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FEMA 361 design loads

FEMA 361 design loads

FEMA 361 design loads

(OP)
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?

RE: FEMA 361 design loads

I don't think so.

Quote:

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.

Quote:

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.

Quote:

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.

Quote:

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.

Quote:

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).

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