Design Topics

The four major design topics are the crane design, the placement of the system, the crane foundation and the lifting mechanism. Crane Design Due to the constraints of the room, only two main design ideas were sufficient. These designs included a ceiling mounted trolley system and a cantilever rotating system. A previous proposal for a ceiling mounted trolley system from the Navy was quoted at $40,000. This showed that a ceiling mounted trolley design would greatly exceed the project budget. Therefore, the cantilever rotating system was chosen for further investigation. The team was able to find a state of the art product in the research process. The crane type is a jib crane produced by Gorbel [6], which is able to rotate 360 degrees. Gorbel provides a large range of span lengths and height clearances. A picture of the crane is shown in figure six below.
Figure 6
 
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Placement of the Crane

There were two main variables involved in deciding where to place the crane. The system had to be able to reach all six cans and move them to the working area. The system also had to be mounted far enough away from the side of the isolated slab to provide enough counter-balance to overcome the loading moments. Calculations concerning counterbalance are included in the Calculations section below. Figure seven below shows the final placement of the crane, which fulfills all the requirements. The span of the jib crane for this particular placement was set at 16 feet.
Figure 7

Crane Foundation Problem

Gorbel specified a four by seven by seven-foot concrete foundation to mount the crane on. A one-foot thick isolated slab already existed in the room making it impossible to meet the foundation requirements of Gorbel. Two main design ideas were discussed during the design stage to solve this foundation problem. A three by seven by seven-foot slab of concrete could be built on top of the old foundation meeting the specifications of Gorbel. Or, a metal plate foundation could be designed to accommodate the loads induced by the crane. There was not enough room to build a slab with needed dimensions, therefore, it was decided to design a metal plate foundation.

This metal plate would be fastened to the existing slab using an anchor system. The crane would be fastened on top of the metal plate using bolts or possibly by welding. Decisions on fastening systems, metal plate dimensions, and how to fasten the crane to the plate are shown in the analysis section of this report.

  

Analysis

Plate Thickness

An "ASTM – A36" carbon steel distributed by Earle M. Jorgensen Co [10] was chosen for the metal plate foundation. This material provides an ultimate tensile strength of 58,000 psi. The total loading moment at the base of the crane, including the periscope can, the lifting device and the mass of the I - beam, was determined to be 48,850 ft. - lbs. Failure of the plate caused by shear and bending was examined [See Analysis for the Plate Thickness below]. The thickness of the plate was calculated with a safety factor of two. With bending as the controlling mode of failure, the minimum plate thickness was calculated to be 1.1 inches. Plate Widths A Powers Rawl epoxy anchor system was chosen to fasten the metal plate to the existing foundation. This system has high bond strengths, is easy to install and is offered at a reasonable price [2]. Every anchor has an ultimate load capacity of 8,915 lbs. in a 2000 psi. concrete foundation. The anchor diameter will be 7/8" and the holes to be drilled in the concrete will be 1" in diameter. Using the strengths of this anchor system it was then possible to calculate the plate widths. By calculating the total moment at the crane base and inserting this into a static model it was found that the minimum widths of the plate need to be 4.63’ x 4.63’ using eight epoxy anchors. [See Analysis for the plate widths below] Welding An A.W.S. E60xx weld was specified during the design process. The height of the fillet weld must comply with the failure analysis calculations as well as A.W.S. standards [5]. Therefore, the final height of the weld was determined to be 3/8". [See Weld Analysis below]  

Calculations
 

Weight of I-Beam

Analysis for the Plate Widths

Analysis for the Plate Thickness

Concrete Counter-Balance

Weld Analysis