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Bridge Engineering

What are the potential advantages of continuous multiple-span deck over simply supported multiple-span deck?

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.

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What are the main potential benefits in using the bridge form of precast prestressed beams supporting in-situ concrete top slab?

The potential benefits of using the bridge form of precast prestressed beams supporting in-situ concrete top slab are:

(i) For bridges built on top of rivers and carriageway, this bridge form provides the working platform by the precast beams so that erection of falsework is not required.

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Why is creep a major concern in balanced cantilever method?

In balanced cantilever method, the moment is balanced along the length of the piers. However, along the extended cantilevers only a part of negative bending moment is balanced by prestressing bending moment arising from normal force induced by prestressing.

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What is the difference between span-by-span construction and progressive placement?

Balanced cantilever construction simply cantilevers segments from a pier in a balanced manner on each side until the mid-span is reached and a closure is made with a previous half span cantilever from the preceding
pier.

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In span-by-span construction, which prestress layout is better (i) single-span coupled cable or (ii) two-span overlapped cable?

For single-span coupled cable, the length of cable is one span and they are coupled at the construction joint which is located at 0.25 of span. The use of single-span coupled cable in span-by-span construction suffers the following drawbacks:

(i) Stressing all tendons in one span is time consuming. Moreover, the construction team has to wait until the concrete has gained enough strength before all tendons in the span to be stressed.

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