Kingsway Tram Tunnel
Steel Beam replacement
With over 30 years' experience in the repair of bridges and similar structures, Topbond are often able to 'think outside the box' and come up with innovative solutions to tricky problems.
When Topbond were first invited to tender for this project, which involved the replacement of 8 road- supporting steel beams, the proposal was to splice the beams since it was felt that there was insufficient room to install the beams in one piece.
Topbond realised that, whilst this might make for easier installation, it would certainly have maintenance implications and since life cycle costs are now an essential consideration, they looked for alternatives.
With a distance of 6 metres between the tunnel walls and a diagonal distance of just 6.4 metres, it looked at first sight as if it would be impossible not to have a splice. However, they calculated that by removing a 1000x600x600 deep section of the concrete ballast wall adjacent to the existing beam it might just be possible to install the beams in one piece. However the as-built drawings indicated that there were brick-built service tunnels on each side of the tram tunnel just 800mm away from the ballast wall so great care needed to be taken not to cause any damage.
In order to put their theory to the test, a 10:1 scale model of the tunnel and the new beams was constructed and it was agreed that this was a viable proposition.
The beams were manufactured, shot-blasted and painted prior to delivery and further calculations using the scale model were used to determine the optimum positioning for the lifting position, given the extremely limited space available.
A system of temporary works was required to carry the loads whilst the old beams were being removed and the new beams installed and a RMD Megashore temporary support scheme was selected.
When the temporary beams were in place and final checks were made to ensure they were taking the load, the first old beam was removed using gas cutters. The exposed troughing was shot-blasted to SA2.5 and painted with Acothane weld coat which cures in approximately 1 hour. During this curing period the new beam was jacked across to replace the old beam. The load then had to be transferred back to the new beam by placing jacks between the top of the new beam and the top of the troughing. Load was applied until there was no load on the temporary works. The gaps between the top of the new beam and the bottom of the troughs were packed with galvanised shims and the bearing ends welded to the top of the columns.
To complete the new beam works all of the formed voids were shuttered and pumped with concrete.
This procedure was then completed for each of the 8 beams