Fire Performance Of Structures Research Articles

Numerical study of LSF floors made of hollow flange channels in fire

Light gauge steel frame (LSF) floor systems are generally made of lipped channel section joists and lined with gypsum plasterboards to provide adequate fire resistance rating under fire conditions. Recently a new LSF floor system made of welded hollow flange channel (HFC) section was developed and its fire performance was investigated using full scale fire tests. The new floor systems gave higher fire resistance ratings in comparison to conventional LSF floor systems. To avoid expensive and time consuming full scale fire tests, finite element analyses were also performed to simulate the fire performance of LSF floors made of HFC joists using both steady and transient state methods. This paper presents the details of the developed finite element models of HFC joists to simulate the structural fire performance of the LSF floor systems under standard fire conditions. Finite element analyses were performed using the measured time–temperature profiles of the failed joists from the fire tests, and their failure times, temperatures and modes, and deflection versus time curves were obtained. The developed finite element models successfully predicted the structural performance of LSF floors made of HFC joists under fire conditions. They were able to simulate the complex behaviour of thin cold-formed steel joists subjected to non-uniform temperature distributions, and local buckling and yielding effects. This study also confirmed the superior fire performance of the newly developed LSF floors made of HFC joists.

Fire performance of earthquake-damaged reinforced-concrete structures

A full-scale reinforced-concrete (RC) three-dimensional (3-D) frame under vertical sustained loads has been subjected to biaxial lateral loads representing earthquake actions followed by a pool fire in a single compartment. A number of sensors were used to monitor the kinematic and thermal fields during the test. The results (strains, displacements and temperatures) provide valuable information about an earthquake-damaged RC structure subjected to fire in the fully developed and decay stages. The thermal field is observed to be non-uniform within the compartment on fire, in contrast to the uniform thermal field assumption (as often adopted and suggested in codes). The earthquake-damaged frame subjected to fire was found to resist the applied vertical loads, despite the reduction in its residual capacity to about one-third of the original value.

Predicting the performance of LSF walls made of hollow flange channel sections in fire

Fire resistance of load bearing Light Gauge Steel Frame (LSF) wall systems is important to protect lives and properties in fire accidents. Recent fire tests of LSF walls made of the new cold-formed and welded hollow flange channel (HFC) section studs and the commonly used lipped channel section (LCS) studs have shown the influence of stud sections on the fire resistance rating (FRR) of LSF walls. To advance the use of HFC section studs and to verify the outcomes from the fire tests, finite element models were developed to predict the structural fire performance of LSF walls made of welded HFC section studs. The developed models incorporated the measured non-uniform temperature distributions in LSF wall studs due to the exposure of standard fire on one side, and accurate elevated temperature mechanical properties of steel used in the stud sections. These models simulated the various complexities involved such as thermal bowing and neutral axis shift caused by the non-uniform temperature distribution in the studs. The finite element analysis (FEA) results agreed well with the full scale fire test results including the FRR, outer hot and cold flange temperatures at failure and axial deformation and lateral displacement profiles. They also confirmed the superior fire performance of LSF walls made of HFC section studs. The applicability of both transient and steady state FEA of LSF walls under fire conditions was verified in this study, which also investigated the effects of using various temperature distribution patterns across the cross-section of HFC section studs on the FRR of LSF walls. This paper presents the details of this numerical study and the results.

Structural fire resistance: Rating system manifests crude, inconsistent design

This paper highlights a shortcoming in the current system of structural fire resistance design, proposes how it can be addressed and shows how the perceived barriers to change can be overcome. It is an opinion piece intended to stimulate discussion.Whilst structural fire engineering knowledge may be relatively underdeveloped compared to other engineering disciplines, the industry has made great progress in recent decades in understanding and analysing fire behaviour and the response of structures, as well as developing fire protection products that can be accurately specified to meet performance criteria. In addition, through modern fire and risk engineering there are also methods to establish the appropriate fire resistance rating for a building (or element) based on risk profile, fire loading, building fabric and potential ventilation amongst other things. It is the objective of many within the industry for structural fire engineering to become an integrated part of the design process, ultimately leading to safer and more efficient structures. However, this paper questions whether current structural fire resistance design methods achieve the consistent level of crudeness required for this, or whether the means by which structural performance in fire is quantified, standard fire resistance, represents a weak link that undermines the entire process.Although the concept of standard fire resistance, benchmarked against performance under normalised furnace test heating regimes, is useful in that it allows for the comparison necessary to safeguard consistency across products, design methods and geographies, the historic 15-min fire resistance increments (for example 60, 75, 90min) result in inconsistent levels of safety. Refined grades, as in fact already allowed under fire resistance testing standards, would yield significant benefits for reliability and design efficiency. The paper uses hypothetical case studies to exhibit the merits of refined fire resistance grades and explains how implementing the enhanced classification system may be readily achievable.

