Failure criterion for RC members under biaxial bending and axial load

A new failure surface and criterion are developed for prismatic reinforced concrete structural elements subjected to biaxial bending and axial load. The failure criterion is a smooth surface in 3D space (two moments and axial load). It is governed by eight parameters, four of which are strengths that can be computed directly from strain-based failure criteria. The remaining four are exponential coefficients whose values are calculated using optimization techniques. Since the failure criterion is intended for use in automated design-optimization procedures, methods for parameter estimation based on design of the RC structural element are developed and tested. The parameters of the proposed surface are calculated first by simply minimizing approximation errors and then by allowing only conservative approximation errors. A conclusion of this work is that the proposed methods are reliable and can be used to rapidly check allowable capacity constraints in load space during design optimization of reinforced concrete structures undergoing dynamic loading.