Can fasteners be used for fixing metal roofing and cladding into pre-stressed concrete portal frame beams?
- Read time: 3 minutes
- Date: 24 Jun 2021
- Sheeting & Cladding
Agricultural and industrial buildings are often constructed from portal frames with pre-stressed concrete purlins and sheeting rails. Traditionally profiled cladding is secured to the concrete beams with hook bolts, which are designed to secure the cladding without penetrating the pre-stressed structural members.
To install hook bolts it is necessary for the installers to be working simultaneously on both the top and the underside of the sheeting.
When these buildings are refurbished there is sometimes a requirement to fix either a composite panel, single skin or a built-up system to the prestressed concrete beams. However, this is not recommended because fasteners should not be used in this application.
Why shouldn’t fasteners be used into pre-stressed concrete beams?
There are three main reasons that fasteners are not recommended for this purpose.
Drilling/installing fasteners into the beams will affect the structural integrity of the beams
Pre-stressed concrete beams are difficult to fix into due to reinforcing bars, which are generally just 50mm below the surface.
It is difficult to drill accurately into the centre of the pre-stressed member accurately enough to prevent the concrete spalling off the side and therefore causing the fixing to fail.
These issues make drilling and fixing into pre-stressed concrete impossible without compromising the structural integrity of the beam.
As a result, drilling into prestressed concrete is not secure, and is far too unreliable to be certain of adequate pull-out values for wind uplift.
If fastening into prestressed concrete beams isn’t possible, what are the options?
Some roofing system manufacturers offer their own system of attaching timbers to the concrete beams, with the roof panels then fixed to the timber.
If one of these proprietary systems are not being used, we would always recommend that professional advice is taken to ascertain the suitability of the proposed replacement roof.
