Study of Skewness Angle in Reinforced Concrete Girder Bridges

Mohan Lal, Vedpal , Ravinder Kumar

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 there. 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. In this paper an attempt has been made to study the effect of skewness directly on the design parameters i.e. B.M, Shear Force and Maximum Reaction in simply supported RC T-Beam 3 lane bridges. For this purpose a parametric study of Simply Supported 3-Lane T-Beam 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. Live Load “Class 70R Tracked “and “Class 70R Wheeled” were applied as per IRC 6 guidelines. The spans used were 10 m, 15 m, 20 m and 25 m. The skew angles were taken at an interval of 150 starting from 0⁰ up to a maximum of 60⁰. Bridges with skew angle more than 45 ⁰ are rare.From the study it was observed that as the skew angle increases from 0⁰ to 60⁰there is a consistent reduction in Moment Distribution Factor (MDF) of the inner longitudinal girder of bridge. Similar trend of reduction in MDF were observed for other spans. This suggests that skew bridges designed, ignoring the skew effect is conservative with respect to the bending moment. The effect of skew angle was also studied on the shear coefficients. The shear coefficients as increases almost linearly with skew angle and span. Hence it can be concluded that proper estimation should be made in the live load shear when designing skew bridges.