Dissertations / Theses on the topic 'Post-tensioned Slab'

In this investigation strength and structural behaviour of prestressed concrete is studied with one full scale test of one flat slab, 16000 mm x 19000 mm, and three slabs on ground each 4000 mm x 4000 mm with thickness 150 mm. The flat slab was constructed and tested in Aalesund. This slab has nine circular columns as support, each with diameter 450 mm. Thickness of this test slab was 230 mm and there were two spans in each direction, 2 x 9000 mm in x-direction and 2 x 7500 mm in y-direction from centre to centre column. The slab was reinforced with twenty tendons in the middle column strip in y-direction and eight tendons in both outer column strips. In x-direction tendons were distributed with 340 mm distance. There were also ordinary reinforcement bars in the slab. Strain gauges were welded to this reinforcement, which together with the deflection measurements gives a good indication of deformation and strains in the structure.

At a live load of 6.5 kN/m² shear failure around the central column occurred: The shear capacity calculated after NS 3473 and EuroCode2 was passed with 58 and 69 %, respectively. Time dependent and non-linear FE analyses were performed with the program system DIANA. Although calculated and measured results partly agree well, the test show that this type of structure is complicated to analyse by non-linear FEM.

Prestressed slabs on ground have no tradition in Norway. In this test one reinforced and two prestressed slabs on ground were tested and compared to give a basis for a better solution for slabs on ground. This test was done in the laboratory at Norwegian University of Science and Technology in Trondheim. The first slab is reinforced with 8 mm bars in both directions distributed at a distance of 150 mm in top and bottom. Slab two and three are prestressed with 100 mm² tendons located in the middle of slab thickness, and distributed at a distance of 630 mm in slab two and 930 mm in slab three. Strain gauges were glued to the reinforcement in slab one and at top and bottom surface of all three slabs. In slab two and three there were four load cells on the tendons.

Each slab were loaded with three different load cases, in the centre of slab, at the edge and finally in the corner. This test shows that stiffness of sub-base is one of the most important parameters when calculating slabs on ground. Deflection and crack load level depends of this parameter. Since the finish of slabs on ground is important, it can be more interesting to find the load level when cracks start, than deflection for the slab. It is shown in this test that crack load level was higher in prestressed slabs than in reinforced slab. There was no crack in the top surface with load in the centre, but strain gauges in the bottom surface indicate that crack starts at a load of 28 kN in the reinforced slab, and 45 kN in the prestressed slabs. Load at the edge give a crack load of 30 kN in reinforced slab, 45 kN and 60 kN in prestressed slabs. The last load case gives crack load of 30 kN in reinforced slab, 107 kN and 75 kN in prestressed slabs. As for the flat slab, FE analyses were performed for all of the three slabs on ground, and analyses shows that a good understanding of parameters like stiffness of sub-base and tension softening model, is needed for correct result of the analyses.

This study consists of a numerical investigation of a post-tensioned flat slab without conventional longitudinal reinforcement; only steel fibres were employed to ensure sufficient ductility and shear capacity of the slab. Results were taken from a reported experiment conducted on a full scale steel-fibre reinforced flat slab (0.38 % fibre content) which was tested until failure, undergoing a ductile bending failure at a load of 6.5 kN/m2. A nonlinear finite element analysis was employed to study the experiment, including the ultimate state. A parametric study was performed using the numerical model to investigate the influence of the tensile behaviour of steel fibre-reinforced concrete (SFRC) the response of the structure. The model proved to be relatively sensitive to changes in the tensile behaviour, but the differences were not prominent until entering the nonlinear area of the load-displacement curve. A constant curve with tensile stress equal to the residual tensile strength of the SFRC provided a robust numerical model and results on the conservative side. Including a peak stress with a multilinear tensile curve provided a less stable analysis but more accurate results, however the model behaviour was stiffer than the experiment, providing too small deformations at failure. Nevertheless, the numerical model was able to display the ductile bending failure mode and moment redistribution.

