Diaphragms With Vertical Offsets - The Analysis of Irregular Shaped Structures - page 268

F i g u r e 7.34 Transfer frame forces.

The chord forces along grid line A are the same, but are in compression.
The braced frame OCBF1 and OCBF2 resultant hold-down forces are shown in
Fig. 7.34, neglecting gravity loads.
Loading in the longitudinal direction is shown in Fig. 7.35. Assume that the calculated
seismic unit strip load is equal to 560 plf. The uniform load per section is distributed in
accordance with the depth of the sections.

wD
D

560 30
280

()

12 −

w = = = 60 plf

12 −

wD
D

560 200
280

( )

23 −

w = = = 400 plf

23 −

wD
D

560 50
280

()

34 −

w = = = 100 plf

34 −

Wind loading in the longitudinal direction should be applied in accordance with
Chap. 6 of ASCE 7-05. The magnitude of the unit load to the section between grid
lines 1 and 2 will be much higher than to the other sections because of the magnitude of
the windward pressures. The combined windward and leeward wind load to the
high roof will be small because of the small vertical offset, and the wind load to the
section between grid lines 3 and 4 will be that equal to the leeward pressures.
Each diaphragm section acts as an individual diaphragm in this direction due to the
vertical offset.
Diaphragm section between grid lines 1 and 2:

VV wL
AB

60 80
2

()

== = = 2400 lb reactionsatgrid lines Aand B

2