Bridge Competition Rules

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Bridge Competition Rules David Knaack 4/4/12 9:26 AM
Below are the rules for the Bridge Competition.

Please ask if you would like clarification of the intent of the rules. 

The general idea is that it needs to function as a bridge for a toy car, allowing the toy to cleanly traverse the entire length of the bridge, with a realistic maximum allowable grade.

If you plan to use a really exotic construction method, plan on providing detailed documentation or demonstrating the method.

----

Bridge:

May contain only balsa wood and Titebond 2 wood glue.

Must fit within a 50 x 20 x 10 cm rectangular volume.

May not contain more than 6oz of glue by wet volume.

Must have a smoothish road deck no less than 6cm in width.
 - suitable for a HotWheels-style car to easily roll over

Deck ends must contact the upper surface of the test rig support planks.

Deck must have no more than a 10% grade (where grade = 100 * (rise/run))

Deck must accommodate the load plate.

Some part of the load plate must fall across the midpoint of the span.

There are no limits on construction tools or technique.



Scoring:

The load plate is 10 x 5 x 1 cm, and has a loading hook extending from the center of the bottom surface which requires 1 cm annular clearance through and below the bridge deck.

Bridges will be loaded progressively (w/ minimum shock load), starting at 5kg and progressing in 1Kg increments to 10Kg.

Upon reaching the maximum load, the bridge must hold for 1 minute.
 - Disputes as to whether a bridge 'held' will be resolved by vote

Bridges that fail will be ranked by the weight carried without failure and bridge mass.

Bridges that do not fail will be ranked by the mass of the bridge.



Testing:

The open span between the support planks is 30cm.

The open span is between rectangular, fixed, smooth, level, coplanar planks with a thickness of ~2cm.

The bridge may touch the top or inner surfaces of the supporting planks, but may not touch any other surface, nor be affixed to any surface.

The load plate will support a wire or rod from which the test load will be suspended.


Re: [OMG] Bridge Competition Rules ejk00 4/4/12 10:03 AM
Just for grins, here are some resources:


Blick also offers a kit of supplies for (24) bridges for classroom education.  Although this level does not include material for the road decking of the bridge, it might be a good value if several folks wanted to split the package - $70
--

Eric J. Kaplan                                       


Re: [OMG] Bridge Competition Rules Luke 4/4/12 12:52 PM
i'm thinking a linear increasing load source with a load-cell that holds the max load value on a digital readout would be cool.
Re: [OMG] Bridge Competition Rules Kevin Fusselman 4/4/12 1:54 PM
Are you volunteering? :)
Re: [OMG] Bridge Competition Rules Luke 4/4/12 2:33 PM
Thinking about it

Luke
Re: [OMG] Bridge Competition Rules Kevin Fusselman 4/4/12 5:10 PM
I did some price research on balsa, and it looks like Hobby Lobby carries it fairly reasonably, though it still costs over twice what you can order it for (before shipping)...

If anyone is interested in splitting shipping, let me know by Monday, as I'll be ordering the first part of next week.
Re: [OMG] Bridge Competition Rules ejk00 4/4/12 5:32 PM
Count me in. 

Sent from Eric's iPhone
Re: [OMG] Bridge Competition Rules s. 4/4/12 6:55 PM
me as well.
Re: [OMG] Bridge Competition Rules s. 4/6/12 1:52 PM
Could the glue be diluted with water and/or the wood be treated with water?  (It would be dry, with nothing but balsa and glue at the time of testing) 

On Wed, Apr 4, 2012 at 11:26 AM, David Knaack <david...@gmail.com> wrote:

Re: [OMG] Bridge Competition Rules Kevin Fusselman 4/6/12 1:59 PM
uh oh... we're gonna get schooled by Stephanie again...
Re: [OMG] Bridge Competition Rules David Knaack 4/6/12 2:18 PM
Yes, water may be used to alter the behavior of the materials during construction, provided that during testing the structure is dry.

In fact, I'm kind of hoping to see some woods that have been vacuum impregnated with glue solution, and some steam-formed shapes.

