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shp6 (Structural) (OP)
17 Oct 07 22:08
I am currently working on an existing steel building.  The composite floor was originally designed for 50 PSF of live load.  The building owner now wants to add some heavy equipment to the floors.  Based on my analysis, the floor beams need to be strengthened.  However, the floor below belongs to other company and strengthening is impossible.  

Now my question is can I limit the number of occupancy in these areas (rooms) in order to satisfy the original floor capacity?  For example, if the floor can take 20 PSF after the heavy equipment and I limit the number of occupancy to 5 persons in each room and limit the furniture too.  Does code allow to make this kind of arrangement?  I checked ASCE-7 and IBC but have not found any code requirements.

Please comment on this approach.  If you can reference any code that will be even better.  Thank you.
msquared48 (Structural)
17 Oct 07 23:08
My initial reaction to the 50 psf vaue is that this seems like an office loading, which is accompanied by a 20 psf partition load in addition to the dead load.  Do the drawings specify the type of the 50 psf load?

Mike McCann
McCann Engineering

hokie66 (Structural)
18 Oct 07 3:19
I think that the owner is stuck with 50 psf live load if you can't get at the steel to strengthen it.  One of the disadvantages of strata title buildings.

You can't really limit the occupancy load of some rooms on a floor.  Put up the sign, and someone will take it down.  
Helpful Member!  lkjh345 (Structural)
18 Oct 07 8:52
If it is a limited floor area that the owner wants to place heavy equipment on, depending on the type of construction, there are ways to strengthen the floor from above.

If you have rolled beams and metal deck with concrete fill, it is possible to core out the deck in areas and add (more)composite shear studs.

Have done this a couple of times in buildings where we did not have access to the area below due to other tenants occuping the space and the owner wanted to add high-density filling systems to rooms.  

Helpful Member!  csd72 (Structural)
18 Oct 07 9:44
You cant rely on occupation limits for rooms - a lady gets married and shows off her new ring, in the excitement a dozen of her friends come in to look at it. This is a feasible scenario.

In this type of situation I would look at putting the equipment over the main supporting members (where it makes the least difference). Loads imposed at the end of a joist span make minimal difference which can probably be made up for by calculating the actual partition load rather than the 20psf. I have issued plans marking out zones where the equipment could be placed.

Other option - put a raised section of floor in to allow for additional members above the existing.

The most important thing in this situation is to give the client options.

csd
shp6 (Structural) (OP)
18 Oct 07 10:26
Thank you for all comments.

The equipment are computer servers with an average of 200 PSF.  These rooms will be highly secured and limited personnel.  We feel comfortable to limit the live loads for our personal opinion.  However, we are looking for a code support so we can stand in front of county building officials to defend ourselves for permit.

According to owner, there is absolutely no construction allowed.  It is a highly secured area/building.

Any help I can get?  Thanks.
Helpful Member!  VoyageofDiscovery (Structural)
18 Oct 07 11:08
shp6,

This is absolutely ridiculous, as you are now responsible for life below that floor.  Don't try to find a code reference to hide behind, to satisfy the Owner.  Once the heavy loading is placed do you think anyone will consider that live load is restricted years from now!

If every ounce helps leave a layer of concrete as a form and replace the concrete flooring with low density concrete and increase the studs.
JAE (Structural)
18 Oct 07 11:11

Quote:

if the floor can take 20 PSF after the heavy equipment and I limit the number of occupancy to 5 persons in each room and limit the furniture too.  Does code allow to make this kind of arrangement?

No

The code does not allow you to cherry pick where live loads go in the future.  

Remember - as a PE - think:  "Public safety and welfare"

nutte (Structural)
18 Oct 07 12:42
I agree with JAE.  What would you do if one 300 pound person walked in?  Would that mean only three more people could enter?  I don't know that the code prohibits this, but I would be extremely surprised to learn that it didn't.
csd72 (Structural)
18 Oct 07 12:48
One more thing - have you thought about how they are getting these things into place - e.g. are they wheeling these across the 50psf floor?
JLNJ (Structural)
18 Oct 07 12:48
If the floor were originally designed for more than you need you could de-rate it down to the code-required minimum. I have done this occaisionally in manufacturing facilities.

