Gulf Construction Online - Pour-stop option offers a quick fix

Glass & Aluminium

Pour-stop option offers a quick fix

With building construction increasingly moving towards steel frames, a problem faced by the industry is to establish where the curtain-walling should be fixed. RICHARD LEE of Brital Limited* provides a solution.

01 October 2009

A VERY large number of buildings constructed in the Middle East region in the past 25 years have used curtain-walls as their external facades, with some of them having become iconic buildings of the region.

Many of these buildings have been constructed using in-situ cast concrete frames and floor slabs, which has allowed the curtain-walling to be fixed using traditional expanding anchors or cast-in fixing channels in the face of the concrete.
Now there is a growing tendency to use steel frame construction, which increases the speed of erection and very often incorporates trapezoidal steel permanent formwork to support the concrete floor slabs while curing.
In such floors, the edges are supported on steel beams and the thickness of the slab is often only 160 mm at the thickest part and 80 mm in the thinner parts. Such floor slabs do not allow fixing into the edge and as many Middle Eastern buildings do not have raised access floors or even screed on top of the slab, this creates the problem of determining where exactly the curtain-walling fixing can be located.
One option is to locate the fixing on the steel beam. However, in many instances, the steel beam is set back from the edge of the slab, creating a number of problems such as the requirement for large non-standard brackets and for steel beams to be site-drilled. Other problems are that the brackets interfere with the beam’s fire protection; and the loads from the fixings can affect the torsional stability of the beams.
A popular method to overcome these problems, which has been used elsewhere in the world, is to incorporate a continuous fixing channel in the angle pour stop at the edge of the concrete. Whilst this may at first appear to be a more expensive method, the greatly increased speed of installation of the curtain-wall system more than offsets the increased initial cost. If we also consider the major cost benefits to other construction trades on the building in terms of the savings in time, manpower, equipment and subsequent costs, this method proves to be a much more economical solution.
Alternative methods of curtain-wall fixing are likely to be significantly more expensive to the total cost of the building.
The pour-stop system incorporates a continuous fixing channel, which is anchored back into the body of the concrete slab and, because it is continuous, there is no risk that the fixing will be incorrectly positioned.
Some of the advantages that such fixings offer are:
• No requirement for drilling the steel or concrete to install the fixing brackets;
• Rapid installation of fixings; and
• Sufficient variation to accommodate construction tolerances.
The benefits of such construction methods are significant with the commonly used stick curtain-walling systems.
However, in recent years, unitised curtain-walling systems have become more widely used and in order to fully benefit from the advantages of the rapid erection that these systems offer, the fixing brackets need to be installed quickly and with sufficient allowance for adjustment to allow the panel to be positioned to the millimetre. The installation of unitised curtain-wall systems requires such fixing methods to ensure the full benefits of these systems are enjoyed.

Planning
The key to making such innovations work is planning. Very often, the curtain-walling contractor is not involved in a project until the frame of the building is well advanced and it is too late to incorporate fixing channels within the pour stop. Therefore, it is essential to establish if such fixings will be required for fixing the curtain-walling (or similar types of facade construction) early in the construction of the main building frame. This requires the main contractor and the curtain-wall contractor to be communicating and co-operating at an early stage in the building construction.

Check
If the answers to the following questions are yes’ then it is likely that pour stops with integral fixing channels will be an advantage and will ultimately result in cost savings on the project:
• Is curtain-walling or similar cladding being used on the building?
• Are steel frames (columns and beams) being used on the building?
• Is trapezoidal permanent steel formwork being used on the building?
If the conclusion is that a pour stop with an integral fixing channel is required, then the next stage must be to discuss the requirement early, either with the curtain-walling subcontractor or the structural engineer, who can advise specifically on a project by project basis and thus ensure that pour-stop channels are incorporated into the concrete casting programme.

Link for Brital curtain-wall fixing model graph:

* Brital Limited was initially established to design and market aluminium curtain-wall and facade systems in the Gulf. Over the past decade, the UK-based company has grown significantly to the point where the product range it offers encompasses all types of facade solutions ranging from doors and windows through to structurally glazed curtain-wall systems. All systems are available in both thermally-broken and non-thermally-broken versions.