INFLUENCE OF SKEW ANGLE ON LIVE LOAD DISTRIBUTION IN AN I-BEAM COMPOSITE BRIDGE

Bridges constructed on Skew alignment have the most complex behavior. In this study bridges with skew angles of 45 and 63.4 degrees were analyzed under the loading models of 1994 AASHTO code, keeping all other parameters same as those of corresponding right bridges. Whenever a skew is introduced, the bridge (specially bridge deck) behaves as a much stiffer unit relative to its right counterpart, bridge deck tries to bend perpendicular to the skew abutment in the short diagonal direction. Also, part of a loaded lane gets closer to the support, and these features of skew bridge reduces the composite moment of critical interior and exterior girders, i.e. Mcg-skew/Mcg-right . is less than one. Generally, the reduction in composite moment of all the girders in a skew bridge relative to a right bridge, is primarily, due to the fact that part of the loading model gets closer to the supports of a skew bridge. This forces the slab to transmit the loads directly to the abutments, rather than through supporting girders. This observation is substantiated by the fact, that sum of LLF of all the girders in skew bridge is less than one, whereas, this sum of LLF for all the girders in a corresponding right bridge is always equal to one, suggesting that all the LL on skew bridge is not transferred by girders. It should also be noted that, when skew is introduced to a bridge the volume of slab increases as the c/c of girder spacing, b, of a right bridge increases to b/Cos(α) in a skew bridge with an angle of skew equal to α. This increase in volume of a slab increases the stiffness of a bridge structure as a whole, which decreases the deflections and girders composite moments.