Statically indeterminate beam problem

[sethmcnear]

I have a beam 85.4 inches long that is fixed at one end. There is a load of 600 lbs at the other end. It is supported by a pin support (0 defelection) at 6.8 inches from the fixed end. I need the reaction forces at the fixed end, at the support and the moment at the fixed end. I have done the calculations and gotten the following:

Reaction at fixed end: -10,404 lb
Reaction at support: 11,004 lb
Moment at fixed end: 23,587.2 inlbs counterclockwise

It's been a long time since I've done this and want to check my work.

Thanks,
Seth

 

[sethmcnear]

rb1957: I'm assuming that you mean "squat" as in that's not a lot of stress? What do you have the yield stress of HRS being? The person who did the previous calculations used 39ksi, giving a safety factor of a little more than 2. We need a safety factor of four. I assumed his number was correct. Is it wrong? I'm thinking it may be because when I look up the elastic strength of HRS I get between 62 and 76 ksi depending on % carbon.

 

[rb1957]

if HRS is Hot Rolled Steel, then i think your numbers are good (for me, i'm gauging against 4130N which is 75ksi). you can see both calcs, and so can see the differences and judge which is more appropiate. i'm guessing that the other calc assumed that only a potion of the thickness (maybe 50%) is effective.

in my business i only need a safetey factor of 1.5, so 15ksi is no problem.

back to your problem, this is a simple linear bending anaylsis. You could try a plastic bending analysis, this'll increase the allowable alot.

a couple of design ideas ...
a) you could extend the top surface of the tube back, so that it covers the top of the vertical post. this would give you twice the weld area (compared with the end edge of the tube), and the welds would be in shear.

b) are you married to the weld concept ? given your forces, i'd have thought a fastener group would accomplish the end joint more effectively.

c) is weight an issue for you ? add lightening holes in the webs.

good luck

 

[sethmcnear]

Yeah, HRS is hot rolled steel. I'll have to doublecheck the numbers again I guess. Thanks for your suggestions.