Rating of constructed timber bridges repaired with steel beams

This paper presents load ratings for timber bridges repaired with hollow steel sections (HSS) made of ASTM A500C. Two bridges are selected (F -22-V and H -20-T built in 1938 and 1935, respectively) and upgraded with HSS steel beams. A field test is conducted with a known-weight truck of 267 kN and responses are recorded. For numerical analysis, finite element models are formulated and validated. The model is then employed to investigate the behavior of the bridges under 17 live loads specified in the manual of a transportation agency. A mechanics-based rating approach is proposed to holistically rate these bridges before and after the repair. The configuration and position of the live loads affect the bending moment and shear force of the bridges; especially, the spacing of axles plays a role in increasing deflections. The capacity of the girders with the steel beams is as high as 2.56 times that of the control girders. Likewise, the allowable stress of the timber is improved by a factor of 1.39 and 2.09 for flexure and shear, respectively. The effectiveness of the repair becomes pronounced when the deterioration level of the timber girders rises, and the geometric properties of the steel beams are a crucial consideration that alters the rating of the repaired girders. The placement of grouped steel beams is recommended to raise the efficacy of the repair system. Owing to the repair, the failure probability of the bridges is reduced by up to 99.2%.