Thermal and structural performance of GRP panels and short columns under fire conditions

Abstract

This paper presents the results of an experimental study of the behaviour of different types of GRP structures under fire conditions. The experiments were conducted in two stages. The first part is concerned with the thermal performance of GRP sandwich panels and stringer systems when exposed to fire on one side. The objective of this study is to provide experimental information of temperature developments in GRP structures in fire. The products examined in this investigation include: glass reinforced phenolic laminate sheets, lightweight phenolic foams, sandwich panels made from GRP sheets and phenolic foams, sandwich panels made from plasterboards and phenolic foams, stringer systems made from GRP sheets and pultruded GRP channels insulated with mineral wool and stringer systems made from plaster boards and pultruded GRP channels with mineral wool. For comparison, fire tests were also carried out on conventional steel stud systems consisting of plasterboards and cold-formed-thin-walled steel channel sections insulated with mineral wool. In all these tests, the core materials were 100 mm thick. Plasterboards were 12.5 mm thick and the GRP sheets were 3 mm thick. Fire exposure was according to the standard BS: 476 Part 20 – Cellulosic fire temperature–time relationship. The second part gives results of compressive tests on pultruded short GRP channel sections at elevated temperatures to evaluate their residual strength in fire. The objectives of these tests are to assess the feasibility of using GRP based products as wall construction in low storey buildings such as accommodation units and also to provide experimental data for the calibration of numerical models of heat transfer and structural analysis. Results of these tests indicate that the low-density phenolic foam used in this study was involved in burning very early in the fire test and would not be suitable for fire resistant construction. Initially the fire exposed thin GRP sheet could not provide as much insulation as the plasterboard, however, the GRP sheet prevented direct heating of the core material and was able to reduce the core material temperatures considerably. At 30 min of the standard fire exposure, temperatures in large parts of the GRP stringer systems were less than 100 C. For compressive tests, pultruded channel sections 100 x 30 x 4 mm by 400 mm long were heated in an electric kiln furnace to different levels of temperature and then loaded to failure in compression in a specially constructed loading facility. The test temperatures were 20, 60, 90, 120, 150, 200 and 250°C. The results of these tests indicate that GRP materials lose their strength and stiffness at relatively low temperatures, however, due to their low thermal conductivity, temperatures in large parts of the pultruded GRP channel sections were very low (less than 100°C) enabling them to carry some loads (up to 70%) under fire conditions.