Analysis of Continuous Fixed Beam 1

[Nargo7]

I have been assigned the task to analyze the supporting structure of a gantry crane but, being a mechanical engineer, I need to find the applicable methods to determine shear forces and moments on all elements. The supporting structure of the movable bridge beam, as I show in the picture below, is composed of two runway beams joined to three support beams, which are joined to six columns. All twelve joints are rigid, each one made with four bolts. Years ago, I calculated continuous beams using the Three Moment Theorem, but in internet I only find this method applied to beams with more than two simple supports (one of them pinned), but not three fixed supports like in this case. I don’t know how to analyze a 3D structure composed by seven rigid frames joined together, and the company where I work does not have any analysis software. My second question is, after knowing the reaction moments and shear forces at base plates of columns, I need to calculate tension forces at the anchor bolts to the floor. I will have to assume the worst concrete, 2,000 psi, as we don’t have the construction drawings of the building. Any help will be greatly appreciated. Thanks!

 

[r13]

Ron,

You meant the 10% longitudinal thrust on the runway rails (crane bridge travel transverse to the bent), yes, it has domino effect on all columns in the system. The 20% lateral thrust (crane stationery, trolley travel in direction of bent) will punish two columns in this case.

I agree with STrctPono that the runways beams are simply supported, thus need to pay attention to the positive moment and deflection.

 

[r13]

Nargo7,

Just to make sure we understand each other. Note the distance "a" can conservatively taken as "0", the physical limits of trolley dimension, or suggested by the manufacture.

[ADD] From the sketch, it is understand that all columns need to be fixed in both directions to resist the shear and the bending moment. Otherwise, the frame will be shaking badly, if not collapse. Also, when check the runway beam, don't forget to check effect of fatigue due to cyclic loading/unloading (in this regard, I think the simply supported beam has some advantage over continuously supported beam, as there is no stress reversal in the former case).