Moments of Inertia

1 / 17

# Moments of Inertia - PowerPoint PPT Presentation

Moments of Inertia. Polar moment of inertia – Used when calculating the torsion Indication of resistance to torsion Solid Shaft J = π R 4 / 2 Area moment of inertia – Used when calculating bending stresses Indication of resistance to bending moments I = π r 4 / 4

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## Moments of Inertia

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Moments of Inertia
• Polar moment of inertia – Used when calculating the torsion
• Indication of resistance to torsion
• Solid Shaft
• J = π R4 / 2
• Area moment of inertia – Used when calculating bending stresses
• Indication of resistance to bending moments
• I = π r4 / 4
• Polar and area moments of inertias use a variety of different formulas
• For example, solid versus hollow
Cranes and Slings
• Major Causes of Crane Accidents
• Contact with power lines
• Overturns
• Falls
• Mechanical failures
Rated Capacities
• Make sure the crane operator can see the:
• Operating Speeds
• Special Hazard Warning or Instruction
• APPLICABLE OSHA STANDARD
• 1926.1501 (a)(2) Rated load capacities, and recommended operating speeds, special hazard warnings, or instruction, shall be conspicuously posted on all equipment. Instructions or warnings shall be visible to the operator while he is at his control station.
Know the Weight of the Load
• Refer to shipping ticket or other documentation
• Ensure lift calculations are correct
• Crane is rated by the maximum weight it will lift at a minimum radius and minimum boom length – the further from its centerpoint, the less it will lift
• Not level
• Wind
• On its wheels
• Lifting over the side
• Use of extensions, jibs and other attachments
• Limits of wire rope, slings and lifting devices
Load Example – 30 ton crane
• Will lift 60,000 pounds at 10 feet from the center pin of the crane
• Based on level surface, no wind, and outriggers fully extended
• At 25 feet from the center pin with an 80 foot boom, the capacity is only 14,950 pounds
• At 74 feet from the center pin, the capacity is only 4,800 pounds

Alloy Steel Chains

Can damage by sudden shocks

Best choice for hoisting very hot materials

Must have an affixed tag stating size, grade, rated capacity, and sling manufacturer

Wire Rope Slings
• Used to hoist materials
• Selection considerations:
• strength
• ability to bend without cracking
• ability to withstand abrasive wear
• ability to withstand abuse

Wire

Core

Center

Strand

Wire rope

Synthetic Web SlingMarkings
• Mark or code to show:
• Name or trademark of manufacturer
• Rated capacities for the type of hitch
• Type of material
Sling Stress Example
• From the table, a single branch with a 90 degree loading is rated at 3,250 lbs.
• If there is a safety factor of 4, the chain could lift 13,000 lbs before breaking.
• Two legs at 90 degrees would be rated at 6,500 lbs.
Sling Example
• From the table, a two leg sling that forms a 60 degree angle off of the horizontal is rated at 5,560 lbs.
• This means the most weight in this configuration the sling should be used to lift is 5,560 lbs.
• Preforming this list would result in what type of stress each leg?
• What if the sling were used to list 5,560 lbs and the angle off the horizontal were 40 lbs?