Positioning of Bearings for Skew Bridges in Beam-and-Slab Construction
Bridge Engineering • Skew Bridges • Bearing Arrangement • T-Beam & Slab Construction
The positioning and orientation of bearings in a skew bridge require special attention, particularly in bridges having T-beam, girder-and-slab or multi-girder construction.
Unlike a straight bridge, the supports of a skew bridge are not perpendicular to the longitudinal axis of the bridge. Consequently, the geometry of the supports, girder orientation, bearing orientation and permitted movement directions must be considered together.
The principal objective is to ensure that the bearing arrangement allows the required longitudinal translation and end rotation of the girders while avoiding unintended restraint, excessive transverse forces, torsional effects, differential movement or uplift at the supports.
This becomes particularly important as the skew angle increases or where the bridge has large spans, heavy loading, multiple girders or bearings with directional movement restrictions.
Key Takeaways
- Bearing orientation should be compatible with the intended direction of girder movement.
- Skew angle, girder orientation, support geometry and bearing type should be considered together.
- Increasing skew can produce more significant torsional effects, differential movement and uplift tendencies, particularly at acute corners.
- Fixed, guided and free bearings should be arranged according to the approved articulation and movement system.
- For large spans, heavy loads or significant skew, the bearing arrangement should be verified by detailed structural analysis.
- There is no single bearing arrangement that is universally applicable to every skew bridge.
2. Small Skew and Large Skew
3. Arrangement for Large Span and Heavy Loading
4. Wide Slab and Multi-Girder Bridges
5. Single-Slab Arrangement
6. Multiple Spans with Concrete Hinges
7. Multi-Girder Hinged-Column Arrangement
8. Important Design Considerations
9. Site and Design Checklist
10. Frequently Asked Questions
11. Conclusion
1. Why Bearing Positioning is Important in Skew Bridges
In a conventional straight bridge, the relationship between the girder longitudinal axis, bearing orientation and support line is comparatively simple. In a skew bridge, however, the supports are inclined relative to the bridge centreline.
The bearing arrangement must therefore be selected so that the intended translation and rotation of each girder can occur without creating unintended restraint.
Depending on the structural system, inappropriate bearing orientation can contribute to:
- restricted longitudinal movement;
- unintended transverse forces;
- torsional effects in the girder and deck;
- unequal load distribution between girders;
- uplift tendencies at acute corners; and
- additional demands on bearings, diaphragms and substructure elements.
Therefore, bearing orientation should be determined from the structural analysis, bridge articulation and bearing movement requirements, rather than solely from the visual geometry of the skew support.
In many skew girder bridges, bearings are oriented in relation to the individual girder axis and the intended movement direction rather than simply being aligned with the skewed support line. However, this is not a universal rule. The final orientation should be established from the approved structural design and the specific bearing system adopted.
2. Small Skew and Large Skew
The effect of skew becomes increasingly important as the skew angle increases. For relatively small skew angles, conventional bearing arrangements may often be adopted with appropriate detailing and structural verification.
As the skew becomes larger, the interaction between girder movement, support geometry and bearing orientation becomes more significant. Particular attention may be required at the acute corners of the bridge.
Figure 1 – Conceptual comparison of bearing positioning for small and large skew bridges
Small Skew
For relatively small skew angles, the effects associated with skew may be less pronounced. A conventional bearing arrangement may therefore be suitable, subject to structural analysis and the requirements of the selected bearing system.
Large Skew
With increasing skew, greater attention should be given to differential movement between girders, rotation of the deck, torsional response and possible uplift or reduced bearing reactions near acute corners.
There is no universally applicable limiting skew angle at which a particular bearing arrangement must be adopted. A commonly encountered preliminary-design range such as 20°–25° may be used as an indicator for closer investigation, but the actual requirement should be established from project-specific analysis and applicable design provisions.
3. Arrangement for Large Span and Heavy Loading
Large-span bridges and bridges subjected to substantial dead and live loads require more careful consideration of bearing capacity, movement, rotation and restraint.
Figure 2 – Conceptual bearing arrangement for large-span or heavily loaded skew bridge
Depending on the structural requirements, bearing systems such as pot, spherical, guided or sliding bearings may be considered where controlled translation and rotation are required.
Such bearings can provide defined movement characteristics and may be configured as fixed, guided or free bearings as required by the bridge articulation system.
The selection should consider vertical load, horizontal forces, longitudinal movement, transverse movement, rotation, friction, temperature effects and construction tolerances.
4. Bearing Arrangement for Wide Slab and Multi-Girder Bridges
In wide deck bridges and multi-girder systems, the bearing arrangement becomes particularly important because the individual girders may experience different movements and rotations.
The designer should consider:
- relative longitudinal movement of individual girders;
- transverse distribution of loads;
- deck and diaphragm stiffness;
- torsional response of the deck system;
- rotation at supports;
- possible uplift at acute corners; and
- compatibility between fixed, guided and free bearings.
5. Bearing Arrangement for Single Slab
For a single slab or relatively simple deck arrangement, the bearing system may be comparatively straightforward. Nevertheless, the skew geometry should be incorporated into the structural analysis.
Figure 3 – Conceptual bearing arrangement for a single-slab skew bridge
6. Multiple Spans with Concrete Hinges and Fixed Bearings
In multi-span bridges incorporating concrete hinges or other defined articulation arrangements, the location and function of fixed bearings should be considered together with the complete structural load path.
