has also been found to result in a significant reduction in flexural, torsional and coupled flexural-torsional or lateral buckling loads.

As we move into the twenty-first century, the renewal of our lifelines or deterioration of infrastructure becomes a topic of critical importance. The structures may have to carry larger loads, require change in building use, suffer steel corrosion problems, or errors made during the design or construction phases so that the structure may need to be repaired or strengthened before it can be used. The use of fiber reinforced polymers (FRP) in the last few years in various engineering application, forums and configuration offers an alternative design approach for the construction of new concrete structures and the rehabilitation of existing ones. The use of FRP materials for external strengthening of reinforced concrete (RC) structures has emerged as one of the most exciting and promising technologies in material and structural engineering. Externally bonded FRP reinforcement is relatively unprotected against impact, vandalism or severe environmental conditions. Their structural performance can be greatly affected by these drawbacks. But if the composite material is placed in slots inside the concrete cover some of these drawbacks can be overcome. This method is designated by Near Surface Mounted (NSM) method. Therefore, the presented work is carried out using this advantageous strengthening technique utilizing the non-corrodible FRP materials. My research involved both experimental and analytical investigations on the use of FRP systems for strengthening concrete structures using NSM techniques. The main objectives of my research were to (1) develop/utilize an NSM system composed of FRP bars and adhesives, (2) investigate the bond performance for the proposed NSM system, (3) investigate the effect of freeze and thaw cycles on the of the new proposed system, (4) study the flexural behaviour of RC beams strengthened with NSM FRP bars, (5) develop an analytical model using non-linear finite element analysis (ADINA) taking into consideration the interfacial behaviour between the concrete and FRP bars and (6) establish design recommendations for the use of FRP bars for the NSM method. To achieve these objectives, the research program was divided into two parts. The first part included the experimental work while the second part included the analytical work. The first part consisted of two phases. The first phase included the pullout testing of 76 C-shape concrete blocks including 16 conditioned blocks. The second phase included testing 20 flexural strengthened concrete beams using the NSM method. The second part included developing an analytical model to be used in a non-linear finite element program and to analyze and predict the behaviour of concrete beams strengthened for flexure using NSM FRP bars. The efficiency and accuracy of the model was verified by comparing its results to the experimental results. The developed analytical model was used to study the effect of different parameters. Test results are presented in terms of deflection, strain in the concrete, steel and FRP and modes of failure. Test results showed the superior performance of the proposed NSM FRP/adhesive system. The NSM system is able to increase both the stiffness and flexural capacity of concrete beams by approximately 100% over the unstrengthened one. The FEM was able to predict of the behaviour of the strengthened beams in flexure with NSM. Based on the experimental and analytical study, useful conclusions and recommendations for flexural strengthening with NSM FRP were provided.||Alors que nous entrons dans le XXIème siècle, la dégradation des infrastructures devient un sujet d'une importance cruciale. Les structures doivent supporter des charges plus grandes et subir des changements d'utilisation. En plus de cela s'ajoute les problèmes de corrosion de l'acier, des erreurs de conception et de construction, ce qui souvent nécessitent que la structure soit réparée ou renforcée, des fois même avant sa mise en service. L'utilisation de polymères renforcés de fibres (PRF) dans les dernières années dans divers domaines d'ingénierie a permis une avancée technologique, et leur utilisation dans la construction de nouvelles structures en béton ainsi que la réhabilitation des anciennes. L'utilisation de matériaux en PRF pour le renforcement externe des structures en béton armé est une technologie des plus prometteuses dans l'ingénierie structurale ou de matériaux. Cependant le renforcement par collage externe de PRF n'offre pas une bonne protection contre les chocs, le vandalisme ou les conditions environnementales sévères, ce qui pourraient affecter les performances structurales des éléments réhabilités. Ces inconvénients peuvent être surmontés si le PRF est inséré dans des rainures réalisées dans le recouvrement de béton. Cette méthode est appelée « mise en place d'Armatures Encastrées Près de la surface (AEPS)». Le présent travail s'articule autours de cette technique de renforcement utilisant des matériaux non corrodables. Mes travaux de recherches se focalisent sur l'utilisation des AEPS en PRF pour le renforcement des structures, et cela d'un point de vue expérimental et analytique. Les principaux objectifs de mes recherches sont: (1) développer/utiliser un système d'AEPS composé de barres en PRF et d'adhésif, (2) étudier les performance d'adhérence du système proposé, (3) étudier l'effet des cycles gel-dégel sur le système proposé, (4) l'étude du comportement en flexion de poutres en béton armé, renforcées avec des barres d'AEPS en PRF, (5) développer un modèle analytique utilisant des méthodes non-linéaires d'analyse par éléments finis (logiciel ADINA) en tenant compte du comportement de l'interface béton-barres en PRF, et (6) mettre en place des recommandations de calcul pour l'utilisation des barres en PRF comme AEPS. Pour atteindre ces objectifs, le programme de recherche a été divisé en deux parties. La première partie comprenait les travaux expérimentaux tandis que la deuxième comprenait des travaux d'analyse. La première partie elle même était constituée de deux phases. La première phase comprenait des essais d'arrachement direct de blocs de béton en forme de «C», dont 16 blocs conditionnés dans une chambre environnementale. Alors que la deuxième phase comportait des essais de flexion 20 poutres en béton armé, renforcés par des AEPS en PRF. La deuxième partie a consisté au développement d'un modèle analytique non-linéaire par éléments finis de façon à pouvoir analyser et prédire le comportement en flexion de poutres en béton armé, renforcées par des AEPS en PRF. L'efficacité et la précision du modèle ont été vérifiées en comparant ses résultats analytiques aux résultats expérimentaux. Le modèle analytique développé a été utilisé pour étudier l'effet de différents paramètres. Les résultats des tests sont présentés en termes de déflexion, de contraintes dans le béton, l'acier et le PRF et les modes de rupture. Les résultats des essais ont démontré les bonnes performances du système armatures PRF/adhésif proposé, ce dernier a permit d'augmenter à la fois la rigidité en flexion et la résistance des poutres en béton d'environ 100% par rapport à la poutre non renforcée. L'analyse par éléments finis a été en mesure de prédire le comportement en flexion des poutres renforcées avec des AEPS en PRF. Basé sur ces travaux, des conclusions et des recommandations utiles concernant le renforcement en flexion avec des AEPS en PRF ont été fournis.

