Six months after the 4 September 2010 Mw 7.1 Darfield (Canterbury) earthquake, a Mw 6.2 Christchurch (Lyttelton) aftershock struck Christchurch on the 22 February 2011. This earthquake was centred approximately 10km south-east of the Christchurch CBD at a shallow depth of 5km, resulting in intense seismic shaking within the Christchurch central business district (CBD). Unlike the 4 Sept earthquake when limited-to-moderate damage was observed in engineered reinforced concrete (RC) buildings [35], in the 22 February event a high number of RC Buildings in the Christchurch CBD (16.2 % out of 833) were severely damaged. There were 182 fatalities, 135 of which were the unfortunate consequences of the complete collapse of two mid-rise RC buildings.
This paper describes immediate observations of damage to RC buildings in the 22 February 2011 Christchurch earthquake. Some preliminary lessons are highlighted and discussed in light of the observed performance of the RC building stock. Damage statistics and typical damage patterns are presented for various configurations and lateral resisting systems. Data was collated predominantly from first-hand post-earthquake reconnaissance observations by the authors, complemented with detailed assessment of the structural drawings of critical buildings and the observed behaviour.
Overall, the 22 February 2011 Mw 6.2 Christchurch earthquake was a particularly severe test for both modern seismically-designed and existing non-ductile RC buildings. The sequence of earthquakes since the 4 Sept 2010, particularly the 22 Feb event has confirmed old lessons and brought to life new critical ones, highlighting some urgent action required to remedy structural deficiencies in both existing and “modern” buildings. Given the major social and economic impact of the earthquakes to a country with strong seismic engineering tradition, no doubt some aspects of the seismic design will be improved based on the lessons from Christchurch. The bar needs to and can be raised, starting with a strong endorsement of new damage-resisting, whilst cost-efficient, technologies as well as the strict enforcement, including financial incentives, of active policies for the seismic retrofit of existing buildings at a national scale.

Seismic performance of reinforced concrete buildings in the 22 February Christchurch (Lyttelton) earthquake

Precast concrete facilitates a construction method using durable and rapidly erectable prefabricated members to create cost-effective and high-quality structures. In this method, the conne...

Seismic-Resistant Precast Concrete Structures: State of the Art

A new seismic diaphragm design methodology has been developed for precast concrete floor diaphragms. The knowledge required to create the design methodology was obtained through an integrated analytical and experimental research project using two Network for Earthquake Engineering Simulation (NEES) equipment sites. The activities of the project involved a sequence of integrated research tasks that systematically developed knowledge about diaphragm behavior from the reinforcement detail level to the structural system level. These tasks included the use of state-of-the-art experimental techniques made possible through the NEES facilities including hybrid simulation and large-scale shake table tests. Such techniques were crucial to the research as the complex behavior of precast diaphragms is not well described by simple analytical models or idealized experiments. Valuable industry oversight in the planning, execution, and technology transfer stages of the project guided the research activities, incl...

Integrated Analytical and Experimental Research to Develop a New Seismic Design Methodology for Precast Concrete Diaphragms

This paper presents an analytical study used to establish design factors for a new seismic design methodology for precast concrete floor diaphragms. The design factors include diaphragm force amplification factorsΨ and diaphragm shear overstrength factors Ωv. The Ψ factors are applied to the ASCE7-05 diaphragm design forces to produce diaphragm design strengths aligned to different performance targets. These performance targets are based on diaphragm detailing choices, and include: (i) elastic diaphragm behavior or (ii) limiting inelastic deformation demand on the diaphragm reinforcement (connectors between precast units or reinforcing bars in a topping slab) to within their reliable deformation capacities. TheΩv factors provide overstrength relative to the diaphragm bending strength for capacity protection against shear failure. The analytical study was performed by conducting nonlinear time history analyses of a simple evaluation structure, of which the dimensions and structural properties were varied. The analytical model used in the study is constructed and calibrated on the basis of extensive physical testing. The analytically obtained values of the diaphragm design factors are presented as functions of the geometric and structural properties of the building. The design factors presented here have been verified through evaluation of a set of realistic precast prototype structures. The diaphragm design methodology is currently in the codification process. Copyright © 2015 JohnWiley & Sons, Ltd.

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Establishment of performance‐based seismic design factors for precast concrete floor diaphragms

A variety of connector details are used to provide integrity and force transfer between precast concrete panels in building floor diaphragms. To assess the adequacy of these connectors a large number of experiments have been conducted on discrete welded connectors used in precast concrete double-tee floor panels. A standard procedure for developing simplified response curves from original test data is used to generate simplified curves from each of the tests conducted. The calculated results of over 200 experiments are summarized in a comprehensive performance database. This database provides the stiffness, strength, and deformation properties of each connector detail examined. The connectors are divided into one of the following three displacement-based categories: low deformation element (LDE), moderate deformation element (MDE), and high deformation element (HDE), based on the performance measured in the experiments. A simplified pushover modeling approach is developed to estimate the in-plane ...

Precast Concrete Diaphragm Connector Performance Database

Precast concrete diaphragm seismic response is examined in experimental research integrating model-based simulation with physical testing. The experimental substructure is the diaphragm critical flexural region of a prototype precast parking structure. This region is expected to undergo significant inelastic flexural deformation, while potentially nonductile regions remain elastic on the basis of capacity design rules from an emerging design methodology. The physical test is conducted at half-scale. The test specimen is detailed using diaphragm reinforcement intended to meet deformability requirements. Predetermined displacement histories are applied to the test specimen on the basis of nonlinear transient dynamic analyses of the prototype structure. The loading history is applied by a test fixture capable of simultaneously providing shear, axial, and moment to the joint. Moment strength, stiffness, rotational deformation capacity, and progressive damage are examined under a sequence of increasing intensity earthquakes. Design recommendations are provided.

R Ren

Papers

Experimental Evaluation of Pretopped Precast Diaphragm Critical Flexure Joint under Seismic Demands