What every bridge and structural engineer should know about selecting and specifying structural bearings.

Your project requires the use of bearings to support a structure while resisting or accommodating movements or rotations – what do you need to know?

Main considerations

Maximise long-term performance and minimise life-cycle costs

A structure’s bearings will inevitably be less robust than the structure as a whole, and more prone to damage and deterioration. Maintaining, repairing and replacing bearings throughout a structure’s service life can be very onerous and expensive, and poorly-performing bearings can even impact on the structure’s safety and serviceability. Therefore, the bearing solution used in a structure should be correctly selected and specified to maximise long-term performance and minimise life-cycle costs.

First and foremost, the engineer specifying a bearing solution must understand that the initial supply costs are typically just a very small percentage of the life-cycle costs associated with a bridge’s bearings, especially when the costs of bearing repair and replacement works – and any associated “user costs” due to traffic management and traffic disruption, etc. – are considered. In this context, any additional supply costs incurred in purchasing well-specified, high-quality bearings from a reliable supplier can be considered an excellent long-term investment, for the bridge owner and its users.

The responsible engineer can play an important role in optimising the overall costs of a structure’s bearings by paying due attention to the issues described below.

Key factors

Steps to maximise the suitability, durability and quality of the bearings

1. Specification of the demands to be satisfied by the structural bearings

It is important to define the demands to which the bearings will be subjected. This assessment should not be limited to just the six degrees of freedom, in particular the deck forces, to be carried and resisted, but should consider all other relevant factors such as the cumulative movements and rotations during the lifetime of the bearings. 

2. Selection of the optimal bearing type

The selection of bearing type (e.g. pot, spherical, disc, elastomeric, cylinder, shear key, ILM or a seismic isolator) will be largely defined by the principal functions the bearing is required to fulfil for the bridge – in particular, in terms of resisting forces and accommodating movements. Long-term performance should be maximised and maintenance effort should be minimised, as should the frequency of bearing replacement works and the required effort when replacement becomes unavoidable. 

3. Verification of bearing performance

It is most important that the ability of the selected bearing, as designed and fabricated by its manufacturer, to withstand the loads and facilitate the movements to which it will be subjected during a long life on a structure, should be verified in advance of its use. The best verification of this is a strong track record on the part of the bearing supplier, with evidence of satisfactory performance of similar bearings over many years on comparable structures. Laboratory testing also serves a useful purpose.

4. Evaluation of the needs of the preferred bearing type

Once the type of bearing which can optimally satisfy the structure’s needs has been identified, it is important, at an early stage, to ensure that the bridge deck is designed to receive the selected bearings, with proper access, adequate clearance between substructure and superstructure, correctly sized and reinforced connecting surfaces of the appropriate concrete strength (e.g. for high-performance RESTON® bearings we recommend a contact strength of at least 50 N/mm2), and allowance for suitable anchorage. Inadequate access to the bearings may cause difficulties with inspection and maintenance at a later stage, and incorrectly dimensioned main structures may necessitate changes to approved plans, or even adaptations to the constructed bridge structure on site.

5. Designing to maximise durability and service life

A key factor in maximising durability is the proper application of a suitable corrosion protection system (e.g. painted, galvanised etc.), appropriate to the bridge’s  environment. An appropriate level of protection must be specified, and properly applied, with adequate verification of quality and particularly layer thickness and adhesion. Another important factor is the design and orientation of bearings to protect sensitive sliding surfaces.

6. Designing to optimise inspection and maintenance

The integration in a bearing’s design of structural health monitoring (SHM) functionalities can help to optimise inspection and maintenance work, thereby ensuring that important data about a bearing’s condition and performance are efficiently recorded and notified in real time, maximising the bearing’s service life. And of course, as noted previously, the design of the main structure must ensure adequate access for inspection and maintenance activities.

7. Designing for replaceability

When the time comes to replace a bridge bearing that is anchored to a concrete structure, the effort required will be greatly reduced if the existing bearing, when installed, was equipped with anchor plates. The bearing can then be removed without any breaking out of concrete and with only minimal lifting of the bridge deck. The design of the bridge should also consider future bearing replacement needs, including lifting of the superstructure as required and temporary transfer of functionality (e.g. resisting horizontal forces) to a neighbouring bearing where appropriate.

Life cycle costs of bridge bearings

Typical total life-cycle costs of a bridge's bearings during full life of a bridge

Initial supply costs are typically just a very small percentage of the life-cycle costs associated with a bridge’s bearings.

In detail understanding of the capabilities of particular bearing types requires specialist expertise and experience.

Please feel free to contact us when you require the suitable bearing solution for your structure – we are happy to assist you.

Any questions?

Expert Knowledge

To learn more about "Life-cycle cost analysis of structural bearings, please read our “Expert Knowledge”.

Structual bearings

Find specific information on structural bearing products.

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