How to Select the Orientation of Wing Wall in the Design of Bridge Abutment?

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A wing wall is a structural member located at the end of a bridge structure. When it is constructed integrally with the abutment, it is termed as cantilever wing wall and when separated from the abutment with expansion or construction joint, it is called an independent wing wall.

The function of the wing wall is to retain the fill that supports the roadway and provide protection against erosion. Wing wall is not a main load-carrying capacity element in a bridge structure, but its size, capacity, and connection to the abutment stem may influence the performance of the entire bridge structure.

The orientation and connection details of the wing wall affect the distribution and magnitude of forces throughout the bridge structure. The orientation of the wing wall may be parallel, perpendicular, or at an angle with the abutment. Each orientation has different impacts on the performance of the bridge and the distribution of forces. For example, when the orientation of the wing wall changes from parallel to perpendicular to the abutment, the soil would be more confined.

Wing Wall Orientation to Abutment

1. Wing Wall Parallel to Abutment

A wing wall designed parallel to the abutment is simple and takes a short time to construct compared to other wing walls with different orientations, but it is not the most economical wing wall arrangement. Due to this design, the disturbance of existing utilities and slope embankment is minimal. 

However, the inline design of the wing wall to abutment affects the magnitude of girder curvature and axial forces induced with parallel wing wall due to larger constraints imposed to the bridge expansion by the passive backfill soil pressure.

2. Wing Wall Perpendicular to Abutment

Perpendicular orientation of wing wall to abutment provides continuous alignment with the bridge deck, supporting a share of load from the bridge deck. However, it is not the most economical design. The transverse wing wall increases passive earth pressure but declines the approach fill settlement.

The construction of a wing wall perpendicular to the abutment causes great disturbance to the neighboring structures and utility services. Additionally, for a curved bridge, this type of wing wall design may hinder the curvature of the bridge.

Nonetheless, when the wing wall is constructed integrally with the abutment, a structural advantage can be taken by the stability of the box structure.    

3. Wing Wall at an Angle to Abutment

The design of wing wall orientation at an angle to the abutment provides the best economical option from the material cost point of view.

Considerations in Selecting Orientation of Bridge Abutment 

From the above discussion, it can be concluded that several factors need to be considered while selecting the orientation of the wing wall to the bridge abutment. 

Therefore, the designer should specify the best possible direction based on the above considerations. For instance, they can go for the simplest and easiest design but with higher cost as in the case of wing wall parallel to abutment wall, or slightly challenging and more detailed design and minimum disturbance to the existing fill embankment and utilities. 

Table-1 summarizes different considerations with the suitable degree for different orientations of wing walls.

Table-1: Wing Wall Orientation Selection Considerations

Orientation consideration	Wing wall Parallel to Abutment	Wing wall Perpendicular to Abutment	Wing wall at an Angle to Abutment
Material cost	●●	●●	●●●
Design complexity	●●●	●●●
Ease of construction	●●●	●●	●
Passive earth pressure	●●●	●	●●
Disturbance to existing utilities and backfill material	●●●	●	●●
Supporting loads	●	●●●	●●
Reduction of backfill material settlement	●	●●●	●●

●●● Good

●● Medium

● Bad

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