Averaging Loads
Averaging Loads
(OP)
My client wants to use the second floor of a former jail facility (which was designed for a 40 psf live load) for storage of Banker's Boxes, stacked seven high in a rack system (live load = 146 psf at the boxes).
I produced a report which shows how to lay out the boxes, with wide aisles in between, so as not to exceed the 40 psf live load. The Building Inspector in the city where the facility is located will not accept this, stating that our State's Building Code requires 125 psf minimum uniform live load for storage.
Any ideas? The client does not want to upgrade the existing floor.
I produced a report which shows how to lay out the boxes, with wide aisles in between, so as not to exceed the 40 psf live load. The Building Inspector in the city where the facility is located will not accept this, stating that our State's Building Code requires 125 psf minimum uniform live load for storage.
Any ideas? The client does not want to upgrade the existing floor.
DaveAtkins






RE: Averaging Loads
Change gravitational acceleration from 386 in/sec^2 to 386*40/125, LOL?
RE: Averaging Loads
Either:
1. If you have enough information check that the existing structure works under the loads.
or
2. Do a calculation justifying that the moment is no more than 5% above the design moment (There is a 5% increase allowed somewhere but I cant remember).
RE: Averaging Loads
RE: Averaging Loads
The problem the Building Official is trying to avoid is future change in what is stored and how it is stored. The current owner, if he recieved approval to follow your shelving plan, at some time in the future, he could narrow up the asiles and add more storage.
After all structural engineers and building inspectors are overly conservative. We always determine the load and double it don't we.
A more important consideration is a future owner who decides that since the room is a storage area that he can load it up to 125 psf because that is what is required by the state code.
An additional comment about engineers; I have been told that after hurricane Katrina, that there was a new respect for the engineers that had over designed all the buildings built before the hurricane.
RE: Averaging Loads
RE: Averaging Loads
I suspect that your client knew of the possible problem from the change of use and wanted to find someone to sign off and minimize or eliminate his liablity.
Dick
RE: Averaging Loads
You could probably successfully convince the building official that your bankers boxes, stacked as required by you (and the layout permanently posted on the wall) is NOT a use designated by the table - i.e. the 125 psf light storage isn't what you are technically doing.
However, you would then need to convince the official that your layout, and the resulting 40 psf average live load, is OK.
RE: Averaging Loads
It is not an impropbable sceanrio that a future tennant or owner will increase the amount of storage on that floor 'assumming' it it fit for that type of loading, i.e. 125 psf (6 kPa).
RE: Averaging Loads
RE: Averaging Loads
I would agree that the building official is interpreting the code the right way for this application, but the previous posts are assuming the space is being designated as "storage".
Consider a typical office building where the original design for the second floor is 50psf (office space). A future client wants to use a portion of the room for storing boxes. Does this mean that the original design should have been for 125psf? We can't assume what future tenants/clients will use the space for. DaveAtkin's client is using this room/space for storage, but may not be reclassifying the space. A future tenant could use it for anything.
For this application, the current tenant should be able to use this space to store the boxes with an approved plan from an engineer while satisfying the building inspector. If a new tenant moves in, he/she has a responsibility to verify the space has the capacity to be used as storage or whatever use he/she intends.
I think DaveAtkins is on the right track as long as the client understands that deviation from his layout plan could spell disaster for the floor framing. With that said DaveAtkins needs to weigh his liability if the plan isn't followed to the T.
RE: Averaging Loads
Second case was in Canada, where the engineering firm loaded a 100 years old 5 store structure, at one of the floors with 15 rows of concrete blocks, ( equal to approx 5 times a normal live load), and nothing happend, just a small diflection of 5 milimeters.
I suggest that you go and test the slab with the required loads, keep it loaded for few days, and come to a solution.
This is my best advice.
Thanks
RE: Averaging Loads
RE: Averaging Loads
LOL
RE: Averaging Loads
I think it's too much to expect engineers to design for "what somebody might do to the structure in the future."
DaveAtkins was asked to check out a well defined current situation. If the owner wants to add a bunch of other stuff 10 years down the road, it's his responsibility to get it checked out at that time. Like rgerk typed, an owner could always change the loading without asking anybody.
RE: Averaging Loads
RE: Averaging Loads
I can understand both sides of the argument. I kind of like what kslee1000 is suggesting, except...what if I made the Owner paint lines on the floor, showing where the aisles MUST be? I wonder if the Building Official would accept that.
DaveAtkins
RE: Averaging Loads
RE: Averaging Loads
Can't hurt to ask! That seems to be a sensible compromise to me.
RE: Averaging Loads
Sounds like the Building Official is being a stickler. If it was called out as "Storage" you got lucky w/ only 125psf for light storage in lieu of 250psf for "Storage"
Stay away from calling out aisles.
Aisle = Corridor = 80psf
I'd go for laying out where the racks go and label it as "Files" on the dwg. Show the room as a "File Room".
Per IBC, "Files and Computer rooms shall be designed for heavier loads based on the anticipated occupancy."
Which it seems you've done.
RE: Averaging Loads
RE: Averaging Loads
RE: Averaging Loads
DaveAtkins
RE: Averaging Loads
A light-duty rack system could be the choice.
RE: Averaging Loads
RE: Averaging Loads
Sorry, I couldn't endorse that approach.
