The behaviour of external glazing systems under seismic in-plane racking

Abstract

The in-plane behaviour of external curtain wall glazing systems when buildings respond to seismic loading is not understood. This is a cause of great concern for the safety of pedestrians and occupants of buildings during earthquake attacks. This work forms the second phase of a research programme undertaken by BRANZ to determine the performance of external glazing systems used in multi-storey buildings when subjected to seismic induced racking. The objective of this study was to verify that the performance of curtain wall glazing systems can be adequately modelled within a laboratory environment. Another objective was to identify the parameters which affect the performance of curtain wall glazing systems when subjected to seismic in-plane racking, thereby enabling a suitable test method to be developed.

This report describes the experimental racking tests carried out on five full-size generic glazing systems. The parameters studied included displacement rates (period); boundary conditions (building deformation characteristics and two specimen configurations); number of cycles at each amplitude, and different incremental cyclic displacement. To investigate the effect resulting from torsion, a 30 mm out-of-plane skewness was also introduced to three systems. The effects at corners of buildings and the bidirectional deformation of glazing systems were not studied.

The results indicated that the displacement rate is the main parameter affecting the behaviour of the systems tested. Multiple cycles at each amplitude increased the amount of gasket slipping out of framing members, thus affecting its serviceability. No significant difference in behaviour of the glazing systems was observed under different incremental displacements. The effect of the 30 mm skewness, different boundary conditions, and different specimen configuration affected different glazing systems in different ways. The results of the glazing systems tested indicated that in general, they would perform well under an earthquake attack when installed upon buildings designed to current code requirements. In addition, the stiffness and damping of the systems were calculated. Unless glazing systems are actively separated from the structure, their stiffness contribution to the total storey stiffness may be significant, particularly in the initial stage.