Structural System

Type

Description

S

Frames

1
2

Moment-resisting frame.
Ductile moment-resisting frame.

Shear walls

Two or more parallel and approximately symmetrically arranged ductile cantilever shear walls.
Ductile coupled shear walls.
Single ductile cantilever shear walls.
Shear walls not designed for ductile flexural yielding but having the ability to dissipate a significant amount of seismic energy. (This includes walls other than those listed above.)

Diagonal bracing

8

Buildings with diagonal bracing capable of plastic deformation in tension only:
(a) Single-story
(b) Two or three stories
(c) More than three stories
Buildings with diagonal bracing capable of plastic deformation in both tension and compression.

Box system

Both horizontal and gravity forces resisted by wall system.

1.33
in each
direction

Shared force-

11

12

Buildings with a dual bracing system consisting of a ductile moment-resisting frame plus shear walls conforming with the following conditions:
(a) The frames and shear walls shall resist the total lateral force in accordance with their relative rigidities considering the interaction between the shear walls and frames;
(b) The shear walls acting independently shall resist the total lateral force; 
(c) The ductile moment-resisting frame shall have the capacity to resist at least 25% of the total lateral force.
Shear walls plus a ductile moment resisting frame that do not satisfy the conditions of Type 10.
Buildings with bracing of Type 7 plus a frame of Type 2.

 0.80

1.33

*

Miscellaneous

15

Small tanks on the ground.
Freestanding elevated tanks with full contents, on four or more cross-braced legs and not supported by a building.
Freestanding structure of an inverted pendulum type, including elevated tanks on three or less cross-braced legs, or on unbraced legs.

3.20

Other structural
concepts

Structural systems other than those of Types* 1 to 15 above may be accepted where evidence shows that equivalent ductility and energy absorption are available sufficient to relate behavior of such alternative structural systems to any of Types 1 to 15.