Forklift load on City Hall Plaza over their parking garage 1

[AsherDK]

I am authorized to use a forklift but not a crane to bring in a sculpture on a City Sculpture Garden Plaza that is actually the roof of their underground parking lot. Assuming they built it to "California Codes" what can we estimate reasonable about maximum safe loads? The City-owned forklifts are limited to 4,000 lb loads. I need to lift a maximum initial load of 9,000 lb and it will be on a 3/4" steel plate 80"x80", to distribute the load. Then I will add a further 3800 lb on top to complete the sculpture. So the total load on 80" X 80" steel plate is 12,800 lb.

One works through the Public Art Department and they kindly channel questions to the City Engineers! They don't just hand over plans! Obviously, so far, I do not have the rebar or steel structure details, but is it safe to assume the concrete in such a modern City structure is "well designed" and should be at least 6" thick with appropriate rebar and steel spans?

What are minimal the critical questions to ask the Public Works department to enable estimates of safe loading?

I will choose a forklift with the largest tires and lowest weight for the job. Your ideas will be helpful. In any case the city Engineers will approve the proposal beforehand.

Thanks,

Asher

 

[JStephen]

If the city is responsible for checking the construction, then give them the proposed loads, load distribution (for the sculpture, and also for the loaded forklift), access route, and let them check the construction.
If they built it to a specific code, that would establish minimum strength, but it could very well be adequate for higher loads, too.
I've noticed in several previous posts, the issue of fire-truck loading came up for areas that would otherwise be subject only to fairly light loads.

 

[BUGGAR]

It sounds like the "foundation" for the installation has been designed and you are responsible for erection loads? Who designed the permanent "foundation"? A 9000 lb sculpture in CA with seismic may be significant. And if located in a public space, even more so.
Along with your responsibility, the owner also has the responsibility to advise you what he or she knows.
And if it's a typical City Contract - you know the risk!

 

[AsherDK]

J, you are right on! I am giving them the proposed access routes and the specifications of the Toyota fork lift I am renting and the resultant 330 lb per sq ft load on the concrete.

They have to approve everything bum it I would love transparency where I can just have access to their own engineering drawings to check!

6" of well engineered concrete should be able to take the load and even 3 times more.


Asher

 

[AsherDK]

Buggar,

Yes we have to think of seismic issues. The sculpture has the largest risk, I consider, from ocean winds on the surface of a steel sail approx triangle height and base of 16 ft. As the winds vary from 0-20 mph most of the time it's no big worry but once in a hundred years it might be 100mph. So the main art part, a boat is on a bearing assembly so that it will align with the wind and minimize the load to the sail.


The City can recommend any extra requirements for seismic considerations and I would be happy to comply. I even have holes ores rolled for extra anchoring if they would request that

Mostly I am looking for experience in loads 6" concrete in City Structures and what sort of issues came up.

Asher

 

[dhengr]

AsherDK:
There have been several other OP’s on this same subject, you might search them in the structural forum. You could take the base plates in as two slightly smaller (footprint < 80") .5" stl. pls. You could also put down some 3" oak planking, along with .25" stl. running pl. if you wished, to distribute and improve the forklift loading conditions a bit. The City should be able give you the loading info. you need, they would more than likely have had the plaza designed for some of these kinds of situations.

 

[AsherDK]

Dhengr,

Thanks for the comments. When I find out the weight of the fork lift I might indeed need to have plates or wood planks down to distribute the load.

I will add that as an option based on roof specs they provide if it is needed.

What specific questions would you ask about the roof structure.

I think I may simply offer to do the calculations for them if they provide the plans.

Asher

 

[Ron]

If I understand this correctly, you are installing a sculpture on a plaza deck that is over a parking garage.

The plaza deck has probably been designed for pedestrian or occupancy loads, maybe up to about 50 psf live load. I would doubt that the plaza deck has been designed for vehicle loads as the parking garage. Given that, I would [highlight yellow]definitely not[/highlight] put a forklift on it without significant analysis. Seismic considerations would not apply to the temporary forklift loading, but would apply to the "permanent" installation of the sculpture.

Your forklift will apply two types of loads....the wheel loads and the overall load of the forklift. The slab must be able to withstand both, obviously.

Also, I would disclaim any damage to the waterproofing as a result of the need to travel across the plaza deck with the forklift. You don't want to be responsible for future leaks that might result.

 

[Lomarandil]

I'm with Ron here. It's quite possible that the roof has not been designed for any vehicular loads. Even if the deck is 6" thick concrete, without enough reinforcement or with long enough clear spans that can mean very little.

Now, don't get me wrong. We recently put pretty good size excavators on top of the Moscone Center roof in SFO. Some structures can handle it. But you're right to want some assurances (from an engineer or from the city) before driving up there.

The easiest question is what the design load of the roof was. Ideally, that's listed on the first sheet of the original as-builts -- easy for the city to find. Then it's a exercise of comparing that design load to your forklifts. Sometimes apples-to-apples, sometimes not.

If there isn't a listed design load, and you have to get into analyzing the structure, that's either time to hire an engineer or get the City to take the risk (and still have someone run some numbers to make sure your operator doesn't get hurt).

Like Ron pointed out, you need to consider the local tire load (punching through the slab) -- usually not evenly split among 4 tires when carrying load. 330psf is pretty darn light for a tire load -- in fact, too light. Is that correct?

Also need to consider the total weight of the forklift and sculpture for a more global failure. This is the easier of the two, if the structure is consistent throughout.

Depending on how long the sculpture garden has been around, also consider the current surcharge load-- concrete, soil, plants. If those have changed over the years, it may eat into the margin you have left to run your machine on top.

 

[DBronson]

AsherDK:

If I'm reading your description correctly, the load center is 40" from the edge of the plate. The rated capacity of a lift truck is with the load at 24" from the vertical face of the forks. A 40" distance will require a much larger (and heavier) truck than you might think. To extend Ron's thought, why are you even using a forklift - its presence is adding a considerable amount of weight to the system. Have you looked at using machinery skates? They are very commonly used to move heavy loads such as yours. Multiple skates can be used to spread the load. Link
Better yet, why don't you get a rigging contractor involved? They routinely move 50,000 lb machine tools and are well attuned to all the issues associated with moving and lifting heavy objects.

Regards,

DB

 

[AsherDK]

Thanks DBronson,

Of course, I have already asked riggers for proposals but am waiting! Meanwhile I want to install the base for the sculpture at least to show we have started installation.

The use of skates is a superb idea and I appreciate the link and will learn a lot from talking with them!

I am really interested in discovering how one removes the rollers at the desired location and lowers the load safely.

Unfortunately, the City may not be able to come up with structural plans of their own building!

Use of skates seems like a wise approach and I now wouldn't be surprised that, when the riggers finally make a proposal, it will be with skates! They are slow in responding as they are busy beevers!

Is there a way I can facilitate using skates by fabricating attachments to my 80" X 80" 3/4" steel plate that supports the sculpture base.

It is reinforced by a central 48" square welded 2" X 2" ridge in the center and from the corners, diagonal arms to each corner of the 80" X 80" plate to prevent flexion.

I will talk to the company in the morning.

Appreciate your input!

Asher

 

[SlideRuleEra]

What is the distance from stable ground at the edge of the plaza to the statue's location? If space is available and the distance is reasonable, have a suitable size crane positioned at the edge of the plaza lift the statue into place without putting a forklift or any other sizeable moving load on the plaza deck.

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