I was disheartened when I read this line: 1

[JJMEI]

ASCE/SEI 41-13 Seismic Evaluation and Retrofit of Existing Buildings:

I am doing the structural engineering for a new building adjacent to an existing multi-wythe church originally constructed in the 1920s. The two are linked by a connector. The impact to the existing church is minimal but significant enough that I would like to thoroughly examine the mechanics of the structure considering the new openings in what I must assume to be unreinforced masonry of one of the towers. Does anyone know of a similar resource for this type of application? Through the research I've done it seems that there is somewhat of a debate about applying new building codes to existing buildings and what type of approach should be utilized in these situations.

 

[canwesteng]

Idk about in the states but there is a section of the national building code devoted to this - the guidance is to apply new codes with reduced load factors if the structure has performed satisfactorily, as long as you aren't modifying the existing structure.

 

[jayrod12]

That line is in that standard because that standard strictly is meant to provide guidance regarding the seismic capacity and not wind or gravity capacity.

There must be a different standard that addresses the other requirements.

 

[JAE]

Not sure exactly what you are asking ([blue]"Does anyone know of a similar resource for this type of application?"[/blue]).

Are you asking if there is a resource for checking gravity and wind forces on new and existing buildings?

For new buildings - ASCE 7

For existing buildings - ASCE 7 - Appendix 11B and also provisions in the IBC or applicable building code - IBC Chapter 34.

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[JJMEI]

I need guidance on the evaluation process of the "existing strength" because we are making alterations to it.

 

[EngineeringEric]

You can just evaluate it for wind and gravity... I am confused why you would expect a seismic evaluation code to apply to wind and gravity... Apply the loads and check your stresses. If it works for gravity most likely it will work for wind of equal size (most likely). And gravity, keep your masonry in compression even when laterally loaded if all your brick stress is in compression you are most likely fine.

Don't use new hard mortar with old brick!

 

[msquared48]

Design and analysis are two different functions.

The code disclaims design, but not analysis. You can still use it for such.

Mike McCann, PE, SE (WA)

 

[UcfSE]

Did you check the existing building code, IEBC if you fall under the IBC for new stuff? If so, the alteration level will guide you for what codes you have to meet (new vs original).
Do you have any existing plans or other data to help you limit or bound your assumptions of the existing conditions?

These are usually my first two steps for evaluating existing structures. Next is a site visit and examination of everything you can reasonably get access to.

 

[JJMEI]

There are no known structural plans. Thanks EngineeringEric "keep masonry in compression" was what I was looking for sort of. I just thought that there might have been a standardized method out there. ASCE 7 - Appendix 11B is very brief, and the only thing I got out of it was that you can't reduce the seismic design strength by more than 10%

 

[KootK]

I find the seeming overabundance of seismic design guidance relative to other things a little frustrating at times. Wanna know the cracked stiffness of a seismic corewall or how to do a performance based seismic analysis on some old stone? There's research papers and design guides o'plenty for that. Want the same info for wind? Tumbleweeds blowimg by...

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.

 

[EngineeringEric]

KootK, I think its because Seismic is sexy from an academic perspective. Wind is just a bi-directional static force qz...

 

[JAE]

EngineeringEric - so I guess based on that - wind is for blowhards....seismic is for the movers and shakers.

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[EngineeringEric]

JAE. I guess that means i am mostly a blowhard due to the Mid-Atlantic work I do and i pretend to move and shake only when required (and any dancing partner would argue I do it poorly)

 

[KootK]

any dancing partner would argue I do it poorly

It's all about relative hip to shoulder displacement. Core drift ductility as it were.

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.

 

[TLHS]

This may be slightly offtopic, but hey!

I don't see a lot of unreinforced masonry, so I don't really have renovation experience with it. What's the actual construction sequence for putting a new hole in a wall? From a design standpoint, you could presumably just design a new ledger beam at the top of the hole... but how do you actually make the hole and build the new beam without the wall collapsing down on you?

 

[KootK]

Depends on the size of the opening:

1) For a small opening, you'll cut a pair of angles into the wall to function as a header and then remove the block below. Similar for plates or channels bolted to the side of the wall. no matter what you spcify, there's a pretty good chance in these situations that the mason will just remove the block ahead of installing the header and, for the most part, the block above will just kinda hang there in tension.

2) For larger openings, schemes like needle beams can be used as shown below. The one shown below is more complex than usually required but you'll get the idea.

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.

 

[JJMEI]

I assume if the contractor wants to be cautious he would use needle beams with adjustable shores to cut the opening and implement the new lintel, but there are other methods as well. I don't think that you can design the new structural elements without considering the alterations to the existing structure. That's my issue is how to prove that the changes we are making will not effect the performance of a structure that is already not in compliance with modern building criteria.

 

[TehMightyEngineer]

...there's a pretty good chance in these situations that the mason will just remove the block ahead of installing the header and, for the most part, the block above will just kinda hang there in tension.

Seconded this; it's been about 50:50 in my experience.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

http://www.americanconcrete.com

 

[XR250]

I'll third that.

 

[EngineeringEric]

Masonry Arches. It is as simple as that. masonry can arch or corbel a decent distance before really failing... and also this is at below design loads. Don't go cutting holes during a design snow load or 100mph hurricane and if I knew more i would urge against doing it during an EQ but i don't think this is realistic to predict.


Back to the original post (My fault!), I would analyze the walls as segmented shear walls. take there self-weight (100%) and 60% DL (from others) and check the chord uplift. keep that in compression and you should be good for wind.