ASCE 7 section 12.3.3.4

[McEngr]

What is the purpose of mentioning collectors for this section? I'm trying to think of when they apply seeing as how the overstrength combination would always govern for SDC D-F.

Thanks.

 

[McEngr]

I suppose there could be a cantilevered column system that could control for the 1.25 increase, but it seems like a rather rare occurance.

 

[dakota_79]

I read it that the resulting design force on the collector would become 1.25*design force = 1.25*Omega*Eh (in most cases as you mention).

 

[McEngr]

Section 12.3.3.4 says that the 1.25 increase need not be considered for collectors using the overstrength factor, but overstrength factor is required for SDC D-F from section 12.10. However, section 12.10 says that for light-framed construction, it can be omitted. That brings me to the rho-factor ASD/LRFD equations from section 12.4. I assume for light frame construction, I could easily have a rho x Qe x 1.25 collector due to the irregularity requirements of 12.3.3.4.

Can anyone follow my logic? Thanks.

~ps~ Thanks for helping dakota. It has caused me to dive in again and make sure I'm asking the question properly.

 

[dakota_79]

You're right, and I now see the circlular logic you're talking about, and I now have the same question!

 

[kevo_55]

I'll take a look at this during my lunchbreak guys.

 

[kevo_55]

Guys, this applies more to non-light frame construction where you could have tall buildings where this could control.

Example, if you have a steel SMF you would still need diaphragms and their connections.

It is true that section 12.10 talks about collector elements (drag struts), but this is more for the pure collector element where mainly a tension or compression force is involved.

Section 12.3.3.4 is far more general. It has to do with forces connecting to diaphragms including both collectors and vertical elements. Vertical elements are not governed by section 12.10.

Does this clear stuff up?

 

[McEngr]

I guess I was under the impression that section 12.3.3.3 rules the vertical element scenarios. I'll have to dig deeper when I get home tonight on the rest of your post.

Thanks kevo!

 

[dakota_79]

Pretty sure that makes sense to me, kevo. Thanks! That's why you get paid the big bucks around here (of course, by "the big bucks" I mean "with many thanks").

Not gonna spend too much more mental energy on it. If it comes up on the exam, I'll tip my cap to them and move on.

 

[kevo_55]

Big bucks? Ha!

I'm kept around here for my good looks.