City Research Online

Abstract

A mainshock-aftershock sequence can pose a substantial threat to buildings in seismically active areas, especially those that have already been damaged or weakened by an earlier earthquake. The damage progression and cumulative damage, as well as degradation of strength and stiffness, may result in a structure collapsing under a strong aftershock. This study addresses a critical research gap by evaluating the seismic response of corner-supported steel modular building systems (MBSs) subjected to sequential mainshock-aftershock (MS-AS) scenarios. Unlike conventional steel structures, MBSs exhibit distinct dynamic characteristics due to their modular connections. The current study identifies these limitations and presents the first fragility analysis that is specific for MBSs. Therefore, this paper aims to analyse the seismic risk assessment of corner-supported steel volumetric braced MBSs during sequential earthquake events, with emphasis on MS-AS sequences. The study explores how aftershocks affect the performance of modular buildings, particularly when initial mainshocks have already caused damage. Based on the equations proposed by FEMA P58, it considers four damage states with respect to maximum inter-story drift. MBSs are modeled using OpenSees software using the modified Ibarra-Median-Krawinkler model. The structural responses of MBS models of varying heights (4, 8, and 12 storeys) are captured by a suitable number of nonlinear dynamic analyses using Incremental Dynamic Analysis (IDA). Under MS-AS sequences, fragility curves can be obtained to quantify the likelihood of surpassing different DSs for MBSs. The Collapse Margin Ratio (CMR) can be used to assess the resilience of MBSs at different damage states by examining structural collapse probabilities. Results show that aftershocks significantly increase the likelihood of collapse of modular buildings, in particular those severely damaged by major earthquakes. Fragility curves confirm this, indicating an increased collapse probability across all building heights for higher damage states. When buildings are subjected to aftershock sequences, their CMR values are decreased on average by 9.9%, 13.17%, and 6.5% for 4-, 8-, and 12-story MBSs, respectively. The findings emphasize the importance of incorporating aftershock considerations into MBS design standards to enhance earthquake resilience and safety.

Publication Type:	Article
Additional Information:	© 2025. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/
Publisher Keywords:	Modular Steel Buildings; Collapse risk; Mainshock–aftershock sequence; FEMA P-58; Fragility curves; Residual drift; Collapse Margin Ratio
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TH Building construction
Departments:	School of Science & Technology School of Science & Technology > Engineering
SWORD Depositor:	Symplectic Administrator

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