Abstract: Recently, fiber-reinforced polymer (FRP) composite materials have been used in the field of civil engineering constructions especially in corrosive environments. They can be used as internal reinforcement for beams, slabs, and pavements, or as external reinforcement for rehabilitation and strengthening different structures. One of their innovative applications is the concrete-filled FRP tubes (CFFTs) which are becoming an alternative for different structural members such as piles, columns, bridge girders, and bridge piers due to their high performance and durability. In such integrated systems, the FRP tubes act as stay-in-place forms, protective jackets for the embedded concrete and steel, and as external reinforcement in the primary and secondary direction of the structural member. Extensive research was developed on CFFTs as columns, but comparatively limited research was carried out on CFFTs as beams especially those with rectangular sections. The circular sections exhibit magnificent confinement efficiency in case of columns. However, the rectangular sections have higher moment of inertia and flexural stiffness to resist the applied loads and deformations in case of beams. Moreover, the construction and architectural requirements prefer the rectangular section of beams, rather than the circular beams, due to its stability during installation and its workability during connecting to other structural members like slabs and columns. Also, CFFTs that are completely filled with concrete are not optimal for applications governed by pure bending, because the excess weight of the cracked concrete below the neutral axis may increase the transportation and installation cost. This dissertation presents experimental and theoretical investigations on the flexural behaviour of rectangular CFFT beams with steel rebar. These hybrid FRP-concrete-steel tubular rectangular beams contain outer rectangular filament-wound glass-FRP (GFRP) tubes to increase the sectional moment of inertia, to provide flexural and shear reinforcement, and to protect the inner structural elements (concrete and steel) against corrosion. The outer tubes were fully-or-partially filled with concrete and were reinforced with steel rebar at the tension side only. Inner hollow circular or square filament-wound GFRP tubes, shifted toward the tension zone, were provided inside the CFFT beam to eliminate the excess weight of the cracked concrete at the tension side, to confine actively the concrete at the compression side and to act as reinforcement at the tension side. The surfaces of tubes adjacent to concrete were roughened by sand coating to fulfill the full composite action of such hybrid section. Several test variables were chosen to investigate the effect of the outer and inner tubes thickness, fibers laminates, and shape on the flexural behaviour of such hybrid CFFT beams. To fulfil the objectives of the study, twenty-four full-scale beam specimens, 3200 mm long and 305×406 mm2 cross section, were tested under a four-point bending load. These specimens include eight fully-CFFT beams with wide range of tube thickness of 3.4 mm to 14.2 mm, fourteen partially-CFFT beams with different outer and inner tubes configurations, and two conventional steel-reinforced concrete (RC) beams as control specimens. The results indicate outstanding performance of the rectangular fully and partially-CFFT beams in terms of strength-to-weight ratio and ductility compared to the RC beams. The fully-CFFT beams with small tube thickness failed in tension by axial rupture of fibers at the tension side. While, the fully-CFFT beams with big tube thickness failed in compression by outward buckling of the outer tube compression flange with warning signs. The results indicate also that the flexural strength of the fully-CFFT beams was ascending nonlinearly with increasing the tubes thickness until a certain optimum limit. This limit was evaluated to define under-and-over-reinforced CFFT sections, and consequently to define the tension and compression failure of fully-CFFT beams, respectively. The inner hollow tubes act positively in reinforcing the partially-CFFT beams and confining the concrete core at the compression side. The strength-to-weight ratio of the partially-CFFT beams attained higher values than that of the corresponding fully-CFFT beams. Generally, the partially-CFFT beams failed gradually in compression due to outward buckling of the outer tube compression flange with signs of confining the concrete core at the compression side. The inner circular voids pronounced better performance than the square inner voids, however they have the same cross sectional area and fiber laminates. Theoretical section analysis based on strain compatibility/equilibrium has been developed to predict the moment-curvature response of the fully-CFFT section addressing the confinement and tension stiffening of concrete. The analytical results match well the experimental results in terms of moment, deflection, strains, and neutral axis responses. In addition, analytical investigation was conducted to examine the validity of the North American design codes provisions for predicting the deflection response of fully and partially-CFFT beams. Based on these investigations, a new power and assumptions were proposed to Branson’s equation to predict well the effective moment of inertia of the CFFT section. These assumptions consider the effect of the GFRP tube strength, thickness and configuration, in addition to the steel reinforcement ratio. The proposed equations predict well the deflection in the pre-yielding and post-yielding stages of the hybrid FRP-concrete-steel CFFT rectangular beams.<br>Résumé: Les matériaux composites en polymère renforcé de fibres (PRF) ont récemment été utilisés dans le domaine des constructions de génie civil, en particulier dans les environnements corrosifs. Elles peuvent être utilisées comme une armature interne pour des poutres, dalles et les trottoirs, ou comme une armature externe pour la réhabilitation et le renforcement de différentes structures. L'une de leurs applications novatrices est les tubes de polymères renforcés de fibres remplis de béton (TPFRB ) qui sont en train de devenir une alternative pour divers éléments structuraux tels que les pieux, les colonnes, les poutres et les piliers de ponts en raison de leur haute performance et durabilité. Dans de tels systèmes intégrés, les tubes PRF agissent comme un coffrage permanent, une chemise protectrice pour le béton et l'acier encastrés, et comme une armature externe dans les directions longitudinale et transversale de l'élément structural. La recherche a été concentrée sur les TPRFB comme des colonnes, mais très peu de recherche a été effectué les TPRFB comme des poutres particulièrement celles à section rectangulaire. La section circulaire présente une efficacité de confinement efficace en cas de colonnes. Toutefois, la section rectangulaire a un moment d'inertie plus élevé et une rigidité flexionnelle plus efficace pour résister les charges appliquées et les déformations dans le cas des poutres. Par ailleurs, les travaux de construction et les exigences architecturales préfèrent la section rectangulaire des poutres, plutôt que les poutres circulaires, en raison de sa stabilité pendant l'installation et sa maniabilité lors de la connexion à d'autres membres structuraux comme les dalles et les colonnes. En outre, les poutres TPRFB qui sont complètement remplis de béton ne sont pas optimales pour les applications contrôlées par la flexion pure, puisque le béton fissuré en dessous de l'axe neutre ne contribue pas à la résistance et augmente le poids propre et les coûts de transport et d'installation. Cette thèse présente des études théoriques et expérimentales sur le comportement en flexion de poutres rectangulaires (TPRFB) en béton armé. Ces poutres rectangulaires tubulaires hybrides en PRF-béton-acier sont composées de tubes rectangulaires externes fabriquées par enroulement filamentaire. Ces tubes fournissent un renforcement de flexion et de cisaillement; et protègent le béton armé contre la corrosion. Les poutres peuvent être soient entièrement ou partiellement remplies de béton. Des tubes intérieurs ( de section circulaires ou carrés) en polymères renforcés de fibres de verre (PRFV) sont positionnés dans la zone tendue de la poutre afin de réduire le poids et d’éliminer le béton fissuré en traction. Pour augmenter l'action composite de la section hybride, les surfaces des tubes adjacents au béton ont été rendues rugueuses par enrobage de sable. Plusieurs variables ont été choisis pour étudier l'effet de l’épaisseur des tubes extérieurs et intérieurs, les laminés de fibres, et la forme sur le comportement en flexion de ces poutres hybrides (TPRFB). Pour atteindre les objectifs de l’étude, vingt-quatre échantillons de poutre pleine grandeur, ayant une longueur de 3200 mm et une section transversale de 305×406 mm2, ont été testés sous une flexion à quatre points. Ces échantillons comprennent huit poutres de TPRFB entièrement remplis avec une large gamme d'épaisseur du tube externe de 3.4 mm à 14.2 mm, quatorze poutres de TPRFB partiellement remplis avec différentes configurations de tubes extérieurs et intérieurs, et deux poutres en béton armé conventionnel, comme échantillons de référence. Les résultats indiquent une performance exceptionnelle des poutres rectangulaires de TPRFB entièrement et partiellement remplies en termes du rapport de la résistance sur la masse et de la ductilité par rapport aux poutres en béton armé conventionnel. Les poutres de TPRFB entièrement remplies avec un tube de petite épaisseur ont rompu de façon moins ductile en tension par rupture axiale des fibres. Les poutres de TPRFB entièrement remplies et ayant une grande épaisseur ont rompu de façon ductile en compression par flambage local vers l’extérieur des parois en compression du tube externe. Les résultats indiquent également que la résistance à la flexion des poutres de TPRFB entièrement remplies augmente d’une façon non linéaire avec l'augmentation de l'épaisseur des tubes jusqu'à une certaine limite optimale. Cette limite a été évaluée pour définir les sections TPRFB sous-armées et surarmées et, par conséquent, pour définir la rupture en tension et en compression des poutres de TPRFB entièrement remplies, respectivement. Les tubes creux intérieurs agissent positivement dans le renforcement des poutres de TPRFB partiellement remplies et en confinant le noyau de béton du côté en compression. En général, les poutres de TPRFB partiellement remplies ont rompu en compression par flambage local vers l'extérieur des parois en compression du tube externe. Les vides circulaires intérieurs ont montré une meilleure performance que les vides carrés intérieurs, bien qu’ils aient la même superficie de la section transversale et le même taux de PRF. Une analyse théorique basée sur la compatibilité des déformations d’une section en flexion a été développée pour prédire la réponse moment-courbure de la poutre TPRFB en tenant compte des pourcentages de confinement externe et interne. Les résultats analytiques et les résultats expérimentaux s’accordent en termes de moment, flèche, déformations, et positions de l'axe neutre. En outre, une étude analytique a été menée afin d'examiner la validité des codes de conception nord-américains pour prédire la réponse en flexion des poutres TPRFB. En se basant sur les résultats de ces études, de nouvelles équations ont été proposées pour mieux prédire le moment effectif d'inertie de la section et une nouvelle procédure de conception pour prédire les capacités ultimes. Ces équations considèrent l'effet de la résistance des tubes en PRFV externe et interne que le taux d’armature en acier. En outre, ils prédisent bien la flèche dans les phases avant et après la limite élastique des poutres rectangulaires hybrides à haute performance.

