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