Existing Mechanical Space - Heavy Equipment

[jz123]

I am currently checking an existing mechanical space (composite steel structured floor) for its ability to support new chiller units. The space was originally designed as a mechanical space and the original drawings state 100 psf live load. After modelling the floor, it appears that the original engineer designed most members to just about 100% utility.

The new chillers equate to much more than 100 psf, approximately 250 psf when taking weight divided by footprint. Therefore, if I put 250 psf (or point loads) under the new equipment footprint, and maintain 100 psf in all areas outside the unit footprint, I get structural failures everywhere.

My question is: what are others using for engineering judgement for live loads in existing mechanical rooms when the heavy equipment is known and accounted for already? Its obviously not 0 psf, but I'm not sure it should be 100 psf either.

I'm interested to know if other engineers have run into this. I can't seem to find literature that addresses this.

 

[ANE91]

I model the load distribution and strengthen the structure as needed. Sounds like your chiller is simply too heavy.

 

[HTURKAK]

If you use 250 psf for the chiller area of footprint and 75 psf for the remaining areas ( assuming access corridors , walkways ) will it be OK ?
I will suggest you to look Process Industry practice PIP STC01015 Structural Design Criteria for loads and combinations.

 

[jz123]

If you use 250 psf for the chiller area of footprint and 75 psf for the remaining areas ( assuming access corridors , walkways ) will it be OK ?
I will suggest you to look Process Industry practice PIP STC01015 Structural Design Criteria for loads and combinations.

I will take a look at that. Thanks for the reference. And not quite... I would need to go down to about 50 psf to make things work.

 

[HTURKAK]

I will take a look at that. Thanks for the reference. And not quite... I would need to go down to about 50 psf to make things work.

Yes.. Please have a look . I have a sense that there could be some misinterpretation of the dead loads and moreover with combinations. Copy and paste from PIP STC01015 regarding type of dead loads;

4.1.2.3 For this Practice, dead loads are designated by the following
nomenclature:
Ds, Df, De, Do, and Dt, where
Ds = Structure dead load is the weight of materials forming the structure (not the empty weight of process equipment, vessels, tanks, piping, nor cable trays), foundation, soil above the foundation resisting uplift, and all permanently attached appurtenances (e.g., lighting, instrumentation,
HVAC, sprinkler and deluge systems, fireproofing, and insulation, etc.).
Df = Erection dead load is the fabricated weight of process equipment or vessels (as further defined in Section 4.1.2.4).De = Empty dead load is the empty weight of process equipment,vessels, tanks, piping, and cable trays (as further defined in Sections 4.1.2.4 through 4.1.2.6).
Do = Operating dead load is the empty weight of process equipment, vessels, tanks, piping, and cable trays plus the maximum weight of contents (fluid load) during normal operation (as further defined in Sections 4.1.2.4 through 4.1.2.7).
Dt = Test dead load is the empty weight of process equipment, vessels, tanks, and/or piping plus the weight of the test medium contained in the system (as further defined in Section 4.1.2.4).

If sharpening the pencil works, that is fine. But at the end of the day strengthening the structure could be only option.