Bridge B/C

[mklinger]

Imagine the space a car/truck/train would actually move through on a bridge. This is the space that needs to stay clear. Or, that is how I understand it (not official..etc...).

My opinion is that this is what the rules say - that if you imagine a truck of the specified cross-section, it needs to be able to "drive" though the bridge at some height, thus allowing a bridge "deck" holding the sides together at the base. dholdgreve, in this thread, expressed the opinion that the rules mean that the "truck" has to begin in contact with the support block, and travel horizontally until it contacts the other support block, thus precluding anything tying the two sides together at the base. I don't think he's right, but I see how he can read the rules the way he does, and agree that this warrants clarification.

I think this video might answer this question once and for all. There are pieces across the bottom connecting the two sides. This video is on the Science Olympiad official YouTube channel. While maybe it is not OFFICIAL, it pretty much is official (in my opinion).

https://www.youtube.com/watch?v=ZELNwoTXA6E

Nice find! I concur that this really makes it clear that you can have supports across the bottom.

FWIW, I would not recommend using their design plans, even to start with... that thing is very complex to build and not very efficient.

[sneepity]

How are you guys making sure the width is 7cm for the new pass thru block but also make sure the loading block which is 5cm wide sits on the top. Do we have to bend the top of the sides in??

[mklinger]

How are you guys making sure the width is 7cm for the new pass thru block but also make sure the loading block which is 5cm wide sits on the top. Do we have to bend the top of the sides in??

Hi! I would try the most simple solution first, just two carefully selected cross pieces. Something like what I show in this video:

https://youtu.be/nzDV02CiU94

[sneepity]

How are you guys making sure the width is 7cm for the new pass thru block but also make sure the loading block which is 5cm wide sits on the top. Do we have to bend the top of the sides in??

Hi! I would try the most simple solution first, just two carefully selected cross pieces. Something like what I show in this video:

https://youtu.be/nzDV02CiU94

I see! What I'm currently wondering is a little different, if the trusses are directly 90 degrees vertical to the ground or the testing base, and 8cm apart, how are they going to hold the testing block which is 5cm apart. Are the trusses going to be assembled so they pinch in where the testing block is going to rest?

[JonB]

How are you guys making sure the width is 7cm for the new pass thru block but also make sure the loading block which is 5cm wide sits on the top. Do we have to bend the top of the sides in??

Hi! I would try the most simple solution first, just two carefully selected cross pieces. Something like what I show in this video:

https://youtu.be/nzDV02CiU94

I see! What I'm currently wondering is a little different, if the trusses are directly 90 degrees vertical to the ground or the testing base, and 8cm apart, how are they going to hold the testing block which is 5cm apart. Are the trusses going to be assembled so they pinch in where the testing block is going to rest?

You have ran into what I think will be one of the largest challenges of the year for division C.... I think we will find multiple good solutions- some designs will taper inward while others will be >7cm wide and then have cross beams to support the loading block. What is going to work best? Not sure yet. I can suggest that the tapered design will be more difficult to build due to the odd angles, but very do-able.

[mklinger]

How are you guys making sure the width is 7cm for the new pass thru block but also make sure the loading block which is 5cm wide sits on the top. Do we have to bend the top of the sides in??

Hi! I would try the most simple solution first, just two carefully selected cross pieces. Something like what I show in this video:

https://youtu.be/nzDV02CiU94

I see! What I'm currently wondering is a little different, if the trusses are directly 90 degrees vertical to the ground or the testing base, and 8cm apart, how are they going to hold the testing block which is 5cm apart. Are the trusses going to be assembled so they pinch in where the testing block is going to rest?

What that video shows is one way to address your exact situation. My little test devices are exactly 8cm apart. The 2 beams that the cross members are sitting on simulate the top part of a real bridge. If you go with a solution like this, you can test it independently from the rest of your bridge so you don't have to build a complete bridge every time you want to test the strength of your block support.

Like JonB mentions, you could also do a tapered design, and maybe that will be overall lighter, but it will certainly be more complex to build and it will be wider at the bottom which means more material, at least at the base connection points and that might add more mass than just using simple cross bracing on top.

I would start with a very simple design first and see if you can get that working well before trying a more complex tapered build.

[knightmoves]

Like JonB mentions, you could also do a tapered design, and maybe that will be overall lighter, but it will certainly be more complex to build and it will be wider at the bottom which means more material, at least at the base connection points and that might add more mass than just using simple cross bracing on top.

I'm wondering about some sort of arch shape, although that's obviously going to be harder to build. There's a picture I've seen from a previous bridge competition, where someone built a beautiful laminated arch.

But I think your suggestion of starting with a simple design, and then using that as a benchmark to compare more "interesting" creations is a good one.

[mklinger]

Like JonB mentions, you could also do a tapered design, and maybe that will be overall lighter, but it will certainly be more complex to build and it will be wider at the bottom which means more material, at least at the base connection points and that might add more mass than just using simple cross bracing on top.

I'm wondering about some sort of arch shape, although that's obviously going to be harder to build. There's a picture I've seen from a previous bridge competition, where someone built a beautiful laminated arch.

But I think your suggestion of starting with a simple design, and then using that as a benchmark to compare more "interesting" creations is a good one.

For sure. Don't underestimate the importance of a repeatable design you can build fairly quickly. It has been my experience, especially when the rules involve the bonus for holding 15kg, for big competitions like States/Nationals, you really want to have at minimum about 5 or 6 devices to pre-test and choose the best one from.

Most of the competitive "failures" I've seen from dozens of teams usually comes from building a single device (usually overly complex and heavy) and bringing it to competition and hoping for the best.

This event is almost unique for build events in Science Olympiad as you only get one chance on competition day, but that doesn't mean you can't have already tested dozens of similar devices before and be so confident in your design and build skills that there are no surprises on competition day.

[JonB]

Like JonB mentions, you could also do a tapered design, and maybe that will be overall lighter, but it will certainly be more complex to build and it will be wider at the bottom which means more material, at least at the base connection points and that might add more mass than just using simple cross bracing on top.

I'm wondering about some sort of arch shape, although that's obviously going to be harder to build. There's a picture I've seen from a previous bridge competition, where someone built a beautiful laminated arch.

But I think your suggestion of starting with a simple design, and then using that as a benchmark to compare more "interesting" creations is a good one.

Arches are structurally very strong IF they are built perfectly- which is basically impossible since wood we use in this event has natural variation. I would stay away from the arch design. I am not saying it will not work (it can work), I am just saying I have not seen many successful arch design over the year in Sci Oly.

[sneepity]

Hi! I would try the most simple solution first, just two carefully selected cross pieces. Something like what I show in this video:

https://youtu.be/nzDV02CiU94

I see! What I'm currently wondering is a little different, if the trusses are directly 90 degrees vertical to the ground or the testing base, and 8cm apart, how are they going to hold the testing block which is 5cm apart. Are the trusses going to be assembled so they pinch in where the testing block is going to rest?

You have ran into what I think will be one of the largest challenges of the year for division C.... I think we will find multiple good solutions- some designs will taper inward while others will be >7cm wide and then have cross beams to support the loading block. What is going to work best? Not sure yet. I can suggest that the tapered design will be more difficult to build due to the odd angles, but very do-able.

Yeah! I think tapering is possible but it's harder to do, but I'm going with the cross beams! Thanks for the help JonB.