Page 60 of 241 THE INFLUENCE OF THE CONCRETE CYCLIC LAWS ON THE DYNAMIC RESPONSE OF SLENDER RC WALLS Daniele BARALDI Ph.D. student Dipartimento di Ingegneria, Università di Ferrara Via Saragat 1, 44121 Ferrara brldnl@unife.it* Nerio TULLINI Associate Professor Dipartimento di Ingegneria, Università di Ferrara Via Saragat 1, 44121 Ferrara nerio.tullini@unife.it Ferdinando LAUDIERO Professor Dipartimento di Ingegneria, Università di Ferrara Via Saragat 1, 44121 Ferrara ldf@unife.it Abstract The cyclic laws for dynamic analyses of reinforced concrete (RC) structures usually neglect the concrete traction strength and the re-loading branch from traction to compression. These assumptions may lead to unreal results in cyclic or dynamic analyses. For example, flag- shaped moment-curvature diagrams of slender RC walls are presented. For this reason, the behaviour of concrete in cyclic tension, determined by Reinhardt et al. [1,2] and modified by Ferracuti and Savoia [3], is added to an existing cyclic stress-strain law. Making use of the finite element (FE) software OpenSees, the resulting concrete law is firstly validated by simulating experimental tests on RC cantilever beams cyclically loaded. Then, slender RC walls in multi-storey buildings are considered and dynamic analyses are done. Moment- curvature curves at base sections are obtained, together with force and displacement envelopes. The results obtained with the implemented law are compared against the ones obtained with a common law. Results show that the concrete reloading behaviour from tension to compression affects significantly the walls designed for a larger response in the inelastic field. Keywords : Fibre model, non linear dynamic analysis, RC walls. 1. Introduction In the last decade, dynamic analyses of RC structural elements were often developed by adopting fibre models introduced by Spacone et al. [4,5]. These models allow the possibility to consider the distributed plasticity along elements by adopting different mechanical behaviour of concrete and reinforcement bars. Thus, fibre models represent an excellent tool for the analysis of RC shear walls. Nevertheless, the concrete cyclic laws often neglect the traction strength and usually assume to be coincident the re - loading and unloading branches from tension to compression. The mechanical behaviour of concrete in monotonic or cyclic tension was deeply studied [6]. Among the various cyclic laws proposed, the monotonic traction behaviour described by Reinhardt et al [1] is adopted in this paper. To describe the reloading branch from traction to compression, the expressions of Reinhardt and Yankelevsky [2] are modified following the