Three unequal supports, two concentrated loads problem..
Three unequal supports, two concentrated loads problem..
(OP)
Attached is a loading diagram that I have come across for a test gantry we are building.
I have not come across such an abnormal loading set-up before, and cannot find any literature that addresses my problem ie. shear and bending moment diagrams and Max shear and bending moment.
Can somebody please help me?
Regards.
I have not come across such an abnormal loading set-up before, and cannot find any literature that addresses my problem ie. shear and bending moment diagrams and Max shear and bending moment.
Can somebody please help me?
Regards.






RE: Three unequal supports, two concentrated loads problem..
Your beams statically indeterminate, have a look at this site and scroll down to the "three moment equation" "under continous beams"
thats a theory you could use.
http:/
desertfox
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
Regards.
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
As hokie66 noted...routine analysis.
RE: Three unequal supports, two concentrated loads problem..
Try this free online calculator for continous beams:-
http:
but remember to check it against a hand calc.
desertfox
RE: Three unequal supports, two concentrated loads problem..
Anyone care to donate an example of a hand calculation of this?
Regards.
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
Is your structure a trailer with an 80 ton load on it, composed of the two 40 ton line loads across the trailer? Are reactions R2 & R3 actually axle sets supported by springs or air suspension? The trailer is a beam with some elastic stiffness, and R2 & R3 are reactions with some spring stiffness. And, there should be compatibility btwn. the beam and those two reactions as they deflect under the load.
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
There is only a 4000 mm working span of which we can place the item to be tested.
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
If it were routine there would be tables set up as there is for simply supported beams...
Anyhow - I'll stay in touch
Regards.
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
One might ask how you get two 40ton downward loads from an 80ton hydraulic ram pushing up on your beam? Then, one might ask, if you are designing and going to build this testing structure (gantry) why are you going out of your way to make it more complex by making it indeterminate? Finally you might want to consider getting an engineer involved in this design and analysis if the good suggestions above are meaningless to you. Most engineers, during their careers, run across several problems which aren't exactly covered by an example problem in a text book or covered by a tabulation which fits every possible problem and condition. Real engineering involves engineering experience and judgement, which is gained by practicing real engineering, and during the early stages of this development a local mentor is really beneficial. You can both be looking at the same specs. and drawings, do some quick sketches on the spot, and he/she can direct you where to look and how tackle exactly this kind of problem.
RE: Three unequal supports, two concentrated loads problem..
I am looking at solving your beam, perhaps tomorrow or saturday i might get to post a solution.
desertfox
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
i think you may have been looking for precisely this problem but the general problem (an indeterminate beam) is (should be) in just about every textbook. the 3 moment equation works well (looks a little scary but it is easy to apply), unit force method is an approach i'd use. google "indeterminate beam", "3 moment equation", "unit force method".
RE: Three unequal supports, two concentrated loads problem..
If you will use plastic analysis there is very simple method related to work or energy (don't remember the exact name). you can solve this problem in a half page or less by that method.
Note (As I understood, the loads are not moving, if they moves you might need to draw the influence line).
Regards
RE: Three unequal supports, two concentrated loads problem..
try to get this book:
Plastic methods for steel and concrete structure - by Stuart S.J.Moy.
The method written in my previous post is (virtual work method).
It allows you to find the collapse load, then you can compare it with the applied loads. or If you want the applied loads to be the collapse load you can find the plastic moment then determine the steel section to be used.
regards
RE: Three unequal supports, two concentrated loads problem..
BA
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
-- MechEng2005
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
BA
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Three unequal supports, two concentrated loads problem..
BA
RE: Three unequal supports, two concentrated loads problem..
RE: Three unequal supports, two concentrated loads problem..
My soluton as promised, my answers are those of handex.
Also if you convert your beam to english units and use the on line calculator I provided you will obtain similar results, I say similar results because you can't place more than one point load per span, just put a resultant force of 80T on span 1.
desertfox
RE: Three unequal supports, two concentrated loads problem..
Folks - to say that I am overwhelmed by the responses is an understatement! Thank you all so much for your advice, concern etc.
I got the exact same result as handex with the Space Gass model, so am confident with its accuracy. I am still battling with the hand calculation to be honest, but when I get some time (after hours) I will sit down and nut it out.
I have attached a photo of the frame in question. We are widening the "working area" to four metres so wanted to check for Max. Bending Stress. I have spoken to another Engineer - one with a little more structural experience than I, and he has told me that two "310 UC 118" members welded side by side will be more than enough, so all good. This is a stock Australian Standard beam. "Full penetration weld all around" of course.
Looking forward to my next encounter with this forum.
Regards.