Design procedure and analysis of innovative hybrid coupled shear walls

An innovative seismic resistant hybrid coupled shear wall (HCSW) developed within the European RFCS research project INNO-HYCO (INNOvative HYbrid and COmposite steel-concrete structural solutions for building in seismic area) is illustrated in this article. The proposed HCSW system is made of a reinforced concrete shear wall coupled to steel side columns by means of steel links (Fig. 1). The connections between links and side columns are pinned ensuring the transmission of shear force while the side columns are subject to compression/traction with small bending moments. The structure is conceived to limit the damage under earthquake excitation to the link elements so to obtain a seismic resistant system that is simple to repair. To this end, it is important to develop a suitable connection between the steel links and the concrete wall that ensures the easy replacement of the damaged links and, at same time, the preservation of the wall. The proposed hybrid system is effective as seismic resistant component if the yielding of a large number of links is obtained. Such systems should permit to exploit both the stiffness of reinforced concrete elements, necessary to limit building damage under low-intensity earthquakes, and the ductility of steel elements, necessary to dissipate energy under medium- and high-intensity earthquakes. Various design procedures were attempted during the course of this research project. Preliminary designs based on the conventional force approach were made in order to identify possible optimal geometries [1]. A large number of HCSWs with different dimensions of the reinforced concrete shear walls and link lengths were evaluated in this preliminary design stage [1][2]. The results obtained in this first design stage directed the research towards the definition of a design approach [3] that inherited recommendation for capacity design from other structural systems involving similar dissipative mechanisms in the links, i.e. eccentric braces in steel frames, as well as indication to reduce damages in the reinforced concrete wall. Applications of this design approach on a number of case studies gave interesting results [3][4][5] through procedures that are familiar to structural engineers trained to steel seismic design according to Eurocode 8. However, some problems were also highlighted as significant quantities of longitudinal bars were required, in some cases exceeding Eurocode upper limits. Thus, a different approach was attempted, this time taking inspiration from the ASCE recommendations for conventional hybrid coupled shear walls [6]. This proposed performance-based design approach [7] as well as its application to a case study are illustrated in this paper.