Leaning Column Loading

[RaminZ]

Dear Opensees team members,

I have a question regarding leaning column modeling. What percent of the total gravity load on each floor should be assigned to the leaning column node on the same floor.

Imagine a 1-bay 2-story moment frame. Each of its four nodes has a gravity load = P . Then, what should be the gravity load on two nodes of leaning columns?

Is there a general rule for their loading and load combination?

Moreover, what is the difference between geomTransf PDelta and using leaning column? I mean, when should we use leaning columns to consider PDelta effect?

Thanks in advance,
Sincerely,
Ramin

[RaminZ]

Since no one has answered it yet, I am posting the answer that I received from someone expert in OpenSees.

""Leaning columns are aimed to represent the effect of gravity columns present in a 3-d structure but being neglected in modeling the system by including only the lateral system. Gravity columns are commonly encountered in perimeter or tubular systems and excluded from the model since they do not contribute in resisting lateral loads.
In a 3-d structure, however, the gravity columns tend to amplify the P-Delata effects posed on lateral load resisting system. That is, when the system deforms laterally, second order moments are excited at the base of gravity columns. Since these columns are not capable of resisting these moments, they can only remain stable by the aid of horizontal forces these columns exert on the lateral system. In other words, these columns lean on the lateral system to remain stable while displaced laterally.
So, when to use leaning columns? When gravity (pin-supported) columns of a 3-d structure are neglected in a 2-d model; and, what percent of story weight must be placed on these columns? The tributary area of the gravity columns and the ratio of this area to the total tributary area remaining after symmetry considerations are applied, will tell you this.
In a simple square plan in which only perimeter frames resist lateral loads, symmetry sais you should model one moment frame carrying half of the gravity weight imposed on the structure. For defining leaning columns forces, two scenarios are possible and accurate:
a) Apply 50% of story weight on the leaning columns and turn on p-delta effects for these columns and turn it off for lateral (main) columns;

b) Subtract the story weight tributary to the lateral columns (half of a bay) from the 50% above being applied on leaning columns and turn on p-delta effects for both leaning and lateral columns.""

[nilz]

what do you mean by "turn on and off" in the two scenarios ?
how can turn off or on p-delta effects in Opensees?

[selimgunay]

You can turn the p-delta effects on using the pdelta transformation. Please see the link below:

http://opensees.berkeley.edu/wiki/index ... sformation

[fmk]

To include PDelta effects in a 2d or 3d model the 2d frame takes that load the gravity framing puts on it (trib. area loading) (to put more than could actually come into the column can effect the result (think effect of different axial loads if a concrete column) .. as for how much goes in the leaner column (if 3d a sngle column down the cg of the building with all load not being taken by the frame) .. for 2d it depends on how many frames and what percent each column will take.

when using pdelta do include a rigid floor (otherwise the side of the frame you put the column on can in theory effect the result (think concrete frame again and how the PDelta loads get transferred through axial loads again to all the columns)

[hosnieh]

hi
I have 2D moment resisting frame model with p delta effects .
how should assign mass and loading of frame and leaning column from 3D structure????