BRIDGE JOINTS
Background of a Bridge Joint
It has been found that the durability of bridges is dependent on the effectiveness of the bridge deck waterproofing and the movement joints.
Aggressive chloride contamination must be prevented from entering the structural fabric to avoid unseen corrosion from damaging the concrete, steel elements, and support bearings.
The expansion joints must be continuous to prevent water percolation through permeable road surfacing and resist the hydraulic water pressure developed by the traffic movement.
Function of a Bridge Joint
Bridge expansion joints have to function as “riding plates” to carry the imposed traffic loads and also accommodate the thermal movement, shrinkage, pre-stress creep and rotation of the deck.
These joints can be simple buried or flexible joints or complex mechanical joints according to the range of movements to be accommodated. The expansion joint should give good riding characteristics without generating excessive noise from traffic, especially in urban areas with adjacent residential property. It must also be functional for all road users whilst having good skid resistance and be suitable for the road curvature and alignment.
If pedestrians, animals and cyclists use a bridge the expansion joint should be of a design which does not cause safety issues.
The installation of Bridge Joints
Installation of the joints for new works / structures should be delayed for as long as possible to allow for shrinkage and creep of the deck and settlement of the supports.
The gap widths should be formed to suit the bridge deck temperature in relation to the mean deck temperature.
Further information on this relationship can be obtained from TRL Report SR479 “Bridge temperature for setting bearings and expansion joints”
Bridge Joint Design
The bridge designer must define the relevant design codes including the total movements related to the imposed loadings, temperature range, deck/abutment movement. In this way the manufacturer or supplier can provide the correct technical solution which can be incorporated into the working drawings.
It is essential to detail the particular design features of various bridge expansion joints so that box-outs and plinths can be formed without resorting to changes in reinforcement, etc, at a later state.
It is vital that the bridge expansion joint is formed continuously from parapet to parapet taking into account footpaths, kerbs, central reserves and skew angles. In most cases the aggregated longitudinal movement and skew movement should be used to select the correct size and performance of the joint.
Serviceability Limit State (SLS) may not be appropriate in areas of seizmic activity.
The installation of Bridge Joints
Installation of the joints for new works / structures should be delayed for as long as possible to allow for shrinkage and creep of the deck and settlement of the supports.
The gap widths should be formed to suit the bridge deck temperature in relation to the mean deck temperature.
Further information on this relationship can be obtained from TRL Report SR479 “Bridge temperature for setting bearings and expansion joints”
