Numerical Investigation of Reinforced Concrete Frames Considering Nonlinear Geometric, Material and Time Dependent Effects with Incremental Construction Loadings

摘要

Reliable prediction of forces, stresses, and deflections in reinforced concrete structures has long been the goal of structural engineers. In fact analytical determination of the displacements, internal forces, stresses and deformations of reinforced concrete structures throughout their load histories has been complicated by a number of factors. Non homogeneity of the material, continuously changing topology of the structural system due to cracking of concrete under increasing loads, nonlinear stress-strain relationship of concrete and reinforcing steel, variation of concrete deformations due to creep, shrinkage, and applied load history are classified as complicating factors. Due to mentioned difficulties, engineers in the past have been relying heavily on empirical formulas derived from numerous experiments for the design of concrete structures. In this study, it has been tried to determine the real behavior and vulnerability of reinforced concrete frames in the basis of developed numerical nonlinear analytical procedure, considering nonlinear response of the structure. In fact, in order to obtain more accurate results, material and geometric nonlinearities plus time dependent effects of creep and shrinkage in addition to incremental construction loadings are included in the analyses. More over the structural response of the structure is traced through its elastic, inelastic and ultimate load ranges. The analyses are adopted with a finite element displacement formulation coupled with a time step integration solution. Also an incremental and iterative scheme based upon a constant imposed displacement is used so that local instabilities or strain softening can also be analyzed accurately.