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National Fire Research Laboratory Metrology Project

Summary:

The ability to conduct safe, repeatable and accurate intermediate and large scale fire experiments is essential to understanding fire behavior and structural response to fire.  The National Fire Research Laboratory (NFRL) will provide researchers with well quantified large-scale fire and structural measurements to support fire model validation studies, enable fire investigations, support post disaster and failure studies, and enable advances in fire standards and codes. New measurement methods and instrumentation are required to enable accurate fire calorimetry for fires as large as 20 MW in the NFRL. New measurement methods are needed to provide accurate quantification of displacements and strains of structural systems exposed to fire conditions. The project will build on the findings of the exploratory project titled “Structural Property Measurements in Fire Environments”.

Description:

Objective: By 2016, to develop, improve, and maintain capabilities necessary to safely conduct measurements of structural-fire response with quantified accuracy by 2016.

What is the new technical idea? The NFRL will be used to safely conduct fire and structural fire resistance experiments, support advances in fire metrology, enable fire model validation studies, enable advances in codes and standards for structures in fire conditions, and support building and fire safety investigations and post disaster and failure studies. New instrumentation and standardized test methods will be developed to provide reference data for comparison against numerical predictions at multiple levels: sub-scale, component response to fire, and full scale assemblies. In order to meet the needs of the researchers that use the NFRL (both NIST staff and external collaborators), a focus is placed on improving the measurement capabilities of the large fire calorimeters. Statistical methods for uncertainty analysis and computational fluid dynamics modeling will be used to systematically examine and improve the heat release rate (HRR) measurement system. Using the new capabilities of the NFRL, NIST will develop experimental data on the performance of large-scale structural systems under realistic fire and mechanical loading. New data acquisition and control methods will be developed to improve the measurement and safety systems in the expanded NFRL.

What is the research plan? By 2014, the NFRL will resume non-structural fire testing operations in the legacy laboratory. In addition, NFRL staff will provide metrology and technical support to commission the new NFRL capabilities. New instrumentation, data acquisition systems, and test fixtures will be developed and maintained, including installation and functional testing of the exhaust hood skirts. A new fuel delivery system will be installed. Oxygen consumption calorimetry for the new hood and the NFRL Operations and Control Center instrumentation will be completed. This will allow both calibration of the new 20 MW hood, as well as improvement of the operating capabilities of the three existing (3 m, 6 m, and 9 m) large calorimeters. By 2015, NFRL staff will enable the full range of measurement systems for structure-fire research in the NFRL.

New measurement capabilities will be developed to allow accurate quantification of structural response parameters (strains and displacements) in a fire environment. Measurement techniques for structural response at room temperature are well developed. Current methods at fire laboratories typically measure the deformations and strains at few critical locations in a structure, chosen in advance of the test. Other deformations can be inferred from those measurements. Measurements under realistic fire conditions require instrumentation that can withstand harsh fire environment. Additionally, strain measurements need to be resolved into thermal and mechanical components. Total strain measurements may comprise thermal strain, elastic strain, plastic strain, and creep strain, each of which depends on the element temperature history.

Digital Image Correlation (DIC) methods offer the potential of providing hundreds of simultaneous point measurements, and even the ability to map deformation and displacement fields. In addition, as long as the area of interest is imaged during the test, post-test data analyses of specific areas of interest are possible. Digital-image correlation relies on the random, high-contrast pattern of light and dark regions that define, through their gray level, a region that can be located in each image. Pattern marking methods that can survive elevated fire temperatures are needed. Coupon scale tests will be conducted with strain measurements validated by traditional extensometry methods to assess the accuracy of the DIC methods.

Fiber-optic sensors measure strains and temperature at multiple points along the length of the fiber. The optical fiber must be either attached to the surface of a steel component or embedded in a concrete section. Similar to strain gages, attachment methods other than epoxy bonds are required at elevated temperatures. Attachment methods between the fiber-optic sensor and/or fiber and the steel or concrete component are not well developed for fire conditions.

Exploratory testing using both DIC and fiber optic methods will be used during the NFRL commissioning to assess the accuracy of these methods in measuring displacements and strains in a structure-fire test in the NFRL, and to quantify the uncertainties associated with such measurements.

Major Accomplishments:

Outcome:

  • Technical requirements and guidance for the NFRL construction project to allow new structural fire performance measurement capacities.