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erected over capping bars thatslided over a concrete beam,covered by a steel rail.

A 12 m steel launching nose wasused to control the structurebending during the launching.

Two jacks, erected in the nosesfront were enabled to lift the

structure, thus compensating thedeflection, allowing the nose toreach the pile bearings.

These special free-slidingbearings, supplied by VSL/CTT,had an inox sheet cover thatwould be removed when thelaunching was completed,allowing the structure to beconnected to the bearings.

During the incrementallaunching, elastomeric padswith PTFE were placed betweenthe beam and the bearing,assuring a minimum frictionforce. At the pre-cast yard thesteel work structure was

Perdigo viaduct is part of theA23 highway, consisting on twoindependent decks; each formedby two steel girders and a pre-cast concrete slab.

Only the steel structure waslaunched.

The viaduct is 600 m long, withextreme 40 m spans and 52 mcurrent spans and the variationon the launching leaning from-0,5% to +4,6%.

SLU jack connected to the steel girder

Perdigo Viaduct- Portugal

Steel structure incremental launching.

Perdigo Viaduct with 600 m length

Scope of works performed

Design and execution oflaunching method

Structure lifting Special pot bearings supply Joints supply Prefabrication area layout Steel details design.

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OWNERACESTRADA

ENGINEERLisconcebe

MAIN CONTRACTOR

Soares da Costa

VSL ENTITYVSL Sistemas Portugal

SLU jacks 70/330 were used topull the structure.

Tendons were installed along thecasting yard with dead-endanchorages in each edge. Thejacks (one for each girder) arethen connected to the structure,moving along with it.

This assembling allows to reversethe process, pushing back thestructure, in case of strong windsor any other unforeseen situation.

Hydraulic jacks at the tip of the nose

The two decks in place One more segment being launched

www.vsl.comEdited

2006

To do so, it is only necessary

to remove the jacks and installthem backwards.

The current spans wereassembled and launched ona weekly cycle, allowing theconstruction schedule to becompleted in time.

A free-sliding bearing placed at theabutment