Light Detection and Ranging (LiDAR) is a powerful tool to characterize and track the surface geometry of solid objects. In a fire, however, no method has excelled at measuring three-dimensional shapes at millimeter precision while offering some immunity to the effects of flames. This paper applies coherent Frequency Modulated Continuous Wave Light Detection and Ranging to capture three-dimensional measurements of objects in fire at meters of stand-off distance. We demonstrate that despite the presence of natural gas flame depths up to 1.5 m obscuring the target, measurements with millimeter precision can be obtained. This is a significant improvement over previous work making the technique useful for many fire research applications. An approach to achieve sub-millimeter precision using spatial and temporal averaging during post-processing is presented. The technology is demonstrated in case studies of structural connection and vegetation response in fires.

The National Fire Research Laboratory at the National Institute of Standards and Technology conducted a series of large compartment fire tests to investigate the behavior and fire-induced failure mechanisms of full-scale composite floor assemblies with a two-story steel gravity frame, two bays by three bays in plan. A total of three 9.1 m × 6.1 m composite floor specimens with varying slab reinforcement and fire protection schemes for the secondary beam were tested under combined mechanical loads and compartment fire exposure. This report presents the experimental design and results from the third composite floor fire experiment (Test #3). The first experiment (Test #1) was designed to achieve a 2-hour fire resistance rating per current U.S. practice and create baseline data for the behavior of the building. Test #1 specimen exhibited mid-panel slab integrity failure at 70 mins of fire exposure. Test #2 was conducted to study the effect of enhanced slab reinforcement with larger area and ductility on the fire resilience of the composite floor systems. Test #2 showed that the use of enhanced slab reinforcement maintained the structural integrity of the tested slab for more than two hours. Test #3 was conducted to study the effect of enhanced slab reinforcement as well as unprotected secondary beams on the fire resilience of the composite floor systems. Similar to Test #2, the floor slab in the test bay was reinforced with 9.5 mm diameter deformed bars with a center-to-center spacing of 30 cm (230 mm2/m). Unlike in Test #1 and Test #2, the secondary beam and its end connections in the test bay were left unprotected in Test #3. The test floor was mechanically loaded to 2.7 kPa to mimic the code-prescribed gravity loads for fire conditions. The compartment test fire created upper-layer gas temperatures like those in standard fire resistance tests. A total of four natural gas burners distributed over the compartment floor created a peak gas temperature exceeding 1100 °C below the test floor. A wide transverse crack with flame leak above the floor developed at 132 min in the mid-panel region. The mid-panel vertical displacement reached 535 mm (equivalent to the ratio of L/17 where the span length L = 9.1 m) It reached a peak value of 655 mm (L/14) at 140 min, when the actuator loading was removed. The Test #3 showed that the use of deformed steel bars (230 mm2/m) for the slab reinforcement maintained the structural integrity of the tested slab longer than the specified rating period with an unprotected secondary beam. The experimental results presented in this report can be used for validation of predictive models to perform parametric studies incorporating the variability in the steel reinforcement scheme (area, spacing, and material) for safer and cost-effective composite floor construction for fire safety.

Coherent laser detection and ranging is applied to capture 3D images of objects placed in or behind large fires. A ranging precision of 300 µm through natural gas flame at a 6-meter standoff is achieved.

Strap-braced, cold-formed steel framed walls are frequently used as the lateral force resisting system in cold-formed steel construction. While the behavior of these walls has been studied under lateral loading and (to a lesser extent) under fire conditions, there is a need to comprehend the influence of multi-hazard interactions, in particular the effect of fire pre-damage on the lateral load resistance of the walls. In this paper, a numerical model of a strap-braced cold-formed steel wall is developed to analyze the thermal and structural response when subjected sequentially to fire followed by shear deformation. The numerical model is validated against full-scale experiments. Coupon tensile tests are conducted to characterize the post-fire properties of the cold-formed steel that are used as inputs to the model. The results show that the numerical model can capture the post-fire response of the cold-formed steel walls including the wall strength, stiffness and ductile failure by yielding of the strap. The lateral behavior of the walls depends primarily on the maximum temperature reached in the cold-formed steel members and the resulting residual properties. Thermal analysis by the finite element method can be used to predict the maximum temperatures across a wall section under a variety of design-relevant fire scenarios, but the results are strongly affected by the quality of the data on thermal properties and by the loss of integrity of the gypsum sheathing. This study validates the numerical modeling strategy and suggests that the post-fire lateral capacity of the walls can be predicted from ambient temperature methods with use of the cold-formed steel residual mechanical properties.

