Seamless Floors has recently designed and constructed a concrete floor slab for Bluestone at Poole. The floor was suspended on piles and incorporated steel fibres as the primary method of reinforcement. A gas venting system was installed in conjunction with the slab construction therefore permitting the use of laser screed machine and concrete placement by direct discharge. The project highlighted the important role that flooring subcontractors can now play in the design process.

Integrated Design Solutions
As the UK's longest established Laser screed Flooring Operator, Seamless Floors is well placed to have viewed the revolution that has occurred during recent years in the concrete flooring industry. Flooring contractors are now required to offer fully indemnified design and build packages allied to an ever-expanding scope of works. Flooring solutions have to be high quality, cost effective and exactly tailored to end user requirements.

As a result it is now essential that flooring companies become involved at an early stage in the design process. Working closely with other teams ensures that all design solutions are harmonised and sympathetic to other facets of the building programme. On occasions flooring companies are consulted too late in the design process leading to discontinuity and a loss of dynamism. The design criterion becomes rigid and solutions are not optimised. It is not uncommon for flooring companies to be asked to formulate a design as the last pile is being driven at site. This could be critical to the Contractor at tender stage and ultimately costly to the client.

The Design Process
Expending the time and effort to bring all parties around a table early on in the design process proved very rewarding for Bluestone. Seamless Floors ensured that the pile type and grid were ideally suited to the design philosophy employed.(l) Computerised design calculations were processed and detailed drawings and proposals were drawn up and circulated. The elimination of the need for steel fixing allied to the integrated installation of the gas membrane provided enormous benefits in terms of scheduling and cost. The joint free nature of the floor design also ensures minimum future maintenance costs for the end-user as joint degradation due to trafficking is reduced.

The Design
The floor was designed as a fully continuous steel fibre reinforced slab with a pile spacing of 3.5 x 3.0m and an edge span of 2.25m. The slab thickness was 220mm and the fibre dosage rate 40kg/m3. Unlike other Steel Fibre Reinforced Piled Systems there is no additional requirement for steel cages over piles and other secondary bar reinforcement. This allows for a simple construction process and eliminates the potential for steel fixing error at site.

There was, however, a specific factor involving a requirement for portal ties in the building that needed a suitable design resolution. The portal restraints were tied together within the floor depth utilising additional loose reinforcing bars. Additional mesh reinforcement was provided at all positions of horizontal restraint to reduce the risk of shrinkage cracks occurring.

The design needed to accommodate a uniformly distributed loading of 32.5 KN/m2 and a portal horizontal restraint in excess of 10 tonnes.

The Tolerance
The floor was constructed to Technical Report 34 1997 Supplement "Concrete Industrial Ground Floors" FM2 Property 4.

The Reinforcement
The fibres supplied by Estate Wire (a subsidiary company of TrefilArbed) are made of a special high tensile wire. Produced primarily for piled supported floors they are added at site directly into the concrete trucks as they arrive using specialist machinery under the ownership and control of Seamless Floors. This process ensures an even mix of fibres throughout the concrete matrix ensuring specified dosage rates are achieved. The fibres 1mm in diameter and 60mm long are undulated in shape this unique design promotes enhanced anchoring qualities ensuring shrinkage cracks are minimised. A joint free floor is subject to shrinkage stresses caused by vapour loss at all ages of the concrete, shrinkage is not eliminated but is controlled. Minute random cracking is normally expected.

Construction joints utilised were Alpha DD10 by Permaban Ltd.

The concrete mix.
The selection of the correct concrete mix is always essential and especially so with steel fibre reinforced technology. Aggregate grading curves are employed to ensure successful interlock between the concrete matrix and steel fibre reinforcement. The fines content is also controlled and graded to aid the finishing process and enhance the finished floor product. Seamless Floors also carried out cube testing throughout the entire construction process to ensure concrete has met the stipulated standard.

The Construction Process.
The laying of a gas membrane simultaneously with the concrete slab had successfully been achieved by Seamless Floors on an earlier project in Taunton during 2000. This experience allied to a fully trained and skilled workforce ensured the slab was completed on schedule and within tolerance.
Work on site needed to be carefully coordinated. Concrete supply was regulated in order to allow steel fibres to be integrated and mixed at site in a controlled manner. This element of control was reflected throughout the whole construction process. Concrete was directly discharged and immediately leveled by a Somero laser machine, dry shake topping was applied by means of an automated machine and specialist-finishing processes were employed Power floating of the slab was subsequently carried out and a curing agent was applied.

Health and safety.
The importance attached to matters of health and safety on site has been increasingly been drawn into focus in recent times, and rightly so.

All members of the Seamless Floors workforce are fully trained and aware of potential dangers on site. Guidelines and working practices are constantly reviewed. The company's decision to fully embrace the CSCS card scheme a number of years ago has contributed to the skills and awareness needed to successfully complete the project at Poole.

Conclusion,
"Value engineering" is a phrase that has been banded around for sometime in the construction industry, but on occasions it is taken to mean the cheapest solution to a given set of design parameters regardless of quality considerations. During the project in Poole credit should be given to Bluestone for achieving a high quality end product at a cost-effective price. Paul Gale of Bluestone states " experience has told our company that it is essential to communicate well at an early stage with all parties, as this leads to major benefits down the line."

(1). TAB - S. (TrefilARBED Bissen, Structural Design Procedure).