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Three storey timber terrace house design, proper guidance?  


Tom Shen
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Joined: 4 years ago
Posts: 1
21/04/2022 4:28 pm  

Hi all, is there any documents showing us how to do three storey bracing design? It becomes more common these days and council has been asking us to do SED for all three storey ground floor bracing. Previous method was to use equivalent static method and distribute the load at the ground floor as per NZS3604, but the council starts refusing this methodology, it is impractical to model every single terrace house and put a diaphragm at the 1st floor. 

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Nick Calvert
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Joined: 4 years ago
Posts: 4
11/05/2022 3:15 pm  

Hi Tom,

I also have issues with multi-storey terraced houses. I am unsure if SESOC actively moderate this forum given you havent had a response in 20 odd days, however I will voice my concerns.

Typical intertenancy wall systems to terraced houses have not been tested to tie adjacent buildings together to prevent differential drift of adjacent units. Some engineers assume that because they have the same theoretical mass and the same theoretical strength and stiffness (on the assumption they are identical) then they wont drift differentially, however that “assumption” is a poor one give a huge number of factors that mean adjacent units will almost certainly differentially drift both parallel with the IT wall and perpendicular to it. A further concern to this is that if those systems are not designed or tested to tie the diaphragms together and drifting occurs, the connections between units will fail and in the case of IT systems with an AAC interlayer, the interlayer may be unsupported following burnout of one unit, resulting in failure of the fire wall and potentially a fire developing in the next unit.

There are a few issues that need to be addressed for my particular concern but mostly the IT wall systems need to be developed such that they can tie the diaphragms together so that they continue to perform as a fire wall following an SLS earthquake.

So the big technical question to get all the boffin structural engineers juices flowing is this: If you have two adjacent buildings, with theoretically the mass and theoretically the same strength and stiffness (and also each unit carrying its own seismic weight), how do you determine the force that the diaphragm ties need to be designed for?

Looking forward to the discussion!!

Regards, Nick

Nic Brooke
Member Admin
Joined: 4 years ago
Posts: 28
11/05/2022 4:24 pm  

SESOC do moderate the forums in the sense of approving posts before they appear.

Josiah – apologies, your reply appears to have been missed. Typically the moderation is rapid.

Notwithstanding – moderators will tend to leave it to other members to provide their expertise for replies, unless a particular topic falls within the moderators knowledge and desire to comment!