The primary objective of the Structure Separation Experiment project is to assess structure-to-structure fire spread for structures located in the wildland-urban interface (WUI). As part of this project, full scale fire experiments will be conducted in which various types of structures (sources of fire) will be used to generate typical radiative and convective heat exposures on target structures (residential dwellings). The spacing between the source and target structures will be varied to identify safe structure separation distance (SSD). Most experiments will be conducted with construction materials currently listed in State of California building codes and using code compliant structural assemblies. A limited number of experiments will be conducted with enhanced, ignition resistant, materials that may not currently be listed by the State of California. The project is divided into three phases. Phase 1 will test sheds as fire sources, Phase 2 will test “in-law” buildings and Phase 3 will test single-family homes. Source terms from 1.39 m² to 24.8 m² (15 ft 2 to 267 ft 2 ) will be tested in Phase 1. Phase 2 will examine exposures from a 40.87 m² (440 ft 2 ) “in law” building and Phase 3 will characterize exposures from approximately 92.90 m² (1000 ft 2 ) residences. The goal of this report is to present a preliminary modeling approach for estimating an upper bound for the safe structure separation distance (SSD). This work is part of the larger modeling effort for the Structure Separation Experiments project and is intended to compliment the vast number of full-scale experiments that are being performed as part of this project.

This paper presents the application of a microplane based finite element approach for three-dimensional, nonlinear, reversed-cyclic analysis of reinforced concrete members. The constitutive relations and the finite element model used in the analysis are first described. The model’s performance is assessed by comparison with experimental work performed previously at the University of California, Berkeley. The method is shown to accurately represent global hysteretic behavior up to failure for cases with a limited number of cycles, while simultaneously providing information about local behavior such as concrete cracking and steel to concrete bond interaction. Issues related to the modeling of steel to concrete bond and the importance of accurate representation of boundary conditions for three-dimensional cyclic analysis are addressed.

360-degree video recorded in fires provides a unique perspective that allows the viewer to change the viewing direction as regions of interest change during a fire. Use of 360-degree and traditional cameras at some locations in intense fires for extended durations has been hampered in the past by the high levels of radiant heat flux that will damage the camera's imaging sensor. This paper describes how a thin layer of moving water can be used to significantly reduce unwanted infrared radiation generated by a fire while allowing visual imaging using a simple and inexpensive enclosure. Essential details to replicate this system are provided and three illustrative example deployments are discussed.

The primary objective of this project is to assess structure-to-structure fire spread for structures located in the Wildland Urban Interface (WUI). Full-scale fire experiments will be conducted in which various types of structures (sources of fire) will be used to generate typical radiative and convective heat exposures on target structures (residential dwellings). The spacing between the source and target structures will be varied to identify safe structure separation distance (SSD). Most experiments will be conducted with construction materials currently listed in State of California building codes and using code compliant structural assemblies. A limited number of experiments will be conducted with enhanced, ignition resistant, materials that may not currently be listed by the State of California. The project is divided into three phases. Phase 1 will test sheds as fire sources, Phase 2 will test in-law buildings (small accommodation structures built close to primary residential structure) and Phase 3 will test single-family homes. Source terms from 1.39 m to 24.8 m (15 ft2 to 267 ft2) will be tested in Phase 1. Phase 2 will examine exposures from 40.87 m (440 ft2) in-law buildings, and Phase 3 will characterize exposures from approximately 92.90 m (1000 ft2) residences. Dimensions of Phase 3 single residences (source term) will be finalized after numerical modeling of the results from Phase 1 and Phase 2. This test plan focuses on Phase 1 research. Phase 1 aims to quantify the effects of shed sizes, construction types, fuel loading, and separation distance on the ignition of primary structures (residential dwellings). Experiments will be conducted at the National Institute of Standards and Technology (NIST) and the Insurance Institute for Business and Home Safety (IBHS). The NIST experiments will be conducted at the National Fire Research Laboratory (NFRL), and the IBHS experiments will be conducted just outside of the wind loading test cell. The opening of the test cell (13.7 m (45 ft) wide) will dictate the largest source structure that can be evaluated at IBHS.

