T&G Guernsey GROW - Part 3 Floor Slabs
May 25, 2022
Part 3: Floor Slabs
The team at T&G Guernsey are delighted to be supporting the fantastic redevelopment work underway for the Guernsey Rural Occupational Workshop (GROW Limited).
Those following the structural development of the GROW project in Guernsey will be interested to learn our focus of attention has now moved to the ground and first floors and the important concrete elements of the new building. (Those coming fresh to our project updates can find out about earlier progress Part 1 – The Introduction and Part 2 – The Frame .)
As noted in our previous update, the first floor’s concrete element is an integral part of both the building’s vertical and horizontal stability design. The slab used forms a composite floor, designed using the MetFloor80 trapezoidal product supplied by UK-based CMF.
Fixing this metal decking to the steel floor beams involved a ‘through deck stud welding’ process, used to provide a shear key into the concrete component of the system. Once welded in place, the shear studs ensure the site has a robust working platform onto which concrete is poured.
Up to 140mm thick to provide the one house fire resistance, this concrete was a grade of C35 and reinforced with a mix of polypropylene and steel fibres to provide strength. Achieving the required finish involved using power-floats to produce a smooth flat floor.
The entire system provides both a diaphragm to distribute horizontal loads, and, through interaction with the steel floor beams through shear studs, also enhances the floor beams’ stiffness and strength.
Laying and fixing the decking to the steel beams, and pouring concrete, proved to be straightforward site activities, which resulted in a rapid and safe installation process. This very common form of construction is used globally, saving on the cost of materials and time while resulting in high-load suspended floor slabs and solid structural frames.
It is also a speedy process – at Grow, we installed the 900 square metre concrete slab over a single 24-hour period.
Specified as a 150mm thick ground bearing slab on insulation, two polythene membranes and a minimum 150mm layer of well compacted granular fill, the ground floor slab’s design underlines the finish needed to resist punching loads of the various use-cases of GROW’s operation.
In common with the first floor, it will contain reinforcing polypropylene fibres to control shrinkage cracking, to be added to the mix at the batching plant in controlled conditions.
The slab is yet to be cast, with discussions currently ongoing with the contractor to determine their requirements for size and casting sequence.
Given the specification, allowing the contractor significant flexibility in the approach to this element is important, as four, three, two or even one sections with each section sawn into max 5m x 6m elements within around 24 to 36 hours after casting.
The contractor’s construction logistics requirements will determine final size and sequence, along with the installation of under slab services and – of course – the weather.
Planned next steps and more information
The final instalment of this article series will focus on over-site drainage – the site’s flat ground and proximity to surrounding slopes creates a major challenge given the combined area of the main building and two glasshouses covers approximately three quarters of the site.
Last, a visit to the GROW website (www.grow.gg) is strongly recommended, to understand what the organisation does for the island’s local disabled community, and what this new building will allow them to do in the future, including services to be offered.
There is also an opportunity for you to support GROW, and, at the bottom of their redevelopment page, you can access the ongoing timelapse film of the development to date.
Why choose T & G?
Over more than 30 years in business, we have been involved in projects across the Channel Islands, spanning every type of construction, working on large commissions and small, encompassing the requirements of private and public sector clients. Each has been approached with the same determined, creative professionalism that drives everything T&G does.
Choosing to work with T&G in Guernsey or Jersey provides assurance of the same high quality approach. We take pride in understanding and meeting client requirements, in finding solutions to engineering challenges and ensuring satisfaction at the completion of every project or piece of work.