LGCAA

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The Building Of Square Pool Bridge

 

 

About this time last year (May 2005) the fisheries management committee decided that the bridge to the island on Lake 2 needed to be replaced. The decision was taken for two reasons; firstly the existing bridge was coming to the end of its life, and secondly we wanted to gain access to the island with a mini digger to aid us with the planned regeneration works on the island.After some initial investigations we decided to build the bridge some 15 meters to the right of the existing one, into what was swim number 2. Once the position of the bridge was finalised, some initial investigations were carried out to find out the depth of the water and the depth of the silt (approx 2.9 meters or almost 10 feet all together). The depths and measurements were double checked and the details sent to a structural engineer for calculation.

When we decided to move the bridge we also increased the length of the bridge by about 2 meters, you might be mistaken into thinking that the addition of an extra meter either end would not make to much difference, well you could not be further from the truth. With the addition of the extra length we came across another problem. The original bridge design had one central pair of support legs going down to the lake bed, with each steel cross beam being 7.250 meters long and weighing 26kg a meter (to put in layman?¢‚Ǩ‚Ñ¢s terms 7.250x26=188.5kg, 188.5x2.2=414.7lbs, 414.7/14=29.62 stone). With a deflection of almost 50mm (that?¢‚Ǩ‚Ñ¢s the amount the beams will bend and straighten when the digger runs over them) we decided that this was not acceptable and probably beyond our capabilities to install the beams of such a weight. Once again more details were sent to the structural engineer, and the design was changed to include 2 pairs of support legs effectively dividing the construction of the bridge into three sections instead of two.
After the structural engineer had made his final calculations and we had accepted them we complied a list and acquired prices for all the materials required to complete the works. Drawings were made, and issued to the members who required them along with the list of materials we required and was presented to the GPC (General Purposes Committee) for approval and funding. On the GPC?¢‚Ǩ‚Ñ¢s approval and funding the order for the steel was placed and arrived in February of this year (2006). We had planned to start the construction of the bridge straight away but this was delayed until the start of the work parties.

On the first work party I gathered the team of men that I had previously asked for, but as with all projects that are undertaken by volunteers you do not know who is going to be there on the day until they arrive. Fortunately all the men I asked for arrived for an early start on the first day.
After an initial briefing we started work by checking all the measurements for the steel, these we found to be correct. Next on the agenda was to set out the positions of the concrete bases and dig out all the unwanted spoil. Once the bases had been dug, wooden shuttering was assembled and placed in position. Approx 3 cubic meters of concrete was ordered (this is about 6 to 6 and a half tonnes). Half of this we were able to tip into the base using Daisy our dumper, unfortunately the other half had to be pushed from the car park, over the old bridge to the island in wheel barrows and tipped in to the shuttering. At this point I would like to thank the 10 guys who turned up on the Saturday morning to help with this task.

On the Sunday after the concrete was poured we started the drilling of the RSJ?¢‚Ǩ‚Ñ¢s (each steel leg was drilled 8 times with holes up to 13mm) this was to allow us to fix the 500x500mm base plates to the bottom of each leg, giving them feet to prevent them sinking into the lake bed. Additionally each steel leg has a 150mm wide PCF channel attached to the top, this is for the steel beams that carry the bridge deck to sit in.100mmx50mm timber plates were attached to the top of the steels for when we were ready to install the decking boards again these were fixed via a bolt through the timber and steel. These works took us two weeks to complete, when I say two weeks I mean two work parties.

Once all the drilling was completed we had to erect a scaffold in the lake so that we could safely carry the steel legs on to and position them in the lake This was a difficult task to complete, and had to be done with 2 people in a boat and 4 people on the bank, it took almost 4 hours to complete, after which we installed the one pair of legs. The legs were then leveled and plumbed and we attached the first 2 RSJ?¢‚Ǩ‚Ñ¢s to the concrete base by drilling a 10mm hole in the steel and a 15mm hole in the concrete and inserting a 100mm long rawl bolt. We then slid the first 2 beams into position and fixed them to the pad and also to the channels we had bolted to the tops of the legs. Unfortunately during the installation process of the steel legs we discovered that we had miss-calculated the depth of the water and silt. We had to remove the legs from the lake bed and shorten each one by 300mm then re-drill the brackets that hold the channel. We then proceeded to complete the installation of the first side of legs and decking.

