Damage Assessment of Steel Structures Subject to Sarpol-e Zahab Earthquake of Iran: From Poor Construction to Design Code Deficiencies

This paper addresses the main important reasons for structural collapse of steel structures during the 2017 Sarpol-e Zahab earthquake in Iran. Lessons learned from a field survey on more than 70 buildings having steel structure are somewhat different from the previous ones since the majority of damaged and ruined steel structures are designed based on the third edition of Iranian steel structures code (2013) which addresses specific seismic section compared to previous editions of the code. This paper categorizes the structural collapse reasons for code-conforming steel buildings imposed by the earthquake including poor construction, workmanship errors and highlights the shortcoming of the utilized codes for design of the damaged structures elaborately. Connection fracture, soft story mechanism, brace buckling, and column instability, with relative percentages of 43, 22, 19, and 16, are the most significant structural failure causes. The field observations and inspections confirm that built-up steel members, which are currently used in engineering practice of developing countries, e.g., Iran, and was allowed by the Iranian steel structures code (2013) instead of the steel member with wide-flange sections, are not able to provide the required seismic performance satisfactorily. Finally, field surveys indicates that ignoring strong-column weak-beam criterion, which is permitted by Iranian steel structures code and AISC Seismic provisions (2016) for Intermediate Moment Frame (IMF), results in structural collapse for the majority of building having moment frame system. Furthermore, as a key result of this research, employing intermittent fillet weld line for fabricating built-up columns, which was allowed by Iranian steel structures code (2013) and AISC (2016) for use in IMF, leads to local buckling of the column and eventually structural failure.