Pre-Stressed Concrete Construction

Types of Prestressed Concrete Construction

1.       Precast complete

-       pre-tensioned factory products and post-tensioned members.

-       manufacture may take place on or off the site, and the units are lifted into place with suitable tackle. In either case the actual prestressed cannot be applied to the concrete until sufficient strength has been developed, but economy in formwork is usually possible, particularly if steam curing is applicable.

2.       Precast in sections

-       a prestressed member may be composed of a series of sections united by prestressed. This allows precasting of units which may then be transported to the site for assembly.

-       the joints between the segments are most important. In order to minimize delays in assembling the member, they may be made with Ciment Fondu, but usually epoxy mortar or cement mortar or concrete using high early strength Portland cement is satisfactory. segments must of course be precisely aligned before jointing, to permit exact location of tendons.

3.       Cast in situ

-       construction is similar to reinforced concrete work, the usual falsework and formwork being employed. To enable early stripping, the concrete is usually made with high early strength cement. With bridges a methods for saving falsework is to cast one girder at a time across the gap; after stressing, either the falsework or the girder is moved sideways to the next position.

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4.       Composite construction

-       Prestressed concrete elements and plain or conventionally reinforced concrete elements, interconnected structurally so that the two act integrally, may be adopted in cases where such composite construction provides an economical structure.

-       The prestressed elements may be pre-tensioned or post-tensioned,a nd may be precast or cast-in-place; the plain or reinforced concrete elements are usually cast in place.

5.       Circular structures

-       Reservoirs and similar structures may be economically built in prestressed concrete. The latter may be either wrapped round the wall with a special wire winding machine which tensions the wire as it is applied; or tendons may be laid round the wall or cast into the wall sheaths, and subsequently stressed with jacks. When tendons are on the outside of the wall, subsequent protection is obtained with a dense Gunite coating. When the tendons are buried inside the concrete they emerge  through special anchor blocks spaced uniformly round the periphery, and are protected by grouting.

Posted in: Pre-Stressed Concrete Construction