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Resilient Bridge Design Framework to Extreme Fire Loading



Several recent fire-induced bridge failures have highlighted the need for improved simplified tools to evaluate the response of bridges to fire. A streamlined design framework has been previously developed [1] for efficient calculation of a steelsupported bridge’s response to an open-air hydrocarbon pool fire resulting from a tanker truck crash and subsequent fuel spill. The framework consists of four steps: (1) calculate the fire’s characteristics; (2) calculate the heat transfer from the fire to the structural elements; (3) calculate the temperature increase of the structural elements; and (4) calculate the resulting material and mechanical response of the structural elements. The approach synthesizes calculation techniques based on both first principles and empirical data to quantify the extent of damage caused by the fire hazard. Due to its efficiency, this approach can be used to calculate an envelope of effects for a wide range of fire parameters. This paper proposes a new framework that uses the point source fire model for quantitative measure and mathematically reproducible definitions of structural resiliency as it pertains to a bridge's ability to minimize the potential for undesirable consequences. The resiliency assessment and design process follows logical progression of steps, starting with the characterization of fire hazards, continuing through analysis simulations. The outcomes of each process are articulated through a series of generalized variables, termed as topology, geometry, damage, and hazard intensity measures. A rigorous probabilistic framework permits consistent characterization of the inherent uncertainties through the process. The proposed framework is well suited for design process through stochastic characterization of assessment measures. Through stepwise approach, the framework facilitates a system wide approach to multi-fire hazard threats by establishing functional relationships between the development of appropriate models, design methods, damage acceptance criteria and tools necessary for implementation. The proposed methodology can be implemented directly for performance assessment, or can be used to as a basis for establishing simpler performance criteria and provisions to achieve resilient structural solutions.

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