Definition, Substantial Structural Damage? 1

[SteelPE]

I have a question regarding the definition of substantial structural damage:

“Substantial Structural Damage. A condition where:

1. In any story, the vertical elements of the lateral-force-resisting system have suffered damage such that the lateral load-carrying capacity of the structure in any horizontal direction has been reduced by more than 20 percent from it predamaged condition; or

2. The capacity of any vertical gravity load-carrying component, or any group of such components, that supports more than 30 percent of the total area of the structure’s floor(s) and roof(s) has been reduced more than 20 percent from its predamaged condition and the remaining capacity of such affected elements, with respect to all dead and live loads, is less than 75 percent of that required by the International Building Code for new buildings of similar structure, purpose and location”

Part 1:
If I have a building that uses moment frames as a LFRS and only the beams are damaged due to a roof collapse from an overload of snow load would this be considered substantial? It doesn’t appear so to me with the definition above.

Part 2:
If I have a building that is 400x400 and I have a few bays of roof members that fall down due to snow load (say 80’x40’) does this qualify as substantial structural damage? I would think it would, however, since the effected area is only 2% of the structure then it appears that you would not fall under this definition. What if this bay was the only bay affected by snow drift loading?

 

[JAE]

Part 1 - are the beams that are damaged part of the LFRS? AND - does their damage result in a 20 percent reduction in lateral capacity (I assume they are talking about strength and not stiffness). How many beams are damaged and do they result in the limited gravity capacity?

Part 2 - I agree - if the percentages are less (based on the way it reads) then you don't technically fall under that definitition.

 

[SteelPE]

JAE,

This is more hypothetical than a real question. We may be asked to look into some existing structures that have had some snow problems and I just want to make sure I have the code correct in my mind.

Part 1:
I have no idea how large the frame is. I have been told that there was some damage to some beams that were in moment frames. No mention of the columns though.

Part 2:
So, what if the snow drift was due to a higher adjacent addition that was added w/o proper account for snow drift (as I have been told)? Since the collapse was in a localized area, would you be allowed to just replace the existing members w/o consideration for the additional load created by the higher structure?

 

[DWHA]

I would say if the structural system can no longer preform its design function then there is substantial damage.

 

[SteelPE]

DWHA,

I would agree with you.... but that is not the definition. We are basically talking about the difference between replacing what is there and bringing the failed areas up to new code standards.

When I initially read the code, I was thinking that if a section of roof failed, then we bring that area up to code together with the girders and columns at that section of roof. However, upon looking at the definition, depending on how large your roof is, you may not have to do that. Do I agree..... not really, but I am not the one in charge of writing the code so I guess I can't complain.

Interestingly enough. This section and definition is new to the 2009 IBC and 2009 IEBC building codes.

 

[Ron]

Both of your definitions only apply to columns.

 

[SteelPE]

Ron,

I disagree. The second definition applies to "vertical gravity load-carrying component"s. I would interpret this as being any element that supports the vertical load imposed by gravity. Meaning both beams and columns.

At first glance it does appear to only apply to columns though.

 

[a2mfk]

I've worked with engineers who have convinced me of Ron's interpretation. It is poor technical writing of the code in my opinion, they could elaborate a bit. The term vertical is the key, which Ron and I would say is the adjective describing the component, so it is a vertical component that carries gravity loads. To describe a gravity load as "vertical" would be redundant since gravity for what we are talking about is a vertical force.

Sounds like a bunch of semantics, I know, but it can be a bunch of money in the difference.

I have had this discussion in regards to a house with CMU walls and wood trusses that was damaged by fire. The trusses are horizontal spanning components so this does not meet the definition, though they are placed in a vertical position The walls are the vertical gravity load-carrying components. In many cases wood trusses are badly damaged by fire but the CMU walls are fine, so according to some codes you could just replace the roof trusses and not bring the CMU walls up to code.

 

[SteelPE]

a2mfk,

I can see your argument, however, in your instance the damaged was caused by a fire.

In my instance, the damage would be caused by snow.... and some of the damage was cause by snow drift that appears to not have been accounted for when a higher addition was placed next to the building. Seems foolish to just replace the damaged system with the same system that just failed under loading because the portion that failed was less than 30% of the entire structure. Especially if the snow requirements have been changed since construction of the original system.

 

[BAretired]

SteelPE,

I believe you have to carry out such remedial work as needed to render the structure safe for occupancy. This would be determined in accordance with your best engineering judgment. No building code can anticipate all possible situations.

BA

 

[Ron]

BAretired...I agree with you and certainly most of us will strive to do so; however, some of our code language makes that extremely difficult for us to justify or rationalize.

I primarily deal with two codes...The International Building Code and its subsets, and The Florida Building Code and its subsets. The Florida Building Code is based on the International Building Code, with some local wrinkles thrown in. For the noted discussion, the Florida Building Code-Existing Buildings (which is where all this argument takes place) in its infinite wisdom, removed the term "gravity" as noted in the definition above, thus clearly making it refer to columns only.

As we all know, a building can suffer a lot of damage (you will note that I did not use the term "substantial"!) without significantly affecting the columns. In fact, depending on the connection and framing design, you can have beams in plastic failure without causing anything other than an increase in compressive axial load to the column. We all know this...why don't the code people? We assist in writing code language, but through the political process of adoption of code changes, the language gets muddied, mutilated, magnified such that, in some cases, it is literally uninterpretable.

SteelPE...I don't agree with the code definitions, but as a2mfk pointed out, the definitions can make or break a project. As engineers, we know the right thing that needs to be done. Now we have to battle with the insurors and the code interpretors to see that it gets done, without literally and figuratively leaving our client in the cold.

