THEORETICAL STUDY ON THE IMPACT FACTOR OF CRESCENT-SHAPED MULTI-RIB CONCRETE FILLED STEELTUBE TRUSS ARCH BRIDGES

Crescent-shaped multi-rib concrete filled steel tube truss arch bridges have attractive figures but complex structural types.The impact factors of arch rib,main girder deflection and cable tension were investigated in this paper.The reasons causing impact effect considered in this paper involves road surface roughness,vehicle speed,and the damping ratio of the structure.The following conclusions can be drawn according to analyzing results:(1)Impact factors of bridges will be reduced by smoothing road surface.(2)The effect of vehicle speed on impact factors is related with the primary modes inducing the response,and hence increasing vehicle speed may not increase impact factors.(3)The maximum impact factor is associated with the vehicle speed of 60 km/h.(4)Impact factors for different components and sections are quite different,although vehicle travels under the same condition.(5)Impact factors of arch rib deflection in mid-span are obviously larger than that in the 1/4 span.(6)For girders,the deflection impact factors between mid-span and 1/4 span are close.(7) Impact factors of tension in short cables at the end of the span are larger than that of long ones at the mid-span.(8) Damping ratio of structure does not affect impact factors significantly.