BRIDGE EXPANSION JOINTS AND THEIR PERFORMANCE CRITERIA

Expansion joints (or movement joints) are proprietary items and strictly following the basic principles of a proprietary design system is of utmost importance. Bridge expansion joints are designed to enable continuous traffic between two parts of structures and are necessary to accommodate structural movements due to creep and shrinkage effects, temperature variations, or deformations under live load. They are suitable for reinforced concrete, pre-stressed concrete, composite and steel structures, and particularly for bridge decks.

Bridge expansion joints are also designed to allow sufficient vertical movement so that bearings can be replaced without disassembling the expansion joint. The presence of numerous movable parts makes the Modular Joints particularly susceptible to fatigue and wear. The expansion joints are the point of weakness in the bridge because of their function. There are various occurrences of joint leakages that have caused problems with the proper functioning of the bridge. The corrosion of the reinforcement of the bridge commonly happens when the de-icing salt-laden water seeps onto the pier support or bearing shelves. Expansion joints are often one of the first components of a bridge deck to fail and may require multiple replacements throughout the life of a bridge. These replacements are critical to extending bridge life and protecting the substructure components. Currently, the replacement of an expansion joint can take anywhere from a few days to many weeks. These replacements typically involve extensive traffic interference and lane closures.

To ensure the performance requirement of the joint components against fatigue and/or wear, Cl. 8 of IRC: SP:69-2011, stipulates furnishing sufficient evidence of the reliability of the proprietary products. Several types of tests are carried out by recognized laboratories /universities/institutes on the joint components, as a part of the product development. The Client / Client's representative has the responsibility of checking the reports thoroughly to ensure that the components used in actual products and those used in the fatigue/wear tests are the same.

Performance Criteria of Expansion Joints Used in Bridges

The different types of expansion joints in bridges may include

Buried expansion joint

Finger plate expansion joint

Sliding plate expansion joint

Strip seal expansion joint

Modular expansion joint

Asphaltic plug expansion joint

Nosing expansion joint

Reinforced elastomeric expansion joint

Elastomeric in metal runners expansion joint

Cantilever comb or tooth expansion joint

Modular expansion joints (MEJ) are usually provided where the movement demand is higher because of long spans. Modular expansion joints divide the total movement requirement of the superstructure among individual, smaller gaps. It consists of multiple steel beams (center beams) arranged side by side to form a continuous system across the bridge deck. These beams are supported over cross beams, spaced at certain intervals, spanning between two decks. Some type of control mechanism is generally provided to ensure equal opening and closing of the gaps between the center beams. The gaps are fitted with elastomeric sealing pro?les, to prevent the ingress of water, chemicals, and debris.

The qualities of the expansion joints that may satisfy the proper functioning of bridges are:

• It must resist the loads and the movement without causing any failure to itself and the other sections of the structure;
• They should prevent the ingress of water and debris through the expansion gap;
• They should give a smooth ride and pose no danger to road users like cyclists, equestrians, and pedestrians;
• They should be easy to maintain and inspect. In addition, the noise emission from the expansion joints should be minimal, especially when the bridge is near residential areas.
• It is also important for the accepting authority to check pre-approved WPS (Welding Procedure Specification) for specialized connections. The weld joint should pass the Ultra-sonic test for welding. Fatigue test report from a recognized laboratory of butt welded splicing of Centre beams with 2 million load cycles should be furnished by the manufacturer according to Cl. 8.2.5 of IRC: SP:69-2011. The actual splice welding should be carried out adopting a similar procedure, as adopted for testing.
• An integrated shuttering plate should ideally be provided with modular expansion joints to properly seal the space between the underside of the joint and the vertical face of the recess. Without appropriate shuttering, there is a strong possibility of concrete intrusion within the moving parts of the joints, thereby compromising the functionality of the joint.
• Most importantly, during the selection of critical bridge components like bearings and expansion joints, it's important to consider the life-cycle costs associated with these products. In addition to the direct cost involved in the replacement work, the hardships to the bridge users during the replacement, which might need one or multiple lane closures, should also be considered. A little more upfront cost in selecting the right product and strict quality control in the design, manufacture, and installation of such products might go a long way in saving subsequent costs and hassles.

Opinion of Experts

Expansion Joints are an important element of any bridge and are subjected to fatigue and corrosion. Modular Expansion Joints are used when the expansion of the bridge deck is beyond the range of that which can be accommodated by strip seal joints (> 80 mm).

This report published in the current issue (reference) on the failure of modular expansion joints in a long flyover brings out the reasons why in some cases, early-age failures of modular expansion joints occur - either due to design deficiencies, manufacturing issues, poor workmanship, or improper installation. IRC SP:69-2011 "Guidelines and Specifications for Expansion Joints" gives substantial guidance on the types of tests to be carried out and quality control to be exercised during manufacture and installation. Early-age failures of expansion joints lead to direct costs as well as indirect user delay costs when viewed in the Life Cycle Cost framework. It is very important to achieve high-quality control of expansion joints during manufacturing and installation at the site as per the manufacturer's specifications and method statements so that early age failures are avoided and life cycle costs are kept as low as possible.

The expansion joints are proprietary items. Selection of manufacturer for supply, with proven records, adherence to the manufacturer's specifications and installation procedure, testing requirements and acceptance criteria, and presence of manufacturer's representative at the site during installation to guide the contractor, are key to ensuring expansion joints achieve their intended design life.

Reference:

Confidential Reporting Of Structural Failures And Lessons Learnt (CROSFALL) Newsletter, Vol. 3 No. 2, Apr.-Jun., 2024, A Publication of IAStructE

Also See:

https://blog.belzona.com/expansion-joint-repair/#:~:text=Without%20expansion%20joints%2C%20the%20concrete%20can%20crack%20or,stresses%20that%20may%20cause%20concrete%20spalling%20or%20shattering.

https://files.library.northwestern.edu/transportation/online/unrestricted/repository/2020/Accelerated-Repair-and-Replacement-of-Expansion-Joints-REM.pdf