Fire Resistance Rating Research Articles

Fire performance of LSF walls made of hollow flange channel studs

PurposeThis paper aims to present an investigation conducted to evaluate the effects of important parameters affecting the structural fire performance of light gauge steel frame (LSF) walls. It also evaluates the applicability of commonly used critical hot flange temperature method to determine the fire resistance ratings (FRR) of different LSF walls.Design/methodology/approachThe effects of important parameters such as stud section profiles and their dimensions, elevated temperature mechanical property reduction factors of the steel used, types of wall configurations and fire curves on the FRR of LSF walls were investigated. An extensive finite element analysis-based parametric study was conducted to evaluate their effects (finite element analysis – FEA). For this purpose, finite element models which were validated using the full-scale fire test results were used. Using the structural capacities obtained from FEAs, the load ratio versus FRR curves were produced for all the different LSF walls considered.FindingsStud depth and thickness significantly affected the fire performance of LSF walls because of the differences in temperature development pattern, thermal bowing deflections and the failure modes of stud. The FRR of LSF walls increased significantly when steel studs with higher elevated temperature mechanical property reduction factors were used. FRR significantly changed when realistic design fire curves were used instead of the standard fire curve. Furthermore, both the critical hot and average flange temperature methods were found to be unsuitable to predict the FRR of LSF walls.Originality/valueThe developed comprehensive fire performance data would facilitate the development of LSF walls with enhanced fire performance, and, importantly, it would facilitate and advance the successful applications of hollow flange channel section studs in LSF walls.

Determination of fire resistance ratings for glulam connectors within US high rise timber buildings

Multi-storey mass timber buildings constructed with cross laminated timber and glulam are being developed globally. Where engineered timber such as glulam is utilized, the column to beam connections need to be constructed with a fire resistance rating equal to that of the connecting members. The preferred glulam connectors are either a concealed steel plate with bolts and dowels; or a concealed proprietary screw-in sleeve type connector. The fire resistance of connectors for glulam members is an unresolved design issue, as there is no clear methodology to assess their capacity under fire, when the timber is exposed and not clad behind fire protective plasterboard. There is limited fire test data on concealed connectors under shear forces, which is the normal loading condition within a constructed building. Fire test data is also limited on full-size specimens. Correlations developed to date to calculate concealed connector fire resistance have only limited application.A methodology for the design of glulam beam to column connections has been developed based on an extensive literature review, examining the key issues for connection failure. It has been determined that char rate for the timber at the connection needs to be increased above the normally accepted design values, due to the influence of the steel connectors. Secondly, the reduction in timber strength behind the char layer needs to be accounted for, by including a greater depth of reduced strength and stiffness timber, such that the connection can effectively transfer the applied forces through the timber to the steel connector. The methodology detailed within this paper provides a simple approach to evaluate the timber cover to the concealed steel connector, where the timber strength and stiffness are effective.

Experimental and numerical study of temperature developments in PIR core sandwich panels with joint

This paper presents the results of an experimental and numerical investigation of temperature developments in sandwich panels consisting of steel sheeting and polyisocyanurate (PIR) core. Fire experiments were carried out on individual PIR sandwich panels and PIR sandwich panels with joint. The fire test results were used to validate a temperature dependent thermal conductivity model for PIR, through numerical heat transfer modelling using the general finite element package ABAQUS. The fire test results indicate that the temperatures at the joint on the unexposed side of a sandwich panel is initially lower than that on the panel. However, at high temperatures, the ablation of PIR core creates large gaps up to 25mm. Due to high radiation within the gap, the joint temperature becomes much higher than the panel temperature. The results of a numerical parametric study indicate that if the joint gap can be controlled to be no greater than 5mm, the joint and the panel temperatures on the unexposed surface would be similar. Joint gaps of 10mm or greater would result in joint temperatures much higher than panel temperatures and would reduce the sandwich panel system insulation performance of less than 60min even though the panel may be able to reach much longer standard fire resistance rating.

