New Opening in Existing Brick Wall - Lateral Concerns 1

[melann189]

Here's the situation: Existing (3) story 15' wide rowhouse / brownstone (middle of the block), double wythe brick masonry rear wall. New addition to be added to the rear which will require large openings be installed in the rear masonry.

My concern is lateral design requirements. Per the IRC (NJ edition) it appears I do not have to consider the rowhouse as a structurally independent building because of the fire rated party wall. With that in mind I could easily say that any lateral load is simply taken by the adjacent buildings and no real harm done. The argument is that in a worst case scenario both neighboring buildings could at some point no longer exist. But I would think that the existing masonry as is would be well overstressed at that point as well.

However, I am certainly reducing the lateral capacity of the building with these openings (approx. 10' wide floor to ceiling opening on two levels), so instinct tells me that lateral reinforcement should be installed. So, I guess the question is, to what requirements do I design the reinforcement? If I plan for a steel moment frame and assume it takes full wind / seismic loading, I imagine it will become a cost and aesthetic issue, but I don't see a way around it.

I seem to be coming across this more and more lately and have been told by my clients that their other engineers just put in a lintel, and no additional reinforcement. Thus, I am concerned that I will be said to be "over-engineering" the renovation. Anyone else come across this or have a good code reference for why it needs to be reinforced (or not reinforced)? Also has anyone had experience with the NJ Rehab code? I am finding it very vague which is not helping this issue.

 

[jfmann]

In high-seismic areas, I certainly understand going to such lengths (and I am not versed in code requirements for California that may require such upgrades) ........though I continue to wonder about the inconsistency of major upgrade while other key parts of building do not conform. Such as......what about the other shearwall at opposite end of building?

Not to be forgotten of course is that (per stated condition at start of thread) this is row house within row of houses.

Doug......by "remove rubble wall" do you mean you are replacing entire foundation wall underneath?

Trying to "round out" my 2 basic points.......which, first of all, is risk tolerance.......which is foundation shall we say of all design requirements.

Risk of full design wind force (again, staying away from seismic) is of course low.......for now, lets just say (conservatively) 2-percent in any year.
But then, on top of that, you have probability that adjacent row houses will be torn down (on both sides), so that the subject row house remains all by its lonesome....although such risk can vary widely, I venture to say such risk is quite low......how about, very conservatively, 2-percent in any year (though that risk might grow as time marches onward). So now you have combined risk of 0.04 percent......which may actually be way too high.

Second point (not to rehash too much) is, again, just that the end result provides an assumed building (assumed standing alone) with numerous major deficiencies relative to overall wind resistance.........and one area that can withstand a tornado.

If this can be accomplished at relatively low cost, I understand.........but it sounds like this is a major alteration having relatively large cost. Ok, I think I have reached the end on this one ;-)



John F Mann, PE

http://www.structural101.com

 

[SteelPE]

Good thread as some issues discussed are ones that I struggle with as well. Hard to justify modifications to a 100+ year old building especially when the code says the structure only needs to comply with the loads applicable at the time of construction (I'm not sure the example posted would comply with this provision).

Didn't even notice the stair in the front at first, ugh. I guess you get some benefit from the floors being framed in wood hence the low seismic loads. So what do you do with the wind loads? Do you design for the full wind assuming your structure were to "stand alone"?

 

[bookowski]

No, not full wind loads. I don't have a good answer - see various responses above. If I was doing a peer review I think I'd be ok with just about anything as long as someone showed here are the loads that I assumed or original capacity etc. and here is an engineered solution. I just don't agree with doing nothing.

A decent book on renovations has a section on this, you can see enough of a snippet here in google books. The co-authors both own two locally well known large firms that specialize in renovation, both of which I see putting frames or other engineered systems into the these openings.

 

[Archie264]

Bookowski,

Thanks for the pictures, that's some beautiful work.

 

[KootK]

@Bookowski: I bought Friedman's book on your recommendation. Best $6 I ever spent, I'm sure. He also has a book on building investigation that I was tempted to buy. Are you able to recommend it?

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.

 

[bookowski]

I don't know about the 'investigation of buildings' book, I don't have that one.

Did you get the 'design of renovations'? If so I would recommend his other one 'historical building construction, 2nd edition'. It's less about specific examples and instead follows the progress of structural evolution in the US, starting with masonry & timber and moving through steel and all the various concrete systems that people tried in the early days. In the back it has nice tables that summarize the progression of code requirements for loading, allowable stresses etc. For an engineering book it's a nice read and well written, it's more of a cross between a history book and an engineering text.

 

[KootK]

Sweet. I ordered that one at the same time. The cover called to me.

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.