support sat on both side of a expansion joint 1

[struengineer]

I need to design a steel dunnage support for a HVAC unit. Four supporting posts will be sat on four existing building columns which located at both sides of an expansion joint. (2 columns on one side of the joint and the other 2 columns on the other side of the joint).

I am afraid of either horizontal movement due to temperature at the base of the Dunnage support or vertical movement due to different settlement on both sides of expansion joint will cause a problem of my dunnage support.

Is anybody here who solved this problem before? What kind of details I should use to handle this problem? Please help

 

[Ron]

Design the support so that two independent systems sit on either side of the joint. Mount the HVAC unit on rubber isolation mounts. These will allow a fair amount of lateral and vertical movement.

 

[jike]

Not a good situation! I would try to place all 4 columns on one side of the exp. jt. and cantilever the frame over the exp. jt.

 

[rowingengineer]

I think you need to work out the expected expansion/contraction (if this is truly an expansion joint). Give us more inf, is this inside a building, on top of a roof?, I assume it is a suspended concrete, structure is this right? Depending on the likely movement will give you the possible solutions. ie if the movement is smallish Ron's idea is a goer, however is the movement is largish, then you may have to do more to get you isolation.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[jike]

Is this support hanging below the roof or supported on top of the roof?

 

[struengineer]

Jike, Columns are existing. No other structure member can be used to support the HVAC unit.

Ron, it is difficult to support a independent system by 2 column on each side. Unit size is 25'x21'.

 

[struengineer]

Hvac unit is located on the top of roof

 

[struengineer]

Estimated movement: lateral: 4" vertical, 3"

 

[jike]

Have you told the HVAC guy to move the unit to a more reasonable location? Straddling an expansion joint is not very smart!

 

[paddingtongreen]

If you really must cross a joint with those rather incredible movements, I suggest that you need to examine teflon slide plates for the horizontal movement and constant force support springs for the vertical movement.

Does the piping and ductwork cross the joint? if so, how is that handled? I used to do pipe supports on refineries and those movements are radical.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[rowingengineer]

Since the vertical movement is settlement, I would design this such that the support can be adjusted over time and require re-levelling every 6 months. I am assuming little bit of tilting won't be a problem.

For the horizontal movement do you know the time period? Is this 3”max with a 1” variation over a day/week/season/year? or +/- 3" everyday?


Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[hokie66]

struengineer didn't say what caused the estimated vertical and horizontal movements. I thought it was an earthquake.

 

[rowingengineer]

hokie,
read his first post, horizontal due to temp, vertical due to differential settlement.


Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[hokie66]

Guilty. With those amounts of temperature and settlement movements, the building has more problems than support of a mechanical unit.

 

[cntw1953]

A sketch of the building framing with the proposed HVAC on it could be helpful. Sme as above, I don't get where is the temp and differential settlement came from. Is it an occurrance due to the HVAC operation characteristics, that is to be accommodated by the existing building system, or else?

 

[autokoz]

Movement sounds very high but if you want a screwball idea...

Construct a platform to set the unit on.

Construct column extensions from the existing columns.

Suspend the unit platform with steel pins, clevis, turnbuckle and threaded rod. The horiaontal movement is taken care of by the swing action of the steel pin/clevis connection (keep this lubricated)

Periodic Check the level of unit platform. Adjustment of each corner with turnbuckles.

If there is as much vertical movement as noted the amount of adjustment available with a particular turnbuckle will need to be considered. If that dosen't work consider using two rods from one end and a third from the other meeting at a middle plate with rod extension through the plate adequate to make the adjustment and locke with double nut.

 

[struengineer]

Thanks guys.

The unit has to be installed here and Pipe can be adjusted.

Estimated movements come from the following:

Horizontal movement: The existing expansion has a 6” gap (say, joint filer material 2” under pressure). I therefore assume that existing building is designed for 4” expansion. If my structure can handle 4” movement, it should be fine. Actually, any detail can handle 2” lateral movement, I will use it.

Vertical movement: According to original foundation design guild line, foundation should allow max. 3” settlement. I take it as max different settlement. Building has already been there for over 10 years. I guess it may not be 3” now.

 

[cntw1953]

A suspend support system with lateral expansion/contraction is feasible as many have pointed out. I wouldn't worry vertical settlement after 10 years in service without noticeable problem.

 

[hokie66]

struengineer,
The 6" gap could be to prevent the buildings crashing together in an earthquake. The 3" settlement could be total or differential, but would not be differential over the small distance of your mechanical unit. You may have defined a problem that doesn't exist.

 

[struengineer]

cntw1953, what is suspend support system, could you please give more detail?

Hokie66, You are right, it might not have problem. However, I cannot rule out the possibility. Therefore, I still need to consider it in the design.