1. Sep 20, 2011

### 1884ram

1. The problem statement, all variables and given/known data

A mild steel beam has a solid square cross section of 100mm and is simply supported by two supports 3m apart. calculate the dead load that can be safely supported when applied to the middle of the beam?

2. Relevant equations

3. The attempt at a solution

given data:

square cross section of 100m

Ultimate strength in bending is σb = 450N/mm2

Ultimate shear in strength = Tut 320 N/mm2

The maximum bending moment is under the load

So from the bending formula
Bending stress (σb) = P / A

A = Area of cross section

= 450 x 1002 / 4
= 1125000N (1125KN)

Can anyone confirm that this is the correct answer.

2. Sep 20, 2011

### nvn

1884ram: That currently looks incorrect. It looks like you have the wrong formula for bending stress. Find the correct formula for bending stress, and keep trying.

By the way, N/mm^2 is called MPa. Use the correct unit symbol, MPa. Also, the unit symbol for kilonewton is spelled kN, not KN. Always use the correct capitalization. Also, always leave a space between a numeric value and its following unit symbol. E.g., 3 m, not 3m.

3. Sep 21, 2011

### 1884ram

I have looked into some other equations and i have found the following:

M / I = σb / y = E / R

(PL / 2) / a4 / 12 = σb / y

Are these correct?

I have tried to use these formulas to calcualte dead load but not sure what the E and R values are:

M = 480 x 166 666 / 4 = 1 999 992 0 / 1000 = 1 999 9.92 N m

I = 1 / 12 x 100^4 = 8 333 300 mm^4

σb = 450 mpa

y = 1 / 2 x 100 = 50 mm

E =

R =

L = 100