FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

Volume II DETERMINING SITE-SPECIFIC LOADS 8
EXAMPLE 8.5. ROOF UPLIFT CONNECTOR LOADS (continued)
• For ASD, multiply by the ASD wind load factor of 0.6, which comes from Load
Combination 7 (See Section 8.10) 0.6D + 0.6W:
The largest uplift forces occur for a roof slope of 20 degrees where wind is perpendicular to the
ridge. The addition of an overhang also increases the roof-to-wall uplift connection load. For
the windward overhang, a pressure coefficient of 0.68 is used based on the gust factor of 0.85
and pressure coefficient of 0.80 from ASCE 7-10. Otherwise, pressure coefficients for other
elements of the roof are based on GC pi = 0.18 and GC pf from the edge zone coefficients shown in
Figure 28.4-1 of ASCE 7-10.
Pressures and moments given below contain subscripts for their location:
• W = windward
• L = leeward
• O = overhang
• R = roof
The design wind pressure is determined from Equation 8.14 as follows:
• The roof/ceiling dead load is adjusted for the load case where dead load is used to resist uplift
forces as follows:
Dead load where 0.6 is the ASD load factor for dead load in the
applicable load combination
• Wind loads on the roof have both a horizontal and vertical component. The uplift connector
force, located at the windward wall, can be determined by summing moments about the
leeward roof-to-wall connection and solving for the connector force that will maintain
moment equilibrium. Clockwise moments are considered positive.
Moment (M) created by windward overhang pressures is solved as follows:
Vertical component, windward overhang (VWO):
COASTAL CONSTRUCTION MANUAL
8-55