interpretation, these combinations could also

various structural systems are provided in Table

include different systems in the same vertical

7-1.

plane (e.g., a two-story building with steel

(2) Modification factors, *m*, for enhanced

moment frames in the second story and a

performance objectives for beams, columns, and

concrete shear wall system in the first story). In

connections in fully restrained moment frames

the first case above, FEMA 302 permits the use

are provided in Table 7-12, and for partially

of the appropriate *R *factor pertaining to the

restrained moment frames in Table 7-13.

structural system in each orthogonal direction.

For the second case, the FEMA provision states:

(3) Modeling parameters and numerical

"The response modification coefficient, *R*, in the

acceptance criteria for nonlinear procedures are

direction under consideration at any story shall

provided in Table 7-22 for fully restrained

not exceed the lowest response modification

moment frames, and in Table 7-23 for partially

factor, *R*, for the seismic-force-resisting system

restrained moment frames.

in the same direction considered above that

story, excluding penthouses. For other than dual

(4) Expected strength of columns, beams,

systems where a combination of different

and other deformation-controlled components

structural systems is utilized to resist lateral

shall be determined using the expected yield

forces in the same direction, the value of *R *used

strength, *F*ye, as defined in the AISC Seismic

Provisions and the plastic section modulus, *Z*,

in that direction shall not be greater than the least

value of any of the systems utilized in the same

where applicable.

direction. If a system other than a dual system

(5)

The lower bound strength of

with a response modification coefficient, *R*, with

connections

and

other

force-controlled

a value of less than 5 is used as part of the

components shall be determined in accordance

seismic-force-resisting system in any direction of

with the nominal strength and *N *factors

the structure, the lowest such value shall be used

prescribed by AISC Seismic Provisions.

for the entire structure. The system overstrength

factor, Ω o , in the direction under consideration

at any story, shall not be less than the largest

value of this factor for the seismic-force-resisting

system in the same direction considered above

that story."

(1) Combinations of structural systems.

The connotation of dual systems is sometimes

erroneously

interpreted

to

mean

different

systems in each orthogonal direction of structural

(a) Supported structural systems with a

To clarify this point, FEMA 302

weight equal to or less than 10 percent of the

describes that condition as "combinations of

weight of the structure.

structural systems."

In addition to the above

7-105

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