What ails Hammersmith bridge?

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Most of you will know the news today, which is of course the great possibility that Hammersmith bridge ‘may be shut to drivers for good.’

What is it that ails Hammersmith bridge? Was it really a bridge poorly constructed as the Standard claims?

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Comment in the Standard 10 July 2019.

I don’t think its a poorly designed bridge, its just a bridge that wasn’t ahead of its time and rather was one built between a rock and a hard place. It compromised by being considerably basic in terms of construction. Indeed it is an iron/steel structure (the steel being used to replace the older iron parts) however the most expensive part of it would have been the road deck and so that was built in wood, using readily available second hand railway sleepers. It was a quick replacement for the older bridge that stood here and a means of continuing to provide bridging across the Thames at this important location. No-one expected anything above the tare weight of a substantial horse and cart!

What is most surprising is compared to other suspension bridges of substantial historic note, this one has kept its wooden deck! Its absolutely amazing that this wooden road deck has remained well into the 21st Century carrying loads far beyond what were originally envisaged. Not one engineer or architect in their right minds would today design a bridge with a wooden deck to cater for over 21,000 vehicles a day!

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Article in the Standard today 10 July 2019. Online version here

I was there a few days ago just as it had been revealed by My London there were a number of aspects regarding the bridge which had not been revealed before including the millions previously unknown that had been spent on it.

Basically its said millions of pounds had been spent on Hammersmith bridge whilst major problems went undetected. Surprinsingly, TfL took over management of the bridge in 2015 and between then and 2019 spent £5.3 million on it.

In that time period it was agreed a major job costing £27 million was needed to repalce corroded bolts, undertake resurfacing and repainting, but this programme was not pursued.

LBHF itself began a series of checks starting in 2015 and found micro fracures in the bridge in April 2019 which led to their decision to close the bridge immediately. The council said:

This is a new problem that only came about because in 2015 we began a series of thorough checks. That’s essentially the issue that led us to close the bridge. It is not a failure of our relationship with TfL… It’s a failure of a 132-year-old bridge which no-one checked for decades.

I have photographed the bridge in depth before however this time I focused on its wooden deck. Before we look at that aspect with my photographs, the image below probably taken in the 1920s maybe the 1930s shows clearly what the bridge is about. All its decks are made of wood – both road and pedestrian walkways. And this is basically what the bridge still is about today.

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The bridge 1920s/1930s clearly showing the wooden decking. Source: Keeping things local. The traverse iron beams can be easily seen.

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Huge banners declaring both LBHF and TfL’s intention to restore the bridge to full working order. Is that even possible?

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Looking up at the bridge from the ground and its wooden deck is most evident. It consists of generally two or three layers of railway sleepers and then a specially prepared plywood topmost layer to form the roadway.

Clearly the bridge can’t be laid with a normal tarmac roadway as that would be too heavy. Not only that the tarmac would break up almost instantly.

The problem however is, to convert the bridge to support a modern all purposes flexible roadway would mean all sorts of things. The bridge would have to be substantially re-engineered in order to support any new additional weight for the roadway infrastructure.

The steel beams that are underneath the roadway would need to be strengthened before a new all-steel preliminary deck could be built to accommodate a new roadway. I think the issue here is the height this new roadway would be and that would change the bridge’s historic appearance completely.

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Part of the wooden decking, clearly with wooden inserts and cuts wedged in over the years to part replace life expired timber sections.

Basically to repair the bridge and restore it to use whilst keeping its historic appearance would require lightweight materials of immense strength such as graphene or something else in the nanomaterial sphere. The problem is such materials have not been widely developed yet and are certain to be immensely expensive. Thus the bridge needs something which is ultra-strong and yet also light. Perhaps something like High Specific Strength Steel which has recently been developed. Its currently a very tall order and it might mean the bridge would have to be strengthened using traditional materials which isn’t what is wanted if we really wish to see the bridge given a substantial life-extension.

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One of the more substantial sections of decking. This consists of a substantial bottom layer of wood which might be railway sleepers turned on their side or specially cut timbers. That sits across the steel beams beneath the bridge. On top of this are two layers of railway sleepers, placed transverse on top of each other to provide maximum strength.

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The suspension links clearly go down to the traverse steel beams. These in turn hold up the wooden roadway and specialist anchor points have to be made to keep the whole wooden structure in place.

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Some of the pedestrian wooden decking moves considerably. This particular bit has had patches applied to try and keep it stable however when one walks along this, it bounces up and down in unison to peoples’ footsteps.

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Cyclists enjoying the bridge all to themselves! Will this be the new norm?

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So many parts of the bridge are rotten one does not really know where to begin!

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LBHF/TfL poster on several points at the bridge explaining both authorities’ plans for its future.

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General view of the bridge approach with staff on hand to ensure motorised vehicular traffic does not attempt to cross.

Early estimates for the complete repair of the bridge and restoring it to traffic was though to be in the region of £40 million however its now been deferred to August this year. In the mean time further investigation work is ongoing and by then the Mayor of London will be in a position to announce costings and a programme of repairs, although many are questioning why the Mayor has to wait until August to do this!

On top of that today’s reports indicate the work will now cost over £100 million. Its said TfL haven’t even got that kind of money, and neither have LBHF. And that is why its being said the bridge will not re-open to traffic.

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New monitoring equipment has been installed underneath the bridge.

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The equipment is provided by BDITest.com

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Total Station: New precise level monitors installed to keep a watch on the bridge’s movement.

I was intrigued by the fact the bridge is lit up with numerous lights in broad daylight and its clear the lights are on 24/7. Quite a few people have complained saying there seems to be no reason for it other than an expensive electricity bill!

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Old and new lights – switched on 24/7!

News reports say the installation of the lights apparently coincided with a flurry of workmen seen about and on the bridge not doing very much! I dont know if that is true or not! I think its not that they haven’t been doing nothing they installed scaffolding and steps in order to be able to examine the structure and the towers, and engineers have been surveying those.

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Accessing the tunnels in which the chains descend underground. Source: LBHF

I can tell you these surveyors have also been deep inside the foundations of the bridge in very difficult conditions to inspect the chain tunnels and the anchor bases deep down. The chains go through very narrow tunnels at a very steep angle towards their anchor points some way out from either end of the bridge itself – access to these parts of the bridge is extremely limited. The following image (known as a pointcloud) shows how the structure is built and where the suspension chains eventually lead underground.

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Side view of Hammersmith bridge showing its exact nature of construction. Source: ABA Surveying

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