Pre-assembly of a complex steel frame building and a big floating lift have given Southend-on-Sea’s famous pier a new focal point.
Back in the days of kiss-me-quick hats, Southend-on-Sea in Essex was a big day-trip destination for nearby east Londoners. Fish and chips, candy floss and funfairs could be savoured on or in sight of the “longest pleasure pier in the world”, stretching more than 2km out over the flat tidal sands of the Thames estuary.
Cheap flights to the Costas cut its appeal back somewhat, and then a disastrous fire in the 1970s knocked out most of the pier-end attractions housed in a three-storey building. Volunteer effort saved the long pier itself, and its little train, but there was only a café to visit at journey’s end. Now Southend Borough Council has boosted its main attraction with construction of a new £2.75M cultural centre at the end of the pier, which recently housed its first events.
Building the cultural centre was an adventure for contractor Kier, says project manager Roy Francis. The pier end location is essentially offshore and was therefore exposed and difficult. The weather was a factor, notably last February when it was cold and snowy. In addition, everything had to be done over water and construction logistics were difficult, with deliveries coming mainly by barge.
“We took a lot of time to understand the existing structure and see what we could use, researching in the town archives”
Emmanuel Verkinderen, Price & Myers
“There was some materials supply from land during the last stages of fitting out,” says Francis, “and there was a special train laid on for smaller items along the pier in the morning. But mostly it had to be by boat.”
A strategy of pre-assembly for the building elements - putting together sections on shore - seemed the way to go as this allowed as much fabrication and construction work as possible to be done away from the harsh conditions. The plan evolved to the point where its was decided that almost the entire building should be assembled as a single module and then lifted into place by crane.
Only service connections, internal fitting out, and some exterior work on steps remained to be done this summer.
The pre-assembly method evolved over a period of time after the contractor won a two-part contract in autumn 2010. This included a construction-focused redesign and value engineering exercise. Originally it was envisaged that the unusual asymmetrical building, the result of an architectural competition set by the council, should sit on new concrete piles alongside the pier end.
But this was expensive.
“It would also have raised complex questions of land acquisition from the Crown Estates, which owns the seabed offshore,” says Francis.
Kier, together with Swedish architect White Arkitekter, working in partnership with London’s Sprunt, and structural engineer Price & Myers, found a way to reduce the floor plan and to position the building on the original pier, which helped bring down costs.
“It sat where there had once been the much larger building, so we were confident the Victorian foundations would be strong enough,” says Price & Myers designer Emmanuel Verkinderen. “Like many piers, Southend has cast iron screw piles installed by steam hoist and these are in good condition. Load tests gave better results than we were expecting.”
To sit the new 350m2 building in position, it was necessary to provide an even platform above the pile tops, which had settled over the last century. The work meant stripping back some corroded elements of the pier frame and building up new steel beams. These will hold the base of the building 1.5m higher than the current deck, a level chosen to cope with a 100-year storm and sea level rises from global warming.
“We had to pull things forwards a day by making the move overnight and then were a couple of hours behind the high tide”
Roy Francis, Kier
“We took a lot of time to understand the existing structure and see what we could use, researching in the library and town archives,” says Verkinderen. Francis adds that “five bargeloads of scaffolding were needed underneath the pier”.
But the major focus was on the main building. Once it had been decided to prefabricate it and lift it into place using a floating crane, the challenge was to find wharfage where it could be built.
“There had to be enough draft to bring in a floating crane with a 400t capacity,” says Francis. Allowing for a 25m radius lift during positioning, this meant that the module could weigh no more than 200t.
The next problem was finding somewhere to assemble the building module over a six-month period.
“Looking for somewhere was almost impossible,” Francis recalls. “There are places around the Thames estuary with docks and shipping facilities. But when we rang people it was very difficult to get them to take it seriously.”
An initial option was in the Medway but that was across the estuary and, for supply chain reasons, the Essex side was preferred. A container facility was investigated but eventually space was found at Tilbury docks just up river.
Assembly work involved putting together the main shell and core comprising the steel frame, timber flooring and walls. Work included adding a special waterproofing membrane on the outer surfaces using a new spray technique developed in Europe, called Procol. “It is just 2mm thick and dries in seconds,” says Francis.
The steel frame was complex. Verkinderen explains that the architect had devised a sloping curve to the roof, which has to taper to almost no thickness at all at the edge. There are also some complex folded shapes for the interiors.
“No two beams are the same size and they have a complex form,” he says. Modelling this in 3D was vital and the firm used French Dassault originated steel structural software Catia, which is parametric and allows constant modification and re-adjustment. “If you adjust something it re-draws immediately,” says Verkinderen.
This is effectively a BIM model and was used for the steel fabricator’s specification.
Aside from matching the architect’s complex shapes, the frame included a truss structure as the base. This doubled as the lifting frame for the installation. The whole thing eventually weighed around 170t. “We weighed it during trial lifts before the move just to check,” says Francis.
The lift required detailed organisation and a variety of permissions, says Francis. First the Port of Tilbury had to give clearance, fitting in with other river traffic.
“They have huge container vessels moving in and out all the time, with massive tonnages, and our thing was very small potatoes for them. But they were very accommodating in the end.”
“Even booking a time slot in the lock was difficult,” he adds. Tilbury is a non-tidal basin with a lock exit to the river.
The Port of London Authority (PLA) was the main controller, especially for the move down the Thames, which is very busy with large scale shipping traffic.
Initially it was hoped to make the journey simply by moving the unit with the floating crane “but the PLA were unhappy about the risks under hook and the chance of having a building at the bottom of the river”, says Francis. Instead it had to be put on a barge by lifting company GPS Marine.
The move was finally set up for May 17 this year after some detailed monitoring of the weather and tidal patterns. Forecasts are available a month ahead but get more precise as the time reduces.
“You have to push the button finally at seven days in order to get the marine equipment underway - it is very busy and in demand for other jobs,” says Francis.
Even with the forecasts the move was touch and go, with some strong easterly winds expected - the worst possible scenario.
“We had to pull things forwards a day by making the move overnight, and then were a couple of hours behind the high tide,” Francis adds. The low tide sees the sands exposed so timing is critical for the crane.
Placing the unit was a delicate operation. A floating crane could manoeuvre better than a land unit, working off winch connections. A jack-up barge had to provide the anchor point, however, as the cast iron pier structure was too brittle for mooring such a large vessel.
“We had some ‘stubbing points’ - like cones - to sit the frame onto and the drop was within 20mm,” says Francis.
Once in place there was some curtain walling to do, and a lot of glazing. The glass could not be placed earlier because the structure was expected to flex during the lifts.
“We also had to finish the spray cladding,” says Francis. “The weather was so bad this year would we could not complete it at Tilbury.”
Work was completed in time for the new venue to house a comedy festival at the end of July this year.