How Much Dead Load Can a Square Cross-Section Beam Support?

[rad10k]

Can someone please give me and equation for solving the following question. Q. A beam has a solid square cross section of 100mm and is simply supported by two supports 3m apart. Calculate the dead load that can safely be supported when applied to the middle of the beam?

 

[john.phillip]

http://www.efunda.com/formulae/solid_mechanics/beams/casestudy_bc_simple.cfm

 

[PhanthomJay]

You can't calculate the safe load without knowing the safe allowable stress for the material. Please show an attempt at a solution.

 

[rad10k]

thanks , Does this mean the question is incomplete as I need to know the type of material used for the beam? I really consfused with this question and the coursework doesn't have any examples of this.

 

[PhanthomJay]

thanks , Does this mean the question is incomplete as I need to know the type of material used for the beam? I really consfused with this question and the coursework doesn't have any examples of this.

That's correct. A hi strength steel beam can safely carry about 5 or 10 times the safe load of a wood beam with the same cross section and length. You need to know the allowable safe stress of the material. Once that is known, then you can calculate the value of the max point load at the center, P, by finding the moment and stress produced by that load , as a function of P and the the given properties (you need to calculate I) of the section, and set it equal to the allowable stress to solve for P.

 

[rad10k]

thank you very much. This makes me think that this question in my course work is incomplete too " A mild steel columm of cross section 100mm x 50mm Assume a safety factor of 6, calculate the safe load it can withstand? " from this I decided to use rankine's formula for columms Oc=510 A=5000mm2(not sure if that is the correct square mm for xsection) divided by K=6 x [1+{a=7500(A mutplied by Ee(WHICH IS EQUIVLENT LENGTH IN MM -- THE QUESTION IS THE ONLY QUESTION IN THE COURSE WORK WHICH DOESNT GIVE THE LENTGH OF THE COLUMM IN QUESTION -- AM I BEING STUPID OR IS THE QUESTION MISSING THE INFO?) then divide all this by I = 104666.7 and the answer is given. thanks for any help. I have noticed some of the progress check questions were wrong and a tutor confirmed one of them. I don't want to waste time wondering why I casnt find the answer if its the course work that's wrong!

 

[PhanthomJay]

You can't determine the critical buckling load without knowing the end conditions and the column length. I suppose tou can look up the other properties of mild steel, like max stress and Young's modulus, but you definitely need to be given the length and end conditions.

 

[rad10k]

thanks jay that's saved me a lot of time trying to work out why I can't solve the problem )