In my experience with those definitions, I just simply stick to my guns and get really stubborn about what MUST be done. I'm willing to go to the mat with that and have no problem committing to such under oath. After all, I consider my engineering license to be an "oath" of sorts and I must hold that my engineering judgment is fact not fiction for the benefit of any particular party. Can two reasonable engineers have a difference of opinion as to what MUST be done? Of course....but he knows his is wrong!!

 

[BAretired]

Ron,

I guess I'm still not clear on the significance of defining "substantial structural damage". Why does it matter? Even if the damage is deemed unsubstantial, it still must be fixed as determined by the responsible engineer.

SteelPE said:

So, what if the snow drift was due to a higher adjacent addition that was added w/o proper account for snow drift (as I have been told)? Since the collapse was in a localized area, would you be allowed to just replace the existing members w/o consideration for the additional load created by the higher structure?

That type of damage could affect the culpability of the various parties involved but it does not alter the remedial measures recommended by the engineer responsible for repair. To bring the structure back to its former state without considering the additional load created by the higher structure would be absurd. To do so would invite future litigation against the engineer involved with repair.

I do not understand the word "allowed" in the last quote. Allowed by whom?


BA

 

[Ron]

BAretired,
Under our code, it is a matter of what level of design is required to be used. Under one definition (less that substantial structural damage) you are required by code to only require remediation to the original code from which the building was designed. If you fall under the "substantial structural damage" criteria, you are required to design to current code. The difference in cost impact can be substantial (no pun intended there!).

Yes, as engineers we would like to follow the most recent code for all of our design...however, for existing buildings, that is not always practicable.

Ron

 

[msquared48]

As in allowed by the local building jurisdiction.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

Ron,

In our code, "substantial structural damage" or similar terminology is not defined. If damage has occurred, it must be remedied in accordance with the requirements of the responsible engineer. Any remedial measures must be in accordance with current codes.

We do have something similar to your requirement, however. When an existing building is to be renovated, remedial work must be in accordance with the current code but when the area to be renovated exceeds a certain percentage of the total building area (I can't remember what percentage it is but I think it is 20%) then the entire building must be made to conform to the latest code.

BA

 

[SteelPE]

BA

As stated above, this is a new definition in the IBC building code. I was shocked when I read the definition because prior to reading the definition I thought substantial structural damage would be defined as any area that failed. As Ron states, it's a matter of just replacing what was there originally vs upgrading parts of the structure to the new code.

I actually don't have any projects that require this definition at the moment. I know that some may come along and I want to make sure that I get it correct.

I know one person in my office was trying to justify demolition of a structure that was still standing (a PEMB). In this instance, the building was built in 1984 and it just so happens that we know the original engineer involved with the project who was the chief engineer at the PEMB company at the time. One way the code has changed since 1984 is the requirement of considering drift on gabled structures. This was never considered in 1984 and can be quite significant (in speaking with the original EOR). I don't know the specifics of the job other than that there appears to some purlin damage and some major problems with the frames. This damage is localized to one small section of the building. However the damage is so severe in this one area that the building is shut down until further notice and no one is allowed on the roof because of the damage (orders from the building inspector reinforced by the engineer from my office). Now, the question is, do you upgrade the building to account for the new loads (gravity and lateral) or not?

I'm not asking the question here, it's just the question that someone is faced with. Based upon how you interpret the code could be a financial burden to the owner (It already is, because the owner has millions of dollars of product in the building he can't access until the snow melts). Or if you make the wrong interpretation then you may be in trouble one way or the other.

 

[BAretired]

SteelPE,

I agree that decisions are not always easy. We just have to use our best judgment case by case.

BA

 

[a2mfk]

Steel PE
What caused the damage makes no difference, that was just an easy example I picked. I have had to do the same thing for roof damage caused by wind that did not damage the CMU. The insurance company will only pay for what it HAS TO under the obligations of the policy and thus the Code, and they ask us to do the evaluation and state an opinion. Many times we are not involved with the actual repairs.

BA
The type of work Ron (I think, sorry Ron if I am overstepping) and I are sometimes involved with often involves insurance companies, lawyers, and other engineers who may have differing opinions. We are asked for our opinion per code what is REQUIRED to be done to this building, and often that may mean ignoring existing problems. That does not mean as an engineer you do not report your entire findings to all of those involved, but there is no code or other legal action REQUIRING these upgrades. Because after a hurricane or flood or any disaster there are millions of dollars of damage to older buildings that do not meet current codes. Insurance companies will not pay for costly upgrades if not required to do so by the policy and/or code.

Maybe you are fortunate in Canada where there aren't so many law schools pumping out attorneys to give you such headaches (though I have a good friend who is an attorney and from BC). Well, in my case, they provide quite a bit of work. But maybe the final call is up to you and is not spelled out so by code.

Its actually way more involved at least in Florida than we are letting on, the FBC: Existing Code has a lot more rules and in some cases you have to do an analysis of the entire existing structure and submit it to the building official, and then more steps...

It should also be noted that in many cases if I am the engineer of record actually designing the repair, I do exceed the code requirements for all of the reasons BA and others have stated. I've not made clients too happy in the past by pointing out problems that I have said we must correct. Maybe I will or have lost jobs because of that.

STEELPE- You can tackle this a few ways, but what I would do is prepare a report or letter telling your client your findings and your interpretation of the letter of the code, and what this means to his structure. Then, you can make your own recommendations and include bring other portions of the structure up to code even though it is NOT required. If the client balks at that and you are not comfortable with that decision, be prepared to walk away...

 

[Ron]

a2mfk...exactly. Nicely stated.