Field Visit by Price & Myers

Ian Fussel of Price & Myers visited the site on 28th November to survey the bridge prior to designing one or two new end-plates. We made some final adjustments to the two side beams, but it is impossible to iron out the twist with beams cut to a profile for a 'twisted' bridge. We were heartened to find that there will only be one end-plate required for redesign. This Ian was to do so that we could try and get it fabricated and in place before the Xmas break.

The top photo shows the "twisted" bridge, taken on 14th September. This is followed by a photo showing Ian Fussel standing to the right of the "level" bridge. The photo below reveals the bridge supported by three trestles and a quantity of jacks.

Crisis Meeting in London

I convened a crisis meeting in London on 15th November. William McMorran from consulting architects, McMorran & Gatehouse, identified that the new endplate drawings may well twist the bridge in the opposite direction. As Price & Myers had designed two new end-plates for fabrication it was time to get together and talk about the bridge design and the options which faced us with regards to the end-plates. Price & Myers were represented by Tim Lucas and Ian Fussel.

Tim took us through the chosen geometry of the bridge which resulted in a twist. Discussion was had around the redesigning of the end-plates and the possibility that they might well not suit the purpose. It was agreed that Ian would send me some drawings which would identify the location of three trestles to be built to support the bridge so that the decking would be level. Once the bridge was secured on the trestles P&M would make a visit to design new endplates around the level bridge configuration.

Endplates

I spent an hour and a half securing the raised beams and making a template of the end-plate which I removed yesterday. Another beautiful day in the gardens with autumn colours coming through ... I am unsure as to how long I will have to wait for the new end-plate to turn up? There is not a lot I can do until it does.

Price & Myers have now decided to redesign the two endplates, have them fabricated and sent up to the site. The design work will be completed on Monday 15th October by Ian Fosell. I can guess that the galvanised plates won't be up here for at least 3 to 4 weeks.

Removal of Endplate

Spent four and a half hours today, Monday 1st October, removing the left-hand end-plate which is to be scrapped. A gorgeous Indian Summer sort of day ...

Proposed Solution to Design Problem

Will McMorran met with Tim Lucas of Price & Myers on Friday to alert him to the design fault. A letter will be written to the client and signed by both parties. I would hope that I can post a full account of the design fault and solution if I can persuade McMorran & Gatehouse or Price & Myers to write a report on the issue as requested.

In the meantime the proposed solution is to remodel the design based on actual levels at site, rejig the right-hand end-plate and design and build a new left-hand end-plate. I was instructed to take new measurements and submit them to Will McMorran. I await the readings on site levels from the surveyors, Digital Survey Ltd.

On Thursday I went to see Stephen Mather who made the original end-plates to see if he would consider making another one. He was not at all amused and unfortunately Stephen doesn't want to make a new plate so it will have to be made down south somewhere.

At least everyone knows what the problem is and the solution.

Visit from the Engineer

Tim Lucas

Tim Lucas, from Price & Myers 3D Engineering, visited the site on Wednesday 26th September to review progress and get to grips with the distortion problem. I fear that it could be one of those projects which is designed on computer but in real life takes on a different form. Tim modelled the problem on his computer. His theory is that the bridge was designed to be built on a flat level surface, whereas in reality we have a difference in levels of some 560mm. There have always been a difference in foundation levels for this project. His immediate solution is to raise the lower end by 560mm and the problem will be greatly reduced. The other option voiced by me was to jack up the lower short end by 185mm and the higher short end by 65mm. Tim thought that this would best be done without sacrificial chocks. The beams will twist and my fear is that we are going to have a major headache defining and placing the balustrades.

It has been agreed that Tim will have a look at the geometry of the bridge and come up with some possible solutions. In the meantime I have asked Will McMorran of McMorran & Gatehouse to press for a meeting to review the problem and come up with a solution. Will McMorran remarked that there are many innovative design projects which throw up all sorts of problems which you never hear about...a solution will be found and you will hear about it!

Later the same evening Will telephoned me to say that he and his son had made a model of the deck. Will explained briefly that the design replicates a barrel vault and that Price & Myers took a line straight over rather than from one corner to the other. The consulting architect and the consulting engineers failed to pick up on this.

Construction of the Bridge

Stephen Mather securing End-plates to concrete foundations

On Tuesday 11th September, Stephen Mather secured the steel end-plates in position and with the help of Tim & Damian Fison and Charlie Poulsen we were able to swing the centre beam into position and secure it. The garden staff helped to move a workshop table and lathe to the site. A gazebo was erected as a temporary workshop and a generator was hired.


Charlie Poulsen & Tim Fison

At 08.00 on Wednesday 12th, the gardening staff, Neil, Nick, Kevin, Michael, Jimmyand Pavlov assisted Charlie and I to place four more beams in place. Charlie and I secured them and placed the necessary sacrificial chocks (spacers) and placed cargo straps to pull the bridge together. It was noticeable that the beams were going to tell the same story as found at Brackenside - namely that the bridge was not level throughout its length.

At 08,00 on Thursday 13th, the garden staff assisted Charlie and I to place the last two outer beams. They were secured and strapped into place. We started to construct a shelter over the site.




James Barber keeping his eye on the job
Contact was made with the consulting architect and engineer. Tim Lucas of Price & Myers is to visit the site on Wednesday 26th September. The left hand end has a distortion of 185mm whilst the right hand side has a distortion of 55mm.



On Friday 14th Charlie and I finished construction of a moveable cover over the bridge.

Trial Build at Brackenside

Marking out the profiles for the steel end-plates

I decided to undertake a trial build at Brackenside Farm, where I live. This would enable us to work through any difficulties with easy access to the workshop and a forklift. John Barber kindly allocated an area of concrete outside his grain drier, for the purpose. I contacted Peter Bennett of Digital Surveys to arrange a surveyor to set out the positioning of the steel end-plates, at the final site and at Brackenside. This was completed on Thursday 2nd August. There was a 5mm difference in slope between the two sites.

Stephen Mather and Stuart Graham of Holburn Smithy, anchored the endplates to the concrete on August 3rd.

Rolland and Hugo McMorran, sons of William McMorran the architect, pitched up on Sunday 5th August for a week of hard work assembling the bridge structure. This was completed on Friday 10th August. To our consternation we found that the two longest projections of the bridge upset the level of the deck. One end was out by 180mm and the other by 60mm. We overcame the problem by jacking up those corners, thanks to the analysis of the problem by James Barber who is studying engineering at Newcastle. The consulting architect and engineer both thought that the beams were fighting each other and that there was a need to have the noggins placed and tightened up within the structure to resolve the problem. The jury is out on this until the visit of the engineer to the finall site on Wednesday 26th September.



Rather than begin to take measurements for the oak noggins which are to seperate the beams, Charlie Poulsen and I decided to take the bridge apart and get it down to the final site.

The beams were delivered to the site by Hugh Burn on Wednesday 29th August. Thanks to the Estate forestry deppartment and Neil Mole we were able to bring the beams through the wood and into the garden more easily than had been originally antiscipated.


Hugh Burn at the controls!

Arrival of Timber at Brackenside & Bending of Beams

Somerscales delivered the 7 beams and timber for the decking and cladding on Monday 16th July, 2007. George Barber and I immediately laid out the beams on trestles and attached tractor weights to the ends of the beams in order to create the required curve in the timbers. The beams then sat for three weeks bending gently.

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.

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.