Master of Science
Department of Civil Engineering
Robert Peterman
A flowable hybrid concrete mix with a spread of 17 to 20 inches was created with a superplasticizer to be used in post-tension haunch-slab (PTHS) bridges where rebar congestion is heaviest. The mix would allow for proper concrete consolidation. A conventional concrete mix with a slump of three to four inches was also created to be placed on top of the hybrid mix. The conventional mix would be used to create a sloping surface on the top of the concrete. The two mixes could be combined in the PTHS bridge deck and act as one monolithic specimen. Standard concrete tests such as compressive strength, tensile strength, modulus of elasticity, permeability, freeze/thaw resistance, and coefficient of thermal expansion were determined for the mixes and compared. Core blocks were cast using both mixes and composite cores were drilled. The cores were tested and their composite split-tensile strengths were compared to the split-tensile strengths of cylinders made from the respective mixes. A third concrete mix was made by increasing the superplasticizer dosage in the hybrid concrete mix to create a self-consolidating concrete (SCC) mix with a 24-inch spread. The SCC mix was created as a worst-case scenario and used in the determination of shear friction. Eighty-four push-off shear friction specimens were cast using the SCC mix. Joint conditions for the specimens included uncracked, pre-cracked, and cold-joints. Uncracked and pre-cracked specimens used both epoxy- and non-epoxy-coated shear stirrups. Cold-joint specimens used both the SCC mix and the conventional concrete mix. Joint-conditions of the cold-joint specimens included a one-hour cast time, a seven-day joint with a clean shear interface, and a seven-day joint with an oiled shear interface. The shear friction specimens were tested using a pure shear method and their results were compared to the current American Concrete Institute code equation.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado.
Since the last decade there is an important increase of high-rise buildings in Peru, especially in urban areas. Therefore, it is necessary to assess if the Peruvian Seismic Code is applicable for this type of buildings which have long natural periods as their main characteristic. The main objective of this article is to compare the results of the base shear and story drift ratios of Peruvian seismic design code E.030 with those of the ASCE 7-16 standard to the case of high-rise buildings, this due to the fact that there is limited information for tall buildings in Peru or comparison between national or international code for this type of structures. These high rise buildings have square and rectangular plan floors. Half of them have moment frames and reinforce concrete slab around the rigid core and the others have post-tensioned slab as their vertical load resisting system and central core walls with peripheral columns as the lateral force resisting system. Hence, the response spectrum analysis (RSA) is carried out for every case of the four tall buildings with different configurations using both seismic codes. Then results are compared with the linear response history analysis (LRHA) considering five Peruvian ground motions records, which were scaled to 0.45g PGA. It was verified that generally both the base shear and the interstory drifts calculated using ASCE7-16 are less than that obtained with the seismic code E.030.

Post-tensioned (PT) concrete slabs with unbonded tendons have been widely used in residential and commercial buildings. However, fire may cause irrecoverable damages to such slabs including rupture of prestressing steel tendons, concrete spalling, large downward deflection and even progressive collapse. Therefore, thorough investigations of the slabs under fire condition are desirable to formulate performance-based fire resistance design guidance. Numerical modelling of PT concrete slabs with unbonded tendons under fire condition was carried out based on available test results in the literature. Finite element (FE) models were established employing the commercial package ABAQUS. Results from the preliminary study achieved acceptable agreement with the test results. Parametric study was further conducted for better understanding of the structural responses and failure modes of the slabs. The behaviour of prestressing steel tendons at elevated temperature was then investigated with emphasis on thermal creep, where a three-dimensional (3D) model incorporating Harmathy’s thermal creep model was proposed and verified. As there was limited data of thermal creep, thermal creep tests of prestressing steel to GB/T 55224 and BS 5896 were conducted, from which parameters of Harmathy’s creep model were obtained. Making use of the parameters obtained and the proposed 3D model, the thermal relaxation of prestressing steel tendons could be accurately predicted as compared with the results of thermal relaxation tests of the both types of prestressing steel conducted in the present study. The proposed 3D model for prestressing steel was further incorporated into the FE models of PT concrete slabs to investigate the effects of thermal creep of prestressing steel tendons on the structural responses of the slabs. Numerical results show that thermal creep has slight effect on the downward deflections of slabs, but has obvious effect on the tendon stresses. Moreover, the transient creep strain of concrete was further incorporated into the FE models of PT concrete slabs, and the results showed that the transient creep strain had obvious effect on the downward deflections of slabs, and hence the transient creep strain should not be ignored. Tests and numerical modelling of PT two-way slabs with high-strength self-compacting concrete and unbonded tendons under ISO 834 standard fire condition were conducted. Useful results were obtained from four fire tests including the vertical and horizontal deflections, crack patterns, possible tensile membrane action and explosive concrete spalling. Based on the tests, numerical modelling was further improved in consideration of tendon distributions, levels of prestressing and areas exposed to fire, where the thermal creep of prestressing steel and the transient creep strain of concrete were explicitly considered. Better understanding of the structural responses and failure modes was obtained. The results obtained were then examined for more insight into the structural fire performance of PT concrete slabs and formulation of performance-based fire resistance design guidance.
published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy

