Cursorily Review of Concrete Details

[Tim_Crouse]

Would someone involved in daily RC Concrete design mind looking over an equipment slab I setup.

In summary, the pad is an equipment pad designed to accommodate (3) uniform wall loads of approx 450 LBS/FT.

The equipment is a chiller skid weighing approximately 17,000 LBS with the pad sized to accept (2) future units.

I designed the PAD using the PCA (basically the slab on grade subject to heavy load document) method and double-checked it with the Gradslab spreadsheet (the slab on grade spreadsheet from the website).


Any feedback is welcome.

Thanks in advance
-Tim C.

 

[r13]

Nothing in the attached PDF, and I don't have CAD viewer.

But basically your wall, foundation, and slab shall be sized for all units expected, and the effects from eccentric loading condition raised from one or two units in place with the remaining space unoccupied.

 

[HTURKAK]

I think 17,000 LBS is the total weight. If this is true, the thickness and reinforcement is OK. You do not need saw cut expansion joint. The pad size is OK. The space between chiller units seems 3 ft.. seems the spacing is narrow..

 

[Tim_Crouse]

I understand that my numbers are based on total chiller skid weight vs the actually linear weight per foot of a single chiller.
My reasoning for this was that it would make the pad more than thick enough, and second, if I went with a single chiller liner weight per/FT, the pad thickness would be quite thin in comparison to
other slabs on grade I have seen that hand rotating machinery equipment. Most likely 6-inch slab would work and I have a hard time setting industrial equipment on any pad smaller than 8" thick
some old school habits


17,000 is the total weight of four chillers on the skid

Not knowing exactly how the chiller skid support frame would be laid out from the OEM, I worked the design under the following assumptions:

For simplicity, I am neglecting the short side supports and adding the weight to only the long sides which will ensure the pad is thick enough.

17,000 LBS / 2 = 8,500 LBS >> 8,500 / 28 Feet Long = 303 LBS / Ft Add a safety factor of 2 = 600 LBS / Foot

600 LBS / Foot for Four Units works out to 600 / 4 units = 150 LBS / Foot >>> So for a total of Six units the LBS/FT will be 900 LBS / Foot (which includes the safety factor of 2)


And lastly, another reason I went with the bigger numbers was in case the skid elevation frame that will raise the assy 24 inches above the slab for air flow turns out to be some sort of W-Beam frame that would add 50+ pounds per foot.


One question that was brought up previously was that the pad would not be loaded eccentric as the two future chillers will not be present. What precautions should I take to account for this?

The 12 inch thick monolithic footers are set at a depth of 12 inches below grade, which is at least 6 inches below the frost line.

Thoughts / Comments?
Thanks in Advance
Tim C.

 

[HTURKAK]

Your load calculation for gravity loading conservatively O.K. But you should consider wind and seismic loads.. The drawing shows a
24" TALL SKID FRAME TO BE PROVIDED BY MECHANICAL CONTRACTOR . Moreover, the skid frame also has reserve pad space for future modules. That is, you shall not provide saw cut EJ.

The pad thickness 8 in . IMO , more than enough..the pad has been provided with perimeter beam with ht 20 in and the skid frame is supported on edge beam.

I think , you do not need further precautions for future chillers. The skid frame with 24 in ht rigid enough and linearly distribute the chiller loads . You may calculate the line load distribution assuming assuming the skid frame is rigid.

 

[r13]

Hope the sketch below helps.

 

[Tim_Crouse]

R13 if you have a moment could you explain what you are relaying to me in the sketch

Thanks in Advance
-Tim C.

 

[r13]

The sketch below shows the general concept of the effect of the eccentric load on the slab. I assume you have a slab on grade system. If so, you need to check soil bearing strength, as well as the stress in the slab. Since you have used full load in sizing the slab, the eccentric load case might not be govern, but I still would check to ascertain the design.

 

[Tim_Crouse]

Ahh, I see

I will look into this aspect.

When (in your experience) an equipment slab is set, is it common practice to get a soils report? Or if the soil is compacted to the 95% density on the proctor test is this sufficient to handle an equipment slab?

