Performance-Based Design Methodologies for Structures in Fire Project

Summary

This project will develop and implement performace-based tools, methodology, guidance, and draft standards for designing and evaluating structures for fire performance, including the development of: (1) a database of large-scale experiments documenting the performance of structural connections, components, subassemblies, and systems under realistic fire and loading conditions for validation of analytical models; (2) verified simulation models and tools to predict structural fire performance, based on fire dynamics and thermal-structural modeling; (3) risk and reliability-based tools and models to predict structural temperature histories and fire effects and; (4) design guidance on performance-based approaches for determining fire effects on structural systems.

Description

Objective: By 2016, to develop performance-based methods to predict and evaluate fire behavior of steel and concrete structures and to deliver validated and improved tools, guidance, and draft standards for the fire resistance design and assessment of structures.

What is the new technical idea? 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 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. This proposed approach will, for the first time, consider fire as a design condition in the building design process. In addition, the proposed approach will develop experimental data on the performance of structural members and systems, including connections, subject to realistic fires rather than controlled furnace conditions. The data will be used to develop and validate computational models which 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 performance-based 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.

The research plan has four thrust areas:

• Fire-Structural Experiments: The project will develop a database of full-scale experiments that documents the performance of structural connections, components, subassemblies, and systems under realistic fire and loading conditions. The database will be used for validation of predictive models.
• Fire-Structural Modeling: The project will conduct pre-test prediction and post-test validation of performance of predictive models. The project will also develop tools and methods to couple or transfer data between fire-thermal-structural models.
• 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.

There are two parallel efforts that address these thrust areas.

Task 1 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.

Task 2 will support the full-scale experimental work in real fire conditions for validation of structural models in fire. This project will support NFRL planning and testing activities for structural systems subject to fire, including pre-test design, planning, and predictions, and post-test validation of developed models.

Major Accomplishments

Research Outcomes:

• McAllister T.P. (2013) "Sensitivity of composite floor system response at elevated temperatures to structural features", submitted to Engineering Structures.
• Banerjee D. (2013) "Uncertainties in Steel Temperatures during Fire", accepted to Fire Safety Journal.
• Banerjee D.K., (2013) "Uncertainty Estimation in Temperatures of Concrete Slab during Fire", submitted to Engineering Structures.

Potential Research Impacts:

• Seif, M. and T.P. McAllister (2013) "Stability of wide flange structural steel columns at elevated temperatures", Journal of Constructional Steel Research, 84 (2013) 17–26.
  
• Banerjee, D. (2013) "A sensitivity study on the fire-induced heating of concrete slabs in composite floor systems", Journal of Fire Sciences, Volume 31, Issue 3, May 2013, pp. 227-244.
• McAllister, T.P., et al., (2012) "Overview of the Structural Design of World Trade Center 1, 2, and 7 Buildings", Fire Technology, DOI 10.1007/s10694-012-0285-6.
• McAllister, T.P., et al., (2012) "Structural Analysis Approach and Reconstruction of Impact Damage to World Trade Center Buildings 1, 2 & 7", Fire Technology, DOI 10.1007/s10694-012-0286-5.
• McAllister, T.P., et al., (2012) "Structural Response of WTC 1, 2 & 7 to Impact and Fire Damage", Fire Technology, 49 (3), 709-739.
• McAllister, T.P., et al., (2012) "Analysis of Structural Response of WTC 7 to Fire and Sequential Failures Leading to Collapse", Journal of Structural Engineering, 138 (1).
• Banerjee, D. (2012) "A Sensitivity Study of the Heating Behavior of a Composite Floor System during a Fire Resistance Test", Journal of Fire Sciences, 31(3), 227-244.

Impact of Standards and Tools:

• Submitted elevated-temperature structural steel properties to the AISC Task Committee on Design for Fire including stress-strain model and proposed Specification language. Changes to be balloted for the 2016 edition.
• Submitted guidance on PBND procedures for structures subject to fire effects as an Appendix to the ASCE 7 standard in 2013, in collaboration with the ASCE Fire Protection Committee. The draft appendix is undergoing the process of incorporating comments prior to formal balloting.
  
• Software-independent tool to transfer thermal analysis output data to input data for FEA structural models.
• Fire protection of secondary structural members (structural frame requirements) were adopted by the 2009 IBC.