Energy-based time equivalent approach to determine the fire resistance ratings of light gauge steel frame walls exposed to realistic design fire curves

PurposeThis paper aims to present the details of a study undertaken to develop an energy-based time equivalent approach to obtain the fire resistance ratings (FRRs) of light gauge steel frame (LSF) walls exposed to realistic design fire curves.Design/methodology/approachThe energy-based time equivalent method was developed based on the performance of a structural member exposed to a realistic design fire curve in comparison to that of the standard fire time – temperature curve. The FRR predicted by the energy-based method for LSF wall configurations exposed to both rapid and prolonged fires were compared with those from fire design rules and finite element analyses (FEA).FindingsThe proposed energy method can be used to obtain the FRR of LSF walls in case of prolonged fires and cannot be used for rapid fires as the computed FRRs were higher than the results from FEA and fire design rules due to the influence of thermal bowing and its magnification effects at a high temperature gradient across the studs for rapid fires.Originality/valueThe energy-based time equivalent method was developed based on equal fire severity principles. Three different wall configurations were considered and exposed to both rapid and prolonged fires. The FRR obtained from the energy-based method were compared with fire design rules and FEA results to assess the use of the energy-based method to predict the FRR of LSF walls.

Fire behavior and resistance of partially encased and slim-floor composite beams

In this study, fire behavior and resistance of unprotected H-section, partially encased (PE), and slim-floor (SF) composite beams were experimentally and numerically investigated under standard fire condition. Experimental results of this study showed that unreinforced or reinforced PE beams and reinforced SF beams can achieve the standard fire resistance of 2hours or more up to the load ratio of about 0.30. The use of fire reinforcements in SF composite beams was shown to be very effective in increasing the fire resistance time. It was again confirmed that the maximum and average temperature criteria can significantly underestimate or overestimate the realistic fire resistance of PE and SF composite beams. The test-validated coupled thermal-stress analysis indicated that the fire resistance predicted by the bending moment capacity criterion alone can be unconservative for the types of composite beams of this study. It is emphasized that the deflection-related criteria should be considered for the rational fire resistance rating of PE and SF composite beams.

Особенности пожарной опасности зданий из деревянных конструкций

Experience of modern multistory wooden buildings has shown that as the main structural schemes there are used frame and volumetric-modular technology with the use of cross-laminated timber (CLT) panels. It is a steady tendency to increase the number of stories of buildings. In the article the analysis of normative requirements in the field of fire safety of high-rise buildings of wooden structures is presented. In the Russian Federation the construction of one- and two-storey wooden residential houses are allowed with maximum floor surface of 800 and 500 m 2 , respectively. In this case, the limits of fire resistance of building structure are not standardized. It’s allowed the construction of three-storey houses of the class of constructive fire danger of the C2 and fire resistance of building structures not less than REI 15 (E 15). Basic regulatory requirements for wooden houses in Europe and North America are associated with the number of floors, the fire resistance rating of load-bearing structures and the application materials of wood finishes and facades. As a rule, the construction of two-storey wooden residential buildings has no limitations. With increasing number of stories there are used various fire protection system: fire detection, automatic fire extinguishing system, etc. Special attention is paid to the creation of fire compartments and limit the use of combustible materials in interior and exterior decoration. However, in some countries (Sweden, France, Netherlands) the construction of eight-story buildings of wooden structures without the use of automatic fire suppression systems is allowed. Results of fire tests of wooden constructions from laminated veneer lumber are presented. It is shown that wooden structures have a fire-resistance required for use in the construction of multi-storey buildings of different functional purpose. The parameters of the speed of charring of different wood structures are given. The main directions of research and development of the regulatory framework in the field of fire safety of buildings of wooden structures are defined. Special attention is paid to the further conduct of fire tests for evaluating the fire resistance of wooden structures using new composite materials and technologies, and conducting full-scale fire tests of wooden buildings and constructions in order to simulate the development of fires.

