State-of-the-Art on Composite Cold-formed Steel Flooring Systems

The current study presents a comprehensive review of the state-of-the-art on composite cold-formed steel flooring research over the past couple of years. The most relevant and significant literature references were reviewed to provide some profundity in the trends and development of the composite cold-formed steel floors. Advantages of this type of composite flooring system are also highlighted. A broad description of mainly two types of the composite floors mainly consisting cold-formed steel and concrete, and cold-formed steel and timber-based floorboards have been outlined in this study. The experimental and numerical investigations that have been carried out worldwide is likewise discussed in the paper. The most important aspects covered are shear connection behaviour, flexural and dynamic behaviour of the floors, and a brief description of fire testing

Full scale fire tests of a new light gauge steel floor-ceiling system

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 (LSF) systems are widely accepted in industrial and commercial building construction. An example application is in floor-ceiling systems. Light gauge steel floor-ceiling systems must be designed to serve as fire compartment boundaries and provide adequate fire resistance. Fire-rated floor-ceiling assemblies formed with new materials and construction methodologies have been increasingly used in buildings. However, limited research has been undertaken in the past and hence a thorough understanding of their fire resistance behaviour is not available. Recently a new composite floor-ceiling system has been developed to provide higher fire rating under standard fire conditions. But its increased fire rating could not be determined using the currently available design methods. Therefore a research project was carried out to investigate its structural and fire resistance behaviour under standard fire conditions. In this research project full scale experimental tests of the new LSF floor system based on a composite ceiling unit were undertaken using a gas furnace at the Queensland University of Technology. Both the conventional and the new steel floor-ceiling systems were tested under structural and fire loads. Full scale fire tests provided a good understanding of the fire behaviour of the LSF floor-ceiling systems and confirmed the superior performance of the new composite system. This paper presents the details of this research into the structural and fire behaviour of light gauge steel floor systems protected by the new composite panel, and the results

Improvements to the fire performance of light gauge steel floor systems

Light gauge steel frame (LSF) structures are increasingly used in commercial and residential buildings because of their non-combustibility, dimensional stability and ease of installation. A common application is in floor-ceiling systems. The LSF floor-ceiling systems must be designed to serve as fire compartment boundaries and provide adequate fire resistance. Fire-rated floor-ceiling assemblies have been increasingly used in buildings. However, limited research has been undertaken in the past and hence a thorough understanding of their fire resistance behaviour is not available. Recently a new composite floor-ceiling system has been developed to provide higher fire rating. But its increased fire rating could not be determined using the currently available design methods. Therefore a research project was conducted to investigate its structural and fire resistance behaviour under standard fire conditions. This paper presents the results of full scale experimental investigations into the structural and fire behaviour of the new LSF floor system protected by the composite ceiling unit. Both the conventional and the new floor systems were tested under structural and fire loads. It demonstrates the improvements provided by the new composite panel system in comparison to conventional floor systems. Numerical studies were also undertaken using the finite element program ABAQUS. Measured temperature profiles of floors were used in the numerical analyses and their results were compared with fire test results. Tests and numerical studies provided a good understanding of the fire behaviour of the LSF floor-ceiling systems and confirmed the superior performance of the new composite system

On power minimisation and SNR maximisation of distributed beamforming in cooperative communication systems

A comparison of relay power minimisation subject to received signal-to-noise ratio (SNR) at the receiver and SNR maximisation subject to the total transmitted power of relays for a typical wireless network with distributed beamforming is presented. It is desirable to maximise receiver quality-of-service (QoS) and also to minimise the cost of transmission in terms of power. Hence, these two optimisation problems are very common and have been addressed separately in the literature. It is shown that SNR maximisation subject to power constraint and power minimisation subject to SNR constraint yield the same results for a typical wireless network. It proves that either one of the optimisation approaches is sufficient

Numerical and experimental studies of cold-formed steel floor systems under standard fire conditions

