Design Considerations for Earthquake Forces - Simplified Design of Reinforced Concrete Buildings - page 282

Bearing Wall System Building Frame System

Moment-Resisting Frame System Dual System

Figure 11-7 Earthquake-Resisting Structural Systems of Reinforced Concrete

(4) Dual System: A structural system with space frames and walls to provide support for the gravity loads.
Resistance to earthquake loads is provided by shearwalls and moment-resisting frames. The shearwalls and
moment-resisting frames are designed to resist the design base shear in proportion to their relative rigidities.
The moment resisting frame must be capable of resisting at least 25 percent of the design base shear (1617.6.1).

Based on ASCE 7, Table 12.2-1 shows the permitted system and height limitation for each SDC. The table also
shows the values of R and C d . The table could be used to select the required seismic-force-resisting systems
for a specific SDC. The building frame system and the moment-resisting frame system are commonly used and
are suitable for buildings of regular shape and moderate height. Bearing wall and dual system buildings are,
therefore, not discussed in this publication.

11.4 STRUCTURES EXEMPT FROM SEISMIC DESIGN REQUIREMENTS

The 2009 IBC allows certain structures to be exempt from the seismic design requirements (1613.1). These
structures include: detached one- and two-family dwellings with SDC A, B, or C or located where the mapped
short-period spectral response acceleration S s is less than 0.4g. Agricultural storage structures intended only
for incidental human occupancy are also included in the exemption.

Also structures located at the following locations are assigned SDC A:

a) Where S S ≤ 0.15g and S 1 ≤ 0.04g

b) Where S DS ≤ 0.167g and S D1 ≤ 0.067g