Unreinforced masonry (URM) structures have a low resistance against lateral loading and are vulnerable to earthquake and wind effects due to their low flexural capacity and relatively brittle mode of failure. Strengthening of the masonry walls against lateral loading usually aims for increasing their load bearing capacity and ductility. The application of fibre reinforced polymer (FRP) composites as externally bonded reinforcement in repairing and strengthening of masonry walls has become more attractive than the traditional methods. Determination of the flexural out-of-plane behaviour of FRP strengthened masonry walls with different types and configurations of FRP composites is the main objective of this research. Experimental program has been developed including small-scale and large-scale experiments. In addition, theoretical finite element (FE) modelling has been developed and verification of the models via comparison with, experimental results is conducted. Small-scale experiments are designed to measure the mechanical properties of masonry and mortar samples. As a result, the values of elastic modulus and compressive strength has been evaluated and used as material properties for the FE model. For large-scale experiments, seven specimens of masonry walls were constructed with clay bricks and mortar. Six samples were constructed as thin masonry walls with 1/2 brick thickness equal to 102.5 mm and one full brick thick sample was constructed with 215mm thickness. The walls are strengthened with different types and configurations of FRP materials. The specimens are subjected to uniformly distributed lateral load, applied by an airbag, on one side and over the whole surface of the wall. Theoretical FE models are developed using ANSYS software and are verified via comparison with the experimental results. Further analysis on the behaviour of FRP, strengthened walls have also been conducted. The results show that the use of FRP strengthening has increased the out-of-plane capacity of URM walls by almost 3 times and significantly improved the ductility of the walls. The comparison of the load-deflection graphs from the theoretical modelling with the corresponding results from experimental investigation shows good compliance in elastic range of loading.

Until recently, the hot-rolled steel members have been recognized as the most popular and widely used steel group, but in recent times, the use of cold-formed high strength steel members has rapidly increased. However, the structural behavior of light gauge high strength cold-formed steel members characterized by various buckling modes is not yet fully understood. The current cold-formed steel sections such as C- and Z-sections are commonly used because of their simple forming procedures and easy connections, but they suffer from certain buckling modes. It is therefore important that these buckling modes are either delayed or eliminated to increase the ultimate capacity of these members. This research is therefore aimed at developing a new cold-formed steel beam with two torsionally rigid rectangular hollow flanges and a slender web formed using intermittent screw fastening to enhance the flexural capacity while maintaining a minimum fabrication cost. This thesis describes a detailed investigation into the structural behavior of this new Rectangular Hollow Flange Beam (RHFB), subjected to flexural action The first phase of this research included experimental investigations using thirty full scale lateral buckling tests and twenty two section moment capacity tests using specially designed test rigs to simulate the required loading and support conditions. A detailed description of the experimental methods, RHFB failure modes including local, lateral distortional and lateral torsional buckling modes, and moment capacity results is presented. A comparison of experimental results with the predictions from the current design rules and other design methods is also given. The second phase of this research involved a methodical and comprehensive investigation aimed at widening the scope of finite element analysis to investigate the buckling and ultimate failure behaviours of RHFBs subjected to flexural actions. Accurate finite element models simulating the physical conditions of both lateral buckling and section moment capacity tests were developed. Comparison of experimental and finite element analysis results showed that the buckling and ultimate failure behaviour of RHFBs can be simulated well using appropriate finite element models. Finite element models simulating ideal simply supported boundary conditions and a uniform moment loading were also developed in order to use in a detailed parametric study. The parametric study results were used to review the current design rules and to develop new design formulae for RHFBs subjected to local, lateral distortional and lateral torsional buckling effects. Finite element analysis results indicate that the discontinuity due to screw fastening has a noticeable influence only for members in the intermediate slenderness region. Investigations into different combinations of thicknesses in the flange and web indicate that increasing the flange thickness is more effective than web thickness in enhancing the flexural capacity of RHFBs. The current steel design standards, AS 4100 (1998) and AS/NZS 4600 (1996) are found sufficient to predict the section moment capacity of RHFBs. However, the results indicate that the AS/NZS 4600 is more accurate for slender sections whereas AS 4100 is more accurate for compact sections. The finite element analysis results further indicate that the current design rules given in AS/NZS 4600 is adequate in predicting the member moment capacity of RHFBs subject to lateral torsional buckling effects. However, they were inadequate in predicting the capacities of RHFBs subject to lateral distortional buckling effects. This thesis has therefore developed a new design formula to predict the lateral distortional buckling strength of RHFBs. Overall, this thesis has demonstrated that the innovative RHFB sections can perform well as economically and structurally efficient flexural members. Structural engineers and designers should make use of the new design rules and the validated existing design rules to design the most optimum RHFB sections depending on the type of applications. Intermittent screw fastening method has also been shown to be structurally adequate that also minimises the fabrication cost. Product manufacturers and builders should be able to make use of this in their applications.

Until recently, the hot-rolled steel members have been recognized as the most popular and widely used steel group, but in recent times, the use of cold-formed high strength steel members has rapidly increased. However, the structural behavior of light gauge high strength cold-formed steel members characterized by various buckling modes is not yet fully understood. The current cold-formed steel sections such as C- and Z-sections are commonly used because of their simple forming procedures and easy connections, but they suffer from certain buckling modes. It is therefore important that these buckling modes are either delayed or eliminated to increase the ultimate capacity of these members. This research is therefore aimed at developing a new cold-formed steel beam with two torsionally rigid rectangular hollow flanges and a slender web formed using intermittent screw fastening to enhance the flexural capacity while maintaining a minimum fabrication cost. This thesis describes a detailed investigation into the structural behavior of this new Rectangular Hollow Flange Beam (RHFB), subjected to flexural action The first phase of this research included experimental investigations using thirty full scale lateral buckling tests and twenty two section moment capacity tests using specially designed test rigs to simulate the required loading and support conditions. A detailed description of the experimental methods, RHFB failure modes including local, lateral distortional and lateral torsional buckling modes, and moment capacity results is presented. A comparison of experimental results with the predictions from the current design rules and other design methods is also given. The second phase of this research involved a methodical and comprehensive investigation aimed at widening the scope of finite element analysis to investigate the buckling and ultimate failure behaviours of RHFBs subjected to flexural actions. Accurate finite element models simulating the physical conditions of both lateral buckling and section moment capacity tests were developed. Comparison of experimental and finite element analysis results showed that the buckling and ultimate failure behaviour of RHFBs can be simulated well using appropriate finite element models. Finite element models simulating ideal simply supported boundary conditions and a uniform moment loading were also developed in order to use in a detailed parametric study. The parametric study results were used to review the current design rules and to develop new design formulae for RHFBs subjected to local, lateral distortional and lateral torsional buckling effects. Finite element analysis results indicate that the discontinuity due to screw fastening has a noticeable influence only for members in the intermediate slenderness region. Investigations into different combinations of thicknesses in the flange and web indicate that increasing the flange thickness is more effective than web thickness in enhancing the flexural capacity of RHFBs. The current steel design standards, AS 4100 (1998) and AS/NZS 4600 (1996) are found sufficient to predict the section moment capacity of RHFBs. However, the results indicate that the AS/NZS 4600 is more accurate for slender sections whereas AS 4100 is more accurate for compact sections. The finite element analysis results further indicate that the current design rules given in AS/NZS 4600 is adequate in predicting the member moment capacity of RHFBs subject to lateral torsional buckling effects. However, they were inadequate in predicting the capacities of RHFBs subject to lateral distortional buckling effects. This thesis has therefore developed a new design formula to predict the lateral distortional buckling strength of RHFBs. Overall, this thesis has demonstrated that the innovative RHFB sections can perform well as economically and structurally efficient flexural members. Structural engineers and designers should make use of the new design rules and the validated existing design rules to design the most optimum RHFB sections depending on the type of applications. Intermittent screw fastening method has also been shown to be structurally adequate that also minimises the fabrication cost. Product manufacturers and builders should be able to make use of this in their applications.

