STRUCTURAL BEHAVIOUR OF MULTI-LANE SIMPLY SUPPORTED REINFORCED CONCRETE SKEW BRIDGES

Abstract

A very limited study has been carried out in the field of skew bridges and even that does not hold much relevance in Indian perspective due to difference in design live load standards and type of bridges being built here. Therefore it does not provide any help to designers regarding the quick estimation of design bending moments and shear forces which are of prime interest. For this purpose a parametric study of Simply Supported three-lane reinforced concrete T-Girder Bridge has been performed in STAAD PRO. The parameters varied were span and skew angle. The effect of same was observed on maximum live load bending moment, maximum live load shear force and maximum live load reaction at critical locations in terms of Moment Distribution Factor (MDF) and Shear Coefficients. Live Load "Class 70R Tracked", "Class 70R Wheeled" and "Class A" were applied as per IRC 6 guidelines. Also, analysis was carried out for dead load of the superstructure. The spans used were 12 m, 15 m, 18 m and 21 m. The skew angles taken for the analysis were 00, 100, 200, 300 and 450 respectively. Bridges with skew angle more than 450 are rare. From the study it was observed that as the skew angle increases from 0° to 450, there was a consistent reduction in Live load Moment Distribution Factor (MDF) of the longitudinal girders. Similar trend of reduction in MDF were observed for all other spans also. This suggests that skew bridges designed, ignoring the skew effect was conservative with respect to the bending moment. The effect of skew angle was also studied for the shear and reaction. The shear coefficients increase with skew angles and spans. Hence, it can be concluded that proper estimation should be made in the live load shear when designing skew bridges. From the dead load analysis, it was also observed that as the skew angle increases Dead load MDF decreases for inner girders where as it increases for outer girders. Similar pattern of decrease in inner girders and increase in outer girders are observed for shear and reaction coefficient. A comparative study was done for longitudinal girders with and without torsion. From this study it can be concluded that torsion increases with increasing skew angles. So, at smaller skew angle, torsion effect was negligible. However for skew angle more than 20° torsion effect must be considered in design. III