Bracing

soccerkid812
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Re: Bracing

Post by soccerkid812 » February 16th, 2011, 3:32 pm

phillies413 wrote:For the bracing in towers in general, it it optimal to use butt (end) joints, or lap joints?
lap joints are alot better

exocytosis
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Bracing the chimney to the base!

Post by exocytosis » February 16th, 2011, 4:45 pm

how do I efficiently connect the chimney to the base, while keeping the connection strong?

I'm in division C, and most of my towers are breaking at the chimney-base connection.


Thanks,
exocytosis

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Re: Bracing the chimney to the base!

Post by SLM » February 16th, 2011, 5:23 pm

exocytosis wrote:how do I efficiently connect the chimney to the base, while keeping the connection strong?

I'm in division C, and most of my towers are breaking at the chimney-base connection.
Can you post a picture or diagram of the lower part of your tower including the chimney-base connection?

soccerkid812
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Re: Bracing

Post by soccerkid812 » February 17th, 2011, 3:35 pm

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)
sorry, this is rather hard to explain.

the following tower is where the four pieces of bracing connect: http://gallery.scioly.org/details.php?image_id=3296
the one with the bracing sides connected all the same are where the top part of the chimney all go one way, and the next part go the other way, ect.

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Re: Bracing

Post by yousef213 » February 17th, 2011, 3:38 pm

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)
sorry, this is rather hard to explain.

the following tower is where the four pieces of bracing connect: http://gallery.scioly.org/details.php?image_id=3296
from an engineering standpoint it is better to have the same bracing, ie left to right, right to left pattern on all four sides so each gets support insteal 2 strong legs and 2 weak ones
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_HenryHscioly_
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Re: Bracing

Post by _HenryHscioly_ » February 17th, 2011, 11:39 pm

My first tower I made I used lap joints, but it performed very poorly.
So I've been using end joints for all my parts now, and my tower's have been breaking at the base because the legs end up sliding outwards, the joints fail
Should I use lap joints instead?And my first tower didn't do well because it was my first one?
How about notched joints?

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Re: Bracing

Post by iYOA » February 18th, 2011, 9:13 am

USE LAP JOINTS no joke. The reason it performed poorly was probably because it was your first one and there may have been some construction issues. anyways, the joints most likely were not the reason for breaking. a good tower should not have a joint failure so there is no point in going through the effort of notched joints. An ideal tower failure is probably when an unbraced length of the primary compression members buckles. A joint failure is usually fixed with improved construction.
West Windsor-Plainsboro High School South

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Re: Bracing

Post by hogger » February 18th, 2011, 9:15 am

_HenryHscioly_ wrote:My first tower I made I used lap joints, but it performed very poorly.
So I've been using end joints for all my parts now, and my tower's have been breaking at the base because the legs end up sliding outwards, the joints fail
Should I use lap joints instead?And my first tower didn't do well because it was my first one?
How about notched joints?
At the spot where the top meets the legs, I would stay with butt joint (end joint as you put it) but use gussets on both sides of the pieces that have the same parallel plane. In fact, you can keep adding more pieces of gusset next to the first one outward up and down the joining pieces. Make sure you don't violate the 8 cm cylinder diameter rule at the joining spot though. Everywhere else especially for the braces, I would use lap joints. See Double Gusset 2 below.

http://www.garrettsbridges.com/building/bridge-joints/

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Re: Bracing

Post by SLM » February 18th, 2011, 11:23 am

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.

Image
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:

Image

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:

Image

Now, let’s look at a different bracing orientation for the four sides.

Image

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.
Last edited by SLM on February 19th, 2011, 6:02 pm, edited 1 time in total.

soccerkid812
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Re: Bracing

Post by soccerkid812 » February 18th, 2011, 12:31 pm

although I was referring to the P2 bracing, but I understand the main point

thanks SLM

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