Three-dimensional non-linear finite element analysis of reinforced concrete beams in torsion. Reinforced concrete members under torsion and bending are analysed up to failure. A non-linear concrete model for general states of stress including compressive strength degradation due to cracking is described.

摘要

This thesis describes a non-linear finite element model suitableudfor the analysis of reinforced concrete, or steel, structures underudgeneral three-dimensional states of loading. The 20 nodedudisoparametric brick element has been used to model the concrete andudreinforcing bars are idealised as axial members embedded within theudconcrete elements. The compressive behaviour of concrete isudsimulated by an elasto-plastic work hardening model followed by audperfectly plastic plateau which is terminated at the onset theud. crushing. In tension, a smeared crack model with fixed orthogonaludcracks has been used with the inclusion of models for the retainedudpost-cracking stress and the reduced shear modulus.udThe non-linear equations of equilibrium have been solved using anudincremental-iterative technique operating under load control. Theudsolution algorithms used are the standard and the modifiedudNewton-Raphson methods. Line searches have been implemented toudaccelerate convergence. The numerical integration has been generallyudcarried out using 15 point Gaussian type rules. Results of a studyudto investigate the performance of these rules show that the 15 pointudrules are accurate and computationally efficient compared with theud27(3X3X3) point Gaussian rule.udThe three- dimensional finite element model has been used toudinvestigate the problem of elasto-plastic torsion of homogeneousudmembers. The accuracy of the finite element solutions obtained forudbeams of different cross-sections subjected to pure and warpingudtorsion have been assessed by comparing them with the available exactudor approximate analytical solutions.udBecause the present work is devoted towards the analysis ofudreinforced concrete members which fail in shear or torsional modes,udthe computer program incorporates three models to account for theuddegradation in the compressive strength of concrete due to presenceudof tensile straining of transverse reinforcement. The numericaludsolutions obtained for reinforced concrete panels under pure shearudand beams in torsion and combined torsion and bending reveal that theudinclusion of a model for reducing the compressive strength of crackedudconcrete can significantly improve the correlation of the predictedudpost-cracking stiffness and the computed ultimate loads with theudexperimental results.udParametric studies to investigate the effects of some importantudmaterial and solution parameters have been carried out. It isudconcluded that in the presence of a compression strength reductionudmodel, the tension-stiffening parameters required for reinforcedudconcrete members under torsion should be similar to those used forudmembers in which bending dominates.