Crane
File: PVE-424
Last Updated: Dec. 16, 2003
LB
The Problem:
A 250 foot wide, 85 foot high, 90,000 lb capacity freight handling crane had cracks in its main structural girder under both the main and balancing wheels along most of its length. Repair welding was tried but the crane was re-cracking in the same locations after short periods of use.
Finite Element Analysis was considered to escape the continual repair cycle. Could the crane design be modified to eliminate the need for repairs and to make the crane safe?
Analysis:
A plate model of the overall crane was used to check the overall stress in the crane from gravity, the trolley main load wheels, and from the reaction wheels.
The plate model allowed the interaction between the support legs and the crane to be accounted for. The highest stresses were found with the trolley in the center position shown below.
 Crane under gravity load - deflection is greatly magnified in this and the following shots. |
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 Trolley main wheel load: the trolley is at its centre travel position resulting in the highest deflection and stresses. |
 Trolley reaction wheel load: the trolley is at its centre travel position also the location of the highest deflection and stresses. |
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Brick models of one section of the crane girder were made. The original design and a series of design alternatives were checked. Various load conditions were checked with the wheels properly centered and also offset on the rails. The best design alternative was a modification where the original cracked plate material was removed and a new thicker plate was replaced. Several alternative repair plate thicknesses and heights were tried to get an optimum design.
The pictures below are for the girder under the main wheels - similar analysis was done for the reaction wheel stresses.
 Existing crane design - main wheel load on the brick model. Again deflections are highly magnified in this partial girder model. |
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 Different alterations were analyzed - this one with gussets on the inside and outside did not work. |
 The best design for the trolley wheel loads - the original cracked plate was replaced with a thicker plate. |
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 A comparison of the stresses in the original design and with alterations - trolley wheel loads. |
The Solution:
The design option where the original cracked plate was removed and replaced with new thicker material was adopted and the crane was repaired. The solution chosen cost less than any of the alternative considered prior to the start of the Finite Element Analysis, and it provided lower stresses. Without Finite Element Analysis, this solution would not have been considered.
Credits:
This analysis was commissioned by and the repair was done by Top Lift Enterprises Inc., 21 Teal Avenue, Stoney Creek, Ontario, Canada, L8E 2P1, 1-905-662-4137
This analysis was done in partnership with Reed Structural Engineering, 62 South Drive, St. Catherines Ontario. L2R 4V2. 1-905-688-3895
