Moment Frames

[BAGW]

Hi,

I am analyzing moment frames in FEM. Its a 8 bay moment frame. First column and the intermediate columns pretty much have the same shears. I am not able to understand why this is happening. I was expecting first column to see 50% shear as compared to intermediate columns. Any comments? I have a felling this behavior is because of rigidity in the frame rather than hinge formation at the center of column like in portal analysis.

 

[dik]

it's a measure of the deformation... and, depending on stiffness, deformation may be similar.

Dik

 

[KootK]

The portal frame method presupposes relative beam & column stiffnesses within a certain range and, if you're well outside of that, it's reasonable to expect deviation. Any chance your beams are very stiff? As an extreme example, consider what would happen if your beams were infinitely stiff. All of your columns would attract the same shear and that would be altogether reasonable. We might be able to provide better assistance with some additional detail such as:

1) Bay width
2) Frame height
3) Beam size
4) Column size
5) Number of stories
6) Assumed based fixity
7) Locations of column inflection points

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.