This diploma thesis is about analysis of post-tensioned cantilever beam, which is part of cantilever of commercial building. The main part of thesis is evaluation of behavior of building structure in time and determination of the most suitable staging. Next part of thesis is design and evaluation of reinforced slab and beam.

Aim of this master's thesis is an optimized design of locally supported ceiling slab of building of social center with account of span of columns and height of slab. Structure must be assessed in terms of limit state and service limit state by ČSN EN 1992-1-1 General rules and rules for buildings after design.

The aim of this diploma thesis was the design of three possible variants, how to span the wide and deep valley with a bridge. After an evaluation, situation of the highway on the only wide load-bearing structure which is constituted by a box girder with transverse cantilevers supported by prefabricated bar braces, was chosen as an optimal solving. The load- bearing structure made of post- tensioned concrete is going to be incrementally launched and be supported by one-column pillars along an axis of the motorway. The work is composed of a detailed design of this preferred variant, which is processed according to the ultimate and serviceability limit state including the construction stage analysis of the bridge by the construction technology by an incremental launching method.

Diploma thesis is focused on structural assessment and strengthening of the reinforced concrete flor slab disturbed by excessive deflection. Thesis included assesment of the existing construction and design method of strengthening of the floor structure with system using prestressing strands without bond.

På grund av bostadsbristen de senaste åren har byggbranschen varit tvungen att möta den höga efterfrågan på bostäder. Ett sätt att underlätta det tryck som skapats på grund av den höga efterfrågan är att rekonstruera byggnader avsedda för annan användning än bostäder till bostadshus. Ett problem som har uppstått vid ombyggnation av till exempel ett kontorshus som består av spännarmerade pelardäck, är känsligheten för nya hål som krävs för nya installationer som går igenom de efterspända bjälklagen (bestående av betongplattor). Problematiken består av att håltagningar som vanligtvis är lokaliserade nära pelarna måste göras på ett större avstånd från pelaren på grund av de spännkablar som går över och nära plattans pelaranslutning. Efterspända kablar är normalt sett belägna över plattans pelaranslutning enligt dagens dimensioneringsnormer för att bidra till plattornas genomstansningskapacitet.I detta examensarbete undersöktes det om det finns vetenskapligt stöd för att flytta kablarna till en längre distans från pelaren (än vad normerna rekommenderar) med hänsyn till genomstansningskapaciteten, och därmed förenkla vid en potentiell ombyggnation.Huvudsyftet med arbetet var att med hjälp av en litteraturstudie samt beräkningar jämföra ett experiment som utförts av Ghassem Hassanzadeh och Håkan Sundquist vid KTH 1997- 1998 (som visade att kablar på ett längre avstånd från pelaren ger ett visst bidrag till betongplattans genomstansningskapacitet) med dagens normer samt nyare studier. Dagens dimensioneringsnormer inkluderar inte bidraget till kapaciteten när spännkablarna placeras utanför det så kallade grundkontrollsnittet (området som undersöks vid dimensionering enligt normerna).Ett annat syfte med detta examensarbete var att studera och uppdatera de beräknade resultaten (enligt dåtidens normer) från studien. Denna rapport uppdaterar studien genom att undersöka rådande normernas beräknade resultat samt jämföra med liknande tester från andra forskare. Dimensioneringsnormerna som undersöktes var Eurokod 2, ACI 318 och MC2010Som del av litteraturstudien redovisas även en liknande försökserie från Portugal av A. Pinho Ramos, Valter J.G. Lúcio & Duarte M.V Faria samt en sammanställning av olika försök som genomfördes i Schweiz av Clément T, Ramos A.P, Fernández Ruiz M, Muttoni A. Sammanställning i Schweiz beräknade genomstansningskapaciteten för 74 olika plattor där plattorna från försöket vid KTH finns med. Den här studien tyder på att dagens dimensioneringsnormer har en säkerhetsmarginal vid approximationer (vid både normalfall och vid flytt av kablar), men att det fortfarande saknas tillräckliga belägg för att rättfärdiga en flytt av spännkablar.Rapporten är skriven för CBI Betonginstitutet där G. Hassanzadeh har varit handledare.