You can't go below the minimum just by putting up a sign! The only thing you might get away with is sharpening your pencil in the analysis to see if the actual capacity exceeds the rated load.
JedClampett (Structural)
18 Oct 07 13:09
Maybe this is a little off the wall, but could you add hangers between the floor members and the floor supports above and strengthen them (the beams above you do have access to)?  It would tend to chop the floor up, but if you could bury the hangers in partitions, it might work.
msquared48 (Structural)
18 Oct 07 15:10
Shp6:

"According to owner, there is absolutely no construction allowed.  It is a highly secured area/building.

Any help I can get?  Thanks"

The owner has created an impossible situation here, he wants to increase the allowable live load by a factor of 4 with no construction?  WHAT IS HE SMOKING?

Run away from this one and don't look back.  If you already nave a contract, exercise the escape clause.  Hopefully you have one?

Mike McCann
McCann Engineering

shp6 (Structural) (OP)
18 Oct 07 16:33
Thank you all.

I guess the bottom line is "Limiting occupancy" is not a solution for this case.

Does anyone know any code saying "Limiting occupancy approach is absolutely prohibited"?

I understanding that structurally this approach is not a good idea. But politically, I need to make this work in order to satisfy my client.  My client is willing to take the responsibility for the limited live load.  I feel comfortable to do this way.  But I need something is code to tell me that it is absolutely wrong or it is okay to perform my engineering judgement.  

Can anyone point out anything in any code rather than purely personal opinions.  Don't make me wrong.  I appreciate your opinions and these comments are correct.  

Thank you.
VoyageofDiscovery (Structural)
18 Oct 07 16:34
A contract that requires one to do something illegal is null and void.  If does not meet building code and you are forced to do this, you don't need an escape clause.  Know you rights and the law.
shp6 (Structural) (OP)
18 Oct 07 16:39
By the way, the 200 PSF of equipment does not apply to the entire room.  These computer servers are spread out in the rooms.  It is similar to filing cabinet case but lighter.

Based on my analysis, if I can limit the live load to 20 PSF rather than code required 50 PSF, these beams will not be overstressed.  

Now the oint is "can I limit the live load by code"?  I don't see any code saying NO but no code saying Yes either.  Can we justify it using our engineering judgement in this case?
VoyageofDiscovery (Structural)
18 Oct 07 16:40
"I understanding that structurally this approach is not a good idea. But politically, I need to make this work in order to satisfy my client.  My client is willing to take the responsibility for the limited live load.  I feel comfortable to do this way."

The Client cannot decide you takes responsibility, that occurs after the fact in court.  Don't be fooled with this line of thought.  The Code is for your protection, if its not there, its not there.

We are trying to help you.
lkjh345 (Structural)
18 Oct 07 16:45
IBC 2006, Paragraph 1607.3 states in part 'Live loads used in the design .....shall in NO CASE be less than the minimum uniformly distributed unit loads required by Table 1607.1.

Seems pretty clear that you can't arbitarily go below the prescribed loading.

Also, note that table 1607.1 requires, IMHO, if the computer room has an access floor system, that the computer room be design for at least a 100 psf uniformly distributed live load  
msquared48 (Structural)
18 Oct 07 16:53
"But politically, I need to make this work in order to satisfy my client.  My client is willing to take the responsibility for the limited live load."

The client being willing to take the responsibility will not keep you out of court.  Remember the deep pocket theory.

I do not think you will find that limiting occupancy is prohibited in the code as long as it is posted, however, it may not be allowed by local jurisdictions.  Professionally, I would never do it because I would be assuming  responsibility for the actions of others over whom I have no control.  

What happens in the future if the client gets another tenant for the space and he tells the tenant that the floor is good for 200 psf, the floor fails, falling onto the space below, and someone gets killed.  Ane you think you, your firm, and your reputation will not be drug into court?  Think again.  They will search the ends of the earth for you.  YOU COULD LOSE YOUR LICENSE.

DO NOT DO THIS.

