Performance-based slenderness limits for deformations and crack control of reinforced concrete flexural members

Abstract

The use of high strength materials allows flexural members to resist the design loads or to cover long spans with a reduced depth. However, the strict cross section dimensions and reinforcement amount required in ULS are often insufficient to satisfy the serviceability limit states. Due to the complexity associated to a rigorous computation of deflections and cracks width in cracked RC members along their service life, an effective way to ensure the satisfaction of the SLS is to limit the slenderness ratio l/d of the element. In the present study, the slenderness limit concept, previously used for deflection control, is generalized to incorporate the crack width limitations in the framework of structural performance-based design. Equations for slenderness limits incorporating the main parameters influencing the service behaviour of RC members are derived. Cracking and long-term effects are accounted for through simplified coefficients derived from structural concrete mechanics and experimental observations. The proposed slenderness limits are compared with those derived from a numerical non-linear time-dependent analysis for two case studies, and also with those obtained using the EC2 procedure for deflection calculation in terms of constant applied load and constant reinforcement strain. Very good results have been obtained in terms of low errors and scatter, showing that the proposed slenderness limits are a useful tool for performance-based design of RC structures.