Wall Opening in Existing Shear Wall

[EngineerRam]

I am working on a project where the client wants to create an 18'-0" opening in the center of an existing 33'-0" bearing/shear wall. The issue is that there are no as-builts or record drawings to speak of and the structure is heavily cladded, so it would be near impossible to create as-builts to model the structure. The approach I am considering taking in order to evaluate the proposed change is to match the cumulative stiffnesses, shear capacities, flexural capacities, and axial capacities of the remaining (2) - 7'-6" wall piers to that of the original 33'-0" wall pier. My main concern in this project is that if we decrease the stiffness of the wall pier, the lateral load will go elsewhere in the building, where the original building was not designed for it to go. To avoid that, the wall will need to be thickened significantly, as well as the addition of extra reinforcement. What are your thoughts on this approach? I understand that a huge assumption needs to be made that the original building was designed correctly, but I really don't see any better way of tackling the problem currently.

 

[Guastavino]

High seismic or high wind region?

In my area of the country, most other engineers wouldn't do anything (for lateral)...doesn't make that right, but low seismic, low wind, and no code enforcement means that if one engineer tells you something you don't want to hear, the client goes to the next one to find an easier solution...

Now, some engineers on this board will cringe when they read the above...

As for what I would do, it depends on where it is in the country and what the loads are. I would bet that you couldn't get the building to figure to today's codes without modifying it though. If it was a high wind/high seismic area, I would tell them a horror story of what it could be (because you don't know at this point), set the expectations at the moon in terms of what they could have to do, take a high fee, and go to town if they agree. If they said I was crazy, I'd let them go with the next guy.

I think ASCE 41? might have some guidance on this too.

 

[RPMG]

Alterations are covered at the end of the IBC. If the wall is replaced or reinforced like for like, the huge assumption that the original building was designed correctly does not need to be verified. Depending on your specific situation, that may be difficult to do.

 

[WARose]

With no as-builts or drawings.....it's going to be tough. You would have to assume some minimums for amount of vertical re-bar to see if you've got enough (equivalent) jamb steel for the ends. The first thing to do is to check what it does to the lateral load distribution......see how this changes things. (And all this is not even getting into the vertical load.)

It may sound silly to say, but be sure you actually have a RC wall system. I've seen people think they've got one.....but they really have a pre-cast panel system. (And you cut those tendons and then you're dead.)

 

[EngineerRam]

Gustavino,

This is in an area with 1.5g Ss and 0.6g S1, and 170 mph wind (still on ASCE 7-05), so the client should understand that lateral loads are a big deal.

RPMG,

I checked IBC chapter 34. Having no drawings to create a model off of whatsoever, I cannot verify if my new D/C is only 10% over that of the original.

WARose,

I am currently assuming a healthy amount of rebar to match for horizontal steel and jamb steel to be safe. We have access to a Hilti scanner that we can use to check the wall reinforcing when construction starts to verify. However doing that now is not an option due to the heavy cladding (high-end jewelry store).
The owner verified that the walls are not precast panels. However, the deck is prestressed (spans greater than 30'). Tying in the thickened wall to the deck (drill/epoxy) will be a challenge for the same reasons you stated for the wall panels.

Thank you to all for your input.

 

[EDub24]

I'm not convinced that that approach will work. If it were me I would require some serious investigation and testing of the existing materials so I could do a thorough analysis. That will likely involve removing some cladding and other items as necessary.