Seismic Retrofit Argument 9

[bookowski]

Probably no b&w answer here, just looking for opinions for and against the following argument.

I've got a client looking at a 3 story conc building that is approximately 100yrs old and was originally a manufacturing plant. Based on the column and beam sizes it was intended for very heavy use. Given the age there would not have been any explicit LFRS that would comply with current codes. This is in a relatively high seismic area.

Here's the catch. There are photos and documents that clearly show that this was originally a 4 story building and for whatever reason the top floor was removed at some point. Based on the photos the top floor appeared to be less heavy duty, still the same beam and slab construction but smaller members and a shorter story height - maybe offices for the factory. The project only makes sense for the client to purchase if they can add back the 4th floor. My first opinion was that they'd have to do a seismic upgrade but after some cajoling from them I'm considering if there's a valid argument to be made to the local bldg dept that we are not increasing the seismic demands. The EBC states that when evaluating increased demand in lateral loads "For purposes of this exception, comparisons of demand-capacity ratios and calculation of design lateral loads, forces and capacities shall account for the cumulative effects of additions and alterations since original construction." Usually this would happen in the reverse direction but in this case the cumulative alterations have reduced the lateral demands and we'd only be restoring them. Either way I've told them that they need to get the ahj to opine, it's too atypical for me to guess how they'd treat it. But looking for any opinions here on how reasonable this argument sounds to an engineers ears.

 

[bookowski]

The curve has shifted over quite a bit towards the negative region.

I don't feel that it is productive for us to be overly focused on whether or not the 100 year old building has modern rebar detailing appropriate for high ductile seismic design. I guarantee that it does not.

100%, there is zero chance that it meets any modern detailing requirements.

The AHJ may not be astute enough to catch on

To be clear, I am not trying to get away with something. I'm not posting on a public forum about a plan to try and sneak something past the authorities that I think isn't right. Getting the AHJ read on a grey area is not in the hopes of sneaking it past them, if I was trying to do that I'd just not ask at all (this is not an area with a vigorous review process). By the letter of the code it seems to be allowed, based on all cumulative alterations we would not be increasing the demand to capacity. But I see that the spirit of that language could be applied in various ways here, so I'm looking to them for their opinion.

Perhaps you are simply more blase than me

I am almost definitely more blase than you, and in general probably much less risk averse then most on this forum.

I'd certainly not want to be in your shoes

Again, I'm not trying to get away with anything here. I'm trying to figure out what a reasonable read on this is given the code language, spirit of the code, and relative risks. For now assume that I have a terminal illness and will perish the day after submitting drawings.

To come full circle. I see both sides of the argument, which is why I was questioning whether I should even be presenting this to the AHJ for their opinion, i.e. should I be so against this philosophically that I don't want to do it even if they OK it. But it looks like I'm definitely nowhere near as strident as most on this one. There is clearly a valid, and code recognized, acceptance of risks with existing (and new) buildings and that certain levels of alteration don't warrant imposing significant upgrades. It is not nearly so black and white as thinking that if the story is restored the building will clearly fail, or even if it did that it wouldn't have anyway. Under a modern analysis would this work on paper? No definitely not, but it also doesn't work on paper as is and we accept that risk. Where the exact cutoff should be seems like less of an engineering decision than a society/financial one, or a mix of the two. So in this case I'm looking at the letter of the code and it seems to comply.

To concede that I am probably geographcially biased, I am typically working in the nyc area where adding onto buildings and doing lots of paper tricks to justify it is the name of the game. nyc does not use the iebc but instead has it's own local, and quite aggressive, approach. If we want to add onto a building here we can avoid any seismic upgrade if a) no new foundations or reinforcement of foundations is required and b) the scope of work doesn't exceed 60% of the value of the building - not much engineering in that, but it's done every day here (

https://www.nyc.gov/assets/buildings/ppn/tppn499.pdf)

 

[Greenalleycat]

Appreciate the balanced response, TLHS
It does not change my view though

All this 'it originally had 4 floors so have we really changed the load blah blah' is academic arguments that are more akin to lawyers arguing a technicality than engineering judgement
As engineers we are concerned with the REALITY of how it will perform and the RISK to occupants

In my experience, there is a lack of appreciation for what seismic performance actually means because it is fundamentally so different than gravity
People accept that if they buy an old building it will probably have moved, sagged, leant more than a new building - and they're ok with that because it is old
They're even OK with undertaking alterations that could worsen some aspects of that, provided that nothing collapses
This is NOT how earthquakes work: they work on what exists, and if you get it wrong, the building collapses and people die...but because that is maybe 20 years in the future, we downrate the risk in our minds

