Ductility is a measure of the ability of a material, section, structural element or structural system to sustain deformations prior to collapse without substantial loss of resistance. The Australian design standard, AS 3600, imposes minimum ductility requirements on structural concrete members to try to prevent premature non-ductile failure and hence to ensure adequate strength and ductile-type collapse with large deflections. The requirements also enable members to resist imposed deformation due to differential settlement, time effects on the concrete and temperature effects, whilst ensuring sufficient carrying capacity and a safe design. Current AS 3600 requirements allow a limited increase or reduction in elastically determined bending moments in critical regions of indeterminate beams, accommodating their ability to redistribute moment from highly stressed regions to other parts of the beam. Design moment redistribution limits and ductility requirements in AS 3600 for bonded partially prestressed beams are a simple extension of the requirements for reinforced members. The possibility of premature non-ductile failure occurring by fracture of the reinforcement or prestressing steel in partially prestressed members has not adequately addressed. The aim of this research is to investigate the overload behaviour and deformation capacity of bonded post-tensioned beams. The current ductility requirements and design moment redistribution limits according to AS 3600 are tested to ensure designs are both safe and economical. A local flexural deformation model based on the discrete cracked block approach is developed to predict the deformation capacity of high moment regions. The model predicts behaviour from an initial uncracked state through progressive crack development into yielding and collapse. Local deformations are considered in the model using non-linear material laws and local slip behaviour between steel and concrete interfaces, with rigorous definition of compatibility in the compression and tension zones. The model overcomes limitations of past discrete cracked block models by ensuring compatibility of deformation, rather than strain compatibility. This improvement allows the modeling of members with multiple layers of tensile reinforcement and variable depth prestressing tendons having separate material and bond properties. An analysis method for simple and indeterminate reinforced and partially prestressed members was developed, based on the proposed deformation model. To account for the effect of shear in regions of high moment and shear present over the interior supports of a continuous beam, a modification to the treatment of local steel deformation in the flexural model, based on the truss analogy, was undertaken. Secondary reactions and moments due to prestress and continuity are also accounted for in the analysis. A comparison of past beam test data and predictions by the analysis shows the cracking pattern and deformation capacity at ultimate of flexural regions in reinforced and partially prestressed members to be predicted with high accuracy. The analysis method accurately predicts local steel behaviour over a cracked region and deformation capacity for a wide range of beams which fail either by fracture of steel or crushing of the concrete. A parametric study is used to investigate the influence of different parameters on the deformation capacity of a typical negative moment region in a continuous beam. The structural system consists of a bonded post-tensioned, partially prestressed band beam. The primary parameters investigated are the member height and span-to-depth ratio; relative quantity of reinforcing and prestressing steel; material properties and bond capacity of the steels; and lastly the compression zone properties. Results show that the effects of the various parameters on the overload behaviour of partially prestressed beams follow the same trends as reinforced beams. A new insight into the local steel behaviour between cracks is attained. The deformation behaviour displays different trends for parametric variations of the local bond capacity, bar diameter and crack spacing, when compared to past analytical predictions from comparable studies. The discrepancy in findings is traced back to the definition of the plastic rotation capacity and the sequencing of the yielding of the steels. Compared to the other local deformation models, the current model does not assume a linear distribution of strain at a crack. The current findings highlight an important difference between predicted behaviours from different deformation compatibility requirements in local deformation models which has not yet been discussed in the literature. The local deformation model evaluates the relationship between maximum steel strain at a crack and average steel deformation over a crack spacing for the entire loading history. The total steel percentage, hardening properties of the steel and concrete strength are shown by the model to have the greatest effect on these steel strain localisation factors. Section analysis, as currently used in design, can be improved with the proposed simplification of the relationships to identify and quantify the effects of steel fracture on deformation capacity and strength. The numerical effort required to simulate the overload behaviour of practical beam designs with multiple reinforcement elements and a prestressing tendon are currently too great to be used in an extensive numerical study. The numerically more efficient smeared block approach is shown to accurately predict the ultimate carrying capacity of prestressed beams failing by crushing of the concrete. Consequently, this method is adopted to study the allowable limits of moment redistribution in the present investigation, Simplified relationships of the steel strain localisation factors evaluated in the parametric study of deformation capacity is used to predict maximum steel strains and premature failure. The limits of moment redistribution in bonded, post-tensioned partially prestressed band beams are explored by comparing the design load and predicted carrying capacity, for different section ductilities and design moment redistribution. In addition, the effects of different concrete strengths, up to 85 MPa, along with as three reinforcing and prestressing steel ductilities are quantified and compared to current Australian and international design requirements. Limitations in the carrying capacity are investigated for different reinforcement and prestress uniform elongation capacities. More than one thousand beam simulations produce results showing that current design moment redistribution and ductility requirements in the Australian design code for concrete structures (AS 3600) are sufficient for normal strength concretes (less than 50 MPa). A suggestion for design moment redistribution limits, section ductility requirements and steel ductility limits is made for members constructed from higher strength concretes. A special high steel ductility class is proposed for both the reinforcement and prestressing steel to allow moment redistribution in higher strength concrete. No moment redistribution is proposed for members reinforced with low ductility (Class L) steel. An increase of the current elongation limit of Class L steel from 1.5 % to 2.5% is suggested to ensure strength and safety. An increase in the current ductility requirements from fsu/ fsy=1.03 and elongation equal to 1.5% to fsu/fsy=1.05 and 2.5% elongation for low ductility Class L steel is suggested to ensure strength and safety. / Thesis (Ph.D.)--Civil and Environmental Engineering, 2004.

