The same weight of round and rectangular steel tube bending Who better performance 
     The assumption that the length and width of rectangular steel tube 40 * 60 * 3.5 steel tube diameter is 60 * 3.5, the quality of their per meter are almost
Steel stand to place, who better flexural capacity?
     40 * 60 * 3.5 per meter weight 5.5KG, and steel tube 60 * 3.5 weight 4.88KG, although similar, but still can not compare, you have said if the beam used in the design of a reasonable amount, in fact, the two tube will not exceed its elastic phase, and the normal use stage, the corresponding formula for the greatest moment:
     Mxe = fy * Wnx, fy for the concentration of the house roof, Wnx to the X-axis of the net-section elastic modulus
     However, if more than the elastic stage, the cross-section shape factor γF on the shape of the cross-section, and with the nature of the material, have nothing to do outside the load, the rectangular cross-section of 1.5, 1.7 circular section, and the circular tube bending ability better, in fact, if the super-elastic stage, however, are the same, you are asked the purpose of loading it! Do not collapse like! ! Hei hei, I hope to help you!