Simplified Methodology To Estimate Earthquake-Induced Expected Life Cycle Costs of Low-Rise Steel Moment Resisting Frame Buildings

Abstract eng:
Seismic design codes are primarily aimed at protecting human life, but they are not intended to minimize or even calculate the earthquake-induced economic losses that a building might experience during its service life. Fortunately, the Performance Based Earthquake Engineering (PBEE) framework introduced by the Pacific Earthquake Engineering Research (PEER) Center allows evaluation of decision variables such as earthquake-induced economic losses, downtime, fatalities and environmental impacts. The evaluation of these decision variables shows the level of performance of a given structure, allowing owners and stakeholders the selection of higher levels of performance if they are not satisfied with the minimum code requirements. These higher levels of performance are associated with higher initial investments that also need to be estimated to provide complete information for a satisfactory decision-making process. However, the computation of economic losses under the PEER-PBEE framework is very time consuming to conduct on a routine basis. These difficulties highlight the importance of simplified methodologies to calculate building-specific earthquake-induced economic losses towards optimizing the structural design, and significant work has been developed in this area since the early 1970s. However, these simplified methods are still not widely used in real practice. Therefore, more research is needed towards developing simpler methodologies (based on the PEER-PBEE framework) that can be used in performancebased design. Consequently, this study develops a simplified methodology to estimate the earthquake-induced expected life cycle cost (ELCC) of buildings, which is the summation of the expected construction cost (CC) and the net present value of the earthquake-induced expected annual loss (EAL). In particular this study focuses on low-rise steel special momentresisting frame (SMRF) buildings since these structures are very flexible, first-mode dominated, and their EAL values are dominated by small spectral acceleration (S a ) intensities where the structures are behaving linearly or under the equal displacement rule, presenting a distribution of engineering demand parameters, such as peak story drift ratios (PSDR), that is relatively uniform along the height of the structure. To develop the simplified methodology, firstly a series of 4-story steel SMRF buildings are designed with varying degrees of lateral stiffness. While designs are code-conforming, the variation in lateral stiffness affects the ELCC of the structure. The ELCC of each structure is assessed via the PEER-PBEE framework, using nonlinear response history analyses in OpenSees to perform seismic simulations and commercially available construction cost databases to estimate variations in construction costs. Based on these numeric results, this simplified methodology is developed and calibrated to estimate the ELCC as a function of the fundamental period of vibration (T 1 ) for low-rise SMRF buildings. For the estimation of the CC, this study extends previous work, and for the estimation of the EAL this study develops a closed-form solution that does not require performing incremental dynamic analyses and numerical integrations. Finally, approximate values obtained using the proposed simplified methodology are compared to exact numeric values obtained using the PEER-PBEE framework for a series of 4-story steel SMRF buildings designed, and results are promising.

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