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?
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
FEMA 361 is a guide. ICC 500 is the new specification covering storm shelter design.
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.
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.
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.
No - that is not correct. The wind pressure used is not related to the design method (strength vs. allowable).
RE: FEMA 361 design loads
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