Seismic behavior of steel-encased reinforced concrete composite shear walls with openings

Shear wall structures are commonly used as lateral-loading resisting system in high-rise building. Due to architectural requirement, large openings are often needed in the first floor. Compared with the upper floors in a structure, the shear capacity over demand ratio of the first floor is relatively poor. RC shear walls in the first floor usually suffer brittle shear failure under severe earthquakes. To improve seismic capacity of the building, Steel-encased Reinforced Concrete (SRC) composite shear walls are proposed instead of traditional reinforced concrete (RC) shear walls. This scheme mitigates the weakness of low resistance to tension of RC walls and the poor performance of buckling in steel member. In this study, the influence of opening to the response of SRC was specifically investigated. A total of 11 specimens of one story shear wall were designed, constructed and tested. The specimens were 115 in length scale, and can be classified into 3 groups: (1) Shear walls with small opening (the width of the opening in this group is 200 mm); (2) Shear walls with large opening (the width of the opening in this group is 300 mm); (3) Shear wall with no opening. For each group, an RC shear wall was constructed and tested, serving as basis of comparison for the SRC shear wall specimens. The SRC specimen represents a "dual" load resisting system. In the beginning, the RC shear wall will bear most of the lateral load, after the stiffness of the shear wall deteriorates, the steel moment frame will act as a primary load resisting system. Therefore, it will help prevent large lateral drift and collapse failure of the structure. Comparisons between walls with the same height of the opening indicate that the shear wall with wider opening experience much fuller hysteresis loop or dissipate more energy than the shear walls with narrower opening. Comparisons between walls with the same width of the opening show that the shear walls with higher opening have fuller hysteriesis loop or dissipate more energy than the shear walls with shorter opening. This behavior indicates that the ductility is increasing with increase of the area of opening.