NONLINEAR TORSIONAL ANALYSIS OF REINFORCED CONCRETEFRAMES

摘要

A number of computer programs exist which can analyze the full flexural and axialbehaviour of reinforced concrete space frames. They account for concrete cracking, crushing andnonlinearity under different states of stress, and for steel yielding and strain hardening. The sameprograms, however, use crude torsional models. They often use simplistic bi-linear torque-twist relationsfor pre- and post-cracking stages. Since in statically indeterminate space frames the distribution ofmoments at a joint are a function of both the flexural and torsional stiffness of the beams converging onthe joint, incorrect estimate of the torsional stiffness leads to incorrect estimate of the member endmoments. Thus, despite the accuracy of the flexural stiffness coefficients, the final results may not be asaccurate as one may believe.To address this problem, in this paper a detailed procedure is describe and used to develop the nonlineartorque-twist relation of any arbitrary reinforced concrete cross-section. The method is based on the actualgeometric and material properties of the cross-section, including the amount and distribution of thelongitudinal and transverse reinforcement designed to resist torsion. The torque-twist relation accounts foryielding of transverse and/or longitudinal reinforcement, concrete crushing and reduction in diagonallycracked concrete compressive strength due to concomitant transverse tensile strain. While other methods,such as the modified compression field theory MCFT) also account for these effects, unlike the MCFT, thepresent model is non-iterative. The accuracy of the proposed model is established by comparing its resultswith available experimental data and good agreement is observed between the two.