Kenneth J. Elwood

Out-of-Plane Dynamic Stability of Unreinforced Masonry Walls in One-Way Bending: Shake Table Testing

Given sufficient anchorage to the diaphragms, an unreinforced masonry (URM) wall subjected to out-of-plane inertial forces will likely develop a horizontal crack at an intermediate height about which the wall will rock as semirigid bodies. The effect of wall slenderness on out-of-plane stability has been demonstrated in past studies, but treatment of the effects of diaphragm flexibility and ground motion variability has been limited. This paper presents an experimental study examining the out-of-plane stability under seismic loading of URM walls connected to flexible diaphragms. Five full-scale unreinforced solid clay brick wall specimens spanning one story were subjected to earthquake ground motions using a shake table. The top and bottom of the walls were independently connected to the shake table through coil springs, simulating the flexibility of diaphragms. Variables examined experimentally included diaphragm stiffness and wall height. Both the amount of rocking observed as well as the ground motion scale causing collapse varied significantly with changes in the diaphragm properties. The test results provided data used for validation of a rigid-body rocking model, enabling an extensive parametric study on wall stability and the development of new assessment guidelines in a companion paper.

Factors Influencing Post-Earthquake Decisions on Buildings in Christchurch, New Zealand

The high demolition rate (∼60%) of reinforced concrete (RC) buildings that generally performed well in Christchurch, New Zealand, has been one of the most important lessons from the Canterbury Earthquakes. In an effort to understand such an outcome, various factors influencing the post-earthquake decisions on buildings (demolition or repair) are explored, focusing on multi-story RC buildings in Christchurch Central Business District (CBD). Using empirical data, logistic regression analysis was conducted to explain the likelihood of building demolition. Several explanatory factors were found to be statistically significant: assessed damage, occupancy type, heritage status, number of floors, and construction year. From in-person interviews conducted in New Zealand, contextual factors such as insurance policy and changes in legislation were also found to play a significant role in the post-earthquake decisions on buildings.

A Detailed Inventory of Non-Ductile Concrete Shear Wall Buildings

A detailed inventory of about 350 concrete shear wall buildings in western Canada with 7 or more stories and built prior to 1980 was created. About one hour was spent collecting information from drawings for each building so wall capacities could be estimated and simplified linear dynamic analysis could be used to estimate seismic demands on the building. Non-ductile behavior is expected in many of the buildings because of insufficient and/or poor arrangement of shear walls to adequately control building drifts, thin walls that are poorly detailed, and discontinuities in the shear walls. The analysis indicated that the drift demands on the buildings for the 2% in 50-year hazard level were not particularly large, however the flexural capacities of the walls are low considering their limited ductility. The shear capacities of the walls were typically less critical. The current study demonstrates that a detailed inventory can be used to distinguish between the performance of similar buildings, which can be used to refine a regional risk assessment or inform policy decisions for the group of buildings.

Out-of-Plane Behavior of Slender Reinforced Masonry Shear Walls under In-Plane Loading: Experimental Investigation

AbstractThis paper presents the results of a multiphase research program aimed at investigating the out-of-plane stability of slender reinforced masonry shear walls (RMSWs) under in-plane reversed-...

Preface to the special issue “Post-earthquake assessment and reconstruction”

Earthquakes striking densely built areas may produce disastrous damage and casualties, as unfortunately happened at L’Aquila in 2009. However, they also provide important data and information that raise the awareness and increase the level of knowledge for earthquake-induced disasters that affect the built environment as well as societies worldwide. Looking at the timeline of engineering activities in the post-earthquake environment, it can be observed that the bulk of efforts involving building tagging and damage reconnaissance are generally concentrated in the first months after the event. On the other hand, especially when it regards issues involving policies, reconstruction and community resilience, for which mid-to-long term assessment is required, some time is needed before useful conclusions can be drawn. Building inventory in peace-time as well as available data on damages and costs in the aftermath of an earthquake are important instruments for effective quantification of earthquake impact and the evaluation of possible strategies for the mitigation of seismic risk. In addition, reconstruction policies play a fundamental role in the recovery process, allowing the decision makers to consistently address key considerations such as public safety protection and reduction of future economic losses. Establishing such policies usually encompasses balancing between several often contrasting issues, such as enforcing higher standards for mitigating seismic risk, the urgent need for restoring normal life conditions, restoring the cultural heritage, preserving the historical centres and their social structure, and last but not least the stringent economic constraints. To this end, in order to

Collapse Probability of Existing Concrete Buildings: The Evolution of Seismic Rehabilitation in North America

Existing reinforced concrete buildings lacking details for ductile response during earthquake shaking represent a significant life safety risk in high seismic zones around the world. The poor seismic performance of these non-ductile concrete buildings is evident from recent earthquakes in Chile, New Zealand and Japan. Seismic rehabilitation of these existing buildings plays an important role in reducing urban seismic risk; however, with the massive inventory of existing concrete buildings and the high costs of seismic rehabilitation , it is necessary to start by identifying and retrofit ting those buildings which are most vulnerable to collapse. Numerous sources of uncertainty complicate the ability to identify buildings which are vulnerable to collapse. For this reason, it is important to develop estimates of collapse probability to account for all significant sources of uncertainties. This chapter will introduce the concept of collapse indicators , design and response parameters that are correlated with “elevated” collapse probability. The methodology for identifying collapse indicators is based on results of comprehensive collapse simulations. Appropriate collapse indicators and corresponding limits are evaluated by seeking trends between probability of collapse and collapse indicators . This chapter will discuss significant challenges which pose a barrier to the assessment of collapse indicators that are applicable for the wide range of existing concrete buildings.

Performance-Based Issues from the 22 February 2011 Christchurch Earthquake

At 12:51 pm local time on 22 February 2011, a Mw 6.2 aftershock of the September 4, 2010, Darfield Earthquake shook the city of Christchurch, New Zealand. The aftershock occurred on an unmapped fault less than 8 km from the city center resulting in the collapse of two reinforced concrete office buildings and one concrete parking garage, and severe damage to numerous others. The region has continued to suffer from aftershocks and further damage to building structures throughout the year following the February earthquake. This paper summarizes the observed damage to buildings in the Central Business District (CBD), with a specific focus on identifying future research to support the development of performance-based design procedures.