Openings of metal decks

Openings are often encountered during the construction of metal deck composite floor slabs. Solideck introduces how to deal with openings in various cases.

Classification of openings

Openings are categorized according to size, and different measures are taken depending on the size.

• Small – openings up to 300 mm square – unlikely to present a problem structurally and do not normally require additional reinforcement.
• Medium – openings between 300 mm and 700 mm square – normally require additional reinforcement to be placed in the slab. This is also the case if the openings are placed close together.
• Large – openings greater than 700 mm square – should be trimmed with addition permanent steelwork back to the support beams.

Treatment of open holes

• For small to medium sized openings, it is common practice for the contractor to “box out” the floor slab area with timber inserts to create the opening prior to placing concrete, as shown in Figure below. The slab should not be cut until the concrete has reached 75% of its design strength. It can then be cut to form the opening.

• Additional reinforcement is required around medium sized openings. This often takes the form of bars placed in the troughs of the decking adjacent to the opening, with additional transverse bars used to smooth out’ the load transfer around the opening (see figure below). The distance between an opening and an unsupported edge should not be less than the greater of either 500 mm and the width of the opening. If the opening falls within the usual effective breadth’ of concrete flange of any composite beams (typically span/8 each side of the beam center line), the beam resistance should be checked assuming an appropriately reduced effective breadth of slab.

It is very important to cut opening in a metal deck composite floor slab because of the safety issues involved. When pouring concrete, if the opening is not handled properly, it could trigger the concrete to leak in the opening, causing a powerful impact that could damage workers on the next floor or the building.