Thermal elongation of sandwich panels Available to Purchase

Sandwich cladding panels with two thin metal faces separated by a lightweight core are well-established cladding products. There have been several instances recently in which the thermal elongation or contraction of sandwich panels has been cited as a possible cause of leakage or local damage in a roof. Historically, the industry has always designed sandwich panels for proper combinations of conventional loading together with a temperature gradient across the panel. This temperature gradient gives rise to ‘thermal bow' which can cause stresses of the same order of magnitude as those from wind or snow load. As a result of this, designers have generally dismissed longitudinal thermal movements from consideration because it is argued that they are taken out by ‘thermal bow' rather than by linear expansion or contraction. Conversely, it is not unusual for roofing and cladding ‘experts' to argue either that thermal bow has little influence on longitudinal thermal movements or that, although it may help in the summer case, it can be of no benefit when the panels try to contract in winter. Surprisingly, there does not appear to have been any previous attempt to determine the actual thermal expansion or contraction of multi-span sandwich panels and appropriate calculation procedures are described for the first time in this study. Perhaps unsurprisingly, it transpires that neither side is correct. Thermal bow results in a significant reduction of longitudinal temperature movements, but it does not eliminate them completely. The formal calculations are not trivial, but it is possible to make a relatively simple estimate of the movements arising in a long panel which has several approximately equal spans.