Tuesday 19 August 2014

After a pause for the weekend, and a concrete pouring session at Little Buckland bridge on Monday, we can give you a further update today:

Bridge 1, Broadway

This continues to receive the attention of the fabricators, who have been drilling, bolting and welding non stop these last few days. Here's what they were doing yesterday:




This is where it is going.

New plate ready for bolting on


The last major plate is now all drilled and ready to be fitted to the northernmost major cross beam, so here is a photo of the plate and a view of the original beam which has been cut back to allow the insertion of replacement plates to form the horizontal leg to the bottom flange angles, and to which the plate will then be bolted. Got that? All good stuff, replacing parts rusted and/or bent by anonymous passing lorries.

 Bridge 5, Little Buckland

 Here progress is a little bit more obvious. They are putting in a big concrete wall behind each of the two abutments, and at the moment they are busy with the northern, Broadway end. Here are some pictures of what was happening yesterday and today:
Concrete going in via mini digger bucket.
 
Carefully filling in behind the shuttering.

Finished! After the shuttering was removed again.
The 3rd lift of concrete was poured on Monday behind the Broadway end abutment and wing walls. Placing was by delicate use of the excavator bucket, not a pump this time.

Then the Cheltenham end was prepared for the final pour:
 
Mini digger lifting in place the Cheltenham end shuttering.




Here we see the shuttering, dismantled from the Broadway end, being put back in place at the Cheltenham, end for the final lift to thew top. Nearly there now. Great work !

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3 comments:

  1. Anonymous20 August 2014 at 13:36

    Will they be putting a coat of some sort of preservative on the metal (both sides) before they bolt the new plate in place? From the pictures, even with rivets to hold them very tightly together, water was able to work its way between them, and cause rust...

    Noel

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  2. sreevesjc22 August 2014 at 14:30

    No. The faying or mating surfaces must NOT be painted as that impairs the friction between the plates. The transfer of forces along the flange, through splices, into the angles and web depend upon friction; the bolts are not intended to behave as dowels.

    Most of the corrosion seen in the pictures has initiated at a plate edge due to water seepage through the deck, or is as a result of vehicle impact damage. When riveted plates have been separated, the faying surfaces have been found to be as smooth and bright as at the time when they were erected.

    The Tension Control Bolts being used are preloaded and apply a high clamping force that enables the friction between the plates to be realised (with an assumed coefficient of 0.45), as well as preventing water ingress. To give an indication of the forces involved, the preload in a single 22mm diameter high strength friction grip bolt is 177kN (18 tonnes). The TCBs apply a higher force, and have the additional advantage of ease of installation with safety, as there is no torque reaction from the wrench. Furthermore, one side has the appearance of a rounded rivet head. Some bolts are installed ‘up’ and others ‘down’ depending on the space available around the nut for the wrench.

    There are strict rules governing the maximum spacing of bolts to prevent water ingress and rust jacking. Rivets work in the same way as pre-loaded bolts as they are installed hot and apply a clamping force as they contract upon cooling. There is no chance for water ingress by capillary action, but the tough and durable paint coating is specified to give full protection.

    John C Sreeves
    Bridge Engineer
    CH2M Hill

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  3. Anonymous22 August 2014 at 22:51

    Thanks for that most enlightening explanation!

    Noel

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