Prestressed Composite Section Design

Prestressed Composite Section Design

The design of a composite section depends upon the type of composite section, the
stages of prestressing, the type of construction and the loads. The type of construction
refers to whether the precast member is propped or unpropped during the casting of
the CIP portion. If the precast member is supported by props along its length during the
casting, it is considered to be propped. Else, if the precast member is supported only at
the ends during the casting, it is considered to be unpropped.

The advantages of composite construction are as follows.
1) Savings in formwork
2) Fast-track construction

3) Easy to connect the members and achieve continuity.

The prestressing of composite sections can be done in stages. The precast member
can be first pre-tensioned or post-tensioned at the casting site. After the cast-in-place
(cast-in-situ) concrete achieves strength, the section is further post-tensioned.
The grades of concrete for the precast member and the cast-in-place portion may be
different. In such a case, a transformed section is used to analyse the composite



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