RE: Averaging Loads
RE: Averaging Loads
RE: Averaging Loads
The fire marshall usually will keep an eye on the space doing annual inspections and if the layout changes, can let the building inspector know, who can order the owner to correct the violation.
I would ask the building official for an adjudication order. Typically, this means submitted for plan review so I would discuss this plan before applying.
Don Phillips
http://worthingtonengineering.com
RE: Averaging Loads
Also I think that zero live load is a bad idea, should never be permissible in any situation, and would not be at all wise. Technically this would mean that will all your boxes in place, you can never retreive them or go in to look at them. We cannot simply eat our live load and material resistance factors: That is not what they are intended for, and they are already serving their purpose by being factored into the solution. Bear in mind that our loadings are purely static simplifications of a much more complicated reality. The fact that they are higher than normally needed is partly due to our "hiding" dynamic effects within the static specified load. I would encourage you to consider a 15psf live load between the boxes, and factor it up with a dynamic load factor of 1.25 as per designing a crane rail. That would be realistic, in my opinion, for a light duty load involving a couple of people accessing, adding to, and working with the stored files. After all, are you really sure no one will ever tip over one of your lines of seven high bankers boxes? Or chase their child around them?
One last point: Two very eminent and respectable engineers have both, independantly, in two seperate countries, given me the following advice (paraphrasing, of course):
"The client has a problem. We have specialist knowledge which allows us to understand and potentially help aleviate the client's problem. We do not have a problem, and must not act as if we did."
to which the Canadian engineer added:
"We have a duty of care first and foremost to the public, not our client. We have a duty to discharge our services with loyalty towards the client, but life safety must govern our recommendations to the client".
and the Kiwi engineer added:
"It's difficult to say No. Particularly for professional problem solvers like us, itching to not let the problem beat us. Don't be affraid to say No when it's the right answer."
What the client is asking might not be possible. That's life, and no matter how you cut it, its not your problem.
Good luck, and keep us up to date!
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: Averaging Loads
Someone mentioned, if you have enough information, checking the capacity of the system. I've found that some structures will surprisingly exceed what is expected. If you do not have the drawings them maybe you could determine the specifics with proper testing.
RE: Averaging Loads
This kind of variance happens a lot when a warehouse is converted to an assembly use, and you have to adjudicate occupancy to 299 to avoid a whole lot of systems and requirements that cost money, and the tenant will only have 50 to 100 people. Occupancy reductions like this must be adjudicated and the fire marshall enforces the posting of that occupancy. The exception is toilet rooms, where the building official can accept a lower occupancy to reduce fixture counts. When houses are converted to some sort of commerical use, occupancy reductions are a lot cheaper than structural modifications of a floor system covered in finishes.
This is coming from a former building official.
Don Phillips
http://worthingtonengineering.com
RE: Averaging Loads
RE: Averaging Loads
don't existing structure (higher phi values for concrete design, coupled with exactly strength and not design strength) apply?
RE: Averaging Loads
RE: Averaging Loads
RE: Averaging Loads
I talked to a representative from our State Department of Commerce (they have responsibility for Plan Reviews), who said pretty much what you are all saying (but he was more conservative). He said he could not accept zero live load between the boxes, but could accept 50 psf. When he was told that this is more than what the floor was designed for, he sympathized, but said a floor designed for 40 psf should not be used for storage.
As for finding the existing structure's actual capacity, I was not given enough fee to do that (it is a post tensioned structure, and I do not have shop drawings). I told the Owner that I doubt it was overdesigned to the point that it could carry 146 psf at the boxes, and 50 psf between the boxes.
DaveAtkins
RE: Averaging Loads
Youngstructural makes some very good points but I must say that I make a point of never saying no to a client.
In our profession almost anything is possible it is usually the cost that is prohibitive.
I would usually phrase my answer as "The only way that I see this to work is by X,Y or Z." and to cover yourself mention that you expect it to be expensive.
I also think that the building official is, in a way, doing you a favor by giving you an out. If anything went wrong with this floor lawyers would have a field day with the grey areas.
RE: Averaging Loads
However, what you are missing is the significant amount of creep and long term deflection that will accompany this load. Your floor system will crack and deform to the point where the doors will start sticking. Post tensioned concrete is highly susceptible to creep due to the higher compressive stress and thin sections and with the higher sustained load you will have big problems. If this is a direct applied texture ceiling such as hotel construction, the lower floor tenant will not be happy with you at all.
You can bet that your buddy that is trying to talk you into this has all kinds of contractual protections and will be handing your business card to the lawyers when they arrive. He/She may even hire them! They will save on the initial construction because of your recommendations and then ask you to pay to have it done correctly. Free upgrade, what a deal!
RE: Averaging Loads
Let us know what the client decides to do,
I'm very curious!
Thanks,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: Averaging Loads
The most critical issue with increasing load on a PT floor is typically concern of punching shear, which could determine an upper bound for the increase in the slab capacity fairly quickly. Look at that value and work backwards.
Regards,
AUCE98
RE: Averaging Loads
I designed a similar situation in a telecommunications facility and heavy battery loads. I was able to locate the loads along a bearing wall and develop a bracket system that attached the wall and cantilevered out at the base to pick up the batteries. I am not sure if you can live with this type of layout, but we were able to make it work for our project. Best of luck.
p.s. The building official has a valid point. It is difficult enough to argue with a building official even when they are completely wrong.