Saturday, November 5, 2011

Methods of Erection

Methods of Erection
-       methods depend upon the ff. sites condition:
a.       size and shape of the members
b.      the relatuve quantities of precast and cast-in-place work.
c.       availablity of equipment
d.      etc.
-       ingenuity of the engineer in charge of wthe project plays an important role.

Examples of these in practice are the following:

a.       Choisy-le-Roi Bridge, France (Architect Jacques Ferrier of Paris)
-       Built by cantilever principle with precast hollow-box section were placed on a mobile frame running inside the structure joints by epoxy resin.
-       Post tensioning of each section through its opposite number then followed.
-       70 meters long

b.      King’s Avenue Bridge,  Canberra

-       2 independent bridges, 7 spans of 272 meters.
-       Span lengths are 28.5 from the abutments to 47 meters at the center.
-       The deck system comprises of 4 longitudinal prestressed T-Beams, connected by reinforced concrete deck slabs cast in situ.
-       Beams were precast in sections and stressed in full length behind the abutmen; they were then rolled out by trolleys to a launching truss, which itself was previously launched by cantilevering across the span to be erected.
-       This truss had overhead trolley gear with hydraultick jacks, which enabled the beam to be picked up one end and run out to the next pier; the truss could also traverse sideways across the bridge width to cover all girder positions.

c.       Woolloomooloo Viaduct, Sydney
-       a post-tensioned precast box girder bridge of 10 spans, 11 m wide, with a total length of 425 meters, part of which is on a 400 meters radius curve.
-       the precast segments, 2.36 meters long and the full width of the bridge, were erected by travelling gantry into falsewor, and stressed together in lengths of about 45 meters using the VSL system, each length bbeing stressed back to its predecessor, so that the completed bridge is continuously prestressed between abutments.


The conception of any structure in prestressed concrete requires the closest possible cooperation between the designer and the contstructor in order to acieve the best method s of erection to suits the economics of each individual project.


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