Soft Story versus Weak Story

Structural Layout Vignette and Multiple Choice

Soft Story versus Weak Story

Postby Harrye » Sun Mar 30, 2014 3:17 pm

Isn't soft a form of weak? Are we just splitting hairs here? Is it even worth worrying about this difference? Should I bother researching this?
User avatar
Harrye
 
Posts: 49
Joined: Mon Jun 04, 2012 7:35 am

Re: Soft Story versus Weak Story

Postby AREcoyogi » Mon Mar 31, 2014 5:26 am

Seems they are terms that are often mistakingly interchanged...probably mostly by Architects!!

End of first paragraph on the 3rd page highlights the technical difference although I doubt it would be called out on the ARE.

http://www.iitk.ac.in/nicee/wcee/article/WCEE2012_0183.pdf
User avatar
AREcoyogi
 
Posts: 169
Joined: Mon Nov 04, 2013 10:18 am

Re: Soft Story versus Weak Story

Postby Mike-SE » Tue Apr 01, 2014 10:58 am

serviceability vs strength. soft means it moves too much. weak means it is not as strong as it should be.
Mike-SE
 
Posts: 1108
Joined: Fri May 31, 2013 7:10 pm

Re: Soft Story versus Weak Story

Postby hnQ_9999 » Wed Apr 02, 2014 8:04 pm

Soft-story is a term by itself, no interchangeable to "weak-story".
As in "Last year, San Franscisco adopted a measure to
have all soft-story apartments taller than 3 levels to retrofit to latest
seismic codes."
hnQ_9999
 
Posts: 1029
Joined: Tue Nov 26, 2013 1:35 am

Re: Soft Story versus Weak Story

Postby mwelch » Tue Jun 17, 2014 12:52 pm

Mike-SE wrote:serviceability vs strength. soft means it moves too much. weak means it is not as strong as it should be.


Mike SE:

Say a building had under ground parking is that a 'weak story'? Now say there is an earthquake and the upper floors collapse on to the ground floor, is that a 'weak story'? See attached picture

I guess what I'm asking is can you a weak-soft story (combined irregularities)
You do not have the required permissions to view the files attached to this post.
User avatar
mwelch
 
Posts: 79
Joined: Tue Feb 19, 2013 1:39 pm

Re: Soft Story versus Weak Story

Postby Mike-SE » Tue Jun 17, 2014 4:44 pm

You may have both a soft story and a weak story at the same level.
Mike-SE
 
Posts: 1108
Joined: Fri May 31, 2013 7:10 pm

Re: Soft Story versus Weak Story

Postby laurstar » Sun Jul 06, 2014 8:21 am

would a "weak story" be a garage condition (because there is an opening) and a "soft story" be an open plaza level (because there are only columns while the upper stories have shear walls, for example)?

if i have an applicable example, it is easier for me to understand the concept

thanks!
laurstar
 
Posts: 418
Joined: Fri Feb 21, 2014 2:21 pm

Re: Soft Story versus Weak Story

Postby plus » Mon Jul 07, 2014 11:05 am

Weak Story - where the structural members are "incapable" of or are "underdesigned" to handle the lateral / seismic loads
Soft Story - where the structural members are "capable" of or are "designed" to handle the lateral / seismic loads but are the weakest at a spot.
This spot is soft story - typically parking on the first floor, garage door openings etc

Hope this helps

Plus

laurstar wrote:would a "weak story" be a garage condition (because there is an opening) and a "soft story" be an open plaza level (because there are only columns while the upper stories have shear walls, for example)?

if i have an applicable example, it is easier for me to understand the concept

thanks!
plus
 
Posts: 133
Joined: Tue Oct 01, 2013 10:52 am

Re: Soft Story versus Weak Story

Postby Mike-SE » Tue Jul 08, 2014 6:54 pm

There is NO WAY you can tell if there is a soft story or weak story by looking at a building, it is way to complicated.
A garage, with a Simpson moment frame is probably NOT a weak story but may be a story.
For the ARE understand the following:
A soft story is where the strength of a floor is less than the floor above. An example is a Chevron brace (CBF) That becomes a eccentric brace (EBF) at the first floor to allow for a doorway. An EBF drifts more than a CBF and therefore may have create a soft story.
A 20' shear wall that at the first floor has a 15' opening in it creates a weak story. It may also be a soft story.
Weak = less strength (lower area)
soft = less stiff (lower moment of inertia)
Mike-SE
 
Posts: 1108
Joined: Fri May 31, 2013 7:10 pm

Re: Soft Story versus Weak Story

Postby laurstar » Tue Jul 08, 2014 7:54 pm

as always, thank you mike!
laurstar
 
Posts: 418
Joined: Fri Feb 21, 2014 2:21 pm

Re: Soft Story versus Weak Story

Postby mfgarrod » Sun Oct 22, 2017 8:09 pm

'Weak Story', 'Soft Story', and 'Extreme Soft Story' are three separate types of stiffness irregularities technically defined in the ASCE Minimum Design Loads for Buildings and Other Structures. I found what I think is an older version here: https://law.resource.org/pub/us/cfr/ibr/003/asce.7.2002.pdf. See Table 9.5.2.3.3, which includes other irregularities as well, such as re-entrant corners and discontinuous shear walls or diaphragms.
mfgarrod
 
Posts: 2
Joined: Tue May 16, 2017 5:00 pm

Re: Soft Story versus Weak Story

Postby iDefy » Mon Oct 23, 2017 4:43 pm

Thanks mfgarrod for adding this resource to the thread. Dumbing it down to my intelligence does it mean that
Weak story = bad
Soft story = very bad
Extreme soft story = very very bad (run outside)
User avatar
iDefy
 
Posts: 207
Joined: Wed Sep 05, 2012 9:45 am


Return to SS - STRUCTURAL SYSTEMS

Who is online

Users browsing this forum: No registered users and 3 guests