huangyhg

request for correct way to model beam / shaft forces (specia
hi everyone,
i would like to ask if anyone could please help me with the following problem.
if you go to this link
sum moments about each bearing to find the load on the other. the two loads you get should total up to the applied load- there isn't any additional load. the bearing loads you calculated are vertical loads, up or down, at that point. for simplicity, treat them as point loads, though they would be distributed over some area in reality. you could actually develop a moment in one bearing (essentially a load up at one end, down at the other end) but don't have enough information to calculate that.
for modeling, treat it as a beam with simple supports at the bearing points, applied load at the end, no moments or torques. you don't need structural software but can use it if that's easier. add elastic deflection to the deflection due to slack in the bearings that you're calculating. there will be some additional deflection due to the bearings themselves, the support plate, etc.
maximum stress should be at or near the connection to the plate in either case; the moment is just the load times the distance. check on fatique stress as well as yielding.
it's possible you may yield the support piece rather than the pin, or may work the pin out of the hole under cyclic loading.
hi jstephen,
thanks for your reply.
>jstephen wrote:
>the bearing loads you calculated are vertical loads, up or >down, at that point. for simplicity, treat them as point >loads, though they would be distributed over some area in >reality. you could actually develop a moment in one >bearing (essentially a load up at one end, down at the >other end) but don't have enough information to calculate >that.
john2004:
using the formula i gave, could the load on bearing #2 be considered downward and the load on bearing # 1 upward ? would this be more accurate than modeling two downward loads ?
the housing / bearing loading seems the same as it would be if you would slide a hollow pipe over the shaft, with two contact points on the shaft, and then try to bend the shaft with the pipe. it seems the housing load is trying to bend the end of the shaft, between the two bearing contact points, in the same manner. with this in mind, i was considering modeling this in my beam design program as a torque moment, with the rotation axis in-between the two bearings, and the moment arm length running from the rotation axis to the housing loading point . is this wrong ?
i have been using point loads in the center of the bearings, to try to keep it as simple as possible.
>jstephen wrote:
>for modeling, treat it as a beam with simple supports at >the bearing points, applied load at the end, no moments or >torques. you don't need structural software but can use >it if that's easier.
john2004:
i'm not sure i follow you here. the shaft is cantilever mounted, and pressed into a steel support at one end. if i put simple supports at each bearing, in addition to the cantilever support at one end, it seems the beam will be to well supported to give an accurate model.
>jstephen wrote:
>sum moments about each bearing to find the load on the >other. the two loads you get should total up to the >applied load- there isn't any additional load.
john2004:
i'm not sure i completely follow you here. can i use the formula i gave, and/or the torque moment method i suggested, to get the bearing loads ? how do i calculate the moment about each bearing individually ?

thanks again for your help.
john

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