Function and Type Of Expansion joints In Bridges | Details of Expansion joints

 What is Expansion Joint? Type Of Expansion Joints in Bridges, The function of Expansion Joints, Defects In Expansion Joints, Remedial Measures/ Preventions/ Precautions, etc. are described here.

Figure-1: Function and Type Of Expansion joints In Bridges.

What is Expansion Joint: 

       Bridge Expansion Joint can define as the joint which is designed for bridge deck to allow deck movement, deformation, expansion, or contraction due to external loads, Seismic effect, and thermal variation without disturbing the traffic. Neoprene seal retains silt, debris and also drains the surface water to avoid any damage to the structural members under the bridge deck. 

Type Of Expansion Joints in Bridges:

       Different type of expansion joints in bridges is Filler Type expansion joint, Strip seal type expansion joint, Gland slab elastomeric seal type expansion joint, Modular expansion joint, Compression seal type expansion joint, Finger type expansion joint, Sawtooth Type expansion Joint.

   Bridge Expansion Joint Types || Different types of expansion joints in bridges are following-

       

          1. Filler Type expansion joint: 

        Filler-type expansion joints are suitable for simply supported deck slabs. 20-25 mm gap provides for the filler type expansion joint and the gap filled with bitumen filler material. Sometimes foam uses to fill the expansion joint gap. During the service life, cracks may develop on wearing coat over the expansion joints due to movement of the deck. Damaged filler material needs to replace and cracks on wearing coat over the filler expansion joint needs to fill with asphalt to avoid seepage through the expansion joints.

Figure 2: Filler Type Expansion Joint

Figure-3: Bitumen Filler Expansion Joint

        2. Compression Seal Type Expansion Joint: 

                         Compression Seal type expansion joints are suitable in a Simply supported deck and a continuous deck bridge allows longitudinal movement up to 40 mm (Skew angle up to 30 degrees). Sealing material foam or neoprene. Steel angle provides to guide edge of the deck. Regular maintenance requires to keep its properly functioning. Damage sealing material needs to be replaced during the service life of the expansion joint to avoid seepage from the expansion joint. 

                          

Figure-4: Foam Compression seal expansion Joint

Figure-5: Elastomeric compression seal expansion joint

      3. Sliding Plate Expansion Joint:

Steel plate is provided at top of the expansion joint. one side of the steel plate is fixed and another side is free to slide. sliding plate expnaison joints type of expansion joint allow longitudinal movement upto 40mm. But cracks on wearing coat over the steel plate can be developed easily and led damages to the wearing coat.

4. Strip seal type expansion joint: 

               Nowadays, this type of expansion joint is widely used. Strip seal type expansion joint is suitable in moderate to large span, simply supported bridge/ cantilever /continuous deck and having the right, skew, or curved deck with maximum horizontal movement up to 70 mm. Regular maintenance requires to keep it is properly functioning.  The damaged strip seal needs to be replaced during the service.

Figure-6: Strip Seal type expansion Joint

         5. Gland slab elastomeric seal type expansion joint:

                      Gland slab elastomeric seal type expansion joint is suitable in simply supported or continuous spans (having Right or skew less than 70 degrees) and horizontal alignment is moderately curved with maximum horizontal movement up to 50 mm. But elastomeric slab seal expansion joint is not suitable in heavy rain areas. In heavy rain areas, making moisture on structural members below the deck is due to seepage from the expansion joint.

Figure-7: Gland Slab Seal Expansion Joint

        6. Finger type expansion joint 

    Finger expansion joints are designed to handle movements of 80 mm to 1,200 mm are composed by steel finger plates, CR sheet, anchor bolts and other components. The rubber sheet is placed on the retractable steel, and anchor bolts help to fix the whole structure. 
The orientation of the fingers is in the direction of vehicle travel, which can reduce noise and improve driver's comfort. There is a drainage channel that allows rainwater to enter the bridge's drainage system, hanging beneath the joint.

The orientation of the fingers is in the direction of vehicle travel, which can reduce noise and improve driver's comfort. There is a drainage channel which allows rainwater to enter the bridge's drainage system, hanging beneath the joint.

Figure-8: Finger type Expansion Joint

    

             7. Modular Strip Seal Expansion Joint:

                      Modular strip seal type expansion joint is suitable in the large-span bridges (continuous span or cantilever span bridges. This type of expansion joint allows maximum horizontal movement in excess of 70 mm. Regular maintenance requires removing silt and debris from the expansion joint to make it proper functioning. Elastomeric strip seal may replace during its service life to avoid moisture on structural members below the deck. The service life of the modular strip seal expansion joint is 25 years. 

Figure-9: Modular Strip seal expansion joint

      

       8. Saw-tooth Type Expansion Joint

Figure-9: Saw-Tooth type Expansion Joint

Defects In Expansion Joints:

1. Silt, debris and bitumen may interrupt the function of the expansion joint.
2. Damaged/split/detached/leaked neoprene seal in expansion joint allow water seepage through expansion joints. 
3. Rust and corrosion at steel angle/steel edge beam.
4. Cracks/delamination/spalling/honeycomb/exposed steel/exposed anchor studs/loosed steel angle etc at the header of expansion joint.
5. Rattling in expansion joints.
6. Buckling/kinking at steel angle
7. Hardening/cracking in bitumen filler expansion joints.

Remedial Measures/ Preventions/ Precautions:

1. Silt, debris and bitumen shall be removed from the expansion joint to make it proper functional.
2. Deteriorated/flattened/split/ detached/leaked neoprene seal shall be replaced to avoid water seepage through the expansion joint.
3. Cracks in the bitumen filler expansion joint shall be refilled with asphalt. in case of widened cracks or damaged filler material, bitumen filler material shall be replaced.
4. Cracks at the header of expansion joints shall be treated with epoxy grout.
5. Spalling/delaminated/disintegration/honeycomb/exposed steel shall be repaired with polymer-modified cement concrete. 
6. In case of a damaged header/damaged steel angle, the expansion joints shall be replaced. 

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 "DEFECTS IN BRIDGE EXPANSION JOINTS AND THEIR PREVENTION"

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