We have a 100 year old building...100 years ago my country didn't even have a building code, let alone a developed seismic code
Even the best 100 year old building is comparatively high risk relative to a new building: 100 year old buildings, as Koot has nicely expressed, are not designed for ductility
Even if this thing was genuinely "designed" for a 4th floor on top, it will be woefully under code, even assuming it is still in perfect condition (no rusting reo etc)
Adding a fourth story on top will SIGNIFICANTLY increase the real and true risk of the building regardless of academic arguments around when the 4th story did or did not exist
I repeat, those are academic arguments, not engineering judgements of the actual performance of the building and the risk to occupants

The only pathway is to undertake the steps that Book outlined i.e. detailed investigations and then quantify the strength of the building
Once that is done a design to accommodate the extra weight of the 4th story can be undertaken - I would expect this to require comprehensive strengthening

Lawyers argue technicalities under Code, engineers design.

 

[JLNJ]

If the building were designed without sprinklers 100 years ago, but the same building would require them now, I seriously doubt that an AHJ or Fire Marshall would let you omit sprinklers if you were to add a 4th floor. They'd make you sprinkler the whole building.

 

[bones206]

Would this be a change in occupancy and/or higher risk category? Some IEBC Chapter 10 requirements might trigger full IBC compliance.

Given it's a relatively high seismic area, my gut reaction is to want to bring the lateral system up to modern standards. Maybe you could do something like retrofit BRB's or something that creates a new aesthetic that would appeal to the owners and present a new value proposition. Anyways, it's just better for society overall to improve the quality of our building stock in high seismic areas when we have the opportunity.

Edit: I misspoke. I meant viscous dampers not BRBs. This type of retrofit system:

https://www.taylordevices.com/retrofits/

 

[bookowski]

@Greenalleycat - You seem blinded by seismic rage. I'm not suggesting that adding a 4th floor doesn't increase the risk relative to its current state. I also don't think that there's any lack of appreciation for seismic behavior, but it doesn't trump all other considerations. Why let them use the building as is? Because we accept the current level of risk as a society. The argument, as I attempted to suggest in my last post, boils down to more than just an engineering analysis of whether or not the risk is at all increased. If they add new floor finishes would you suggest it has to be upgraded? Clearly we decide as a society on some line, this case is fuzzier than most in application of that line.

At least I titled the post correctly.

 

[Rabbit12]

I wouldn't try to justify this based on the existing building code. With proper analysis adding a 4th floor may be acceptable but not just by simply citing a section in the IEBC.

 

[Greenalleycat]

I wouldn't say seismic rage, but I would say that I am very passionate about seismic risk as my adult life and career has been shaped by the earthquakes here
Some people experienced immediate consequences as their loved ones got flattened inadequate buildings
Others are still suffering less visible consequences today - many many houses and commercial buildings are STILL wrapped up in insurance disputes or are simply poorly repaired and causing ongoing issues and stress for their owners
Because of my experiences I think I have a different perspective than most on the role that engineering plays in society, and the risk of trying to 'legalese' adding an additional story to a building that clearly isn't near code

To address your 'society accepts a level of risk': you want to add a 4th story so let's say 33% higher occupancy = 33% benefit to society
However, you now have 33% more people exposed to risk AND we all know that this building can't support the extra weight of the extra story seismically, so it will perform structurally worse, likely by a significant amount
So the benefit:risk of this extra floor is significantly higher not just for the 33% occupancy you add, but also for everyone already using the building
Imagine you own an apartment or tenancy in that building and your landlord adds a story above that significantly increase your risk of dying by adding a 4th floor without strengthening...

Edit: referring back to your original post
"But looking for any opinions here on how reasonable this argument sounds to an engineers ears."
I hope that the strength of my opinion actually makes you think that what you're proposing is not a good idea, rather than just dismissing me as a dude in a "seismic rage"...

 

[Tomfh]

The way the code reads is that it's wrt all cumulative alterations, i.e. measured relative to the original.

That’s a fairly legalistic reading of it, that seems intended to beat the intent of the code. You might get away with it, but as you’re seeing here, you’ll find no shortage of people saying no.

 

[rowingengineer]

Existing building are a very grey area, and good luck to finding a balance between codes and engineering standards.

My question would be used of the building after purchase? if you client intends to convert it front the original use of heavy manufacturing to something different, then in my neck of the woods that would trigger a seismic review and reasonable upgrades.

 

[rowingengineer]

Also get some legal advice on the grandfathering assumption, in my area grandfathering is per code published, not from said date.

 

[Smoulder]

Interesting one. You said you want AHJ opinion anyway so is this to prep for argument with them? Couple of things first on where I come from. First this would be a question for BCA consultant or certifier and not for engineer here. Sounds like that job doesn't exist where you are. Second your system sounds looser. This would be major alteration here so can't use original condition exception.

