Parametric Study for Performance-Based Fire Design of US Prototype Composite Floor Systems

Design requirements for passive fire protection of steel structures in the United States are primarily based on prescriptive approaches. Yet performance-based design has gained attention in recent years for its potential to unlock design solutions that are robust, cost effective, and applicable to complex architectural configurations. For example, prior research has shown that fire protection on selected secondary beam elements in composite floor systems is not necessary due to the development of membrane action in the concrete slab during fire. In addition, the evaluation of a structure's performance under realistic fire scenarios, required in a performance-based approach, is enabled by recent developments in advanced computational modeling. However, currently there are no systematic guidelines to determine the reliability of a performance-based fire engineering design. This study provides a comparative analysis of the fire performance of a floor system designed following prescriptive and performance-based approaches. The floor system is adopted from a prototype steel-concrete composite office building. Further, a parametric study is conducted to investigate the effects of several parameters on the thermal-mechanical response including the modeling approach, fire curves, applied gravity loads, and hazard scenarios. Performance is measured using survival time at the structural system level, but also with predefined thresholds in deflection and reinforcement bar temperature. The results demonstrate that the performance-based design is robust, and verification of safety is not dependent on a particular demand value or performance measure. Most importantly, the performance-based design shows resistance when subjected to natural fires with large percentage fractile of fire load as well as in multihazard post-blast fire situations.