Sunday, 19 August 2007

Cutting of Beams



On the 15th June, 2007, I was able to see the beams being cut to their correct curvature at the Somerscales sawmill near Grimsby, Lincolnshire. The logs had previously been through the large mill where one tree was found to have pipe rot and had to be rejected for the job. Three trees were milled and the boards were taken into the workshop where Melvin & David marked and cut out the required profile, provided by Price & Myers. The boards were marked and cut to in the first pass in order to release the tension in the wood. The final scribing represented the requirements of the drawing and again the large circular saw did its deed. Thereafter the beams were planed with an electric hand-planer with an 18 inch cut. Melvin and David were masterly under the watchful eye of Andrew Somerscales and his father, Stuart. The time spent watching these characters at work was most rewarding.











Stuart Somerscales

Fabrication of Endplates



The design incorporates two galvanised endplates which have been fabricated from large angle-iron, onto which a number of fins have been welded. The endplates are anchored to the foundations by 6 bolts. This fabrication was undertaken by our local blacksmith, Stephen Mather and his able assistant, Stuart Graham. The plates were collected on 6th July 2006.



Once the end-plates were put in place and final drawings were provided in May 2007, it became noticeable that the
foundations were set too far apart. This was remedied by digging a new 250mm trench, securing tie-bars, and pouring concrete assisted by Caroline Burn and Kevin.

Timber Preparations 2006


Stuart Somerscales

Unfortunately the estate didn't have any oak timber available for the project, so all requirements had to be sourced further afield. I put the cutting list to a number of sawmills within the UK with a poor response. David Williams, Head Forester on the estate, suggested that a sawmill at Keelby, near Grimsby. At this time I had a contract to make some oak seats for the new Library at Lewes in Sussex, so I contacted the sawmill owned by Stuart Somerscales, placed and order and visited them to collect. I was able to meet Stuart and we had the first of a number of meetings to discuss the bridge. Drawings were placed before him, many cups of coffee and sucking on pipe. He could do it and all would be well in 6 weeks for delivery. This was back in April 2006. The oak beams didn't arrive in Northumberland until July 2007! Stuart was invaluable for many reasons as he knows his stuff about wood and once he is enthused and cajoled a bit the results have proved positive!



On 15th June, 2006 I collected all the green oak required for cutting out the noggins which were to be used to separate the seven beams. I was also to return to collect the mature oak to be used for the balusters. The summer of 2006 was unusually hot, and as such is not good for green oak as it makes it dry out too quickly. Had the beams arrived during that heatwave I would have anticipated major problems associated with twisting and cracking.



As it would happen we needed to dip the end of the noggins in hot wax and cover them in wet sacking to prevent them drying out too quickly. This photo shows Damian Fison and myself doing just that.







The Balustrades needed to have their paper templates transferred onto plywood before they were matched against the oak boards, marked and cut out. I was ably assisted by Hugo Saunders who has continued to give valuable advice and support.

Foundations



The bridge is to become part of a well established arboretum and garden. Whilst the brook is only about 2m wide the banks have determined that the bridge needs to be 10m in length. There is about a 560mm drop in levels between the two foundations. There is limited access to the site, with established cherry and magnolia trees adjacent, which means that the bridge will have to be constructed in situ.


The foundations were set out by David Dobson, Brian Thompson, Clerk of Works to the estate, and myself on 3rd May, 2006.


A platform needed to be constructed across the brook to facilitate access and onto which a mobile gantry will be used to manoeuvre the beams into place. Twenty-nine sleepers, lent by John Barber, were placed in the bottom of the brook to help spread the load. This was completed on 9th May, 2006.



The foundations were dug by myself, Caroline Burn and the gardening staff which included Neil Mole, head gardener, Kevin, Michael and apprentice Allan during week of 19th May, 2006. A trench 4m x 1.2m x 500mm was dug one either side of the bank with shuttering as necessary.



The concrete was poured on 25th May, 2006 with myself, Caroline Burn, Neil and Jimmy Mole, Michael, Kevin and Nick in attendance. We hired a 9 tonne dumper for the job. All went to plan.

Wednesday, 15 August 2007

Research & Design



A decision was made to make the bridge entirely of European oak. As it was going to prove difficult to obtain full length, curving trees of this scale Price & Myers developed an idea of having just two beams with stainless steel brackets supporting a number of cross beams. This was discarded as we wanted to build as much as possible with wood. Another Price & Myers idea was to have each beam made into three sections, joined by an internal stainless steel plate. McMorran & Gatehouse, architects, decided that the beam was not going to flex enough with internal steel plates. So we were back to the full length design concept. McMorran and Gatehouse posed the idea of laminating the oak. I had experience of lamination in my workshop. This was not to prove possible after following research papers emanating from USA and discussions with eminent and most helpful American researchers. Trials had been made on a small scale which would be risky to consider for the length of bridge we had proposed.

What we were trying to do was to come up with a new design which would work and could be costed accurately and constructed without any surprises. This was the first timber bridge that Price & Myers' 3D department had designed. Eventually we arrived at a design which we were all happy to take forward with confidence, and which received approval from the client.

Oak Bridge



I was commissioned by a client in north Northumberland to design and build a bridge. The brief required the design to be narrower in the centre than at either end. I was prepared to undertake the commission on the understanding that I would engage a consultant architect, William McMorran of McMorran & Gatehouse, and a consultant engineer, Tim Lucas of Price & Myers.

I was asked by my client to visit a bridge at Luxmore's Garden, Eton College to view a design made by Jamie McCullough. A wonderful piece of design and engineering. I also visited the celebrated Mathematical Bridge at Queen's College, Cambridge for inspiration.



William McMorran suggested that I keep the design simple and develop the theme of my Elliptic seat series. Andy Hayne, then working for Price & Myers made a field visit with William McMorran to ascertain the scale, orientation and dimensions required. We visited the maritime boat collection at Eyemouth to see if we couldn't use some of the design principles embodied in a number craft on view. Andy Hayne thereafter came up with a sketch which suggested the use of seven beams which would form a solid deck, onto which the balustrade and sheathing could be attached. Sketch drawings were made, presented and accepted.



A scratch model was made by me to a scale determined by William McMorran and shown to the client, who accepted it. There was discussion as to whether or not it could have just one clinker skin rather than two, but the original design prevailed.