Shear Force & Bending Moment Diagrams

Depending on the location of the winch loads and stresses will vary. I have illustrated the shear force and bending moments on the beam.

The beam length will have to extend past the 4 metre distance required to move the load and so 4.2 metres has been selected.

The problem which may arise during practical use of the gantry is at the midpoint. A 4metre beam will not be able to be transported manually and therefore a break will be present in the finished crane. At this point the loads will be exerted on the method of joining and could create loads unsustainable by the joining method.

The weight of the beam has been selected from existing beams. The beams researched are used in portable gantry cranes and are light weight with the sole purpose of manual assembly.

With constant movement of loads across the vertical beam fatigue could be an issue. Fatigue will be cause by continually changing loads on the crane.

It can be seen from the Diagrams shown that higher shear forces and bending moments will be present towards the location of the load. If this continually changes the beam could fail under fatigue stress and so the lifetime of the crane will be dependant on the ability to withstand this factor.