標準火災加熱を受けたカラマツ集成材梁の放冷過程における挙動<br>構造用集成材梁の耐火性に関する研究 その１

Timber elements, which are different from other structural elements, have a characteristic problem in that the load bearing capacity decreases due to self-burning in the case of a fire, and this self-burning may continue after other fuel in the room has been exhausted. Therefore, the structural fire performance of timber elements should be clarified during not only the heating phase, but also the cooling phase. However, in examining the load bearing capacity of timber elements in a fire, few studies have considered the cooling phase. In the present paper, the fire performance of glued, laminated timber beams is discussed based on load-bearing fire tests that take the cooling phase into consideration.

Analytic Study of Structural Stability for H-Section Column Made of Submarine Structural Steels Based on Boundary Conditions and Column Lengths at High Temperature

Structural steels require performance, such as structural performance, constructional one, and fire performance as an efficient constructional material. However, structural steels have a fundamental weakness in a fire and need to improve constructional performance of welding which resulted in the development submarine structural steels, such as SM 400, SM 490, and SM 520. Their yield strengths are the same as general structural steels, but the weldability was better. Therefore, the application of submarine structural steels increases in steel building market annually. However, the fire resistance performance isnt determined when these are used as main materials in H-section columns in the case of different boundary conditions and different column lengths. In this paper, to confirm and suggest a new guideline for fire protective materials, an advanced engineering design was used with mechanical properties at high temperature and a heat stress analysis. The findings showed that fire resistance of H-section columns with longer lengths and other boundary conditions are determined to satisfy the fire resistance performance if the fire protective materials derived from 3500mm in length and hinge to hinge boundary condition apply to longer column lengths and other boundary conditions.

Structural Fire Performance of Innovative Moment-Resisting Connection Joining Steel Beams to HSS Columns

In this paper, experimental results of the structural fire behaviour of four large-scale steel frame test assemblies are presented. Test assemblies were made of HSS beams and columns connected together using an innovative extended end-plate moment connection configuration. Two different parameters were investigated, the connection end plate thickness and the degree of beam axial restraint. The fire performance of this beam-to-column configuration was compared to the behaviour of a commonly-used connection configuration with similar parameters and fire testing conditions. The newly-developed connection configuration behaved in a more flexible manner at elevated temperature than the regular configuration. In addition to improved constructability and pleasant appearance, the new connection configuration exhibits greater moment-carrying capacity and enhanced fire resistance characteristics.

Simulating the Response of Composite Plates to Fire

The present paper introduces a numerical study on the fire behavior of composites during exposure to a heating source at high incident power. A novel numerical model is proposed which is able to simulate the behavior of composite materials in fire environment providing the composites mass loss rate and heat release rate during heating source application. Two commercial software have been selected as platforms for the implementation of the proposed numerical model COMSOL and ANSYS. In COMSOL the model has been implemented by introducing proper field equations, while a macro, written in Ansys Parametric Design Language, has been used to allow the ANSYS FEM code to numerically simulate, by an incremental procedure, all the relevant physical phenomena related to fire. As an application, an experiment on thermal degradation over a laminated composite plate has been numerically simulated and the numerical model has been validated by comparing the COMSOL and Ansys numerical results to experimental literature data in terms of temperature profile over the panel thickness, Mass Loss Rate and Heat Release Rate. An excellent agreement has been found between the obtained numerical results and the experimental test data for both the adopted numerical platforms. However the ANSYS implementation, which showed to be the most effective in terms of accuracy of results and perspectives of applications to complex numerical models, led to the definition of a powerful tool able to assesses the fire performance of composite structures.