Thanks in Advacne
-Tim C.


Sent From My TI-84+

 

[r13]

For industry setting, I would suggest to get soil report. As others noted, have you considered lateral load cases, and dynamic loading, if any.

On top of bearing capacity, you shall ask for "modulus of subgrade reaction" to optimize your design, by using PC and analyze the slab as beam on elastic foundation. You should watch out for differential settlement, and any part of slab is lifted above the ground. If so, the effective length needs to be reduced due to the lose in contact with the subgrade. Good luck.

 

[Tim_Crouse]

There is no dynamic loading, the slab is sized for the equipment only. No vehicle traffic on fork truck (or none of the sort).

The seismic aspect is not a concern here.

I will look into the wind loading aspect. The gear is surrounded by a facility on three sides, the gear is basically sitting in an equipment area with facility walls 48" away on three sides. The fourth side
has a cooling tower next to it, about 48" away, it's kinda tucked into a surrounded area.

When is wind loading to be considered a design concern? We do have hurricanes. I could look at a worst-case scenario of say one side being completely exposed to a 110 MPH wind stream and see what the forces would be.

Thanks for the insight

-Tim C.



Sent From My TI-84+

 

[Tim_Crouse]

R13

When I request the soil report for a 28 X 10 Foot area how many samples should I expect to be taken? I would expect sample need to be taken throughout the slab area of coverage.

Thanks in Advance
-Tim C.

Sent From My TI-84+

 

[dik]

Soft soil or frost heave issues? Looks not too bad. I would use bars @ 16... easier to walk between and add edge reinforcing as shown below. If your loads are light, the slab could be reduced to 5" or 6". You include details that I don't usually include and sawcutting at 12 hours is too long... a max of 6 or 8 hours. If you wait 12, you may as well wait until the microcracking has finished and sawcut on the cracks.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Tim_Crouse]

Dik

The bottom of the slab (footers) are set at 12" below grade in this project, The code in this area requires 6" (mid-Atlantic region). So I think I am covered for frost heave.

I like the way you rolled the stirrup into the upper grid, I may borrow that vs the dual hook setup I show in my details. The design I show in the attached thread files has a #3 stirrup (edge stiffner), What bar size are you using in the provided detail?

What does "DP" refer to in the provided detail?

Does undisturbed mean zero compaction?

I like the idea of 16" for ease of construction, good tip, Thank You for your feedback.

-Tim C.

Sent From My TI-84+

 

[dik]

What does "DP" refer to in the provided detail?
Deep...
Does undisturbed mean zero compaction?
Yup, generally native soil is fairly sound, whether cohesive or granular, and for the project I lifted the detail from it was firm clay.

I've done hundreds, or thousands of this type of stiffened slab... I have standard sheets with notes, edge details, corner details and sawcuts... I'll try to dig one up and can post the *.dwg file... Use 6mil PEVB underneath and rfg is 2" from top... and chaired. I never use WWM for rebar.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[r13]

When I request the soil report for a 28 X 10 Foot area how many samples should I expect to be taken? I would expect sample need to be taken throughout the slab area of coverage.

Your footing is quite small, with static load only, the code prescribed bearing pressure can be used conservatively, and satisfactorily. However, if your equipment is sensitive to displacement, I suggest to talk to a geotechnical engineer, who is practicing in your local and know the area well.

 

[dik]

typ details...


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Tim_Crouse]

Thank You dik



Sent From My TI-84+

 

[Tim_Crouse]

dik

Those are some nice details, simple but add a lot of value

THANK YOU

Sent From My TI-84+

 

[dik]

I couldn't find it... but, I have 2 sheets (connected) with an L shaped slab, notes, soil section, and details for corner, re-entrant corner, saw-cut and typical edge... just can't find it... if I dig it up I'll post it... Just a matter of stretching the edges to accommodate L, square, rectangular slab... dimensions automatically adjust... used to turn them out for $800 to $1000 and spent 30 minutes preparing the drawing. Titleblock was a block with attributes...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik