Shipping Container - Roof Capacity

[TLHS]

Ah the joys of someone on an industrial project deciding that they should just jam a process into a shipping container.

I'm acting more as a specifying engineer in this case. The new-ish ICC/IBC guidelines on shipping container design make all the questions of lateral capacity pretty straightforward now, for small applications. My issue is roof capacity under high snow loads. I don't think there's a problem, but I also want to make sure I can evaluate that the design engineer does check the boxes on it. Has anyone seen a design guide or literature about this?

I'm not seeing anything in the way of generalized guidance, which would mean that I'm going to have to ask for capacity calcs or something similar based off the measured corrugations and thicknesses.

It seems a little weird, though, that I'd have to direct them to go that route. One would think that it's a standard profile and minimum thickness, but I can't even find documentation that indicates that.

 

[TLHS]

With more reading, the test load is 300kg over 2sqft at any location. That is... not enough that the capacity is acceptable for moderate to high snow loads unless there's a fair amount of reserve strength in there above the test capacity.

 

[JStephen]

I would be kind of surprised if there was a rated snow load for them.

 

[dik]

They are likely much stronger than that...

From the net... "The roof load test is 660 lbs over an area of 2' x 1' applied to the weakest part of the roof. The load is usually applied at the center of the containers positioned with the 2' dimension aligned longitudinally. Thus the roof is able to support an imposed load of a minimum of 330 lbs/sq. ft."

You can confirm the numbers... not big on unsubstantiated numbers. [Edit] Minimum loading would be moment produced by PL/4 for point load being equal to ql^2/8 for UDL... just noticed. will be greater than 660x8/4/2 = 660 ft-lbs. 660x8/8^2 = 82.5 psf. Dead load from container included already.

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

-Dik

 

[dik]

The following is from my Project Notes for a container project I did... ballast is for loading stipulated. I've bolded some important stuff...

CONTAINERS
-ALL CONTAINERS SHALL BE SIMILAR SIZE, WEIGHT AND CONSTRUCTION.
-CONTAINERS SHALL BE FABRICATED TO ISO 1496-1990 EDITION MINIMUM.
-CONTAINER DESIGNATION SHALL BE 1D OR 1DX MINIMUM.
-CONTAINERS SHALL BE MINIMUM GRADE B, THESE ARE GENERALLY CONSIDERED AS CONTAINERS HAVING A FEW DENTS AND SCRATCHES, BUT CAN BE USED FOR STORAGE. THEY SHOULD NOT HAVE SUSTAINED MAJOR DAMAGE OR HAVE SIGNIFICANT CORROSION.
-CONTAINERS SHALL BE CERTIFIED AS CARGO WORTHY (CWO) AND WIND AND WATERTIGHT (WWT).
-CONTAINERS SHALL PASS THE FOLLOWING TESTS STIPULATED IN ISO 1496, U/N:
TEST 01- STACKING;
TEST 02- LIFTING FROM THE FOUR TOP CORNER FITTINGS;
TEST 03- LIFTING FROM THE FOUR BOTTOM CORNER FITTINGS;
TEST 04- RESTRAINT (LONGITUDINAL);
TEST 05- STRENGTH OF END WALLS;
TEST 06- STRENGTH OF SIDE WALLS;
TEST 07- STRENGTH OF ROOF;
TEST 08- FLOOR STRENGTH;
TEST 09- RIGIDITY (LONGITUDINAL);
TEST 10- RIGIDITY (TRANSVERSE);
TEST 11- LIFTING FROM FORKLIFT POCKETS;
TEST 12- LIFTING FROM THE BASE AT GRAPPLER ARM POSITIONS; AND
TEST 13- WEATHERPROOFNESS;
-IF LIFTING FROM THE FOUR BOTTOM CORNERS ONLY COMPLIANCE WITH TEST 02, TEST 11, AND TEST 12 CAN BE WAIVED.
-IF LIFTING FROM THE TOP CORNER CASTINGS COMPLIANCE WITH TEST 02 IS REQUIRED.
-THE FOLLOWING COATING SYSTEM IS RECOMMENDED. CLEANING SHALL BE TO SSPC-SP 1 AND SSPC-SP 6. PRIMER SHALL BE DEVOE 'DEVGUARD 4160 - MULTIPURPOSE TANK AND STRUCTURAL PRIMER'. TOPCOAT SHALL BE DEVOE 'SPEEDENAMEL 4318 - QD GLOSS ENAMEL' . COLOUR SELECTED BY OWNER.
-CONFORMANCE WITH ANY MECHANICAL OR ELECTRICAL REQUIREMENTS OF THE NATIONAL BUILDING CODE HAS NOT BEEN REVIEWED.
-CONFORMANCE WITH ANY REQUIREMENTS OF THE NATIONAL ENERGY CODE HAS NOT BEEN REVIEWED.