Mike McCann
McCann Engineering

MarcbSE (Structural)
18 Oct 07 16:54
"if I can limit the live load to 20 PSF rather than code required 50 PSF"

You've already answered your own question right here.  The code specifies the "minimum" design live load for the floor.  If this is the minimum, it is not possible to justify or permit anything less.  This is the code's way of saying: "No, limiting the occupancy load is not permitted."

I agree with the others that this approach is a very bad idea, and one that could potentially put the occupants below this floor is danger.

One possible option for squeezing out a higher live load capacity is using the area load reduction if you are not already considering it.  Unfortunately, if the floor beams are relatively short this will not help you.

The bottom line is don't put the public in harms way just to satisfy the owner.  Remember that they are your primary responsibility, not the owner!
Helpful Member!  mfrad (Structural)
19 Oct 07 6:39
I would approach this problem differently.  You represent the tenant who was guaranteed 50 psf live load capacity by the building owner.  there is no such thing as a uniform load in an office setting. You have people and file cabinets that make up the 50 psf maximum. Some areas have a higher unit loaded area and others are less than 50 psf.  If the actual 200 psf equipment is a small percentage of the room area you shouldn't have a problem by placing equipment near columns and girders of the floor system. You can then determine the moment diagram of actual loads placed and use the 20 psf for the walkway areas.  If the moment and shear diagrams are less than the equivalent 50 psf M and V diagrams you are good to go. If it is slightly higher, try LRFD if you have the beam sizes etc. I would suggest making a floor plan of the equipment placement and loads for the tenants and owners record and submit them.
shp6 (Structural) (OP)
19 Oct 07 8:25
Thanks, mfrad.

That is the support I am looking for.  That is exactly the approach I am going to.  

The challenge is the computer racks have to go to some exact locations.  According to my analysis, few beams under these racks are overstressed from 2% to 20%.  I can live with a 5% or less overstress.  However, I have to limit the live loads in order to satisfy these 20% overstress.  If I can limit the live load to 20 PSF, these rooms are safe by code.  Since these rooms are highly secured, there will be very few people in the rooms for maintenance only.

I feel comfortable to limit the live load but I need code support.  Engineering judgement is one thing, CMA is even more importance as everyone else pointed it out.

So far, no one can find any code to allow this approach.  I think I know what to do now.

Thank you all for give me your thoughts about this questions.  We are engineers but also businessman/women.  We need to satisfy codes also our clients.  I don't like to run away projects or challenges.  We need to provide "solutions" to our clients eventhough sometimes the solutions are a little bit out of ordinary.  We are trained to provide solutions and that is why we are called consultants.  Just a thought and share with you all.  Thanks again.
bvanhiel (Mechanical)
19 Oct 07 8:59
Hang the racks from the ceiling.
lkjh345 (Structural)
19 Oct 07 9:12
If your under IBC, try Table 1607.1 Part 26:

Office Buildings: ' File and omputer rooms shall be designed for heavier loads based on ANTICIPATED occupancy.'

I suppose, if you say that your limited occupancy is the ANTICIPATED occupancy, you are OK.

Still think you are in a grey area, and if the room has an access floor system you are under Table 1607.1 Part 2, and the whole room needs to be checked for a 100 PSF live load. But thats my opinion.

Keep in mind that any 'solution' we provide for our client must also meet the legally precsriped code that is in force in the jurisdiction we are working in. Its not a 'solution' if it doesn't meet the code.

shp6 (Structural) (OP)
19 Oct 07 9:58
Thanks to lkjh345.  That is a positive approach for challenge questions.  That is exactly the code language I am looking for.  What I will do now is to write a letter to ICC to request an explaination for my case.

Excellent.  Thanks again lkjh345.
csd72 (Structural)
19 Oct 07 10:02
shp6,

There are not solutions to every problem, it is one of the hardest things to tell a client but in some cases it is true.

csd
VoyageofDiscovery (Structural)
19 Oct 07 11:16
Hi shp6,

I understand your position with regards to solutions for the Client, however I don't condone the end result of your position.  Testing the Code wording such as "anticipated" on its own by semantics is a dangerous position.  Minimums must still be adhered to while actual loads may govern.

VOD
civilperson (Structural)
19 Oct 07 11:27
A client can not protect you after the building is sold and the next owner experiences a failure.  You are the engineer responsible for good judgement, (i.e. following the code).

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