Experimental study of light gauge steel framing floor systems under fire conditions

Cold-formed steel members can be assembled in various combinations to provide cost-efficient and safe light gauge floor systems for buildings. Such light gauge steel framing floor systems are widely accepted in industrial and commercial building construction. Light gauge steel framing floor systems must be designed to serve as fire compartment boundaries and provide adequate fire resistance. Floor assemblies with higher fire resistance rating are needed to develop resilient building systems for extreme fire events. Recently, a new composite panel system based on external insulation has been developed for light gauge steel framing floors to provide higher fire resistance rating under fire conditions. This article presents the details of an experimental investigation of light gauge steel framing floors made of both the conventional (with and without cavity insulation) and the new composite panel systems under standard fires. Analysis of the fire test results showed that the thermal and structural performance of externally insulated light gauge steel framing floor system was superior than conventional light gauge steel framing floors with or without cavity insulation. Details of the experimental results including the temperature and deflection profiles measured during the tests are presented along with the joist failure modes. Such fire performance data can be used in the numerical modelling of light gauge steel framing floor systems to further improve the understanding of their fire behaviour and to develop suitable fire design rules.

Fire Performance of Columns Made of Normal and High Strength Concrete: A Comparative Analysis

The use of high strength concrete (HSC) in multi-story buildings has become increasingly popular. Selection of HSC over normal strength concrete (NSC) allows for reducing the dimensions of the columns sections. However, this reduction has consequences on the structural performance in case of fire, as smaller cross sections lead to faster temperature increase in the section core. Besides, HSC experiences higher rates of strength loss with temperature and a higher susceptibility to spalling than NSC. The fire performance of a column can thus be affected by selecting HSC over NSC. This research performs a comparison of the fire performance of HSC and NSC columns, based on numerical simulations by finite element method. The thermal and structural analyses of the columns are conducted with the software SAFIR®. The variation of concrete strength with temperature for the different concrete classes is adopted from Eurocode. Different configurations are compared, including columns with the same load bearing capacity and columns with the same cross section. The relative loss of load bearing capacity during the fire is found to be more pronounced for HSC columns than for NSC columns. The impact on fire resistance rating is discussed. These results suggest that consideration of fire loading limits the opportunities for use of HSC, especially when the objective is to reduce the dimensions of the columns sections.

Fire resilience of composite beams with simple connections: Parametric studies and design

Simple (shear) connections are designed to resist vertical shear forces resulting from gravity loading. During a fire event, floor systems expand and rotate, imposing axial forces (compressive and tensile) on simple connections. This paper presents the results of analytical parametric studies conducted to expand the experimental database and evaluate the structural response of composite beams with simple connections subjected to combined gravity loads and design fire scenarios. The parametric studies were conducted using 3D finite element models of partial frame assemblies consisting of composite beams with simple connections. These models were developed and benchmarked previously by the authors [1] using experimental data [2, 3]. These models explicitly accounted for the effects of geometric and material nonlinearity including concrete cracking and crushing, steel yielding and fracture, and the interaction between various structural components. The parameters included in the analytical studies were the connection type (shear-tab, single-angle, double-angle), deck type (flat slab, perpendicular metal deck), composite slab continuity across multiple bays, slab reinforcement type (wire mesh, mild steel), fire resistance rating of the design, and the design fire scenario (1hour fire with cooling, 2hour fire with cooling, E119). The results from the parametric studies indicated that for typical composite beams and simple connections designed with certain (n-hour) fire resistance rating, and subjected to design fire scenario with the same (n-hour) heating followed by cooling, there was no premature fracture failure of the connection leading to collapse of the composite beams. The continuity of composite slab across bays and the steel reinforcement has a significant influence on the performance of the simple connections, and the resilience of the composite beam system.

