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Experimental study of a bolt-bushing connection system for structural composite lumber

University of British Columbia

The results of an experimental study are presented on the use of polyurethane lined bushings in bolted connections of structural composite lumber. Monotonic tension tests and cyclic axial tests were performed on 80 specimens of varying dimensions made with Douglas Fir parallel strand lumber. All the connections were made with a single fastener, which consisted of a 12 mm bolt, with or without bushing. The bushings consisted of an inner and outer steel ring with a mouldable polyurethane filling. Varying diameters and steel ring thicknesses were tested. To prevent brittle splitting failures of the connections, the end distance was varied and transverse reinforcement of the wood with threaded dowels was introduced. Material tests were conducted on the structural composite lumber and the polyurethane filling. The introduction of a polyurethane bushing in a single fastener connection served to increase the ductility of the connection under tension loading. A high degree of variability in capacity and ductility were observed, however, which can be attributed to a lack of filler material consistency in the fabrication process. Significant improvements in ductility and resistance were achieved when transversely placed treaded dowels were introduced as reinforcing elements of the structural composite lumber. This effect was most pronounced for connections with bolts only. For the connections with bushings, splitting failures still prevailed and a need for more elaborate reinforcements was identified. In the absence of reinforcing elements, it was found that the end distance of connectors has to be increased when bushings of a diameter larger than the bolt were introduced. The cyclic behaviour of bushing connectors showed hysteresis loops with a significant amount of degradation under repeated cycles. Although cyclic compression tests on polyurethane cylinders exhibited stable hysteretic behaviour with significant energy absorption, the high deformation demand of the material in the bushings showed that a more suitable material needs to be found for application in bushing connections that are subjected to severe earthquake motions. The results from this study provide important information on the behaviour of polyurethane bushing connections and paves the way for refinements of innovative connection techniques that are suitable for structures in high risk seismic zones.

Thesis/Dissertation

application/pdf

2009-04-29

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http://hdl.handle.net/2429/7684

Civil Engineering

University of British Columbia

UBCV

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