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
settlements. However, the effect of continuity is undermined by the
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 joints.
Moreover, the reduction of joints in bridge structures represents substantial
cost savings arising from the construction and maintenance costs of
movement joints. The reduction of deck thickness helps to cut the cost for
both the deck and foundation. In particular, the number of bearings in each
piers is substantially reduced when compared with the case of simply
supported multiple-span deck.
3. For the loading pattern to obtain maximum positive moment in a
span of a continuous beam, why should alternative spans on each
side of the span be loaded? (SA1)
To acquire a maximum sagging moment in a span of a continuous beam,
the general rule is to load the span under consideration and alternative
spans on each side of the span. To account for this rule, let’s consider the
following example. For instance, loads are applied to the mid-span of a
multiple-span continuous beam. It is noticed that this loads induce positive
moments near mid-span in all even spans. Therefore, if all even spans are
loaded simultaneously, this will result in the increase of positive moments in
all other loaded spans.
Similarly, to obtain maximum negative moment at a support, load adjacent
spans of the support and then alternative spans on each side.
4. What are the advantages of piers constructed monolithically with
the bridge deck over usage of bearings?
Basically, piers constructed monolithically with the bridge deck are
advantageous in the following ways:
(i) Movement of the bridge deck is achieved by the bending
deformation of long and slender piers. In this way, it saves the
construction cost of bearings by using monolithic construction
between bridge deck and piers. Moreover, it is not necessary to
spend extra effort to design for drainage details and access for
bearing replacement. On the other hand, in maintenance aspect
substantial cost and time savings could be obtained by using
monolithic construction instead of using bearings as bridge
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