Detrimental effects of plasterboard joints on the fire resistance of light gauge steel frame walls

Light gauge Steel Frame (LSF) walls are commonly used in building construction. In general, they are lined with single or double layers of gypsum plasterboards with and without cavity insulation. Gypsum plasterboards act as a thermal barrier to protect the thin-walled steel studs from rapid temperature rise. In these walls, plasterboard joints are located along the studs for ease of construction and are protected by filler materials. During fires, these plasterboard joints crack and open up, and thus allow the stud temperatures to rise rapidly and initiate premature structural failures in LSF walls. This research investigated the detrimental effects of these plasterboards joints on the fire resistance rating of single and double plasterboard lined walls based on the hot flange time-temperature profiles of studs from full scale fire tests. To overcome the detrimental effects of plasterboard joints, the back-blocking technique was used, where plasterboard joints were placed between studs with 150mm wide plasterboards as back-blocks. Full scale fire tests and numerical studies were performed on single plasterboard lined load bearing LSF wall panels to investigate the improved fire performance by using this technique. They showed that the fire resistance rating of these LSF walls was increased by 25% in comparison to the conventional plasterboard joint arrangement over the studs. This paper presents the details of this research on the detrimental effects of plasterboard joints on the fire resistance of load bearing LSF walls, and the results. It also includes a discussion and results for non-load bearing LSF walls.

Thermal performance of LSF floors made of hollow flange channel section joists under fire conditions

Light gauge steel frame (LSF) floor systems used in the building industry are made of cold-formed lipped channel section (LCS) joists and lined using gypsum plasterboards. The recently developed LSF floor systems made of welded hollow flange channel (HFC) section joists exhibited superior fire performance in the full scale fire tests. Since full scale fire tests are expensive and time consuming, finite element (FE) models were used in this research on LSF floor systems. In this paper 2-dimensional FE models were developed using a finite element analysis software SAFIR to predict the thermal performance of LSF floors made of HFC joists, and validated using the fire test results. The developed FE models predicted the thermal performance of LSF floor systems exposed to standard fires reasonably well. The validated model was then modified to include plywood subfloor and was used to investigate the effects of important parameters such as joist size, shape and subfloor thickness on the time–temperature profiles of the outer hot and cold flanges of HFC joists. These time–temperature profiles can be directly used to estimate the fire resistance ratings (FRR) of LSF floors made of HFC joists without performing expensive full scale fire tests. This paper presents the details of this thermal analysis study and the results.

Fire design of LSF floors using hollow flange channel joists

Predicting the fire performance of commonly used Light gauge Steel Frame (LSF) floor systems is important in designing them for fire situations. In the past, many researchers conducted full scale fire tests and numerical analyses for this purpose. However, some researchers have proposed fire design rules to predict the fire resistance ratings of LSF floor systems to avoid expensive fire tests. Their proposals were developed only for LSF floors made of conventional lipped channel section (LCS) joists. Therefore this research was aimed at developing fire design rules for the new LSF floor systems made of hollow flange channel (HFC) section joists. It used the fire performance data from an extensive parametric study based on validated finite element models of the new floor system with varying floor component configurations. Three different fire design rules were proposed to predict the fire resistance ratings of LSF floors based on the available design equations from past research and current design standards. The proposed design equations were validated by comparing the fire resistance rating predictions with the finite element analysis results obtained from the parametric study. Further a new Direct Strength Method based fire design rule was also developed and validated using finite element analysis results. The fire design rules proposed in this paper can be used to predict the fire resistance ratings of LSF floors made of HFC section joists with varying sizes and steel types, and plasterboard/insulation configurations without the need for further fire testing and numerical analyses.

Fire resistance of LSF floors made of hollow flange channels

Light gauge Steel Frame (LSF) floor systems are generally made of conventional lipped channel section (LCS) joists and lined using fire resistive gypsum boards. Although the use of LSF floor systems has significantly increased in the construction of fire rated buildings, it is limited to those made of LCS joists. Since the fire resistance ratings (FRR) for steel sections other than LCS joists are not available, engineers are reluctant to use innovative steel joists in LSF floor systems exposed to fire conditions. To overcome these limitations, a new LSF floor system recently developed using a welded hollow flange channel (HFC) section as joists was investigated using both experimental and numerical studies under standard fire conditions. Both these studies demonstrated higher fire resistance ratings in comparison to those made of LCS joists. However, they were limited to one welded HFC joist section. Hence a detailed parametric study of LSF floor systems made of HFC joists was undertaken to investigate the effects of joist sizes and shapes, steel types and service openings on the FRR using the validated finite element models. This paper presents the details of this finite element analysis based parametric study and the load ratio versus time curves. These results can be used in designing the LSF floors made of HFC joists with varying sizes for different industry applications without the use of expensive fire tests.

