Submerged Wall Stability

[SteelPE]

I am currently working on the design of a building for a marina. The building is placed in a coastal AE zone with the SOG placed approx 4.5’ below the base flood elevation. The building is dependant on proximity to the water and therefore we do not need to design the exterior of the building to “breakaway” during a design flood event (something the owner does not want).

I need to design a concrete wall at the base of my structure that will resist the wave loading of Chapter 5 of ASCE 7. Chapter 2 of ASCE requires me to apply 1.5 Fa (Fa = flood load) to load combinations 5 6 and 7 using Allowable Stress Design. This would give me an equation to resist overturning of 0.6D + 1.0W + 1.5Fa. This equation is wreaking havoc on the stability of my concrete wall. Would others use the 1.5 factor for Fa or just use 1.0 Fa?

A large part of what is causing the problems has to do with the fact that the system is submerged when considering flood loading, therefore I need to use the buoyant weight of water and concrete in my design.

 

[ishvaaag]

I don't think you can forfeit an equation so explicitly presented in the code if you are still wanting to dwell within its specifications; for if even you were to find some other code less stringent on the matter it would rarely be understood to be of "equivalent performance" to what asked in the code.

So in my view I would start to plan to anchor the foundations or whatever seems proper.

 

[ron9876]

I agree. You have to follow the code requirements. If you are underwater with wave action you should expect to get large results.

 

[SteelPE]

I pretty much came to the same conclusion you guys did. The client is not going to be happy with the results.

What I did do was reduce the amount of the wave loading applied because the building axis do no align with the shoreline axis. So I was able to reduce the amount of force taken into the wall in accordance with equation 5-9 of ASCE 7-05. This at least helped a little bit.

This whole design was a killer because I had to reduce the weight of everything by 64pcf.

 

[cvg]

make sure that if you have scour, you do not rely on the earth dead load on the heel of the wall. this is similar to a floodwall design as presented by the USACE in their publication:

Publication Number: EM 1110-2-2502
Title: Engineering and Design - Retaining and Flood Walls

http://140.194.76.129/publications/eng-manuals/em1110-2-2502/toc.htm

 

[RFreund]

I would look at the Retaining and Flood wall design manual. Note- It is a little intense.

EIT