fixed beam-to-column

huangyhg

fixed beam-to-column
hi,
i am just curious what is your opinion: in global analyse of structure beams and columns are represented its axes. generally when i perform a calculation of connection i take internal forces from theoretical intersection of beam and column axes. i am just thinking if it is ok to consider that beam is actually conected on column flange and based on this if it is ok to take the value of bending moment in hc/2 distance from theoretical column axe instead taking the value directly from intersection. what do you think ?
primary i am looking for suggestions consistent with ec3-1-8, but any opinion is welcomed.
lubo
only hope you will understand my poor english...
in the risa analysis program (and perhaps some other programs also) there is a way to identify rigid offsets at joints.  these are specified lengths of the ends of the beams and columns that are considered infinitely rigid for analysis purposes.  
thus, the bending moments in the beams and columns are taken at the ends of the offsets.
for example.  you have a 14 inch column with two 18 inch beams framing into it.  the rigid offset length on the beam would be 1/2 the column depth or 14/2 = 7 inches.

yea, i know that ram structural system takes this into account. so, in reality, moment will be introduced into a gravity column based on the eccentricity of the connection.  i usually neglect this for low-span construction.  this is one of the reasons, my bosses don't like to push columns to unity stress ratio.
one thing to note is that, in general, the moments for an interior column will balance out since you will usually have framing from each side to cancel out.  one instance in which i could see it being very significant would be the corner column of a mid-to-high rise building.  the moments would add up significantly over the numbers of stories and biaxial bending could be an issue.