Deflection limits of a TV sign 1

[micks87]

Hi All,

Any thoughts on deflection limits for a large TV sign mounted in a stadium. See attached crude image.

I was thinking about H/100 to H/150. Does anybody have an SLS reference for such a structure?

Cheers

 

[sdz]

You will find a range of values in different references. You have a portal frame in one direction but the wind load will be small for this and it's unlikely to be problem.
I would suggest for the cantilever H/125, including rotation in footing. This comes from AS4100 Appendix B. You probably won't have a good estimate of deflection in the footing but assuming it's reasonably small use H/150 for the above ground part.

 

[Agent666]

Also fatigue from wind should also be considered at SLS, as this may drive sizes and detailing if your sign is wind governed. AS/NZS1170.2 has provisions for this.

Maxing out the deflection could max out the stress at the SLS (at least over the limiting fatigue values), potentially causing a fatigue issue.

I've seen one investigation into a sign here in NZ that had collapsed due to fatigue. The original designer did not even consider fatigue at all.

In terms of overall deflection limits, you also don't want to make it so flexible that you have any issues with dynamic effects. I'm not sure if 1170.2 covers anything like this for non-building structures.

Also don't forget for 'hoardings' like this you need to evaluate the wind at 22.5 degree increments from memory around the structure and apply the eccentricities noted in the code when the wind isn't orthogonal to the barrier. So, it's not just checking the wind orthogonal to the screen which you might logically think is the worst case but often it actually isn't.