Performance-Based Fire Design for Composite Steel-Concrete Buildings with Consideration of Natural Fire Models

Performance-based structural fire design provides a rational methodology for designing modern buildings with cost-effective solutions. However, fire engineering in the United States still largely relies on design at the component level using prescriptive approaches. With performance-based approach, there is an opportunity to benefit from increased flexibility and reduced cost in the design, but these advantages need to be explicitly described and disseminated to promote the shift in paradigm. This thesis has two primary objectives: (a) to investigate a scenario-based fire modeling to derive realistic natural fire curves to be used in a performance-based design (PBD), and (b) to investigate and confirm that PBD in the U.S. can lead to a more efficient design for fire.;Compared with code based time-temperature curves, natural fire time-temperature curves provide a more realistic evolution of fire temperature over time. In this thesis, the Dalmarnock fire test, together with the two-zone fire model software CFAST, is used as a test-bed to illustrate the characteristics of a natural fire. An algorithm has been developed to guide the designer to formulate different fire scenarios and generate a set of scenario-based fire curves.;In the second part of the thesis, a comparative analysis is conducted on a multi-story steel-concrete building designed following the performance-based and the U.S. prescriptive approaches. The steel-concrete composite structure allows taking advantage of tensile membrane action in the slab during fire, and therefore removing the fire protection on secondary beam elements. The nonlinear finite element software SAFIRRTM is used to model the behavior of the building under the standard ASTM fire and a natural fire determined using the two-zone fire model CFAST. The numerical simulations show that PBD can be used to achieve the required level of safety currently enforced in the U.S. prescriptive guidelines, while providing an opportunity for cost reduction in fire protection material.