Split Concrete Model (SCM) is a unified approach towards modeling shear behavior in concrete. SCM is essentially a rational model which is evaluated and modified using a large experimental database.The shear strength of the concrete beam is modeled as the sum of the contribution of concrete, transverse reinforcement, longitudinal reinforcement and bond between concrete and longitudinal reinforcement. Concrete does not contribute to the shear strength after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the second branch of the critical crack while computing the contribution of concrete towards shear strength of the beam. Formation of the second branch of the critical crack and immediate subsequent failure of the beam has been compared to the split-cylinder test, which forms the conceptual basis of SCM.SCM computes the concrete contribution using the split tensile strength and the area under compression of the concrete beam. For cases where a split-cylinder test is not performed, a mathematical model is proposed to compute the split tensile strength using the compressive strength of concrete available from experimental results. This model is proposed using advanced statistical methods, including weighted residuals and Box-Cox transformation and is validated using various statistical procedures. The transverse reinforcement contributes to the shear strength of the concrete beam only after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the first branch of the critical crack while computing the contribution of the transverse reinforcement towards shear strength of the beam, instead of the conventional approach of considering the entire length of the crack. The contribution of the longitudinal steel and bond between concrete and longitudinal steel and concrete is accurately modeled unlike the conventional approaches which do not consider this contribution.Evaluation using the database shows that SCM can predict accurate results for all ranges of strength, depth, reinforcement ratio, and shear span to depth ratio of the beam. This shows that all the influencing parameters for concrete shear strength have been correctly modeled in SCM. SCM gives more accurate results as compared to current codified approaches as verified with design examples. Finally, specific recommendations have been made indicating how the shear design requirements in the current ACI code can be modified.

No description available.

No description available.

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references (p. 202-209).

No description available.

No description available.

The spans of precast prestressed concrete bridge girders have become longer to provide more economical and safer transportation structures. As the spans have increased, so has the depth of the girders which in turn have increased the slenderness of the girders. Slenderness in a beam or girder would increase the likelihood that a stability failure would occur. Stability failures could pose a danger to construction personnel due to the sudden nature in which a stability failure would occur. Furthermore, stability failures of prestressed concrete girders during construction would cause a detrimental economic impact due to the costs associated with the failure of the girder, the ensuing construction delays, damage to construction equipment and potential closures to highways over which the bridge was being constructed. An experimental and analytical study was performed to determine the stability behavior of prestressed concrete beams. Two stability phenomenons were investigated: (1) lateral-torsional buckling and (2) global stability. An emphasis was placed on the effects of initial imperfections on the stability behavior; the effect elastomeric bearing pads and support rotational stiffness was investigated. The experimental study involved testing six rectangular prestressed concrete beams for lateral-torsional buckling, a PCI BT-54 for thermal deformations and the same PCI BT-54 for global stability. The 32-ft. long rectangular beams were 4-in. wide and 40-in. deep. The PCI BT-54 had a 100-ft. long span. A material and geometric nonlinear, incremental load analysis was performed on the six rectangular beams. The nonlinear analyses matched the experimental load versus lateral displacement and load versus rotation behavior, and the analysis predicted the experimental maximum load within an error of 2%. The nonlinear analysis was extrapolated to several different initial imperfection conditions to parametrically study the effect of initial lateral displacement and initial rotation on the inelastic lateral-torsional buckling load. A simplified expression for lateral-torsional stability of beams with initial imperfections was developed. The data from the parametric study were used to develop reduction parameters for both initial sweep and initial rotation. The rollover stability behavior of the PCI BT-54 was investigated experimentally, and it was found that support end rotations and the elastomeric bearing pads had an adverse effect on the global stability. The nonlinear analysis was employed with the addition of a bearing pad model. It was found that the behavior was sensitive to the bearing pad stiffness properties and the assumption of uniform bearing. From the research, it was apparent that rollover stability was the controlling stability phenomenon for precast prestressed concrete bridge girders, not lateral-torsional buckling.

