soccerkid812 wrote:for the top part of the tower chimney,
is it better to have the bracing sides connected all the same way or where four pieces of bracing connect? (assuming you use one bracing per part of the tower) ...
An interesting question with no simple answer.
In towers, bracings mainly control member buckling and lateral movement of the structure.
With regard to member buckling, it does not matter how the bracings are oriented on the four sides of the chimney. What matters is how the bracing pattern on each side divides the long (vertical) compression members into shorter (un-braced) segments. As long as these segments are short enough (according to the Euler’s buckling equation), then theoretically no buckling will take place.
Lateral movement of the structure, however, could be effected by the orientation of the bracing pattern on each of the 4 sides of the tower. Let’s use an example to see how.
Consider the example tower used in my third post on the previous page. Let’s assume the tower uses bracing pattern P3 on all four sides where the diagonals are slanted with a negative slope (connecting an upper left node to a lower right node), as shown below.
Note: For visual clarity only bracing on two sides are drawn.
As it was shown previously, each side of the tower, if considered in isolation, displaces slightly to the left at the top of the tower, like this:
Here is a visualization exercise. In your mind, move round the tower and examine each side. As you face a side, you should see it being deformed in a manner similar to the image shown above. Can you see what happens to the whole tower when each side behaves the same way (sidesway to the left)? The tower twists, like this:
Now, let’s look at a different bracing orientation for the four sides.
In this case, let's assume the bracings on the opposite sides are oriented in the same direction, but the adjacent sides are mirror image of each other. Can you figure out how the tower is going to deform? Give it a try. Hint: It is not going to be by twisting.
The point is that different bracing patterns or different orientations of the same pattern on the four sides of a tower lead to different deformation patterns for the tower. As to which bracing pattern or orientation is a better choice, there is no simple answer. Bracing orientation A could result in excessive twisting in a member causing it to fail. On the other hand, orientation B could create significant stress at a glued joint causing it to come apart. You need to run experiments to determine what works best for your tower.