Investigation into the fire and racking behaviour of structural sandwich panel walls : a methodology to assess load bearing sandwich panels in fire

The aim of this investigation is to evaluate the fire and racking behaviour of loadbearing lightweight sandwich wall assemblies. Structural sandwich walls are innovative building units, which due to their composite build-up combine low weight, high loadbearing ability and excellent insulation qualities. The wall panels are composite sections of threelayered construction, in which stiff, thin facings are bonded to both sides of a low-density core substrate. The work has developed a methodology in which fire testing in three-scales is used to model the fire damage and its effect on both fire and structural performance of the structural wall systems. The fire performance evaluation was undertaken using bench, intermediate and full-scale tests, enabling the parametric study into the influence of material and panel composition to wall performance. The methodology links the results of the different fire tests to determine critical failure and behaviour patterns within the building system, also covering different end-use conditions, to model the progressive fire damage in sandwich walls. Based on the findings an analytical model was developed to predict the fire resistance of structural sandwich walls. The performance of sandwich walls was found to be governed by the degradation behaviour of the exposed panel layers and since the smaller scaled testing exhibited the critical design factor to the fire resistance of structural sandwich walls, the need for full-scale testing was reduced. Minor changes to the sandwich wall composition are suggested to be evaluated using the analytical model and/ or minimal bench-scale testing, also allowing the assessment of wall performance in a range of fire scenarios. To further enhance the versatility of the methodology an analytical FDM procedure for predicting the heat build-up in the layered wall unit has been assessed. Whilst the technique was found to provide an easy and reliable tool, the lack of detailed material properties in their various degradation stages made meaningful correlation to test results difficult. The second area of research concentrated on evaluating the racking behaviour of the composite walls and examined the current Code of Practice (BS EN 594 and BS EN 5268: 6.1) for use with structural sandwich wall assemblies. Whilst the testing method was found to be adequate, the modification factors employed to adopt the test results to different wall configurations were only partially applicable. The work examined the principal differences between timber frame and sandwich wall constructions and found the horizontal rail configuration to be the overriding influencing factor in the racking behaviour of sandwich walls. The vertical load performance of the wall was affected in particular and to account for the differences in behaviour, changes to the design Code for use with structural sandwich walls are proposed; further testing is needed to endorse exact modification factors.

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