PurposeThe purpose of this paper is to report the first of four planned fire experiments on the 9.1 × 6.1 m steel composite floor assembly as part of the two-story steel framed building constructed at the National Fire Research Laboratory.Design/methodology/approachThe fire experiment was aimed to quantify the fire resistance and behavior of full-scale steel–concrete composite floor systems commonly built in the USA. The test floor assembly, designed and constructed for the 2-h fire resistance rating, was tested to failure under a natural gas fueled compartment fire and simultaneously applied mechanical loads.FindingsAlthough the protected steel beams and girders achieved matching or superior performance compared to the prescribed limits of temperatures and displacements used in standard fire testing, the composite slab developed a central breach approximately at a half of the specified rating period. A minimum area of the shrinkage reinforcement (60 mm2/m) currently permitted in the US construction practice may be insufficient to maintain structural integrity of a full-scale composite floor system under the 2-h standard fire exposure.Originality/valueThis work was the first-of-kind fire experiment conducted in the USA to study the full system-level structural performance of a composite floor system subjected to compartment fire using natural gas as fuel to mimic a standard fire environment.

Cold-formed-steel construction frequently relies on strap-braced, cold-formed-steel framed walls as the lateral-force resisting system. While the behavior of these walls has been studied during fire and under lateral loading separately, the influence of multi-hazard interactions and particularly the effect of fire remains poorly understood. This paper presents a simulation procedure to analyze the thermal and structural response of cold-formed-steel walls when subjected sequentially to fire and lateral load, which is validated against full-scale experiments. The results indicate that the numerical model can capture the post-fire response of cold-formed steel walls, including lateral strength, stiffness, and ductile failure. The lateral behavior of the walls was found to depend primarily on the maximum temperature reached in the cold-formed steel members, and their resulting residual material properties. Then, the validated simulation procedure was used to estimate the residual lateral performance of a strap-braced wall after exposure to various high temperatures. For the residual strength of the cold-formed steel material, data collected from the literature was combined with new test data from the authors to study the effect of variability in material post-. The outcomes of this research will help engineers to determine the post-fire performance of a wall as a function of the severity of the fire event.

This study explores an instrumentation strategy using distributed fiber optic sensors to measure strain and temperature through the concrete volume in large-scale structures. Single-mode optical fibers were deployed in three 12.8 m long steel and concrete composite floor specimens tested under mechanical or combined mechanical and fire loading. The concrete slab in each specimen was instrumented with five strain and temperature fiber optic sensors along the centerline of the slab to determine the variation of the measurands through the depth of the concrete. Two additional fiber optic temperature sensors were arranged in a zigzag pattern at mid-depth in the concrete to map the horizontal spatial temperature distribution across each slab. Pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA) was used to determine strains and temperatures at thousands of locations at time intervals of a few minutes. Comparisons with co-located strain gauges and theoretical calculations indicate good agreement in overall spatial distribution along the length of the beam tested at ambient temperature, while the fiber optic sensors additionally capture strain fluctuations associated with local geometric variations in the specimen. Strain measurements with the distributed fiber optic sensors at elevated temperatures were unsuccessful. Comparisons with co-located thermocouples show that while the increased spatial resolution provides new insights about temperature phenomena, challenges for local temperature measurements were encountered during this first attempt at application to large-scale specimens.

Detailed information about temperature distribution can be important to understand structural behavior in fire. This study develops a method to image three-dimensional temperature distributions in steel–concrete composite slabs using distributed fiber optic sensors. The feasibility of the method is explored using six 1.2 m × 0.9 m steel–concrete composite slabs instrumented with distributed sensors and thermocouples subjected to fire for over 3 h. Dense point clouds of temperature in the slabs were measured using the distributed sensors. The results show that the distributed sensors operated at material temperatures up to 960 °C with acceptable accuracy for many structural fire applications. The measured non-uniform temperature distributions indicate a spatially distributed thermal response in steel–concrete composite slabs, which can only be adequately captured using approaches that provide a high density of through-depth data points.

