FEMA 361 design loads

[ntpe]

I am looking at a small storm shelter within a larger building. I am designing per
FEMA 361. I am considering reinforced masonry for the walls. When designing the
MWFRS using ASD method, I know that I use .6W in all of the load combinations.
When designing the reinforcing in the walls for out of plane loading, can I use .6W
of the component & cladding wind pressure?

Also, if I go with reinforced concrete, using the strength method, I know that I replace
1.6W with 1.0W for all load combinations. Can I also use 1.0W with the C&C wind load
when designing for out of plane loading?

It seems to me that for extreme wind, the calculated C&C wind pressure is the ultimate
value, and does not get factored up for the strength method, and actually gets reduced for
the ASD method.

Am I interpreting this correctly?

 

[JAE]

I don't think so.

I am looking at a small storm shelter within a larger building. I am designing per
FEMA 361.

FEMA 361 is a guide. ICC 500 is the new specification covering storm shelter design.

When designing the MWFRS using ASD method, I know that I use .6W in all of the load combinations.

No - you use all required load combinatinos - that includes D+W and others. 0.6D+W is one of many that you need to check all designs with.

When designing the reinforcing in the walls for out of plane loading, can I use .6W of the component & cladding wind pressure?

The use of MWFRS or C&C depends on what you are designing and the area of exposure of that element. For smaller wall segments you'd probably be using C&C wind
as the tributary area of a vertically spanning wall is H^2/3 where H is the wall height. For areas less than 700 s.f. you would use the C&C wind pressures.
Again - the load combinations ALL have to be checked, not just 0.6D+W.

Also, if I go with reinforced concrete, using the strength method, I know that I replace 1.6W with 1.0W for all load combinations. Can I also use 1.0W with the C&C wind load when designing for out of plane loading?

If you use strength method - you would use the LRFD load combinations per the code. The use of a 1.6W assumes a strength design method. The use of 1.0W presumes the use of ASD design. These are independent of whether you are using C&C wind pressures or not.

It seems to me that for extreme wind, the calculated C&C wind pressure is the ultimate value, and does not get factored up for the strength method, and actually gets reduced for the ASD method.

No - that is not correct. The wind pressure used is not related to the design method (strength vs. allowable).

 

[ttobin]

Really should go to the You Tube video.
This really shows a viable option to what you are a looking to do.

https://www.youtube.com/watch?v=k0tp4GGAH8A

Tim Tobin
ttobin1955@gmail.com