Considering P-Delta Effects in bracing frames

Forum for OpenSees users to post questions, comments, etc. on the use of the OpenSees interpreter, OpenSees.exe

Moderators: silvia, selimgunay, Moderators

Post Reply
afshina
Posts: 15
Joined: Sat Aug 23, 2014 4:55 am

Considering P-Delta Effects in bracing frames

Post by afshina » Thu May 28, 2015 12:26 pm

Heloo
Please Explain to me This Matter:
How do i Consider P-Delta Effects (Large P-Delta) in a bracing frame without Using Leaning Column Algorithm (Mrs-Laura Eads, Stanford University, 2010 ).
Because it Seems that way is Just for moment frames.
Thanks a lot

fmk
Site Admin
Posts: 5866
Joined: Fri Jun 11, 2004 2:33 pm
Location: UC Berkeley
Contact:

Re: Considering P-Delta Effects in bracing frames

Post by fmk » Thu May 28, 2015 2:06 pm

it is not just for moment frames! .. why would you think so?

afshina
Posts: 15
Joined: Sat Aug 23, 2014 4:55 am

Re: Considering P-Delta Effects in bracing frames

Post by afshina » Sun May 31, 2015 8:05 pm

Dear, Thanks a lot for your reply.
I thought that way is just for moment frams , Because I have following opacities in this field. Please help to my understanding:
1- we have a bracing frame that columns are pinned at bottom. Must We add leaning column for Simulating P-Delta effects with changing pinned base columns to fixed base columns ?? (Beacause leaning column is pinned at base)
2- Mrs-Laura Eads (Stanford University, 2010) didn't apply all of Frame’s Gravity Loads to Leaning Colums’s points For Simulatig P-Delta effects. She applied a ratio of Gravity Loads to Leaning Columns’s points and applied remaining amount to beam-column intersections of frame. And so she didn’t any explain about this Separation. Please explain this matter to me.
3- I want to use element nonlinearBeamColumn with Fiber Section instead of element elasticBeamColumn for beams and columns , could I erase this Part <<Define Rotational Springs for Plastic Hinges>>??
Thanks a lot.

fmk
Site Admin
Posts: 5866
Joined: Fri Jun 11, 2004 2:33 pm
Location: UC Berkeley
Contact:

Re: Considering P-Delta Effects in bracing frames

Post by fmk » Mon Jun 01, 2015 9:20 am

1) the PDelta column is for including the effect of the gravity frame PDelta effects on the lateral system .. whether the lateral system is pinned or fixed at the base has no bearing on their use.

2) the PDelta loads that are applied are for that portion of the gravity framing system that the lateral system is responsible for, e.g. if external moment frame building, there would be 2 2d moment frames, each taking half the PDelta loads, a portion of this 1/2 will be loads on the moment frame itself and so would not be added to loads on the leaner column.

3) just swap out the hinges and elastic ea columns and replace with force beam column elements.

afshina
Posts: 15
Joined: Sat Aug 23, 2014 4:55 am

Re: Considering P-Delta Effects in bracing frames

Post by afshina » Thu Jun 04, 2015 3:14 pm

Dear, Thanks a lot for your quite complete response
Now, I have some opacities, Please help to my understanding:
1- It means that in a braced frame we must apply all PDelta loads to leaning column’s nodes. Is it right?
2- I want to know about effect of this leaning column in Capacity Curve’s shape. It Seems that adding Leaning column increases Total Base shear Forces. So, in case of using leaning column if we sum amounts of leaning column’s base shear and other columns’s base shear, we will have larger capacity curve .
In other words, since Mrs-Laura Eads (Stanford University, 2010 ) proposed that : << These columns have moments of inertia and areas about two orders of magnitude larger than the frame columns in order to represent aggregate effect of all the gravity columns (Aleaning column= 1,000.0 in^2 and Ileaning column = 100,000.0 in^4)>>, it causes a very large base shear for leaning column and we have two or three times larger capacity curve. Do you have any idea about this matter?
3- In this Algorithm we must calculate masses of Floor’s nodes from seismic weight of floors By using acceleration due to gravity.
I want to know if we have two braced frames located at the perimeter of a building for each direction, Should we put total seismic mass of building on external braced frame’s nodes ?? (Or Just should put actually seismic mass of each frame on its nodes)
4- in Pushover Analysis of each building’s braced Frame, Which gravity loads should we put on the braced frame? (gravity loads of bay near braced frame ….or…. gravity loads of overall plan) ,, And which load Combination must consider for gravity loads case in Pushover Analysis ?? [(DL+LL) or (1.2DL+LL) or (0.9DL)]
Thanks a lot again, Dear.

baikunthasilwal
Posts: 24
Joined: Wed Feb 20, 2013 4:23 pm
Location: University of Virginia

Re: Considering P-Delta Effects in bracing frames

Post by baikunthasilwal » Fri Jun 19, 2015 4:59 am

Hi,
1. You have to apply the portion of the gravity load that comes from the space frames in between the moment resisting frame. It means that the gravity load that comes from the moment resisting frame along the perimeter should be applied in that perimeter MRF. Then, the remaining gravity loads of the frame should be applied on the leaning columns.

2.Since adding leaning column increase the total base shear, the actual base shear of the MRF can be calculated summing all base shears comes from the columns including leaning column and then deduct the P*deflection/H to get the actual base shear.

3. Please clarify about your statement what are you doing here calculating mass or other forces using g or applying mass or forces.

4. The gravity load of the perimeter MRF should be applied in that braced framed. Please see the clarification in statement 1.

afshina
Posts: 15
Joined: Sat Aug 23, 2014 4:55 am

Re: Considering P-Delta Effects in bracing frames

Post by afshina » Thu May 05, 2016 8:49 am

Thank you Dear, Thanks a lot.

Post Reply