Certain commercial entities, equipment, or materials may be identified in this document to describe an experimental procedure or concept adequately.Such identification is not intended to imply

Detailed information about temperature distribution can be important to understand 15 structural behavior in fire. This study develops a method to image three-dimensional temperature 16 distributions in steel-concrete composite slabs using distributed fiber optic sensors. The feasibility 17 of the method is explored using six 1.2 m × 0.9 m steel-concrete composite slabs instrumented with 18 distributed sensors and thermocouples subjected to fire for over 3 hours. Dense point clouds of 19 temperature in the slabs were measured using the distributed sensors. The results show that the 20 distributed sensors operated at material temperatures up to 960 °C with acceptable accuracy for 21 many structural fire applications. The measured non-uniform temperature distributions indicate a 22 spatially distributed thermal response in steel-concrete composite slabs, which can only be 23 adequately captured using approaches that provide high density of through-depth data points. 24

This paper examines the structural response of cold-formed steel-framed building lateral force-resisting systems under combinations of simulated earthquake and fire loading. Full-scale experiments with gypsum-sheet steel composite panel sheathed walls, oriented strand board sheathed walls, and steel strap braced walls are presented. Twenty-two test specimens are subjected sequentially to combinations of cyclic shear deformation and fires of varying intensity; some approximate temperatures in standard furnace tests, and most have characteristics of actual building fires. In select tests, the walls are predamaged to simulate fire following an earthquake. The results show a progressive decrease of postfire lateral load capacity with increasing fire intensity for all walls; however, each wall type exhibits varied sensitivity to the fire intensity as well as to predamage. By understanding the response of these structural systems in real fires, designers can better plan for situations in which multiple hazards, including fire, exist.

Certain commercial entities, equipment, or materials may be identified in this document to describe an experimental procedure or concept adequately.Such identification is not intended to imply

This paper presents the results of compartment fire experiments on four 12.8 m long composite floor beams with various end support conditions. Specimens were constructed as partially-composite beams, consisting of W18×35 steel beams and 83 mm thick lightweight concrete slabs cast on top of 76 mm deep ribbed steel deck units. Test variables included two types of simple shear connections (shear-tab and welded-bolted double-angle connections) and the presence or absence of slab continuity over the girders. Each specimen was subjected to gravity loading using hydraulic actuators and 4000 kW compartment fires produced using natural gas-fueled burners. This study evaluated the characteristics of the fire loading and thermal and structural responses of the specimens. The test results indicated that there were significant effects of thermal restraints on the behavior and failure modes of the specimens with simple shear connections. The specimens resisted gravity loads at large vertical displacements near midspan (approximately a ratio of span length over 20) without collapse under fire loading. However, various limit states and vulnerabilities to fires were observed, including local buckling of steel beams near supports, flexural failure (yielding of steel beams and concrete fracture near restrained end supports), and connection failure (weld shear or bolt shear) during heating and cooling which could lead to partial or total collapse of the floor system.

We show that coherent laser detection and ranging can see through flames and capture 3D images of a deforming object. A ranging precision of 30 µm through acetylene flame at a 2-meter stand-off is achieved. © 2019 The Author(s)

The behavior of engineering structures in fire is commonly studied through large-scale experiments. Full-field, noncontact measurement techniques such as Digital Image Correlation (DIC) are potentially ideal for such experiments; however, the presence of light emitted by the flames, thermal radiation from the heated structure, and convective thermal gradients in the air make this a challenging application for DIC. A simple method has been developed to enable the use of DIC in large, low-soot, fires using narrow-spectrum blue light and spectrally-matched bandpass optical filters to increase signal-to-noise ratio and filter undesired radiant energy before it reaches the camera. The method is applied to full-scale experiments in which a 6-m long W16 × 26 steel beam is supported over a 700 kW fire from a natural gas diffusion burner. The resulting images are temporally and spatially averaged during post-processing to smooth out false distortions of the images caused by the thermal gradients in and around the flames before DIC techniques are applied to resolve strain.