FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

8 DETERMINING SITE-SPECIFIC LOADS Volume II
EXAMPLE 8.6. LATERAL DIAPHRAGM LOADS FROM WIND PERPENDICULAR TO
RIDGE (continued)
Find: The roof diaphragm load using the envelope procedure for low-rise buildings (see Figure 28.4-1
in ASCE 7-10).
Solution: The roof diaphragm load using the envelope procedure for low-rise buildings can be found
as follows:
• Lateral loads (see Illustration A) into the roof diaphragm are a function of roof slope and wall
loads tributary to the roof diaphragm.
• Pressure coefficients for elements of the roof GC pi and GC pf are given in Table A.
Table A. Pressure Coefficients for Roof and Wall Zones
Roof diaphragm
Floor diaphragm
Diaphragm Zone GCpi GCpf Wall interior zone
Windward
Leeward
0.18
0.18
0.56
–0.37
Wall end zone
Windward
Leeward
0.18
0.18
0.69
–0.48
Roof interior zone
Windward
Leeward
0.18
0.18
0.21
–0.43
Roof end zone
Windward
Leeward
0.18
0.18
–0.53
0.27
Wall interior zone
Windward
Leeward
0.18
0.18
0.53
–0.43
Wall end zone
Windward
Leeward
0.18
0.18
0.80
–0.64
• GC pi is determined using the Enclosure Classification (enclosed building in this example) and
Table 26.11-1 from ASCE 7-10
• GC pf is determined using Figure 28.4-1 in ASCE 7-10
• Both interior zone and end zone coefficients are used to establish an average pressure on the
wall and roof.
The design wind pressure is determined from Equation 8.14 (q = q h in this case) as follows:
Step 1: Roof Diaphragm
• L = leeward
• W = windward
8-58 COASTAL CONSTRUCTION MANUAL