On Fri, Apr 6, 2012 at 3:52 PM, Stephanie Jensen <sjen...@gmail.com> wrote:
Could the glue be diluted with water and/or the wood be treated with water?  (It would be dry, with nothing but balsa and glue at the time of testing) 
Re: [OMG] Bridge Competition Rules s. 4/6/12 3:08 PM
that's where I was going with this..... 
Re: Bridge Competition Rules patrick 4/7/12 7:24 AM
Could you please make a diagram of the bridge surface? Or box structure with out lines of the limitations of the design? Perhaps a 3D model from which actual designs can be implemented. That way every one knows exactly what can and can not be done.
Re: [OMG] Re: Bridge Competition Rules David Knaack 4/7/12 12:02 PM
Here are two approximate, non-binding illustrations of conforming bridges. I've removed the sides so the interior can be seen, but the only technically necessary part is the 6 cm wide passage for the vehicle. I didn't specify height of the passage in the rules, but it needs to be tall enough to allow a Hot Wheels type vehicle to pass. I would think that 6 cm would be safe, which is what is shown here.

Practically, I'm sure we'd all appreciate it if the area where the load plate goes (note the hole in the image below) is easy to access for installing the load plate.

Inline image 4

This next design illustrates a sloped deck surface with no more than a 10% grade. The important point to remember with respect to a raised deck is just that the ends where the car enters needs to be in contact with the support plank, so a car could drive onto it. Also, the load plate will be flat, so one would probably want to provide a flat surface for it, as shown here, but this is not necessary, if you prefer the load to be less distributed, a smaller area may be provided, so long as there is room to install the plate.

Inline image 3


Here is another conforming design:

Inline image 5

Here, rather than using a sloped deck to accommodate load bearing elements below the deck, the bridge structure extends below the upper plane of the support planks (again, the sides are cut away for visibility). The width of the part that extends below the support is the maximum width, 30 cm.

Here is another conforming design:
Inline image 7

This one places the structure of the bridge below the deck, with only the deck and the rails that rest on the support planks above the upper plain of the support planks.
Re: Bridge Competition Rules s. 4/9/12 7:28 AM
If part of the testing is that the hot wheels car drives over the bridge, does that occur with the load plate on or off the bridge at the time? 


On Wednesday, April 4, 2012 11:26:54 AM UTC-5, David Knaack wrote:
Re: [OMG] Re: Bridge Competition Rules David Knaack 4/9/12 7:32 AM
Car first, then the load plate will be installed.

The load plate will be a flat aluminum bar with a tapped hole in the center. It'll go on the bridge deck, then a piece of threaded rod will go up through the bottom of the bridge to screw into the plate. 

So we'll just need room to slip the plate in there.

DaveK
Re: [OMG] Re: Bridge Competition Rules ejk00 4/9/12 8:51 AM
I would like to suggest that we spend some time on Wednesday building the testing structure, and then have it "on display" at The Makery (maybe on our new shelves along the front wall) so that everyone can see what they have to conform to.  I'm willing to devote some time to this effort.
Re: [OMG] Re: Bridge Competition Rules David Knaack 4/9/12 9:14 AM
That's what I was figuring on. Should be pretty simple, we just need a clean, flat board about 70 x 40 x ~2 cm, an aluminum plate and some threaded rod with a way to attach weight at the bottom.

Also need to locate the weights before long, so if anyone wants to do some load testing the equipment will be available.

DaveK


On Mon, Apr 9, 2012 at 10:51 AM, Eric Kaplan <ekap...@gmail.com> wrote:
I would like to suggest that we spend some time on Wednesday building the testing structure, and then have it "on display" at The Makery (maybe on our new shelves along the front wall) so that everyone can see what they have to conform to.  I'm willing to devote some time to this effort.

Re: [OMG] Re: Bridge Competition Rules Kevin Fusselman 4/9/12 9:17 AM
Seems like some pieces of 1x lumber out of the scrap bin at Menards would work...
Re: [OMG] Re: Bridge Competition Rules ejk00 4/9/12 9:32 AM
I assume the "clean flat board" is for building the bridge support structure?

I've been looking at some ideas for weights for a project in my home shop.  If I come up with something soon, we could certainly use those, too.  If not, I might (_might_) be able to borrow some from work.  We have a supply of 2.5-pound weights from Sports Authority that we use for our in-house testing.