Performance-based fire behaviour analysis for underground parking structures

ABSTRACTThe current design code for building structures in South Korea specifies the minimum fire resistance ratings and fire-resisting performances for each structural component, for which a standard fire curve is required to be applied. There are, however, obvious differences between the standard fire curve and the actual fire behaviour observed from real events. In this study, a fire dynamic-based simulation was conducted on a typical underground parking structure, from which a realistic fire design curve was obtained. In addition, thermal behaviour and fire-resisting response of hollow-core slabs in the underground parking structure were estimated by using the realistic fire design curve, which was compared to those based on the design fire curve specified in the current code. On this basis, it is considered that more rational and economic fire resistance design of underground parking structure is possible by utilizing the realistic fire curve.

Robustness assessment of a generic steel fire-protected moment-resisting frame under travelling fire

Due to their vulnerability to high temperatures, steel structures are typically protected against fire by insulation materials, as recommended by fire codes. The fire resistance rating of a protected member is determined based on a standard fire test, which simulates post-flashover fire conditions. Empirical evidence has shown that fires in large open-plan compartments do not burn uniformly, and a method called “traveling fire” has been introduced in previous research to simulate the effects of spreading fires. An investigation is performed here to examine the robustness of a generic four-story moment-resisting steel structure with one-hour fire resistance rating subjected to travelling fire. Various fire sizes are considered: 12.5, 25, 50 and 100% of the floor area. The results show that while no collapse occurs during the 12.5, 50 and 100% fire sizes, the structure collapses under the 25% fire size at 85 min due to the inability of the system to transfer the load after one of the columns buckles. This seems to be in contradiction with traditional belief that a fire covering a larger portion of the floor plan would reduce the safety margin. The investigation performed underlines that the fire protection of structures based on the standard time-temperature curve does not necessarily provide adequate resistance under travelling fires. With the lack of adequate fire regulations codified for large compartments, more research is required before arriving at a better understanding of the application of travelling fire to large compartments.

Thermal and mechanical transient behaviour of steel doors installed in non‐load‐bearing partition wall assemblies during exposure to the standard fire test

SUMMARYIn this paper, the authors present experimental results and observations of four full‐scale standard fire tests on single‐leaf steel doors and steel frames installed in 3 × 3 m non‐load‐bearing partition walls. Three full‐scale fire tests were performed on steel doors installed in lightweight partition walls constructed by using steel C‐section studs with gypsum boards fixed on both sides. Two lightweight walls incorporated Rockwool cavity insulation, while the third lightweight wall was constructed without cavity insulation. The fourth fire test involved a steel door installed in a masonry partition wall. While the steel door leaf and door frames were identical in all four full‐scale tests, only the steel door installed in the masonry wall achieved the desired fire resistance rating of 30 min. The integrity criterion for fire resistance was determined for the scenario when the door opened away from the furnace. The duration of fire resistance according to the integrity criterion was found to be 38, 25 and 19 min for the same door when installed in masonry wall, uninsulated lightweight wall and insulated lightweight wall respectively. For the thermal insulation criterion of fire resistance, the scenario of the door opening into the fire was found to be the most onerous. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Comparative experimental study of fire-resistance ratings of timber assemblies with different fire protection measures

This article presents the results of a comparative experimental study to investigate the effects of using three different fire protection measures to improve the fire endurance of timber assembly. The three fire protection measures were fire-retardant intumescent coating, gypsum plasterboard and filling the timber assembly void with mineral wool. The fire-resistance period obtained from the fire endurance tests was based on the integrity and the insulation criteria. Compared to the reference timber assembly without any fire protection (fire-resistance time = 37 min), the increases in fire resistance using the three different fire protection measures were 6 min (16%), 37 min (100%) and 142 min (384%) for using intumescent coating (specimen F2), 12-mm-thick gypsum plasterboard (specimen F4) and infill mineral wool (F3), respectively. The specific intumescent coating used in the test failed to expand. Therefore, this specimen (F2) behaved very similarly with the control specimen (F1) without any fire protection. Attaching an additional layer of gypsum plasterboard to the timber assembly on the fire-exposed side improved the fire-resistance rating by about 30 min, which is higher than that obtained from using the current design guidance such as Eurocode EN 1995-1-2. Among these three fire protection methods, filling the void between the top and bottom timber boards gave the best result because the mineral wool not only provided insulation but also stopped direct flame attack of the timber board on the unexposed side.

