The South African National Roads Agency Limited’s (Sanral’s) Gauteng Freeway Improvement Project (GFIP) has come one step closer to completion with the placement of the 140-t Lynnwood Glen pedestrian and pipe bridge on December 20.

The process to lift the bridge made use of the biggest crawler crane in South Africa, with a lifting capacity of 850 t. In order to complete the project, the N1 between the Atterbury and Lynnwood interchanges was closed from 05:00 to 12:00, with the actual lift taking about 30 minutes.

Once completed, the pedestrian bridge will weigh 400 t, through the addition of handrails, a concrete walkway, and two water mains, says ARQ Consulting Engineers bridge engineer Tiaan Kramer.

ARQ designed the Lynnwood Glen pedestrian and pipe bridge.

The structure was manufactured by Cadcon, located in Centurion, from where the bridge was transported in six segments. Cadcon is a subcontractor of the BRCD (Basil Read, Roadcrete, Chavani and Dipcivil) joint venture.

The main parts of the bridge are manufactured from grade S355JR steel.

The steel bowstring arch bridge spans 73 m, has a width of six metres, and is 13 m high at mid-span, notes Kramer.

He says this particular type of bridge is relatively unique to South Africa.

“The bottom chord is usually supported from the main arch via cables, but in this case we made use of oblong shaped diagonals to give a perspective of a truss,” adds Kramer.

The new bridge replaces the old prestressed reinforced concrete pedestrian and pipe bridge, which was demolished to accommodate the widening of the N1 as part of the GFIP.

The R15,1-billion first phase of the GFIP aims to upgrade 185 km of freeway network by 2011, through, for example, improved lighting and the widening of freeways by adding new lanes.

Further phases will include 223 km of upgrades, and new roads of 158 km.

The final GFIP scheme will encompass 561 km.

PUBLICATION: Engineering News
AUTHOR: Irma Venter
DATED: 6th January 2010