Fire Research Seminar Series

A New Paradigm and Framework for Risk-Informed Performance-Based Fire Safety Design

Alberto Alvarez, Brian Meacham, WPI, Worcester, MA 

Date:    Tuesday , July 10, 2012
Time:    10:30 AM
Place:    NIST, Bldg. 224, Rm. B245
 
In the past two decades, more and more countries developed and adopted performance-based design as an option regarding building fire safety. Nevertheless, review of this worldwide experience using standards, codes and guidelines related to performance-based fire protection design for buildings has identified shortcomings in the interpretation, application and implementation of the performance-based design process, wide variation in the resulting levels of performance achieved by such designs, and several opportunities to enhance the process. While others have highlighted shortcomings in the past, as well as some ideas to enhance the process, it is proposed that a more fundamental change is needed. First, the political and technical components of the process need to be clearly delineated to facilitate better analysis and decision-making within each component. Second, the process needs to be changed from one which focuses only on fire safety systems to one which views buildings, their occupants and their contents as an integrated system. In doing so, the activities associated with the normal operation of a building and how they might be impacted by the occurrence of a fire event become clearer, as do mitigation options which account for the behaviors and activities associated with normal use. To support these changes, a new framework for a risk informed performance-based approach to fire protection design is proposed: one which is better integrated than current approaches, that treats a fire event as a perturbation of a larger and more complex building-occupant system, and that provides more specific guidance for engineering analysis with the aim to achieve more complete and consistent analysis. This presentation outlines the challenges with the existing approaches, presents the 'building-occupant' system paradigm, illustrates how viewing fire as a perturbation within the larger building-occupant system can increase fire safety performance over the life of a building, and outlines a framework for a risk informed performance-based approach to fire protection design. Organization of a future roadmap allowing the implementation of the proposed process is also presented.

Application of Hollow Structural Sections (HSS) toward Innovative Earthquake Resistant Design Modified

Matthew Fadden, University of Michigan, Ann Arbor 

Date:    Tuesday , July 10, 2012
Time:    1:00 PM
Place:    NIST, Bldg. 224, Rm. B245
 
HSS members provide an opportunity to further improve upon structural performance of earthquake resistant moment frame systems. These sections have many favorable properties including good bending, compression, and torsional resistance and a high strength-to-weight ratio, which can lead to a decrease in the weight of the structure reducing the response during a seismic event. However, there remains a significant need to better understand HSS cyclic bending behavior and appropriate HSS-to-HSS seismic connections before these advantageous properties can be fully utilized in practice. This research first aims to characterize the ability of HSS beam members to form stable plastic hinges under cyclic bending through large-scale experimental testing and finite element modeling. The experimental testing considers 11 different HSS members to which a finite element model (FEM) is calibrated capturing both the local buckling and global hysteretic behavior. The FEM is then run to analyze the behavior of 133 different HSS beam members. Both experimental testing and FEM suggest that the width-thickness and depth-thickness ratios have a large effect on the local buckling behavior and hysteretic load carrying capacity with continued cycling. From these findings, limit states based on geometric properties are developed that aim at ensuring stable hysteretic behavior under earthquake type loading. With an understanding of the beam behavior, the suitability of HSS-to-HSS moment connections in seismic applications is considered. Full scale experimental testing of fully welded HSS-to-HSS moment connections allows for the evaluation of several connection details that may improve the hysteretic behavior by reducing undesirable non-ductile limit states failures. These experiments help to produce recommendations for the design and construction of HSS-to-HSS earthquake resistant moment frame connections and systems.

Exposure, Exposure, & Exposure – The Key for Addressing the National Wildland Urban Interface Fire Problem using a WUI Hazard Scale

Alexander Maranghides, William Mell and Nelson Bryner, National Institute of Standards and Technology
 
Date:    Thursday, July 12, 2012
Time:    10:30 AM
Place:    NIST, Bldg. 224, Rm. B245
 
Destruction of homes and businesses from Wildland Urban Interface (WUI) fires have been steadily escalating.  In the United States over 70,000 communities and 45 million structures are at risk of WUI fires.  Since 2000, over 3,000 homes per year are lost to WUI fires, compared to about 900 homes in the 1990s, and 400 homes in the 1970s.  In 2011, in Texas alone, over 2,000 homes were destroyed during WUI fires. The WUI fire problem affects both existing communities and new construction. In the U.S, the problem is most acute in the western and southern states; however, WUI fires have also recently destroyed homes in the Mid-Atlantic States and the Pacific North-West.
 
One of the fundamental issues driving the destruction of homes at the interface is the fire resistance of structures/communities.    There has been very limited coupling between the potential fire and ember exposure and the building codes and standards. The limited understanding of fire and ember exposure currently available does not address the full range of realistic WUI exposures and offers little context for the design of ignition resistant landscapes and buildings. While the principles of ignition and fire spread at the WUI have been known, actual exposure quantification has not taken place. The resulting gap between exposure and structure ignition has therefore resulted in a lack of tested and implementable hazard mitigation solutions. As an example, there is currently little quantifiable information that links the ember generation from wildland fuels to building assemblies testing.
 
A WUI fire and ember exposure scale (WUI-scale) needs to be created to help consistently quantify the expected severity of WUI fire events based on measures, or scales, of expected ember and fire exposure. Once established, these science-based ember and fire exposures can form the technical foundation for the development of a suite of performance based testing methods and protocols which in turn will allow development of building codes aimed at providing a level of structure ignition protection commensurate with the expected fire and/or ember exposure.
 
The WUI scale concept is based on quantifying expected fire and ember exposure throughout an existing WUI community.  The proposed WUI-scale can be used to explicitly identify WUI areas that have a potential fire problem, as opposed to areas that meet housing density or wildland vegetation requirements as is frequently done.  The scale can therefore be used to provide the boundaries where specific materials, vegetation, and structure designs may be implemented to improve the fire resistance of structures and communities.