Mill Building Crane Advice

[SteelPE]

I am in the process of completing a preliminary design on a single story mill building addition. The building currently contains multiple 10 ton and 5 ton cranes. Our initial design called for the cranes to be bracketed off the side of the columns as we estimated the wheel loads to be approximately 15.2 kips (static) and the bracket loads to be 30.4 kips (including impact). The client said that they would not allow for the cranes to be placed in the same bay at the same time.

Since our initial design was completed the client gave us the actual wheel loads to be 22.5 kips (static) and the bracket load to be 47 kips. This seemed high to me, but the crane manufacturer stated that these loads are indeed correct as each crane has 2 heavy duty hoists.

I seem to remember reading something saying that the loads on a bracketed crane column should not exceed 50 kips. Is this limit correct? I am leaning towards putting these cranes on their own separate column system however, the existing building utilizes bracketed columns.

 

[DaveAtkins]

I typically use separate columns if the bridge crane is 20 ton or larger, and brackets if the bridge crane is less than 20 ton.

I have never heard of "heavy duty hoists."

DaveAtkins

 

[SteelPE]

Dave,

I seem to remember breaking the columns around 15 tons.

I understand what you are saying about the hoists, however, the static wheel load is 22.5 kips where we estimated 15.2 (using available data we have her on file). That's a rather large difference. When we questioned the crane company they said the increase in load was due to "dual heavy duty hoists" in each crane.

They gave me a bracket live load of 41.9 kips and dead load of 4.5 kips but couldn't tell me whether or not those was load included impact (should have been a warning sign). I requested the wheel loading and wheel spacing from them and calculated my own bracket live load of 39.2 kips with impact. This is slightly better than what I was dealing with originally.

What's the magnitude of the bracket loads are you getting with 20 ton cranes? Are you talking about 50kips or so?

 

[JAE]

The weight of the bridge and hoists (and the resulting wheel loads) can be significantly affected by the CMAA Service Class of the crane.

"Heavy Duty" may imply a Service Class E or F....much heavier materials.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[DaveAtkins]

It has been a long time since I designed a crane building, so I don't remember reactions. I just remember that 5 ton and 10 ton bridge cranes could easily be supported by brackets.

DaveAtkins

 

[SteelPE]

That's how I remember it as well. However, the reactions for this 10 ton crane (at 22.5k/wheel) mean the bridge and hoists weight over 25k to support a lifted load of 20k. The bridge isn't overly large either (at 58' in length). This load is about 50% larger than what we anticipated.

In the end, I calculated a bracket load of 43 kips (including impact and runway weight) and decided to continue on with the crane placed on brackets.

 

[12345abc6ttyui67]

Dual heavy duty hoists = 2x 10 ton per crane, 20ton total?

 

[FLCraneBuilder]

1) wheel loads can also increase dramatically if it s a long span crane - or a heavy cranes - ie walkways, high end mechanical equipment etc.
2) If its high speed hoisting equipment, wheel load with impact goes way up. Same for bridge motion, if High speed, longitudinal & end stop forces go way up. You need to design the structure and foundation to withstand impact as well


3) I don't normally associate 5 & 10 ton cranes with "Mill Buildings"... I equate Mill buildings to VERY high speed & severe service cranes and would then use AISE Tech Report 13 building design criteria,
if this is simply a class C or D crane with moderate speeds & service it changes things a a lot
4) I call BS on limitation of 50 kips on Brackets... I've heard people use it often, but it makes no sense.
the limiting factors becomes column design - not the bracket itself.. Make the bracket a 24' long 36x300.. it will carry the whole world, but its connection to the column is limiting.
I've seen an A&E firm successfully apply 130 kip bracket load - but the bracket was welded to a W36x230 column - and used 110' long W36 x 182's for the PEMB mainframes - it was a fairly hardworking concrete facility too - two 60 ton Cranes bumper to bumper 45' in the air!!

 

[FLCraneBuilder]

Ive attached a pic of a 10 ton x 130' Steel Warehousing Crane we built on 2007 (one of 5 of this size for this customer)
10 ton 130' crane - although not on brackets, be advised the column load was 97 kips

 

[FLCraneBuilder]

and forgive me if I wasn't supposed to paste the pic
I see you folks usually attach it

Its the first time I've added a pic to a post

 

[TLHS]

I'm a big fan of building independent supports for cranes whenever it's vaguely reasonable. Exceptions being when they're small loads or when it's a bridge crane over the whole building. There are times when it makes sense to hang from the building, but I tend to find that the design goals can get pretty different and having the cranes supported on the building tends to screw up the design or build process at some point due to co-ordination issues.

I'm also really wary of the idea that the owner won't put the cranes in the same bay as part of your design assumptions. That scares me. What if the owner changes one day? What if someone doesn't tell new employees? What if someone just screws it up? Maybe I'd go that way if I could document it as part of the official ratings of the cranes, including the crane rating on the rail, with lots of big signs, but even then I'd be worried. Maybe it's justifiable to reduce the load combinations for combined loading in the condition you're talking about, but I'd be super careful.

 

[SteelPE]

Thanks for the information FLCraneBuilder, I never quite understood the 50 kip limit, but I have always tried to follow it. The document I follow for the design of these types of buildings is the AISC DG #7. The issue I have in general in terms of crane buildings is the general use of terms. I believe the DG in a few instances states.... for large cranes. Well, what is the definition of the term large? 10k wheel load, 20k wheel load, 100k wheel load? Very vague. What is large for me may be tiny for you.

TLHS, I understand your concern, however, I believe they have mechanical ways to limit the position of the cranes in relation to each other. As in an electric eye that measures the distance between the two. If they get too close they shut them down. We can play what if's all day long, but that will get us no where, and in the end make for a very unhappy client as costs will skyrocket.

Just for reference, in this instance, we provided a preliminary design based upon what we thought was right (with an independent column system). The building went into budgeting and came back as a metal building. This was due to the costs associated with the preliminary design. We have been told the project will continue as a metal building if the costs are not brought under control. I don't believe a metal building is justified here, but the owner has the costs associated with a metal building and the difference is significant. I started this thread to see if the elimination of the independent column system was justified or not.

Thank for your help