Flood Zone impact and hydrostatic forces

[tngolfer]

I'm in a High Hazard Flood Zone Class VE on the Gulf of Mexico. The project is a public pavilion approximately 70 ft. x 140 ft. with columns and bowstring trusses. The columns are spaced roughly 11'-9" on center along each side of the building with the trusses spanning the function area. I'm designing for a 1,000 lb impact load which is giving me an impact force of 14.6 kips on my columns at roughly 7.5 ft. above top of slab. The equation I'm using is from the ASCE 7-05 commentary:

F = [ 3.14 W Vb Ci Co Cd Cb Rmax ] / [ 2 g deltaT ]

It isn't really clear if this force needs to be applied to every column at the same time. What have you all done in the past?

IBC 2006

Thanks.

 

[tngolfer]

I think I answered my own question - FEMA 55, Coastal Construction Manual, gives a couple of load cases:
1. Breaking wave load on every pile/column + impact load on corner or critical pile/column
2. breaking wave on front row of piles/columns + hydrodynamic load on all others + impact load on corner or critical pile/column.

In working through the FEMA 55 equations, I don't understand how the impact load is so different. The 14.6k impact load per ASCE 7 is only 1.7k per FEMA 55. Any ideas? One seems very conservative or one seems very unconservative.