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Joint Type and Details for Reduced Steel Bridge Maintenance

Description:

Bridge deck joint are subject to various performance demands which are difficult to satisfy for the life of the structure. These demands coupled with infrequent maintenance often result in premature failure. The consequences of failure are damage to beam and girder ends as well as other bridge elements beneath the joint. Repairs and preservation work to replace failed joints is costly and typically requires bridge or lane closures.

Study is needed to provide owners with comprehensive information on the best practices for selecting, detailing, installing and maintaining bridge joints and joint assemblies.

Bridge deck joints and bearings beam are typically provided at steel girder or beam supports to accommodate the dimensional changes (relative translation and/or rotation of abutting structural elements) caused by thermal movements as well as externally applied loads, creep, and shrinkage. Bridge deck expansion joints installed in the structural discontinuity created at roadway surface are designed to prevent the passage of debris and run-off, which is often contaminated with deleterious substances such as deicing salts, through the joint and on to the steel girder/beam ends, bearing assembly and pier cap beneath the joint. However, experience shows other than the deterioration of the concrete deck itself, the single most prevalent bridge maintenance problem is the deterioration of beam ends, bearings, pedestals, piers, and abutments due to percolation of waterborne road salts through the deck joints (AASHTO, 2017). Detailing a structurally continuous deck, via use of integral abutments, link slabs, and continuous or continuous for live load spans, appears to provide the best protection for components below the deck. Indeed, the AASHTO bridge design specifications require the number of deck joints be kept to a practical minimum.

When deck joints cannot be eliminated, e.g. on long structures, bridge owners struggle to identify suitable durable and watertight closed joint systems that do not require frequent maintenance. Bridge deck joints are subjected to various demands, such as traffic impact loads, thermal movements, live load induced rotations, etc., which must be satisfied for the service life of the bridge. Unfortunately, many joints fail prematurely for a variety of reasons, which is coupled with lack of maintenance resulting in damage to bridge elements beneath the joint.

Bridge deck joints may be armored or unarmored. Unarmored joints typically consist of a foam joint seal which is adhesively attached to the vertical faces of the joint opening. Foam joints can reasonably accommodate thermal movements up to 2.5 inches. For these types of joints, the concrete at the edge of the joint opening may spall due to impact of wheel loads resulting in joint failure. To mitigate this problem some States, require an elastomeric concrete header at the joint opening. However, the elastomeric concrete must have enough strength and resiliency to absorb wheel impact loads. Selecting an elastomeric concrete with the appropriate combination of mechanical properties is key to good performance, which is a challenge because the important properties are not well understood. Foam seals are also known to be susceptible to compression set, which may cause the seal to fail at the bonding interface when the joint opening increases. In short, foam joints, which are relatively inexpensive and suitable for low traffic volume roads, have a relatively short service life of 3 to 5 years. Other joints that function in a similar manner include compression joint seals, which are often difficult to install and often result in a damaged joint seal from the outset.

Bridge deck joints on national highway system (NHS) are typically armored, with steel shapes which are cast into the concrete at the joint opening. The amount of thermal movement that needs to be accommodated determines the type of the expansion joint assembly that is selected and detailed. The simplest armored joint typically consist of a pair of steel rails and a silicone or elastomeric gland for the joint seal.
The more complex modular expansion joints often consist of multiple rails or bars and multiple joint seals between the rails. In addition, there is a large box which is cast into the concrete with limited access for maintenance. Other large movement expansion joints, such as cantilever finger joints, typically have a drainage trough beneath the roadway, with limited access for maintenance. Finger joint may become misaligned over the service life, causing the joint to seize.

Experience with many types of joint seals shows debris accumulation over the joint seal is a major maintenance problem that often results in the compromised seals or seizing of the joint assembly. The joint seals are not self‑cleaning as some vendors claim. In addition, armored expansion joints are heavy and difficult to handle during construction, which presents significant challenges with properly supporting the joint rails during the deck pour, such that they end up properly aligned and slightly recessed below the roadway riding surface. Another challenge is devising hardware that will support the rails during installation, and accommodate girder deflections, end rotations and relative thermal movements during deck casting and curing.

Objective:

Provide bridge owners with comprehensive information on best practices for selection, detailing, installation, in-situ performance, including traffic durability, and recommended maintenance practices for various types of commonly available/installed unarmored as well as armored bridge joint systems on bridges with various geometries on new and retrofit projects, which may be stage constructed.

Benefits:

Experience with many types of joint seals shows debris accumulation over the joint seal is a major maintenance problem that often results in the compromised seals or seizing of the joint assembly. The joint seals are not self‑cleaning as some vendors claim. In addition, armored expansion joints are heavy and difficult to handle during construction, which presents significant challenges with properly supporting the joint rails during the deck pour, such that they end up properly aligned and slightly recessed below the roadway riding surface. Another challenge is devising hardware that will support the rails during installation, and accommodate girder deflections, end rotations and relative thermal movements during deck casting and curing.

Sponsoring Committee:AKB20, Steel Bridges
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Gichuru Muchane
Date Posted:04/09/2020
Date Modified:05/06/2020
Index Terms:Steel bridges, Bridge maintenance, Maintenance, Expansion joints, Bridge decks,
Cosponsoring Committees: 
Subjects    
Highways
Maintenance and Preservation
Bridges and other structures

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