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A collapse study of a lightly reinforced concrete shear wall building during the February 22, 2011 Christchurch earthquake

University of British Columbia

The Canterbury earthquake sequence in New Zealand started with the September 2010 earthquake, followed by large aftershock events throughout the following year. This sequence displayed the vulnerability of lightly reinforced concrete buildings built prior to 1980; specifically, the Pyne Gould Corporation (PGC) building, which collapsed during the February 22, 2011 event in Christchurch, New Zealand. PGC was a lightly reinforced concrete shear wall building with an exterior gravity frame built in 1964. A previous seismic study by Beca Carter Hollings and Ferner (Beca) of PGC was prepared for the Canterbury Earthquake Royal Commission and concluded flexural failure of the shear core governed the collapse. Failure initiated by rupture of the reinforcement in the west wall flange, followed by crushing of the east wall flange, leading to an increase in deformation demand on the building causing the exterior frame to lose its vertical-load-carrying capability. A seismic performance study and collapse analysis was performed on PGC during the September and February earthquakes. The study focuses on the vulnerabilities of the shear core and the exterior gravity frame, as well as the torsion irregularity and how it may have contributed to the collapse. Two comprehensive nonlinear models, a fiber element model and a multiple-vertical-line-element model were used to simulate the September and February earthquakes within the computer software OpenSees. Non-linear time history analyses were performed to determine the primary cause of failure, how the gravity frame lost its vertical-load-carrying capacity and how the torsional irregularity affected the seismic response. The analysis concluded failure of the core walls was likely initiated by shear failure in the highly perforated wall at the north end of the core. This conclusion is consistent with the observation of sizable diagonal cracks in the third story of the north wall, indicating possible shear failure. By comparing multiple configurations the analysis concluded the location of the core had minimal influence on the collapse. This is consistent with the post collapse photos of the floor slabs indicating minimal plan rotation. Post-processing indicated the exterior gravity frame was governed by joint shear failure causing the frame to fail in a sidesway mechanism.

Text

2014-02-12

Attribution-NonCommercial 2.5 Canada

http://hdl.handle.net/2429/46010

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc/2.5/ca/