Structural Post-Fire Behaviour of the Steel I-Shape Beams-to-Cylindrical Columns

Previous researchers have tried to predict the response of different types of structures under elevated temperatures. The results are important in preventing the collapse of buildings in fire. Post-fire status of the structures is also of interest for ensuring the safety of rescue workers during the fire and in the post-fire situations. Determining the extent of the structural damage left behind a fire event is necessary to draw up adequate repair plans. Connections play an important role on the fire performance of different structures. Due to the high cost of fire tests, adequate experimental data about a broad range of connections is not available. A vulnerable type of such connections to fire is the weld connections between I-shape beams and cylindrical columns in oil platform topsides. Considering the high probability of fire in oil platforms, study of the behaviour of these connections at elevated temperatures and in the post-fire, is of great importance. In the current study, eight small scale experimental fire tests on welded connections between I-shape beams and cylindrical columns have been conducted. Four tests are aimed at investigating the structural performance of this connection at elevated temperature. In other tests, post-fire behaviour of these connections has been studied to investigate their residual structural strength.

Elevated-temperature mechanical properties of high strength structural steel S460N: Experimental study and recommendations for fire-resistance design

Fire-resistance design is one of the most important considerations when structural engineers conduct design of steel structures. As a basis of analyzing fire performance of steel structures, elevated-temperature mechanical properties of structural steels are significant for practical design. The recommendations of current European, American, Australian and British standards were mainly obtained from mild steels, which are in question when used to conduct fire-resistance design of high strength steel structures. In order to reveal the elevated-temperature mechanical properties of high strength steel S460N, tensile tests were conducted at various temperatures ranged 20–700°C. The elevated-temperature reduction factors of elastic modulus, yield and ultimate strengths of S460N were obtained and compared with current design standards and available literature. According to the comparison between this research result on S460N and the available research results in literature on S460N, S460M and various mild steels, it is found that the deterioration of mechanical properties of structural steels at elevated temperature is dependent on steel grades. Thus the recommendations in current design standards are not applicable to high strength structural steels. Further unique predictive equations for the deterioration of high strength structural steel S460 at elevated temperatures were proposed and validated with available literature.

Fire and Post-Fire Performance of Space Grid Structures

A fire performance finite element (FE) model of space grid structures in fire and after fire is proposed, and deformation, stress redistribution, failure modes of grid structures are also studied. The result shows that tensile membrane action arises when the grid is loaded after fire, and the load bearing capacity after fire is reduced by fire damage.

The Mechanical Performance Analysis of Steel Truss in the Fire and Damage Assessment after Fire

At present, based on the fire test results of single components, the design method of structure fire resistance performance is put forward. However, the cases for fire resistance research of space structure are not widely researched by scholars. Making use of finite element software to analyze structural fire resistance performance will be development trend of the research topic. In the paper, the author regards the truss structure in practical engineering as the research object. And by using thermal software (FDS), the environment temperature in every space position can be calculated to get steel’s fire temperature further. In the hot-force coupling module, structural mechanical behavior is analyzed after fire, and structural damaged degree is judged on the basis of the building identification level standard, which will be helpful to provide the repair opinion.

Deterioration of mechanical properties of high strength structural steel S460N under transient state fire condition

911 World Trade Centre Tragedy put fire safety of constructional steel structures into question. Since then, more and more research attention has been paid to the elevated-temperature mechanical properties of structural steels, which is a critical basis of evaluating the fire performance of steel structures. In the literature the available mechanical properties of structural steels under fire conditions were mainly obtained from steady state test method, as steady state test method is easier to perform than transient state test method and offers stress–strain curves directly. However, the transient state fire condition is considered to be more realistic to represent the real condition when constructions are exposed to fire. In order to reveal the deterioration of mechanical properties of the commonly used high strength structural steel S460N under transient state fire condition, tensile tests were conducted under various constant stress levels up to 800MPa. The reduction factors of elastic modulus, yield and ultimate strengths of S460N under transient state fire condition were obtained and compared with current leading design standards and available literature. The application of such accurate elevated-temperature mechanical properties reduction factors of S460N can ensure a safe fire-resistance design and evaluation of steel structures with high strength steel S460N under transient state fire condition. This experimental study also supports other relative research on fire performance of steel structures with S460N under transient state fire condition.

