## Model a diagonal gap

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

Moderators: silvia, selimgunay, Moderators

soroshaghabeigi
Posts: 2
Joined: Thu Mar 11, 2021 10:24 am

### Model a diagonal gap

Hi Engineers,

I would like to model a gap inside a truss. When the truss is horizontal, OpenSEES gives correct results. But it fails when the truss is diagonal or has an angle.

Consider a cantilever column and a truss, with two configurations: in Configuration 1 (Fig. 1), the truss is horizontal and in configuration 2, the truss is diagonal with an angle of 45 degree(Fig. 2).

In both configurations, there is a gap inside the truss with a gap distance of "D".

I modelled the gap with the ZERO-Length element and defined a PPgap metrail. For the diagonal configuration (Fig. 2), I also defined the gap orientation as below:

-Orient -1 1 0 -1 -1 0

Both trusses are subjected to a Horizontal force "F". Thus, for the horizontal configuration (Fig. 1), the gap is closed when the lateral displacement at the top of the column reaches "D". The model confirmed this.

However, for the diagonal configuration (Fig 2), the gap is expected to be closed earlier, say " D1 ". But I was not able to capture this in OenSEES. The gap works well in other software such as SAP, SeismoStruct, ANSYS, etc.

When the gap is horizontal, OpenSEES gives correct results. But it fails when the gap has an angle.

Any thought is appreciated. Did I miss something? or is there anyone else who had similar issues?

F ----> _ _ _ _ _ _ _ |gap| _ _ _ <|
|
|
|
|
|
|
|
|
|
|
--------

Fig. 1 (horizontal gap)

F ---->
| \
| \
| \
| \
| \
| \
| /
| gap /
| \
| \
-------- -^-

Fig. 2 (diagonal gap)

selimgunay
Posts: 889
Joined: Mon Sep 09, 2013 8:50 pm
Location: University of California, Berkeley

### Re: Model a diagonal gap

Your model with the gap could be unstable when the truss is at an angle

soroshaghabeigi
Posts: 2
Joined: Thu Mar 11, 2021 10:24 am

### Re: Model a diagonal gap

Dear Selimgunay:
Thank you for your response.
actually, i got better results by changing the shear and the rotational stiffness of the link and using p-delta for geomTransf