Dynamic amplification factor for the design of reinforcement in the transverse direction of deck slab of box girder bridges

Abstract

This thesis studies the dynamic responses of moving vehicle loads. This response is measured for both transverse stresses and deformations in the cantilever slab adjacent to the main deck of concrete highway bridges. The whole analytical process regarding this investigation is based on finite element analysis. A finite element model to analyze the cantilever three-span box girder bridge has been developed using shell element. A vehicle is simulated according to the HS20-44 truck design loading contained in the AASHTO specifications and vehicle load is applied at various points on the vehicle path. A step by step full transient dynamic analysis has been performed. Parameters like vehicle speed, span length, width of the cantilever part and damping condition are included in the investigation with a systematic approach. Span length variation is done with appropriate slab thickness and deck height for being realistic practice. Dynamic amplification factors (DAF) are evaluated at various points along the middle span of the bridge. From the numerical results, it has been found that dynamic amplification factor is critical at the piers rather than mid span or other part of the span. The effects of vehicle speed, span length and cantilever slab width on dynamic amplification factor were significant. But the variation of the DAF with respect to those parameters is rather arbitrary. Again, it was also found that 0% damping caused abnormally high value, whereas, 2.5% and 5% damping gave closely similar values which was more realistic. Based on the overall findings, DAF value for vertical deflections of the cantilever part of deck slab is recommended as 1.7 near pier and 1.64 near midspan i.e. recommending 70% and 64% impact increment near pier and midspan over static results calculated for deflections. Again, for stresses in the transverse direction DAF value is suggested as 1.91 near pier and 1.78 near midspan i.e. recommending 91% and 78% impact increment near pier and midspan over static results calculated for stresses.