Why the nodal displacement at the same floor different?

[tthdl]

Hello everyone.

I was doing a pushover on a 3 story 2 bay 2D RC frame with nonlinearBeamCoumn element, every beam/column was divided into 6 element.

Pushover Direction was from left to right, and columns from left to right was numbered as column 1,2, and 3.

I output the displacement of each column in each floor, but I found that displacement of the nodes in Column 1 was lower than in Columns 2 and 3.

Moreover, the base shear force of Column was also different, specifically, Col3>Col2>Col1.

It is normal? Or my model was wrong?

Please tell me. Thank you very much!

[selimgunay]

Differences of the nodal displacements are due to the axial stiffness of the beams. Beam axial stiffness is generally much higher than the column lateral stiffness, but it is still a finite value and this causes the differences at the two ends of a beam (or the top of the columns). It depends on the size of the beam, but these differences should be small.

If all three columns have the same size, shear force of the interior column should be higher than the shear force of each of the exterior columns at the first few steps of the pushover when the response is elastic, because the interior column is stiffer due to the two beams connecting to it at the top, versus one beam connecting to the exterior column. With the same size columns (and same reinforcement if RC), the moment capacity is affected by the column axial forces. In addition to the compressive forces due to gravity, lateral loading causes compression in column 3, tension in column 1 and small axial force in column 2. Under the balanced point, moment capacity increases with axial force, which may explain why the base shears at the inelastic steps of pushover are Column 3> Column 2> Column 1.

[tthdl]

Thank you very much selimgunay! Your reply really help me a lot!