On Mon, Apr 9, 2012 at 11:14 AM, David Knaack <david...@gmail.com> wrote:



--

Eric J. Kaplan                                       


Re: [OMG] Re: Bridge Competition Rules David Knaack 4/9/12 9:47 AM
On Mon, Apr 9, 2012 at 11:32 AM, Eric Kaplan <ekap...@gmail.com> wrote:
I assume the "clean flat board" is for building the bridge support structure?

Correct. I plan for it to have a central rectangular hole 30 x 20 cm for the bridge to span. The board itself will be supported between tables/benches.
 

I've been looking at some ideas for weights for a project in my home shop.  If I come up with something soon, we could certainly use those, too.  If not, I might (_might_) be able to borrow some from work.  We have a supply of 2.5-pound weights from Sports Authority that we use for our in-house testing.


We have a fairly big pile of aluminum ingots that we can probably select from and modify to get close to the right weight.

DaveK
Re: [OMG] Re: Bridge Competition Rules ejk00 4/9/12 10:09 AM
Oh. I was thinking of 2 vertical uprights, like a real bridge would sit on. Guess I read the rules wrong. 


Sent from Eric's iPhone
Re: [OMG] Re: Bridge Competition Rules Dan Linder 4/9/12 10:17 AM
On the subjects of weights, is there a documented order that the weights are applied, and by whom?

If there's a link just reply RTFM and I'll slink back to my hole. :)

In the past when I've worked with similar bridge competitions, the weights were hung by the  team that owned the bridge so any "dropping" of the weight to sabotage the test would be their fault.  The decision as to which weight to put on was up to them too.  And the judges required that the team member(s) placing the weights leave the weight un-touched for a number of seconds (8-10?) before counting that the bridge held the weight.

Sounds fun!  Hope someone takes photos!

Dan--
***************** ************* *********** ******* ***** *** **
"Quis custodiet ipsos custodes?"
    (Who can watch the watchmen?)
    -- from the Satires of Juvenal
"I do not fear computers, I fear the lack of them."
    -- Isaac Asimov (Author)
** *** ***** ******* *********** ************* *****************
Re: [OMG] Re: Bridge Competition Rules David Knaack 4/9/12 10:29 AM
The bridge can be up to 50 cm in length, and must span a 30 cm gap, so the support structure must provide 20 cm of support at each end (well, to be precise, 10 at one end, 20 at the other). 

For stability and to guarantee co-planar surfaces, it seemed simplest to have the two supports made from one board. Depending on what material we've got to work with, I'd like to have the opening large enough to provide good visibility in case a bridge breaks or sags dramatically. Maybe it can be 'C' shaped, with one side open for observation.

On Mon, Apr 9, 2012 at 12:09 PM, Eric J. Kaplan <ekap...@gmail.com> wrote:
Oh. I was thinking of 2 vertical uprights, like a real bridge would sit on. Guess I read the rules wrong. 

Re: [OMG] Re: Bridge Competition Rules David Knaack 4/9/12 10:39 AM
On Mon, Apr 9, 2012 at 12:17 PM, Dan Linder <d...@linder.org> wrote:
On the subjects of weights, is there a documented order that the weights are applied, and by whom?

The rules say:

Bridges will be loaded progressively (w/ minimum shock load), starting at 5kg and progressing in 1Kg increments to 10Kg.

But we didn't specify who will do the loading or much about how. I like the owner-load idea though. Lets say it's up to the bridge owner, they can do it themselves or delegate it.

The max weight (for the first round) is 10Kg, which really isn't much of a challenge in an absolute sense, anybody should be able to meet that, the challenge is really to minimize the materials used while still carrying the load.

There will be a less-formal 'to destruction' test after the main competition, though, so hopefully there'll be some splinters-a-flyin' at some point.

 Maybe we can relocate a web cam to the test rig while we're testing.

DaveK
Re: [OMG] Re: Bridge Competition Rules ejk00 4/9/12 11:20 AM
The attached is what I was thinking.  The support structure could itself be a go/no-go gauge for the geometric envelope.

On Mon, Apr 9, 2012 at 12:29 PM, David Knaack <david...@gmail.com> wrote:
The bridge can be up to 50 cm in length, and must span a 30 cm gap, so the support structure must provide 20 cm of support at each end (well, to be precise, 10 at one end, 20 at the other). 

