(b) Detached one- and two-family dwelling of light-frame construction.
(2) Dual systems in the FEMA 302 provisions are defined as moment frames with either braced
frames or shear walls that jointly resist lateral forces along the same line of force. The lateral forces are
distributed to the various structural components in accordance with their relative rigidities, but the moment
frames are designed to be capable of resisting at least 25 percent of the design forces. The moment frame
shall be part of an essentially complete space frame system providing support for vertical loads. These dual
systems are described further in the following paragraphs.
Moment Frame/Shear Wall Systems. As limited by this document, these dual systems shall consist
of either structural steel or reinforced concrete moment frames resisting lateral forces jointly with either
reinforced concrete or reinforced masonry shear walls. Appropriate R factors and other design coefficients
for other systems are provided in Table 7-1.
Moment Frames/Bracing Systems. As defined by this document, these systems shall consist of
steel moment frames with selected braced bays so that lateral forces are resisted partly by moment frame
action and partly by braced frame action. The bracing system can consist of either concentrically or
eccentrically braced frames. R factors and other design coefficients for these various systems are provided
in Table 7-1. The use of concrete moment frames with either concrete or steel bracing is not prescribed by
this document, as the detailing requirements are very demanding, and the performance of these systems has
not been satisfactory.
(1) Response modification factors, R, for Performance Objective 1A for various dual systems are
provided in Table 7-1.
(2) Modification factors, m, for enhanced performance objectives, and modeling parameters and
numerical criteria for nonlinear procedures are prescribed in the following paragraphs;
Reinforced concrete shear walls... .... para. 7-2f(3)
Precast concrete shear walls... ... ... ...para. 7-2g(5)
Unreinforced masonry shear walls... para. 7-2h(5)
Concentric braced frames... ... ... ... ..para. 7-3b(9)