Loadbearing capacity criteria in fire resistance testing

The European system for fire testing and classification of loadbearing building elements lacks consistency because the two standards that have to be applied prescribe different criteria for assessing the loadbearing performance. This article analyzes the implications of the present conflict between the standard for testing and the standard for classification. The prescribed criteria for loadbearing performance are related to the exceedance of deflection and rate of deflection thresholds. A database of 46 fire resistance tests performed at the University of Liege is collected that contains the time at which these thresholds are reached in fire tests with different typologies of elements (walls, floors, columns and beams). Then, the loadbearing performance (and hence the fire resistance rating) can be derived according to the two standards. The evolutions of deflection and rate of deflection during the tests are also analyzed to gain a better understanding of the adequacy of the standards. The selection of one or the other standard affects the time at which “failure” is deemed to occur in fire tests. Statistically speaking, the difference in terms of failure time that results from using one or the other standard has a 25 % probability to exceed 10 %. In certain cases, this results in a difference in fire resistance rating; this was observed for three of the analyzed tests. The apparent contradiction in two codes in application has potential practical implications and therefore needs to be solved. The article suggests some guidelines for defining homogenized and consistent criteria.

Numerical study of high strength LSF floor systems in fire

Light gauge steel frames (LSF) are commonly used in floor systems. The LSF floor systems must be designed to serve as fire compartment boundaries and provide adequate fire resistance. However, limited research has been undertaken on LSF floor systems, particularly on those made of high strength steel joists, and hence a thorough understanding of their fire resistance behaviour is not available. Recently a new composite floor system was also developed to provide higher fire resistance rating. But its increased fire rating could not be determined using the currently available design methods. This paper presents the details of finite element models of high strength LSF floor systems developed to simulate their structural performance under standard fire conditions. The numerical analyses of LSF floor joists were undertaken using the finite element program ABAQUS based on the measured time–temperature profiles obtained from full scale fire tests under both steady state and transient state conditions. Finite element models were calibrated using full scale fire test results and used to further investigate the structural fire behaviour of LSF floor systems. Numerical analyses provided a good understanding of the structural fire behaviour of LSF floor systems and confirmed the superior performance of the new composite floor system. This paper has shown that fire resistance ratings of a range of LSF floor systems can be predicted from the critical average joist temperature obtained from finite element analyses.

Fire behaviour of slender, highly utilized, eccentrically loaded concrete filled tubular columns

This paper investigates the fire performance of highly utilized and eccentrically loaded concrete filled composite columns with slendernesses greater than currently permitted by the simple calculation model in Eurocode 4 Part 1.2. The fire resistance rating was calculated by applying implicit as well as explicit finite element analyses and undertaking sequentially coupled thermal-stress analyses. Initially, published fire tests on concentrically loaded columns as well as columns with a modest load eccentrically (e/h≤0.25) were analysed with normal (NSC) and high strength concrete (HSC). Following the validation of the numerical model against the test data, a parametric study was undertaken on a composite column using a 400mm square hollow section with a fixed-pinned boundary condition and a relative slenderness at room temperature of λ̅=0.6. Load levels ηfi,t of 0.47, 0.35 and 0.24 were considered and, using a constant eccentricity of e/h=0.5, a combination of concentric and eccentric loading was applied to the column, as would occur in practice. The results from the parametric analyses show that the FRR reduces significantly as the bending moment increases on the column. Moreover, although the FRR reduced as the utilization increased, it was found that for highly utilized columns the FRR was less sensitive to changes in the magnitude of the bending moments.