oversized columns

[Chster6]

For oversized columns (where it is made larger than needed), can someone confirm that the beams framing into it indeed suffer greater moments during seismic activity?

 

[dtex]

You need to give a lot more information:

Is this a simple house type of structure, or a medium to large building or a bridge or what? What materials are used? What type of connections are used between columns and beams? What are the relative spacings of members relative to each other? All of these things must be considered before even attempting to answer your question.

For non-simple structures.... I generally like to analyze models rather than simply rely on my engineering judgement about such things. I find loads and forces often have a way of doing things other than what you think they are going to do.

Dan

 

[SteelPE]

I always thought forces in frames were distributed to members based upon EI/L? Unless this is a code specific thing (ACI,AISC etc...). More information is required to answer your question.

 

[Chster6]

Create a simple concrete beam and columns at etabs. Subject it to seismic loading. When you change the size of the columns bigger, the beams framing into it has bigger moments.. so oversize columns can introduce higher moments to the beams?

 

[TXStructural]

This depends on many factors. What you are seeing is likely a higher moment at the end of the beam due to increased rigidity of the column. This stiffness results in less column rotation - to follow (attempted) rotation of the beam-column joint due to forces in the beam. Also, in resisting lateral forces, the columns are part of the frame that is attempting to sway. The sway is not a pure lateral translation (particularly near the lower floors) so the lateral movement causes columns to lean, rotating the beam-column joints, which becomes forced bending in the beams. This will not be the same in all columns and beams as you move up the building, so the statement you make in the first post is not universally true.