The Effects of Rotational Components of Near-Fault Earthquakes on Self-Centering Base-Rocking Walls

Nowadays, self-centering (SC) lateral resistant systems are able to reduce residual displacement and post-earthquake repairing costs. By concentrating damages on fuse elements, these systems reduce repair costs and allow immediate occupancy. To resist against lateral load, the SC systems have two mechanisms including: 1) restoring force mechanism, 2) energy dissipation (ED) mechanism. Both mechanisms are needed to provide flag shape pushover behavior. The restoring force mechanism provided with post-tensioned (PT) prestressed core to supply prestressed used unbounded tendons. The reason using unbounded tendons is to prevent their yielding suddenly and creating cracks in core. Usually, the restoring force mechanism is accompanied by gap opening in systems. This gap opening can cause damage to other structural and nonstructural members. Then, the system should be isolated in location of joints. The ED mechanism provided with fuses. Fuses can have different types, including:  1) hysteric, 2) viscous, and 3) shape memory alloy (SMA) dampers. Among these dampers, hysteric elements are more used due to their low price than other fuses. The SC systems implemented in different types, including: 1) rocking cores, or frames, 2) moment frames, and 3) braces. The moment frames and braces need specially detailing, and expert worker for building and construction. Furthermore, rocking frames needed total system rotated that is constructive details difficult. Among these systems, rocking cores have mostly been used and studied. The rocking cores are made with three cores of concrete shear wall, wooden wall and bracing frame.According to seismic codes, lateral resistant system must have the necessary strength to withstand earthquakes. The records of earthquakes have three translational and three rotational components. Usually, the structures investigated under translational component and rotational component ignored. To produce the rotational component, there are two methods, including single station procedure (SSP) and multiple stations procedure (MSP) or geodetic method. The SSP method extracts the rotational components from the translational ones. In this method, many researchers employ the information of a single station individually to obtain the rotational components. In the MSP method, the rotational components use translational recorded data by the numerous ground motions distributed in a closely dense zone. Utilizing this method requires a vast range of information of many ground motions, which was unreachable for the authors of this manuscript. Therefore in this research, to produce the rotational components of ground motions use SSP method. Furthermore, near-fault ground motions were considered for time history analysis. Near-field ground motions have some characterizations that make them different from far-field ground motions. The most remarkable characterization of these records includes: 1) distance less than 10 km from the fault, 2) the existence of long-period pulses in their velocity time series, 3) high Peak Ground Acceleration (PGA), and 4) high Peak Ground Velocity (PGV).In current study, the behavior of SC base-rocking walls under 25 near pulse-like ground motions was investigated. The structures were studied in two states depending on considering or ignoring the rotational component of the ground motions. In order to compare and consider the rotational components, six seismic load combinations were considered. 2D frames of 4-, 8-, 12-, 16-, and -20 stories were examined. Nonlinear time-history analyses were performed utilizing software. The results showed that considering the rotational component of earthquake can increase structural responses. In this regard, the maximum acceleration, inter-story drift, moment, shear force, roof drift and maximum tendon stress ratio were increased up to 24.6, 9.3, 10.4, 9.6, 623 and 11%, respectively.Furthermore, the results suggested that as the height of the structure increases, the response values of maximum roof drifts and maximum stress ratio increase. In SC base-rocking wall systems studied, the maximum residual roof drift was equal to 0.01 %.