This thesis presents an experimental and theoretical study of the material and structural behaviour of a Steel-Fibre reinforced Reactive Powder Concrete (SF-RPC). The experimental program consisted of three phases. Phase 1 involved the development of a design mix for use throughout the remainder of the study. Phase 2 consisted of an in-depth investigation into the material properties of the mix. The final phase of the experimental component was the testing of 16 plain and prestressed SF-RPC beams. Twelve beams were tested under short-term loading to determine their cracking and ultimate moment capacity. The remaining 4 beams were used to investigate the time-dependent flexural behaviour of prestressed SF-RPC slabs. The material properties were measured using a range of short-term tests and included the compressive and flexural behaviour, static chord modulus of elasticity and crack mouth opening. In addition to the short-term tests, investigation into the time-dependent material behaviour was undertaken and included the creep and shrinkage characteristics of the material. The response of the material to various curing conditions was also investigated. The structural behaviour investigated included the short-term flexural moment-curvature response and load-deflection behaviour of beams and slabs along with the crack patterns of both plain and prestressed SF-RPC members. In addition to the investigations into the short-term flexural behaviour, a study into the time-dependent flexural behaviour was also undertaken. There are currently 2 available models for predicting the flexural response of plain and prestressed RPC cross-sections. The analytical phase of this investigation involved an evaluation of these models. Based on the experimental findings and analysis, a modified model was proposed for calculating the short-term flexural behaviour of plain and prestressed SF-RPC beams. The applicability of an age-adjusted effective modulus method for calculating the time-dependent deformations of prestressed SF-RPC slabs under various levels of sustained loads was also evaluated and found to be adequate with minor refinements.

The use of non-metallic glass fibre reinforced polymer (GFRP) materials as an alternative to steel reinforcement in concrete is gaining acceptance mainly due to their high corrosion resistance. A high strength-to-weight ratio and ease of handling and . fabrication are added advantages. However, the thermal characteristics of GFRP rods . can be sUbstantially different from those of concrete and conventional steel bars. The difference in the transverse thermal expansion between concre'te and FRP rods may cause hoop stresses within the concrete which can adversely affect the bond between the concrete and the rods and, eventually, lead to the formation of cracks within the concrete cover when the temperature increases. This research is an experimental investigation of the influence of transverse thermal expansion of GFRP rod on the flexural performance of concrete slabs. Fourteen concrete slabs (divided into four series, A, 8, C and D) were constructed and tested. The slab specimens, 1S0xSOOx2800 mm, were reinforced longitudinally using GFRP rod of 13, 16 or 19 mm bar diameters. No shear reinforcement was provided. The reinforcement ratio, bar diameter, clear bar spacing, concrete cover and placement configurations of GFRP rods were all varied. Each slab was simply supported and subjected to a two-point incremental load to failure. Prior to these ultimate loading tests, some test slabs were either thermally cycled once (series A, 8 and C) or nine times (series D). One slab from each series (A, 8 and C) was tested as a control specimen at room temperature only (no imposed thermal history). The flexural behaviour of these slabs in terms of crack pattern, crack width, deflections, ultimate strength and mode of failure as well the thermal behaviour of GFRP reinforced slabs was investigated. In addition, an attempt has been made to examine the effect of temperature change (100°C) on the mechanical behaviour of GFRP materials. The properties evaluated included the tensile strength, bond behaviour and maximum bond stress. Finally, the experimental results were also compared with the theoretical predictions obtained from the ACI 440.1 R-06, analytical models and with numerical simulations obtained from nonlinear finite element analysis (DIANA-9, 200S). The experimental results showed that the control slabs performed better than the thermally cycled slabs in terms of: mid-span deflection, surface crack widths and ultimate capacity. A number of parameters: reinforcing placement configuration of GFRP bars, bar size, reinforcement ratio, and thermal actions were found to affect the flexural behaviour of the slabs. Due to the transverse thermal incompatibility between the concrete and GFRP, thermal action appears to influence the bond between the concrete and GFRP bars. It was found that the critical concrete cover for GFRP slabs using single or bundled bars depends on reinforcing placement configuration, the transverse thermal expansion of GFRP bars, bar diameter and the concrete tensile strength. To reduce the potential of thermally-induced transverse cracking in GFRP concrete slabs reinforced with a single bar (13, 16 and 19 mm) at a temperatur~ incr~.ase of up to 60°C, a vertical concrete. cover greater than 1.S times the bar diameter (at least 1.Sdb ), a horizontal concrete cover equal or greater than SO mm, and a higher tensile strength of the concrete (at least 2.4 MPa for 13 mm bars) are recommended. For slabs reinforced with bundled (two) bars (13 and 16 mm),the required concrete cover is 1.Sdb and 2.Sdb with tensile strength ler = 3.2 and 3.6 MPa, respectively.

Corrosion of steel reinforcement causes continual degradation to the worldwide infrastructures and it has prompted the need for challenges to those involved with reinforced concrete structures. Recently, the use of fibre-reinforced polymers (FRP) tubes as structurally integrated stay-in-place forms for concrete members, such as beams, columns, bridge piers, piles and fender piles has emerged as an innovative solution to the corrosion problem. In such integrated systems, the FRP tubes may act as a permanent form, often as a protective jacket for concrete, and especially as external reinforcement in the primary and secondary directions such as for confinement. Furthermore, the use of concrete-filled FRP tubes (CFFT) technique is predicated on performance attributes linked to their high strength-to-weight ratios, expand the service life of structures, enhance corrosion resistance, and potentially high durability. This dissertation evaluates the axial and flexural performances of reinforced CFFT through experimental and analytical investigations. The details description and the findings of the investigations are presented through seven articles. To fulfill the objectives of this research, an experimental program has been designed including pure compression tests (33 specimens), axial-eccentric load tests (4 specimens) and pure flexure tests (10 specimens). Experimental investigations of the behaviour of CFFT have generally been carried out without using internal longitudinal reinforcement. The CFFT system of this study consists basically of filament-wound glass FRP tubes filled with concrete and reinforced internally with steel or FRP bars. Five types of new FRP tubes have been used with different thicknesses and two different diameters, 152 and 213 mm. Pure compression tests have been conducted on 40 specimens with a total height ranging from 305 mm to 1520 mm. One of the main objectives of testing these specimens is to evaluate the design equations of the North American codes and design guidelines to predict the ultimate load capacities of reinforced and unreinforced short CFFT columns. In addition, the effect of three parameters and their interactions on the buckling behaviour were investigated for these specimens; namely, the FRP tube thickness, concrete compressive strength, and slenderness ratio. The effect of eccentric load on the behaviour of four CFFT specimens of diameters 152mm and long 912mm, has been evaluated using four different eccentricity values (15, 30, 45 and 60 mm). Based on the finding of experimental and theoretical investigation for the CFFT columns, a new confinement model is proposed for the confined concrete compressive strength of the CFFT cylinders. Also, the design equations are modified to accurately predict the ultimate and yield loads capacities of internally reinforced and unreinforced short CFFT columns. In addition, the theoretical analysis was utilized to correlate the slenderness ratio of the CFFT columns to various material characteristics and geometric properties of the FRP tubes and concrete. It was found that a slenderness ratio of 12 gave a safe value for the design purposes. However a more precise formula for the slenderness ratio was proposed to control the buckling mode of failure. Pure flexural tests have been conducted on 10 RCFFT and RC beams of a total length 2000 mm with constant diameter 213 mm. The test variables were the type of internal reinforcements (steel or GFRP bars), the FRP tube thickness, concrete compressive strength and the type of transverse reinforcements (spiral steel or FRP tubes). The influence of the considered variables on the flexural behaviour of the tested RCFFT beams is presented. A simplified analytical method is developed to predict the yield and resisting moments corresponding to the failure modes of the tested RCFFT beams. The analysis was conducted according to the equations derived from linear elastic analysis. This analysis was found to be acceptable for predicting the ultimate and yield moments capacities of the FRP or steel-RCFFT beams. In addition, an analytical investigation to examine the validity of the available design provisions for predicting the load-deflection response of CFFT is conducted. The effective moments of inertia of the tested beams are analyzed using the different available code, manuals and design guidelines equations. The results of the analysis are compared with the experimental values. It has been found that the predicted tension stiffening for steel or FRP-RCFFT beams using the conventional equations (steel or FRP-RC member) is underestimated and hence the predicted deflections are overestimated. Based on the experimental data obtained in this study, new proposed equations and a modified expression for the effective moment of inertia of a simply supported CFFT beams reinforced with steel or GFRP bars are introduced.

