Design Fires for Structures Project

Summary

This project will address upcoming needs and take advantage of new resources associated with the completion of National Fire Research Laboratory (NFRL). The project will develop (1) the measurement science to fully characterize, deliver, and measure repeatable structurally significant fires for use in large-scale structural fire experiments in the NFRL and (2) a performance-based design framework linking fire intensity measures with structural performance objectives. The project uses detailed fire dynamics simulations, thermal analyses, and structural response calculations to design fires for the safe and effective conduct of fire-structural experiments. The results of these analyses will also help develop robust fire intensity measures that can be used to assess damage to the structural system and identify corresponding performance levels. The project will result in a standard test protocol for characterization and delivery of fires for structural experiments.

Description

Objective: By 2016 to develop (1) the measurement science to fully characterize, deliver, and measure repeatable structurally significant fires for use in large-scale structural fire experiments and (2) a performance-based design framework linking fire intensity measures with expected structural performance objectives. 

What is the new technical idea? Current design practice for Performance-based Fire Engineering (PBFE) tends to be scenario-based wherein each scenario represents a description of fire development in time, from ignition through full development and decay. For the description of a fire for conducting large-scale fire-structural experiments in the National Fire Research Laboratory (NFRL), this approach presents a challenge in that there are an infinite number of scenarios, and thus designs fire scenarios, that could be postulated for a particular building occupancy. A preferred approach is to define the fire hazard probabilistically as is currently done for wind, earthquake, and flood hazards. A recent survey of non-standard large-scale structural fire resistance test¹  found that researchers used a variety of fire loads ranging from actual building contents, timber cribs representing "typical office furnishings" (ranging from about 32.5 to 54.5 kg/m²), Standard Fire curves (e.g., ISO 834), or prescribed, non-standard heating rates (provided by oil-burners). For researchers around the world to contribute to the technical basis for PBFE, it is important that a standard protocol be established, so that results from a variety of tests can be compared and evaluated on a consistent basis. This project has two inter-related tasks:

• The development of the measurement science to fully characterize, deliver, and measure repeatable structurally significant fires for use in large-scale structural fire experiments. 
   
• The development of the measurement science to establish a performance-based design framework linking fire intensity measures with structural performance objectives.

What is the research plan? This project will be separated into two research tasks with the completion of each task being critical to meeting the overall project's objective.

Task 1 is the characterization, delivery, and measurement of repeatable structurally significant fires for use in large-scale structural fire experiments in the NFRL. This task seeks to establish for a given occupancy, realistic and credible fires with a quantifiable intensity measure and probability of occurrence, which stresses a test assembly to quantifiable damage states.  This task will also develop the means to deliver and control the fire for a given experiment. To conduct high-quality and repeatable fire experiments requires the design of the fuel delivery system (e.g., natural gas burners) to produce the desired heat release within an acceptable level of uncertainty. The research conducted in this task will support the development of a standard test protocol to ensure that results from a variety of tests can be compared and evaluated on a consistent basis.  Commissioning of NFRL will take place mainly during FY14 with the inaugural experimental test series planned for FY15. This task will design the fire environment for both the Phase III commissioning tests and the inaugural test series based on detailed fire dynamics simulations, thermal analyses, and structural response calculations.

Task 2 is establishing a performance-based design framework that links fire intensity measures with expected structural performance objectives for a variety of risk categories. This task will develop a robust fire intensity measures in buildings that can be used to assess the damage to the structural system for a variety of structurally significant fire conditions. To achieve this purpose, the task will consider localized fire, single compartment fires, multiple compartment fires, and multi-story uncontrolled fires. Additionally, this task will consider various levels of performance ranging from no damage (fully operational) to incipient collapse for a range of building and occupancy types. This task will be tightly integrated with the Performance-based Design Methodologies for Structures in Fire project.

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¹ Structural Fire Resistance Experimental Research – Priority Needs of U.S. Industry, NIST GCR 12-958