Hello everyone again,

I've been exploring the topic of bracing and how different people view the concept. While tension bracing is known in this country, carpenters in America most certainly favor the concept of compression bracing. Swiss carpenters are the opposite; compression bracing is used at times, but the vast majority of frames use tension bracing.

We all know the basics of this, tension braces are easy to set, being added after the frame is raised, but can come out or if they shrink they will fail. Compression braces have to be set as the frame goes together and once they are in they will not be coming back out.

But there is an important dynamic I've been thinking about here that has a major reflection of joint design. That is the reactive forces that result in a frame in response to the action of a brace.

For every action there is an equal and opposite reaction. Simple Physics

A compression brace pushes against wind loads,the framing members it connects react to this force. The result is that these braces can potentially pry timbers apart, for example a girt set into a post might be pulled out of joint by the brace connecting the two. The solution to this is to make a tenon long enough so that it can be secured against this force with pegs without shearing out the tenons. Another solution is to use a 4-brace network at every such connection.

But tension bracing doesn't do this. Tension bracing acts in reverse, it is designed to pull back against wind loads. There is of course a resulting force that happens, but it is again opposite. Instead of potentially prying members apart, tension braces actaully pull joints together. This is reflected in joint design, where Bernese Carpenters effectively use very short tenons to connect structural girts to posts.

They also use this aspect of tension braces to their advantage in some cases. They might add a brace where it is not needed to act against the wind. The brace in this case is there to pull the joint together and thus secure the connection.

The big disadvantage is that tension braces have to be very stable. If they twist or shrink excessively, they will fail. The stock used for these needs to be very straight and well seasoned to prevent this. Compression braces can be made of anything -in the past they were cut of the sticks that were not good enough to use for anything else.

Nevertheless, Carpenters in the Canton of Bern certainly consider tension braces superior and continue to use them today. Not to mention the fact that in log building practices, they are the only practical choice for reasons of assembly.