Anyway the public don't get a say on safety standards mostly. Regulators set standards for them. I get the thinking that means you should be on client's side as long as AHJ passes it but remember some people here want you to do better if they're in this building during EQ.

Now if I was AHJ I'd say prove you're <10%. Even if photos show concrete originally and cold form steel going back instead. Show me a number <10% and how you got it or I'm not doing my job. Otherwise show OK by seismic analysis. People are saying it should calc out easily.

About what is code intent. Around here again there are sometimes building upgrades required even if not doing any alterations. AHJ decides old standards weren't good enough and says upgrade. Usually things like sprinklers, fire doors and egress paths but not structural IME. Then there are major alterations that trigger full upgrade to current standards. These are a weak version of the above. AHJ don't want to force these but on average most commercial buildings have some work done they can tack it on to like yours is now.

And last some word play. I looked up cumulative in 3 dictionaries because it felt like it means something always going up. First 2 dictionaries confirmed this with definitions like increasing by successive addition. Third dictionary had same definition first but also another definition that would allow pluses and minuses like your interpretation. But that's 0.5 out of 3. Could make an argument like someone else said above that code exception is for minor works that are all <10% on their own.

 

[bookowski]

I've got a good sample here and that was my goal, getting feedback on how the gen pop would view this. Thanks for the responses.

you want to add a 4th story so let's say 33% higher occupancy = 33% benefit to society
However, you now have 33% more people exposed to risk AND we all know that this building can't support the extra weight of the extra story seismically, so it will perform structurally worse, likely by a significant amount
So the benefit:risk of this extra floor is significantly higher not just for the 33% occupancy you add, but also for everyone already using the building

No one is changing any minds at this point, but to respond to this one - you seem to be implying that an additional story will cause a failure and comparing the benefit (say it was 33% increase in some value) vs a failure. The risk is actually quite low when considered in how we behave in other aspects of our life. I just did a quick wikipedia check, and if that's roughly accurate the area has had 8 eq's > 6.0 since 1970 and a total of 8 deaths. This is a fairly populated area, about 4 mill people locally I think. If I go back to when this building was built it's probably a couple of dozen quakes, I didn't count but there's a good amount. This building stood through those, some with 4 stories on there and some with 3. Does that mean that it will continue to do so? Definitely not. But it does give a rough bar stool level sense of the relative risk. It's not 33% increase in value vs it's definitely going to fail soon. If that were the case it'd be crazy to do it. If you drive 65mph in a 55mph zone do you increase your risk? Yep, for sure. Lets say you've got(65/55)^2 more energy when you hit something, so 20%. But this doesn't mean that you will hit something - we all do this with the acceptance that the general risk is low, so bumping it up slightly doesn't worry us much. And I'm definitely not dismissing your input, this is what I was looking for.

We lose several thousand people per year in the US to food poisoning, but I doubt you'll find lettuce farmers on forums worrying about their triple wash. The SE community's record is quite impressive compared to most, and our risks lower than most fields I'd say.

by successive addition

I take successive addition to include include negative numbers, removals being negative

That’s a fairly legalistic reading of it

Yes, that's the intent - to read the legal intent of it. No one is arguing that the building would satisfy a modern analysis, no way. They wrote the code with some recognition of cutoff points and relative risks, most cases would almost by definition not work by engineering, so the code language is used as stated, or "legally" as you state.

To take this to an obnoxious extreme. What if the top floor (original roof) had extensive corrosion and the owner had to remove it to keep it safe, and it took him 1 year to raise the funds to put it back? What if it took him 5 years? In the 2008 recession there was a wave of building owners in nyc that removed stories of their vacant buildings to reduce their tax burden (amazing how cheap demo is relative to taxes), when they put those stories back should they have to upgrade? All sorts of scenarios are possible with reasonable arguments either way, but all involve decisions beyond does it work on paper.

 

[lexpatrie]

I meant more that the AHJ is not necessarily going to be a "partner" or peer reviewer of merit. You're the designer or EOR or somebody is, it's their design.

Had the original top floor not been removed, it would be allowed to exist "as is" unless there's some mandate to retrofit, but when the top floor is removed, it's not credible to read it as having a history of a top floor, you need to look at it as an addition, and the IEzbC doesn't really contemplate vertical expansion when it talks about additions anyway. This is a new floor added to an existing building, there may be some leniency as part of it exists in the IEBC, but it's not a wholesale waiver that it can be put back on with zero changes from the 1960s.

