Loss Assessment of Tall Buildings From a Vulnerability Perspective

Abstract eng:
As the number of tall buildings in seismic areas around the world continues to grow, the ability to perform loss assessments becomes increasingly important. Due to their size, tall buildings house many businesses and/or residents, and any damage to these buildings has the potential to affect a large number of people. Furthermore, these buildings are expensive to build and repair. The financial resources needed to recover from the damage induced by earthquakes are generally not trivial amounts, and thus the ability to realistically model losses in tall buildings becomes essential. The loss assessment of tall buildings presents unique challenges, including the tendency for significant damage to be concentrated in a few stories rather than distributed throughout the building. The presence of excessive residual drifts in one or a few stories can result in the building being declared a total loss and demolished, even when the levels of damage in the rest of the building are relatively low. Accessibility issues can increase repair costs in a tall building relative to a shorter building as, for example, it is much easier to replace the window on the 2nd story of a 5-story building versus on the 20th story of a 50-story building. The long first-mode periods of tall buildings as well as the significant contribution of higher modes means that the ground motions used to assess the structural response must be carefully considered as both the low frequency and high frequency components of the ground motion affect the response. The evolution of building design is also an important factor in the loss assessment of tall buildings. The trend in recent years toward performance-based designs and a growing awareness for designs that reduce expected seismic losses play an important role in differentiating the expected losses of newer versus older tall buildings. This is in addition to the effects of advances in building codes and design practice that are typically seen over time, such as improvements in designing for ductility and reducing the risk of connection fractures in steel moment-resisting frames. This study examines the loss assessment of tall buildings from a vulnerability perspective, drawing on the unique characteristics of tall buildings previously noted. It discusses how the vulnerability characteristics of tall buildings affect the relative seismic risk and uses examples of major cities in North America and New Zealand to illustrate the effects.

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