Figure 4 – Conceptual arrangement for multiple spans with concrete hinges and fixed bearings
The fixed bearing location establishes an important part of the longitudinal restraint system. Other bearings may need to permit the required translation and rotation while limiting movement in the directions specified by the design.
7. Multiple-Span Multi-Girder Arrangement with Hinged Columns
Multi-girder bridges supported on columns or piers with defined articulation require coordinated bearing and structural movement arrangements.
Figure 5 – Conceptual bearing arrangement for multiple-span multi-girder bridge with hinged-column support
In such systems, the designer should ensure compatibility between the bearing movement directions, column flexibility, deck stiffness and overall bridge articulation.
8. Important Design Considerations
8.1 Skew Angle
Increasing skew generally increases the importance of three-dimensional structural behaviour. The designer should evaluate the effects of the actual skew angle rather than applying a fixed threshold without analysis.
8.2 Bearing Movement Direction
Sliding or guided bearings should be oriented so that their permitted movement direction is compatible with the calculated movement of the supported girder and the overall bridge articulation.
8.3 Fixed Bearing Location
The fixed bearing location should be selected as part of the overall bridge articulation system. It should provide the required restraint while avoiding undesirable accumulation of thermal, shrinkage or other movement-related forces.
8.4 Acute and Obtuse Corners
Skewed supports create acute and obtuse corners. The acute corners can require particular attention because of differential reactions, deck rotation and possible uplift or reduced bearing compression under certain load combinations.
8.5 Bearing Type
Elastomeric, pot, spherical, sliding and guided bearings have different movement and rotation characteristics. The bearing type should therefore be selected based on the calculated vertical and horizontal loads, movement requirements and rotation demands.
8.6 Construction Tolerances
The design should account for practical construction tolerances. Incorrect bearing orientation or positioning during construction can reduce the available movement capacity even when the theoretical design arrangement is correct.
The bearing arrangement should be treated as part of the complete bridge articulation system. Fixed, guided and free bearings should not be selected or positioned independently. Their movement directions, restraint characteristics and locations should be compatible with the behaviour of the entire bridge.
9. Skew Bridge Bearing Design & Site Checklist
| No. | Check Item | Status |
|---|---|---|
| 1 | Actual skew angle verified from approved drawings | ☐ |
| 2 | Bearing orientation matches approved structural drawings | ☐ |
| 3 | Fixed bearing location verified | ☐ |
| 4 | Guided/free bearing movement direction verified | ☐ |
| 5 | Required longitudinal movement checked | ☐ |
| 6 | Required rotational capacity checked | ☐ |
| 7 | Acute-corner uplift/reaction condition investigated | ☐ |
| 8 | Bearing capacity verified for governing load combinations | ☐ |
| 9 | Construction tolerances considered | ☐ |
| 10 | Bearing manufacturer's installation requirements followed | ☐ |
10. Frequently Asked Questions
Why is bearing positioning important in a skew bridge?
Because the support line is inclined relative to the bridge axis, incorrect bearing orientation can restrict intended movement and rotation or introduce unintended forces into the superstructure and substructure.
Should bearings always be placed perpendicular to the skew support line?
Not necessarily. Bearing orientation should be based on the girder geometry, intended movement direction, bearing characteristics and overall bridge articulation. The approved structural design should determine the final arrangement.
Is there a specific skew angle above which a special bearing arrangement is required?
There is no universal skew-angle threshold applicable to every bridge. Increasing skew generally warrants more detailed investigation, and project-specific structural analysis should determine whether a special arrangement is necessary.
Why are acute corners important in skew bridges?
Skew geometry can cause differential reactions and three-dimensional effects at the supports. Under certain load combinations, the acute corners may experience reduced bearing compression or uplift tendencies.
When are guided or sliding bearings useful?
Guided or sliding bearings may be useful where the bridge requires controlled translation in a particular direction while restraining movement in another direction. Their suitability depends on the calculated movement and the overall articulation system.
Are pot or spherical bearings always required for large skew bridges?
No. Bearing selection depends on the calculated loads, movement, rotation, durability requirements, structural system and project specifications. Pot or spherical bearings are possible solutions for particular applications, but they should not be treated as mandatory solely because a bridge has a large skew.
11. Conclusion
Correct positioning of bearings is an important aspect of the design and construction of skew bridges, particularly for T-beam-and-slab, multi-girder and multi-span bridge systems.
The bearing arrangement should provide the required translation, rotation and restraint while minimizing unintended torsional effects, differential movement and uplift.
For relatively simple skew bridges, conventional bearing systems may be adequate. As the skew, span, loading or structural complexity increases, a more detailed assessment of the bearing arrangement and three-dimensional structural behaviour becomes increasingly important.
Ultimately, the final bearing orientation and arrangement should be based on the approved structural design, applicable standards, project specifications, bearing manufacturer's requirements and project-specific analysis.
The diagrams and arrangements presented in this article are intended for technical explanation and general engineering reference. They should not be adopted directly for construction without verification against the approved structural drawings, design calculations, project specifications, applicable standards and bearing manufacturer's installation requirements. Bearing orientation and movement directions must be determined for the specific bridge configuration.
Bridge Bearings • Skew Bridges • T-Beam Bridges • Multi-Girder Bridges • Bearing Arrangement • Structural Engineering
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