Restrained vs. Non-Restrained
Restrained vs Non-Restrained
SUBJECT: UL and ICC Restrained Beam Rating Requirements
Recently there has been numerous inquiries as to the correct use of the of Restrained
Beam ratings in accordance with International Building Code (IBC) and Underwriters
Laboratories, Inc. (UL) guidelines.
In order to determine if your building construction is restrained, Section 703.2.3
restrained classification in the 2006 International Building Code indicates the following:
“Fire-resistance-rated assemblies tested under ASTM E 119 shall not be
considered to be restrained unless evidence satisfactory to the building official is
furnished by the registered design professional showing that the construction
qualifies for a restrained classification in accordance with ASTM E 119. Restrained
construction shall be identified on the plans.”
In addition, in order to meet restrained conditions per Underwriters Laboratories, Inc.
(UL) 263 Guidelines, Page 7, Item 9 of the Fire Resistance Directory indicates the following:
Classifications of floor-ceiling and roof-ceiling assemblies and individual beams
include restrained and unrestrained ratings. ANSI/UL 263 and, specifically,
Appendix C, provides general information with respect to the concept of these
classifications.
Appendix C of ANSI/UL 263 defines restraint in buildings as: ‘‘Floor-ceiling and
roof-ceiling assemblies and individual beams in buildings shall be considered
restrained when the surrounding or supporting structure is capable of resisting
substantial thermal expansion throughout the range of anticipated elevated
temperatures. Constructions not complying with this definition are assumed to be
free to rotate and expand and shall be therefore considered as unrestrained.’’
Restrained conditions for the fire test assemblies are provided by constructing
floor, beam and roof test assemblies within nominal 14 ft by 17 ft frames of
composite steel/concrete cross sections having an approximate stiffness (EI/L) of
850,000 kip-in. and 700,000 kip-in. along the 14 ft and 17 ft sides, respectively.
The frame stiffness remains constant throughout the fire test because the test
frame is insulated from the fire environment.
When applying the published restrained ratings, it is recognized that the
individual responsible for the design of the fire-rated construction may ascertain
that a different degree of restraint may be provided to the building assembly
during a fire condition than was provided to the test sample during the fire test.
Under these conditions, the designer may review the Conditions of Acceptance for
restrained and unrestrained assemblies and beams in ANSI/UL 263 for additional
guidance when determining whether restrained or unrestrained ratings should be
specified.
Once the building is determined to be restrained, we must now determine the proper
thicknesses of fire protection material on the beams. Therefore, the introductory portion
of the UL Fire Resistance Directory, Volume 1 indicates the following:
Classifications resulting from a tested assembly containing a full representation of
a floor or roof construction may include: (1) Restrained Assembly Ratings and (2)
Unrestrained Assembly Ratings. Results from test of these assemblies are
identified as Design Nos. A ____, D ____, G ____, J ____, or P ____. Tested
assemblies supported by beams may also include an Unrestrained Beam Rating,
but do not include a Restrained Beam Rating. A Restrained Beam Rating is
determined only from a test on an assembly with a restrained beam and a partial
representation of a floor or roof. Results from tests on this type of assembly are
identified as Design Nos. N ____ or S ____.
In summary, this means that the only way to achieve a “restrained beam” rating is to
utilize beam substitution. Restrained beam ratings cannot be found in an assembly
(i.e. D, G, J and P Series Designs). They can only be located in “beam only” designs
(i.e. N and S Series Designs)
