Behavior and modeling of infill FRC damper element for steel-concrete hybrid shear wall.

Abstract

The steel-concrete hybrid shear wall investigated comprises two edge steel columns connected by infill FRC damper elements (IDE) made using High Performance Fiber Reinforced Cement Composites (HPFRCCs). The infill FRC damper elements, which are meant to act as energy dissipaters and dampers under reversed cyclic loading, are designed to dissipate energy by a shear-friction mechanism. They are slotted and notched at mid-section to insure the desired behavior. Diagonally positioned unbonded tendons pre-tensioned to about 70% f_pu were used to achieve both stable load resistance and self-centering ability. The analytical work was aimed first at understanding the fundamental mechanisms that controlled the response of infill FRC damper element and providing a simple model that allows for a realistic simulation of its behavior. Also, the connection of the IDE to the steel columns was carefully analyzed. Extra effort was put on the specimen detailing, the size of the slots, and the thickness and reinforcement of the notched section. Structural analysis programs and commercial nonlinear finite element programs were used during different stages of the analytical work. Fourteen FRC-IDE specimens were tested in this study with the objective of obtaining a better understanding of the seismic response of this innovative hybrid wall system including failure mechanism, behavior, modeling, analysis, and optimization. Several parameters were investigated selectively: two different specimen aspect ratios (a/d = 1.5 and a/d = 1), three different dowel reinforcement ratios, three different fibers (ZL30/50 hooked steel fibers, ZL 50/50 hooked steel fibers and Spectra fibers), two different testing configurations (vertical and horizontal) and three different matrices (slurry for SIFCON, mortar and concrete). The performance of the infill FRC damper elements was evaluated in terms of cracking and failure mode, strength, displacement and rotation ductilities, shear deformation, energy dissipation, and stiffness deterioration under cyclic loading. Design recommendations are presented based on the analytical and experimental results. The proposed IDE element satisfied the Acceptance Criteria for Moment Frames Based on Structural Testing - ACI ITG/T1.1-99 requirements and thus proved to be a viable system for steel-concrete hybrid shear walls used in high seismic regions. It may also be a cost-effective system considering its prefabrication and easy replacement.