Objective - To produce validated computational tools, technical guidance, and draft standards that will result in the development of performance based standards for the cost effective fire resistance design and assessment of structures.
What is the new technical idea? To develop a comprehensive approach to structural fire safety that will enable the development of performance based design tools, guidelines, and draft standards for structural systems exposed to fire, and alternate retrofit, design, and fire protection strategies.
Performance based design (PBD) methodologies to evaluate the fire performance of buildings and other structures are needed to move beyond the prescriptive procedures presently in use, which cannot be used to determine actual structural performance in fire. At present, buildings and other structures are designed for primary natural hazards and protected against fire effects. The proposed approach will, for the first time, consider fire as a design condition in the building design process, leading to risk-consistent, cost-effective designs. The proposed approach will make use of experimental data on the performance of structural members and systems, including connections, subject to realistic fires rather than controlled furnace conditions. Experimental data will be developed in the newly-constructed National Fire Research Laboratory (NFRL). The data, developed within the project "Measurement of Structural Performance in Fire: Composite Floor Systems", will be used to develop and validate computational models that are highly nonlinear due to the concurrent effects of temperature dependent reduction of material strength and stiffness and thermally induced load effects.
Additionally, this project will take a risk and reliability based approach to the prediction and specification of the fire hazard, structural fire effects, and calculation of structural response.
What is the research plan? This project aims at developing a unified performancebased methodology to evaluate the fire performance of building structures by incorporating knowledge concerning structurally significant fires and the material and structural system response to elevated temperatures. In particular, the project will develop (1) performance based methodologies for designing and evaluating structures for fire effects, with performance metrics and acceptance criteria, (2) validated predictive tools (including simplified tools for use in practice) for structural connections, components, subassemblies, and systems under realistic fire and loading conditions, and (3) technical guidance for the implementation of comprehensive fire safety design approaches. In addition, the project will support NFRL planning and testing activities for structural systems subject to fire, including pretest design, planning, and predictions, and posttest validation of developed models.
The structure proposed for the inaugural test series in the NFRL is a two-story steel gravity frame two bays by three bays in plan, and employing a composite floor system. The 6.1 m (20 ft) by 9.1 m (30 ft) test bay will be loaded hydraulically to simulate the gravity service load condition (see Project "Measurement of Structural Performance in fire: Composite Floor Systems"). Composite floor systems were selected for this study because of their widespread use in construction and because of the significant challenges in modeling the complex response of the system under fire loading, including the behavior of gravity connections, concrete slab, metal deck, and shear studs. These systems, which utilize costly fire proofing materials, could be vulnerable to fire effects due to significant reduction in strength and stiffness under elevated temperatures. Issues that will be investigated through the experimental and analytical studies include symmetry in floor framing, geometry of floor plates, influence of connections, restraint of thermal expansion, and fire exposure. Pre- and post-test modeling will be conducted for the various configurations with the objective of developing tools for engineers to enable performance-based design of structures under fire conditions.
The research plan has three tasks areas:
- Fire Structural Modeling: In collaboration with the project ""Measurement of Structural Performance in Fire: Composite Floor Systems" the project will conduct pretest prediction and posttest validation of response of steel structures and composite floor systems subjected to fire exposure. The project will also develop tools and methods to couple or transfer data between fire thermal structural models. Pre-test prediction will be used to (1) design test specimens including instrumentation, (2) ensure safe execution of the test, and (3) evaluate accuracy of current modeling approaches to structural response and failure under fire. Post-test analyses will be used to provide engineers with validated system-level modeling tools.
- Reliability and uncertainty in performance: This project will study propagation of uncertainties from fire dynamics modeling through structural response analysis, and develop load and resistance factors for design.
- Performance based Methodology: The project will develop performance based tools, guidelines, and draft standards for the fire resistance design and assessment of structures, including a framework linking fire intensity measures with expected structural performance objectives for a variety of risk categories.