Beam-Column joint modeling in SAP2000

[Lorenzo_S]

Hi everyone!
Maybe this is easy, but it's giving me some trouble. My intent is to model a 2D beam-column joint so as to have the continuous beam only propped by the column, with no bending moment transission from one ement to the other. Both beam and column are continued across the joint, i.e. the node is an internal one to the structure.

Thank you in advance for any help provided.

 

[BAretired]

Use a steel channel, pin supported each side of the column.

BA

 

[Lorenzo_S]

Hi BAretired and thank You for replying so quickly. Your advice is good and I appreciate it, but also I must tell you that I am mandated to use I-beams on both sides of the column (actually, it would be a unique I-beam crossing the column).
My question is more relative to the software usage than the design issue itself.

 

[BAretired]

Maybe this is easy, but it's giving me some trouble. My intent is to model a 2D beam-column joint so as to have the continuous beam only propped by the column, with no bending moment transission from one ement to the other. Both beam and column are continued across the joint, i.e. the node is an internal one to the structure.

You can model a structure with a continuous beam and column, intersecting at a joint. The beam can be specified to be pin connected to the column at that joint by giving it freedom to rotate but not to translate relative to the column.

To build that structure requires either a double column or a double beam, as it is not possible to have the beam running through the column without transmitting a moment.


BA

 

[Lorenzo_S]

Hi again BAretired, and sorry if I'm always so late with my replies. I did some research and finally found this very enlightening explanation, given by CSI itself, whose link to the website I levae here for You to check, if You wish to do so.

https://wiki.csiamerica.com/display/tutorials/Modeling+a+pin+connection+between+crossing+members

Thank you again for the time You dedicated to answering my question.

 

[BAretired]

Interesting, Lorenzo_S. Better late, having thought about the problem than an instant response without giving it a thought. I have not reviewed your file thoroughly, but would make the following preliminary observations.

1. The structure in Fig. 1 cannot be built as shown, without introducing eccentric moments because members are not aligned. If you are planning to use I-beams, the eccentricity will be equal to the width of flange. Bending moments or torsional moments will exist in some members (and I-beams are not noted for their torsional resistance). It is not readily apparent how the eccentricities can be avoided, but I expect it can be done using double members.

2. The vertical reaction at B is 100kN by inspection, so the moment at E is clearly 300kN-m in both member BED and CEF (where F is the end of cantilever).

3. Step 7 should read "Assign a pin support to joint 1, and a roller support to joint 5, not 2"

It would not have occurred to me to use four joints at Point E. I was thinking of two joints, one connecting BE to ED, the other connecting CE to EF. That would require one more member connecting the two joints with translation prevented but rotation permitted.



BA

 

[Lorenzo_S]

Thank You very much for your precious remarks, BAretired. And yes, the example I posted is nothing else but a case study, yet quite useful in its explanation on how to realize joints like the ones I need in my actual job. The four joints that appear at point E are soon after merged by twos to give two joints, which are in turn constrained to have equal displacements.

The real structure would certainly be affected by the presence of eccentric moments, unless use is made of coupled members (as You said). In my case, the analysis gives good results thanks to the fact that I can restrict it to the 2D plane. The bending moments You envisage are the right ones and, should You wish to do it, You could also go about downloading the entire SAP model at the same link I left in my previous reply (go to the bottom of page). I double-checked it by hand computation and everything seems to work correctly.

 

[BAretired]

You are welcome, Lorenzo.

BA