Civil Engineering Reference
In-Depth Information
of the bridge as a whole. The forces and movements in bearings should be
given to the bearing manufacturer to ensure that the bearings provided meet
the requirements. A drawing showing the bearing layout should include the
following: a simplified general arrangement of the bridge showing the bear-
ings in plan, details at the bearing location, a clear indication of the type of
bearing at each location, a table giving the detailed requirements for each
bearing, and bedding and fixing details. Bearings should not normally be
expected to resist moments due to rotational movement. Uplift may cause
excessive wear in bearings if such conditions occur frequently. Where uplift
is unavoidable, prestressing may be used to provide the necessary additional
vertical force. Bearings and supports should be designed in such a way that
they can be inspected, maintained, and replaced if necessary.
EC3 (BS EN 1993-2) [1.27] requires that for line rocker and single roller
bearings, the full implications of uneven pressure along the length of the
roller or rocker should be taken into account in the design of the structure
and the bearing. Also, particular care should be taken in the design of bridges
curved in plan, bridges with slender piers, bridges without transverse beams,
bridges with transverse beams where the line rocker or single roller could
effectively act as a built-in support for the transverse beam, and bridges with
a transverse temperature gradient. Anchorages of bridge bearings shall be
designed at the ultimate limit state. Where the position of a bearing or part
of a bearing is retained either completely or partially by friction, its safety
against sliding shall be checked in accordance with the following:
V
Ed
V
Rd
ð
3
:
129
Þ
where
V
Ed
is the design value of the shear force acting at the bridge bearing
m
K
g
m
V
Rd
¼
N
Ed
+
V
pd
ð
3
:
130
Þ
where
N
Ed
is the minimum design force acting normal to the joint in con-
junction with
V
Ed
,
V
pd
is the design value of shear resistance of any fixing
device in accordance with the Eurocodes,
m
K
is the characteristic value of the
The code [1.27] recommends the following values:
g
m
¼
2.0 for steel on steel
and
g
m
¼
1.2 for steel on concrete. For dynamically loaded structures, the
value of
N
Ed
should be determined, taking into account any dynamic var-
iations in traffic loads. For railway bridges and structures subjected to seismic
situations, friction should not be taken into account (
N
Ed
¼
0). Where
the bearings are designed to resist horizontal forces, some movements will
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