Width of a beam section

[MaryJ]

Could one of the structural experts help me with this strength of material problem.

How can I find the width -b- of a beam section if am given the followings:

Stress max= 108 mpa

I(moment of Inertia)= 1.0417E-5

Bendind moment (M) = 1125 KN*m

(NOTE c = centroid of section given

Wouldn't the height of the section must be given or you must be told that the length and width of the section given is the same dimension?

I am looking at this sample problem and swears that these information is missing from the question and is needed to solve the problem correctly, since the formula to use is:

Stress-max = Mc/I

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Say for example the section is given as h = 10cm then b can easily be found to be 12.5cm, but without h, there is no way to find b, correct.....

Thanks everyone...

 

[civilized_naah]

Could one of the structural experts help me with this strength of material problem.

How can I find the width -b- of a beam section if am given the followings:

Stress max= 108 mpa

I(moment of Inertia)= 1.0417E-5

Bendind moment (M) = 1125 KN*m

(NOTE c = centroid of section given

Wouldn't the height of the section must be given or you must be told that the length and width of the section given is the same dimension?

I am looking at this sample problem and swears that these information is missing from the question and is needed to solve the problem correctly, since the formula to use is:

Stress-max = Mc/I

Assuming ractangular: sigma = Mc/I ----> c = sigma.I/M = 108E6 x 1.0417E-5 / 1125E3

c = h/2 -----> calculate h ----> calculate corresp. b from given value of I

 

[MaryJ]

Could one of the structural experts help me with this strength of material problem.

How can I find the width -b- of a beam section if am given the followings:

Stress max= 108 mpa

I(moment of Inertia)= 1.0417E-5

Bendind moment (M) = 1125 KN*m

(NOTE c = centroid of section given

Wouldn't the height of the section must be given or you must be told that the length and width of the section given is the same dimension?

I am looking at this sample problem and swears that these information is missing from the question and is needed to solve the problem correctly, since the formula to use is:

Stress-max = Mc/I

Assuming ractangular: sigma = Mc/I ----> c = sigma.I/M = 108E6 x 1.0417E-5 / 1125E3

c = h/2 -----> calculate h ----> calculate corresp. b from given value of I

civilized_naah, thanks for your input.. Could you verify these...

So c= 1.00E-3

then h=2*c -------> 2*1.00E-3=2.00E-3

Now since the section is rectungar h=b=2.00E-3 ....correct? and no other calculation is required?

therefore if the section wasn't rectangular (i.e difference h and B) in shape then the formula to find 'b' would be I = (b * h^3)/12

or (12I)/h^3 =b ?

When I back calculate the answers came really close to 108E6, which appears to be correct....