The fire safety assessment procedure of ships and offshore structures can be briefly described as a procedure for assessing safety by defining fire loads according to accident scenarios and analyzing their effects on the structure. In general, safety is reviewed via the temperature criteria of the structures under fire loads, and it is assessed in more detail via thermal-structural analysis, which combines fire simulation-heat transfer analysis with structural analysis in the design stage. Therefore, the accuracy of the thermal-structural analysis is crucial for reliable fire safety assessment, and the most applied method for validating the accuracy is to compare with the experimental results.Although fire experiments have been conducted by many researchers to analyze the characteristics of flames and heat transfer of steel members, constructing the temperature-dependent material property data, verifying the fire resistance performance of the structure itself, developing and validating numerical models, including other experiments have been conducted from the perspective of fluids with a primary focus on measuring gas and steel surface temperatures. On the other hand, fire experiments from the perspective of structure, which measure the displacement of a structure under fire load, were conducted mainly in limited environments such as inside a furnace because it was difficult to measure displacement in a high-temperature environment with a mixture of flames and smoke, as well as controlling the heat of the fire source. In addition, fire experiments conducted in open space have been seldom carried out. The British Steel Corporation (BSC) has summarized standard fire experiment results for structures such as steel beams and columns (Wainman and Kirby, 1988;Wainman et al., 1990). Cong conducted a furnace fire experiment on an I-beam, which is widely used as structural members for offshore structures, under mechanical loads to measure the steel surface temperature and vertical displacement. The vertical displacement was then measured by linear variable differential transformers (LVDTs) installed on top of the specimen exposed to the exterior parts of the furnace (Cong et al., 2005). The results obtained from this experiment have been widely used by other researchers to develop numerical analysis techniques (Kim, 2014;Kim et al., 2017).In addition to steel, fire experiments have also been conducted on sandwich panel structures made of fiber-reinforced plastic (FRP)

For safety design of structures against fire loads, time-variant geometry and material properties depending on the temperature should be considered with fluid-structure interaction (FSI) analysis. One-way FSI analysis is generally applied due to a time consuming task. But, it has big difference of structural response between conducting one-way and two-way FSI analysis. And two-way analysis is also affected by time increment of analysis for updating the geometry, and fire loads. The aim of this study is to investigate the effect of time increments on two-way FSI analysis of structures subjected to jet fire, and to suggest a proper time increment for two-way FSI analysis. In the present study, geometries and material properties are updated at every time increments, and kinds of two-way FSI analysis are performed with different time increments by using computational fluid dynamics (CFD) and nonlinear finite element analysis (NLFEA) and an interface program between CFD and NLFEA.

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