Bridge 2, Childswickham Road
Tramblast have now completed the final painting of this bridge, and it is now nicely protected against the elements for many years to come.
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| Our structures engineer salutes the quality of the work... |
Bridge 4, Peasebrook Farm
The extra steelwork needed to
strengthen the deck of this bridge is now completed, with the twin channel
beams all sitting neatly in the “U” shape part of the troughs, each packed up
to allow the concrete to flow around and under them. The steel reinforcing
fabric is in the process of being laid over the deck area, a tricky task as the
sheets are quite heavy and tend to catch on the shear studs fixed to the tops
of the troughs lap joints. These studs can be seen more clearly on the upside
photo.
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| RSJs can be seen laid in the troughs |
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| Reinforcing fabric being laid over the deck |
The next task is to fit the
reinforcement cages then install the outer shuttering to each end and then it
will be ready for concreting – hopefully later this week.
Hi Jo
ReplyDeleteI can't see any sign of the 2 16mm dia bars which should be welded across the ends of the beam flanges to give stability during concreting (as shown on the drawing you posted recently). Has there been a change of plan? This looks as though the finished bridge will be many times stronger than the original arrangement!
Not sure about that, maybe still to come. Remember they were only laying out the sheets when the pictures were taken.
DeleteIt is indeed the intention to make the bridge stronger than the original design. It didn't impress the engineers, let alone the deterioration.
Well spotted Peter, The tie bars have been held back as they would have created difficulties with getting the re-bar cages for the end bearings into position. The bars will be fitted at the same time as those cages and then will be welded to the channel beams before the concrete is poured. As Jo has said the original design was a bit on the "light" side and will now be upgraded to meet modern design criteria.
DeleteI have reading the 'Bridges Blog' with great interest.
ReplyDeleteI retired as a Railway Bridge Engineer in March and have following your reports.
I was based in Birmingham, but the bridges are identical to a lot of GWR structures in the West Midlands.
It is good to see what you have done especially with the luxury of a closed railway.
I can see many familiar features from the photos amd the typical deterioration you have found.
Keep up the good work.
John Fancote
Thanks for your interest. As you say there is a lot of conformity of the steel structures, in the basic design of the deck beam layout and deckplate work, although, obviously, the main girders changed with the variations in span and skew. Unfortunately the steel had very poor end details from a maintenance point of view, exacerbated by poor deck drainage, leading to rotting of the ends of the deck plates and many of the main and track bearer beams. I guess that there was never enough money around, nor, with a live railway, the time to tackle the amount of repair work needed. Fortunately, although over 110 years old the steel is weldable, which has simplified repairs considerably. On a personal note, my family business was in major dismantling and demolition, which included the removal of Birmingham New Street Station and the Queens Drive bridge, back in the sixties!!
DeleteI was struck by your comment about "poor end details"; I've been very taken by the 'drip strips' (sorry, don't recall their proper name) added to the ends of the deck plates, to prevent water running back up under the plate. Such an elegant device - but they don't seem to have been known, back when the bridges were first constructed. Does anyone happen to know who/when/where they were invented? Like many things, they seem 'obvious' once you know of them, but clearly they _weren't_ obvious before some clever person dreamed them up, as they seem to be a recent innovation?
DeleteNoel
This drip strip suggestion came from our Engineer at CH2MHill (formerly Halcrow). He has worked with a large number of Heritage railways, in varying capacities, over many years, but whether he thought it up himself, or saw it used elsewhere I am not sure. When you see the effects of water "run-back" under the deck plates and then down into the supporting girders, eating through 3/8" steel deck plates it is quite amazing. I suppose after 110 years the steel has held up pretty well. Much of the steelwork between the abutments looks as though it came from the rolling mill just a few years ago!!
DeleteJohn,
DeleteIn a previous life I have carried out waterproofing to similar bridges. Sometimes a concrete haunching was put at the end of the deck and the waterproofing membrane draped over it to run the water off.
As these repairs were done in a possession (about 16 hours) we didn't have time for drip strips.
John,
DeleteWe have managed both the drip strips and the concrete haunching, so hopefully it will last even longer. The waterproofing has been taken down well below the tops of the padstones, as many of our bridges have water coming out at that level, and which is then running down the faces of the abutments, as well as corroding the main steel bearing points.
John,
DeleteThis is a common fault on a lot of railway underbridges.
We also tried laying a drainage channel at the base of the haunch to pick up the water and discharge it through the abutment end or wingwall.
This depends on the bridge and is not aleays possible.
We could have done with you when we were designing the scheme!! We have done the same, with a drain at the end of the haunch, about 900 deep then taken down the embankments. Unfortunately I don't expect to be around for another 110 years to see if it was really effective!!
DeleteJohn,
DeleteThanks for the comment.
Sorry for the delay on replying, but I have been in hospital for 6 months and was discharged to home today.
Your works have helped keep me sane!
I would be glad to pass on any information or experience I have gained, although I think it will be some months before I could visit the railway.
John,
DeleteSorry to hear of your hospitalisation, and glad that we have given you something to occupy you during your recovery. It has been an exciting period for me starting about 18 months ago preparing the share offer document, then the tender documentation and finally actually starting construction in May. I hope that you will make a speedy recovery and that you may eventually feel fit enough to come and join our Civil Engineering department, in some role or another. Please contact me via our head office at Toddington, if you feel that you might like to participate in some way. We have everything from inspections and record keeping to hands on construction work available.
Thanks for the information about the drip strips. If you happen to run into the person from CH2MHill, maybe they will remember where they got the idea from? Yes, I was struck by the amount of damage the 'run-back' can cause - which is why I'm so taken with the strips! :-) Such a wonderfully simple and inexpensive, yet effective, solution... Engineering at its best!
DeleteI hear you about the 'won't be around to see if it works'; that's common to all branches of engineering, alas. We just have to do the best job we can of thinking forward, and hope we mostly get it right!
Noel
Our Engineer says that he thought up the idea himself based on similar details with window cills and stone lintels etc.
DeleteEspecially interested in the close ups of the goods shed available by blowing up your photos. I was planning to visit the caravan site and ask if I could look closer but did not get around to it. I see they just filled in under the lintel with a glass screen, looks very neat actually. Many thanks, makes my day, these blogs.
ReplyDelete