Solid Basement walls design for the coastal construction VE zones

[Naga131]

Hello All,

I'm facing a challenge with high flood loads on a coastal basement wall project (220 kips/ft, VE zone). FEMA 55 analysis indicates significant hydrostatic, breakaway, and hydrodynamic components. I'm open to any ideas or collaborations to verify these loads or explore strategies for potential reduction. Let's brainstorm some solutions!
Thank you for your help in advance.

 

[Apple234]

You are not required to design above the BFE? I was under the impression that in coastal zones you cannot build a habitable basement.
Why don't you build on stilts or piers?

 

[Naga131]

This remodel project involves significantly expanding the basement of the existing water treatment plant. The original 1960s building's basement, with its 16" walls and pumps at the basement, is being demolished and replaced with a new one featuring a 5ft larger footprint.
Due to updated flood load requirements, the new basement walls will need to be nearly double the thickness, at approximately 30", to achieve sufficient resistance.

 

[phamENG]

If they're demolishing it and building a new one, the new one should meet the current requirements. And that should mean not putting critical infrastructure below BFE in a VE zone. You should have a good long talk with your client about that one.

 

[Naga131]

While Table 4-10 indicates that coastal construction is not permitted. He outlined some specific expectations for this project.

 

[SlideRuleEra]

Naga131 - Which edition of FEMA P-55 are you using? I don't find a Table 4-10 in the current fourth edition.

Anyway, FEMA P-55 is intended for residential construction (it says so in the Preface). Sometimes industrial projects must do things that are outside typical building code restrictions. If it takes 30" thick wall to meet hydrostatic, hydrodynamic, etc. loading, you have the answer. Don't go trying to "cut corners". The type loads that water imposes are "real", not "statistical probabilities" such as live, wind & seismic loading.

 

[Naga131]

Thank you @SlideRuleEra. I just want to make sure the number is reasonable.

 

[SlideRuleEra]

Naga131 - One easy way to do a crude sanity check is to see what wall thickness is needed for only hydrostatic load and/or flotation. The difference between this wall thickness for just hydrostatic / flotation loading and 30" is needed for all other loads.

Would not be surprising if hydrostatic / flotation loading needs about 16" wall thickness... probably the design criteria in the 1960s.

 

[Naga131]

Thank you @SlideRuleEra it makes sense now.