New door opening in existing reinforced concrete wall

[mortiereng]

Looking at putting a 3ft man door in an existing reinf. concrete wall. The wall is on the first level of a 4 level parking structure. Half the structure uses double T's and the other half concrete beams with a waffle slab. The wall is 15ft long by 16ft tall and 18" thick. In the past I've used channel face bolted and HSS posts to handle gravity and shear(seismic). In this case the opening is in a retail space where a steel frame is not very desirable. If there's a way I can justify something less invasive or show that the wall is sufficient without reinforcement I would like to see this. I've seen many posts on here that they justified this way, but no explanation behind the calculations used. Thoughts?

Thanks,
CK

 

[jike]

Have you determined whether this is a shear wall and if so what are the forces? How does the wall opening affect the forces?

 

[KootK]

Given the wall's position, thickness, and siting in a high seismic region, I'm betting that it's a hard working shear wall. Losing 3' of 15' will cost the wall roughy 20% of it's shear capacity which is significant and may warrant a detailed analysis.

Where along the wall will the door be located? Does the wall continue up the full height of the building? Does the wall reinforcing or footing design look suggestive of a shear wall?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[spats]

I think you should stop worrying about what reinforcing would look like, and start worrying about severely weakening an obviously major shear wall. There's another similar shear wall in line with the one you want to modify. You're not just losing 20% of shear capacity, your're changing the relative stiffness of this pair of walls, and thus how the lateral loads will be distributed. Does it affect drag struts? What kind of additional bending from in-plane loads are you putting into the "legs" on either side of the cut? The further the door is off center of the wall, the more problematic it will become. Lots to think about.

 

[haynewp]

IBC Section 3404 will be triggered for removing that much of that shear wall.

 

[HouseBoy]

Since I am not very familiar with seismic design, nor am I familiar with commercial buildings of this sort, I have the following questions:

The building was designed in 1974. How well or how poorly does anyone think it conforms to current seismic design thinking and practices?

NOT THAT IT DOESN'T NEED TO BE CONSIDERED BUT....I'm curious about how likely it is that this wall is behaving well as a shear wall now.

Again, not being too familiar, does it seem to anyone else that this is a pretty small shear wall for such a large (footprint) building?

Steve

 

[racookpe1978]

I am reminded of the Physician's Oath.

"First, do no harm. "

This is a stupid idea. Put the chopsaw and concrete blade down, and slowly back away with your hands up.

 

[spats]

I love it racook... I couldn't have said it better!

 

[mortiereng]

I would assume it to be a shear wall due to its size and location. Location of the door is more than likely towards the middle third. The reduction in shear capacity of that wall and overall stiffness of the structure does worry me. My boss has asked me to show whether it is possible to even achieve this task at this point. The overall shear capacity of the wall is easy to determine, however the designed loading may be more difficult then it is worth.

 

[Teguci]

Given the possibility that someone provided a 16 ft tall shearwall for a 4 story garage, we've got a real mess trying to figure out loading so I think the strategy hear is to fully replace any potential capacity of what is being taken out. I would attempt a steel strapping system with post installed anchors or even through bolts both sides of the wall. Provide straps at top and bottom of the new opening and extend them 8 ft +/- to either side. Add diagonal steel straps that are tied to the top and bottom straps. Also provide vertical straps at the jambs.

Properly sized, I think this steel braced frame could replace any shear, bending and axial stresses that could have been taken by the removed concrete.