Fire Resistance Levels

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In 2006, a series of fire tests were done on Alphalite masonry. When calculated to the requirements of AS3700:2001, Section 6, they were proved to achieved much higher FRLs than standard concrete masonry units:

Structural Adequacy FRL:
The maximum slenderness ratio (Srf), which governs the Structural Adequacy FRL, is 25.15 for Alphalite at a 120-minute FRL (The industry standard is 16).

Integrity FRL:
The 90mm thick Alphalite test achieved a 240-minute Integrity FRL which is the highest requirement in the Building Code of Australia (BCA).

Insulation FRL:
Alphalite masonry requires a material thickness of 78mm to achieve a 120-minute FRL (standard concrete masonry requires 120mm).

Achieving the required FRLs the Insulation FRL is the easiest to prove. It is governed by the material thickness of the masonry unit. The 12-01 block, with 2-cores has a material thickness of 74mm which gives it a 90-minute Insulation FRL.

All other Alphalite masonry units have a material thickness greater than 78mm, which gives them a minimum 120-minute Insulation FRL, calculated as per AS3700:2001, Clause 6.5.4(b) (ii).

The highest FRL requirement is 240-minutes. Austral Masonry achieves this by reducing the core size of 15-01 and 20-01 blocks to give them a material thickness greater than 117mm as per AS3700:2001, Clause 6.5.2. To distinguish these from the 120-minute rated blocks, their code numbers are 15-401 and 20-401

INSULATION FRL (mins)					Code Nos
60	90	120	180	240
					12-01 (2-core)
					10-01; 10-31; 15-01; 20-01
					Twinbrick & 12-01 Chaser
					15-401 & 20-401

The Integrity FRL is 240 minutes in all non-loadbearing masonry with t > 90mm. In loadbearing masonry, it is 240 minutes when the Structural Adequacy FRL is 240 minutes and t > 90mm; otherwise, it is 120 minutes.

The Structural Adequacy FRL is the most complicated. It is governed by three formulae in AS3700:2001, Clause 6.3.2.2 which use the masonry panel’s height, length, thickness and restraint conditions around the perimeter to calculate the panel’s Slenderness ratio for fire (Srf).

The maximum Slenderness ratios for Alphalite masonry are:
27.80 at a 60-minute FRL
27.10 at a 90-minute FRL
25.15 at a 120-minute FRL
22.40 at a 180-minute FRL
20.45 at a 240-minute FRL.

Alphalite masonry that is designed for other loads (vertical, bending, earthquake etc.) can be checked for its Structural Adequacy FRL by using the following graphs. The three formulae are graphed, with a line for each wall thickness: 90, 110, 140 and 190mm.

How to use the charts:

First, find the page with the required FRL: 60, 90, 120, 180 or 240 minutes. Next, find the graph with the restraint conditions of your proposed wall. Note: walls unrestrained at either end are governed by the “height” formula only. The maximum height for each thickness is given at the foot of the page. Finally, plot the intersection of your wall’s height and length on the appropriate graph. The thickness required is represented by those lines clear of the intersection point.