Deterioration of mechanical properties of high strength structural steel S460N under steady state fire condition

Fire is one of the most severe conditions to which steel structures may be subjected to. In order to analyze the fire performance of steel structures, mechanical properties of steels at elevated temperatures are significant for practical design. The recommendations of current European, American, Australian and British standards were mainly obtained from mild steels, whose validity should be checked when used to conduct fire-resistance design of high strength steel structures. In order to reveal the deterioration of mechanical properties of the commonly used high strength steel S460N under steady state fire condition, tensile tests were conducted at various elevated temperatures ranged from 20°C to 700°C. The reduction factors of elastic modulus, yield and ultimate strengths of S460N under steady state fire condition were obtained and compared with current design standards and available literature. It is found the deterioration of mechanical properties of steels under steady state fire condition is dependent on steel grades. Hence the recommendations in current design standards are not applicable to high strength steels, and unique reduction factors should be proposed for various high strength steels. The elevated-temperature properties reduction factors of S460N presented herein can be used as input data to conduct safe fire-resistance design of steel structures with high strength steel S460N.

The Practical Application of Structural Fire Engineering on a Retail Development in the UK

The British Building Regulations allow the application of performance based design methods to ensure the fire resistance of buildings. This has led to significant amounts of research and testing on the fire performance of structures. This research generated the understanding that steel framed buildings have an inherent fire resistance, which has in turn resulted in the development of specialist numerical calculation tools as well as simplified design methods for the fire design of steel-framed structures. The paper describes the practical application of these structural fire engineering methods using a large retail and cinema complex in the UK as a case study. The finite element software Vulcan has been used to analyse the behaviour of large parts of this multi-storey building during a number of likely design fire scenarios in order to optimise the amount of applied passive fire protection to the structure. The building is constructed as a steel composite structure with normal down-stand composite beams supporting a composite floor on trapezoidal metal deck. This type of structure is ideal to utilise the benefits of tensile membrane action during a fire which can be used to omit fire protection from off grid secondary beams. Due to the size and the multiple usage and changing floor construction of the buildings five different sub-frames haven been analysed. In the UK a number of simplified methods are currently applied to justify partially protected steel structures. These methods are based on individual bays only and therefore do not consider the effects of the surrounding structure. In order to investigate the differences further, the behaviour of the large sub-frame models has been compared with the results of individual bay analysis methods.

Role of Insulation Effectiveness on Fire Resistance of Steel Structures under Extreme Loading Events

Fire performance of steel structures is highly dependent on the effectiveness of applied fire insulation. However, insulation materials are susceptible to damage under extreme loading events. A state-of-the-art review on the role of insulation damage on fire resistance of steel structures is presented. Parametric studies on a six-story steel-framed building were carried out to illustrate the effect of insulation damage on fire response of a steel structure. In the analysis, realistic fire scenarios, loading, and failure criteria were taken into consideration. Analysis results indicate that the fire resistance of a steel-framed structure is significantly influenced by the extent of insulation loss, type of fire scenario, and level of lateral load. Insulation damage causes faster deterioration in the structural response of framed buildings under the combined effect of fire and lateral loading. The need for accounting for any insulation damage, arising under extreme loading events, in fire design of steel-framed structures is highlighted, and a performance-based design strategy incorporating fire resistance analysis is discussed.

Numerical modelling of light gauge cold-formed steel compression members subjected to distortional buckling at elevated temperatures

Fire safety design of building structures has received greater attention in recent times due to continuing loss of properties and lives during fires. However, fire performance of light gauge cold-formed steel structures is not well understood despite its increased usage in buildings. Cold-formed steel compression members are susceptible to various buckling modes such as local and distortional buckling and their ultimate strength behaviour is governed by these buckling modes. Therefore a research project based on experimental and numerical studies was undertaken to investigate the distortional buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. Lipped channel sections with and without additional lips were selected with three thicknesses of 0.6, 0.8, and 0.95 mm and both low and high strength steels (G250 and G550 steels). More than 150 compression tests were undertaken first at ambient and elevated temperatures. Finite element models of the tested compression members were then developed by including the degradation of mechanical properties with increasing temperatures. Comparison of finite element analysis and experimental results showed that the developed finite element models were capable of simulating the distortional buckling and strength behaviour at ambient and elevated temperatures up to 800 °C. The validated model was used to determine the effects of mechanical properties, geometric imperfections and residual stresses on the distortional buckling behaviour and strength of cold-formed steel columns. This paper presents the details of the numerical study and the results. It demonstrated the importance of using accurate mechanical properties at elevated temperatures in order to obtain reliable strength characteristics of cold-formed steel columns under fire conditions.

