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Can we use load modifiers in this case?

Can we use load modifiers in this case?

Can we use load modifiers in this case?

(OP)
I am checking wind uplift on a light gauge steel framing roof in Southern California. I am seeing ni the cold-formed design software an input for load modifiers, the documentation states:

"Some Building Codes allow loads to be modified for combinations including wind,
seismic or multiple transient loads. Previous versions of LGBEAMER used a simple ‘Wind or
Earthquake’ check box that, if checked, would cause all loads to be multiplied by 0.75 when
checking strength interactions. Newer building codes use a more complex set of rules for load
modification and have eliminated the simple 0.75 factor for load combinations containing wind or
earthquake forces. "

My question is, since this is a load combination for wind, am I allowed to use the 0.75 load modifier on top of the usual ASD load factors? Thanks.

RE: Can we use load modifiers in this case?

0.75 is the inverse of the old 1.33 allowable stress increase, which is not permitted anymore.

DaveAtkins

RE: Can we use load modifiers in this case?

You could get with the times and design to LRFD, which may or may not helpful to you. But at least you wouldn't be getting confused between old versions and new.

Is this a new design or are you load checking an existing construction, because that would also make an impact as to what's applicable as well.

RE: Can we use load modifiers in this case?

(OP)
It is an existing construction. Thanks.

RE: Can we use load modifiers in this case?

Are you modifying it or just literally doing a capacity check, because if it's the latter you should be checking it against the design code at the time of construction first.

RE: Can we use load modifiers in this case?

Quote (jayrod12)

Are you modifying it or just literally doing a capacity check, because if it's the latter you should be checking it against the design code at the time of construction first.


I have never agreed with this line of thinking. If you are checking the capacity of an existing structure, you should check it using today's codes.

DaveAtkins

RE: Can we use load modifiers in this case?

I also agree. But you should also check under the code at the time of design to know if it was originally designed adequately. That way you have all the info required when you explain to the owner that his roof needs reinforcement.

RE: Can we use load modifiers in this case?

It also gives you a good check to see if you may have missed something. If it fails under the original code, you want to try verifying a bit harder because you might have missed something that the original designer too into account.

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