FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

8 DETERMINING SITE-SPECIFIC LOADS Volume II
S = snow load
R = rain load
T = self-straining force
W = wind load
Loads combined using the ASD method are considered to act in the following combinations for buildings
in Zone V and Coastal A Zone (Section 2.4.1 of ASCE 7-10), whichever produces the most unfavorable
effect on the building or building element:
Combination No. 1: D
Combination No. 2: D + L
Combination No. 3: D + (Lr or S or R)
Combination No. 4: D + 0.75L + 0.75(Lr or S or R)
Combination No. 5: D + (0.6W or 0.7E)
Combination No. 6a: D + 0.75L + 0.75(0.6W) + 0.75(Lr or S or R)
Combination No. 6b: D + 0.75L + 0.75(0.7E) + 0.75S
Combination No. 7: 0.6D + 0.6W
Combination No. 8: 0.6D + 0.7E
When a structure is located in a flood zone, the following load combinations should be considered in
addition to the basic combinations in Section 2.4.1 of ASCE 7-10:
In Zone V or Coastal A Zone, 1.5F a should be added to load combinations Nos. 5, 6, and 7, and
E should be set equal to zero in Nos. 5 and 6
In the portion of Zone A landward of the LiMWA, 0.75F a should be added to combinations Nos. 5, 6,
and 7, and E should be set equal to zero in Nos. 5 and 6.
The ASCE 7-10 Commentary states “Wind and earthquake loads need not be assumed to act simultaneously.
However, the most unfavorable effects of each should be considered in design, where appropriate.”
The designer is cautioned that F is intended for fluid loads in tanks, not hydrostatic loads. F a should be
used for all flood loads, including hydrostatic loads, and should include the various components of flood
loads as recommended in Section 8.5.11 in this chapter. It is important to note that wind and seismic loads
acting on a building produce effects in both the vertical and horizontal directions. The load combinations
discussed in this section must be evaluated carefully, with consideration given to whether a component of
the wind or seismic load acts in the same vertical or horizontal direction as other loads in the combination.
In some cases, gravity loads (dead and live loads) may counteract the effect of the wind or seismic load,
either vertically or horizontally. Building elements submerged in water have a reduced effective weight due
to buoyancy. Example 8.10 illustrates the use of load combinations for determining design loads.
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