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
stainless steel plates are normally selected where the plates should be
larger than PTFE surface to allow movement without exposing the PTFE.
Moreover, it is recommended that the stainless steel surface be positioned
on top of the PTFE surface to avoid contamination of dirt and rubbish.
Lubricants are sometimes introduced to reduce the friction between the
PTFE surface and the upper stainless steel plate. Hence, the PTFE may
be designed with dimples to avoid the lubricant from squeezing out under
repeated translation movements.
7. What is the purpose of dimples in PTFE in bridge bearings? (TB1)
PTFE is a flurocarbon polymer which possesses good chemical resistance
and can function in a wide range of temperature. The most important
characteristic of this material is its low coefficient of friction. PTFE has the
lowest coefficients of static and dynamic friction of any solid with absence
of stick-slip movement [43]. The coefficient of friction is found to decrease
with an increase in compressive stress. However, PTFE do have some
demerits like high thermal expansion and low compressive strength [43].
In designing the complementary contact plate with PTFE sliding surface,
stainless steel plates are normally selected where the plates should be
larger than PTFE surface to allow movement without exposing the PTFE.
Moreover, it is recommended that the stainless steel surface be positioned
on top of the PTFE surface to avoid contamination by possible
accumulation of dirt and rubbish on the larger lower plates. Lubricants are
sometimes introduced to reduce the friction between the PTFE surface and
the upper stainless steel plate. Dimples are designed on PTFE surfaces to
act as reservoirs for lubricant and these reservoirs are uniformly distributed
over the surface of PTFE and normally they cover about 20%-30% of the
surface area. Hence, the PTFE may be designed with dimples to avoid the
lubricant from squeezing out under repeated translation movements.
8. What is the purpose of dowel bar in elastomeric bearing? (TB2)
Elastomeric bearing is normally classified into two types: fixed and free.
For fixed types, the bridge deck is permitted only to rotate and the
horizontal movements of the deck are restrained. On the other hand, for
free types the deck can move horizontally and rotate. To achieve fixity,
dowels are adopted to pass from bridge deck to abutment. Alternatively, in
case there is limitation in space, holes are formed in the elastomeric
bearings where anchor dowels are inserted through these holes. It is
intended to prevent the “walking” of the bearing during its operation.
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