8/2/2019 Bearings and Railings
1/14
3/26/12
BEARINGS AND RAILINGS
BEARINGS
Bearings are structural devices
positioned between the bridgesuperstructure and the substructure.
Their principal functions are as
follows:1. To transmit loads from thesuperstructure to the substructure, and
2. To accommodate relative
8/2/2019 Bearings and Railings
2/14
3/26/12
Movements should be accommodatedproperly and these result from
q longitudinal movement due to temperaturechanges-reversible
q rotation due to deflection of girders- live loaddeflection is reversible
q vertical movement due to settlement of support-irreversible
q movement due to shrinkage, creep orprestressing-irreversible
Bearings are categorized in to two as
q Fixed bearings are fixed against translation, butfree to rotate
q Expansion bearings-are free to translate and
8/2/2019 Bearings and Railings
3/14
3/26/12
Selection of the type depends on thetype of superstructure, type of
substructure supports and the length ofthe span.
qA simply supported span requires
fixed bearings at one andexpansion joints at the other.
qA continuous girder require fixed
bearing at one and expansionbearing on all other supports
qA two span girder will have fixed
bearing at the centre support and
8/2/2019 Bearings and Railings
4/14
3/26/12
Bearings are important components ofbridges and call for care in design,skill in execution, regular attention inmaintenance.
Faulty design or malfunctioningbearings due to clogging by debrishave often resulted in collapse ofbridges due to the high stresses
induced due to restrained motion. On certain major bridges bearing cost
is as high as 10-15% of the total cost.
It is worth designing carefully and
8/2/2019 Bearings and Railings
5/14
3/26/12
Types of Bearings
For slab bridges no special bearingsare provided because thetranslational movement is very small.
Edges of supports are beveled toallow for rotation.
8/2/2019 Bearings and Railings
6/14
3/26/12
The following are the different types of bearings for girder bridgesSliding plate bearing- is the simplest type of bearing. This utilizes one platesliding on another. This type is used for bridges up to 30m span. Flat plateswere common but due to freezing and high frictional forces the surface ofthe upper plate is slightly curved as shown in Figure below.
Figure: Sliding plate bearing
8/2/2019 Bearings and Railings
7/14
3/26/12
Roller bearing- in this type rotation is accommodated by the pinand translation by the use of a roller or a group of rollers. SeeFigure below. This is used for spans of moderate length.
Figure: Roller bearing
8/2/2019 Bearings and Railings
8/14
3/26/12
Rocker bearing- this is used for longer spans and isused to accommodate large live load deflections.
See Figure below.
Figure: Rocker bearing
8/2/2019 Bearings and Railings
9/14
3/26/12
Rocker bearing- this is used forlonger spans and is used to
accommodate large live loaddeflections. See Figure below.
Figure: Rocker bearing
In seismic areas suitable guides
should be provided to prevent theroller and rocker components frombeing displaced off abutments and
piers during earthquakes.
8/2/2019 Bearings and Railings
10/14
3/26/12
8/2/2019 Bearings and Railings
11/14
3/26/12
8/2/2019 Bearings and Railings
12/14
3/26/12
RAILINGS
Railings are provided along edges ofbridges for protection of traffic andpedestrian. There are three types ofrailings.
qTraffic railings
q Pedestrian railings
q Combination railings The following guideline indicate the
application of various types of rails
8/2/2019 Bearings and Railings
13/14
3/26/12
8/2/2019 Bearings and Railings
14/14
Top Related