1. The problem statement, all variables and given/known data Q: A beam has a solid square cross section of 100 mm and is simply supported by two supports 3 m apart. Calculate the dead load that can be safely supported when applied to the middle of the beam. * The question doesn't state material but I'm informed that it is mild steel. * Modules of Elasticity - E = 204 000 N/mm^2 (Stated in appendix of course book) Safety Factor - k = 4 (Stated in appendix of course book) Square beam - d = 100 mm (Stated in question) Distance between supports - L = 3 M (Stated in question) Average ultimate strength in bending = 480 N/mm^2 (Stated in appendix of course book) 2. Relevant equations Moments of Inertia - I = 1/12d^4 Moments of Inertia - y = 1/2d Maximum Deflection - Y = wL^3/48EI Maximum Bending Moment - M = wL/4 3. The attempt at a solution Ok, so my understanding of this question is that by calculating at what force the beam will fail then using the safety factor, divide this by 4. This problem has been covered in thread here www.physicsforums.com/showthread.php?t=463768 however there seemed to be a lot of confusion over the problem, without a resolve. Moment of Inertia to start then... I = 1/12d^4 1/12 = 0.0833 x 100^4 I = 8 330 000 mm^4 Maximum Deflection as far as can be solved... Y = wL^3/48EI wL^3 = w27 48EI = 48 x 204 000 x 8 330 000 = 8.156736 x 10^13 Y = w27/8.156736 x 10^13 It is around now that I loose myself and hit a wall. I don't understand how to extract w from the above without having Y, but can't get Y without w!!! Is there another way to calculate Deflection without a load?? I've searched the net and come in empty handed. I would like to solve this myself and therefore don't want an answer to the problem, just a kick in the right direction would be fantastic. Thanks in advance, Richard.