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New New Zealand timber std.... NZS/AS1720.1

New New Zealand timber std.... NZS/AS1720.1

New New Zealand timber std.... NZS/AS1720.1

So it was released a few days ago with no fanfare, after a 29 year wait...

Some things from the draft retained which I thought would be gone or clarified further.

Axial load capacity got crapped on, it's like no one calculated anything to compare. Or if it was the intent no one bothered mentioning something so major... Since the rho_b and rho_c factors include the ratio of E/f and are tuned to aussie timbers, I was hoping they would realise NZ timbers have quite a different ratio which results in significantly lower axial capacity for NZ timber.

They managed to retain that deflection scaling factor (k_dt), but make it so vague that no one knows what to do anymore, referencing special studies just to design a plywood shear wall....
I was really hoping it would just go away as I think it is all bollocks, OK include it if you let us work out the seismic forces based on the actual damping but not 5%. It refers you to the wood seismic design guide, and this just refers back to the draft for the large scaling factor everyone was moaning about.

In the seminars they had a few weeks ago before it was released they mention this was probably gone. But here it is as vague as ever. Basically makes designing any wood system impossible unless you're designing for really low ductilities.and then you're designing for massive forces that timber just cannot handle...

Anyone else got some thoughts?


RE: New New Zealand timber std.... NZS/AS1720.1

I lean on the orange/pink(?) Timber Design book for now... so does the new Timber Material Design code take into effect immediately? Or do we have to wait for it to be referenced officially in B1/VM1. I ask because I imagine I need to spreadsheet up soon *eye roll*.

RE: New New Zealand timber std.... NZS/AS1720.1

Usually takes a while to be cited, but usually people start using it and reviewers requesting it is used as a matter of best practice especially if there are larger changes that might completely change the approach or answers (which there is for more than a few things.

For example we've been mindful of these massive axial capacity changes and the lower bearing capacities perp to grain in our designs for a while now. The bearing using the draft 4.5MPa almost governed everything, they backed off on this value a little in the final code, but still something that will govern a lot of the time, compared with prior 8.9MPa which never really governed.

Once you consider that NZS3604 isn't being immediately updated, the divide between SED and non SED design gets very wide, and a simple stud wall design starts looking very stupid sitting next to the NZS3604 equivalent.


RE: New New Zealand timber std.... NZS/AS1720.1

Another thing I've noted is how the authors have worded things around the rope effect for fasteners, the capacity enhancement is 1/4 of the values in the Eurocode. This seems intentional as the draft had it identical to EC5...... but possibly an error.

Add it to the list of errors I guess....


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