topic Re: Influence Lines on Trusses in Robot Structural Analysis Professional in Robot Structural Analysis Forum

Influence Lines on Trusses in Robot Structural Analysis Professional

ted.mckenna — Thu, 17 Oct 2019 08:16:36 GMT

Hi!

I'm using Robot to undertake 'Influence Line' analysis of various structures and have a number of issues which include the following:

1) Available guidance on how to undertake influence line analysis with Robot is extremely limited/non-existent - Do you know where I might find comprehensive guidance?

2) When undertaking influence line analysis on a pin-jointed truss, the load causes a moment in the diagonal members which should not be the case - How might I resolve this issue so that the moving load in applied to the bottom chord only?

Thank you in advance for any assistance offered.

Re: Influence Lines on Trusses in Robot Structural Analysis Professional

Rafacascudo — Thu, 17 Oct 2019 10:13:41 GMT

On moving load dialog window ,try selecting only the bottom chord as application plane.

Re: Influence Lines on Trusses in Robot Structural Analysis Professional

ted.mckenna — Thu, 17 Oct 2019 12:30:46 GMT

Hi Rafael,

Thank you for that suggestion, it seems to have worked. With this element now behaving as expected, I have moved on to viewing the Influence Line (IL) for the moving load. When viewing the IL for the top chord all appears in order as shown in screenshot #1 below, however, the IL for bottom chord as shown in screenshot #2 below. I welcome any suggestions on where I might be going wrong. Thanks in advance!

Screenshot #1

Screenshot #2

Re: Influence Lines on Trusses in Robot Structural Analysis Professional

Rafacascudo — Thu, 17 Oct 2019 15:24:15 GMT

It may seem strange , but for this particular truss geometry and load position , the result is correct. Calculate it manually and you will notice it.

Re: Influence Lines on Trusses in Robot Structural Analysis Professional

ted.mckenna — Thu, 17 Oct 2019 16:48:03 GMT

Hi Rafael,

Thank you for the response, you are correct. My confusion was coming from the fact that when I was selecting the criteria within the 'Influence Lines' options box, I selected a 'Point' on 'Element' 2 with a 'Position' of 0.5. As I was selecting a point midway along the beam, I expected symmetry in the IL. However, I now note that selecting a 'Position' of 0.5 results in Robot providing an IL for element 2 between nodes 2 and 3, while a 'Position' of 0.5001 results in Robot providing an IL for element 2 between nodes 3 and 4 (Diagram below refers).

Thank you for the your time and assistance, very much appreciated!

Re: Influence Lines on Trusses in Robot Structural Analysis Professional

Rafacascudo — Thu, 17 Oct 2019 17:15:10 GMT

you should divide the chords into 4 bars. Results will be the same.

Re: Influence Lines on Trusses in Robot Structural Analysis Professional

ted.mckenna — Thu, 17 Oct 2019 17:53:25 GMT

Thank you!