I'm designing a transverse floorbeam for a 6 lane typical section bridge. The floorbeam supports longitudinal stringers which in turn support the concrete deck. The floorbeam is supported at it's 1/3 points thus creating cantilevered ends. The maximum positve stress at mid-floorbeam is caused by the two interior lanes loaded and the maximum negative stress at mid-floorbeam is caused by the two exterior lanes loaded. AASHTO allows a 25% lane load eduction when 4 or more lanes produce maximum stresses. Does this apply here even though the stress range is caused by 4 consecutive, rather than simultaneous lanes loaded? Bottom line, due to the odd geometry, the beam is about 100% overdesigned for strength, but exceeds the allowble fatigue range.
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