Sequentially coupled structural modelling of LSF floor-ceiling systems

Fire resistance levels provide a standardised measurement of building elements' fire resistance under structural, integrity and insulation criteria, and are usually obtained from standard full-scale fire tests. However, these tests consume excessive time and money and thus the use of validated advanced numerical models is preferred. This paper presents the details of a sequentially coupled structural modelling study of LSF floor-ceilings made of Lipped Channel beam (LCB) and rivet fastened Rectangular Hollow Flange Channel beam (RHFCB) section joists used in eight different floor-ceiling configurations, and its results. Ambient temperature structural finite element (FE) models of LCB and RHFCB joists were developed first and validated using experimental results. Full scale fire test results of LCB floor system were then used to validate a structural FE model developed and analysed using a sequentially coupled approach utilising the time-temperature profiles from the same fire test. Finally, using the validated sequentially coupled structural FE models, the effects of a range of influential parameters such as joist types and floor-ceiling configurations were investigated. The results of structural fire resistance/failure times versus load ratio showed that the new RHFCB joists gave only minor improvements, however, they provided superior load bearing capacities. Fire resistance improved significantly when more gypsum plasterboard layers were used. The use of thin steel sheathing also improved the failure times, and is recommended as the fire exposed layer due its ability prevent plasterboard fall-off. Finally, suitable critical mid-web temperatures are proposed for predicting the structural fire resistance times of LSF floor-ceiling systems