It has come to the attention of CISC that the architectural and structural engineering professions are not fully aware of a ULC Bulletin related to "Sample Loading Requirements", dated June 14, 2006 that dealt with modifications to the fire test standard, CAN/ULC-S101. The third edition of CAN/ULC S101 was published in April 2004 as CAN/ULC-S101-04 and requires the load applied on test assemblies to be calculated using Limit States Design (LSD) methods, since Working Stress Design (WSD) methods were no longer applicable in Canada. However, the Full Load Condition for fire tests performed prior to the 2004 Edition was calculated using WSD, and because the two methods often yield different results, Designs that were once unrestricted, now fall under the category of Restricted Load Use Conditions.
As a result, ULC's online directories listing fire rated designs for floor, roof and load bearing wall assemblies now include an important revision directed to the engineer of record. If applicable, the revision is found immediately below an assembly’s Design No. and reads as follows:
Load Restricted – Assembly evaluated in accordance with Working Stress Design methods, for use under Limit States Design methods; refer to information under Guide BXUVC.
Guide Information BXUVC explains the changes and contains Table 1 (see excerpt of table below) that lists a series of Load Restricted Factors for six type of assemblies of which three include structural steel, i.e., noncomposite steel beams, composite steel beams and floors/roofs supported by open web steel joists. If not stated in the Design, the value in Table 1 is to be used. However, the owner of the Design, usually the fire protection material manufacturer, has the option of applying for a more precise determination of the Load Restricted Factor for a particular Design, which would then be stated in the Design.
Table 1
|
Type of Assembly
|
Percent Load Reduction
(LSD-WSD) / LSD
|
Load Restricted
Factor
|
|
W200x42 noncomposite steel beam
|
12%
|
0.88
|
|
W200x42 composite steel beam
|
29%
|
0.71
|
|
Floor / Roof supported by open web steel joists
|
4%
|
0.96
|
In addition to the tabulated information in the Guide Information BXUVC, additional directions read as follows:
“The Load Restricted Factor shall be applied to the factored resistance of all structural members or components, φR, including but not limited to, factored moment resistance, (Mr ), factored shear resistance (Vr ), factored tensile resistance, (Tr ), and factored compressive resistance, (Cr ).
The ratings for steel columns do not have a “Load Restricted Factor” because these ratings are based on temperature limitations. No loading is applied to steel columns during the fire test.
The engineer of record shall be consulted whenever fire resistive assemblies with “Load Restricted Factors” are selected. The indicated load reductions are based upon Factored Load effects that are governed by the reduced Factored Resistance of the structural elements. The selection of structural elements is, at times, based upon service limits such as deflection and vibration. These factors and others, such as the change in material strength properties as a function of temperature, should be considered when selecting fire resistive assemblies with Load Restricted ratings.”
The above mentioned details regarding this restricted load use condition have also been added to BXUV7, Fire Resistance Ratings – CAN/ULC-S101 Certified for Canada in the cUL Directory.