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Why are excessive movement joints undesirable in bridges?

Expansion joints used to accommodate the movement of a bridge superstructure. The movement arises from several factors such as temperature change, shrinkage, creep, and elastic shortening due to the post-tensioning of a bridge. It is not recommended to increase the number of expansion joints. The increasing number of expansion joint will increase the cost of constructing a bridge. Expansion joints required periodic inspection and maintenance to stay in good condition and to function properly. In some events, the maintenance will require a partial or full closing of a bridge, which may lead to traffic jam and inconvenience for road users. Therefore it is recommended to minimize or eliminate the expansion joint to reduce the cost associated with installation and maintenance of expansion joints. 




Integral bridges, bridges without movable deck joints, should be considered where the length of the superstructure and flexibility of substructures are such that secondary stresses due to restrained movement are controlled with intolerable limits. AASHTO-C14.5.2.1.



Figure 1

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.





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