Comparative Study on the Structural Behavior of RCC and Steel Skew Bridges with Increasing Skew Angles

Abstract

Skew bridges are widely adopted in highway and railway projects where roads, rivers, or rail tracks intersect at oblique angles, making conventional right-angle bridge construction impractical. The structural behavior of skew bridges is significantly influenced by skew angle, resulting in complex load distribution, increased torsional effects, and non-uniform support reactions. This study presents a comparative analysis and design of Reinforced Cement Concrete (RCC) and Steel skew bridges with skew angles of 30°, 50°, and 70° using the Finite Element Method (FEM) in STAAD.Pro. A bridge model having a 36 m span and 10 m carriageway width was analyzed under IRC 70R moving load, including dead, live, impact, and wind load combinations. Structural responses such as bending moment, shear force, torsional moment, deflection, and support reactions were evaluated and compared. The results indicate that increasing the skew angle significantly alters bridge behavior. RCC bridges perform efficiently and economically at lower skew angles, whereas Steel bridges exhibit superior structural performance at higher skew angles due to reduced bending, torsion, and deflection. The study provides practical recommendations for selecting suitable bridge materials based on skew angle, structural efficiency, serviceability, and overall design performance.

Introduction

Bridges are essential transportation structures that provide connectivity across natural and man-made obstacles. In many modern infrastructure projects, roads and railways intersect at oblique angles, making skew bridges an effective solution. Unlike straight bridges, skew bridges have supports that are not perpendicular to the bridge deck, resulting in complex structural behavior such as uneven load distribution, increased torsional effects, non-uniform support reactions, and shifted maximum deflections. These complexities require advanced analytical methods for safe and economical design.

This study presents a comparative analysis of Reinforced Cement Concrete (RCC) and Steel skew bridges with skew angles of 30°, 50°, and 70° using the Finite Element Method (FEM) in STAAD.Pro CONNECT Edition. A bridge with a 36 m span and 10 m carriageway width was analyzed under IRC 70R moving load, along with dead, live, impact, and wind loads, following relevant Indian Roads Congress (IRC) standards.

The research identifies key challenges in skew bridge design, including the effects of increasing skew angle on bending moments, shear forces, torsional moments, deflections, and support reactions. While RCC bridges are economical, durable, and suitable for small- to medium-span bridges, their higher self-weight reduces efficiency at larger skew angles. In contrast, steel bridges offer a superior strength-to-weight ratio, better torsional resistance, and improved performance under complex loading, although they involve higher construction and maintenance costs.

The literature review indicates that increasing skew angles generally increase torsional effects and alter load distribution, making conventional straight-bridge design methods inadequate. Previous studies recommend detailed finite element analysis for accurate prediction of bridge behavior and emphasize that moderate skew angles improve performance while larger angles require careful design.

The proposed methodology develops identical RCC and steel bridge models, applies standard IRC load combinations, and compares structural responses including bending moment, shear force, torsional moment, deflection, and support reactions. Material properties are assigned according to Indian Standards (M40 concrete, Fe500 reinforcement, and Fe345 structural steel), ensuring realistic modeling and fair comparison.

Conclusion

From the comparative analysis, it is concluded that RCC skew bridges are suitable for 30° skew angle due to their economical construction and satisfactory structural performance. However, as the skew angle increases to 50° and 70°, Steel skew bridges perform significantly better by exhibiting lower bending moment (214.07 kN-m), shear force (15.71 kN), torsion (59.82–64.23 kN-m), and deflection (909–990 mm) compared to RCC bridges. Therefore, RCC bridges are recommended for low skew angles, whereas Steel bridges are recommended for medium and high skew angles because of their superior strength, stiffness, and serviceability. 1. Development of FEM Models : Finite element models of RCC and Steel skew bridges were successfully developed and analysed under standard loading conditions. 2. Effect of Skew Angle : The study confirmed that increasing the skew angle from 30° to 70° significantly influences the structural behaviour and load distribution of the bridge. 3. Structural Parameters : Bending moment, shear force, torsional moment, and deflection were successfully evaluated, showing noticeable variation with increasing skew angle. 4. Comparison of RCC and Steel Bridges : Steel skew bridges exhibited better structural performance than RCC bridges under identical loading conditions, particularly at higher skew angles. 5. Suitability Assessment : RCC bridges were found suitable and economical for 30° skew angle, whereas Steel bridges provided better load-carrying capacity, serviceability, and structural efficiency at 50° and 70°. 6. Final Recommendation : Based on the analytical results, RCC bridges are recommended for low skew angles (30°), while Steel skew bridges are recommended for medium and high skew angles (50°–70°) due to their superior overall performance.

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Copyright

Copyright © 2026 Mohammad Nadim Iqbal Sheikh, Shilpa Samrutwar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.