Structural fire performance of earthquake-resistant composite steel–concrete frames

Seismic and fire design of a building structure may be two very demanding tasks, especially if included in a performance based design philosophy. For the time being, the necessary harmonization on the regulations concerning these two design fields is almost missing, thus preventing the effective possibility of an integrated design. Besides, while many countries have already moved towards the use of performance-based codes for seismic design, the application of such methodologies for the fire design of structures is still limited in scope. Within this framework, the development of suitable procedures introducing structural fire performance issues for a comprehensive design methodology is needed. In this paper, a numerical investigation for the assessment of the structural fire performance of earthquake resistant composite steel–concrete frames is presented. With reference to a case study defined in the framework of a European Research Project, a great effort was devoted to the identification of the key structural parameters allowing for a possible correlation between the predictable performances under seismic and fire loadings, when these two are considered as independent actions. At the conceptual design level, the most suitable structural solution with respect to both design actions was chosen, including composite beams and circular steel concrete-filled columns. The frame was designed in order to resist severe seismic action according to the ductile design approach provided by Eurocode 8; the parameters affecting members’ sizing were outlined in this phase. Afterwards, the seismic performance of the designed frame was investigated by means of non-linear static analyses; once the seismic performance objectives were met, in order to evaluate the structural fire performance of the whole frame a set of criteria was defined. To this purpose, thermo-mechanical analyses under different boundary conditions were developed and in order to identify the possible mechanisms leading to structural failure, the state of stress at the critical cross-sections at different times of fire exposure was investigated. Another point of main concern was represented by the assessment of the influence of different restraining conditions on the achieved fire resistance rating and kind of structural failure. Moreover, the proposed methodology allowed making an estimate of the amount of axial restraint provided to the heated beams by the surrounding structure; in this view, the importance of choosing column elements in function of their flexural stiffness was revealed, in order to correlate it with the predictable performances under both seismic and fire loadings.

Fire Design Concepts for Tall Timber Buildings

Based on the current knowledge in the area of fire design of timber structures this paper presents a generic fire safety concept for tall timber buildings. The first part of the paper gives an overview of fire action and fire safety concepts and presents the main differences between medium-rise and tall buildings with regard to fire safety. The analysis enables the formulation of a generic fire safety concept for tall timber buildings. In the second part of the paper some experimental results on the fire performance of timber structures under natural fire conditions relevant for tall timber buildings are presented.

Influence of water content on failure of phenolic composites in fire

This paper evaluates the structural performance of flame resistant phenolic matrix composites exposed to fire. Experimental fire tests were performed on a glass–phenolic composite under combined static loading and one-sided radiant heating. The reduction to the tension and compression failure strengths of the phenolic composite was measured in these tests for heat flux conditions ranging from 10 kW/m 2 (∼225 °C) to 75 kW/m 2 (∼700 °C). It was discovered that the failure strengths of the phenolic composite decreased rapidly in the event of fire, particularly under compressive loading when failure occurred more rapidly than under tensile loading. The phenolic composite, despite having high flame resistance, loses strength more rapidly and fails sooner than a more flammable vinyl ester composite. The study shows that greater flammability resistance does not necessarily result in better structural performance in fire. The poor structural performance of the phenolic composite was due to explosive delamination damage and cracking caused by vaporisation of water in the matrix phase. It is shown that removing water from phenolic composites by natural or artificial ageing reduces the incidence of delamination cracking and thereby improves the materials' structural performance in fire. It is concluded that phenolic composites do not provide good structural performance in fire, even though they have low flame and smoke properties. However, reducing the water content in the matrix phase below about 10% can greatly improve the structural performance of phenolic composites during fire.