UFC 4-023-03
25 January 2005
Examples of partially restrained and fully restrained steel connections are
listed in Table B-1 and shown in Figures B-11 and B-12. Figure B-13 presents two
weak axis connections. Note that testing in accordance with Appendix S of AISC 341-
02 can be used to verify and quantify the rotational capacities of connections that are
not listed in Figures B-11 and B-12.
B-4.7
Time Effect Factor for Wood.
As discussed in AFPA/AWC "LRFD Manual for Engineering Wood
Construction", the time effect factors, λ, were derived based on reliability analysis that
considered variability in strength properties, stochastic load process modeling and
cumulative damage effects. The time effect factors are applied to the reference
strengths used in the code, which are based on short-term loading test values. Time
effect factors range in value from 1.25 for a load combination controlled by impact
loading to 0.6 for a load combination controlled by permanent dead load. Common
building applications will likely be designed for time effect factors of 0.80 for gravity load
design and 1.0 for lateral load design. Further ANSI/ASCE 16-95 indicates time effect
factors of 0.7 when the live load in the basic gravity load design combination is for
storage, 0.8 when the live load is from occupancy, and 1.25 when the live load is from
impact. It is desirable that the structure is stable following local damage to allow for
rescue operations and the installation of temporary shoring, however stability in the
damaged state is not a permanent condition. Therefore a time effect factor greater than
that associated with permanent occupancy and less than that associated with impact is
warranted. For this reason and to avoid overly conservative values for such an extreme
loading, a time effect factor of 1.0, consistent with the time effect factors used for
gravity-lateral load combinations, is specified.
B-5
ADDITIONAL DUCTILITY REQUIREMENTS.
Additional ductility requirements are specified for all construction types, for
structures with MLOP or HLOP. The main goal is to insure that the failure mode for all
external columns and walls is flexural and ductile, rather than shear and brittle, by
requiring that the shear strength exceed the flexural strength. As the flexural strength
can often be increased by compression membrane effects under dynamic load, the
engineer must consider this in determining the capacity of the columns and walls. Park
and Gamble 1999 and UFC 3-340-01 provide guidance on compression and tension
membrane effects.
For reinforced concrete columns, the shear capacity can be increased by
simply increasing the number of column stirrups or by providing spiral reinforcement.
Shear capacity can also be increased by adding external hoop reinforcement in the form
of circular or square steel or composite jackets, which can be used as stay-in-place
forms. For structural steel columns, the shear capacity can be enhanced by filling the
section core with concrete and enclosing with steel plates. For masonry walls, fiber-
impregnated polymer coatings can be applied to one or both surfaces.
B-18
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