M20 Pedestrian bridge struck and collapses

[Helvellyn]

I am surprised they are only removing the fallen section of the bridge. I know the rest is structurally sound but it will also be an attraction for people to try and walk across to see the "precipice".

I think it's safe to assume that it'll be fenced off.

[roadtester]

I am surprised they are only removing the fallen section of the bridge. I know the rest is structurally sound but it will also be an attraction for people to try and walk across to see the "precipice".

I think it's safe to assume that it'll be fenced off.

I think that what kit is getting at is that they appear to be leaving half the bridge, the bit over the less affected carriageway, in place, supported only at one end.

It does look a bit precarious to a layman like me but I'm sure they know what they're doing!

[RichardA35]

The existing half span is balanced by the back span over the batter and is integral with, and fixed over the pier support. The fallen span was supported by this half span so it should be stable with the weight removed. The use of these half span joints is, I think, banned on new structures unless allowed by departure.

[kit]

I am surprised they are only removing the fallen section of the bridge. I know the rest is structurally sound but it will also be an attraction for people to try and walk across to see the "precipice".

I think it's safe to assume that it'll be fenced off.

There are plenty of people - kids and urbex - who could probably get past ahy fence.

[Chris5156]

The existing half span is balanced by the back span over the batter and is integral with, and fixed over the pier support. The fallen span was supported by this half span so it should be stable with the weight removed. The use of these half span joints is, I think, banned on new structures unless allowed by departure.

Yes, I agree it looks bizarre but will be perfectly safe. In layman's terms, the remaining bridge deck is anchored at the "land" end and has a support pier halfway along its length, so its weight continues to be balanced safely on the pier on the north side of the motorway. It's designed to have half a bridge resting on its hanging end, which is now gone, so there's no chance it will just fall down. It's undamaged and standing in exactly the way it was designed to, and now doing an awful lot less work than it was designed to.

Bridges like this with a joint halfway along are all over the motorway network and I wonder if we'll see a review or a scheme of strengthening works to prevent the supported beams being shunted out sideways like this. I can imagine surveys being carried out on all the remaining ones and retrofitting extra fixings to hold them in place when struck.

[Brenley Corner]

The existing half span is balanced by the back span over the batter and is integral with, and fixed over the pier support. The fallen span was supported by this half span so it should be stable with the weight removed. The use of these half span joints is, I think, banned on new structures unless allowed by departure.

I totally agree that the remaining section of bridge is safe structurally but I would be far more concerned about it becoming an item of both attraction and distraction - with endless videos taken from vehicles of the now infamous half-bridge across the M20. Not often an advocate of a reduced limit, but think a 50 would be prudent given the circumstances.

[Conekicker]

And it's just reopened.

[kit]

Not often an advocate of a reduced limit, but think a 50 would be prudent given the circumstances.

I think if you're in the 1% who are going to film it on your phone ("WTF BRIDGE LEFT HANGING OVER m20 LOL!!!") then 50mph is no safer, and will only slow the remaining 99% down .

[Johnathan404]

I am surprised they are only removing the fallen section of the bridge. I know the rest is structurally sound but it will also be an attraction for people to try and walk across to see the "precipice".

Crossed posts with Tony, but my immediate thought when hearing the bridge would stay half demolished wasn't about the explorers, but about drivers who can't pass a news story without posting it on Snapchat.

I understand this is a massive problem whenever a road is partially opened past a dramatic accident scene (overturned lorries being a particular camera-magnet - much higher than 1%), so where we have a news story which has been well-publicised in advance of the road reopening I think there is a genuine risk of people living nearby altering their journey to take in and/or film this unusual sight. The scene sounds really dangerous - not because of the debris, but because of the rubbernecking.

The problem isn't the one vehicle filming it while driving, it's that combined the drivers either side of it taking their eyes off the road to have a look. 50mph wouldn't go down well and does sound excessive, I'm just surprised drivers were trusted near it at all.

[MotorwayGuy]

Still a nightmare around the entire area, and for some reason they've decided to close access to the A21 from the anti-clockwise M25 as well.

[kit]

Maybe this is underestimating people's stupidity but is it really going to be that much of an attraction? From the news report photos it looks very dull and I can't imagine it being that much less dull in person.

In Didcot we had the half collapsed power station boiler house within a couple of hundred metres of the perimeter road for a few months but drivers seemed to be able to control the urge to take pictures of what was published in the papers anyway.

[Glom]

The decorative feature is so cool. It should be listed like the Give Peas a Chance viaduct.

[Helvellyn]

I am surprised they are only removing the fallen section of the bridge. I know the rest is structurally sound but it will also be an attraction for people to try and walk across to see the "precipice".

I think it's safe to assume that it'll be fenced off.

There are plenty of people - kids and urbex - who could probably get past ahy fence.

Such people manage to cause problems everywhere anyway, putting too much effort into dealing with them gets counterproductive.

[SteveA30]

The M25 to A21 slip has been closed throughout, to prevent the A25 being used I suspect. The A20 from Swanley was still available though. Oddly now, the M26 is still shown as closed on Google maps or ROMANSE. HE says it has reopened.

Immediate update at 20.04. A21 slip open but M26 not.
20.16 - M26 opened 1 minute ago. Queues back past Clacket Lane.

[ais523]

I'm actually more surprised that MotorwayGuy's picture shows a 20 limit (unless I misread the sign). That seems excessively low for the M25 even if it is running as two lanes with a queue coming up soon. You'd expect that just allowing traffic to concertina would be faster than such an extreme reduction.

[roadtester]

Sky News is saying that concrete blocks have been placed around the base of the surviving bit of the bridge - I think they said this was to protect it, presumably against collision. Not sure if there is any intention for this to support it in any way, and they didn't actually show the concrete blocks on-screen.

[kit]

I'm actually more surprised that MotorwayGuy's picture shows a 20 limit (unless I misread the sign). That seems excessively low for the M25 even if it is running as two lanes with a queue coming up soon. You'd expect that just allowing traffic to concertina would be faster than such an extreme reduction.

A 20 limit seems to be the default "bloody hell this is bad" manually set limit on the M25 for things like new accidents and debris in road. MIDAS only goes down to 40.

[LeedsKing]

As I see it there are two options for the future.
1. Remove the remaining hanging bridge at night and the spiral walkways at each end. May require road closure for one or two nights and a demolition?

2. Remove the bridge and replace it: will take much longer.

Option 1 will presumably irritate local former bridge users.

[kit]

Option 1 will presumably irritate local former bridge users.

You cannot just close a footpath, it has to have a legal order to be stopped up. Bearing in mind this is high profile, it will probably be easier just to replace the bridge especially as the (very expensive) bill will most likely be picked up by the haulier's insurance.

[Darren]

I'm actually more surprised that MotorwayGuy's picture shows a 20 limit (unless I misread the sign). That seems excessively low for the M25 even if it is running as two lanes with a queue coming up soon. You'd expect that just allowing traffic to concertina would be faster than such an extreme reduction.

A 20 limit seems to be the default "bloody hell this is bad" manually set limit on the M25 for things like new accidents and debris in road. MIDAS only goes down to 40.

I passed those 20s yesterday at around 6AM - just as well there aren't any speed cameras there, as the little traffic there was meant that 20 wasn't being adhered to by anyone.

They were preceded by a 40 and a few 50s, including at the gantry with the cameras on it a bit further back (and people were hurtling through there at 70+... they're in for a shock!)