Why we specified… April 2011

Cast in situ concrete sawtooth roof by Shepherd Construction

Loughborough University Design Centre

Nicholas Burwell, partner, Burwell Deakins Architects

The Loughborough University Design Centre is a £15M project to construct more than 7,500 m² of new research, workshop teaching and lecture facilities.

The main reason we made the decision to go with a concrete frame was due to its thermal mass properties. The building will be naturally ventilated and to that end we’ve got exposed concrete walls, floors and roof soffits.

Another reason for specifying concrete is that there are a lot of workshops fitted out with heavy machinery such as lathes and plastics formers, and these obviously create vibrations that we’d need to dampen down for the sake of other areas of the building.

We did look at building the roof from steel off the top of the frame, but this was a design and build job and as Concentral, the subcontractor building the concrete body of the building, was already on site, there were robust cost and logistical reasons for getting them to build the roof.

While we would have liked to have cast the whole sawtooth roof monolithically, the cost would have been prohibitive, so in the end we decided on just building the south-facing slopes of the roof from concrete.

We cast the 11m x 7.5m wide, 12 degree angled roof sections out of 150mm-thick concrete using 3m x 1.5m resin-faced shuttering and high viscosity concrete, to avoid slumping.

The elevations’ sawtooth elements are zinc-clad aluminium honeycomb backed pre-fabricated insulated Metsec panels, which match the rest of the facade. The roof itself is a zinc standing seam on a layer of rigid insulation.

The sawtoothed north lights make for work spaces with a great quality of light, with the concrete angled roof giving good thermal stability and cutting out both glare and solar gain.

Product news

The concrete frame of the Christian Street affordable housing development in the London Borough of Tower Hamlets made it through the worst of the winter on time and on budget, helped by Hy-Ten’s Bamtec roll-out reinforcing carpet. Laying concrete reinforcing is usually a time-consuming manual process that is susceptible to bad weather. Hy-Ten’s system converts the engineer’s rebar layouts into bespoke “carpets”, welded together and incorporating all the different rebar diameters, which can then be laid out on site and cast around.

www.hy-ten.co.uk

Last month at Ecobuild, timber frame specialist Cygnum launched a new closed panel frame system, a new kind of structurally insulated panel (SIP). The insulation comprises 80% recycled paper and was developed with partial funding from the EU’s Eco-innovation programme. After the paper has been broken down, the resulting cellulose fibres are compacted to produce high-density, high-performance insulation that exceeds the requirements of current Building Regulations.

www.cygnum.co.uk

The New Zealand government’s independent research laboratory on bio-materials, the Sion Institute, has published a report suggesting that Accoya timber, which has undergone a natural, non-toxic “acetylation” process, outperforms hardwoods such as cedar, cypress, teak, kwila and radiata pine, in both durability and resistance to fungus decay. Tests were carried out over five years in both accelerated decay chambers and under exterior ground contact conditions. Under these tests Accoya performed nearly twice as well as its nearest rival.

www.accoya.com

Tips of the Trade: Tackling vibration in construction

Conduct a site assessment prior to gaining planning permission to identify any potential vibration challenges, such as passing vehicles and/or trains. Project managers can use this information to determine the intensity and frequency
of transmissions and plan an appropriate anti-vibration treatment.

New build high-rise developments near existing transport systems are potentially vulnerable to ground-borne vibrations, such as perceptible movement, nuisance noise and structural resonance. Buildings should be decoupled from the vibrating source with an isolation treatment at foundation level, such as sustainable rubber-based material with steel interleafs.

Floating floors provide a cost-effective means of isolating a vulnerable development by breaking the path through which the vibration would naturally travel. Depending on the frequency attenuation required, create an air gap of one to four inches using fibreglass pads.

For applications that require attenuation of very low frequencies, select a jack-up floor system to combat both ground-borne vibrations and noise disturbances. Mount the floor to the required height using fabricated spring assemblies and apply an isolating perimeter.

Changes in the physical environment as a result of new transport infrastructure can result in vibrations. To prevent these penetrating a building, tackle the cause at source, for example with active trackbed and road surface isolation.

By Jim Herbert, technical sales manager, CMS Vibration Solutions