dann2707 Posted April 14, 2013 Report Share Posted April 14, 2013 Hey. The final touch for extra marks on my report for tomorrow is to work out the actual maximum bending moment from a bridge beam. Can anyone tell me what is it or how to work it out? The two upwards facing arrows are where the supports are. Cheers! Quote Link to comment Share on other sites More sharing options...
forteh Posted April 14, 2013 Report Share Posted April 14, 2013 Maximum bending moment to achieve what criteria? If the maximum stress exceeds the yield stress it will plastically deform, if it exceeds the ultimate tensile strength it will fail. To calculate it you would need to know what material it is (in other words know the yield and ultimate strengths) and what the section size and loadings are. If you don't know this information then it can only be a hypothetical answer 1 Quote Link to comment Share on other sites More sharing options...
bing Posted April 14, 2013 Report Share Posted April 14, 2013 (edited) You need to know the properties of the material you are trying to bend, or as the lad says, it can only be an Estimate/hypothetical answer. The base information has to be accurate, or the force you would need to use would be too much, or not enough. Edited April 14, 2013 by bing Quote Link to comment Share on other sites More sharing options...
dann2707 Posted April 14, 2013 Author Report Share Posted April 14, 2013 The beam is made from square hollow section steel. I know some other figures that we were given / ive worked out M: The max bending moment = 400Kn/m (this figure is given to us but we are supposed to work out the actual max bending moment) Ixx: The total second moment of area = 29.71 x10^-3 m^4 y: Distance between neutral axis and bottom of the lower beam = 0.875m E: Youngs modulus = 207 Gn/m^2 Quote Link to comment Share on other sites More sharing options...
Pete.M Posted April 14, 2013 Report Share Posted April 14, 2013 (edited) σ = y F L / 4 I So 8.84 MPa I think... EDIT: oops I worked out max bending stress rather than moment 2nd Edit: I think max bending moment is actually quite simple for this simple beam. M=FL/4 -> 300KNm I think.... Edited April 14, 2013 by Pete.M 1 Quote Link to comment Share on other sites More sharing options...
munkee Posted April 14, 2013 Report Share Posted April 14, 2013 For a simply supported beam in that instance the maximum bending moment would be at the center. Pete was close with PL/4 however that is not your max. That will give you the moment for just the point load. You need to also take in to account the UDL. Max = PL/4 + WL2/8 Quote Link to comment Share on other sites More sharing options...
dann2707 Posted April 14, 2013 Author Report Share Posted April 14, 2013 Thanks a lot! What do the P, L, W stand for? Guessing L is length Quote Link to comment Share on other sites More sharing options...
munkee Posted April 14, 2013 Report Share Posted April 14, 2013 P = point load force L = beam length W = UDL Quote Link to comment Share on other sites More sharing options...
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