Sandwich panels comprise a thick, light-weight plastic foam such as polyurethane, polystyrene or mineral wool sandwiched between two relatively thin steel faces. One or both steel faces may be flat, lightly profiled or fully profiled. Until recently sandwich panel construction in Australia has been limited to cold-storage buildings due to the lack of design methods and data. However, in recent times, its use has increased significantly due to their widespread structural applications in building systems. Structural sandwich panels generally used in Australia comprise of polystyrene foam core and thinner (0.42 mm) and high strength (minimum yield stress of 550 MPa and reduced ductility) steel faces bonded together using separate adhesives. Sandwich panels exhibit various types of buckling behaviour depending on the types of faces used. Three types of buckling modes can be observed which are local buckling of plate elements of fully profiled faces, flexural wrinkling of flat and lightly profiled faces and mixed mode buckling of lightly profiled faces due to the interaction of local buckling and flexural wrinkling. To study the structural performance and develop appropriate design rules for sandwich panels, all these buckling failure modes have to be investigated thoroughly. A well established analytical solution exists for the design of flat faced sandwich panels, however, the design solutions for local buckling of fully profiled sandwich panels and mixed mode buckling of lightly profiled sandwich panels are not adequate. Therefore an extensive research program was undertaken to investigate the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. The first phase of this research was based on a series of laboratory experiments and numerical analyses of 50 foam-supported steel plate elements to study the local buckling behaviour of fully profiled sandwich panels made of thin steel faces and polystyrene foam core covering a wide range of b/t ratios. The current European design standard recommends the use of a modified effective width approach to include the local buckling effects in design. However, the experimental and numerical results revealed that this design method can predict reasonable strength for sandwich panels with low b/t ratios (< 100), but it predicts unconservative strengths for panels with slender plates (high b/t ratios). The use of sandwich panels with high b/t ratios is very common in practical design due to the increasing use of thinner and high strength steel plates. Therefore an improved design rule was developed based on the numerical results that can be used for fully profiled sandwich panels with any practical b/t ratio up to 600. The new improved design rule was validated using six full-scale experiments of profiled sandwich panels and hence can be used to develop safe and economical design solutions. The second phase of this research was based on a series of laboratory experiments and numerical analyses on lightly profiled sandwich panels to study the mixed mode buckling behaviour due to the interaction of local buckling and flexural wrinkling. The current wrinkling formula, which is a simple modification of the methods utilized for flat panels, does not consider the possible interaction between these two buckling modes. As the rib depth and width of flat plates between the ribs increase, flat plate buckling can occur leading to the failure of the entire panel due to the interaction between local buckling and wrinkling modes. Experimental and numerical results from this research confirmed that the current wrinkling formula for lightly profiled sandwich panels based on the elastic half-space method is inadequate in its present form. Hence an improved equation was developed based on validated finite element analysis results to take into account the interaction of the two buckling modes. This new interactive buckling formula can be used to determine the true value of interactive buckling stress for safe and economical design of lightly profiled sandwich panels. This thesis presents the details of experimental investigations and finite element analyses conducted to study the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. It includes development and validation of suitable numerical and experimental models, and the results. Current design rules are reviewed and new improved design rules are developed based on the results from this research.

Sandwich panels comprise a thick, light-weight plastic foam such as polyurethane, polystyrene or mineral wool sandwiched between two relatively thin steel faces. One or both steel faces may be flat, lightly profiled or fully profiled. Until recently sandwich panel construction in Australia has been limited to cold-storage buildings due to the lack of design methods and data. However, in recent times, its use has increased significantly due to their widespread structural applications in building systems. Structural sandwich panels generally used in Australia comprise of polystyrene foam core and thinner (0.42 mm) and high strength (minimum yield stress of 550 MPa and reduced ductility) steel faces bonded together using separate adhesives. Sandwich panels exhibit various types of buckling behaviour depending on the types of faces used. Three types of buckling modes can be observed which are local buckling of plate elements of fully profiled faces, flexural wrinkling of flat and lightly profiled faces and mixed mode buckling of lightly profiled faces due to the interaction of local buckling and flexural wrinkling. To study the structural performance and develop appropriate design rules for sandwich panels, all these buckling failure modes have to be investigated thoroughly. A well established analytical solution exists for the design of flat faced sandwich panels, however, the design solutions for local buckling of fully profiled sandwich panels and mixed mode buckling of lightly profiled sandwich panels are not adequate. Therefore an extensive research program was undertaken to investigate the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. The first phase of this research was based on a series of laboratory experiments and numerical analyses of 50 foam-supported steel plate elements to study the local buckling behaviour of fully profiled sandwich panels made of thin steel faces and polystyrene foam core covering a wide range of b/t ratios. The current European design standard recommends the use of a modified effective width approach to include the local buckling effects in design. However, the experimental and numerical results revealed that this design method can predict reasonable strength for sandwich panels with low b/t ratios (< 100), but it predicts unconservative strengths for panels with slender plates (high b/t ratios). The use of sandwich panels with high b/t ratios is very common in practical design due to the increasing use of thinner and high strength steel plates. Therefore an improved design rule was developed based on the numerical results that can be used for fully profiled sandwich panels with any practical b/t ratio up to 600. The new improved design rule was validated using six full-scale experiments of profiled sandwich panels and hence can be used to develop safe and economical design solutions. The second phase of this research was based on a series of laboratory experiments and numerical analyses on lightly profiled sandwich panels to study the mixed mode buckling behaviour due to the interaction of local buckling and flexural wrinkling. The current wrinkling formula, which is a simple modification of the methods utilized for flat panels, does not consider the possible interaction between these two buckling modes. As the rib depth and width of flat plates between the ribs increase, flat plate buckling can occur leading to the failure of the entire panel due to the interaction between local buckling and wrinkling modes. Experimental and numerical results from this research confirmed that the current wrinkling formula for lightly profiled sandwich panels based on the elastic half-space method is inadequate in its present form. Hence an improved equation was developed based on validated finite element analysis results to take into account the interaction of the two buckling modes. This new interactive buckling formula can be used to determine the true value of interactive buckling stress for safe and economical design of lightly profiled sandwich panels. This thesis presents the details of experimental investigations and finite element analyses conducted to study the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. It includes development and validation of suitable numerical and experimental models, and the results. Current design rules are reviewed and new improved design rules are developed based on the results from this research.

