Límites de esbeltez basados en prestaciones para vigas de hormigón armado para el control de deformaciones y el control de tensiones en la armadura

Abstract

Current flexural design procedures of RC elements, based on ULS, provide enough strength to resist the design loads with a reduced depth. However, the strict cross section dimensions and reinforcement amount computed to satisfy the ULS may be insufficient to avoid excessive deformations that can produce damage in non-structural members, or to ensure the control of cracking to satisfy durability, functionality or aesthetics requirements. 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, which are valid for rectangular I or T shaped cross sections and for simply supported or continuous members. Cracking and long-term effects are accounted for through simplified coefficients derived from structural concrete mechanics and experimental observations. The proposed slenderness limits obtained both for a constant applied load and for a constant reinforcement strain, are compared with those obtained using the EC2 procedure for deflection calculation based on integration of curvatures. 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. The mechanical character of the formulation facilitates its modification to situations different to those used for its derivation, for example different load types, partially pre-stressed beams or FRP reinforced concrete members, among others