PSI - Issue 64

Patrick Covi et al. / Procedia Structural Integrity 64 (2024) 1774–1781 Patrick Covi and Nicola Tondini./ Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction The usual approach in structural design involves analyzing seismic and fire events as distinct actions. However, numerous historical events highlight that the impacts of fire following an earthquake (FFE) can be notably greater compared to the damages and losses caused only by the earthquake (Scawthorn, 2005; Elhami-Khorasani and Garlock, 2017). Major FFE events that occurred in the past include the San Francisco earthquake (1906), the Tokyo earthquake (1923), the Kobe earthquake (1995) and the Tohoku earthquake (2011). A FFE event recently occurred in Wajima (Japan) after the Noto earthquake (2024), in which the fire affected an estimated 200 buildings (NHK 2024). Post earthquake ignition sources identified from past earthquakes are reviewed by Botting (1998) and Scawthorn (2005). In brief, the principal ignition sources are the overturning of electrical appliances, short-circuiting of electrical equipment, gas leakage from damaged equipment and pipework, and leakage of flammable fluids. Damage to gas equipment and pipes can cause sparks and fuel fire propagation, while electrical appliances may ignite sparks with combustible materials. Incidents of leaking gas and damaged electrical appliances causing fires were observed after earthquakes such as Kobe and Northridge. Earthquakes can result in single or multiple building ignitions, compromising the structural fire performance by damaging the fire protection elements and compartment measures, leading to rapid fire spread. Moreover, post-earthquake fires are challenging to control due to multiple ignitions and potential disruptions in infrastructure networks like water supply systems. In this context, the structural fire performance could be deteriorated because the fire acts on a previously damaged structure. The earthquake may damage fire protection elements and the compartment measures with the consequence that the fire can spread more rapidly. Moreover, it is harder to control post-earthquake fires as there can be multiple ignitions across a community at once as well as possible disruptions within the infrastructure networks, such as water supply system, that hinder timely intervention (Scawthorn, 2005). 2. Case study A four-story, five-bay steel frame was selected as a case study, as shown in Fig. 1. The office building, as described in NIST Grant/Contract Reports 10-917-8 by Kircher et al. (2010), is designed according the seismic design standards outlined in ASCE 7-10 (2010) for regions prone to high seismic activity. In particular, the city of Los Angeles was selected as the site for this case study. The structure is designed with a rectangular layout measuring 42.70 m from east to west and 30.50 m from north to south. Each story maintains a height of 4.00 m, except for the ground floor, which stands at 4.60 m. The window widths range from 1.5 m to 6 m in increments of 1.5 m . The moment resisting frames are designed with typical reduced beam section connections (RBS). The gravity columns are oriented around their weak axis with respect to the east – west (EW) loading direction. The structure was not fire protected. a b

Fig. 1. Configuration of the frame.