Dissertations / Theses on the topic 'Design of reinforced concrete column'

A parametric analysis on 58 beam-column joint specimens has been conducted. The analysis considered 14 fundamental parameters in the design of each specimen and two performance indicators: the horizontal shear strength ratio between the maximum measured strength and the theoretical strength at beam yield, and the nominal curvature ductility of the adjacent beams. Each parameter was varied by a power function, while the linear correlation coefficient between each parameter and performance indicator was recorded. A combined multiple parameter analysis was then conducted to show the interaction of the design parameters and show the representative influences of each parameter based on the magnitude of the applied power functions. Two design equations were constructed from the most influential design parameters, one for each performance indicator. The shear strength ratio was found to be governed by the horizontal joint shear stress, the column axial stress and the yield strength of the longitudinal beam reinforcement. The available curvature ductility of the adjacent beams was also found to be governed by the horizontal joint shear stress, the column axial stress and the yield strength of the longitudinal beam reinforcement, but also the quantity of the horizontal joint shear reinforcement. The influence of the column axial stress on both performance indicators was found to be best represented by a quadratic function. This was because the column axial stress was found to be beneficial up to stress levels of , but axial stress levels exceeding were found to be detrimental to the performance of the beam-column joint, compared to a joint with no axial stress on the columns. The non-linear relationship of the column axial stress agreed with the design assumptions in NZS 3101 for low axial stress values, but at higher axial stress values NZS 3101 assumes a continued performance increase as a result of increasing axial stress, which has been found to be un-conservative. Additionally, an interaction between the column axial stress and the horizontal joint shear stress has been identified. As a result, beam-column joints with high column axial stress levels above 0.40 and horizontal joint shear stress levels in the order of have been shown to fail in a brittle crushing of the concrete in the joint core. Considering this behaviour, it is recommended that the column axial stress levels in earthquake designed beam-column joints should not exceed 0.35 . The results of the parametric analysis were then compared against the current NZS 3101 design equations for conservatism. It was found that a reduction in the horizontal joint shear reinforcement may be possible for beam-column joints incorporating Grade 300 steel in the longitudinal reinforcement of the beams and axial stress levels below 0.25 , but when Grade 500 steel is used or the column axial stress is greater than 0.25 , an increase in the joint shear reinforcement is required compared to NZS 3101. The current NZS 3101 design requirement of at least 40% of the joint shear force, to be resisted by means of joint shear reinforcement, has been found to be appropriate.

Beam-column joints are addressed in the context of current design procedures and performance criteria for reinforced concrete ductile frames subjected to large earthquake motions. Attention is drawn to the significant differences between the pertinent requirements of concrete design codes of New Zealand and the United States for such joints. The difference between codes stimulated researchers and structural engineers of the United States, New Zealand, Japan and China to undertake an international collaborative research project. The major investigators of the project selected issues and set guidelines for co-ordinated testing of joint specimens designed according to the codes of the countries. The tests conducted at the University of Canterbury, New Zealand, are reported. Three full-scale beam-column-slab joint assemblies were designed according to existing code requirements of NZS 3101:1982, representing an interior joint of a one-way frame, an interior joint of a two-way frame, and an exterior joint of a two-way frame. Quasistatic cyclic loading simulating severe earthquake actions was applied. The overall performance of each test assembly was found to be satisfactory in terms of stiffness, strength and ductility. The joint and column remained essentially undamaged while plastic hinges formed in the beams. The weak beam-strong column behaviour sought in the design, desirable in tall ductile frames designed for earthquake resistance, was therefore achieved. Using the laws of statics and test observations, the action and flow of forces from the slabs, beams and column to the joint cores are explored. The effects of bond performance and the seismic shear resistance of the joints, based on some postulated mechanisms, are examined. Implications of the test results on code specifications are discussed and design recomendations are made.

This report describes an experimental and analytical investigation of the strength and ductility of reinforced concrete columns. Four columns of square cross-section were tested under axial compression loading and cyclic lateral loading applied at mid-height which simulated seismic loading. The main variable investigated was the quantity of transverse confining steel used, which ranged between 17 to 46 percent of the NZS 3101:1982 recommended quantity for ductile detailing. The experimental results are reported in the form of lateral loaddisplacement and lateral load-curvatures hysteresis loops, curvature profiles, transverse steel strain distributions and concrete compressive strains. The results are discussed and compared with the analytical predictions. A modified equation for the quantity of confining reinforcement in rectangular columns is recommended. Conclusions are made regarding the ductility available from columns containing substantially less transverse confining reinforcement than recommended by the New Zealand concrete design code.

Thesis (Ph.D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008.
Committee Co-Chair: Kahn, Lawrence F.; Committee Co-Chair: Zureick, Abdul-Hamid; Committee Member: Armanios, Erian A.; Committee Member: Gentry, Russell T.; Committee Member: Leon, Roberto T.

Use of fiber reinforced polymer (FRP) material has been a good solution for many problems in many fields. FRP is available in different types (carbon and glass) and shapes (sheets, rods, and laminates). Civil engineers have used this material to overcome the weakness of concrete members that may have been caused by substandard design or due to changes in the load distribution or to correct the weakness of concrete structures over time specially those subjected to hostile weather conditions. The attachment of FRP material to concrete surfaces to promote the function of the concrete members within the frame system is called Externally Bonded Fiber Reinforced Polymer Systems. Another common way to use the FRP is called Near Surface Mounted (NSM) whereby the material is inserted into the concrete members through grooves within the concrete cover. Concrete beam-column joints designed and constructed before 1970s were characterized by weak column-strong beam. Lack of transverse reinforcement within the joint reign, hence lack of ductility in the joints, and weak concrete could be one of the main reasons that many concrete buildings failed during earthquakes around the world. A technique was used in the present work to compensate for the lack of transverse reinforcement in the beam-column joint by using the carbon fiber reinforced polymer (CFRP) sheets as an Externally Bonded Fiber Reinforced Polymer System in order to retrofit the joint region, and to transfer the failure to the concrete beams. Six specimens in one third scale were designed, constructed, and tested. The proposed retrofitting technique proved to be very effective in improving the behavior of non-ductile beam-column joints, and to change the final mode of failure. The comparison between beam-column joints before and after retrofitting is presented in this study as exhibited by load versus deflection, load versus CFRP strain, energy dissipation, and ductility.

Seismic design of highway bridges has improved as a result of the experience gained from large earthquakes of the last thirty years. Ductility demand and reserved capacity are extremely important response measures used in new bridge designs to assess target damage levels. However, the application of practical design approaches specified in bridge design codes is not well-defined for bridges over flexible foundations. Within the scope of this research, thirty two bridge models having varying column aspect ratio, amount of column longitudinal reinforcement and foundation flexibility parameters are investigated through a series of analyses such as response spectrum analysis and inelastic time-history analysis under &ldquo
safety evaluation earthquake&rdquo
hazard level with a return period of 1000 years, and push-over analysis. Using the results of analyses, seismic response of the investigated bridges are identified with several measures such as displacement capacity over demand ratio, global displacement ductility demand, and response modification factor, along with maximum concrete and steel strains of columns. A correlation between concrete and steel strains and seismic response measure values is constructed to estimate damage levels with commonly used response measures. The findings of this research revealed that global displacement ductility demand is not a favorable response measure for assessing damage levels. On the other hand, displacement capacity over demand ratios can be suggested for estimation of damage levels especially where foundation flexibility effects are extensive as system yielding is not taken into consideration.

Experimental studies about the cyclic response of reinforced concrete bridge columns designed to avoid shear failure and subjected to cyclic, reversible, and increasing displacements have been performed in several laboratories around the world. As a consequence there are several force-displacement relationships, called resultant models, that allow to predict the response of those columns. However, the use of the resultant models for earthquake response requires extensive calibration of several parameters. In this investigation a Finite Fiber Element Model, FFEM, is obtained after calibrating first, the response of 30 circular reinforced concrete bridge columns tested under cyclic, reversible, and increasing displacements. Then a re-calibration is carried out in order to simulate the response of two additional columns shake table tested under two earthquake ground motions. After obtaining satisfactory results the FFEM was used to simulate the seismic response of three bridge columns designed according to the prescriptions of the new seismic design bridge code. The FFEM is able to predict directly four flexural failure mechanisms: cracking and crushing of the unconfined and confined concrete, fracture of the longitudinal steel bars due to tension, P-Δ effects, and fatigue of the longitudinal steel bars. Indirectly, the FFEM is able to predict the possible buckling of the longitudinal bars by capturing the confined concrete strain time-history. In order to capture the low-cyclic fatigue, the FFEM through inelastic dynamic analysis is able to calculate the number of cycles and the amplitude of the cyclic plastic strains so these quantities are introduced into the fatigue equation. The fracture of the bars due to low-cyclic fatigue is a failure mechanism that depends on the accumulation of damage along the severe ground motion. The way to estimate the loss of fatigue life in a steel bar is considering the effect of the duration in the calculations since the materials stress-strain relationships are independent of the duration of the ground motion. In order to determine the accumulation of damage in the bridge column a Cyclic Damage Index is proposed here. The Index is based on the energy dissipated by the column at the end of the ground motion.

