Analytical and numerical study of an eccentric continuous cable bracing system with friction slip mechanism

Abstract

This study proposes a very simple and low-cost friction mechanism using a pre-stressed cable passing over two fixed pulleys without rotation along with an eccentric continuous cable bracing as a lateral-resistant system for structures subjected to lateral loading such as earthquake. The performance of this mechanism is investigated using analytical solution method and finite element modeling. The purpose of this system is to provide a structure with sufficient stiffness and lateral resistance as well as energy dissipation through frictional slip between the cable and pulleys. The system exhibits two-phase behavior. In case of a small lateral displacement, the system exhibits high stiffness in the linear elastic phase (first phase) and behaves well under normal winds and small earthquakes. In case of large lateral displacement such as a strong earthquake, the system experiences a nonlinear slip phase (second phase) and, accordingly, exhibits a nonlinear behavior with an increase in stiffness and input energy dissipation which protects the structure from displacement. The seismic performance of the proposed system is investigated in terms of three parameters: friction coefficient, initial pre-stressing force, and span length. As the friction coefficient value increases, the lateral resistance of the system rises. In the event of extra rotation of the cable around the pulleys, the coefficient values at static and dynamic friction phases are 5.6 and 5.1 times those in the frictional state, respectively. The rise of the span length and reduction of initial pre-stressing force decrease the system lateral resistance and the initial stiffness of the system, respectively. Upon increasing the initial pre-stressing force up to twice that of the base state, the slip threshold of the system lateral resistance force increases by 33% and as a result, the system remains more at the static friction phase. Also, by reducing the initial pre-stressing to half of its value in the base state, the lateral resistance force corresponding to the slip threshold of system is decreased by 52%; therefore, the slip of the cable on pulleys is initiated earlier. Finally, the cyclic behavior of the steel moment frame with the proposed system is investigated with ATC24 protocol, which increases the stiffness and energy dissipation by 19% compared to the moment frame without the proposed system.