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
2. What is preset in bridge bearing? (B2)
“Preset” is a method to reduce the size of upper plates of sliding bearings
in order to save cost. The normal length of an upper bearing plate should
be composed of the following components: length of bearing + 2 x
irreversible movement + 2 x reversible movement. Initially the bearing is
placed at the mid-point of the upper bearing plate without considering the
directional effect of irreversible movement. However, as irreversible
movement normally takes place at one direction only, the bearing is
displaced/presetted a distance of (irreversible movement/2) from the
mid-point of bearing in which the length of upper plate length is equal to the
length of bearing + irreversible movement + 2 x reversible movement. In
this arrangement, the size of upper plate is minimized in which irreversible
movement takes place in one direction only and there is no need to include
the component of two irreversible movements in the upper plate.
Note: “Preset” refers to the displacement of a certain distance of sliding bearings with
respect to upper bearing plates during installation of bearings.
Fig. Preset in sliding bearing.
3. What is the purpose of leveling pad in bridge bearing?
Bridge bearings should be installed to lie horizontally on bridge piers and
columns so that it would not induce eccentricity forces on substructure.
However, the bridge superstructure requires different longitudinal and
transverse level and gradient in order to keep in line with the geometry of
the road. As such, it is natural to follow that the superstructure can hardly
meet with substructure horizontally so that a leveling pad is introduced at
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