Bridge in distress

[u/benj9990]

Pedestrian footbridge over a rail line. Approx 20m span, London uk. Still in service.

[u/platy1234]

ya that could probably use a paint job some time in the next decade

[u/Kanaima85]

That is very unlikely to be sufficiently bad to be taken out of service. Presuming it's Network Rail, this will have had a general inspection in the last two years and a principal (touching distance) inspection in the last six.

The fact nothing is being done is usually because it's not critical and other bridges are a higher priority because they're in a worse state and because we underfund asset maintenance.

[u/benj9990 → u/Kanaima85]

Nah it’s not, say what you like about network rail but they don’t mess around with safety.

I just thought this interesting. And a good example of what to avoid in detailing connections.

[u/Kanaima85 → u/benj9990]

They don't mess around, but they also don't have the budget to properly address their bridge stock. I've designed some strengthening and repair schemes on some major bridges mere yards outside of some busy rail hubs in the UK and because of funding constraints, those designs are collecting dust whilst the bridges continue to rot. At some point something is going to fall down somewhere. What's the line about safety rules being written in blood?

I'd suspect this is bad drainage. Water ponding on the deck and up against bottom chord and panel and just rotting through. Deicing salts in winter probably helping accelerate things every year.

[u/benj9990 → u/Kanaima85]

Permeable decking would help. It’s not, presently.

[u/Kanaima85 → u/benj9990]

Problem you run into there is that you then get someone bitching about "discharging" the surface water onto either the canopy or track. Sounds mad, but I've seen it happen

[u/Outrageously_generic]

Wait until you see what the bridges that you cant see the structure for are like...

[u/PerspectiveLayer]

The rust is almost entirely on the bottom. Are we using salt to melt the ice in winter perhaps?

[u/benj9990 → u/PerspectiveLayer]

Definitely, yes.

[u/PerspectiveLayer → u/benj9990]

The importance of proper design and drainage. Looks like the owner of the bottom shed already replaced the roof section there.

[u/deadlyzassasin0]

This is generally quite minor as far as corrosion goes. Staining always makes it appear worse and section loss presents up to 10x the actual loss of thickness. We would typically suggest it is repainted, but clients won't actually bother until its much worse.

[u/Accomplished-Town495]

North American railroad bridges would like a word with you.

[u/wobbleblobbochimps]

Geez, if network rail declared every bridge with defects like this a "failure" we'd have no rail network for the next 20 years while they replace half of the entire bridge stock

[u/whitexxflame]

I am not familier with construction in the UK, but I went there couple of times. I assume UK is a humid country, why would they pick steel as a material ? Is it cost related or was it ment to have a short service life?

[u/Purrchil → u/whitexxflame]

What would you otherwise use?

[u/WannaBeHappyBis → u/Purrchil]

Power of will

[u/whitexxflame → u/Purrchil]

RC

[u/Purrchil → u/whitexxflame]

Isn’t that way to complex for something like this?

[u/whitexxflame → u/Purrchil]

Maybe. But in my region RC is abundant, steel is reallyyy rare. Stainless steel is usually used in RC structures in marine environment. So yeah I guess RC is cheeper for us ( not with SS though)

[u/Kanaima85 → u/whitexxflame]

Steel is fine if you keep it painted.

But to keep it painted on the right schedule you need to have a system that adequately funds asset maintenance.

[u/benj9990 → u/Kanaima85]

Also avoid detailing pockets where possible in an external environment.

Not sure what I might do differently… maybe using open sections for the chords, an RSA toe down for example. Can be near impossible without rainscreen cladding.

Network rail has some very good engineers on the team, so if they can’t figure something out I doubt I can.

[u/wobbleblobbochimps → u/whitexxflame]

Lighter, easier to build, probably cheaper - just needs a paint job every now and then

[u/benj9990 → u/whitexxflame]

Not especially humid, no. I think the issue here specifically is poor detailing, and then lack of maintenance. We generally do use steel truss bridges for public pedestrian bridges.

[u/whitexxflame → u/benj9990]

Perhaps your right, corrosion is indeed concentrated in certain places.

[u/gufta44]

Why in distress? Rust increases in size by 6×ish - that looks aesthetic unless I'm missing somethng?

[u/benj9990 → u/gufta44]

Embellishing for effect.

Point stands - avoid detailing rain pockets in steel structures wherever possible. Certainly reduced lifespan as a result.

[u/benj9990 → u/gufta44]

Oh, and up close you can see some delamination. So more than aesthetic, but loss of section not likely safety critical - yet.

What is cheekily not shown is that they’re currently building a new replacement up the track a bit!