Methods for the design of reinforced concrete bridge columns and piers for strength and ductility are considered. The investigations cover the following areas. An experimental investigation of the influence of reinforcing steel grade and amount of confining steel on the stress-strain behaviour of confined concrete is presented. The results are discussed and compared with theoretical models. Special attention is given to the possibility of fracture of the confining steel. An extensive experimental investigation into the ductile performance of a range of reinforced concrete columns is presented. The columns were subjected to constant axial load and cyclic lateral displacements. The test units included four square columns with the lateral load applied in the direction of a cross section diagonal, six circular hollow columns with different wall thickness to diameter ratios, and four columns with transverse reinforcement from Grade 380 steel. The available strength and ductility of the columns is discussed and compared with the performance of columns tested previously at the University of Canterbury, and with theoretical predictions using monotonic as well as cyclic moment-curvature analyses. The main variables for the solid columns were the influence of biaxial bending, the use of Grade 380 transverse steel for confinement, and the spacing between transverse bars along the column axis. The circular hollow columns were unconfined on the inside face of the tube wall, and the main variables were the influence of the axial load level and the wall thickness. The implications of the column test results, including the results of other investigations, for the design of reinforced concrete columns for strength and ductility are discussed and, where appropriate, used to calibrate theoretical models. In particular, the influence of cyclic loading on the strength deterioration of reinforced concrete columns with high axial loads is emphasized. More realistic definitions of the ideal flexural strength, of the flexural overstrength and of the yield curvature are suggested and, together with a set of criteria for the ultimate limit state, used to establish design charts for the available strength and ductility of reinforced concrete columns. A cyclic moment-curvature analysis was used for this purpose, incorporating cyclic stress-strain models for the concrete and for the steel, thus taking into account the cyclic strength deterioration observed for columns with high axial loads. Finally, a rational step-by-step design procedure is presented that will make less complex the task of considering the great number of variables involved in the seismic design of reinforced concrete columns for both strength and ductility.

Since the early 1970's the design procedures and techniques for building earthquake-resistant bridges have advanced considerably, and have been implemented in the form of design codes. However, many bridge structures in service today were built before the revised design procedures and guidelines were implemented, and their performance in the event of an earthquake is questionable. Following recent moderate earthquakes in California various retrofit techniques have been proposed to increase the earthquake resistance of existing bridge structures. An innovative method to enhance the flexural strength, ductility capacity and shear resistance of existing reinforced concrete bridge columns through externally reinforcing the column with advanced composite materials (ACM) were developed. The ACM composite straps, which were unidirectionally arranged and impregnated with epoxy resin, were wrapped around the potential plastic hinge region at specified intervals. Additional advantages would be gained by laterally prestressing the straps at the time of strengthening. The confinement and the lateral stresses induced by the straps significantly increased the shear strength and ductility capacity, and greatly improved the flexural behavior of reinforced concrete columns under simulated earthquake loading. Both experimental and analytical studies were conducted in the Structural Engineering Laboratory to demonstrate the feasibility of the proposed technique. A total of fourteen column-footing units were constructed with a 20 percent dimensional scale factor to model the typical design of many existing bridge columns. Half of these specimens were with circular cross sections and remaining specimens with rectangular cross sections. All the specimens were tested under inelastic reversed cyclic loading while simultaneously subjected to a constant axial load. The variables in the test program were the type of cross sections, the amount of ACM composite straps, different retrofit schemes and active grout pressure. Analytical models based on an energy balance approach were developed to predict the enhancement in the strength and ductility of retrofitted columns. Design examples and guidelines for seismic retrofitting were also presented.

This research investigated the behavior of nonseismically detailed reinforced concrete exterior beam-column joints subjected to bidirectional lateral cyclic loading using nonlinear finite element analysis (NLFEA). Beam-column joints constitute a critical component in the load path of reinforced concrete buildings due to their fundamental role in integrating the overall structural system. Earthquake reconnaissance reports reveal that failure of joints has contributed to partial or complete collapse of reinforced concrete buildings designed without consideration for large lateral loads, resulting in significant economic impact and loss of life. Such infrastructure exists throughout seismically active regions worldwide, and the large-scale risk associated with such deficiencies is not fully known. Computational strategies provide a useful complement to the existing experimental literature on joint behavior and are needed to more fully characterize the failure processes in seismically deficient beam-column joints subjected to realistic failure conditions. Prior to this study, vulnerable reinforced concrete corner beam-column joints including the slab had not been analyzed using nonlinear finite element analysis and compared with experimental results. The first part of this research focused on identification and validation of a constitutive modeling strategy capable of simulating the behaviors known to dominate failure of beam-column joints under cyclic lateral load using NLFEA. This prototype model was formulated by combining a rotating smeared crack concrete constitutive model with a reinforcing bar plasticity model and nonlinear bond-slip formulation. This model was systematically validated against experimental data, and parametric studies were conducted to determine the sensitivity of the response to various material properties. The prototype model was then used to simulate the cyclic response of four seismically deficient beam-column joints which had been previously evaluated experimentally. The simulated joints included: a one-way exterior joint, a two-way beam-column exterior corner joint, and a series of two-way beam-column-slab exterior corner joints with varying degrees of seismic vulnerability. The two-way corner joint specimens were evaluated under simultaneous cyclic bidirectional lateral and cyclic column axial loading. For each specimen, the ability of the prototype model to capture the strength, stiffness degradation, energy dissipation, joint shear strength, and progressive failure mechanisms (e.g. cracking) was demonstrated.

Ductile plastic hinge zones in beams of reinforced concrete frames are known to incur extensive damage and elongate. This ‘beam elongation’ can inflict serious damage to adjacent floor diaphragms, raising concerns of life safety. In light of this, the slotted reinforced concrete beam was investigated as a promising non-tearing floor substitute for conventional design. It consists of a conventional reinforced concrete beam, modified with a narrow vertical slot adjacent to the column face, running approximately three-quarters of the beam depth. Seismic rotations occur about the remaining concrete “top-hinge”, such that deformations are concentrated in the bottom bars of the beam, away from the floor slab, and beam elongation is minimised. The inclusion of the slot raised several design issues which needed to be addressed. These were the shear transfer across the top-hinge, buckling of bottom longitudinal reinforcement, low cycle fatigue, bond anchorage of reinforcement in interior joints, interior joint design, detailing with floor units and beam torsion resulting from eccentric floor gravity loads. These issues were conceptually investigated in this project. It was found that most issues could be resolved by providing additional reinforcement and/or specifying alternative detailing. As part of the experimental investigation, quasi-static cyclic tests were performed on in-plane beam-column joint subassemblies. Specimens tested included exterior and interior joint subassemblies with slotted-beams and a conventional exterior joint as a benchmark. This was followed by a test on a slotted-beam interior joint subassembly with precast floor units and imposed gravity load. Experimental tests revealed significant reductions in damage to both the beam and floor when compared to conventional beams. Issues of bar buckling, bond-slip and altered joint behaviour were also highlighted, but were resolved in the final test. A simple analytical procedure to predict the moment-rotation response of slotted-beams was developed and verified with experimental results. This was used to perform sensitivity studies to determine appropriate limits for the concrete top-hinge depth, top-to-bottom reinforcement ratio and depth of diagonal shear reinforcement. For the numerical investigation, a multi-spring model was developed to represent the flexural response of slotted-beams. This was verified with experimental tests and implemented into a five-storey, three-bay frame for earthquake time history analyses. To provide a benchmark, a conventional frame was also setup using the plastic hinge element developed by Peng (2009). Time history analyses showed that the slotted-beam frame response was very similar to the response of a conventional frame. Due to greater hysteretic damping, there was a slight reduction in the average interstorey drift and lateral displacement envelopes. The slotted-beam frame also exhibited 40% smaller residual drifts than the conventional frame. The research carried out in this thesis showed slotted reinforced concrete beams to be an effective non-tearing floor solution, which could provide a simple and practical substitute for conventional reinforced concrete design.

Abstract : Steel and fiber-reinforced-polymer (FRP) materials have different mechanical and physical characteristics. High corrosion resistance, high strength to weight ratio, non-conductivity, favorable fatigue enable the FRP to be considered as alternative reinforcement for structures in harsh environment. Meanwhile, FRP bars have low modulus of elasticity and linear-elastic stress-strain curve. These features raise concerns about the applicability of using such materials as reinforcement for structures prone to earthquakes. The main demand for the structural members in structures subjected to seismic loads is dissipating energy without strength loss which is known as ductility. In the rigid frames, columns are expected to be the primary elements of energy dissipation in structures subjected to seismic loads. The present study addresses the feasibility of reinforced-concrete columns totally reinforced with glass-fiber-reinforced-polymer (GFRP) bars achieving reasonable strength and the drift requirements specified in various codes. Eleven full-scale reinforced concrete columns—two reinforced with steel bars (as reference specimens) and nine totally reinforced with GFRP bars—were constructed and tested to failure. The columns were tested under quasi-static reversed cyclic lateral loading and simultaneously subjected to compression axial load. The columns are 400 mm square cross-section with a shear span 1650 mm. The specimen simulates a column with 3.7 m in height in a typical building with the point of contra-flexure located at the column mid-height. The tested parameters were the longitudinal reinforcement ratio (0.63, 0.95 and 2.14), the spacing of the transverse stirrups (80, 100, 150), tie configuration (C1, C2, C3 and C4), and axial load level (20%, 30% and 40%). The test results clearly show that properly designed and detailed GFRP-reinforced concrete columns could reach high deformation levels with no strength degradation. An acceptable level of energy dissipation compared with steel-reinforced concrete columns is provided by GFRP reinforced concrete columns. The dissipated energy of GFRP reinforced concrete columns was 75% and 70% of the counter steel columns at 2.5% and 4% drift ratio respectively. High drift capacity achieved by the columns up to 10% with no significant loss in strength. The high drift capacity and acceptable dissipated energy enable the GFRP columns to be part of the moment resisting frames in regions prone to seismic activities. The experimental ultimate drift ratios were compared with the estimated drift ratios using the confinement Equation in CSA S806-12. It was found from the comparison that the confinement Equation underestimates values of the drift ratios thus the experimental drift ratios were used to modify transverse FRP reinforcement area in CSA S806-12. The hysteretic behavior encouraged to propose a design procedure for the columns to be part of the moderate ductile and ductile moment resisting frames. The development of design guidelines, however, depends on determining the elastic and inelastic deformations and on assessing the force modification factor and equivalent plastic-hinge length for GFRP-reinforced concrete columns. The experimental results of the GFRP-reinforced columns were used to justify the design guideline, proving the accuracy of the proposed design equations.
L’acier et les matériaux à base de polymères renforcés de fibres (PRF) ont des caractéristiques physiques et mécaniques différentes. La résistance à la haute corrosion, le rapport résistance vs poids, la non-conductivité et la bonne résistance à la fatigue font des barres d’armature en PRF, un renforcement alternatif aux barres d’armature en acier, pour des structures dans des environnements agressifs. Cependant, les barres d’armature en PRF ont un bas module d’élasticité et une courbe contrainte-déformation sous forme linéaire. Ces caractéristiques soulèvent des problèmes d'applicabilité quant à l’utilisation de tels matériaux comme renforcement pour des structures situées en forte zone sismique. La principale exigence pour les éléments structuraux des structures soumises à des charges sismiques est la dissipation d'énergie sans perte de résistance connue sous le nom de ductilité. Dans les structures rigides de type cadre, on s'attend à ce que les colonnes soient les premiers éléments à dissiper l'énergie dans les structures soumises à ces charges. La présente étude traite de la faisabilité des colonnes en béton armé entièrement renforcées de barres d’armature en polymères renforcés de fibres de verre (PRFV), obtenant une résistance et un déplacement latéral raisonnable par rapport aux exigences spécifiées dans divers codes. Onze colonnes à grande échelle ont été fabriquées: deux colonnes renforcées de barres d'acier (comme spécimens de référence) et neuf colonnes renforcées entièrement de barres en PRFV. Les colonnes ont été testées jusqu’à la rupture sous une charge quasi-statique latérale cyclique inversée et soumises simultanément à une charge axiale de compression. Les colonnes ont une section carrée de 400 mm avec une portée de cisaillement de 1650 mm pour simuler une colonne de 3,7 m de hauteur dans un bâtiment typique avec le point d’inflexion situé à la mi-hauteur. Les paramètres testés sont : le taux d’armature longitudinal (0,63%, 0,95% et 2,14 %), l'espacement des étriers (80mm, 100mm, 150 mm), les différentes configurations (C1, C2, C3 et C4) et le niveau de charge axiale (20%, 30 % et 40%). Les résultats des essais montrent clairement que les colonnes en béton renforcées de PRFV et bien conçues peuvent atteindre des niveaux de déformation élevés sans réduction de résistance. Un niveau acceptable de dissipation d'énergie, par rapport aux colonnes en béton armé avec de l’armature en acier, est atteint par les colonnes en béton armé de PRFV. L'énergie dissipée des colonnes en béton armé de PRFV était respectivement de 75% et 70% des colonnes en acier à un rapport déplacement latéral de 2,5% et 4%. Un déplacement supérieur a été atteint par les colonnes en PRFV jusqu'à 10% sans perte significative de résistance. La capacité d’un déplacement supérieur et l’énergie dissipée acceptable permettent aux colonnes en PRFV de participer au moment résistant dans des régions sujettes à des activités sismiques. Les rapports des déplacements expérimentaux ultimes ont été comparés avec les rapports estimés en utilisant l’Équation de confinement du code CSA S806-12. À partir de la comparaison, il a été trouvé que l’Équation de confinement sous-estime les valeurs des rapports de déplacement, donc les rapports de déplacement expérimentaux étaient utilisés pour modifier la zone de renforcement transversal du code CSA S806-12. Le comportement hystérétique encourage à proposer une procédure de conception pour que les colonnes fassent partie des cadres rigides à ductilité modérée et résistant au moment. Cependant, l'élaboration de guides de conception dépend de la détermination des déformations élastiques et inélastiques et de l'évaluation du facteur de modification de la force sismique et de la longueur de la rotule plastique pour les colonnes en béton armé renforcées de PRFV. Les résultats expérimentaux des colonnes renforcées de PRFV étudiées ont été utilisés pour justifier la ligne directrice de conception, ce qui prouve l’efficacité des équations de conception proposées.

The performance of reinforced concrete (RC) columns during recent earthquakes has clearly demonstrated the possible failures associated with inadequate confining reinforcement. The confinement reinforcement requirements of older codes were less stringent than present standards. Many studies were conducted by applying different retrofitting techniques for RC columns that have inadequate confinement reinforcement. A new retrofitting technique by means of Carbon Fiber Reinforced Polymer (CFRP) was developed and tested in many countries in the last decade. This technique is performed by CFRP wrapping the critical region of columns. The effectiveness of CFRP retrofitting technique was shown in many studies conducted worldwide. In Turkey, the frame members are considerably deficient from the seismic detailing point of view. Therefore, in order to use the CFRP retrofitting technique effectively in Turkey, experimental evidence is needed. This study investigates the performance of CFRP retrofitted RC columns with deficient confining steel and low concrete strength. It was concluded by experimental and analytical results that the CFRP retrofitting method can be implemented to seismically deficient columns. Moreover, two design approaches were proposed for CFRP retrofit design of columns considering safe design regulations.

The stress-strain relationship of concrete in flexure is one of the essential parameters in assessing the flexural strength and ductility of reinforced concrete (RC) structures. An overview of previous research studies revealed that the presence of strain gradient would affect the maximum concrete stress and respective strain developed in flexure. Previously, researchers have conducted experimental studies to investigate and quantify the strain gradient effect on maximum concrete stress and respective strain by developing two strain-gradient-dependent factors k3 and ko for modifying the flexural concrete stress-strain curve. In this study, the author established a new analytical concrete constitutive model to describe the stress-strain behavior of both normal-and high-strength concrete in flexure with the effect of strain gradient considered. Based on this, comprehensive parametric studies have been conducted to investigate the combined effects of strain gradient and concrete strength on flexural strength and ductility design of RC beams and columns with concrete strength up to 100 MP a by employing the strain-gradient-dependent concrete stress-strain curve using non-linear moment-curvature analysis. From the results of the parametric studies, it is evident that both the flexural strength and ductility of RC beams and columns are improved under strain gradient effect. A design value of ultimate concrete strain of 0.0032and anew equivalent rectangular concrete stress block incorporating the combined effects of strain gradient and concrete strength have been proposed and validated by comparing the proposed theoretical strength with the strength of 198 RC beams and 275 RC columns measured experimentally by other researchers. It is apparent from the comparison that the proposed equations can predict more accurately the flexural strength of RC beams and columns than the current RC design codes. Lastly, for practical engineering design purpose, design formulas and charts have been produced for flexural strength and ductility design of RC beams and columns incorporating the combined effects of strain gradient and concrete strength.
published_or_final_version
Civil Engineering
Master
Master of Philosophy

In design and detailing of a reinforced concrete frame project, there are many engineers who contribute a single project. Wide variety of information is exchanged between these engineers in design and detailing stages. If the coordination between engineers is not performed sufficiently, data exchange may result in loss of important information that may cause inadequate design and detailing of a structure. Thus, a data model developed for different stages of design and detailing of reinforced concrete structure can facilitate the data exchange among engineers and help improving the quality of structural design. In this study, an object oriented data model was developed for the design and detailing of reinforced concrete columns and beam column joints. The geometry of the structure, amount, shape and placement of reinforcement were defined in this data model. In addition to these, classes that facilitate the design and detailing of reinforced concrete columns and beam column joints according to a building codes were also developed. Another focus of this study is to develop a web based, platform independent data management and multi-user framework for structural design and detailing of reinforced concrete frames. The framework allows simultaneous design of a structure by multiple engineers. XML Web Services technology was utilized for the web based environment in such a way that the design related data was stored and managed centrally by the server in XML files. As a final step, CAD drawings of column reinforcement details in DXF format are prepared.

This thesis is concerned with the effects of lateral confining reinforcement on the ductile behaviour of reinforced concrete columns. The contents of the chapters are summarized as follows. In Chapter one, the general problems in seismic design are discussed and earthquake design methods based on the ductile design approach are described. Japanese, New Zealand and United States design codes are compared. Finally, the scope of this research project is outlined. In Chapter two, after reviewing previous research on confined concrete, the factors which affect the effectiveness of lateral confinement are discussed. Especially the effects of the yield strength of transverse reinforcement, the compressive strength of plain concrete and the strain gradient in the column section due to bending are discussed based on tests which were conducted by the author et al at Kyoto University and Akashi Technological College, Japan. In the axial compression tests on spirally reinforced concrete cylinders (150 mm in diameter by 300 mm in height), the yield strength of transverse reinforcement and the compressive strength of plain concrete were varied from 161 MPa to 1352 MPa and from 17 MPa to 60 MPa, respectively, as experimental parameters. It is found that, when high strength spirals are used as confining reinforcement, the strength and ductility of the confined core concrete are remarkably enhanced but need to be estimated assuming several failure modes which could occur. These are based on the observations that concrete cylinders with high strength spirals suddenly failed at a concrete compressive strain of 2 to 3.5 % due to explosive crushing of the core concrete between the spiral bars or due to bearing failure of the core concrete immediately beneath the spiral bars, while the concrete cylinders with ordinary strength spirals failed in a gentle manner normally observed. In addition, eccentric loading tests were conducted on concrete columns with 200 mm square section confined by square spirals. It is found that the effectiveness of confining reinforcement is reduced by the presence of the strain gradient along the transverse section of column. In Chapter three, the effectiveness of transverse reinforcement with various types of anchorage details which simplify the fabrication of reinforcing cages are investigated. Eight reinforced concrete columns, with either 400 mm or 550 mm square cross sections, were tested subjected to axial compression loading and cyclic lateral loading which simulated a severe earthquake. The transverse reinforcement consisted of arrangements of square perimeter hoops with 135° end hooks, cross ties with 90° and 135° or 180° end hooks, and 'U' and 'J' shaped cross ties and perimeter hoops with tension splices. Conclusions are reached with regard to the effectiveness of the tested anchorage details in the plastic hinge regions of columns designed for earthquake resistance. In Chapter four, the effectiveness of interlocking spirals as transverse reinforcement is studied. Firstly, the general aspects and the related problems of interlocking spirals to provide adequate ductility in the potential plastic hinge region of columns are discussed, referring to the provisions in the New Zealand code,the CALTRANS (California Transportation Authority) code and other related codes. Secondly, based on those discussions, a design method to securely interlock the spirals is proposed. Thirdly, the effectiveness of interlocking spirals is assessed based on column tests conducted as part of this study. Three columns with interlocking spirals and, for comparison, one rectangular column with rectangular hoopsandcross ties, were tested under cyclic horizontal loading which simulated a severe earthquake. The sections of those columns were 400 mm by 600 mm. In Chapter five, analytical models to investigate the buckling behaviour of longitudinal reinforcement restrained by cross ties with 90° and 135° end hooks and by peripheral hoops are proposed. The analyzed results using the proposed models compare well with the experimental observations described in Chapter three. Using those proposed models, a method to check the effectiveness of cross ties with 90° and 135° end hooks is proposed for practical design purposes. In Chapter six, a theory for the prediction of the ultimate longitudinal compressive concrete strain at the stage of first hoop fracture referred to as the "Energy Balance Theory", which has been developed by Mander, Priestley and Park at University of Canterbury, is introduced. After discussing the problems in the "Energy Balance Theory", a modified theory for the prediction of the ultimate longitudinal compressive concrete strain at the stage of first hoop fracture is proposed. The predictions from the modified theory are found to compare well with previous experimental results.

La presente investigación radica en la evaluación técnico-económica de dos tipos de reforzamiento estructurales, tales como el polímero reforzado con fibra de carbono (CFRP) y el encamisado de concreto reforzado en los elementos estructurales de vigas y columnas. Esto con el objetivo de determinar la alternativa de solución óptima, teniendo en cuenta que la opción de encamisado de concreto reforzado es comúnmente la más empleada en el sector. En cuanto al proyecto, este corresponde a un edificio de hotel en el cual se requiere hacer cambio de uso en los pisos 3 y 4 incorporando una sala de gimnasio en los pisos ya mencionados. Respecto al diseño de las alternativas de reforzamiento, estas se rigen bajo las exigencias del Reglamento Nacional de Edificaciones del Perú (E020 – Cargas, E030 - Diseño Sismorresistente, E060 – Concreto Armado) y de normas internacionales como la ACI (ACI440.2R – Fibra de carbono, ACI369 - Rehabilitación sísmica de edificios con estructuras de concreto existente, ACI318 – 14 Requisitos de reglamento para concreto estructural). Asimismo, se utilizó el programa Etabs para complementar el análisis del comportamiento estructural de las vigas y columnas. Posterior al diseño, se realizó la evaluación técnico-económica, proponiendo un plan de ejecución (cronograma) acorde con las características y contexto del proyecto, y un presupuesto económico para cada caso. Finalmente, mediante un análisis comparativo que contrasta ambos criterios, se concluye la alternativa de reforzamiento óptima para la edificación de hotel analizada es el CFRP.
The present investigation lies in the technical-economic evaluation of two types of structural reinforcement, such as the carbon fiber reinforced polymer (CFRP) and the reinforced concrete jacketing in the structural elements: beams and columns. The objective is to determine the optimal solution alternative, taking into account that the option of reinforced concrete cladding is commonly the most used in the sector. As for the project, it corresponds to a hotel building in which change of use is required on floors 3 and 4 incorporating a gymnasium in the aforementioned floors. Regarding the design of reinforcement alternatives, these ruled by the requirements of the National Building Regulations of Peru (E020 – Loads, E030 – Seismic Resistant Design, E060 – Reinforced Concrete) and international standards such as the ACI (ACI 440 – FRP, ACI 369 – Seismic Rehabilitation of Existing Concrete Frame Builidings, ACI 318 - Requirements for Structural Concrete). Likewise, the program was used to complement the analysis of the structural behavior of the buildings and the reinforcement alternatives. After the design, the technical-economic evaluation was carried out, proposing an execution plan (schedule) according to the characteristics and context of the project, and an economic budget for each case. Finally, by means of a comparative analysis that contrasts both criteria, the optimal reinforcement alternative for the hotel building analyzed is concluded is the CFRP.
Tesis

A new concept for the structural system for tall buildings, called the “Tubed Mega Frame”, has been developed by Tyréns AB. The structure consists of several hollow reinforced concrete columns at the perimeter of the building and at certain levels, the columns are tied together with perimeter walls. Together they carry all the vertical and lateral loads. A purpose of the new concept is to eliminate the core in the center of the building which allows utilizing more floor spacing compared with other skyscrapers. This kind of structure has never been examined before and thus never been designed for such a large building. In this thesis the vertical hollow concrete columns are designed according to the American concrete design code, ACI 318. A literature study on reinforced concrete columns has been investigated, where the goal was to identify the most critical design aspects for columns in high rise structures, especially utilizing high strength concrete. Since this kind of structure never has been designed before, an evaluation of the ACI 318 has been performed to check if it is possible to design the hollow reinforced columns in the Tubed Mega Frame according to this design code. The loads and forces used for the design were extracted from a global finite element model in ETABS of a concept prototype of 800 meter. The design process consisted of design calculations according to the ACI 318, a buckling analysis in SAP2000 and a non-linear FE-analysis in ATENA. For the buckling analysis in SAP2000 the lower region of the building was isolated between two main perimeter walls. The model was modified several times to analyze how sensitive the structure was to buckling, with regard to different wall thicknesses, cracked cross-sections, openings in the columns and the dependency of intermediate perimeter walls. The non-linear analysis in ATENA focused on a single hollow column between two perimeter walls in the lower regions of the building. Two models were created, one with a full wall thickness and one with a reduced wall thickness where the ultimate capacity and failure behavior of the columns were investigated. The ultimate capacity of the sections designed by hand calculations and analyzed in ATENA were found to be brittle failure modes. To achieve a more ductile failure, an alternative reinforcement geometry with confining reinforcement has been proposed. The results from the design shows that the structure is redundant against buckling, even with reduced bending stiffness and without intermediate perimeter walls. From the analysis in ATENA, the results demonstrated that the columns are capable of carrying all the ultimate loads even if the wall thickness is reduced by 50%, and that it is possible to use the ACI 318 to design the reinforced concrete columns. However, an unexpected brittle failure occurred in the flanges of the column corners in the tensile region were shear lag may affect the behavior and caused the premature failure. A deductive conclusion has been drawn which states that proper confinement will be critical to achieve a ductile failure behavior even in the tensile region, which will require further studies in order to fully understand the behavior. Even though the results show that it was possible to reduce the cross-sectional thickness of the columns, more studies have to be performed to evaluate if the global structure fulfills the requirements with the decrease in column wall thickness.
Ett nytt strukturellt koncept för skyskrapor har utvecklats av Tyréns AB, "Tubed Mega Frame", där strukturen består av flera ihåliga armerade betongpelare i utkanten som hålls samman med omslutande tvärväggar, och tillsammans bär de alla vertikala och laterala laster. Denna typ av konstruktion har aldrig analyserats eller utformats tidigare. I detta examensarbete är de vertikala ihåliga betongpelarna dimensionerade enligt den amerikanske byggnormen, ACI 318 och de kritiska aspekterna med att utforma ett höghus i höghållfast betong med ihåliga pelare undersökts. Eftersom denna typ av konstruktion aldrig tidigare utformats, har en utvärdering av ACI 318 genomförts för att kontrollera om det är möjligt att dimensionera de ihåliga vertikala pelarna i Tubed Mega Frame enligt denna norm. De laster och krafter som används för dimensioneringen extraherades ur en global finit elementmodell för en konceptbyggnad på 800 meter i ETABS. Den dimensionerande processen bestod av dimensioneringsberäkningar enligt ACI 318, en knäckningsanalys i SAP2000 och en icke-linjär FEM-analys i ATENA. För knäckningsanalysen i SAP2000 isolerades en sektion i den nedre regionen av byggnaden, mellan två omslutande tvärväggar. Modellen ändrades flera gånger för att analysera hur känslig konstruktionen var med hänsyn till knäckning, och de ändringar som gjordes var: minskning av väggtjocklekar, reducering för spruckna tvärsnitt, öppningar i pelarna samt de omslutande mellanliggande tvärväggarnas inverkan på knäckningen av konstruktionen. Den icke-linjära analysen i ATENA fokuserade på en pelare mellan två omslutande tvärväggar i den lägre regionen av byggnaden. Två modeller skapades, en med en full väggtjocklek och en med en reducerad väggtjocklek för att analysera brottbeteendet och verifiera den handberäknade kapaciteten enligt ACI 318. De brottmoder som påträffades för tvärsnittsverifikationen i ATENA var spröda och karakteriserades med krossning av betongen, och för att uppnå ett mer segt brott härleddes en alternativ armeringsgeometri med sammanhållande armeringsbyglar i de mest kritiska regionerna av pelarna. Resultaten visade att konstruktionen är robust mot knäckning, även med minskad böjstyvhet och utan mellanliggande omslutande tvärväggar. Av analysen i ATENA visade resultaten att pelarna är kapabla att bära alla de kritiska lasterna även om väggtjockleken reduceras med 50 % och att det är möjligt att använda ACI 318 som norm för dimensionering av pelarna i Tubed Mega Frame. Dock inträffade ett oväntat sprött brott i den dragna flänsen i nedre regionen av pelaren, framförallt koncentrerat till hörnen. Anledningen till det spröda brottet har utvärderats och analyserats där hypotesen är att flänsskjuvning i kombination med höga spänningskoncentrationerna i hörnen orsakar det lokala brottbeteendet i flänsen. Slutsatsen som baseras på hypotesen är att sammanhållande armeringsbyglar skulle vara avgörande för att uppnå ett segt brottbeteende även för den dragna flänsen. Även om resultaten visade att det var möjligt att reducera tvärsnittstjockleken för pelarna, krävs mer studier för att utvärdera om den globala konstruktionen uppfyller kraven för en minskning av pelarnas väggtjocklekar.

Current research with respect to the protection of civilian infrastructure against complex blast loading conditions is primarily focused towards the effect of external explosive sources. As a consequence, the general literature on internal building detonations and specifically in the context of protective design and assessment of structures against these loading conditions is incomplete. Existing guidelines developed for comparatively noncomplex external explosive blast remain unconservative when applied to internal building detonations due to blast wave confinement and complex interaction with structural components. In particular, reinforced concrete (RC) columns in internal blast environments are subjected to time-variant uplift forces coupled with lateral pressures leading to destabilisation and a critical loss of structural integrity. Research presented in this thesis provides an original understanding towards: (i) – the influence of transient uplift forces on the vulnerability of RC columns subject to lateral blast pressures and, (ii) – design and assessment of RC columns against the effect of time-variant coupled uplift and lateral blast pressures due to internal building detonations. Research in this thesis is based on advanced uncoupled Euler-Lagrange numerical modelling splitting the structural and flow solvers for maximum integrity and accuracy. High-resolution simulations of complex flow fields are analysed using the hydrocodes Air3D and Autodyn, whilst Extreme Loading for Structures [ELS] based on the Applied Element Method is used for modelling the transient-dynamic structural response of columns. These numerical techniques are comprehensively ratified and underwritten, both qualitatively and quantitatively, using published independent experimental test data. Verified numerical modelling is subsequently used to conduct a set of comprehensive parametric studies covering both vented (frangible perimeter walls causing pressure venting) and contained (non-frangible perimeter walls causing repetitive wave reflections) internal blast environments. Results of these parametric studies are thoroughly analysed with the use of multi-variable nonlinear regression analysis techniques and are presented in the form of separate assessment and design charts. This thesis also presents a set of column hazard charts developed based on the parametric studies. These hazard charts provide threshold combinations of TNT Equivalency and critical radial distance corresponding to different column damage levels ranging from ‘No Damage’ through ‘Low Damage’ and Moderate Damage’ to ‘Imminent Structural Collapse’. The output of this research will be of direct relevance to both practitioners and researchers involved with protective design of civilian and military buildings.

Thesis (M.S. in civil engineering)--Washington State University, May 2010.
Title from PDF title page (viewed on June 23, 2010). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 90-91).

