Analytical and Numerical Studies on the Behavior of RC and FRP Strengthened RC Members subjected to Various Load Conditions

Ganganagoudar, Anand G (2017) Analytical and Numerical Studies on the Behavior of RC and FRP Strengthened RC Members subjected to Various Load Conditions. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

The f irst part of the study deals with an i mproved softened membrane model for the analysis of reinforced concrete (RC) circular bridge columns under pure torsio n loading. The e xistence of torsion severely affects the structural performance of RC member especially at times where torsion is the primary load action in structural elements like b rid ge columns, outrigger bents etc . In this study , shortcomings of the hi therto models present in the literature are addressed by suitably incorporating the necessary effects that are otherwise ignored . T he i mpact of the strain gradient effect and bi - directional stresses on the torsional response is significant . This study fill s th e knowledge lacuna exist in this vital area of research by pr esenting a modi fied softened membrane model (SMMT) for circular columns under torsional loading by incorporating these effects . The proposed model also recommends a new tension stiffening rel ationship model of concrete for better predictions. Outcomes of the proposed model are also compared with classical rotating angle softened truss model (RA - STM) to illustrate the supremacy of the proposed model. Parameters such as post cracking stiffness, peak torque and corresponding twist are better captured by the i mproved SMMT compared to RA - STM . In addition to this work , th e model has been extended to FRP strengthened RC members wherein analytical and finite element (FE) studies are conducted to invest igate the behavior of FRP (Fiber Reinforced Polymer) composite strengthened reinforced concrete (RC) beams under torsional loading. The p resence of torsion severely affect s the behavior and failure pattern of the members. Therefore, it is imperative to und erstand the efficiency of F RP strengthening under torsion al loading to ensure safe design . The proposed vi model is improvised (SMMT - FRP) by incorporating the effects of FRP composites on the compressive behavior of cracked concrete . The analytical study is s upported by a full - scale nonlinear finite element ( FE ) study using commercial package ABAQUS. The p arameters such as post cracking stiffness, peak torque and corresponding twist are passabl y ca ptured by the improved SMMT - FRP . It is learnt that, FRP strengt hening augmente d the post - cracking stiffness, ultimate strength and localized the damage. In the second part of the study , e xisting FEM based fiber beam element model for RC members subjected to c ombined loading is investigated and part of the work is pres ented in this stu d y . In all practi cal cases, RC members are typically subjected t o one or more types of loading and existence of one load influence s the behavior of other load s . This study envisages at understanding the behavior of RC members modeled as no nlinear beam elements under combined loading . The Newton - Raphson’s nonlinear incremental iterative approach is employed as a solution strategy. T his method employs Timoshenko beam theory and section discretization technique to capture the shear mechanism o f the beams. The c onstitutive model for concrete is derived fro m the softened membrane model and bi linear model is considered for the steel. Forces in each element are obtained by performing an equilibrium - based numerical integration on the section axial, flexural, and shear behaviors along the length of the element . Corroborative study between the fiber beam element model and experimentally investigated RC columns under axial loads is performed and fair agreement was found . I n a companion study which is n ot recorded in this script, it is envisaged to explore the efficiency of this model for shear and torsion problems and to address the limitations associated with the model if any.

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