Since the transverse beams appear to be continuous across both spans, rather than separate for each track, theoretically the centre reaction onto the jacks would be 62.5% of the total load, and the end reactions 18.75% each. In practice the jack supports aren't rigid and it's not a uniformly distributed load, so it will vary from that.
Thanks, I knew someone would have a better idea than me about the relative loads. I think the only thing I was sure about was it definitely wouldn’t be an equal 3 way split…
If the transverse beams had been in two sections, meeting end-to-end above the centre jacks, then the quarter / half / quarter would have been appropriate (subject to the same real-world variations). Years of temporary works design has left these sorts of numbers burnt into my brain much more firmly than more useful things, like what I came upstairs for
.
Yes, great pictures - thank you.
Ah, I see where you are coming from - I thought those numbers looked familiar! But while that assumption of a uniformly loaded beam might work for the deck structure (including the cross-beams), I don't think the three main girders would fit it. Assuming (based on no actual knowledge) that the deck is half the mass, and each girder one sixth, you get about 48% of the weight on the centre support.
Yes, I was making the rather sweeping assumption that in terms of loads onto the jacks, the transverse beam above the jacks acted as a rigid member with a UDL throughout. The reality will depend (among other factors you mention) on the relative stiffness of the bridge beam above and the trusses below. It's also possible that the jacks are interlinked hydraulically to maintain the intended load sharing. Fortunately someone else is being paid to worry about this one!
Thanks for the photos. More here from the Royal Engineers who are also following the work closely. Says the spans have been jacked 600mm. I hadn’t noticed the metalwork on the existing abutment before. Strapping to stop it disintegrating?
Thanks very much!
Yes, good to see them doing it: clearly they intend to get it back open ASAP. Meanwhile I have been enjoying trips on the bus between Swindon and Oxford on which there is a ticket acceptance arrangement. Given the replacement buses between Didcot and Oxford it is probably just as quick, if not quicker, to get off the train at Swindon and use that Swindon - Oxford bus. Cuts the cost of the trip too.
Great photograph too thank you.
Perhaps, though I can't help but feel we are half way through the planned closure, and we are still in the "demolition" phase.
Don't forget that, as well as what's visible in the photo, a lot of design work for temporary and permanent works, mobilisation of workforce and equipment, health and safety checks, method statements and risk assessments will have had to be done in the last five weeks. With working over water, and involving an old structure, the latter will have been a considerable amount of work, with sign off needed from several organisations. I'd say that all that, plus the physical work on site, is an impressive achievement in just five weeks.
For those who are blissfully free of Facebook, there's also some photos on their website.
Seems like NR are a lot faster at demolishing bridges than repainting them!
The new abutment piles are going to a significant depth (20m+ IIRC). There would be little difference in geological profile obtained from a borehole at the centre of the abutment and one at the edge of the embankment (which is the likely location for a test borehole). Given the bridge has been monitored for some time and an alternative ground improvement option was being implemented to prior to the abutment failing, we can be pretty sure that the geotechnical data required for pile design was already available - and this probably explains how NR's designers were able to get the new abutment foundation design done so quickly.
25m according to some earlier posts and the item in Rail magazine mentioned in #732.
That link didn't work for me, just got a blank page.
Yes it is.
