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The events of September 11th showed the combined effects of fire and structural loading on a high-rise building can be disastrous. Understanding the mechanism of structural damage caused by fire will help engineers design safer infrastructures by providing adequate resistance to failure. Contemporary research in computational fluid dynamics and finite element method have produced great advances to simulate both fire and structural behaviors; however the physical and numerical complexities coupled with a lack of validation may lead to erroneous predictions. Physical modeling is inherently free of such complexities. Full-scale tests show the ability to investigate the combined effect on structures exposed to fire. However, the associated size and cost of the full-scale models are often prohibitive. Using of scaled models mitigates these problems, and it provides an economical tool to reveal weakness of structures in fire.

This dissertation gives a comprehensive study on scale modeling of steel structures in fire. The theory of both the fire and structural scaling is presented. Design parameters of compartment fires and associated structural response are determined based on length scale relationships derived from the governing equations of heat transfer. However, not all effects can be scaled in a complex system. The strategy is to scale those parameters that are important to the behavior of the structure while the less critical effects may be allowed to deviate from the scaling rules. The use of this partial scaling strategy is developed and tested experimentally. This dissertation discusses and evaluates the accuracy of the use of scaled models in the study of the combined effects of fire and structural loading.

Experimental results show that the practical scaling rules developed in this dissertation can be used to conduct scaled structural fire tests. Similar steel temperature profiles and structural response are obtained from scaled models at different scales. Although the results are not quantitatively perfect, it is feasible to use scaled models to study fire-induced structural behaviors.