Effectiveness of lag Bolts, CFRP, and HSS in retrofitting salvaged timber girders

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This paper presents the effectiveness of various retrofit techniques in improving the flexural behavior of structural timber. For realistic representation with regard to site application, timber girders are salvaged from a decommissioned highway bridge that has been in service over several decades and are strengthened using lag bolts, carbon fiber reinforced polymer (CFRP) sheets, and hollow steel sections (HSS): the retrofitted girders are referred to as Bolt, CFRP, and HSS, respectively. Each category is repeated three times, and the responses of the 12 unstrengthened and strengthened girders are comparatively evaluated. From a load-carrying capacity point of view, lag bolting is not effective. However, CFRP and HSS result in a capacity increase of up to 156.2% relative to the control girder (Cont). Regarding the load–displacement relationship of these girders, the retrofit systems alter the post-peak behavior of the timber. For instance, the lag bolts that are periodically embedded along the specimens bring about pseudo-yield plateaus. The abrupt failure of the Bolt girder is thus precluded. In addition, the amount of dissipated energy increases in all upgraded girders owing to the presence of the retrofit systems. The failure modes of the individual girders are unique, depending upon the type of retrofit. Except for the HSS girder, the effective elastic moduli of the Cont, CFRP, and HSS girders agree with those measured by a stress wave timer. Parameter estimation theoretically infers the possible range of the experimental findings and ensures the adequacy of the test program.