In this work, long-term behaviour of FRP RC beams has been investigated both analytically and experimentally to further extend the knowledge in this particular research domain. In this respect, a new methodology to determine the long-term deflections due to creep and shrinkage is presented. Based on multiplicative coefficients, the methodology is straightforward and simple, and therefore suitable to be used in design. In addition, an experimental campaign on two series of GFRP RC beams subject to long-term loading has been performed. Different reinforcement ratios, concrete strengths and sustained load levels have been considered. For comparison purposes steel reinforcement has also been used. The experimental long-term results have been reported and discussed. Furthermore they have been compared to predictions using the most representative procedures, as well as, the proposed methodology presented in this work.<br>En aquest treball, es presenta una nova metodologia per a la determinació de fletxes diferides degudes als efectes de la fluència i la retracció del formigó. La metodologia presentada es basa en coeficients multiplicadors, essent així un mètode directe i simple, apte per ser utilitzar en el disseny. Addicionalment, l’estudi presenta els resultats d’una campanya experimental realitzada en dues etapes, on bigues armades amb barres de material compost han estat sotmeses a càrregues a llarg termini. S’han considerat diferents quanties de reforç, resistències de formigó i nivells de càrrega. Per tal de comparar-ne els resultats, també s’han assajat bigues armades amb barres d’acer. Els resultats experimentals han estat analitzats i comparats amb els models de predicció més significatius, així com amb la metodologia desenvolupada i presentada en aquest estudi.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>Nesta dissertação, foi desenvolvido um estudo teórico-experimental de um sistema pré-fabricado de vigamentos mistos de pisos de edificações. O modelo estrutural consiste em vigas mistas do tipo duplo T, onde as nervuras são constituídas por uma viga celular formada a partir de um perfil I laminado, parcialmente embutido na laje de concreto. Após a montagem das vigas-mistas na obra, é feito um capeamento de concreto armado para solidarização do conjunto. Uma grande vantagem deste sistema é proporcionar a integração do piso com o sistema de instalações prediais, por meio da passagem de dutos pelas aberturas do perfil metálico. São apresentados os detalhes do sistema construtivo, bem como as recomendações de projeto. Foi executada uma análise paramétrica para avaliação do comportamento estrutural em termos de eficiência estrutural, visando-se principalmente a redução de custos de fabricação e velocidade de montagem. Com base neste estudo, foi desenvolvido um programa experimental no Laboratório de Estruturas e Materiais da PUC-Rio, para análise do comportamento carga/deformação e da resistência última à flexão dos protótipos submetidos a um carregamento estático. Com os dados obtidos, fez-se uma comparação com os resultados previstos. Os resultados experimentais confirmaram as previsões de resistência fornecidas pelas recomendações de projeto.<br>In this research, is present a theoretical and experimental study of the prefabricated composite beams system. The structural model consists of composite beams of double T type where the ribs are constituted by an asymmetric I-section cellular beam, partially embedded in the concrete slab. After installation of the beams in the work, it is made a reinforced concrete capping for solidarity assembly. A great advantage of this system is integrate the floor with the building installations system, by passing ducts through the openings of the metal profile. This dissertation presents the system with the general details of construction and design. A parametric analysis was performed to assess the structural behavior in terms of structural efficiency. It is mainly aimed at reducing manufacturing costs and speed of assembly. Based on this study, was developed an experimental program in the Structure and Materials Laboratory at PUC-Rio, to analyze the behavior load / deformation and ultimate flexural strength of prototypes subjected to a static loading. With the obtained data, a comparison is made with the expected results analytically. The experimental results confirmed the estimated strength given by the design recommendations.

Includes corrigenda (inserted at front) and list of publications published as a result of this research. Includes bibliographical references (leaves 192-199) Investigates the overload behaviour and modes of collapse of reinforced concrete flexural members containing 500MPa grade reinforcing steel and evaluates the adequacy of current ductility requirements for design according to AS 3600 to ensure strength and safety.

Magister Scientiae Dentium - MSc(Dent)<br>Statement of the problem: Fibre reinforcement of polymethyl methacrylate (PMMA) denture base material is known to improve the strength, as well as the fatigue behavior, of the material. The powder liquid (P/L) ratio of PMMA is often changed to modify the handling properties of the material. Little is known about the effect of this deviation from manufacturer’s guidelines on the fatigue behaviour of the fibre reinforced product. Purpose: This study compared the flexural strength (FS) of PMMA reinforced with glass fibre using different P/L ratios, before and after cyclic loading. Methods and materials: Three groups, with 50 glass fibre reinforced (everStick nonimpregnated fibers) heat-cured PMMA resin (Vertex Rapid Simplified) specimens each, were prepared using a custom-made template (dimensions 10x9x50mm). Each group had a different P/L ratio: the control group (100%) had the manufacturer’s recommended ratio; the 90% and 80% groups had reduced P/L ratios (by weight).Twenty five specimens from each group were subjected to a 3-point bending compression test using a universal testing machine. The remaining 25 specimens from each group were subjected to cyclic loading (104 cycles) before compression testing. The (FS) was calculated using the highest force (Fmax) before specimen failure. Flexural strength was calculated using the equation: FS=3WL/2bd2. Within each group, median FS values before and after cyclic loading were compared by means of a non-parametric analysis of variance. The Aligned Ranks Transform method was used for the analysis. Statistical significance was set at p=0.05. Results: The Fmax (N) of the control (100%), 90% and 80% groups fatigued and unfatigued were 100%: 1665 (fat), 1465 (unfat); 90%: 1679 (fat), 1548 (unfat) and 80%: 1585 (fat), 1467 (unfit) respectively. There was no significant interaction between Mix ratio and Fatigue state, and the 80% mix had a significantly higher mean than either the 90% or 100% mix (with differences of about 0.3 units for both). The Fatigued state had a higher mean than the Un- fatigued state by about 6.0 units. Using FS (MPa) it was found that the fatigued 80% mix specimens had the highest value. The FS MPa of the control (100%), 90% and 80% groups fatigued and un-fatigued were 64.3, 60.6; 66.9, 65.6 and 70.2, 69.3 respectively. The fact that fatiguing strengthened the specimens merits further research. When observing the broken specimens it was found that there was a complete debonding of the fibres and the PMMA. Conclusion and clinical relevance: a) Fibre: The benefit of using glass fibre bundles to reinforce prostheses fabricated using heat cured PMMA is questionable due to problems with bonding between the fibre bundles and the heat cured PMMA resin. b) Fatiguing: An average person chews 107 times during a 3 year period. A limited period of average masticatory forces should not have a detrimental effect on prostheses made from heat cured PMMA resin. c) Mix ratio: Within the normal parameters of laboratory techniques the mix ratio of PMMA resin had no significance on the fracture resistance of the prostheses. Due to the high cost of the fibres used for the reinforcement and the limited success and insignificant results achieved in this study, this researcher cannot recommend using Stickbond or Stick fibers for the reinforcement of dentures made with heat cured PMMA resin.

Reinforcement corrosion is the most common deterioration problem observed in reinforced concrete (RC) structures located at coastal or cold regions. The corrosion process can impact the performance of these structures by inducing damage on the bonding action between concrete and steel, either by the splitting of the concrete cover due to the volumetric expansion of corrosion products or the lubricant effect at the steel/concrete interface as the corrosion by-products accumulate. The current research aims at investigating corrosion-induced deterioration of bond between steel and concrete through finite element (FE) analysis of the flexural behaviour of corroded RC components. By treating the concrete cover as a thick-wall cylinder subjected to internal pressure, the analytical evaluation of impaired bond capacity is studied first and verified against published bonding tests. Then, the formulation of a numerical model is performed using ABAQUS, wherein a link element to simulate the bond behaviour is formulated and implemented through the ABAQUS user-subroutine (UEL) feature according to the validated analytical model. By introducing corrosion-induced damages, i.e., smaller cross-sectional area of reinforcement, splitting of concrete and bond deterioration, in the FE analyses, the results of the numerical model show good agreement with experimental observations. Upon validation of the analytical and FE models, a parametric investigation is conducted, wherein the effects of concrete strength, dimension of reinforcing bars, properties of oxide products, different corrosion damage mechanisms and the corrosion location along the longitudinal reinforcement on the flexural behaviour of RC beams are studied. The results show that the analytical evaluation for bond degradation is impacted by the selection of the post-cracking material model and the thickness of cover that determine the ‘holding capacity’ after cracking initiation. Also, the density of rust by-products affects the results of the analytical model at high corrosion levels. From the FE model results, it was observed that each damage mechanism due to corrosion contribute to different levels of flexural degradation, although the flexural strength degradation is mainly due to the loss of bonding action. The parametric study also demonstrates that flexural members which have reinforcement corrosion initiated near the supports suffer greater deterioration in flexural capacity than those with damages at mid span. Finally, based on these observations, suggestions for the application of both analytical and numerical models are made.

