Stringent reverberation requirements were just one of the challenges faced at Southampton’s new sports centre. Paul Thompson reports.
Project: Solent University Sports Centre
Client: Solent University
Main contractor: Morgan Sindall
Contract value: £28m
Contract type: JCT Design & Build
Start date: August 2017
Completion date: March 2019
There are signposts to the Mayflower Theatre, so named after the ship that took the Pilgrims to America, and plenty of reminders that Southampton was home port of the Titanic.
Like many cities across the UK, it suffered at the hands of the Luftwaffe during the Second World War. While much of the attention was focused on the strategic location of its docks, the city centre did not get away without damage, though thankfully the Victorian splendour of its East Park was saved.
Just on the edge of East Park lies the main campus of Solent University.
Despite only becoming a university in 2005, like its home city it too has a rich history. With roots that can be traced back to Queen Victoria’s reign, Solent University has long held connections to Southampton’s maritime and art heritage. Now it is pushing through a redevelopment programme across its East Park Terrace campus that will help build on those roots and provide an exciting modern centre for its students.
Worth coming out of retirement for
Part of that development is the new sports centre that is currently under construction to the north of the campus.
Main contractor Morgan Sindall is delivering the £28m project under a design-and-build contract with client Solent University. The new building will include sports halls, fitness studios, teaching facilities as well as a health and wellbeing gym and a strength and conditioning gym.
Procured under the Southern Construction Framework, the scheme is scheduled to be delivered in March 2019 after an 85-week project timetable.
“It is an interesting scheme on which to work,” says senior project manager Grant Wild. He was enjoying his retirement sunning himself on a Greek beach when he was coaxed back by Morgan Sindall area director Jon Daines.
“The site had previously been an ambulance station and we needed to deal with the legacy of that”
“We wanted someone who could take the scheme through from design, onto site and then completion. I actually interviewed Grant via a Skype call,” Mr Daines says.
Unusual job interviews aside, the project has been working well since the Morgan Sindall team and the university entered into a preconstruction services agreement in November 2016 before starting on site in August 2017.
The building will have a steel frame, and an insitu hollowcore structural concrete topping to dampen acoustics
“We had eight weeks of enabling works to get through before the main work started,” Mr Wild says. “The site had previously been an ambulance station and we needed to deal with the legacy of that. There had been some fuel storage tanks and contamination linked to that which needed to be sorted out.”
Leftovers from the Blitz
With wartime bomb records indicating the site – full of terraced homes pre-1939 – had been badly hit during the Southampton Blitz of 1940, protocol from the planning department at Southampton City Council required a full unexploded ordnance survey and probe at every pile location.
“We worked every single hour of the eight weeks,” Mr Wild says. “There was plenty to get done.”
The building itself is split into three sections. The main four-storey element features offices and public realm space, seminar space, two gyms and teaching areas, while the lower level two-storey section features two sports halls. Beneath the halls is a basement with undercroft car parking for 69 cars and plant areas for the rest of the building.
The close proximity of exercise space and treatment rooms created a challenge for the design team. Noise and vibration go hand-in-hand with sport and exercise, but less so with physio treatment and study areas. Engineering a solution that would enable the building to be flexible enough to manage both was key to the project.
The makings of an Excellent build
Part of the requirement for the new building, asked for by both Solent University and planning authority Southampton City Council, is that it meets the BREEAM ‘Excellent’ environmental performance rating.
In many situations attaining this evaluation can be difficult for contractors, but the project team was able to tap into a heating network that reaches around the city centre.
“That heating system is a tremendous bonus,” design manager Martin Nicholl explains. “There is a ground-source heat pump that enables buildings on the network to tap into it. There are no boilers and no gas supply on this scheme.”
Aside from the heating, the main areas where the project builds up environmental credit is the re-use of greywater from showers in the changing rooms to flush toilets and the rainwater attenuation tanks that will hold 185 cu m of water at peak loading, before slowly releasing as that load decreases.
Conventional wisdom would suggest that a building of this type with its rigid sound insulation and structural reverberation limits should be built using cast in-situ reinforced concrete. Its mass would help dampen both. With teaching and treatment space sitting cheek-by-jowl to exercise rooms, dealing with sound and vibration is central to the building’s design.
