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Steel Designers' Manual - 6th Edition (2003)
Chapter 28
Bearings and joints
by STEPHEN MATTHEWS
28.1 Introduction
28.1.1 Movement
All structures move to some extent. Movements may be permanent and irreversible
or short-term and possibly reversible. The effects can be significant in terms of the
behaviour of the structure, its performance during its lifetime, and the continued
integrity of the materials from which it is built.
Movements can arise from a variety of sources:
(1) environmental: thermal, humidity, wind-induced.
(2) material properties: creep, shrinkage.
(3) loading: axial and flexural strains, impact, braking, traction, centrifugal forces.
(4) external sources: tilt, settlement, subsidence, seismic loads.
(5) use of the building: heating, cold storage.
(6) others: requirements for moving or lifting bridges, allowances for jacking procedures,
during or after construction.
In general it is necessary to consider the behaviour of the structure at each point
in terms of its possible movement in each of three principal directions, together with
any associated rotations. The movements of a structure are not in themselves detrimental;
the problems arise where movements are restrained, either by the way in
which the structure is connected to the ground, or by surrounding elements such as
claddings, adjacent buildings, or other fixed or more rigid items. If provision is not
made for such movements and associated forces it is possible that they will lead to,
or contribute towards, deterioration in one or more elements. Deterioration in this
context can range from, for example, cracking or disturbance of the finishes on a
building to buckling or failure of primary structural elements due to large forces
developed through inadvertent restraint.
Note that for bridges with total lengths of up to 60 m, it is possible to dispense
with bearings and expansion joints through use of abutments and piers which are
designed to be integral with the bridge deck. Further guidance on this topic can be
found in Reference 1.
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