Ultra high performance fibre reinforced concrete is a relatively new material developed by taking advantage of advances in concrete technology and material science to enhance its microstructure. Short, discrete fibres with a high aspect ratio (50-100) substantially improve its ductility. The material's overall performance is therefore superior to other types of reinforced and fibre reinforced concretes with respect to strength, ductility and durability. However, despite its enormous potential, adoption of the material is still relatively low. This is attributed not only to its higher cost but also to a lack of enough experimental data and widely accepted design standards. While some effort is being made to develop numerical models for UHPFRC, many are based on multiscale frameworks requiring the measurement of microscale parameters. Such parameters are difficult to measure whereas for most practical purposes design normally requires material properties measured at the macroscale. The overall aim of this research therefore is to propose a numerical damage model for UHPFRC that uses material properties from standard tests and that can simulate the flexural behaviour of UHPFRC and predict its failure loads. Initial modelling enabled identification of suitable approaches for estimating the elastic modulus, tensile strength and fracture energy values appropriate for simulating the material's flexural behaviour. A comprehensive experimental investigation undertaken established the existence of size effect on the flexural stress at the end of linearity and flexural strength of notched and un-notched specimens with 2%, 4% and 6% fibre content. The tests also identified the significant effect of fibre content on the elastic modulus, tensile strength and fracture energy values. Therefore the effect of fibre content was incorporated into the proposed damage model by making these three material properties a function of it. This is done by incorporating values of estimated material properties into a bilinear traction separation law thereby also linking the damage to fibre content. The multiple fibre content effects represented include the spacing and number of fibres per unit cross-sectional area. The model adopts a smeared crack approach. It is implemented as a user defined material model in ABAQUS finite element software and written in FORTRAN code. The model's ability to simulate the load deflection response was validated using two case studies. The model's predictions match test data reasonably well for specimens of different sizes, test arrangement and fibre contents. Therefore a validated numerical material model incorporating fibre content is proposed as a simple, practical and economical tool for predicting the material's flexural behaviour thereby achieving the overall aim of the study. This is one of the main contributions of this study. Another contribution is the establishment of size effects on the flexural properties of UHPFRC at 2%, 4% and 6% fibre contents. Finally values of material properties at these fibre contents estimated from test data and comparisons between the different modelling approaches are a valuable resource for similar studies in future.

Cold-formed steel purlin systems are widely used in modem building construction, for supporting the roof and floor structures. The rotational behaviour of beam-to-beam bolted connections, which are used between the sections, significantly affects the performance of purlin systems and is hard to predict. The behaviour models currently available for the connections only offer linear or multilinear predictions with low levels of accuracy. The aim of the research presented in this thesis is to develop and propose a nonlinear, more accurate behaviour model for the sleeved modified Z bolted connections, by means of experimental and numerical analysis. Finite element models are presented for the single-bolt, single-lap connection, sleeved modified Z connections in the simply supported arrangement, and a six-span purlin system. Based on the numerical results that have been validated by the experiments, a nonlinear behaviour model is proposed for the sleeved modified Z connections. In the model, the behaviour of the connections is divided into four stages, based on the dominant mechanism that provides the resistance to the rotation. Different formulas are used in different stages to determine the behaviour of the connection, boundary conditions, and magnitudes of bolt forces. The new model reflects well the true behaviour of the connections, and provides a good understanding of what happens inside the connections. The model reveals the failure pattern of the connections and enables optimization in the design of purl in systems, for improving efficiency in material usage.

The main objective of the thesis is to study the bond behaviour of NSM FRP reinforcement in concrete elements. With this aim an extensive program of experimental tests complemented with numerical analysis has been performed to study the effect of the variables affecting this technique. In the first part of this thesis the modified pull-out test is carried out. A Finite Element Analysis (using the program FEMIX V.4) was used to perform several trials to fit as much as possible (inverse analysis) the force versus loaded end slip responses obtained experimentally in direct pullout tests. In the second part of this thesis an experimental program of flexural tests on RC beams strengthened with NSM FRP has been carried out to study the effect on the flexural behaviour of some of the previous variables studied in the first part<br>L’objectiu principal d’aquesta tesi és l’estudi del comportament adherent entre el reforç NSM FRP i l’element de formigó. D’aquesta manera s’ha realitzat un extens programa d’assajos experimentals complementat amb anàlisis numèriques per tal d’estudiar les variables que incideixen en aquesta tècnica. En la primera part de la tesi es fa un estudi de l’adherència emprant l’assaig de pull-out modificat. S’ha realitzat una anàlisi amb el MEF (emprant el programa FEMIX V.4) per tal de fer diverses proves per ajustar amb la màxima precisió possible (anàlisi inversa) la resposta força-lliscament de l’extrem carregat de la barra obtinguda experimentalment en els assajos de pull-out. A la segona part de la tesi s’ha portat a terme un programa d’assajos a flexió d’elements de formigó armat reforçats amb NSM FRP per tal d’estudiar l’efecte d’algunes de les variables analitzades en la primera part

The final thesis consists of three main parts, each covering a certain aspect of investigation. First chapter presents an extensive literature review, covering such aspects as: application of FRP (fiber reinforced polymer) materials in modern-day civil engineering, characteristics of FRP reinforcement for reinforced concrete structures, advantages and drawbacks of FRP rebars compared to traditional materials, peculiarities of flexural behavior of FRP reinforced members, review of existing empirical stress-strain calculation algorithms and building codes for concrete members reinforced with FRP. Second part aims at presenting gathered experimental data consisting of 51 FRP reinforced flexural members under 4 point bending scheme. Taking into account such parameters as reinforcement ratio, load intensity and elasticity modulus of FRP reinforcement, statistical analysis on a number of calculation algorithms and building codes is performed in order to evaluate their credibility and reliability for use in real-world structures. The final part of the work presents a Simplified Discrete Crack model developed in VGTU Department of Bridges and Special Structures. The model is applied for a series of collected beams. The results are compared with theoretical predictions made by different design codes and experimental values. The final thesis consists of: 90 pages of text (without appendixes), 46 pictures, 17 tables. 3 appendixes are included. Literature list consisting of 82... [to full text]<br>Baigiamąjį magistro darbą sudaro trys pagrindinės dalys. Pirmajame skyriuje pateikiama literatūros apžvalga, kurioje nagrinėjamos temos susijusios su pluoštinės armatūros panaudojimu lenkiamiems betoniniams elementams. Apžvelgiamos tokių elementų panaudojimo galimybės, privalumai ir trūkumai, deformacijų skaičiavimo metodai bei matematiniai modeliai. Antrajame skyriuje nagrinėjama surinkta polimerine armatūra armuotų sijų eksperimentinių duomenų imtis. Siekiant įvertinti skirtingų skaičiavimo metodų patikimumą ir pritaikomumą ne plienine armatūra armuotiems elementams, atliekama lyginamoji statistinė analizė. Jos metu įvertinama armavimo procento, apkrovimo lygio bei pluoštinės armatūros tamprumo modulio įtaka. Trečiojoje darbo dalyje surinktai eksperimentinių duomenų imčiai pritaikytas VGTU Tiltų ir Specialiųjų Statinių Katedroje sukurtas Diskrečiųjų plyšių modelis. Gautos priklausomybės palygintos su kitų skaičiavimo normų rezultatais bei eksperimentiniais duomenimis. Gauti rezultatai parodė, kad pritaikius tikslesnius praslydimo bei armatūros ir betono sąveikos ruožuose tarp plyšių modelius, diskrečiųjų plyšių modelis gali būti sėkmingai taikomas polimerine armatūra armuotų elementų elgsenai prognozuoti.

