Cyclic response of a stress-laminated timber arch bridge

Stress-laminated timber (SLT) arch bridges combine the environmental friendliness and cost effectivity of timber with the arch shape to allow longer spans than with traditional SLT flat deck bridges. Up to now, only pedestrian bridges have been realised using this system. To extend now the use of SLT arch bridges to road bridges in forestry and rural areas, this research project studied their cyclic behaviour under heavy vehicle loads. A full scale 8m span, 1m rise and 1m wide SLT arch was built using UK-grown Douglas fir and tested in the laboratory. First a 60kN and then a 80kN concentrated cyclic load was applied at midspan of the arch and in total 96x10³ load cycles have been carried out. From the recorded maximum deformation at midspan, linear models for the estimation of the residual deformation of the arch under high number of load cycles has been determined. The tests showed that after a service life of 50 years, the estimated residual deformation at midspan of the SLT arch is in the worst case about 8.3mm and therefore acceptable. SLT arch bridges suit therefore well as economical and sustainable solution for bridges on forestry roads.