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Fire Resistance Design and Retrofit of Structures Project

Summary:

This project will develop and implement tools, methodology, guidance, and pre-standards for designing and evaluating structures for fire performance, including:

  1. development of performance criteria,and design guidance to assure adequate performance under fire;
  2. development of verified simulation models and tools to predict structural fire performance, based on fire dynamics and thermal-structural modeling; and
  3. development of risk and reliability-based models to predict fire-induced structural temperature histories and loads, and thermally-induced reduction of structural resistance. This project focuses on steel structures and composite floor systems.

Description:

Objective:  To develop performance-based methods to predict and evaluate fire behavior of steel structures and to deliver validated and improved tools, guidance, and pre-standards for the fire resistance design and assessment of steel structures and composite floor systems by FY 2014.

What is the new technical idea?  The technical approach calls for the development of a unified performance-based methodology to evaluate the fire performance of buildings by incorporating knowledge concerning fire load, material response, and overall structural response to elevated temperatures. This approach will, for the first time, consider fire as a design condition in the building design process. The building layout (compartmentation, geometry), windows (ventilation), materials of construction, passive fire protection systems, and amount and location of combustibles will be included in the proposed approach. Recent technical advances have provided the ability to (1) predict the development and propagation of building fires, influenced by the building characteristics noted above, using application of fire science, and (2) predict structural system performance at elevated temperatures. Additionally, this project will take a risk and reliability-based approach to the prediction and specification of the fire hazard, structural fire loads, the resulting reduction of structural resistance, and calculation of structural response. Such a comprehensive model-based approach to structural fire safety enables sensitivity studies to be conducted to establish the most important factors affecting the fire performance of the entire structure, to understand the behavior of different types of structural systems exposed to the same fire, and to evaluate the effectiveness of alternate retrofit, design, and fire protection strategies.

What is the research plan?  Recommendations from a national workshop, organized by NIST and held in October 2002, formed the basis for a coordinated national plan for problem-focused research on structural fire resistance design and assessment of structures. NIST’s role is to develop a unified performance-based methodology to evaluate the fire performance of building structures by incorporating knowledge concerning fire load, material response, and overall structural response to elevated temperatures. The methodology requires the establishment of specific performance objectives and metrics, the development of acceptance criteria, the development of validated predictive tools (including simplified tools for use in practice), and the development of technical guidance for the implementation of a comprehensive fire safety design approach. To enable full-scale experimental work in real fire conditions for validation of structural models in fire, NIST is expanding the capabilities of the National Fire Research Laboratory (NFRL). 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. Specifically, the project plans to deliver the following products:

  1. Best Practice Guidelines for Fire Resistance Design of Concrete and Steel Buildings, NIST Technical Note 1681. This document includes current practice in fire resistance engineering with current best knowledge in fire risk assessment and characterization, material properties at elevated temperatures, and thermal and structural response calculation methods. Seminars were conducted at 4 locations (Orlando, New York, Chicago, San Francisco) and the final document is available on the EL website. (Completed 2010)
  2. Report on performance of structural systems in fire. This report includes factors that affect building performance, comparisons of system and component approaches, and modified design approaches based on analyses of selected typical building types in realistic fires. Parametric studies of composite floor systems and their connections were conducted to determine the effect of long span floors, girder studs, asymmetrical framing, and shear connections. (2012)
  3. Analytical tools for predicting structural fire performance at two levels. e.g., simplified tools for typical design calculations and comprehensive analysis tools for more complex designs. The following analytical tools will support predicting structural fire performance at simplified and comprehensive levels:
  • Library of steel floor beam connection models (2013)
  • Analysis tool for 3-D structural systems under fire effects (2014)
  • Software-independent tool to transfer nodal temperatures from thermal analysis output for solid elements to input data for structural beam and shell elements. (2013)
  • Visualization software for simultaneous display of fire, thermal, and structural response to fire. (2012)
  1. Visualization software for simultaneous display of fire, thermal, and structural response to fire. (2012) Simplified and comprehensive design approaches and the framework for a decision tool to select the level of design approach. Guidance on simplified and comprehensive performance-based design approaches for determining fire effects on structural systems for available computational methods for fire, thermal, and structural analyses and design of fire resistant structural systems. Resistance factors for LRFD design of steel components and bolts at elevated temperatures based on test data collected for structural steels from the WTC tests and from the technical literature. (2013)
  2. Design guidelines at two levels e.g., simplified procedure for typical designs and comprehensive procedure for specialized designs. Design guidelines for simplified and comprehensive analysis procedures, including reliability-based design approaches and a decision tool, fire loads and fire scenarios, thermal analysis, and performance-based structural analysis procedures. (2014)
  3. Pre-standards for steel buildings for design tools and practices. Guidelines and pre-standard documents to provide technical support in the following areas: (1) performance based design of structures for fire and (2) evaluation of structural fire resistance of existing structures. (2014)

Major Accomplishments:

Recent Results:

Impact:

  • Fire protection of secondary structural members (structural frame requirements), based on WTC recommendations, were adopted by the 2009 IBC.