A modified version of the computer program written by Chan (1986) for the analysis of unbonded prestressed concrete members under third point loading was developed. The new program carries out the analysis more quickly and efficiently while still maintaining the required accuracy level. The program was used to analyse twenty-two unbonded beams with bonded steel tested in China and twelve unbonded slabs with bonded steel and a futher six unbonded slabs without bonded steel tested at the University of Canterbury. All analytical and experimental results were compared . The comparison revealed that the theoretical analyses gave good representation of the flexural behaviour of the unbonded concrete members both with and without bonded reinforcement. The report confirms the Chinese finding that the combined reinforcement index has very significant effect on the ultimate tendon stress increase and moment capacity for the unbonded members However, the effect of span-depth ratio on the flexural behaviour of unbonded partially prestressed concrete members was not significant. It is also confirmed that the unbonded members with bonded reinforcement behave in a more effective way than those without bonded reinforcement. The report recommends that bonded reinforcement should be used in design practice. Two recommendations based on experimental results are proposed for the determination of ultimate moment capacity of unbonded partially prestressed concrete members. The proposed expressions for member without bonded reinforcement is given just for comparison and it is not recommended for use in practical design. It is also recommended that the value of the combined reinforcement index chosen should be greater than 0.06 to prevent the occurrence of flexural instability and less than 0.305 for efficient design of the unbonded system. Value greater than 0.305 lead to a compression failure resulting in a low value of ultimate tendon stress increase and no increase in moment capacity.

Thesis (MScEng)--Stellenbosch University, 2011.<br>ENGLISH ABSTRACT: Strain hardening cement‐based composites (SHCC) are fibre‐reinforced composites designed to form multiple fine cracks under tensile and flexural load. The cracks are controlled to small widths, whereby significant toughness, or energy dissipation, is realised on the one hand, and high resistance to gas and liquid ingress is maintained on the other hand. These two physical phenomena define application fields of SHCC, i.e. for instance elements of buildings and infrastructure for enhanced earthquake resistance, and protection of steel bars under service loads which lead to crack formation. Also exploiting the potential protection offered by SHCC to existing structures, thin overlays have been applied to existing dam faces, reinforced concrete retaining walls, water channels and RC road pavements. The layers vary between 20 and 40 mm in thickness. Considering the fibre length, usually 8 or 12 mm, as well as the application method, such thin layers may have dominantly two dimensional fibre orientation, with little or no component in the layer thickness direction. While several research groups have performed uniaxial tensile tests and flexural tests on SHCC specimens, little or no information is available on SHCC response to biaxial loading, as is to be expected in road pavement repair layers, or other repair layers. This paper reports the results of biaxial testing of 20 mm thick SHCC specimens produced in such a way to have dominantly two‐dimensional fibre orientation, and another group of specimens produced by cutting from larger specimens, whereby three‐dimensional fibre orientation was preserved in the resulting 20 mm thick specimens. Biaxial tests were performed in three quadrants, i.e. compressioncompression, compression‐tension, and tension‐tension. A clear fibre orientation‐related difference in the failure patterns involves out‐of‐plane splitting under biaxial compression of specimens with twodimensional fibre orientation, at significantly lower load, as opposed to in‐plane tensile splitting of specimens containing three‐dimensional fibre orientation.<br>AFRIKAANSE OPSOMMING: Vervormingsverhardende sement‐gebaseerde saamgestelde materiale (SHCC) is veselversterke saamgestelde materiale wat ontwerp is om verskeie fyn krakies te vorm onder trekspanning en buig spanning. Die kraakbreedtes word beheer, waardeur betekenisvolle taaiheid verkry, of energie verlies beheer word aan die een kant, en die hoë weerstand teen die gas en die vloeistof penetrasie aan die ander kant gehandhaaf word. Hierdie twee fisiese verskynsels definieer die toepassingsvelde van SHCC, d.w.s vir byvoorbeeld elemente van geboue en infrastruktuur vir verbeterde aardbewing weerstand, en die beskerming van staal stawe onder die dienslaste wat lei vorming te kraak. By eksploitasie van die potensiële beskerming aangebied deur SHCC aan bestaande strukture, is dun oorlae op bestaande dam walle, versterkte beton keermure, water kanale en staal‐versterkte beton paaie gebruik. Die SHCC lae wissel tussen 20 en 40 mm in dikte. Met inagneming van die vesel lengte, gewoonlik 8 of 12 mm, sowel as die toepassingsmetode, kan so 'n dun lag ‘n oorheersend tweedimensionele vesel oriëntasie hê, met min of geen komponent in die rigting van die laag dikte nie. Terwyl verskeie navorsingsgroepe eenassige trektoetse en buigtoetse op SHCC monsters gedoen het; is daar min of geen inligting beskikbaar op SHCC se reaksie op biaksiale belasting, soos verwag kan word in die pad herstel lae, of ander herstel lae. Hierdie verslag rapporteer die resultate van die biaksiale toetsing van 20 mm dik SHCC monsters wat op so 'n manier gemaak word om dominante twee‐dimensionele vesel oriëntasie te hê, en 'n ander groep monsters wat deur die sny van groter monsters, waarvolgens die drie‐dimensionele vesel oriëntasie verseker is. Biaksiale toetse is uitgevoer in drie kwadrante, d.w.s druk‐druk, druk‐trek en trek‐trek. 'n Duidelike verskil in die falingspatrone, aan die hand van vesel oriëntasie, behels uit‐vlak splyting onder biaksiale toetsing van monsters met twee‐dimensionele vesel oriëntasie, op 'n aansienlik laer lading, in teenstelling met die in‐vlak trek splyting van monsters wat ‘n drie‐dimensionele vesel oriëntasie het.

Gypsum Plasterboard is « commonrliningimateriaL It is often used. with cold+ formed steel in wall, frame systems.'· It is used eitheD with lipped or- unlipped- (plain) C-· sections in the construction of both the load bearing and non-load bearing walls in residential, industrial and commercial buildings. This type of construction is common in Australia, the USA and Europe. In Australia plasterboard is commonly used in external walls with brick veneer as the outer skin of buildings. Plasterboard, however, is considered as a non-structural material and in the design of the studs in wall frames, the strengthening effects of the plasterboard in carrying axial (or other) loads is ignored. The Australian standard for cold-formed steel structures AS/NZS 4600 ( 1996) permits the use of lateral and rotational support to the steel studs in the plane of the wall provided by the lining material. However, it does not specify the magnitude of lateral or rotational support that can be used for the stud wall frames. Miller and Pekoz (1994a) have carried out experiments on studs subjected to axial compression loads and concluded that the experimental results contradict the shear diaphragm model assumed by American specification (AISI, ... , ,..,. .. 1986). A suitable design method to accurately predict the structural behaviour of studs under axial compression, bending and combined ·.axial compression and bending is required. As a first step in the development of the design methods, the axial compression loads must be studied. The objective of this research is therefore to determine a design model for the gypsum plasterboard lined cold-formed steel stud walls that can accurately represent their behaviour and to accurately predict the ultimate strength of the stud walls under axial compression. For this purpose, an extensive research project was undertaken using the following: 20 full scale tests on typical cold-formed steel stud wall frames (unlined, one side and both sides lined), 24 short stud column tests to study the effects of plasterboard lining on local buckling of flanges, fmite element analysis (FEA) of full scale cold- Y.K Telue: Behaviour and design of plasterboard lined cold-formed steel studwall·systems formed steel stud wall frames including validation with full scale test results and a detailed parametric study using FEA. It has been shown in this research that lining the plasterboard on one or both sides can increase the ultimate load of the' stud considerably. The Australian -and AISI specifications were found to be inadequate in predicting the ultimate loads and failure modes of the studs. This research has shown that by using appropriate effective length factors, the ultimate load and the failure modes of both the unlined and the. lined studs can be accurately .predicted using the provisions of AS/NZS 4600 (1996). In the case of lined studs, it has been shown that the effective length factors in the plane of the wall and· .for torsion can be related to the ratio of the fastener spacing to the total unbraced height' of the studs. The thesis also presents design rules that can accurately predict the ultimate load and the failure mode of slender web studs lined on one or both sides.