This shear force must be transferred to the shear walls (A2-A7 & I2-I7) through the horizontal bracing.
The bracing also transfers the shear force from wall lines B & H (tributary to the upper roof diaphragm).
Total shear force transferred through horizontal bracing = 19.8 k + 10.96 kips = 30.8 kips (137 KN)
Total shear to walls A2-A7 and I2-I7 = Horizontal bracing shear + shear due to self-weight:
Weight of wall A2-A7 = 42.75 kips
Shear due to self-weight = CsW = (0.167)(42.75k) = 7.14 k (318 KN)
Total shear to walls A2-A7 & I2-I7 trib. to high and low sloped roofs = 30.8 k + 7.14 k = 37.9 k (169 KN)
Chord forces:
The low sloped roof diaphragm areas are conservatively assumed to span 90 feet (27.45 m) between shear
wall lines 2 and 7 for transverse seismic forces. An equivalent running load, w, is found by dividing the
total shear to the diaphragm by the span. The shear is made up of forces tributary to the low sloped roof
areas and the reactions at the moment frames.
Shear force tributary to the low sloped roof areas = 18.1 kips (80.5KN)
Shear force to each diaphragm from moment frame reactions = 4(4.81 k) / 2 = 9.62 kips (42.8KN)
Total shear force = 18.1 k + 9.62 k = 27.7 kips (123 KN)
Equivalent running load, w = V / L = 27.7 / 90'= 308 plf (4.49 KN/m)
Moment = wL2 / 8 = (.308)(90)2 / 8 = 312 kft (423 KNm)
T = M / d = 312 / 9.67'= 32.3 kips (143 KN)
Chord forces for longitudinal seismic forces are negligible by inspection.
Collector forces:
The beams along grid lines B & H must collect the shear forces from the upper concrete shear / window
walls and distribute them to the horizontal bracing of the low sloped roof area. The beams collect the
shear force from the upper roof area and the shear force associated with wall lines B & H tributary to the
low sloped roof areas.
Shear force from wall line B tributary to the upper roof diaphragm = 19.8 kips ( 88.1 KN)
Weight of wall line B tributary to the low sloped roof area = 15.2 k
Shear force from wall line B tributary to the low sloped roof area = CsW = (0.167)(15.2k) = 2.54k
(11.3KN)
Total shear force collected by beams along grid lines B & H = 19.8 + 2.54 = 22.34 kips (99.4 KN)
Unit collector shear force, v = V / L = 22.34 kips / 90'= 248 plf (3.62 KN/m)
Collector force = v*Lcollector = (248 plf)(18' = 4.46 kips (19.8 KN)
)
Seismic forces to vertical resisting elements from entrance area diaphragm
The concrete shear walls resist seismic shear forces tributary to the entrance area according to their
tributary areas.
H3-25
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