# Cross Section interpolation

Hello,

I have Bridge with a cross-section of 4 “t” shape (TTTT) and the thickness of flanges and webs have certain value at support and decrease while moving to the midspan.

When i draw a structural line with start section (large thickness) and end section (Small thickness[midspan]), SOFiSTiK show me and error message saying that interpolation must be done in identical section. so how can i solve this problem?

Hello,

I did it with adding variables on the axis at the stations in which the cross section has changes. And when I was modeling the cross section , I used cartesian references for the points of the cross section that needs to change their coordinates.

Kind regards

1 Like

Hello,

In order to interpolate a cross-section properly, the two outer sections need to be structural ident. In your case, that means you need to check the cross-section points (in the result viewer or directly in SOFiPLUS(-X)). Make sure that the points of the two cross sections are named identically.

Here’s a short example project:
Querschnittsinterpolation.sofistik (33.2 KB)
Querschnittsinterpolation.dwg (52.5 KB)

Another way to solve variable flange height, as @sofijahris said, is to use variables.

www.sofistik.com > Infocenter - Overview > Documentation - Tutorials > Bridge Design > Balanced Cantilever Bridge

For a general introduction to computer-aided bridge design, see our online bridge design training course.

Best regards
Frederik Höller

I tried to Make sure that the points of the two cross sections are named identically. but also the error still appears. Does this because the sections are not standard ones ?

but the variables approach worked

make first one section → then copy it → open copy → modify second section without adding new element, deleting old element, just change size of existing elements. it’s best way

1 Like

Hello,

I just have a question

I defined variable in the cross section to change the web width along the span stations and i set the value for the variable along the span also i imported the variable in the cross section and i gave it the start value. But after uploading the file to SOFiSTiK the web width doesn’t change along the span and it is just with the start value that i entered in cross section.

So do you know why this occurs ?

Thank you

At first I would advise you to define the placements according to the structural beam sections. Your project is a bit confusing. Additionally, to find the error, try to reduce your system. Keep it simple!

A look into your system makes it clear that the variable #WWEBM does not arrive in the cross section.
So I deleted the structure line and reapplied it to the axis.

SOFiPLUS(-X) > Structural line > select settings > rigt-click in the drawing area > Segment on Axis > Select axis A

I am attaching the simplified system. Now it’s up to you to work out the system.

Bridge 15-16.sofistik (155.5 KB)
Bridge 15-16.dwg (187.0 KB)

Best regards
Frederik Höller