-CONTAINER DESIGN LOADS:
Ss = 1.9 kPa;
Sr = 0.2 kPa;
q (WIND) = 6.4 PSF (BASED ON 5 YEAR RETURN PERIOD, CALCULATED USING THE BC BUILDING CODE METHOD. IN THE EVENT OF A PUBLIC WEATHER ALERT FOR A SEVERE STORM EVENT, FROM ENVIRONMENT CANADA, PEOPLE SHALL DISTANCE THEMSELVES FROM THE SCREEN LOCATION;
Cg = 2;
Ce = 1;
Cp = 0.8 (WINDWARD);
Cp = 0.5 (LEEWARD);
CONTAINER WEIGHT = 5000 LBS MIN FOR 20’ CONTAINERS; AND
CONTAINER WEIGHT = 8250 LBS MIN FOR 40’ CONTAINERS.
-CONTAINER ATTACHMENT SHALL BE ACHIEVED BY USING METAL BANDING OR STRAPS FABRICATED FOR THIS PURPOSE. STRAPS SHALL BE PLACED AT 1/5 THE CONTAINER LENGTH FROM EACH END AND SHALL DEVELOP THE FOLLOWING MINIMUM LOAD CAPACITIES:
TOP CONTAINER TO INTERMEDIATE CONTAINER = 1000 LBS; AND
INTERMEDIATE CONTAINER TO BOTTOM CONTAINER = 2800 LBS.
-DEADLOAD, UNSHIFTABLE BALLAST SHALL BE PROVIDED FOR THE BOTTOM CONTAINERS. PROVIDE 64 PSF BALLAST FOR THE 20’ CONTAINERS, AND 82 PSF FOR THE 40’ CONTAINERS. THE AREA IS BASED ON INTERIOR FLOOR AREA OF THE LOWEST CONTAINER.
-CONTAINERS SHALL BE FOUNDED ON A GOOD COMPACTED GRANULAR BASE HAVING A BEARING RESISTANCE OF 2000 PSF MINIMUM.
-CONTAINER SUPPORT STRUCTURE IS INTENDED FOR SHORT DURATION LOADING ONLY AND NOT FOR OPERATION DURING THE WINTER SEASON.
-THE SCREEN SUPPORTING TRUSSES, SUPPORTED ON THE TOP HAVE BEEN REVIEWED FOR STATIC LOADS ONLY. THEY SHALL NOT BE SECURED AT THE BASE (THIS WILL INCREASE THE VERTICAL LOADING ON THE TRUSSES. THE ENDS OF THE TRUSSES SHALL BE SECURED TO THE CONTAINERS AND SUITABLE BEARING PROVIDED.


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

-Dik

 

[LittleInch]

Have a look at this post as well which might have some data.

You may well need a sloping roof installed.

https://www.eng-tips.com/viewthread.cfm?qid=480914

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Canuck65]

Generally we find about 20 psf capacity based on calcs of the corrugated steel roof assuming simply supported, but there is often more capacity if you test. For the function of a container, it does not need any significant roof capacity, the heavy loads are transferred through the corners. For snow loads we normally specify strengthening, or over framing where the load path gets back to the corners.

 

[dik]

Their loading requirements would indicate a lot higher load capacity than that...

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

-Dik

 

[TLHS]

Thanks for that, dik. I didn't realize you were in BC.

I'm not sure I agree with the way you've back-calculated the roof capacity, though. The test is an ultimate strength test. Despite it being a generally one way spanning corrugated deck, I think there's probably a reasonable amount of additional width being pulled in. I don't think it's got the full 660lbs being resisted by a 1ft strip. Especially since descriptions I'm reading about people walking on the roofs indicates that there's some reasonable deflection going on. I'd probably start feeling comfortable that it's conservative with something in the 4ft wide strip range.

Realistically, I'm not all that worried about collapse, since I'm pretty sure there's a fair amount of capacity post yield in this type of construction when it goes into large deflection tensile load paths. I'm not going to let a vendor rely on that, though.

 

[EdStainless]

I remember a field full of containers used for storage.
And they all had puddles in the middle of the roofs.
This was is WI where a few feet of snow is common, and in Mar/Apr it can be very wet snow.
Over time it had caused all of them to sag, and they were rusting like crazy.
I presume that many had started to leak, because you could see some with much less water on them.


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P.E. Metallurgy, consulting work welcomed