The stress-strain characteristics of concrete developed in flexure is very important for flexural strength design of reinforced concrete (RC) members. In current RC design codes, the stress-strain curve of concrete developed in flexure is obtained by scaling down the uni-axial stress-strain curve to account for the strain gradient effect. Therefore, the maximum concrete stress that can be developed under flexure is smaller than its uni-axial strength, and the use of which always underestimates the flexural strength of RC beams and columns even though the safety factors for materials are taken as unity. Furthermore, the value of strength underestimation was different for RC beams and columns, which indicates that the extent of strain gradient will affect the maximum concrete stress and stress-strain curve developed under flexure. To investigate the maximum concrete stress, 29 column specimens were fabricated and tested in this study. They were divided into 9 groups, each of which was poured from the same batch of concrete and contained specimens with identical cross-section properties. In each group, one specimen was tested under concentric load while the rest was/were subjected to eccentric or horizontal load. To study the strain gradient effects, the ratio of the maximum concrete compressive stress developed in the eccentrically/horizontally loaded specimens to the maximum uni-axial compressive stress developed in the counterpart concentrically loaded specimens, denoted by k3, is determined based on axial force and moment equilibriums. Subsequently, the concrete stress block parameters and the equivalent rectangular concrete stress block parameters are determined. It is found that the ratios of the maximum and equivalent concrete stress to uni-axial cylinder strength, denoted respectively by k3 and , depend significantly on strain gradient, while that of the depth of stress block to neutral axis depth, denoted by , remains relatively constant with strain gradient. Design equations are proposed to relate and  with strain gradient for strength calculation, whose applicability is verified by comparing the strengths of RC beams and columns tested by various researchers with their theoretical strengths predicted by the proposed parameters and those evaluated based on provisions of RC codes. Based on the test results, the stress-strain curve of normal-strength concrete (NSC) developed under strain gradient is derived using least-square method by minimising the errors between the theoretical axial load and moment and the respective measured values. Two formulas are developed to derive the flexural stress-strain curve, whose applicability is verified by comparing the predicted strength with those measured by other researchers. Lastly, the application of the proposed stress-block parameters and stress-strain curve of NSC will be illustrated by developing some charts for flexural strength design of NSC beams and columns. The application will further be extended to develop strength-ductility charts for NSC beams and columns, which enable simultaneous design of strength and ductility. By adopting the proposed design charts, the flexural strength design, as well as that of the plastic hinge forming mechanism during extreme events, will be more accurate. The resulting design will be safer, more environmentally friendly and cost effective.
published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy

Following a major earthquake event, essential public amenities such as medical facilities and transport networks need to remain functional - not only to fulfil their ongoing role in serving the community but also to cope with the added and immediate demand of a population affected by a natural disaster. Furthermore, the economic implications of wide spread damage to housing and commercial facilities should not be discounted. A shift in design approach is required that is consistent with current trends towards performance based building design. The present aim is to achieve seismic energy dissipation during the earthquake event, without the aftermath of damage to structural elements, whilst maintaining design economies. Structures permitted to rock on their foundations and provide recoverable rotations at the beam-column interfaces offer significant advantages over those using conventional ductile detailing. A jointed construction philosophy can be applied whereby structural elements are connected with unbonded prestressing tendons. Supplemental damping is provided by replaceable flexural steel components designed to deform inelastically. For this research a multi-storey test building of one quarter scale has been constructed and tested on an earthquake simulator at the University of Canterbury. A computer model has been developed and a set ofpreliminary design procedures proposed.

Thesis (M.S.)--University of Nevada, Reno, 2006.
"December, 2006." Includes bibliographical references (leaves 88-91). Online version available on the World Wide Web. Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2006]. 1 microfilm reel ; 35 mm.

The application of advanced materials in infrastructure has grown rapidly in recent years mainly because of their potential to ease the construction, extend the service life, and improve the performance of structures. Ultra-high performance concrete (UHPC) is one such material considered as a novel alternative to conventional concrete. The material microstructure in UHPC is optimized to significantly improve its material properties including compressive and tensile strength, modulus of elasticity, durability, and damage tolerance. Fiber-reinforced polymer (FRP) composite is another novel construction material with excellent properties such as high strength-to-weight and stiffness-to-weight ratios and good corrosion resistance. Considering the exceptional properties of UHPC and FRP, many advantages can result from the combined application of these two advanced materials, which is the subject of this research. The confinement behavior of UHPC was studied for the first time in this research. The stress-strain behavior of a series of UHPC-filled fiber-reinforced polymer (FRP) tubes with different fiber types and thicknesses were tested under uniaxial compression. The FRP confinement was shown to significantly enhance both the ultimate strength and strain of UHPC. It was also shown that existing confinement models are incapable of predicting the behavior of FRP-confined UHPC. Therefore, new stress-strain models for FRP-confined UHPC were developed through an analytical study. In the other part of this research, a novel steel-free UHPC-filled FRP tube (UHPCFFT) column system was developed and its cyclic behavior was studied. The proposed steel-free UHPCFFT column showed much higher strength and stiffness, with a reasonable ductility, as compared to its conventional reinforced concrete (RC) counterpart. Using the results of the first phase of column tests, a second series of UHPCFFT columns were made and studied under pseudo-static loading to study the effect of column parameters on the cyclic behavior of UHPCFFT columns. Strong correlations were noted between the initial stiffness and the stiffness index, and between the moment capacity and the reinforcement index. Finally, a thorough analytical study was carried out to investigate the seismic response of the proposed steel-free UHPCFFT columns, which showed their superior earthquake resistance, as compared to their RC counterparts.

Box-girder bridges supported by single reinforced concrete (RC) columns are expected to sustain seismic shocks with minor structural damages in seismically active regions where transportation is substantially required for rescuing and evacuating tasks. Such viaducts are vulnerable to damage when they are subjected to strong ground motions and acceleration pulse records, especially when responding in a flexural mode or having relatively low core confinement. Using a nonlinear dynamic solver that applies the fibre element method, global and local damage curves are computed based on the dissipated energy under hysteretic curves and based on constitutive curves, respectively. The RC bridge with seismic isolation bearing is used as an alternative system to control the damage, and modelled using linkage elements between the substructure and super structure. It was found that seismic isolation can be controlled to dissipate partial seismic energy so that the RC column gains the least possible minor damage. Using a MatLab program, a fibre element nonlinear model was built using a simplified iterative process and simplified constitutive relations. The number of fibres and elements under the dynamic loading was found to be affecting the final results of the analysis. Using crack growth modelling based on fracture mechanics, the combined discrete element/finite element explicit-Elfen code was applied to investigate the crack growth in 3D dynamically loaded RC columns. Despite its excessive computational cost and time, this code provides reliable information about local damage in the RC column core. Earthquake records with the pulse acceleration phenomenon have a severe damage potential on the structure. The difference in damage intensities was detected by crack growth modelling for the same problem using different loading rates. Critically stressed zones can be investigated independently by using the relative response technique, in which responses from the numerically analysed structure are re-used as applied loads onto a small-scale crack model for the critical member. Two general conclusions can be obtained; bridges with single RC columns designed by the demand/capacity criterion could suffer severe damage and possible collapse when subjected to strong ground motions. Secondly; hysteresis-based methods provide a global damage evaluation based on strength and ductility only regardless of the damage growth inside the concrete core and the buckling of bars, which could lead to progressive collapse.

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Even the small buildinging column may have a buckled. It s denoted the difficulty to design and detail this type of element. So this work intends make a description and application of a several simplified process of presizing and column s design. The stability building procedures of the parameters a e γz are analyzed are applied to this kind of structure. Also it s detailing how the wind forces are important in the internal forces and how to consider it in the column s design. The reinforced and the wind force are calculate by using a free program obtains at the internet. Several examples are made considering a characteristic building with one, two, tree and four pavements showing how to analize the stability, the presizing and column s design and showing too the final results. All this samples are solved and compared with a professional program and the it show that all results are too close. Finally a lot of commentary how to design the columns are made to aided engineers to make a good column s design for small and medium buildinging.
Mesmo nas edificações pequenas os pilares podem flambar. É sabido a dificuldade de projetar e detalhe este tipo de elemento. Portanto, este trabalho pretende fazer uma descrição e aplicação de processo simplificado de pré-dimensionamentos de pilares até a sua concepção. O procedimento para a análise da estabilidade de edifício dos parâmetros α e γz são aplicados a este tipo de estrutura. Também é detalhar e demonstrar como as forças do vento são importantes e as forças internas e como considerá-la na concepção dos pilares. O cálculo da força do vento é feito um programa livre obtiver na internet. Vários exemplos são feitos considerando-se uma característica do edifício modelo com uma, duas, três e quatro pavimentos e demonstrando a analise da estabilidade, o pré-dimensionamento e a concepção do pilar mostrando também os resultados finais. Todas as amostras são solucionadas, e isto em comparação com um programa profissional e mostrar que os resultados são muito próximos. Finalmente, vários comentários sobre projeto de pilares são feitos para que os engenheiros possam fazer um bom projeto sobre pilares para as edificações pequenas e médias.

