AS2699 brick ties 4

[demayeng]

Does anyone have a copy of AS2699?

If I am given a 'characteristic capacity' in kN of a brick tie by the manufacturer, what is the phi factor I would apply to this to get my design capacity?
I assume this would be in AS2699?? I am a bit over buying codes and then not finding the info i was after..

Thanks!

 

[sdz]

I think what you need to know is the duty of the ties; light, medium, or heavy. Then use AS3700. Try looking up MET, Abey, and Ancon. Some manufacturers will give tables showing how many ties to use for given wind exposure conditions.

 

[apsix]

By AS3700 Table 4.1 phi = 0.95 for wall ties.

I hope you have AS3700 if you are designing masonry!
AS2699 may be useful for background info, but shouldn't be required for routine design.

 

[demayeng]

Thanks! I didn't realise it was in 3700. That's exactly what i need

 

[apsix]

FYI

 

[demayeng]

Great, thanks

 

[asixth]

So the manufacturer of the wall ties specify whether their product is a light, medium or heavy duty based on compliance tests (I assume) which then gives a characteristic capacity as specified in the code. Let's say medium duty so it has a 400N tension and 480N compression characteristic capacity. The masonry code then says that a 0.95 reduction factor is to be applied to wall ties, giving a design strength of 380N tension and 456N compression and the ties are not to be spaced any greater than 600 x 600 centers.

For my typical situation (Region B; Importance Level 2) the ultimate wind pressure is 1.21kPa (at ground level). The greatest pressure co-efficients occur at side walls -0.65 with an local multiplier Kl of 2.0. This gives a design tension force on the wall ties of 566N. Even if I have my wall studs at 450crs which I usually do, the design tension force on the wall tie is still 424N.

Living in Brisbane, I have always called up medium duty wall ties which I now begin to think is under capacity. Does anyone who designs in Region B call up medium duty wall ties at 600crs. I have only seen one design to date which has called up heavy duty ties and that was for a carpark balustrade wall in Region B.

Also, silly question for asking, but what is the maximum span/deflection ratio for stud walls which are supporting a brick veneer wall. I have been using span/200 which allows movement of 13.5mm in the wall at midspan for a 2700 high wall.

 

[asixth]

An amendment to my earlier post

Living in Brisbane, I have always called up medium duty wall ties which I now begin to think is under capacity.

Under capacity for side walls only, which in the event of a 500yr wind would be the walls which get sucked off the building.

 

[demayeng]

I have seen that the characteristic capacities from manufacturers are generally higher than those given in the code for each duty class, which may allow you to stick with medium duty.

I would assume that if brick veneer deflection caused problems we would have a much more definite deflection criteria to adhere to. Span/200 would be the minimum we would use for any wall. If the frame is designed for span/200 then the added stiffness gained by the brick skin (that we generally don't allow for) would probably take it much higher.

http://www.structuremag.org/article.aspx?articleID=671

 

[asixth]

Cheers mate, they mentioned many limits in that article, L/240, L/360, L/600 and L/720 for 10 and 50 year winds. I'll run with height/200 for 25 year winds.

 

[hokie66]

This has always been an ill-defined issue because the veneer is typically stiffer than the stud backing. The article demayeng posted illustrates the disagreements among various codes and standards.

AS3700, in 7.7.2(b), limits the deflection under serviceability wind load to L/300.

 

[apsix]

asixth
Your proposed H/200 for 1 in 25 yr winds seems sensible for studs where the additional stiffness of the veneer would be significant.

AS1684.1 (residential timber-framed construction)has a stud deflection limit of H/150 or 20mm, but says it 'may not preclude damage to brittle surfaces'. Also wind loads are based on AS4055 (classifications N1-N4 & C1-C3), I don't know the correlation with AS1170.

AS/NZS1170.0 Table C1 stipulates H/400 for masonry walls, face loaded, for 1 in 25 yr winds.

Re wall ties; AS3700 Table 12.5 has spacing requirements for the different tie rating and wind classifications. Again, based on AS4055 where there are no local pressure factors.