A 4-T crane is used to lift a 3m x 1.2m x 200mm pre-c panel. A spreader beam is needed to ensure the prope distribution of load in the lifting chains. Consider modulus of elasticity, E=200,000 MPa, allowable shearing stress of lifting pin is 50 MPa, the steel plate used in the spreader beam has an allowable bearing stress of 40 MPa. ( All measurement in the figure is in millimeters)
Design Against Fluctuating Loads
Machine elements are subjected to varieties of loads, some components are subjected to static loads, while some machine components are subjected to fluctuating loads, whose load magnitude tends to fluctuate. The components of a machine, when rotating at a high speed, are subjected to a high degree of load, which fluctuates from a high value to a low value. For the machine elements under the action of static loads, static failure theories are applied to know the safe and hazardous working conditions and regions. However, most of the machine elements are subjected to variable or fluctuating stresses, due to the nature of load that fluctuates from high magnitude to low magnitude. Also, the nature of the loads is repetitive. For instance, shafts, bearings, cams and followers, and so on.
Design Against Fluctuating Load
Stress is defined as force per unit area. When there is localization of huge stresses in mechanical components, due to irregularities present in components and sudden changes in cross-section is known as stress concentration. For example, groves, keyways, screw threads, oil holes, splines etc. are irregularities.
![A 4-T crane is used to lift a 3m x 1.2m x 200mm pre-cast
panel. A spreader beam is needed to ensure the proper
distribution of load in the lifting chains. Consider
modulus of elasticity, E=200,000 MPa, allowable
shearing stress of lifting pin is 50 MPa, the steel plate
used in the spreader beam has an allowable bearing
stress of 40 MPa. (All measurement in the figure is in
millimeters)
1. Determine the required thickness (t) in millimeters of
the steel plate to be used if the allowable bearing stress
must not be exceeded.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F0f08c9ea-7f19-420a-92ba-3aa101d6cd58%2F8d5e0072-8d8c-4442-a3f4-b9ce48222be6%2Fo47pfo_processed.jpeg&w=3840&q=75)
![22
Lifting Pin
450
450
450
450
Spreader Beam
1200
6.25
Lifting Pin
41
Lifting Chain Spot Detail
Pre-CastPanel
2,300 Kg/cu.m.
Spreader Beam Cross-Section
Side View
Front View
00
Lifting Chain B
000€](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F0f08c9ea-7f19-420a-92ba-3aa101d6cd58%2F8d5e0072-8d8c-4442-a3f4-b9ce48222be6%2F93nd3ey_processed.jpeg&w=3840&q=75)
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