Twintec Projects, specialists in steel fibre concrete flooring, recently completed pile supported floor slabs for a new regional distribution centre at Avonmouth for one of Europe’s leading food retailers to service the supermarket’s expanding operations in the South West of England.
This major food retailer operates its RDCs as multi-channel, multi-product rather than having separate facilities for different product lines. This means that within each RDC there is provision for ambient, chilled and frozen food product plus storage for the wider non-food product ranges that it retails. This multi-channel approach means that there are different zones within the RDC that have different loading criteria and internal temperatures to consider.
Having previously completed the floor slabs for another RDC for this retailer, Twintec were well aware of the impact of the different load-cases and temperature zones and worked closely with the client design team to develop the technical solution used.
Because the ground support value in the area was poor, a piled solution was required and, in line with their company policy, the client would not accept a solution using steel fibres. Normally this would have been a problem but, thanks to their investment in innovative technology, Twintec were able to offer a very competitive, traditionally reinforced solution, which met all the criteria. The solution was designed using software developed by DIANA FEA BV, a Dutch consultant engineering practice with extensive experience in oil, gas, off-shore and nuclear industries, which accurately models the behaviour of reinforced concrete structures including considering the performance of the specific concrete mix and the effect of ambient temperatures at the time of casting.
For those in the know, The UK Concrete Society publication, Technical Report 34, is viewed as the `Bible’ for concrete floor slab design and construction in the UK. Within TR34 (3rd Edition) is the statement, “an ideal floor would be perfectly flat and have no joints” – but can this be achieved? Recent developments in concrete slab design mean that we are getting closer to achieving the second part of this ideal – truly joint-less construction. For Twintec this has led to the development of the Twintec ULTIMATE product – a slab utilising the DIANA design methodology and hybrid reinforcement to provide areas in excess of 60,000m2 without any opening joints. This technology allows the end-user to install any combination of racking or conveyor installation without any constraints to placement of supports – providing true flexibility throughout the life of the building and significantly reducing maintenance requirements.
Normally the ULTIMATE solution using the DIANA programme is based on a minimum crack width and no opening joints but, because of their concerns over temperature effects, the client insisted on having armoured movement joints in the slabs. This introduced additional stresses that then had to be modelled within the design and resulted in extra steel reinforcement being required. The final designs involved the placing and fixing of multiple layers of mesh fabric reinforcement and additional loose bar over pile positions and adjacent to joints. In some cases this meant that over 45 tonnes of steel was required per pour panel – all of which was placed and fixed by Twintec’s on-site team in less than 24 hours. In total 54,500m2 of slab was laid, containing around 1,650 tonnes of steel reinforcement, in a period of just 10 weeks on site. The slabs varied in thickness from 230mm to 250mm, depending on the loads carried and the pile spacing, and the majority of areas included underfloor heating pipes zoned to suit the client’s requirements.
To reduce wheel impact damage and provide a smooth transition in areas of greatest use by MHE, Twintec and the client team defined specific locations where a sinus-wave profile joint was used in lieu of standard steel armoured construction joints. The sinus profile at the joint crossing effectively reduced impact damage at the opening to zero.
The innovative design approach employed by Twintec together with their expertise in delivering quality construction has provided the client with a tailor-made solution meeting and exceeding their needs.
Under Twintec’s unique Design-Build-Guarantee package, total responsibility is taken for the floor slab including design, materials, construction and specialised equipment, together with providing a 12 year warranty.