VIADUCT ERECTION THROUGH CENTURION

Posted on Mar 5, 2009 in Media Releases

To date Gautrain viaduct construction has primarily focused on the Johannesburg, Midrand and Ekurhuleni areas, whilst construction in Centurion has focused mainly on ground improvement and foundation installation. Viaduct erection has however recently commenced on the longest Gautrain viaduct (Viaduct 5) which traverses through Centurion and has a total length of over 4km.

Figure 1 : Aerial view of Viaduct 5 routing near to Supersport Park and Centurion Rugby Club

Viaduct 5 carries the elevated alignment through Centurion and supports the elevated Centurion Station platforms located approximately midway along its length. This viaduct stretches from the John Vorster Interchange crossing the N1 in the south and then continues through Centurion to the Jean Avenue Interchange crossing the Ben Schoeman highway in the north.

Figure 2 : Artists impression of future Centurion station.

Viaduct Construction

Special equipment called ‘Launching Girders’ will be used for the deck erection process in Centurion central. The girders span between two of the bridge piers at any one time. The pre-cast segments of the viaduct (weighing between 45 and 60 tonnes) are placed by crane onto the girders and, using of a system of trolleys, are slid along the top of the girders into their final position.

Figure 3 : File photo of viaduct showing launching girders

Once all the segments for a given span are in position on the girders, steel cables are threaded through ducts cast into the segments and which run the length of the span. These cables are then tensioned (“stressed”) such that all the pre-cast segments are compressed together to form a continuous beam – one bridge span.

Figure 4 : File photo: End view of viaduct showing stressing cables

The girders will then lower away from the span (which can now support itself), leaving it on top of the piers. The girders then launch onto the next pier to begin the process again.

The first girders are already on site and have been assembled close to the Centurion Rugby club. This set of girders will start construction heading in a northerly direction over Lenchen, West, Gerhard, Hall, Von Willigh and Rabie Streets.

Construction from a second girder will commence in a southerly direction. This girder will cross over South Street, Kwartsiet Crescent and John Vorster.

This construction technique has already been implemented on several other areas of the project (including the viaduct into OR Tambo International Airport) and it is safe to drive under the launching girder during construction.