Modelling techniques to capture the backbone envelope behaviour of coupling beams subjected to seismic loading

Structural R/C cores are a popular and efficient choice as lateral-load resisting system in medium to tall buildings. The walls of the cores typically present large openings providing access to elevators placed within them. Shear induced by lateral forces has thus to be transmitted by limited portions of the core (wall between openings) which are commonly named coupling beams. Such beams are subjected to large deformation demands as the system undergoes lateral displacements associated to wind or earthquake forces, and typically govern the response of the structural system. Performance-based assessment and design of these members have been gaining popularity within the structural engineering community approximately during the last 15 years. These techniques rely on accurate definitions of component behavior (shear force – chord rotation) for their successful application to overall system performance. In current seismic design and assessment documents, the influence of some instrumental parameters such as slenderness, reinforcement layout or even failure mode is not (or only partly) addressed. In this paper, the influence of these parameters is investigated on the basis of the results of an experimental campaign. Several approaches to generate force-deformation envelope (backbone) curves for coupling beams are discussed and compared. The use of stress field models is introduced as a promising technique to rationally represent the backbone envelope behavior of elements subjected to cyclic loading.