FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

8 DETERMINING SITE-SPECIFIC LOADS Volume II
EXAMPLE 8.9. SEISMIC LOAD (continued)
• Seismic forces are distributed vertically as follows:
Roof level:
Effective seismic weight, w x roof = 23,900 lb + (0.5)(19,600) lb + (0.5)(16,000/2) lb = 41,700 lb
Height from base, h x roof = 18 ft
w x roof (h x roof ) = 750,600 ft-lb
Floor level:
Effective seismic weight, w x floor = 19,600/2 lb + 16,000/2 lb + 21,600 lb + 12,679 lb = 52,079 lb
Height from base: h x floor = 8 ft
w x floor(h x floor) = (52,079 lb)(8 ft) = 416,632 ft-lb
from Equation 8.16
from Equation 8.16
The force in the shear walls and at the top of the piles will vary by the R factor for the shear wall
system and the pile system (e.g., cantilevered column system).
• Lateral seismic force at the roof level for design of wood-frame shear walls (R = 6.5):
where:
R = 6.5 for light-frame walls with plywood
I = 1.0 for residential structure
using Equation 8.15 for V substituted into Equation 8.16
The design shear force for the shear walls is based on the lateral seismic force at the roof level.
Total seismic force for shear wall design is 3,681 lb
Solution for #2: The shear force to the top of the pile foundation (i.e., cantilevered column system,
R = 1.5) can be determined as follows:
• Roof level
using Equation 8.15 for V substituted into Equation 8.16
8-72 COASTAL CONSTRUCTION MANUAL