Multi-Web Timber-Based Beams Filled with Injected Polyurethane

Abstract

This paper describes a study on the effects of injected polyurethane foam on the structural performance and durability of ply-webbed composite timber beams. The beams comprised timber or LVL flanges with 9mm thick three-ply plywood webs. Profiles considered included Double-I, Box, recess, Boxed-I and Boxed double-I, beams in 2.10m and 4.35 m spans with and without polyurethane infill. Structural performance of the empty and filled beams was examined with regard to their bending, shear and bearing capacities. Accelerated ageing methods were also employed to study the long-term durability of the beams. For example, Box beams of 2.10m span were exposed successively to different 'weathering' conditions in hot water, in a steam room, in a freezer and in a drying kiln. This cycle was repeated six times and at each stage the apparent modulus of elasticity and the maximum shear strength of the beams were measured. It was found that the infill material enhanced the bearing capacity of the beams by up to 23% and enhanced the beam stiffness by up to 7%, but the infill had an insignificant effect on beam bending capacities. Exposing the beams to the severe weathering conditions did not caused any delamination; however the effects of the cyclic procedure were more severe on unfilled beams, reducing bending capacity by 20%, in comparison to the filled ones.