The finite element method is a powerful analysis tool which has facilitated a better understanding of the behaviour of reinforced concrete structures. Its use in the research field is widespread and complements experimental tests and the development of new analytical models. Its application in practice engineering has permitted to deal with complex elements. However, the general structural engineer is still reluctant to consider finite element modelling for his work as he finds most of these models excessively sophisticated for his needs and knowledge. In particular, complexity of many finite element tools usually derives from the adoption of advanced concrete constitutive models. Implementation of more simple models based on engineering practice could facilitate its use by less experienced finite element users. In structural engineering practice finite element analysis can be of great usefulness to deal with those more problematic elements and/or where the application of traditional analysis methods presents limitations. This includes the so-called D-regions with a 3D behaviour. The strut-and-tie method and the stress field method are consistent and rational tools for the analysis and design of D-regions, but while their application to 2D elements is well covered in literature, its extension to 3D is problematic. This generally explains why excessively conservative assumptions are still common in the design of these elements. Refinement of current analytical and design approaches or the use of finite element analysis could lead to more rational solutions which in turn will reduce material requirements and costs. A 3D nonlinear finite element-based tool was developed in this thesis oriented towards the analysis and design of 3D D-regions by less experienced finite element users. Regarding material modelling, an orthotropic concrete model was adopted to permit the use of uniaxial stress-strain relationships. Only one single parameter, the uniaxial compressive strength of concrete, needs to be defined. Additionally, several aid functions were implemented, among which the following can be highlighted: a comprehensive, embedded reinforcement model to facilitate the introduction of complex rebar geometries; special support and load elements permitting an integrated and simple treatment of the boundary conditions imposed by them; and a simple design algorithm for the automatic determination of the required rebar areas. Three examples of applications to representative 3D D-regions are presented to show the capabilities of the tool. In particular, the analyses of fourteen four-pile caps, three socket base column-to-foundations connections and one anchorage block are described in the third part of the thesis. Results prove that realistic response predictions can be obtained considering relatively simple constitutive models. The capacity of the tool to configure consistent stress field models depending on the reinforcement arrangement is also demonstrated. The generation of rational reinforcement configurations by applying the implemented design algorithm is also shown. A strut-and-tie-based method for the analysis and design of four-pile caps with rectangular geometries is proposed in the fourth part. The method is based on a refined 3D strut-and-tie model and the consideration of three potential modes of failure: exceeding the reinforcement strength, crushing of the diagonal strut at the base of the column with narrowing of the strut and splitting of the diagonal strut due to transverse cracking. The main innovation is that the strut inclination is not fixed as in current strut-and-tie-based design procedures, but determined by maximizing the pile cap strength. The method accounts for strength softening of cracked concrete, compatibility constraints and reinforcement details. Its application to 162 specimens of literature led to very good predictions of the ultimate strength and, to a lesser extent, of the mode of failure.
El método de los elementos finitos es una potente herramienta de análisis que ha facilitado un mejor conocimiento del comportamiento de las estructuras de hormigón armado. Su uso en el ámbito de la investigación está ampliamente extendido. Su aplicación en la práctica ingenieril ha permitido la resolución de elementos complejos. Sin embargo, el ingeniero estructural común todavía es reticente a usar la modelización por elementos finitos ya que considera que la mayoría de estos modelos son excesivamente sofisticados para sus necesidades. La complejidad de muchas herramientas de elementos finitos suele derivarse de la adopción de modelos constitutivos de hormigón avanzados. La implementación de modelos más sencillos podría facilitar su uso por usuarios menos experimentados. En la práctica ingenieril el análisis con elementos finitos puede ser de gran utilidad para tratar aquellos elementos más problemáticos y/o donde la aplicación de los métodos de análisis tradicionales presenta limitaciones. Esto incluye las llamadas regiones D con comportamiento 3D. El método de bielas y tirantes y el método de campos de tensiones son herramientas racionales para el análisis y dimensionamiento de regiones D, pero su extensión a 3D es problemática. Este hecho explica por qué se adoptan todavía hipótesis excesivamente conservadoras en el dimensionamiento de estos elementos. La propuesta de métodos analíticos y de diseño más adecuados o la modelización con elementos finitos podría conducir a soluciones más racionales, lo que a su vez reduciría las necesidades de material y los costes. Como parte de esta tesis se ha desarrollado una herramienta de cálculo no lineal basada en el método de los elementos finitos orientada al análisis y dimensionamiento de regiones D tridimensionales por usuarios con menos experiencia en la modelización con elementos finitos. Se ha adoptado un modelo ortotrópico para el hormigón para permitir el uso de relaciones uniaxiales de tensión-deformación. Sólo es necesario definir un único parámetro, la resistencia a compresión uniaxial del hormigón. Adicionalmente, se han implementado varias funciones de ayuda, entre las que destacan: un modelo de armadura embebida para facilitar la introducción de geometrías de armado complejas; elementos especiales de apoyo y de carga que permiten un tratamiento integral de las condiciones de contorno; y un algoritmo de diseño para la determinación automática del área de armado necesaria. Se presentan tres ejemplos de aplicación a regiones D 3D representativas para mostrar las capacidades de la herramienta. En concreto, en la tercera parte del documento se describen los análisis de catorce encepados, tres cálices de cimentación y un bloque de anclaje. Los resultados muestran que se pueden obtener predicciones bastante realistas considerando modelos constitutivos relativamente sencillos. También se demuestra la capacidad de la herramienta para configurar modelos de campo de tensiones consistentes dependiendo de la configuración de armado. Además se muestra la capacidad del algoritmo de diseño para configurar disposiciones de armado racionales. En la cuarta parte se propone un método para el análisis y dimensionamiento de encepados sobre cuatro pilotes con geometría rectangular. El método se basa en un modelo 3D de bielas y tirantes refinado y la consideración de tres modos de fallo posibles: rotura del acero, aplastamiento de la biela diagonal en la base de la columna con estrechamiento de la misma y splitting de la biela diagonal debido a la fisuración transversal. La principal novedad es que el ángulo de la biela no se fija como en otros modelos, sino que se determina mediante la maximización de la resistencia del encepado. El método considera el debilitamiento de la resistencia del hormigón fisurado, condiciones de compatibilidad de deformaciones y detalles de armado. Su aplicación a 162 especímenes dio luga
El mètode dels elements finits és una potent eina d'anàlisi que ha facilitat un millor coneixement del comportament de les estructures de formigó armat. El seu ús en l'àmbit de la investigació està àmpliament estès. La seua aplicació en la pràctica enginyeril ha permès la resolució d'elements més complexos. No obstant això, l'enginyer estructural comú encara és reticent a fer servir la modelització per elements finits ja que considera que la majoria d'aquests models són excessivament sofisticats per a les seues necessitats i el seu conèixement. En concret, la complexitat de moltes eines d'elements finits sol derivar-se de l'adopció de models constitutius avançats de formigó. La implementació de models més senzills basats en la pràctica enginyeril podria facilitar el seu ús per a usuaris menys experimentats en la modelització amb elements finits. A la pràctica enginyeril l'anàlisi amb elements finits pot ser de gran utilitat per a tractar aquells elements més problemàtics i/o on l'aplicació dels mètodes d'anàlisi tradicionals presenta limitacions. Això inclou les anomenades regions D amb comportament 3D. El mètode de bieles i tirants i el mètode de camps de tensions són eines racionals per a l'anàlisi i dimensionament de regions D, però la seua extensió a 3D és problemàtica. Aquest fet explica per què s'adopten encara hipòtesis excessivament conservadores en el dimensionament d'aquests elements. La proposta de mètodes analítics i de disseny més adequats o la modelització amb elements finits podria conduir a solucions més racionals, amb el que també es reduirien les necessitats de material i els costos. Com a part d'aquesta tesi s'ha desenvolupat una eina de càlcul no lineal basada en el mètode dels elements finits orientada a l'anàlisi i dimensionament de regions D tridimensionals per a usuaris amb menys experiència en la modelització amb elements finits. S'ha adoptat un model ortotròpic per al formigó per permetre l'ús de relacions uniaxials de tensió-deformació. Només cal definir un únic paràmetre, la resistència a compressió uniaxial del formigó. Addicionalment, s'han implementat diverses funcions d'ajuda, entre les quals destaquen: un model d'armadura embeguda per facilitar la introducció de geometries d'armat complexes; elements especials de suport i de càrrega que permeten un tractament integral i senzill de les condicions de contorn; i un algoritme de disseny per a la determinació automàtica de l'àrea d'armat necessari. Es presenten tres exemples d'aplicació a regions D 3D representatives per mostrar les capacitats de l'eina. En particular, en la tercera part del document es descriuen les anàlisis de catorze enceps sobre quatre pilons, 3 calzes de fonamentació i un bloc d'ancoratge. Els resultats mostren que es poden obtenir prediccions prou realistes considerant models constitutius relativament senzills. També es demostra la capacitat de l'eina per configurar models de camp de tensions consistents depenent de la configuració d'armat. A més es mostra la capacitat de l'algoritme de disseny per configurar disposicions d'armat racionals. En la quarta part es proposa un mètode per a l'anàlisi i dimensionament d'enceps sobre quatre pilons amb geometria rectangular. El mètode es basa en un model 3D de bieles i tirants refinat i la consideració de tres modes de fallada possibles: trencament de l'acer, aixafament de la biela diagonal a la base de la columna amb estrenyiment de la mateixa i splitting de la biela diagonal per causa de la fissuració transversal. La principal novetat és que l'angle de la biela no es fixa com en els models actuals de bieles i tirants, sinó que es determina mitjan\c{c}ant la maximització de la resistència de l'encep. El mètode proposat considera el debilitament de la resistència del formigó fissurat, condicions de compatibilitat de deformacions i detalls d'armat. La seua aplicació a 162 espècimens de la liter
Meléndez Gimeno, C. (2017). A finite element-based approach for the analysis and design of 3D reinforced concrete elements and its applications to D-regions [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86193
TESIS

