Axial Load on the Top Chord of a Parallel Truss

[lllun333]

Hi guys, I'm modelling a one bay parallel truss on Space Gass. As I know under live load and dead load combination the top chord should be under compression and the bottom chord under tension. However I'm getting positive axial force for the top chord and negative for the bottom chord. Is this wrong? Please help!

 

[Agent666]

Negative is tension in spacegass if I'm not mistaken. So it looks right to me? (don't have access to a license to open it at the moment)

You have some continuity at the ends with the column, so there is an inflection point about 3 panels in so at ends top chord switches to tension.

 

[lllun333]

Hi, thank you so much!
Do I expect compression for the entire top chord? How can I fix this?

 

[hokie66]

Like Agent666, I don't have access to manipulate your model, but suspect it is giving you good results, as Space Gass is a competent program.

Under your gravity load case, it is expected that the top chord in the vicinity of the column will be in tension, and in compression further out in the span. Not sure why you want to "fix this".

With wind loading, it is likely that the signs will reverse, placing the bottom chord in compression.

 

[lllun333]

Thank you so much!

 

[CANPRO]

Take a closer look at your output - the top chord changes from tension near the columns to compression further in the span, and vice versa on the bottom chord. Due to the rigid connection with the column. Makes sense to me. You can kind of see the transition from tension/compression in your deflected shape as well.