Orientador: Vladimir Antonio Paulon / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-13T11:14:39Z (GMT). No. of bitstreams: 1 PregeliNeto_Antonio_M.pdf: 3909884 bytes, checksum: 410b6d25a48bfd9306620ba57294b3d0 (MD5) Previous issue date: 2006 / Resumo: A aplicação de modelos de gestão na construção civil se mostra uma tendência, buscando minimizar riscos em empreendimentos e criar um diferencial competitivo. Neste contexto, o presente trabalho teve por objetivo desenvolver e implantar um modelo de gestão para confecção de vigas pré-moldadas, verificando possíveis ganhos em termos de custo, prazo e qualidade. A metodologia adotada foi o estudo de caso, nas obras de uma ponte. O modelo de gestão desenvolvido dividiu a gestão do empreendimento em três áreas de atuação, sendo Gestão de Engenharia, Gestão de Suprimentos e a Gestão de Recursos. Na Gestão de Engenharia observou-se o parcial atendimento às expectativas no macro planejamento e na metodologia de gestão de informações, no controle de projetos; já as metodologias construtivas mostraram-se adequadas, a exceção da cura e do transporte das vigas; na gestão da segurança do trabalho e meio ambiente mostrou-se eficiente a localização de riscos, porém ineficiente o controle de acidentes de trabalho. A Gestão de Suprimentos foi eficiente no controle de custos, embora partes das análises tenham sido prejudicadas dada a escolha equivocada de alguns dos coletores de custo; no processo de contratação e compras os indicadores adotados se mostraram superficiais para a avaliação de desempenho. A Gestão de Recursos teve um bom desempenho, refletido nos índices de custos. Em geral, o empreendimento mostrou que os indicadores adotados para a avaliação do desempenho do modelo de gestão apontam um rendimento satisfatório para tempo e custo, e não conclusivo na qualidade. Concluiu-se que, embora não se possa afirmar que a aplicação do modelo de gestão fora o único responsável pelo sucesso parcial do empreendimento, certamente este contribuiu significativamente para tal. / Abstract: The application of management models in the civil construction is a new trend which searches to minimize risks in workmanships and to create a competitive differential. In this context, the objective of the present work was to develop and to implant a model of management for confection of precast prestressed beams, verifying possible improvements in costs, schedule and quality. The adopted methodology was the case study, in a bridge workmanship. The developed model of management divided the enterprise in three areas of performance, being Management of Engineering, Supply Management and Management of Resources. The Management of Engineering had a partial attendance to the expectations in the macro planning, the methodology of management of information was observed, in the control of projects; the constructive methodologies was adequate, in exception of the curing and the transport of the beams; the management of the work security and environment was efficient in the control of industrial accidents but inefficient to localize risks. The Supply Management was efficient in cost control, but parts of the analyses were harmed because of a mistake in the choice of some cost collectors; in the purchase process the pointers were superficial for the performance evaluation. The Management of Resources had a good performance, reflected in costs. In general, this job showed that the adopted pointers for the performance evaluation of the management model were satisfactory considering time and cost, but not conclusive in the quality. The conclusion is it cannot affirm that the application of the management model is the responsible one for the partial success of the workmanship, certainly this contributed significantly for such. / Mestrado / Edificações / Mestre em Engenharia Civil

This report details the design and construction of an AASHTO Type IV prestressed girder and a PCI BT-56 prestressed girder. It also details the shear testing and shear performance of the BT-56 girder. The results are compared with results from previous research dating back to 1986. Finally, all research was compared with the AASHTO Standard (2002), AASHTO LRFD (1998) and AASHTO LRFD (2004) Specifications to examine thier overall accuracy in predicting shear strengths.