碩士
國立交通大學
土木工程系所
95
This thesis presents the results of experimental and analytical studies on self-centering moment connections with and without composite concrete slab.Cyclic tests were conducted on four full-scale subassemblies.Two subassemblies consist of steel beams post-tensioned to a reinforced concrete column and reduced flange plates for energy dissipation.Composite concrete slab with partial debonded longitudinal reinforcement through the connection is also included in other two subassemblies in order to examine the effects of concrete slab on the self-centering behavior of the connection.Test and analytical studies indicated that (1) connection moment strengths in positive bending were similar but in negative bending were different on the order of 0.72 and 0.6 percent compared to the bare steel beam subassembly so that the self-centering behavior of the subassemblies with the composite concrete slab was not observed, (2) force-transferring mechanism in the connection proposed was able to predict the force-deformation relationship of the subassembly with the composite concrete slab, and (3) a general-purpose nonlinear finite element analysis program ABAQUS was used to perform the correlation study on the subassemblies with and without composite concrete slab.

The research presented in this thesis focuses on the accuracy of predicting deflections and cambers in partially prestressed suspended slabs. Precision in predicting this behaviour accurately is complex due to the large number of variables which affect the behaviour of suspended prestressed slabs. This level of complexity is particularly relevant for post tensioned slabs due to the numerous on site construction steps. Many of the variables are hard to determine accurately due to their tendency to be unique for each construction site. Variables such as ambient temperatures, concrete material properties, stressing times, applied loads, loading times, prop movement and humidity are all examples of these properties. Hence, when predicting the behaviour of post tensioned suspended slabs of a multi storey building there always remains a degree of uncertainty. The research presented in this thesis addresses crucial areas of this topic and ultimately aims to supply reinforced concrete designers and constructors with additional confidence when predicting this behaviour. The requirement for this project surfaced during the design stages of 151 Pirie, a multistorey building constructed in Adelaide, Australia. The design project for 151 Pirie was particularly complex due to a very ambitious construction timeline. The strict construction timeline was imposed due to the contractual agreement of early occupancy of the top three floors (of a 9 storey building). The client purchasing the top floors required functioning office space within a matter of months. This contract created a construction priority of erecting the bare structural requirements up to and including the top three floors in the shortest possible time. Fittings and services to the top three floors was then the secondary priority. Fitting and services to the lower floors (which would usually be achieved before the upper floors) would be performed at a later date. Excessive deflection limits of the slabs due to the accelerated construction were a major concern for the client. The effect on the deformation performance due to the accelerated construction was difficult to predict for the designer. Therefore, this project was born to help supply confidence to the designer and concrete supplier for this construction scenario. This research project was designed to assist in the close monitoring and recording of the construction process of 151 Pirie. Due to the nature of data collection, data from this construction site would be limited in its benefits for the current construction. However, the data obtained would be vital for future projects by providing a log of onsite slab performance data as well as explanations of delays or other general outcomes with the construction process. Therefore, the aim of this research is to present the issues that were faced, the methods used to overcome these issues as well as displaying the vast amounts of site specific data documented within this project for future reference. In this research a wide range of concrete material properties were collected and monitored closely on site as well as in the laboratory. The experimental testing created large detailed database of concrete material properties as well as other relevant factors such as surveyed deflections and construction timing. Concrete material properties were the primary focus of this research due to their direct effect on member performance. The database was sufficiently large to allow a meaningful statistical data analysis to be performed on the compressive strength (f’[subscript]c), modulus of elasticity (E[subscript]c) and tensile strength (f’[subscript] t) of the concrete samples. This analysis supplied a detailed understanding of the statistical relationship between different concrete material properties. A Monte Carlo simulation was performed, with multiple deflection and camber models, to create a statistical distribution of predicted deflections and cambers from the statistical distribution of concrete material properties. This statistical output is then critically analysed and compared to the surveyed data. Proposed improvements to the process of predicting deflections and cambers have been outlined. These improvements have then been utilised in the construction of a finite element style program. Finally, the multiple predictions of column strip and mid panel deformation are compared to the short term surveyed deflections. It is summarised that the improvements suggested and implemented in the finite style analysis yield results with a higher degree of accuracy. The accuracy and benefits of the suggested improvements has been justified and proven by the application of multiple examples and a parametric study.
http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1366459
Thesis (M.Eng.Sc.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2009

