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
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
bearings is limited and controlled by shear strain requirements. In essence,
the shear strain should be less than a certain limit to avoid the occurrence
of rolling over at the edges and delamination due to fatigue. Hence, it
follows that higher rotations and translations require thicker bearing. On
the other hand, the vertical stiffness of bearings is obtained by inserting
sufficient number of steel plates. In addition, checks should be made on
combined compression and rotation to guard against the possible
occurrence of uplifting of corners of bearings under certain load
combinations.
16. Why are excessive movement joints undesirable in bridges? (EJ1)
Movement joints are normally added to bridge structures to accommodate
movements due to dimensional changes arising from temperature variation,
shrinkage, creep and effect of prestress. However, the provision of
excessive movement joints should be avoided in design because
movement joints always encounter problems giving rise to trouble in
normal operation and this increases the cost of maintenance.
Some designers may prefer to add more movement joints to guard against
possible occurrence of differential settlements. However, the effect of
continuity is disabled by this excessive introduction of movement joints. In
essence, the structural reserve provided by a continuous bridge is
destroyed by the multiple-span statically determinate structure resulting
from the addition of excessive joints.
17. How will inclined bridge deck affect joint continuity? (EJ1)
Bearings are usually designed to sit in a horizontal plane so as to avoid the
effect of additional horizontal force and uneven pressure distribution
resulting from non-horizontal placing of bearings [43]. For an inclined
bridge deck subject to a large longitudinal movement, a sudden jump is
induced at the expansion joint and discontinuity of joint results. To solve
this problem, an inclined bearing instead of a truly horizontal bearing is
adopted if the piers can take up the induced horizontal forces.
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