Fireproof classification in structural steel

Published: 30 March, 2011, 8:07 am PDT

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Many structural steel framed buildings are designed assuming them to be “Thermally Restrained”, with little or no understanding of what this actually means.

 

The ASTM E119 standard used by Underwriters Laboratories to test fireproofing materials defines four hourly classifications for floor ceiling and roof ceiling assemblies. The four classifications are:

 

Restrained Assembly

Unrestrained Beam

Unrestrained Assembly

Restrained Beam

 

Depending on whether or not the assembly is considered to be Restrained or Unrestrained, the beam rating may or may not equal the assembly rating. A Restrained Assembly rating, Unrestrained Assembly rating and an Unrestrained Beam rating are all determined from the same ASTM E119 test. A Restrained Beam rating is obtained from a separate test and not discussed here.

 

The ASTM E119 criteria for the test, more or less, are as follows:

 

1. The specimen shall sustain the applied load during the classification period.

 

2. The unexposed surface temperature shall not ignite cotton waste nor exceed 250°F above ambient.

 

3. No steel temperature at any point on the steel shall exceed 1300°F.

 

4. The average steel temperature at any location shall not exceed 1100°F.

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