For stability and to guarantee co-planar surfaces, it seemed simplest to have the two supports made from one board. Depending on what material we've got to work with, I'd like to have the opening large enough to provide good visibility in case a bridge breaks or sags dramatically. Maybe it can be 'C' shaped, with one side open for observation.

On Mon, Apr 9, 2012 at 12:09 PM, Eric J. Kaplan <ekap...@gmail.com> wrote:
Oh. I was thinking of 2 vertical uprights, like a real bridge would sit on. Guess I read the rules wrong. 




--

Eric J. Kaplan                                       


Re: [OMG] Re: Bridge Competition Rules ejk00 4/9/12 11:21 AM
"Hope someone takes photos!"

Does this mean you aren't going to participate?  Why not, if you don't mind me asking?

On Mon, Apr 9, 2012 at 12:17 PM, Dan Linder <d...@linder.org> wrote:
On the subjects of weights, is there a documented order that the weights are applied, and by whom?

If there's a link just reply RTFM and I'll slink back to my hole. :)

In the past when I've worked with similar bridge competitions, the weights were hung by the  team that owned the bridge so any "dropping" of the weight to sabotage the test would be their fault.  The decision as to which weight to put on was up to them too.  And the judges required that the team member(s) placing the weights leave the weight un-touched for a number of seconds (8-10?) before counting that the bridge held the weight.

Sounds fun!  Hope someone takes photos!

Dan

On Mon, Apr 9, 2012 at 11:47, David Knaack <david...@gmail.com> wrote:
On Mon, Apr 9, 2012 at 11:32 AM, Eric Kaplan <ekap...@gmail.com> wrote:
I assume the "clean flat board" is for building the bridge support structure?

Correct. I plan for it to have a central rectangular hole 30 x 20 cm for the bridge to span. The board itself will be supported between tables/benches.
 

I've been looking at some ideas for weights for a project in my home shop.  If I come up with something soon, we could certainly use those, too.  If not, I might (_might_) be able to borrow some from work.  We have a supply of 2.5-pound weights from Sports Authority that we use for our in-house testing.


We have a fairly big pile of aluminum ingots that we can probably select from and modify to get close to the right weight.

DaveK



--
***************** ************* *********** ******* ***** *** **
"Quis custodiet ipsos custodes?"
    (Who can watch the watchmen?)
    -- from the Satires of Juvenal
"I do not fear computers, I fear the lack of them."
    -- Isaac Asimov (Author)
** *** ***** ******* *********** ************* *****************



--

Eric J. Kaplan                                       


Re: [OMG] Re: Bridge Competition Rules Dan Linder 4/9/12 6:48 PM
On Mon, Apr 9, 2012 at 13:21, Eric Kaplan <ekap...@gmail.com> wrote:
"Hope someone takes photos!"

Does this mean you aren't going to participate?  Why not, if you don't mind me asking?

Well, I might, but I just re-read the OmahaMakerGroup.org site and the Bridge Competition link to this thread but I didn't find a "when"?

I might not compete, but if it works out I think my girls would get a kick out of it.

Dan

Re: [OMG] Re: Bridge Competition Rules ejk00 4/11/12 9:25 AM
Good point!  What _IS_ the actual "when" date????
Re: [OMG] Re: Bridge Competition Rules David Knaack 4/11/12 9:32 AM
I believe we were planning for Sunday, May 6th.
Re: [OMG] Re: Bridge Competition Rules David Knaack 4/12/12 3:06 PM
The load plate that will be used for the competition is at the space if you want to do any testing, or inspect it to ensure that your bridge design is compatible with the plate.

--

As a resource that may save you some physical build time, you may wish to use this truss simulation tool:


It isn't perfect, but it can help you to get a feel for how different shapes affect the tension and compression loads on elements of a truss. 

--

A couple of rules clarifications:

The bridge must fit entirely within a 50 x 20 x 10 cm rectangular volume. This implies nothing about how the bridge can be oriented with respect to the support platform, aside from the obvious constraint that the bridge must span the 30 cm gap between the support platforms. So if you want a bridge that is 20 cm wide and only 10 cm tall, that fits the requirements of the rules.

While the load plate is flat and 5 x 10 cm, you don't necessarily have to have a flat spot in the bridge deck that size. If you have a curved deck surface or whatever such that only a fraction of the plate contacts the bridge, that's fine. It just needs to have some part of the load plate applying the load to the bridge deck, and only the bridge deck. The deck itself must be supporting the plate, you cannot, for example, have the plate sitting on the bridge side beams in addition to the deck (beams under the deck are fine of course). Essentially, the load plate has to go where the cars would drive.

