Flood hydrostatic and hydrodynamic design

[magicming]

Hi there,

I have a client already having the design drawings in Toronto. But the engineer didn't do design for the flood pressure, including hydrostatic and hydrodynamic loads. He doesn't like the previously engineer so he reached me for help to do some calculations for the current design or do some modifications so that the city can issue him the building permit.

I didn't do similar design before but I checked the specifications. It looks ASCE-7-22 has the design. Can someone having experience giving me some guidance? Also, for the flood hydrostatic and hydrodynamic loads, does it need to be considered in combinations with other loads during the calculations? Like regular load combinations such as 1.0D + 0.9L, etc.

Thanks,

 

[JStephen]

A week or two ago, I did one of the ASCE free-for-members continuing ed classes on a related topic:

https://sa360.asce.org/ASCEWebApp/Benefits/Membership/Detail.aspx?productid=286978859

Reasonably informative. And kind of mirrored what I ran into the one time I dealt with it.

 

[jerseyshore]

The FEMA coastal construction manuals are the best for flood design IMO. Great graphics and example problems. Not sure the difference in requirements for US vs Canada, but they certainly detail all the different things very nicely. Good place to start if you are new to flood design.

 

[magicming]

Thanks, JStephen. It seems I have difficulty to get access your presentation. Just wondering for flood, like 0.8m above existing ground, should both hydrostatic and hydrodynamic loads be applied to the ground floor walls and also the foundation?

Also, for the hydrostatic load at foundation, should it consider the soil in ground as saturated so the water pressure will start from top of flood surface and gradually increase to the bottom of footing?

Thanks,

 

[magicming]

Great and thanks for helping, Jerseyshore. I will dig into that manual.

 

[lexpatrie]

ASCE 7-22 has the load cases, it doesn't have the underlying stuff. That's ASCE 24-14. This kind of design is not for the faint of heart. The flood provisions are very uh, "punitive" because they want a robust design, so your client's dissatisfaction with the prior engineer is perhaps more on the "overdesigned junk that guy sent me" versus any technical issue with the design you'd be able to change.

I thought Canada has requirements you notify the previous engineer you're eyeballing their work? It sounds like you are potentially stepping into a replacement structural engineer of record role.

 

[magicming]

Thanks for your comment. @lexpatrie. And yes, ASCE 7 only specifies the minimum loads, but ASCE 24 covers the flood design.

It looks the previous design was not overdesigned but underdesigned. The engineer didn't consider the flood situation at the conservation area but when my client submitted the application to the city, the city replied back flooding was not considered in design. And when my client got back to the previous engineer, they asked for more money to modify the design and my client was not happy about this because he viewed this was the engineer's responsibility to thoroughly consider the design based on the house address.

Indeed, if I stepped in, the design will slightly change for sure. And that is a structural engineer change on record.