Equipment Choice¶
Description¶
Firstly, let's set the scope of what needs to be covered. You have started a new job where the general contractor will be providing all of the heavy equipment, and your boss has asked you to find out what will be the best equipment for the tasks at hand. This is a rather unusual project since it is being funded by Bill Gates, and he is only interested in completing as quickly as possible, and is willing to buy any equipment needed, new.
The equipment that you will need to locate is the following:
- A crane to hoist 42 ton (with a factor of safety of 5 applied) precast wall panels in place. These walls are 35 ft long, 32 ft high, and 1 ft thick. The crane will only be able to be located in the corner of the site (as seen on right, outlined in red) and it will have to reach the entire building, and high enough to place panels two stories up. With the lifting beam, the crane will have to be able to lift the panels to a height of 46 ft, and at least a horizontal distance of 65 ft. (Trusses also need to placed, but those can be installed quickly during what would otherwise be down time for the crane.)
- A forklift (telescopic handler), to lift the blocks (3000 lbs with a safety factor applied) up to the mason's scaffold, at a height of 30 ft.
- A hydraulic scissor lift for working inside the building's atrium. But it also will be used by the HVAC contractor to install the odd, and never-before-seen, wall-tower mounted units on the outside of the building (no images available at this time). It needs to have a lift rating of 1500 lb for personnel and equipment. It also needs to be able to move over rough terrain and reach a height of 40 ft.
- The painters are required to work off of an Articulating Boom, above the masons during construction. The boom needs to be able to have a horizontal reach of 25 ft, and a vertical reach of 35 ft, but only needs a 500 lb capacity.
What you boss means by best, in this case, is the equipment that will do the job, but just do the job. Equipment that can be quickly brought in to do the work, but does not require extra space due to the site restrictions.
Again, he does not care about price, just equipment that most closely matches the specifications of the job at hand. Odds are that there will only be one or two controlling factors in the equipment selection, so you will have to decide what is the critical specification that needs to be met.
One last thing, you have just over heard Bill mumbling about two smaller cranes might be quicker than one big one. If you can find a way to place two cranes (with a smaller reach) on the site at the same time, along with being able to bring the precast walls into their reach, you will be able to get future work for your company with Bill.
Assignment Description¶
Note: What you need to do, is lookup on the web, and find equipment that will do the job. You need to provide either a pdf of the specifications for each piece of equipment or a url link to the specifications. You also need to write a sentence or two explaining the criteria that you used to select this equipment, i.e. boom reach, lift capacity, etc.
About the crane, a crane with a maximum capacity of 60 tons will not do the job. I want you to to a sanity check to verify the crane you choose is a reasonable choice. To do a sanity check draw a free body diagram of the crane and calculate the maximum reach that it can lift the precast walls. See the slide below for some more details.
Keep in mind that you cannot operate equipment while it is over the railroad, unless it is designed to operate on rails. You also may take down part of the perimeter fence to bring in equipment, but it must be in place while the equipment is operating (consider the swinging of the crane boom). Lastly, you need to have enough space to have any fixed crane boom laying down during assembly.
Crane Sanity Check¶
If we assume the weight of the crane and counter weights is equivalent to a point load going through the center of the base we can get a quick estimate of the available reach of the crane. The sum of the moments due to overturning about the edge of the base is zero if the crane just barely works. This can be written as a mathematical expression.
∑M=Wc×base2−L×r=0Where:
- L is the load we are lifting
- r is the distance we have to reach
- base is the maximum width of the base of the crane
- Wc is the weight of the crane with counter weights
To check if a crane is capable of placing the load where we want, just solve the moment equation for r and plug in the numbers.
r=Wc×base2×LFor a particular 60 ton crane Wc=85,400 lbs, base=23.3 ft, and our precast load is 42 tons (84,000 lbs).
r=85,400lbs×23.3ft2×84,000lbsThis is a lot less than the required 65 ft for this assignment. The sanity check should be around 65 ft and a valid selection will actually be greater, even much greater. The reason it should be much greater is that the other failure mode of boom buckling will reduce the usably reach. For this reason when looking at the crane chart always look at the capacity of the crane when the radius is at least half the base plus the reach. The reason for this is that the radius in a crane chart is measured from the center of rotation. In our example the radius would need to be 77 ft.
Change Order¶
Well you know the way construction goes. Bill spent the afternoon on the Internet looking for faster construction techniques than waiting on the precast plant to ship the forty, 3.5 feet wide panels. He has discovered two alternatives and wants you to look up some information for him.
First, Bill wants you to determine what would be the best crane if he had the project build out of Southern Pine cross laminated timber (CLT) instead. He likes the panel sizes but thinks it would be quicker to ship the much lighter wood instead of concrete. (You'll need to figure out just how much lighter the panels are to size the crane.)
As a possible second alternative Bill has see videos of concrete being 3D printed. He wants you to try to find a company that could print his building on site (rather than shipping the pre-printed panels). In this case he is less concerned with having the equipment available right away (though he'll give a bonus if it is) but he is considering the technique for a similar project he is wanting to build in a nearby township. If you can find a way to do it he is guaranteeing your company will get the job. His main concern is that the equipment should only have to be set up once and the placement of the concrete for all the walls should be automatic for the entire structure.
References:¶
Class website (Use this link to if you are taking the course on e-learning.)
Github.io version of course website (Do not use this link if you are taking this course in Summer A or B.)
IPython.org (IPython is the opensource software used in the development of much of this course.)