DaveK
Re: [OMG] Re: Bridge Competition Rules David Knaack 4/13/12 7:22 AM
Does anyone know if we have a scale accurate to 0.1g that we can use to weigh bridges?

Balsa density ranges from 0.06 g/cc for ultra light to 0.22 g/cc for hard balsa. My scale is 0.5 g resolution, which works out to a fairly substantial amount of wood.

DaveK
Re: [OMG] Re: Bridge Competition Rules Kevin Fusselman 4/13/12 7:24 AM
I think the new scale that Eric brought is 0.1 gram...
Re: [OMG] Re: Bridge Competition Rules Ben H 4/13/12 8:41 AM
I have a scale at home good for 0.01 gram.  I'll be using it in secrecy the next few weeks while attempting to beat all the rest of you, but if necessary I would be happy to bring it on competition day for scoring.
Re: [OMG] Re: Bridge Competition Rules ejk00 4/13/12 9:09 AM
I will have to check the accuracy of it.  I know it shows 0.1g, so I assume the accuracy is 0.05g.

On Fri, Apr 13, 2012 at 9:24 AM, Kevin Fusselman <ke...@fusselman.org> wrote:


Re: [OMG] Re: Bridge Competition Rules ejk00 4/14/12 7:18 PM
My new scale is +/- 0.5g. But I have a smaller one that is +/- 0.05g if that works. 

Sent from Eric's iPhone
Re: [OMG] Re: Bridge Competition Rules David Knaack 4/16/12 1:51 PM
Fun software:


Similar to the truss applet, but fancier. Probably not actually more useful for making balsa bridges, but it sure is cool.

DaveK
Re: [OMG] Re: Bridge Competition Rules David Knaack 4/22/12 7:20 PM
Here's an example of testing a bridge. Bridge is in the center of the test platform, and the load plate is placed on the deck. A hook is threaded into the load plate from below, and then a weight (about 8kg in this case) is suspended from the hook.

Re: Bridge Competition Rules Travis Smith 5/6/12 1:16 PM
Its on!!!

http://omahamakergroup.org/2012/05/06/balsa-bridge-bash-is-happening-now/ 

On Wednesday, April 4, 2012 11:26:54 AM UTC-5, David Knaack wrote:
Below are the rules for the Bridge Competition.

Please ask if you would like clarification of the intent of the rules. 

The general idea is that it needs to function as a bridge for a toy car, allowing the toy to cleanly traverse the entire length of the bridge, with a realistic maximum allowable grade.

If you plan to use a really exotic construction method, plan on providing detailed documentation or demonstrating the method.

----

Bridge:

May contain only balsa wood and Titebond 2 wood glue.

Must fit within a 50 x 20 x 10 cm rectangular volume.

May not contain more than 6oz of glue by wet volume.

Must have a smoothish road deck no less than 6cm in width.
 - suitable for a HotWheels-style car to easily roll over

Deck ends must contact the upper surface of the test rig support planks.

Deck must have no more than a 10% grade (where grade = 100 * (rise/run))

Deck must accommodate the load plate.

Some part of the load plate must fall across the midpoint of the span.

There are no limits on construction tools or technique.



Scoring:

The load plate is 10 x 5 x 1 cm, and has a loading hook extending from the center of the bottom surface which requires 1 cm annular clearance through and below the bridge deck.

Bridges will be loaded progressively (w/ minimum shock load), starting at 5kg and progressing in 1Kg increments to 10Kg.

Upon reaching the maximum load, the bridge must hold for 1 minute.
 - Disputes as to whether a bridge 'held' will be resolved by vote

Bridges that fail will be ranked by the weight carried without failure and bridge mass.

Bridges that do not fail will be ranked by the mass of the bridge.



Testing:

The open span between the support planks is 30cm.

The open span is between rectangular, fixed, smooth, level, coplanar planks with a thickness of ~2cm.

The bridge may touch the top or inner surfaces of the supporting planks, but may not touch any other surface, nor be affixed to any surface.

The load plate will support a wire or rod from which the test load will be suspended.