A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Fig. Effect of steel plate in elastomeric bearing.
11. Why do some engineers prefer to use neoprene instead of natural
rubber in elastomeric bearings? (TB2)
Some engineers may choose to design elastomeric bearings to sit on the
piers without a connection. The bearing is held in place by frictional
resistance only. Paraffin used in natural rubber would bleed out and result
in significant decrease in friction. As such, elastomeric bearings would slip
away and walk out from their original locations. To solve this problem,
neoprene, instead of natural rubber, is used as elastomer because paraffin
is absent in neoprene bearings.
12. What is the importance of shear stiffness in the design of
elastomeric bearing? (TB2)
For elastomeric bearing, the shear stiffness is an important parameter for
design because it influences the force transfer between the bridge and its
piers. In essence, elastomers are flexible under shear deformation but it is
relatively stiff in compression. However, elastomeric bearings should not
be used in tension.
Elastomeric bearing should be designed in serviceability limit state only.
The cross sectional area is normally determined by the compressive stress
limit under serviceability limit state. The shape factor, i.e. plan area of the
laminar layer divided by area of perimeter free to bulge, affects the relation
between shear stress and the compressive load. In essence, higher
capacity of bearings could be obtained with higher shape factor.
The long side of the bearing is usually oriented parallel to the principle axis
of rotation because it facilitates rotational movement. The thickness of
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