Design of building structural systems and enhanced partition walls to improve life cycle costs associated with risk of earthquake damage [electronic resource]
Keywords: Civil and Environmental Engineering.

Current seismic design codes are primarily aimed at protecting human life, which has been successfully observed in recent large earthquakes in Chile, and New Zealand, where the number of fatalities due to collapsed buildings was relatively low. However, the economic losses experienced in these countries were significant and the environmental impacts were potentially important, but they have not been accurately quantified. These large earthquake-induced economic losses and environmental impacts suggest that higher seismic performance, beyond the code requirements, may be necessary to meet the expectations of modern society. To face these challenges, the fully probabilistic Performance Based Earthquake Engineering framework introduced by the Pacific Earthquake Engineering Research Center allows assessing decision variables such as earthquake-induced economic losses, downtime, and fatalities. The quantitative evaluation of these decision variables shows the level of performance of a given building, allowing owners and stakeholders to select higher levels of performance if they are not satisfied with the minimum requirements established by design codes. These higher levels of performance are associated with higher construction costs that also need to be accurately estimated to provide complete information for a satisfactory evaluation of the trade-off between higher investments and future reduction of these earthquake-induced economic losses. The objectives of this dissertation are to provide building-specific performance-based earthquake engineering design strategies to reduce economic losses and environmental impacts. In particular, previous researchers have found that the earthquake-induced economic losses in buildings are dominated by nonstructural components, especially by gypsum partition walls. Traditionally, the main strategy to reduce these losses is to stiffen and strengthen the lateral force resisting system of buildings to reduce the damage to non-structural elements. An alternative strategy, which was investigated in this study, is to enhance the resistance of the non-structural components such as gypsum partition walls. The seismic vulnerability of gypsum partition walls is established through the development of fragility functions that show how typical partition walls become damaged at story drift ratios as low as 0.1%. Based on data from previous building loss studies, a seismic performance goal of damage-free partition walls at story drift ratio of 1.0% was set, and a frictional/sliding connection was designed and tested to achieve this goal. The effectiveness of the connection in reducing earthquake-induced economic losses and environmental impacts was evaluated in a steel special moment resisting frame (SMRF) testbed building. The study demonstrates that the enhanced partitions can reduce the annualized losses by a factor of four to seventeen, compared to conventional partitions. These significant reductions offset the slightly higher initial construction costs, thus promoting the use of the connection based on a life cycle evaluation. The more traditional strategy of enhancing the structural system was also evaluated. The strength and stiffness of the SMRF system of a testbed building was varied to assess the influence on earthquake losses. The code-conforming SMRF design (meeting only the minimum code requirements) exhibits an expected annual loss (EAL) of 0.95% (normalized by its initial construction cost), which over a 50-year service-life and using a discount rate of 3.9%, results in an earthquake-induced expected life cycle cost (ELCC) of 121%. An alternative design, with increased strength and stiffness has a reduced ELCC of 114%. This result suggests that while current seismic design codes do not minimize ELCC, stiffening and strengthening of conventional structural systems may not be the most cost-effective way to improve performance, especially considering the significant upfront costs. This study further compares the effectiveness of the alternative strategy of enhancing nonstructural components (gypsum partition walls) versus the traditional strategy of enhancing the structural system, the results of which demonstrate the potential benefits of the alternative strategy. As an example, by implementing the new gypsum wallboard connection detail, developed in this research, the earthquake-induced ELCC of the code-conforming testbed building is reduced to about the absolute minimum ELCC obtained stiffening the SMRF system of the testbed building. The main advantage of the enhanced partition connection is that it has a very little cost premium over conventional construction. Finally, a simplified methodology to estimate the earthquake-induced ELCC based on the fundamental period of vibration of low-rise steel SMRF buildings is proposed. This methodology introduced a closed-form solution for the EAL, thereby eliminating the need for conducting and integrating nonlinear structural analyses to estimate the EAL for design and risk assessment. This methodology was calibrated with data from the low-rise testbed building example, showing promising results.