Seismic Response Evaluation of Zonal Hanging Curtain Wall System Using Hybrid Simulation

Abstract eng:
The outer curtain wall system of Shanghai Tower adopts flexible zonal hanging glass curtain wall (CW) system, which is vertically hung from the suspension beam of the mechanical floor by sag rods. Due to the irregular plan configuration of this CW supporting structure (CWSS), the overhang length of the suspension beam changes in different hanging points, which affects the seismic behavior of the CWSS. Therefore, it is necessary to investigate the influence of the suspension beam stiffness on the behavior of the CWSS under vertical seismic inputs. For this purpose, a simplified 2D model of the CWSS, which focuses on the suspension beam and sag rods, was developed first. Subsequently, a parametric study was carried out to investigate the effect of the suspension beam stiffness, utilizing this CWSS model with acceleration inputs from the corresponding hanging floor obtained from nonlinear analysis of the main structure under design earthquake motions. The parametric study results identified the critical configuration of this CWSS, where the stiffness ratio between the suspension beam and sag rod is 0.1. Nonlinear analyses of the simplified CWSS (SCWSS) for the stiffness ratio of 0.1, with four different inputs, were performed to determinate the critical sag rod position. The results showed that the sag rod in the hanging position exhibits nonlinear behavior prior to other sag rods. Different from the shaking table tests focusing on the seismic performance of CW panels, the hybrid simulation (HS) method was employed herein to evaluate the vertical seismic performance of the most critical configuration of the SCWSS. The HS tests were conducted using the HS system in the Structural Laboratory in the University of California, Berkeley. In the tests, the sag rod in hanging position, determined to be the most critical element from nonlinear analyses, was simulated as an experimental substructure, while the other rods were analytically modeled in OpenSees. Considering the setup capacity and the test purpose, the test specimen was designed to meet the requirements of force-displacement similitude with a length scale factor of 13.0. Other similitude relations were dictated by the material properties of the test specimen, determined before the HS tests. The HS tests with the input of three intensity scenarios, namely frequent, precautionary and rare earthquakes of intensity 7 (based on the Chinese design code), were carried out. The results from the HS tests and pure analysis were compared and it was observed that the HS results matched quite well with the analytical results when the specimen was elastic. With respect to the input of rare intensity, differences appeared between the HS and the analytical simulations after specimen yielding due to uncaptured sources of inelasticity in the analytical simulations. The specimen buckled under the input of rare intensity with maximum full-scale deformation of 64.5 mm before breaking, which is expected to subject the CW panel to compression in the vertical direction and may result in damage of the panel.

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