Short

Short

Short Dir

Number

Short Dir

Max. Add

Short Dir

Direction

Seismic

Dir

Height

Vertical

Frames

Lateral

Shear

Seismic

Total

Response

Base

at Floor

Distribution

in Short

Seismic

Accidental

due to Acc

Story

Panel

Weight

Coefficient

Shear

Level

Factor

Dir

Force/frame

Torsion

Torsion

Shear

Cs

VS

hxS or hxL

CvxS

nS

FxS

Mtax

Qsic

VxS

Level

WS

(k-mass)

(g)

(kips)

(ft)

(kips)

(kip-ft)

(kips)

(kips)

Roof

3rd

284

27.042

0.276

9

10.895

1040

2.529

13.424

Cumulative

284

2nd

726

18.583

0.484

9

19.142

1837

4.469

37.035

Cumulative

1010

1st

734

9.125

0.240

9

9.506

912

2.218

48.758

Cumulative

1744

0.204

356

The vertical distribution of lateral seismic forces in the short direction, FxS, induced at any level shall

be determined using Equation C-25. These values are determined based on the vertical distribution

factor in the short direction, CvxS, calculated in Equation C-26. Values for WxS, hx, wi, and hi used in

Equation C-26 are given in Table D-3. The short-direction lateral seismic forces, FxS, shown in Table

D-3 are the lateral force per frame in the short direction. There are nine frames in the short direction,

5

nS , so that lateral force per frame is calculated as follows:

CvxS VS

FxS =

(Eq D-12)

nS

The barracks building is very regular in plan, so the center of rigidity, CR in both directions should be

at the center of the building. The accidental torsion is accounted for by offsetting the center of mass,

CM, 5 percent in both directions in plan at each floor level (see Figure D-2). The total mass at each

floor level in each direction (long and short) is multiplied by the 5 percent of the building dimension in

that direction to calculate the accidental torsional moment, Mta at each floor level. Similar to the

lateral seismic forces, the accidental torsional moments, Mtax are distributed along the floors of the

building according to the vertical distribution factor given in Equation C-26, which is expressed as

follows:

Mtax = 0.5[VSCvxS (FloorLength) + VLCvxL (FloorWidth)]

(Eq D-13)

Where:

CvxL = vertical distribution factor in the long direction.

VL = the base shear in the long direction.

Table D-3 gives values for accidental torsional moments, Mtax at each floor level.

The torsional resistance, Mtr (see Equation 3-3) is proportional to the square of the distance from the

center of resistance to the plane of each panel. The torsional resistance is also proportional to the

lateral stiffness of each panel. Therefore, because the barracks building is very long in one direction,

the shear panels in the short direction near the ends of the building will dominate the torsional

resistance. For this example it will be assumed that all torsional resistance comes from the shear

panels in the short direction. The torsional resistance from all shear panels, Mtr, in the short direction

can be expressed as follows (from Equation 3-3):

5

The symbol for the number of frames in the short direction, nS, must not be confused with the number of faces with diagonal

straps on a given shear panel, ns.

D-5

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