Br. 08 - REPORT ON REPAIRS TO FRIDAY 4TH FEBRUARY 2022
This contract required two weeks of preparatory work which included: -
1. 4 days for 3 men with a 360 and dumper moving 120 T of ballast from Stanton yard ½ mile to the bridge site and laying it on top of geotextile fabric laid to protect the track, then rolling it to create a firm ballast plateau.
2. 5 days for 5 to 6 men transporting the heavy-duty propping, from Stanton yard and installing the propping on the plateau, including fitting extensive scaffold tube bracings to all faces at ninety degrees.
3. 5 to 6 days for 5 men constructing a heavy-duty, fully boarded working scaffold platform onto which the old steelwork could be lowered, and the new steelwork lifted and trollied to the hoisting and lowering points.
Finally, on Tuesday 18th January all was ready for the steelwork sub-contractors. They duly arrived and spent most of that day getting all of their equipment (grinders, burning gear, generators, and small tools) down to the bridge and getting it lifted onto the scaffold deck.
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| Shows multi ply plates and bottom flange cut out. |
Work was to start on long cross girder 1 (LG 1) with taking off the multi thickness bottom flange plates.
The steelworkers' plan was to burn the head off the bottom (below the plate to come off), then jack the rivets out with a 30 T hydraulic jack suspended from a purpose made frame fixing it with large clamps to the girder above. This worked well for the first few, and then the head of the jack bent over and was no good. The problem was caused by the fact that when up to five thicknesses of plate are hot rivetted together, the holes are never in perfect line and so “corrugated” edges form to the rivets and so become extremely hard to remove.
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| Grinding off rivet heads. |
The fall-back plan was to grind off the rivet heads and then drill out the rivet shank using rotabroaches.
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| On the rotabroach, drilling up. |
Whilst this worked perfectly, drilling upwards was extremely hard. No lubricant could be applied to the cutting edge.
At the end of the first week barely half the 180 rivets were out of the first girder, although many other had their heads or bases ground or burnt off.
They returned the next week with a second and larger rotabroach and set to work again. With one man drilling and grinding and two drilling, progress improved considerably and just a handful remained by Friday 28th Jan.
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| Areas outlined in green for shotblasting. |
However, some areas to which new steel was to be attached were buried in very heavy scale and rust, which needed to be removed. In addition, we had found other areas where extra works were required on the two large outer main girders, which were also heavily scaled and needed blast cleaning. These areas were sprayed in red or green for urgent blasting.
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| Red shotblasting areas required. |
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| Shotblasting going on under Br. 8 |
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| Large compressor needed for the shotblaster |
At very short notice the main contractor was able to get a heavy-duty blasting contractor to come in over the weekend, when no one else was working.
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| Web holes and bottom flange loss exposed by shotblasting |
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| Bricks now being cut out to make room to weld in strengthening plate |
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| Outer main girder above downside track showing wastage from steam. |
... and he did an excellent job which, inevitably, exposed some badly corroded and holed steel. (Pictures above).
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| Old and new plates together. |
Meanwhile the Steelworker was progressing well and on Monday 31st Jan the first old plates were removed and lowered, and the new plates raised onto the platform.
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| On site drilling with 2 rotabroaches. |
Because of the tolerances in holes the old plate was then used as a template to enable the new plate to be drilled with 180 holes for 20mm torsion control bolts.
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| New plate attached to bridge with temporary bolts. |
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| Long girder No.1, seen from the low mileage end. |
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| Long girder No. 1 connection to outer main girder |
By Wednesday 2nd Feb, the new plate had been completely drilled and was hoisted into place and supported by a few temporary bolts (three pictures above).
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| Badly rusted away original plate |
In the picture above you can see how badly eaten away the near end of the old plate was.
The second reason for having blasting done was because what we had seen with the two Outer Main Girders (OMG’s). These have what is called a steel ledger angle rivetted to the web of the OMG. The projecting leg of this angle then supports the curved Jack-arch brickwork, and, a concrete fill to form a level surface, which then carries the road above.
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| High mileage outer main girder. |
In the picture above it can be seen that the horizontal leg holding up the brickwork has gone very thin. Replacement of this is virtually impossible and so, starting on 4th Feb. an extra steelworker has come in to weld into place supplementary angles just below the existing.
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| Low mileage outer main girder, bay 2. |
The space between them will then packed with a special mortar. This was done successfully during the 2007 repairs (above).
Some extra works were required on LG 1 near the L-M OMG connection. In 2007 a strengthening plate was welded onto one side of the web of LG 1, leaving the badly holed piece behind.
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| Long girder No.1, bay 2, plug weld to 2007 repair plate |
We have now plug welded it to the 2007 plate, as can be seen above. The second problem was with the end 2M of the bottom flange angle of LG 1 right up to the connection with L-M OMG, which had gone very thin. A part of the old was cut out and a new piece of plate drilled ready to be welded in.
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| Bracing angle cut out, plate still to be welded. |
In the picture above the new plate is laid in place and yet has to be welded.
The men have been working 10- and 11-hour days, and now have an extra man who started on Friday and is working this weekend, and at least the whole of next week. All vital to get the contract completed by Monday 28th February.
05. 02.2022 - John Balderstone.
With thanks also to Neil Perrins, site manager for Montel Civil Engineering, for many of the pictures.
