Fire resistance of FRP reinforced glulam beams

Thin laminates made of high-strength pultruded fiber reinforced polymers (FRP) are increasingly being used to reinforce glue-laminated timber (glulam) beams, creating a new composite glulam (FRP glulam) significantly stronger in bending than a conventional (unreinforced) glulam of equal size. Large timber members have long been recognized for maintaining structural integrity in fires and this paper presents the results from a test program to determine the performance of FRP glulam beams subjected to standard ASTM E 119 fire exposure. A total of 30 full size glulam beams were tested, of which 26 were reinforced with FRP, of varying type and placement, and 4 were conventional glulams. The test results indicate that the observed time to failure of FRP glulams 79.4-mm (3.125-in.) wide or less is approximately half that predicted using the current code accepted methods for conventional wood members. For beams of equal crosssectional size, the design bending strength of the FRP glulam is about twice that of the conventional glulam. Thus it can be inferred that the FRP used in this test program has relatively little fire resistance, and the fire resistance of the FRP glulam can be attributed to the beam’s gross cross section of wood. Empirical adjustment factors are presented to permit fire endurance calculations for FRP reinforced glulams using conventional methods. INTRODUCTION In the past decade high-strength fiber reinforced polymer (FRP) laminates have been used to reinforce glue-laminated timber (glulam) members, primarily beams, and the resulting FRP-wood composite member (FRP glulam) is significantly stronger in bending than a conventional (unreinforced) glulam of equal size. The FRP laminates are composed of tensioned high-strength pultruded synthetic fibers embedded in a polymer matrix, resulting in a thin FRP panel of appropriate width and length suited for glulam manufacture using traditional gluing and clamping procedures. These panels are sold by FiRP Sales, Inc. and marketed under the trade name FiRP Reinforcement. In the past few years, a variety of structures have been built worldwide (Asia, Europe and North America) using FRP glulams. Prior to a code approved design method (ICBO ER-5100) and subsequent commercialization of FRP glulams, an extensive research program was conducted which involved testing and manufacture of more than 1,000 full-scale beams (Tingley, 1994; 1996), component tests (Tingley et al, 1997), adhesion tests, and fire resistance tests of full scale FRP glulams. The focus of this paper is on the fire performance of FRP glulams. Large timber members have long been recognized for maintaining structural integrity in fires, due to the charring characteristics of wood. A test program has been conducted to determine the performance of FRP glulam beams subjected to standard fire exposure, ASTM E 199-88 (1993), at loads equal to or greater than design loads. A total of 30 full size glulam beams were tested, of which 26 were reinforced with FRP and 4 were conventional specimens. Several different reinforcement configurations were examined, such as: three different FRP laminate types [aramid (ARP), carbon-aramid (CARP) and glass-aramid (GARP)], the effects of external and internal placement of the FRP laminates, as well as single beam members and assembled beam systems. The effect of a fire proof coating was also investigated. Actual time to failures were recorded and compared to calculated values using conventional code accepted fire endurance equations. From this test program, empirical adjustment factors can be calculated to permit accurate fire endurance predictions for FRP reinforced glulams using current conventional methods.