Design Considerations for Earthquake Forces - Simplified Design of Reinforced Concrete Buildings - page 297

The shear force transmitted to each of the two shear walls must be increased due to code required displacement
of the center of mass (point of application of lateral force) 5 percent of the building plan dimension
perpendicular to the force direction. For the N-S direction the displacement considered = 0.05 120' = 6'.

( y
k i

( y
J r

k i x i k i

( y =

V i V x + V x e x

To calculate the force in the shear wall the equation simplifies due to

∑

( y

1
2 V x +

1
120 V x e x

( y =

V i

symmetry in geometry and element stiffness to for this case.

The shear forces and moments for the shearwall at each floor level are shown in Table 11-4:

Table 11-4 Shear Forces and Moments at each shearwall (N-S)

Lateral
Force
F x
(kips)

Story
Shear
V x
(kips)

Height
h x
(ft)

Moment
(kip-ft)

V x e x
(kip-ft)

(V i ) y
(kips)

Level

5 63 88 88 529.8 48.6 583

4 51 87 176 1053 96.6 1741

3 39 67 242 1454 133.2 3340

2 27 46 288 1731 158.7 5244

1 15 26 314 1887 173.0 7839

Load Combinations

For lateral force resisting (shear walls in this case) the following load combinations apply (Chapter 2 Table 2-6):

U = 1.4D Eq. (9-1)

U = 1.2D + 1.6L + 0.5L r Eq. (9-2)

U = 1.2D + 1.6L r + 0.5L Eq. (9-3)

U = 1.2D + 1.6L r ± 0.8W
U = 1.2D ± 1.6W + 0.5L + 0.5L r Eq. (9-4)

U = 1.2D ± E + 0.5L Eq. (9-5) (seismic)

U = 0.9D ± 1.6W Eq. (9-6)

U = 0.9D ± 1.0E Eq (9-7) (seismic)

The seismic load effect E in equations (9-5) and (9-7) includes the effect of the horizontal and vertical
earthquake induced forces (see Section 11.6.3). For SDC C the redundancy coefficient ρ = 1

E = Q E + 0.2S DS D = Q E + 0.2(0.28)D = Q E + 0.056D For Eq (9-5)

E = Q E - 0.2S DS D = Q E - 0.2(0.28)D = Q E - 0.056D For Eq (9-7)

Calculations of Gravity Loads on the Shearwall

Based on dead loads calculated in Chapter 6 Section 6.5.1