Structural Fire Safety Design Research Articles

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.

Experimental study of the mechanical properties of light gauge cold-formed steels at elevated temperatures

In recent times, light gauge cold-formed steel sections have been used extensively as primary load-bearing structural members in many applications in the building industry. Fire safety design of structures using such sections has, therefore, become more important. Deterioration of mechanical properties of yield stress and elasticity modulus is considered the most important factor affecting the performance of steel structures in fires. Hence, there is a need to fully understand the mechanical properties of light gauge cold-formed steels at elevated temperatures. A research project based on experimental studies was, therefore, undertaken to investigate the deterioration of mechanical properties of light gauge cold-formed steels. Tensile coupon tests were undertaken to determine the mechanical properties of these steels made of both low- and high-strength steels and thicknesses of 0.60, 0.80 and 0.95 mm at temperatures ranging from 20 to 800 °C. Test results showed that the currently available reduction factors are unsafe to use in the fire safety design of cold-formed steel structures. Therefore, new predictive equations were developed for the mechanical properties of yield strength and elasticity modulus at elevated temperatures. This paper presents the details of the experimental study, and the results including the developed equations. It also includes details of a stress–strain model for light gauge cold-formed steels at elevated temperatures.

Review of post-earthquake fire hazard to building structures

Fire following an earthquake is an important factor causing damage to buildings and life-line structures. Therefore, besides satisfying structural design requirements for normal loads, such as dead and live loads including the seismic hazard, buildings should also be designed to withstand the fire following earthquakes for a certain minimum duration as required for a desired level of performance. This period of time will allow occupants to evacuate the building safely and the emergency crews to cope with the fire. Also, it is essential to reduce the post-earthquake fire (PEF) ignitions and minimize the damage to active fire protection systems as much as possible to prevent the spread of fire. This paper presents a state-of-the-art review on the PEF hazard and discusses the causes, mitigation measures, and performance of building structures under this hazard. Mitigation measures that could be developed based on the experience from the structural engineering field are identified. Both local and global approaches that should be taken to mitigate the PEF hazard, including structural and nonstructural design, various urban planning aspects, and their interactive combinations, are discussed. Based on the review, it is concluded that that there is a strong need for the development of guidelines for structural fire safety design for PEF scenarios. In addition, appropriate analysis and numerical simulation techniques for the evaluation of the structural performance under earthquake-induced fire conditions need to be developed. It is also necessary to conduct experimental studies to validate such numerical models and refine them.

On the Chinese Code on fire safety design of steel building structures

This work introduces to the international scientific community the Chinese Code on fire safety design of steel building structures. The aim of the Code is to prevent the structure of a steel building subjected to fire from collapsing, ensure safe evacuation of building occupants, and reduce the cost for repairing the damages of the structure caused by fire. The main contents of the Code is presented in this paper, including the fire duration requirements of structural components, fundamental requirements on fire safety design of steel components, temperature increasing of atmosphere and components in fire, loading effect and capacity of various components in fire, and procedure for fire-resistant design of steel components. The analytical approach is employed in the Code and the effectiveness of the Code is validated through experiments.

Assessment Of Performance-based Requirements For Structural Design

The paper presents how actions can be assessed for a performance-based structural fire safety design from the first formulations in the building program to the final derivations of the fire load to be applied for each structural member. In order to indicate what is of importance for the assessment of the requirements, a couple of simple analyses of structural response are made. The examples are chosen deliberately to show the difference between a traditional design based on standard fire resistance and a performance-based approach. A methodology is developed for a decision on the safety level and for a detailed assessment of the requirements. The design requirements to be used for a factory producing elements for industrial housing for unknown costumers are discussed, and a fully developed fire is recommended as a common requirement for domestic houses, hotels, offices, schools and hospitals. In addition it is shown how a fire brigade can be expected to perform in a building designed by means of the methodology. It has been the aim to give a simple and clear presentation and several simplifying concepts are introduced, because it has been experienced that this subject has led to many misunderstandings, and simplicity is needed if the methods presented should be operational.

Fire Resistance of Light-framed Wood Floors Exposed to Real and Standard Fire

A performance-based design method related to fire safety should begin at the stage of fire resistance evaluation using the fire severity to assess the fire risk of any structures. This study developed a new model to predict the fire growth behavior in a real compartment and to provide an alternative to the existing standard fire in terms of fire safety design. This method could provide a quick evaluation of natural fire curves for use in structural fire safety design. In addition, heat transfer through light-framed wood floor was modeled using the temperatures provided from fire growth model as the input values, which predicted the time-dependent temperature distributions at a certain time step. The time-dependent temperature distributions were converted into the distributions of mechanical properties within the structural elements by employing the relationship between temperature and the mechanical properties, which were then transformed into sections with the strength and stiffness at a particular ambient temperature. The fire growth model and heat transfer model were verified using full-scale compartment fire tests.

Performance Based Fire Safety Design of Structures — A Multi-Dimensional Integration

Design codes for fire safety in buildings can be either a prescriptive type or performance-based type. It is now widely recognized that performance-based codes provide greater advantages over the prescriptive codes in that it allows designers to use the fire engineering methods to assess the fire safety of the structure. However, as the assessment of the whole structure performance is not easy, most codes currently used are still prescriptive codes or a combination of prescriptive codes and performance-based codes. The key feature for implementing the performance-based fire design codes is the assessment of the fire resistance of the structure. This paper provides an overall view on performance-based code and the approaches for designing steel structure in fire considering a multi-dimensional integration of fire engineering simulation, emergency evacuation and structural resistance. Various fire models and heat transfer analysis methods are reviewed and discussed. The basis to modelling of large deflection and plasticity using appropriate stress-strain relationship at elevated temperature is explained. Finally, structural response calculations from simplified hand calculation method to advanced numerical procedures are presented. Future trends for research are identified.

Experimental Flame Heat Transfer Correlations For A Steel Column Adjacent To And Surrounded By A Pool Fire

Heat flux and temperature measurements were conducted on a square steel column adjacent to and surrounded by fire sources from the interest in the application to the structural fire safety design of metal structures. The tests on the adjacent fires demonstrate a description of the heat flux profile along the column surface as a single function of the height normalized by flame height for each column-fire distance and notable decrease of surface heat flux by the increase of the column-source distance. Surface temperature of the column in this configuration was found to be notably lower than the estimate from heat flux data based on the uniform heating assumption, which suggests the significance of the conductive heat loss to unheated surfaces of the column. The tests on the surrounding fires has resulted in heat flux profile weakly dependent on heat release rate and coincidence of the measured surface temperature and its estimate from heat flux due to rather even heat flux on all surfaces of the column.

Cib-concept For Probability Based Structural Fire Safety Design

In most countries, the verification of the fire protection requirements gets much more attention than the requirements themselves. It is felt that this renders to a heavily unbalanced fire safety design. In view of this discrepancy, it has been decided within the Fire Commission of the Conseil International du Biltiment (CIB-WI4) to prepare a design concept which covers both afore mentioned aspects in an integrated way and which may serve as a framework for national design guides in this field.