The comparative body model in material and geometric nonlinear analysis of space R/C frames

摘要

Purpose - This paper aims to present a new numerical model for the stability and load-bearing capacity computation of space reinforced-concrete (R/C) frame structures. Both material and geometric nonlinearities are taken into account. The R/C cross-sections are assumed to undergo limited distortion under torsional action. Design/methodology/approach - A simple, global discretization using beam-column finite elements is preferred to a full, global discretization using 3D elements. This is more acceptable from a practical point of view. The composite cross-section is discretized using 2D elements to apply the fiber decomposition procedure to solve the material and geometrical nonlinear behavior of the cross-section under biaxial moments and axial forces. A local discretization of each beam element based on the comparative body model (i.e. a prismatic body discretized using brick elements, element by element, during the incremental-iterative procedure) allows determining the torsional constant of the cross-section under limited warping. The classical global iterative-incremental procedure is then used to solve the resulting material and geometric nonlinear problem. Findings - It has been noticed that, in case of a limited distortion of the cross-section, the torsional constant of homogeneous (linear elastic) materials is greater than the one obtained from the Saint-Venant theory. However, due to low-tensile strength of concrete materials, the torsional constant decreases significantly after an early loading phase, primarily due to the lack of reinforcing flanges. Research limitations/implications - The current study does not cover the torsion analysis of R/C cross-section with stirrups. Besides, the bond-slip effect between concrete and steel reinforcement is not taken into account, nor is the local buckling of the beam flanges and rebar. Practical implications - This new numerical model has been implemented in a computer program for effectively computing the nonlinear stability and load bearing capacity of space R/C frames. Originality/value - The authors believe that the comparative body model should bring a new approach to the solution of torsion problems with limited distortion of cross-sections in material and geometric nonlinear analysis of space R/C frames.