Cyclic shear behavior of composite walls with encased steel braces

Abstract

The composite wall with encased steel braces (ESB wall) is a novel type of steel–concrete composite wall that consists of a steel braced frame embedded in reinforced concrete. This arrangement is supposed to enhance the seismic performance of the wall, as the steel columns encased in the boundary elements can increase the flexural strength of the wall and the steel braces encased in the web can increase the shear strength. This paper examines the cyclic shear behavior of squat ESB walls by conducting quasi-static tests. Two wall specimens with an encased single-diagonal brace, one of which had an I-shaped brace and the other a steel plate brace, were tested. Both specimens had a shear-to-span ratio of 1.06, and they were subjected to a moderate axial force ratio of 0.18. A flanged wall section was intentionally used to ensure that the wall’s flexural strength exceeded the shear strength, resulting in a shear failure mode. The two specimens failed in a similar manner, characterized by crisscrossed-diagonal cracking and crushing of the concrete in the web panel. Hysteretic responses of the two specimens were nearly identical, and both types of steel braces buckled after they yielded. This indicates the potential use of steel plate braces instead of I-shaped braces in ESB walls, as the former allows improved efficiency and quality of construction. A simple method was presented to calculate the cracked shear stiffness of ESB walls, and this method could reasonably estimate the cracked shear stiffness of the specimens. In addition, the JGJ 138-2012 formulas for assessing the shear strength of ESB walls were calibrated through the analysis of data collected in past tests and in the present experimental program. The design formulas, based on the superposition method, are found to provide reasonable and conservative predictions of the shear strength capacity of ESB walls.