The introduction of fibre-reinforced polymers (FRPs) to the field of civil engineering has led to numerous research efforts focusing on a wide range of applications where properties such as high strength, light weight or corrosion resistance are desirable. In particular, FRP materials have been especially attractive for use as internal reinforcement in reinforced concrete (RC) structures exposed to aggressive environments due to the rapidly deteriorating infrastructure resulting from corrosion of conventional steel reinforcement. While FRPs have been successfully implemented in a variety of structural applications, little research has been conducted on the use of FRP reinforcement for short span slab bridges. Furthermore, the behaviour of FRP-RC flexural members cast with self-consolidating concrete (SCC) is largely absent from the literature. The present study investigates the behaviour of an all-FRP reinforcement system for slab bridges which combines lower cost glass FRP (GFRP) reinforcing bars with high performance carbon FRP (CFRP) prestressed tendons in SCC to produce a structure which is both cost-efficient and characterized by excellent structural performance at the serviceability, ultimate and fatigue limit states. An extensive experimental program comprised of 57 large or full-scale slab strips was conducted to investigate the effects of reinforcement type, reinforcement ratio, prestressing level and shear reinforcement type on the flexural performance of slab bridges under both monotonic and fatigue loading. The proposed reinforcement system was found to display excellent serviceability characteristics and high load capacities as well as significant deformability to allow for sufficient warning prior to failure. Lastly, the use of post-tensioned CFRP tendons limited the stresses in the GFRP reinforcing bars leading to significantly longer fatigue lives and higher fatigue strengths compared to non-prestressed slabs. Analytical models were used to predict the behaviour of the slab bridge strips at service and at ultimate. Where these models failed to accurately represent the experimental findings, simple modifications were proposed. The results from ancillary tests were also used to modify existing analytical models to predict the effects of fatigue loading on the deflection, crack width, shear resistance and flexural capacity of each of the tested slabs.

碩士
國立高雄第一科技大學
營建工程所
96
The precast and prestressed concrete structural systems utilize unbonded post-tensioned to connect beams and columns together. The structure may return to its original position without residual deformations due to the prestress under earthquake loads (self-centering function). However, floor slabs designed as a rigid diaphragm may reduce the gap-opening in the beam-column interface in practice. Therefore, it is necessary to investigate the force transfer of the slabs in the precast and prestressed concrete structural system. This research aims to invertigate the force transfer of the floor slabs in the precast and prestressed concrete structure under bi-axial loads. For this purpose, a 3D one story sub-structure was constructed, including four columns, four beams and two slabs to form a gravity frame, a post-tensioned frame and slabs in between. In order to simulate the path of force transfer of inertial load during an earthquake, the lateral loads was applied at the column of the gravity frame and then transmitted to the post-tensioned frame through the floor slabs and transverse beams, where prestress was also applied to have self-centering function without interfering the gap-opening in the beam-column interface. The primary invertigating parameters are the prestress level in the slabs and transverse beams. Test results showed that the sub-structural remained elastic all the time without major damage restored its function after eachtest and returned to its original position without residual deformations.

