James Hehir Building, University Campus Suffolk
A new six storey university building on the Ipswich waterfront is the first construction project in Europe to use a new Lockable Dowel from Ancon.
Although a new concept in Europe, Ancon Lockable Dowels have been used with great success in Australia since 2007. Their use is expected to increase worldwide as the benefits over traditional build methods become more widely recognised.
A key design consideration in post-tensioned concrete, where long uninterrupted spans can be achieved, is the accommodation of normal concrete shrinkage. Traditionally, movement has been accommodated by leaving ‘pour strips’ - 1metre wide openings at various locations on each floor. To provide the desired continuity in the slab, the wet trade would return to each location to fill the strip once the concrete either side had stabilised, a good 4 weeks after the initial pour.
Although a common design feature in most post-tensioned concrete frames, pour strips are not ideal. They require the slabs to be propped throughout this period, restricting site access and delaying follow-on trades below and general site progress above. Pour strips also create an unnecessary trip hazard for site workers, use additional formwork and leave the soffit face marked.
It was these issues, first identified by Ancon in the Australian post-tensioning market, which led the company to develop a Lockable Dowel.
Dowels transfer shear load across joints in concrete and are used with a sleeve component where movement is to be accommodated. The inventive step taken by Ancon was to engineer a dowel for use at a temporary movement joint, where after an initial phase of movement, it could be locked in the sleeve but still continue to transfer load.
This would negate the need for a pour strip to be left, as concrete could be poured both sides of a joint. There would also be no requirement for the slabs to be supported from below, as shear load would be transferred by the dowels.
The Lockable Dowel Range
Ancon’s Lockable Dowel range includes standard solutions for both slab-to-slab and slab-to-wall joints, where pour strips would traditionally have been used.
Both types comprise a stainless steel dowel component, a box-section sleeve with an L-shaped void former, a locking plate and 1.5litres of an Ancon two-part epoxy resin.
The dowel component features a nut and washer at one end when used in a slab or is supplied with a Threaded Anchor when fixing into a wall. The other end of the dowel features a series of grooves to accept the plate.
When movement has stabilised and the joint has been filled, the dowel is locked with the plate and the resin, inserted from the top of the slab. The void former is topped with cementitious material to complete the installation.
UCS’s Ipswich Phase 2
The Lockable Dowel range was launched in the UK in 2009. Matthew Consultants, a specialist in post-tensioned concrete design, saw the potential immediately.
Approximately 30 dowels were specified on each floor of this UK project, replacing traditional pour strips at both wall-to-wall and wall-to-slab junctions, thereby eliminating the site delays associated with onsite propping.
Ben Ume, Director at Matthew Consultants, said,
By using these Ancon dowels we have saved at least 4 weeks per storey on a traditional build programme. The anticipated movement at the joints was achieved without any issues and because of this initial project success we have specified the system again. This construction method is just more efficient. Wet trades finish sooner. It uses a proven engineered solution to reduce on-site man hours.
Ancon Lockable Dowels are a proven, independently-tested solution which is both easy to detail and install on site.
Concrete structures are designed with expansion and contraction joints to allow movement to take place.
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