Bulletin of Earthquake Science and Engineering

Bulletin of Earthquake Science and Engineering

Effect of Various Parameters on the Seismic Vulnerability Analysis of a Group of Steel Structures Using Microtremor

Document Type : Research Note

Authors
Shirin Khoramjahed 1
Mohammad Iman Khodakarami 2
1 M.Sc. in Civil Engineering, Faculty of Civil Engineering, Semnan University, Semnan, Iran
2 Associate Professor, Faculty of Civil Engineering, Semnan University, Semnan, Iran
10.48303/bese.2024.2030803.1163
Abstract
Since the 1960s, seismic vulnerability studies of buildings have gained paramount importance, driven by major earthquakes such as Niigata (1964) and San Fernando (1971), which exposed critical deficiencies in structural performance. These events spurred the development of diverse assessment methods, ranging from empirical fragility curves to advanced analytical simulations. Among the simplest and most cost-effective techniques is ambient vibration analysis using microtremors (Nakamura's HVSR method, 1989), which estimates dynamic characteristics like fundamental periods via horizontal-to-vertical spectral ratios; however, its reliability has long been questioned compared to strong-motion records due to lower excitation amplitudes.
This study rigorously evaluates the feasibility of microtremor-based analysis for seismic vulnerability assessment by directly comparing it against strong ground motion results. A comprehensive inventory of 54 medium-rise steel buildings was analyzed, comprising moment-resisting frames (MRFs: M335S1 to M655S3) and concentrically braced frames (Br335S1 to Br1255S3), spanning 3 to 12 stories across three soil types (classified per Iranian Standard 2800-14). Numerical models were meticulously developed in ETABS for linear elastic analyses and OpenSEES for nonlinear time-history simulations, incorporating soil-structure interaction (SSI) effects via DEEPSOIL profiles and Raychowdhury et al. (2015) relations.
Inter-story drift ratios were computed under real earthquake accelerograms from the PEER database (e.g., Kocaeli 1999, Northridge 1994) and synthetic microtremor excitations calibrated with SeismoSignal. Vulnerability indices were then derived using HAZUS-MH MR5, mapping drifts to damage states (Slight, Moderate, Extensive, Complete) across spectral acceleration levels (S1L/M/H, S2L/M/H) for Design Basis Earthquake (DBE) and Maximum Considered Earthquake (MCE) scenarios. PGV/PGA ratios (0.8-1.2) validated spectral compatibility per FEMA 365.
Results reveal an 80-90% concordance between microtremor-derived drifts and strong-motion predictions, with taller structures (8-12 stories) showing higher sensitivity to SSI and exhibiting Extensive/Complete damage under MCE (probabilities up to 0.04). Braced frames generally outperformed MRFs in DBE but converged at MCE. This validates ambient vibrations as a practical, low-cost alternative for large-scale screening, particularly in developing regions like Iran.
The study proposes an optimal frequency band (0.35-0.58 Hz for HVSR peaks) for future applications on similar steel frames, alongside recommendations for integrating HAZUS with Iranian code updates (e.g., ATC-40 equivalents). Such hybrid approaches enhance post-earthquake rapid visual screening and retrofit prioritization.
Keywords
H/V Spectral Ratio
Vulnerability Assessment
Ambient Vibrations
Strong Motions

Subjects

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  • Receive Date 01 June 2024
  • Revise Date 06 July 2024
  • Accept Date 21 August 2024