Outcomes:

  • Developed an Appendix for submission to ASCE 7, in collaboration with the ASCE Fire Protection Committee, on performance-based design of structures for fire effects. Project research on structural-fire rating methods, testing, performance-based design methods, analysis techniques (simple to comprehensive) for thermal and structural analyses, development of temperatures for structural analyses from thermal analyses with consideration of uncertainty, steel and concrete properties at elevated temperatures, and nonlinear structural issues (large deflections, buckling, role of connections, etc.) are included (2012).
  • Developed a probabilistic FEA methodology for computing uncertainty of structural temperatures based on knowledge of uncertainties in key input parameters for fire and thermal insulation conditions. Key input parameters were identified for calculation of uncertainties in concrete slab temperatures with a sensitivity study using an experimentally validated model (2012).
  • Developed 3-D immersive visualization software and desktop utility for simultaneous display and interrogation of analysis results of fire dynamics, transient heat transfer, and nonlinear structural response (2012).
  • Conducted parametric studies of composite floor systems and their connections to determine the relative contribution of long span floors, girder studs, asymmetrical framing, and shear connections to fire conditions (2012).
  • Submitted stress-strain relationship for structural steels at elevated temperature for adoption by AISC for the 2016 Specification (2011).
  • Published Best Practice Guidelines for Fire Resistance Design of Concrete and Steel Buildings[1] (2010).

Outputs:

  • Conducted a detailed FEA study of the local stability of structural steel wide-flange sections at elevated temperatures.
  • Developed a performance-based design framework for structures and fire effects, which has been used to identify gaps in knowledge and computational needs for codes and standards.
  • Supported development of technical specification and provided design review of NFRL systems, including strong floor, reaction wall, hydraulic loading, and conditioning pit. (2010-2011)
  • Chaired ASCE 2010 Structures Congress/NASCC Session (L5) on Design and Analysis Issues for Structural Response to Fire (May 2010).
  • Conducted a comprehensive overview of available computational methods for fire, thermal, and structural analyses.
  • Awarded unsolicited grant to NFPA Fire Protection Research Foundation to determine priority needs of US industry for structural fire resistance experiments to  support NIST planning of an experimental agenda for the NFRL (2010)

Major presentations:

  • McAllister, T.P., “Fire Effects on Structural Systems: Present Practice and Research Needs”, Invited Presentation at the UL Fire Safety Forum, Aug 2012.
  • McAllister, T.P., “Fire Effects on Structural Systems: Present Practice and Research Needs”, Invited Lecture at the University of Michigan, Jan 2012.
  • McAllister, T.P., “Fire Effects on Structural Systems: Present Practice and Research Needs”, Invited Lecture at the Johns Hopkins University Civil Engineering Seminar, Sep 2011.
  • McAllister, T.P., “Federal Building and Fire Safety Investigation of the World Trade Center Disaster”, Invited Lecture at the Richmond Chapter of ASCE, Sep 2011.
  • McAllister, T.P., “Federal Building and Fire Safety Investigation of the World Trade Center Disaster”, Invited Lecture at the Short Course on Performance of Structures and Materials to Fire, Carleton University, Ottawa, ON, May 2009.
  • McAllister, T.P., “The Collapse of WTC 7, the Forgotten Building”, Invited Lecture at the Nuclear Regulatory Commission, White Flint, MD, Sep 2009.

Publications:

Journal Papers and Reports:

Journal Papers and Reports WERB approved by Sep 2012:

Conference Presentations and Proceedings:

Standards and Codes:

The following expected project outcomes and impacts relate directly to standards and codes:

  • AISC 2016 Steel Specification (ANSI/AISC 360 Standard) – Elevated-temperature structural steel properties have been proposed to the AISC Task Committee on Design for Fire including stress-strain model and proposed Specification language.  Committee comments from June 2012 meeting are being addressed by NIST.  The proposed changes will be balloted for the 2016 edition of the Standard.
  • ASCE 7-16 Standard - Submit “Appendix for Performance Based Approach for determining Fire Load Effects On Structures” for guidance on fire load and fire scenario criteria, thermal analysis, and performance based design of fire resistant structural systems, developed with the ASCE Fire Protection Committee (October 2012).
  • AISC 2016 Steel Specification (ANSI/AISC 360 Standard) – Submit draft of cross-section-specific slenderness limits for structural steel at elevated temperatures (Mar 2013).
  • AISC 2016 Steel Specification (ANSI/AISC 360 Standard) - Submit resistance factors for steel components at elevated temperatures (June 2013).

EL staff participation in the standards and codes committees:

  • Therese McAllister – (1) ASCE 7 Standard Main Committee (Subcommittees: (a) General Requirements for Structural Stability and (b) Load Combinations); (2) SEI-ASCE Technical Council on Life-cycle Performance, Safety, Reliability, and Risk of Structural Systems, Task Group 3, Risk Assessment of Structural Infrastructure Facilities and Risk-Based Decision Making; (3) ASCE Fire Protection Technical Committee; (4) IBC-Structural Committee member for 2012 Code Development Hearings.

[1] An EL near-term strategic outcome.

 

Start Date:

November 3, 2011

Lead Organizational Unit:

el

Staff:

Principal Investigator: Dr. Therese P. McAllister

Co-Investigator(s): Dr. Dilip K. Banerjee, Dr. Mina S. Seif

Related Programs and Projects:

Structural Performance Under Multi-Hazards Program

Disaster and Failure Studies Project

Measures of Building Resilience and Structural Robustness Project

National Windstorm Impact Reduction Program

Wind Engineering and Multi-Hazard Failure Analysis Project

Contact

General Information:
Dr. Therese P. McAllister, Project Manager
301-975-6078 Telephone

100 Bureau Drive, M/S 8611
Gaithersburg, MD 20899-8611