Bridge building went wrong
and writing articles
I’m sometimes asked why the publication of my articles is irregular. I’ve also been told that it’s better to produce stuff regularly so what has been taking up my time recently .. The bridge.
Maybe you remember me talking about ‘the bridge’? Here’s the story.
The original owner of the property bought an extra piece of land in front of the main building and the other side of a small river. He decided to build a bridge with a stone support pillar in the middle. A series of big storms increased the flow in the river and destroyed the support and the bridge collapsed. He then rebuilt it using 7 Douglas fir trunks that were 12 metres long (the whole bridge was 14 metres long and 2.2 metres wide) and pretty massive, these were supported underneath by four struts made from telegraph poles. The whole thing was covered with planks which he numbered in case they got washed away, all of this was about 30 years ago. The trunks weren’t treated and last year I noticed that they were rotting and needed changing so I set to and took off all the planks and started to dismantle the trunks and barriers.
This was the moment when people passing by continually made remarks like ‘that’s much too big a job for you!’ or ‘you’ll never be able to do that on your own!’ and similar. A bit tiring and very annoying! I had my plan, a reconstruction strategy and I was just getting on with it.
These passer-bys also spoke to the project owner expressing their doubts about the reconstruction and proposing alternatives. One person (Mr X) in particular was very persuasive and talked about all the friends he had who were competent and who could take on the project and do a good job. This all started to get right up my nose, especially as I was fine getting on with it and my plan was solid. Eventually, faced with a continuous bombardment of the barrage of comments, criticisms, propositions, suggestions and people getting so far up my nose they felt like a Covid test,I announced that the people making the suggestions could get on with it and I would do other stuff.
Away from the project I followed what was going on with some apprehension because promises made become too often promises not kept. The person (Mr X) who had persuaded everyone that he had a super group of available friends, didn’t. It seemed that he had volunteered them without actually discussing the subject with them. Which seemed strange as people often react badly to being volunteered and rightly see it more as being press-ganged.
One thing that you may have noted during your lives is that it’s usually best to dismantle something rather than let it collapse and then have to deal with a total mess. Because of some ‘delays’ the bridge collapsed.
Now you’ve got a game of fiddlesticks or spillikins involving some big and heavy timber. Mr X managed to find some herberts to help him sort the mess out and a carpenter who came up with a plan for the bridge reconstruction. So far so good except the plan involved oversized sections of timber. Basically 4 and 6 metre long Douglas fir beams that are 35cm by 20cm, they are very heavy. So, question : why use massive sections rather than more lighter and easier to manipulate smaller sections? There is no particular reason not to use lighter beams and increase the number of beams. The other point is the transfer of the various forces and the way the wooden beams respond, it would have been possible to use even lighter beams with added timber to give the classic I shape.
A final point is that the bridge is supported by struts so again we could use more struts and lighter bridge sections. My original plan involved timber sections that were 10cm by 25cm, lighter, easier to manage and a lot cheaper.
The other problem with the plan that the carpenter came up with was to pre-build the bridge sections 3 timbers along with 1m80 across at each end and then float them through the air somehow. Easy enough with a crane but there was no way to get one onto the site so they came up with the idea of running 2 horizontal cables and sliding the sections into place. Keep in mind that the center section would have weighed nearly 2 tonnes, cables resist stretching pretty well but tend to sag badly when they are horizontal and the weight is perpendicular.
Anyway it all started going badly fruit shaped and I got called back in. I then had to figure out how to change the plan to one which was feasible and which I was going to have to execute more or less on my own. The timber had been delivered and as expected it was very heavy so I was feeling very cheerful about the whole thing. I ended up calling a friend who is a carpenter and he agreed to come and help me. Out the window went the original plan and we decided to use 2 beams and not 3 and fill in between them with lighter timber and reinforced with horizontal diagonal braces.
All the timbers are held together with threaded rod, appropriate dome headed screws and a shed load of glue to help resist against the shearing force exerted by the bridge load. Incessant rain delayed the construction but we eventually got it done, you can see that we made it less wide at 1m80 than the original bridge as we don’t intend to drive cars across. All I have to do now is finish the handrails!
Have I learnt anything from all of this? Yes, when starting the project I should have worn ear defenders from the get go which would have meant not hearing all the blather that I had to put up with in the beginning :-)
Epic Steve! Douglas Fir=Good Wood!