Understand what steel framed concrete floor construction can do for you!
Designers wishing to specify a floor construction that will avoid the use of traditional formwork with props, or that will increase space between columns for greater end-use floor capacity will sometimes consider both of these options and their variations.
A pre-cast hollow core concrete plank floor may be selected in particular applications for its long spanning capability, high acoustic properties and the flat soffit, but it does have distinct limitations, particularly during the construction process.
As a concrete floor system, the hollow core planks are considered to be lightweight, but not when compared to the elements of a metal deck system. They also require wider and deeper supporting beams. In addition, the individual installation required for the units results in the use of considerably more crane time, which can adversely affect the critical path, particularly on sites where a single crane is in operation.
Saving on material and labour costs is, understandably, a key consideration for designers and their clients on any construction project, but the programme and buildability impacts of the various options should not be ignored.
As an option, a lightweight, efficient, cost-effective composite steel deck construction has many advantages and SMD can offer a comprehensive range of floor deck profiles in varying depths, steel grades and gauges to suit all project and design criteria. The benefits of using the SMD profiles cover all of the key drivers we’ve already mentioned – cost, programme and buildability.
Bundles of deck sheets are craned into position and then easily manoeuvred into place by operatives working on the frame and deck platform. Up to 400m2 of deck can be laid by a single gang in a day with no further assistance from a crane or other plant. Even taking into account the subsequent concreting operations, this results in a labour cost saving of approximately 20% when compared to installation of precast concrete planks. The speed of laying and the reduced crane time also have a positive impact on construction programme.
The area of decking that can be transported to site in a single load is approximately ten times that of precast planks. As concrete is normally delivered from local batching plants, installation of a composite slab floor system generally results in fewer miles covered during delivery movements.
Metal deck sheets can be cut to suit irregular shaped structures and this system is a more suitable form of construction in confined spaces, such as inner city sites.
Late design changes can be accommodated more easily. During construction of Heathrow Terminal 2A by SMD, some 8000m2 of decking that had already been installed were affected by additional tenant fit-out requirements for lift and stair voids. A large number of deck sheets were taken out, cut down to suit the revised steelwork layout and reinstalled, avoiding the need for costly and wasteful disposal and a complete reorder of more suitable units that would be the case with pre-cast planks.
Integral fixings allow services to be suspended from the deck soffit, making them easily accessible for future maintenance.
Modifications to the slab to incorporate the additions of voids for new services or an altered layout to services or changes in use are relatively straightforward with adequate additional support to the cut edges.
Deck sheets provide a safe working platform even if the concreting operations are delayed or need to be phased.
The VoidSafe™ Protection System, designed and installed as part of the decking operations, covers large voids at the time of construction, minimising risk to operatives without the need for guard-railing.
With a reduction in quantities of steel and concrete, a shortened programme and fewer vehicle miles, this form of construction contributes effectively to sustainable development requirements. A proven reduction in embodied carbon (see the reference to the BCSA report below) is also a distinct benefit.
A study was carried out by the British Constructional Steelwork Association (BCSA), SCI and Gardiner Theobald to provide steel construction cost and programme guidance for quantity surveyors and designers. The objective of the study was to provide a comprehensive comparison of two typical multi-storey office buildings and the report clearly demonstrates that the use of a metal deck system results in lower cost and quicker installation time than the use of pre-cast planks and other popular structural framing solutions.
Cost comparisons are provided in the latest edition of the Costing Steelwork supplement to Building magazine from the British Constructional Steelwork Association Limited. The BSCA regularly reviews material prices for incorporation into the reports on their findings.