The fact that it is a steel frame structure is something of a surprise, but Morgan Sindall design manager Martin Nicholl is more than happy that designer Arup has developed a method that will deal with those issues.
“It is a very slender design,” he says. “Technically it is a very efficient building but we needed to be sure we could get the functionality as well as deal with the different acoustic and reverberation demands.
“The team at Arup has developed the building with a steel frame and with floor slabs constructed from precast hollowcore planks and an in situ structural concrete topping,” Mr Nicholl adds.
This slab is then covered with screed, generally 75 mm thick across the project, although thicknesses vary in some locations.
But it is the use of cast in-situ, spring-mounted jack-up concrete floors that have really helped the engineers meet the project’s stringent reverberation demands.
The system involves casting springs within the floor slab (see box, below) and ensures the transfer of sound and vibration between areas is limited.
“By installing a tensioning rod to tie in the roof to the floor below we can make use of the roof mass to dampen the treatment space in that area”
Across the project, slender 305 x 305 mm UC columns have been used for all the vertical members. However as spans vary so do the sizes of the horizontal steel beams. Across the sports centre, 2 m-deep trusses span from a line of columns that separates the two sports centres, but up on the fourth floor of the main building the slenderness of the steel created an issue that the composite precast / in-situ slab couldn’t fix.
“There are treatment and teaching rooms on the fourth floor where we couldn’t achieve the required change in dynamic frequency,” Mr Nicholl explains. “By installing a tensioning rod to tie in the roof to the floor below, we can make use of the roof mass to dampen the treatment space in that area.”
That tensioning rod is a 20 mm-diameter adjustable bar hidden within a partitioning wall with an access hatch to enable any tweaking. This represented a simple but effective solution for the project team.
Despite the building’s relatively light weight, significant groundworks were required to prepare for the structure.
A 45 m-long sheet pile wall marks the edge of the basement along its western edge. Ground engineering firm Aarsleff installed 80 sheets here to 13.5 m while piling specialist Roger Bullivant installed 180 CFA piles, 600 mm in diameter, to depths of 18 m below the building itself.
A 175 mm-thick cast in-situ ground-bearing slab is installed throughout the basement and undercroft car parking.
Slender 305 x 305 mm UC columns have been used across the project
Here the team needed to carry out localised well-point dewatering to combat the effects of running sand as the basement was excavated. It also meant a rethink of the project’s drainage solution with several smaller rainwater attenuation tanks being used to meet the capacity of the initial single tank.
The bulk of the building is clad in a perforated rainscreen system. These 1,350 x 4,200 mm square panels feature 35 mm and 45 mm-diameter perforations that provide a pattern across the finished elevations. This pattern has been designed to represent the road network in the area before it was so badly damaged by bombs in the Second World War.
With another nine months before handover in March 2019, the project team is relaxed about hitting its completion date. Then perhaps Mr Wild can get back to that Greek beach and focus on his retirement.
Bouncy floor springs to the rescue
Stopping vibration and noise travelling around the building has been key to the success of the design.
In the seminar and gym areas, the mass of the floor is sufficient to take out most of the vibration and the team has installed 20 mm soft joints between the room floor slabs that help isolate them and reduce the amount of vibration that passes.
But in the weight training areas the team has gone a step further by introducing a cast in-situ reinforced concrete sprung floor by specialist installer Mason UK.
Here, a polyethylene release sheet is set on top of the main concrete floor slab and steel reinforcement placed. Steel cups are then located at 1.4 m centres with lugs that clip beneath the reinforcement. The concrete is then poured to slab depth – in this case 125 mm – and left to cure as normal.
Once cured, the top of the cups can be removed and a steel spring inserted into the cup. This can then be screwed into position, an action which causes the newly cast slab to lift from the release sheet, forming a void between its underside and the main floor slab.
At Solent University that void is 85 mm.
“The sequence of loading the springs and lifting the slab is very important,” Mr Nicholl explains.
“There are various sizes of spring that can be installed and working with the university has meant that we have been able to develop the most suitable system for them. This solution works well with the steel frame.”
Source: Construction News (free subscription required)