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Episode 19 – Fundamentals of Bracing

In this episode I will show why diagonal braces work and when flexible (i.e. ropes or cables) can be used and when rigid braces work better.   These pictures go along with the audio file.

A rectangle without bracing being pushed.

In this picture I use 5 Popsicle sticks connected with push-pins to show the problem if only horizontal and vertical structural members are used.

With very little force the rectangle become a parallelogram.




An addition popsicle stick is installed diagonally to the others to make a brace.

To fix the problem I add a 6th Popsicle stick installed at an angle to the other Popsicle sticks.   Again, push-pins are used to fasten the sticks together.




Braced "wall" being pushed.




Now when a force is applied to the sticks the sticks resist and the rectangle resists and does not become a parallelogram.



The reason the unbraced wall can collapse so easily



The unbraced wall can easily collapse because all the upright posts can rotate around the push-pin joints easily. (In the audio I discuss how pin joints are a valid representation of boards nailed together.)


A diagonal brace in one direction.


A diagonal brace in this position must decrease in length to allow the vertical posts to rotate around the pivot points.

The yellow line shows where the brace would be if it remained the original length.


A diagonal brace in the opposite direction.


A diagonal brace in this position must become longer to allow the vertical posts to rotate around the pivot points.

The yellow line in this picture shows how much longer the diagonal brace would have to become to allow the rotation.

A rope or cable would suffice in this application, but would not in the previous situation.

This shows the first wall placed in position for the shed we built at my son’s house.  Three braces are being used, 2 to hold the wall upright and the 3rd one to keep the wall from folding.  The 3rd one is doing exactly the same thing as the Popsicle stick example.





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