Fixing to Top of Unreinforced Masonry Wall

[Toby43]

Hi all,

Here in Western Australia, there is a plethora of residential buildings of unreinforced double brick construction (2 leafs separated by a 50mm cavity). The roof to wall detail typically consists of fixing rafters to a timber plate which is on top of internal leaf, which is strapped down into wall (900, 1200mm down etc..) with light gauge G.I. Straps. Further more either bolts into top of brickwork (top fixed, not face fixed) or nails into mortar joints are used to locate plate on wall (sorry scanner not working, will get sketch up as soon as I can). In my opinion this detail provides an unreliable mechanism in resisting In-plane and Out-of-Plane actions at the plate/wall interface. I personally don't get involved in the design of these types of houses and was seeking others opinions on this detail. The main reason I ask, is a client is looking at putting a timber framed second storey addition on a double brick house - my immediate concern is shear transfer in-plane of the walls from framed shear walls above and from timber floor diaphragm between the two types of construction. Has anyone dealt with this before? If so any information/opinion would be greatly appreciated.

Thanks in advance
Toby
P.S. - My initial concept was to bear joists/blocking on top of existing brickwork and then brick up between to "wedge" them in.

 

[KootK]

Is there a rim board or blocking between joists? Definitely post a detail.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Toby43]

Here is typical detail discussed - opinions appreciated.

As far as the upper storey extension goes, configuration of lower storey wall openings is changing considerably from original, so I have just opted to remove outer leaf and inset steel bracing frame fixed to new floor over.

Thanks
Toby

 

[KootK]

The nailing provides a load path for both in plane and out of plane action st the plate interface so I guess it just comes down to whether or not the per nail capacity is sufficient. Do you have a method available to you to assess the per nail capacity? I don't know of one off hand.

I'm not sure that I understand the steel frame bracing scheme but it sound as though you've solved your immediate problem.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Toby43]

Thanks KootK
Yes, nailing would provide load path, but as you mention, a method to reliably assess its capacity does not appear readily available - Anyone?

 

[txeng91]

Not sure what the exterior covering is on the addition is but if I were to put a second story on this I wouldn't feel very good about bearing on a single wythe. It the grouting between the wythes is sufficient I would have them remove the top two courses of the interior wythe, put a wood plate down to bear on both wythes and drill and epoxy all thread rods into the mortar below and have a rim joist for the floor joist to attach into at the edge of the wood plate and attach it down to the wood plate w/ framing angles. and have the decking and stud wall above it. This is all assuming the architect is not trying to carry the exterior wythe up to the 2nd floor roof as an exterior covering.