Effect of skew angle on longitudinal girder (support shear, moment, torsion) and deck slab of an IRC skew bridge

The behaviour of an RC simply supported bridge was studied by increasing the skew angle. The parameters investigated were section forces such as support shear, longitudinal, lateral and torsional moments of longitudinal girders and deflection and stresses of slab. Results show that the skew angle increase results in increasing the support shear of the obtuse longitudinal girder and decreasing that of the acute longitudinal girder. Although the changes are insignificant for inclusion in the design up to 20° skew, but at higher skew angles the increase is considerable (25% increase for 45° skew). These changes must be taken into account for correctly designing an obtuse girder. Similarly, the mid-span longitudinal moment steadily increases with increasing skew angle for obtuse angled girder and decreases for the acute angled one. The changes are again insignificant up to 30° skew, beyond that the mid-span longitudinal moments of the obtuse girders changes notably, nearly doubles at 50° increasing further up to 65o. Again, for a skew angle above 30°, the design considerations must include these modifications for flexural adequacy of the longitudinal girders. Also, the mid-span lateral moments of the longitudinal girders, both obtuse and acute, register a reduction with increasing skew angle. These reductions are relatively small (from 0 to 65o) for Acute angled Girder, whereas they are appreciable for obtuse angled girder (15% and 35% respectively, from 0 to 65o). These changes can be taken into consideration for economic section design, provided the other factors permit such modification. Most importantly, with the increasing skew angle, torsional moments rise rapidly in obtuse angled girders. This aspect is generally not considered during the design of right bridges. Torsional moments in the obtuse girder increases by 50% for 0 to 20° skew. Further, obtuse angled girder registers a voluminous growth in its torsional moments, tripling itself for 0 to 65° skew. Since torsion is not generally considered for the design of a straight bridge, this factor alone can contribute significantly to the structural failure of a skew bridge designed as a straight one. For the slab, asymmetric bending is observed with increasing deflection at obtuse corner and decreasing deflection at the acute corner with increasing skew angle. For the slab, it has been observed that with the increasing skew angle, the symmetric deflection profile of the right slab disappears and deflection of the obtuse corner increases but deflection of acute corner reduces significantly, giving rise to a warped deck. Also, the direct vertical and shear stress of the acute corner of the slab becomes nearly zero at 65° skew, strengthening the possibility of uplift at higher skew angle and giving rise to an S-shaped deflection profile of the deck.