Over estimating loads in Robot Structural Analysis

[NOONEDASK]

Robot Structural Analysis is over estimating loads in at least 10%. In an excersise, i have performed of a pretty simple structure where the spans are 5mx5m, without considering the self-weight and single-story. I have used panels for two-way distributed load and the value of this load is 200kgf. The column in the middle (axels 2-B) should have to support the load of 5mx5mx200kgf=5000kgf but as can be seen is 5537.87kgf. This means that the distribution and calculation of the loads transferend to columns is at least 10% OVER. So be carefull with the results. This over-estimated load seems to be reducted while the number of floors are added. Lets say, if a single-story is added, wich means that we have a two-story structure, the load in the base of the column in the first floor should be 10000kgf and with the 10% of the over-estimated load should be aroud 11000kgf, but instead is 10655.48kgf. A three-story structure under the same conditions should have a reaction in the same column of 15,000kgf, again, the reaction is 15664.77kgf.

[Rafacascudo]

If the connections between columms and beams are fully fixed , then it is a hyperstatic structure and results may be correct.

If it is not the case , zip and attach the model

[NOONEDASK]

Thaks for the answer Rafacascudo. I have attached the models, one is the single-story model and the other one is a two-story structure. I think there is no difference for the axial load in a column if the connections are released or fully fixed in this case because the load tranfered to the columns comes from the direct shear force acting in the beams, and this shear force comes from the load aplied to the beam. So this aplied load comes from the direct distributed load from the panel. Since the beams have the same span length, then the applied load should be equally transfered to the beams wich leads to think that the column in the axels 2-B have to support the magnitude 5000kgf. Please let me know if this logic is wrong or if i missed something else.

[Rafacascudo · Accepted solution]

I am sorry but Yes , this logic is very wrong!!!

If right, a  2 span continuous beam with equal uniform distributed load on the 2 spans would give half of the total load to middle support reaction , which is obviously not true.

As I said before , your logic would be right if the connections of the beams were not fixed. Releasing the beams moments you will get the reactions you imagine