The diagonal straps stop the rectangle from becoming a parallelogram when you apply force to the any of the sides or corners.
It won’t really stop twisting of the wall structure as it will only protect from forces that come from the same face it is fixed to, and only then for the section of the wall it is fixed to, as it won’t stretch to allow the wall to become convex but will buckle time allow the wall to become concave.
The main thing that stops walls from twisting (other than the rigidity of the timber and it’s fixings) is actually the rigid sheeting (usually) on the outside that forms a structural plane across the frame. It’s also usually this same structural plane that has the same function as the diagonal straps, but in cyclonic winds you are likely to lose the sheets as they are just big sails.
Shear strength is something completely different. It is a materials ability to withstand a shear failure, which is a failure in a parallel direction of the force. The failure can be straight (like a pair of scissors cutting a piece of paper) or diagonal (like you see in concrete columns when the top half comes completely loose of the bottom half and slides sideways to the floor).
Shear failure in a timber wall structure as a whole is unlikely to occur as only the most under strain structural member is likely to fail, rather than the whole wall. Even in the event of a timber stud failing it’s most likely going to be from compressive forces from above rather than lateral forces from the side, and that is most likely going to result in a split starting from one end and running out to an edge rather than a true shear failure because a timber post is actually a whole bunch of intertwined fibres rather than a homogenous material like steel or concrete.
Anyway I am starting to rant now so I will stop this post and go and have dinner with my family.
It won’t really stop twisting of the wall structure as it will only protect from forces that come from the same face it is fixed to, and only then for the section of the wall it is fixed to, as it won’t stretch to allow the wall to become convex but will buckle time allow the wall to become concave.
The main thing that stops walls from twisting (other than the rigidity of the timber and it’s fixings) is actually the rigid sheeting (usually) on the outside that forms a structural plane across the frame. It’s also usually this same structural plane that has the same function as the diagonal straps, but in cyclonic winds you are likely to lose the sheets as they are just big sails.
Shear strength is something completely different. It is a materials ability to withstand a shear failure, which is a failure in a parallel direction of the force. The failure can be straight (like a pair of scissors cutting a piece of paper) or diagonal (like you see in concrete columns when the top half comes completely loose of the bottom half and slides sideways to the floor).
Shear failure in a timber wall structure as a whole is unlikely to occur as only the most under strain structural member is likely to fail, rather than the whole wall. Even in the event of a timber stud failing it’s most likely going to be from compressive forces from above rather than lateral forces from the side, and that is most likely going to result in a split starting from one end and running out to an edge rather than a true shear failure because a timber post is actually a whole bunch of intertwined fibres rather than a homogenous material like steel or concrete.
Anyway I am starting to rant now so I will stop this post and go and have dinner with my family.
