What is a BLT?
A BLT is the highest allowable temperature the structural element can withstand whilst still supporting the load. It is independent of time.
What kind of a beam benefits from a BLT?
All beams with significant holes in the webs benefit from BLTs in order to establish the optimum fire protection thickness if using intumescent protection. See SCI AD319 for further information.
What are the advantages of using BLTs?
- The client will see a reduction in fire protection costs.
- Ensures adequate protection to all beams.
- Designer can demonstrate compliance with HSE requirements.
- Enables all fire-protection providers to quote on a competitive and equal basis
- Can avoid the need to fill trapezoidal floor deck voids – see below
What is the effect of unfilled trapezoidal floor deck on Westok beams?
A further benefit of BLTs is the way the SCI/Westok software CELLBEAM AutoMate can check the effect of filled or unfilled* trapezoidal deck voids on the beam. In many cases the software calculates that unfilled deck voids on composite beam have a very limited effect on the BLT. The ability to avoid the filling of deck voids can result in very substantial cost savings.
*Note
§ If the fire period exceeds 90 minutes the trapezoidal deck voids must always be filled.
§ If the voids in the deck cross a fire compartment all voids must be filled including re-entrant decking.
How do I establish a BLT for my beams?
The SCI/Westok Cellular beam software, CELLBEAM AutoMate, calculates the BLTs for you at the same time as it undertakes the normal cold design. No additional design work is required – simply select the appropriate “Building Type” on the loading page.
What do I do with my BLT’s?
The fire protection sub contractor needs to receive the BLTs.
Use the CELLBEAM AutoMate “Add to table” function to simply collect the data and add to the drawing, or issue onto a separate sheet. (see table 1)
Where do BLTs come from?
Westok and SCI carried out a series of fire-tests to calibrate structural and thermal models developed by SCI. These models are embedded in CELLBEAM AutoMate, which calculates the BLTs for individual cellular beam designs. The software takes into account the type of application, eg office, plant, education etc…and uses the appropriate fire load factors from BS5950 part 8.
What happens if a BLT is not provided?
If the contractor is not provided with the BLTs from the CELLBEAM AutoMate software there are more basic methods to calculate intumescent thickness. However they are simplistic and can be extremely conservative.
It is highly likely that any assumed limiting temperatures will be lower than required, so the client is paying for more protection than would be required.
Contact Westok directly for more guidance - 01924 264121 or design@westok.co.uk