Presently constructed bridges are often skew. The configuration of such a structure is the result of natural or man-made obstacles such as complex intersections, space limitations, and/or mountainous terrains. Gravity loads in many skew bridges take a different path towards the support than right bridges. In skew bridges, this brings about significant torsion moments near the obtuse corner, changes in longitudinal as well as transverse bending moments and changes in support reactions. In this present study, a solid slab bridge deck studied using grillage and finite element method. The effect of different skew angles on same-span of reinforced concrete bridges using the finite-element method and the grillage analogy method is compared. Maximum and Minimum reactions forces, deflections, Bending moments in the central strip and edge strip calculated and compared for both analysis methods. A total of twenty different models prepared, five for each method on skew angles 00, 150, 300, 450 and 600 with rigid supports. The supports then changed to elastomeric bearing supports to compare the change in hogging bending moments. The prototype chosen for comparison is 11m long and 12m wide deck slab without footpath but with edge beam. The slab thickness chosen is 800mm. The longitudinal members aligned along a square direction so that reinforcement can be calculated directly without the need for resolution. The grillage properties are given as per book by E.C. Hambly and FEM elements modelled as per book by G. A. Rombach. It is observed that the finite element method (FEM) and Grillage method yield similar results and in a few cases FEM gives lesser results. Bending moments calculated by using grillage analogy method overestimates the results obtained by the FEM method.

Comparative study of skew slab bridges using Grillage analogy and Finite element method

Skew bridges are built where geometry cannot accommodate straight bridge. The most common and basic type of bridge, that is widely used for roadways is Girder Bridge. The two most common types of girders that are used in practice are beam and Box Girders. Though box girder design is more complicated, it has wide acceptance due to their structural efficiency, aesthetic appearance, better stability and serviceability. Over years simple RCC box girders used for short spans resulted in long span prestressed concrete bridges. The use of pre-stressing enables concrete bridge beams to span long distances. Box girders are constructed in single cell, double cell or multicell. Generally bridge with a skew angle less than 20° is designed as normal bridge. If it is more than 20° there is change in the behavior of the skew bridge. Thus Geometry and behavior of skew bridge are affected by the presence of skew angle. The Structural response of skewed bridge to stresses in slab and reactions on abutments can be significantly altered by the skew angle of the substructure. The objective of present study is to compare normal and skew bridge of box girder type, with parameter such as bending moments, shear forces & torsional moments for two span deck slab by considering IRC CLASS AA TRACKED loading. A simply supported two span, two lane PSC slab bridge deck is considered in the present study. The different bridge spans considered are 50m, 60m and 70 m and skew angle is varied from 0° to 60° at 15° interval. The analysis has been carried out using SAP 2000 software. Keyword: Skew angle, Skew Bridge, FEM analysis, Bending moment, Shear force & Torsional moment.

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Study on Behaviour of Skew PSC Box Girder Bridge

Effect of Skew Angles on Longitudinal Girder and Deck Slab of Prestressed Concrete T Beam Girder Bridges

The study deals with the finite element modeling of simply supported skew slab with varying skew angles using ANSYS software. The behavior of the simply supported skew slab under point load applied at the centre depends on the ratio of short diagonal to its span. Skew slabs with ratio of short diagonal to span less than unity show lifting of acute corners whereas slabs with ratio of short diagonal to span greater than unity do not. Skew slab specimen with ratio of short diagonal to span less than unity is considered here for studying the effect of skew angle on the behavior of skew slab. The dimensions of skew slab were taken from available experimental data. In this paper skew angles varying from 0o to 30o were taken for the study. After the nonlinear finite element analysis of all skew slabs it is revealed that when skew angle increases the uplift at both the acute corners also increases. The result also suggests that the load carrying capacity increases with increase in skew angle.

/pdf/effect-of-skew-angle-on-uplift-and-deflection-of-rcc-skew-4khfsbp22u.pdf

Sabeena Mv

Papers

Effect of skew angle on uplift and deflection of rcc skew slab