Light gauge cold-formed steel frame (LSF) structures are increasingly used in industrial, commercial and residential buildings because of their non-combustibility, dimensional stability, and ease of installation. A floor-ceiling system is an example of its applications. LSF floor-ceiling systems must be designed to serve as fire compartment boundaries and provide adequate fire resistance. Fire rated floor-ceiling assemblies formed with new materials and construction methodologies have been increasingly used in buildings. However, limited research has been undertaken in the past and hence a thorough understanding of their fire resistance behaviour is not available. Recently a new composite panel in which an external insulation layer is used between two plasterboards has been developed at QUT to provide a higher fire rating to LSF floors under standard fire conditions. But its increased fire rating could not be determined using the currently available design methods. Research on LSF floor systems under fire conditions is relatively recent and the behaviour of floor joists and other components in the systems is not fully understood. The present design methods thus require the use of expensive fire protection materials to protect them from excessive heat increase during a fire. This leads to uneconomical and conservative designs. Fire rating of these floor systems is provided simply by adding more plasterboard sheets to the steel joists and such an approach is totally inefficient. Hence a detailed fire research study was undertaken into the structural and thermal performance of LSF floor systems including those protected by the new composite panel system using full scale fire tests and extensive numerical studies. Experimental study included both the conventional and the new steel floor-ceiling systems under structural and fire loads using a gas furnace designed to deliver heat in accordance with the standard time- temperature curve in AS 1530.4 (SA, 2005). Fire tests included the behavioural and deflection characteristics of LSF floor joists until failure as well as related time-temperature measurements across the section and along the length of all the specimens. Full scale fire tests have shown that the structural and thermal performance of externally insulated LSF floor system was superior than traditional LSF floors with or without cavity insulation. Therefore this research recommends the use of the new composite panel system for cold-formed LSF floor-ceiling systems. The numerical analyses of LSF floor joists were undertaken using the finite element program ABAQUS based on the measured time-temperature profiles obtained from fire tests under both steady state and transient state conditions. Mechanical properties at elevated temperatures were considered based on the equations proposed by Dolamune Kankanamge and Mahendran (2011). Finite element models were calibrated using the full scale test results and used to further provide a detailed understanding of the structural fire behaviour of the LSF floor-ceiling systems. The models also confirmed the superior performance of the new composite panel system. The validated model was then used in a detailed parametric study. Fire tests and the numerical studies showed that plasterboards provided sufficient lateral restraint to LSF floor joists until their failure. Hence only the section moment capacity of LSF floor joists subjected to local buckling effects was considered in this research. To predict the section moment capacity at elevated temperatures, the effective section modulus of joists at ambient temperature is generally considered adequate. However, this research has shown that it leads to considerable over- estimation of the local buckling capacity of joist subject to non-uniform temperature distributions under fire conditions. Therefore new simplified fire design rules were proposed for LSF floor joist to determine the section moment capacity at elevated temperature based on AS/NZS 4600 (SA, 2005), NAS (AISI, 2007) and Eurocode 3 Part 1.3 (ECS, 2006). The accuracy of the proposed fire design rules was verified with finite element analysis results. A spread sheet based design tool was also developed based on these design rules to predict the failure load ratio versus time, moment capacity versus time and temperature for various LSF floor configurations. Idealised time-temperature profiles of LSF floor joists were developed based on fire test measurements. They were used in the detailed parametric study to fully understand the structural and fire behaviour of LSF floor panels. Simple design rules were also proposed to predict both critical average joist temperatures and failure times (fire rating) of LSF floor systems with various floor configurations and structural parameters under any given load ratio. Findings from this research have led to a comprehensive understanding of the structural and fire behaviour of LSF floor systems including those protected by the new composite panel, and simple design methods. These design rules were proposed within the guidelines of the Australian/New Zealand, American and European cold- formed steel structures standard codes of practice. These may also lead to further improvements to fire resistance through suitable modifications to the current composite panel system

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

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 design rules to predict the moment capacities of thin-walled floor joists subject to non-uniform temperature distributions

Thin-walled floor joists in LSF floor panels are protected by gypsum plasterboards and are subjected to a non-uniform temperature distribution across their cross-section in fires. Fire tests have shown that the failure of floor panels was governed by the section moment capacity of joists governed by local buckling effects. This research was aimed at developing simple design rules to predict the failure times (fire resistance) of LSF floors made of lipped channel section joists exposed to standard fires. The use of ambient temperature section modulus led to over-estimation of the moment capacity as the mechanical properties of steel varied across the joist cross-section while deteriorating with increasing joist temperatures in fires. New simplified fire design rules were proposed to determine the section moment capacities of joists at elevated temperatures based on the current cold-formed steel design specifications. Their accuracy was verified using finite element analysis and fire test results