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The team was then split into two, one person cut and attached the decking boards to the timber plate. While this was going on the other members of the team removed the scaffolding from the lake and erected it on the island bank. The process was repeated again, that included the installation and removal and subsequent cutting and re-drilling of the steel legs. The scaffolding was removed from the lake completely and installation of the decking boards on the island side of the bridge. This left us with just the central section to fit.

After re-measuring the steel beams that were going to be the centre section of the bridge we decided that a bigger expansion joint was needed and again out came the cutter. We cut the steel to the required length and installed them. This was achieved by sliding them on the decking boards until the point of balance was reached. While we kept sliding the steels toward the support on the opposite side of the lake, three team members took the weight of the steel by pulling on a rope toward them. The beams were positioned and connected to the channels on top of the legs via nuts and bolts. With all the RSJ?¢‚Ǩ‚Ñ¢s now in place we drilled 50mm steel cross braces to the support legs this was to stop the bridge collapsing side ways. The last of the timber top plate was fixed to the centre sections and then the decking boards installed on top.

After the completion of the decking boards we were able to dismantle the old bridge and again I would like to thank the 4 guys who undertook this task in a safe and professional manner.

To make the bridge safer and to comply with the insurance requirements we had to install a hand rail either side of the bridge. This had to be done in such a way that it could be removable but also be able to support an adult if necessary. To do this we cut eight 50mm holes in the deck boards close to the edges but not to close so it weakens the board, scaffold poles were passed through the holes and driven into the lake bed with a sledge hammer once we got to a point that we could not bang them in any further we cut them off just above the deck and fitted a scaffold joint to them, we then extended them to the required height and fixed a handrail to them. In-between the uprights in the lake bed we installed intermediate uprights. This served two purposes; first, to stiffen the handrail, and second, to give us extra supports for the toe board.

This was all completed on 21/05/06 some 15 months since the initial measurements had been taken. The only thing that we have left to do is to paint the steels with green paint and hopefully this will be done either the last Wednesday work party or on the last Sunday one.

I have done some calculations just to show what it could have cost to have had a company to complete the work for us and have allowed for 6 men to be on the project (we sometimes had more and occasionally less)

Sundays 6 men @ 8 hours X 8 work parties = 6x8x8 = 384 hours
Wednesdays 6 men @ 8 hours X 8 work parties = 6x6x8 = 192 hours
Saturdays 2 men@ 16 hours X 2 work parties = 2x16x2 = 32 hours
Total hours worked = 608 hours

So this is what I think it would cost:
Materials (steels, Timbers, concrete etc) = ?Ǭ£1,500.00
Labour 608hrs x ?Ǭ£20per hr) = ?Ǭ£12,160.00
Total cost = ?Ǭ£13,660.00

So with all this in mind, and on the behalf of the GPC and the FMC Iwould like to say thanks to a few people: Firstly, to Tony Hersey and Alan Gentle (lovingly Known as the Chuckle Brothers). Thank you both for all the help and technical Knowledge and know-how you brought to the job and without the help from these to guys the bridge would simply not have been done.
To Jason Byrne (Wonky Eye the 5th Telly Tubby) thanks for all your help and again with out his help we would have struggled to finish.
Mark Thomas, thanks for your help it came at a much needed point in construction.
To the Telly Tubbies (Mike, Nigel and Jim), cheers guys, and finally anybody that I forgot to mention, thanks for all your help, have an extra burger at the BBQ.
Those people that I upset, please accept my apologies for my rudeness, but when you have a project like this its most annoying when you get somebody not involved standing behind you saying ?¢‚Ǩ?ìyou don?¢‚Ǩ‚Ñ¢t want to do it like that?¢‚Ǩ¬ù. I don?¢‚Ǩ‚Ñ¢t really mean it. Have a look at the photos and drawings attached with this article.

Oh and by the way can I have a simple job next year Guys? Building the Olympic village, swimming up a water fall!!

Just to finish our story, 31/5/06 (BBQ night), the bridge was officially opened and christened ?¢‚Ǩ?ìSquare Pool Bridge?¢‚Ǩ¬ù in a short naming ceremony by Malcolm Theakstone our Association Chairman. Champagne was drunk and sploshed about by all those who took part in its construction.

Len Leroux
Assistant Fisheries Manager