碩士
國立高雄第一科技大學
營建工程所
95
In precast and prestressed structural systems, unbondedpost-tensioned tendons passing through beams connect beams to columns. Due to the gap open in the beam-column interface, plastic deformation is eliminated. The restrain of post-tensioned strands provide the stiffness and strength increased along with the drift increase. Since the tendons remain elastic under loads, forcing the structure return to its original position, residual deformation is limited (Self-centering). If the energy dissipating capacity is insufficient, supplementary energy-dissipating devices such as steel angles or steel rods may be installed at the beam-column interface. In this research, force transfer of precast slabs between gravity and moment-resisting post-tensioned frame in a 3D sub-structure subjected to lateral loads were investigated. The 3D structure consisted of four columns, two beams and one slab to form a moment-resisting frame and a gravity frame. To simulate the force transfer between frames under earthquakes, lateral loads were applied to the gravity frame, and then transmitted to the lateral-resisting frame through the precast slab which also can not interfere the gap open of beam column connection in PT frame. To achieve that function, precast slab was also post-tensioned to be self-center after loads. The slab stiffness is the only investigated parameter. Test results show that structures for both tests was indeed self-centering, however, flexible slab was too soft to move the post-tensioned frame. Even the stiffer frame, the movement of the post-tensioned frame was insignificant due to the tortional rotation of beams and slips between the slab and beams. It is found that, the efficiency of the force transfer for the stiffer slab was better than the one having softer slab.

This thesis examines the development of a superstructure for a slab-on-girder wood-concrete composite highway bridge. Wood-concrete composite bridges have existed since the 1930's. Historically, they have been limited to spans of less than 10 m. Renewed research interest over the past two decades has shown great potential for longer span capabilities. Through composite action and suitable detailing, improvements in strength, stiffness, and durability can be achieved versus conventional wood bridges. The bridge makes use of a slender ultra-high performance fibre-reinforced concrete (UHPFRC) deck made partially-composite in longitudinal bending with glued-laminated wood girders. Longitudinal external unbonded post-tensioning is utilized to increase span capabilities. Prefabrication using double-T modules minimizes the need for cast-in-place concrete on-site. Durability is realized through the highly impermeable deck slab that protects the girders from moisture. Results show that the system can span up to 30 m while achieving span-to-depth ratios equivalent or better than competing slab-on-girder bridges.

Unbonded post-tensioned concrete slabs have been widely used in Canada and the United States since the 1960s, as they allow increased span-to-depth ratios and excellent control of deflections compared to non-prestressed reinforced concrete flexural members. The satisfactory fire performance of unbonded post-tensioned concrete slabs in North America was established by a series of standard fire tests performed in the United States during the 1960s. However, there is a paucity of data on the effect of elevated temperatures on cold-drawn prestressing steel, both in terms of post-fire residual mechanical properties and high-temperature stress relaxation, which can lead to significant prestress loss both during and after a fire. A detailed and comprehensive literature review is presented that provides background on the residual mechanical properties of prestressing steel, as well as on the creep-relaxation behaviour experienced at elevated temperatures under stress. The results of two test series are discussed; the first examining the effects of elevated temperatures on the residual mechanical properties of prestressing steel exposed to elevated temperatures. The second test series examines the irrecoverable and significant loss of prestress force that results from steel relaxation and other thermal effects experienced during heating. A preliminary analytical model is presented, capable of predicting the change in prestress force experienced by a stressed strand under transient heating. The model is then compared with experimental elevated temperature relaxation data. Finally, the analytical model developed and residual mechanical properties obtained through experimentation are used along with a pre-existing finite difference heat transfer model (developed for concrete slabs) to examine the effect of elevated temperature exposure on the residual flexural capacity of a typical unbonded post-tensioned example slab. Several parameters, such as heated length and concrete cover, are examined using the example structure. From this it was observed that, after one hour of exposure to a standard fire (ASTM E119), significant losses in effective prestress and moment capacity occurred even with the appropriate amount of concrete cover. This is a finding which is of the utmost practical importance to engineers engaged in the evaluation of fire damaged unbonded post-tensioned structures.
Thesis (Master, Civil Engineering) -- Queen's University, 2007-12-18 17:15:17.521
Natural Sciences and Engineering Research Council of Canada, and the Department of Civil Engineering at Queen’s University