Experimental study of cold-formed steel floors made of hollow flange channel section joists under fire conditions

Fire safety plays a vital role in building design because appropriate level of fire safety is important to safeguard lives and property. Cold-formed steel channel sections along with fire-resistive plasterboards are used to construct light-gauge steel frame (LSF) floor systems to provide adequate fire resistance ratings (FRR). It is common practice to use lipped channel sections (LCS) as joists in LSF floor systems, and past research has only considered such systems. This research focuses on adopting improved joist sections such as hollow flange channel (HFC) sections to improve the structural performance and FRR of cold-formed LSF floor systems under standard fire conditions. The structural and thermal performances of LSF floor systems made of a welded HFC, LiteSteel Beams (LSB), with different plasterboard and insulation configurations, were investigated using four full-scale fire tests under standard fires. These fire tests showed that the new LSF floor system with LSB joists improved the FRR in comparison to that of conventional LCS joists. Fire tests have provided valuable structural and thermal performance data of tested floor systems that included time-temperature profiles and failure times, temperatures, and modes. This paper presents the details of the fire tests conducted in this study and their results along with some important findings.

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.

Numerical studies of gypsum plasterboard and MGO board lined LSF walls exposed to fire

Fire resistance of cold-formed light gauge steel frame (LSF) wall systems is enhanced by lining them with single or multiple layers of wall boards with varying thermal properties. These wall boards are gypsum plasterboards or Magnesium Oxide (MgO) boards produced by different manufacturers. Thermal properties of these boards appear to show considerable variations and this can lead to varying fire resistance levels (FRL) for their wall systems. Currently FRLs of wall systems are determined using full scale fire tests, but they are time consuming and expensive. Recent research studies on the fire performance of LSF wall systems have used finite element studies to overcome this problem, but they were developed based on 1-D and 2-D finite element platform capable of performing either heat transfer or structural analysis separately. Hence in this research a 3-D finite element model was developed first for LSF walls lined with gypsum plasterboard and cavity insulation materials. Accurate thermal properties of these boards are essential for finite element modelling, and thus they were measured at both ambient and elevated temperatures. This experimental study included specific heat, relative density and thermal conductivity of boards. The developed 3-D finite element model was then validated using the available fire tests results of LSF walls lined with gypsum plasterboard, and is being used to investigate the fire performance of different LSF wall configurations. The tested MgO board exhibited significant variations in their thermal properties in comparison to gypsum plasterboards with about 50% loss of its initial mass at about 500 ºC compared to 16% for gypsum plasterboards. Hence the FRL of MgO board lined LSF wall systems is likely to be significantly reduced. This paper presents the details of this research study on the fire performance of LSF wall systems lined with gypsum plasterboard and MgO board including the developed 3-D finite element models, thermal property tests and the results.