The objective of this thesis was to design and check typical elements of the 5th storey of monolithic reinforced concrete structure of residential building. Horizontal load-bearing structure consists of a continuous slab of six fields with reinforcing ribs, which are located under the building envelope, bidirectional slab simply supported, further staircase beam and lintels in the corridors and loggias. Vertical structures consist of walls and columns.

Aim of The Diploma Thesis was to design load-bearing structure of a multi-storey reinforced concrete building, to realize structural analysis in Dlubal-RFEM software and dimension its selected parts. Designed structure is based on already erected building in office edifices campus in Brno-Slatina district. Its original number of storeys was increased from ten to nineteen, so the specific problems connected to high-rise building designing could be solved. Time dependent deformations of vertical structures were analysed in detail, so the changes in load of horizontal elements could be described more precisely, because of its direct dependence on compression of the columns. Within the paper, foundation structure dimensions were designed, assessment and design of composite columns assembly were made, as well of floor slab in 2nd floor with column deformations impact check on the 17th floor. Also, the external walls, pillars and shear core walls were designed and assessed. Formwork drawing of designed structure parts and detailed drawing of reinforcement of assessed elements were elaborated. Based on Diploma Thesis results it can be stated, that if influence of nonuniform load of vertical structures within the high-rise building designing is neglected, consequent project would presumably be uneconomic, or dangerous after an optimization attempts.

The master´s thesis concerns with the design of the construction of the testing centre. The hall is divided in two parts, in one of those parts the office rooms are located. The precast concrete frame of the hall is composed by foundation pads, columns, secondary beams and crane beams, precast slabs, and prestressed girders. The thesis contains report, structural design, drawings of floor plans and sections, drawings of formwork and reinforcement, visualization and steps of construction.

Reinforced concrete is an economical construction material and is widely used throughout the world in buildings and bridges. The shear strength within beam-column joints in reinforced concrete structures has been identified as an area where further research is still needed in order to form reliable design methods. The aim of this research programme has been to develop a rational analytical model which can be used conveniently in the design of beam-column joints. The work consists of a brief literature review, an extensive experimental programme and the development of a new analytical model for predicting the strength of beam-column joints. The new analytical model is a development of the strut-and-tie model and is believed to be original in two ways: (a) The influence of the shear span and the spacing of the links (if any) are considered directly. (b) The inclination of the compression field is determined by maximising the contribution of the concrete to the stiffness of the member in shear. The new analytical model is shown to predict the strength of the test specimens and of many specimens reported in the literature more reliably than current design codes and standards

The master’s thesis is focused on a design of reinforced concrete prefabricated skeleton of the sports hall. Object of the design is internal traverse frame of the hall which consists of reinforced concrete prestressed truss, columns and concrete pile construction of foundation. Thesis includes working-out of static calculation, elaboration drawings of shape, reinforcement of solved elements and evolvement of assembly drawings. The rest of the project parts are not analyzed.

Explosives place large demands on the lateral load carrying capacity of structures. If these loads are applied on columns, the high pressure transient loads from explosives can result in significant damage to the primary gravity load carrying elements. The loss of these elements, which are responsible from overall strength and stability of the structure, may cause collapse of all or parts of the structure. Therefore, it is important to mitigate the blast loads effects on columns. A comprehensive research study into the design, application, and use of different retrofit systems to mitigate damage to columns under blast loads has been undertaken. This research program, consisting of experimental testing and analytical investigation, sought out retrofits that address the strength of columns as well as those that enhance ductility are explored. Different materials and resistance mechanisms are used to increase column capacity. An experimental testing program was conducted using a shock tube to test the capacity of columns under blast loads. For this program, a total of sixteen reinforced concrete columns were constructed and the data from a further two columns from a previous study was compiled. Of these columns, a total of thirteen were retrofitted to mitigate the effects of blast. Carbon fibre reinforced polymer (CFRP) was applied to eight of the columns in the form of jacketing, longitudinal reinforcement, or the combination of the two. The other retrofits included steel prestressed confinement applied to one column, steel bracing acting as compression members applied to one column, and steel bracing acting as tension members applied to three columns. The columns were tested under incrementally increasing shock tube induced shock wave loading up to failure of the specimen or capacity of the shock tube. The performance of the retrofitted columns was compared with the control columns and against other retrofits. Quantitative comparisons of displacements and strains were made along with qualitative assessments of damage. The results indicated that all the retrofits increased capacity to the column, however, certain retrofits out performed others. The best FRP retrofit technique was found to be the combination of longitudinal and transverse FRP. The prestressed steel jacketing proved to be effective at increasing ductility capacity of the column. The compression brace retrofit was found to be effective in significantly increasing capacity of the column. The tension brace retrofits had the best performance over all the retrofits including the compression brace retrofit. The experimental data was used to validate analysis techniques to model the behaviour of the specimens. This technique reduced the columns to an equivalent single-degree-of-freedom (SDOF) system for dynamic analysis purposes. The reduction to the SDOF system was achieved by computing a resistance to lateral load and lateral displacement relationship. Each retrofit was carefully considered in this analysis including the retrofit’s possible effect on material and sectional properties as well as any force resistance mechanism that the retrofit introduces. The results of the modeling and experimental program were used to develop retrofit design guidelines. These guidelines are presented in detail in this thesis.

Prior studies indicated that beam-to-column connections of reinforced concrete (RC) moment resisting frame structures experience considerable deformations under earthquake loading and these deformations have a major contribution to story drift of the building. In current analysis and design applications, however, the connection regions are generally modeled as rigid zones and the inelastic behavior of the joint is not taken into account. This assumption gives rise to an underestimation of the story drifts and hence to an improper assessment of the seismic performance of the structure. In order to implement the effect of these regions into the seismic design and analysis of buildings, a model that properly represents the seismic behavior of connection regions needs to be developed. In this study, a parametric model which predicts the joint shear strength versus strain relationship is generated by investigating the several prior experimental studies on RC beam-to-column connections subjected to cyclic loading and establishing an extensive database. Considering previous experimental research and employing statistical correlation method, parameters that significantly influence the joint behavior are determined and these parameters are combined together to form a joint model. This model is then verified by comparing the results obtained from the dynamic earthquake analysis by Perform 3D with the experimental ones. The main contribution of the developed model is taking into account parameters like the effect of eccentricity, column axial load, slab, wide beams and transverse beams on the seismic behavior of the connection region, besides the key parameters such as concrete compressive strength, reinforcement yield strength, joint width and joint transverse reinforcement ratio.