Components, systems and materials › Bridge components › Modular expansion joint
Modular expansion joint
What it is
A modular expansion joint uses several seals held between intermediate steel centre beams, carried on support bars, to accommodate the large movements of long bridge decks.
Where it is used
Long-span bridges, cable-stayed and suspension bridges and long viaducts where total movement is a few hundred millimetres or more.
How it works
Each gap between beams takes a share of the total movement, and a control system of springs or linkages keeps the gaps roughly equal as the deck expands and contracts. Wheel loads pass from the centre beams to support bars that slide on bearings in boxes cast into the deck.
Types
- Single support bar systems with control springs
- multiple support bar systems
- swivel joist systems that also allow rotation and skew movement
Materials
Steel centre beams and edge beams, support bars, elastomeric bearings and springs, sliding surfaces and neoprene or EPDM strip seals.
Movement range comes from temperature, creep, shrinkage, traffic and seismic actions. Centre beams, support bars and their welds are designed for wheel loads including dynamic effects and fatigue over millions of cycles; fatigue-tested details are essential. Noise, maintenance access and replacement of seals and bearings are planned from the start.
Installation and QA steps
- Form deep recesses with boxes for support bars.
- Lift the pre-assembled joint and set gaps for the installation temperature.
- Fix anchorage and concrete the recesses with careful compaction.
- Release temporary clamps after concreting.
- Inspect springs, bearings and seals regularly and clear debris.
- Fatigue cracking at welded beam-to-bar connections
- worn bearings and springs causing uneven gaps and noise
- seal damage and water leakage onto bearings below
- debris jamming the joint
Codes cited
- IRC:SP:69 (India): Guidelines and specifications for expansion joints in road bridges.
Cited by number only. We do not reproduce code text, tables or figures.
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