## Designs

SLM
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Posts: 195
Joined: January 31st, 2009, 2:24 pm

### Re: Designs

T-B wrote:Are those L beams? On the base, yes? Top section too? We've got to learn how to do that next year.

Got any hints on techniques for that? Did you glue a 3/32 x 1/32 piece to a 1/8 x 1/32 (or thereabouts) in an end joint set up? Or did you try to cut the pieces at a 45 degree angle along the length to get a mitered joint along the length. I think that is what we need to do but I can't figure out how to do that.
The chimney consists of four long members with a rectangular section (1/8 x 1/16). The cross-section of the legs is in the shape of T, not L. The flange (the wider part that is visible in the image) is 1/32" thick and has a width of about 8 mm. The web is 1/8" x 1/16". The advantage of a T section is its ease of construction. We cut the flange and the web to length (about 18 cm), place the flange on a flat surface, put glue on the web (along its length) while holding it in one hand, then place the web on the flange along its centerline.

SLM
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Posts: 195
Joined: January 31st, 2009, 2:24 pm

### Re: Designs

T-B wrote:SLM,

One other thing, it is obvious that you know a ton of technical stuff, and we need to learn that stuff to take it to the next level. Aside from reading every word on the forum, can you think of a book we could read on this topic with some of these formulas for buckling and tensile strength. I can build, and I can understand the basic stuff on compression and tension modeling, but a lot of that stuff I don't even know where to start. Any suggestions for summer reading?
I am not aware of any book that covers these topics in a manner that is accessible to middle/high school students. You can find various mathematical explanations for buckling on the web, but I am not sure how useful they are. A more comprehensive and accurate explanation for buckling, structural stability and strength can be found in most engineering textbooks on structural design. Although such books generally deal with steel and concrete structures, the underlying concepts and techniques are applicable to wood structures as well.

LKN
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Division: C
State: NC

### Re: Designs

SLM,

Did you use all balsa for your tower? I have been using bass on the horizontal "gusset plates" on the base of my towers, and they have been working quite well. I am assuming that you used very dense balsa for tension members on your tower to get your weight that low? Thanks
- LKN
NCSSM '13

SLM
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Posts: 195
Joined: January 31st, 2009, 2:24 pm

### Re: Designs

LKN wrote:SLM,

Did you use all balsa for your tower? I have been using bass on the horizontal "gusset plates" on the base of my towers, and they have been working quite well. I am assuming that you used very dense balsa for tension members on your tower to get your weight that low? Thanks
Yes, the tower is entirely made of balsa. The density is not too low, it is around 200 kg/m^3 for the main members. The bracings are a bit lower in density. The legs (without bracing) are about 2.4 grams in total, the main chimney members weigh about 1.6 g, the rest goes to the bracings and the other tension/compression members.

KBS
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Joined: December 22nd, 2010, 2:03 pm
State: AZ

### Re: Designs

SLM,

in your bracing posts, your analysis showed that a Z brace tendss to have relatively large lateral displacement. Your tower picture shows that you used Z braces on upper tower as well as on the base. I am not sure I understand your rationale for this. Why, for instnace, did you not use the P2 bracing desing which has very little lateral displacement? If I am misquoting P2, I mean the one that goes like:
\
-
/

Thanks!

soccerkid812
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Posts: 169
Joined: December 16th, 2010, 4:43 pm
Division: C

### Re: Designs

KBS wrote:SLM,

in your bracing posts, your analysis showed that a Z brace tendss to have relatively large lateral displacement. Your tower picture shows that you used Z braces on upper tower as well as on the base. I am not sure I understand your rationale for this. Why, for instnace, did you not use the P2 bracing desing which has very little lateral displacement? If I am misquoting P2, I mean the one that goes like:
\
-
/

Thanks!
I am not entirely sure but I think the sides of that tower has a different type of bracing.

SLM
Member
Posts: 195
Joined: January 31st, 2009, 2:24 pm

### Re: Designs

KBS wrote:SLM,

in your bracing posts, your analysis showed that a Z brace tendss to have relatively large lateral displacement. Your tower picture shows that you used Z braces on upper tower as well as on the base. I am not sure I understand your rationale for this. Why, for instnace, did you not use the P2 bracing desing which has very little lateral displacement? If I am misquoting P2, I mean the one that goes like:
Thanks!
Good observation.

Yes, the tower shown above uses Z-bracing for the chimney and the base. We have not yet had a change to experiment with different bracing patterns for the chimney and the base. However, although the Z pattern produces the largest side-sway in the tower, clearly the side-sway is not significant enough to cause the tower to fail. Since patterns P2 and P3 (Z-bracing) require the same amount of material, I suspect they will do equally well for bracing the tower.

havenguy
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State: PA

### Re: Designs

Are X-designs or Z/zigzags better/more effective for bracing?
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SLM
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Joined: January 31st, 2009, 2:24 pm

### Re: Designs

havenguy wrote:Are X-designs or Z/zigzags better/more effective for bracing?
X pattern (with the horizontal pieces) offers more stability than Z pattern, but at a cost; X uses more material than Z. Since, at least in our case, Z pattern works, it is difficult to justify using X bracing.

It is more difficult to compare X pattern without horizontal pieces and Z pattern. The effectiveness of a bracing pattern mainly depends on the geometry of the structure it attempts to brace and the types and directions of the loads. For SO towers, it appears that both patterns work well, they are both effective. But, even without the horizontal pieces, X pattern probably uses a bit more material than Z pattern, making X less desirable than Z.

havenguy
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State: PA

### Re: Designs

SLM wrote:
havenguy wrote:Are X-designs or Z/zigzags better/more effective for bracing?
X pattern (with the horizontal pieces) offers more stability than Z pattern, but at a cost; X uses more material than Z. Since, at least in our case, Z pattern works, it is difficult to justify using X bracing.

It is more difficult to compare X pattern without horizontal pieces and Z pattern. The effectiveness of a bracing pattern mainly depends on the geometry of the structure it attempts to brace and the types and directions of the loads. For SO towers, it appears that both patterns work well, they are both effective. But, even without the horizontal pieces, X pattern probably uses a bit more material than Z pattern, making X less desirable than Z.
How would Z's without horizantal braces work?
University of Pennsylvania Class of 2020
Strath Haven High School Class of 2016

2016 States Results:
Invasive Species: 1st
Dynamic Planet: 1st
Disease Detectives: 5th
Anatomy: 6th

Team Place: 4th

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