Exterior Overhead Bridge Crane End Stop Design...Help!

[honthan]

I am in the process of designing an end stop for an exterior overhead double girder bridge crane application. I am fairly confident in determining the collision force that the end stop needs to be designed for based on the Kinetic Energy Equation (1/2*W*v^2/g*S), however please correct me if I am incorrect. W = 1/2 * weight of bridge + weight of trolley (357656.2 lbf), v = 100% of full rated bridge speed (417 fpm), g = acceleration of earth's gravity (32.16 ft/s^2), and S = hydraulic bumper stroke (16 in.). Evaluating this equation I get a collision force of (103,233.8 lbf). I verified the use of this equation with the AIST Tech. Report No. 6, Whiting Crane Handbook, and AISC Eng. Journal "Tips for Avoiding Crane Runway Problems". The crane manufacturer states in their specifications that the bumper striking force is a 200,000 lbf per bumper, therefore we have used this value to design end stop for since it exceeds our calculated collision force.

Since this is an exterior application and the crane is not inside of a building The Whiting Crane Handbook, AIST Tech. Report No. 6, and AISC Eng. Journal "Tips for Avoiding Crane Runway Problems" state that the end stop design needs to consider wind forces applied over the surface area of the crane...

Whiting Crane Handbook states "Add for 10 pounds per square foot wind on projected area of crane for out-door cranes.".

[li]Do you just determine a wind force based on multiplying 10psf * the surface area of the crane and divide this number by 2 to get the wind load on each stop? or do you determine the wind force, and based on this wind force using the basic physics equation F=ma determine a crane acceleration due to the wind, accelerate the crane over the full length of the runway, and then determine a final velocity at the end of the runway. This velocity can then be used into the Kinetic Energy Equation above to determine the collision force due to wind? Are wheel frictional forces and drag resisting this acceleration to be accounted for in this?[/li]

AISC Eng. Journal states, "Once, this wind force was estimated by calculating the vertical projected area of the crane and multiplying by a force of about 10 psf. Today, the process is a bit more complicated, Refer to pgs. 92 and 93 of Whiting Crane Handbook, wherein a method of calculating wind pressure is explained based on ANSI recommendations".

[li]As mentioned above Whiting Crane Handbook doesn't make it any more complicated than just adding 10psf wind, although I don't have a copy of the ANSI standard the AISC journal refers to secondly...[/li]

AIST TR#6 states, "Wind loads on cranes that operate in exposed locations shall be calculated with consideration of geographic
location, height above ground and shape of the individual components that make up the structure. In the calculation of these
loads, the information in ASCE 7 should be followed. In-service wind shall be calculated as required under Section 2.3.3
of this report, and shall have a magnitude equal to 25% of full wind load."

I decided to use the requirements out of the AIST TR#6 since it seemed to have a little bit more technical information on the design of cranes, and the end stop collision design process for all three really didn't vary much except in the wind force determination.

I guess my main question is how does wind affect the collision force on an end stop and what is the proper way to apply that wind force. Nothing i read seems to give me parameters such as apply the wind over the full length of the runway?, my runway is 350 feet long so is it reasonable to consider an approximated 10psf wind load blowing constantly over 350 feet? do you consider that the hurricane pins and brakes fail since these are a requirement for exterior cranes?

If i assume worst case scenario that the pins fail, brakes stop working and with a 25% of full wind load force over the full length of runway i get a collision force upwards of 1.4 million pounds. This seems pretty unreasonable to design for? Even worse is if you consider a full wind load force.

As you can see i am pretty confused so any help would be greatly appreciated.

Thanks in advance.

 

[JedClampett]

The wind force would only apply to the projected area of the crane, not the length of the runway. And I definitely wouldn't use the wind to accelerate the crane and then expect the stops to hold it. It seems unreasonable.
I might be pretty cavalier, but my desing of bridge crane stopes is "stops by manufacturer" and I'm done with it. I've never run a number on them.

 

[honthan]

Thanks JedClampett. The owner has asked us to analyze an existing stop that has been designed for this crane and determine if it is adequate. The request was to make sure it is overly designed since the reason they are having to purchase another crane is that the original one was blown over in a windstorm. Crane was not secured with hurricane pins, crane did not have automatic brakes, and rolled from one end of the runway to the other and blew through the stops falling to the ground...As unreasonable as it may sound this is what happened to our client and they want to make sure it doesn't happen again. Granted there were some maintenance issues such as not securing the crane with the pins and having an exterior crane with no brakes installed.

 

[honthan]

so what i am hearing from Jed is that code design of an exterior crane for wind doesn't mean accelerating the crane over the length of the runway, but just applying a wind force to the stop such as that applied to the ends of a simply supported beam...ie crane = simply supported beam.

 

[JedClampett]

I didn't realize this was a client request. But saying that, it's hard to idiot proof a design. As they say, there's always a bigger idiot. If the owner doesn't impose operational standards (set brakes, pins etc.) on their employees, what's to stop thme from just exceeding the crane capacity? And if you design the stops for a wind plus running the crane into the stop load, do you carry that load into the building frame? Foundation?
There's no code guidance on this to my knowledge. We apply the manufacturer's loads plus impact and that's pretty much it.