 

[Greenalleycat]

Book, those are some decent shakes so that supports the building having decent capacity
This suggests that you might actually achieve reasonable capacity if you do the full analysis on it - perhaps enough to add a 4th floor on it
Why not just do the investigations and do the numbers? That seems like the simple way to solve this problem

 

[bones206]

Some municipalities in California have specific regulations for handling non-ductile concrete frame buildings. Might find some philosophical guidance there.

https://www.seismicordinances.com/non-ductile-concrete-structures

 

[hardbutmild]

Why let them use the building as is? Because we accept the current level of risk as a society.

Why do we even make a design life if after it has expired twice we still say "oh this is fine"? It's ridiculous.
How long should we let buildings stand without a repeat calculation - 200 years, 500, 2000, until it falls down?
If you want to use a car you need it to pass a test every year, buildings can stand forever without an assessment.

This thing is done in my country all the time and in the worst way possible. I remember seeing a project where a guy added two stories to a three storey house and he just wrote "mass does not change by more than 10 % so it's fine". The tragedy here is that he will probably be dead before an earthquake comes, but in a 50 years someone will analyze the building and say "oh well, we already accept this level of risk so it's fine."

There is a big difference in "we accept the risk because we simply do not have the resources to repair or replace all the old buildings" and "We have the ability to repair it, but we like to spend our money on other things if formally we're not required". One is a necessity, the other one is not.

To take this to an obnoxious extreme. What if the top floor (original roof) had extensive corrosion and the owner had to remove it to keep it safe, and it took him 1 year to raise the funds to put it back?

It depends. This is common where I'm from and usually ministry requires you to update the project if any changes to the code happened - so even in that case it needs to be updated. If the same code is still active then it's fine. This is especially true if you have two separate projects - demolition and building up. No one cares if you make the same thing again, it's a new project and a new permit.
But I think you made a wrong example because if at the begining of demolishing you calculated that it should stand then it's fine until the codes change. You can build it at any time until the new codes come.

Let me take it to an obnoxious extreme on the other side - say you have a 100 yo building that has 10 storeys. Under an earthquake 9 top storeys fall down. You build them up - should you build the exact same building? Why not? It's a 0 % change to the original and that same risk was acceptable just a few days ago.

 

[bookowski]

How long should we let buildings stand without a repeat calculation - 200 years, 500, 2000, until it falls down?
If you want to use a car you need it to pass a test every year, buildings can stand forever without an assessment.

I'm definitely not in favor of yearly assessments for buildings. If this is multiple choice and I have to pick one of your options then I'd choose the until it falls down one.

Interesting that you chose the yearly auto inspection because that's one of my pet peeves. I've got a weird quirk where I've always skipped getting these for years. The fine here is about $40 and you almost never get caught. I just went 4 years, had 2 tickets, well worth the price to not deal with it. After a couple they up the threats and then I cave and start over. Driving is quite risky relative to most things we do but the inspections aren't curbing those risks, maybe at one time they made sense but these days modern cars don't need this. The 16 year old doing 80 while texting will probably take me out, ball joints failing on my car - unlikely.

 

[hardbutmild]

It's highly geography-related I guess, it's very VERY different here regarding cars. Fines for that would be huge and usually people drive really old cars that need a lot of maintenance. But my point is that everything in this world needs a check-up now and then. We even require it for people - you can not work if you don't get a check up every 10 years. And not just a risky job, any job.
Nobody died from their pc not having a software update, yet you need to make that every few weeks.

Regarding buildings, I'm also not in favour of yearly assessments... but if we design them for 50 years does it not make sense to come after 50 years and check if it still works? A lot can change in that time. Surely once every 50 years is not too big of a problem. And when you add to that the fact that every owner can do whatever they want (as long as it is less than 10 %, and even that is rarely checked by authorities) as many time as he wants and you can get buildings that look like swiss cheese very fast.

Let's look at it this way - why should I design something for 50 years if I can say that it is a temporary building and design it for 10 years? This is cheaper for the owner and if he wants (and he surely will) why should I not comply with his wishes? Why insist that this "temporary" building really must get demolished after 10 years, but leave a building designed a hundred years ago for a design life of nobody knows how many years (but probably less than 50) standing for a 100 years without any limitations?

 

[Tomfh]

Design life and whether a structure complies with current codes are two different questions. Design life isn’t reached because codes change.

 

[Rabbit12]

I've completed several building assessments in my career. With those we always issued a report summarizing our results including identifying and usually attempting to classify deficiencies (serious, minor, etc.). Some of the assessments I completed had previous assessments that had been done. Rarely had any deficiencies been addressed. Until there is some system in place that forces compliance an assessment is not likely to change things. And even then, the opinions on these types of assessment are going to very wildly from engineer to engineer and there will undoubtedly be engineers that are incredibly lax on what is acceptable and what isn't.