posted on June 07, 2012 |
Question: Can you make a record-breaking structure from ordinary materials?
Answer: Yes, you can.
About six months ago I was asked to do the “Introduction to Engineering” at University of Nevada Las Vegas or UNLV. My goal was to come up with ideas that would start the young people thinking about technical education and careers.
I decided to use ordinary household cardboard and Elmer’s Wood Glue to make structures that the students could test and measure. After all, I can’t coast on my Fettucini Bridge fame forever.
The results that were obtained were startling. In fact, one of my test structures produced a World Record in a New Category. It was a little stool weighing only 9.5 ounces that was able to resist an astounding static force of 1,113 lbs of weight before yielding to this load.
This started a whole new round of planned project requests, so I came up with an idea to build a bridge. This group would be all young girls so what I needed was something pretty spectacular, interesting to do and on a grand scale.
Early ideas and designs proved to be either too complex or costly and since I am on a retirement pension, keeping things cheap is a very big part of what and why I do things the way I do. So here is my bridge.
This bridge that was using the Warren Truss Design was too unstable. It was no fault of the design which I did not invent, but the struts were made out of a material that was too thin (remember how much I need to keep costs down and weight to a minimum?)
In retrospect I should have used ¾ inch or even 1 inch plywood, but these struts were made out of ½ inch thick redwood plywood, four feet long and only three inches wide. It went together okay but even the desert winds made it sway like a bowl full of jello. It needed bracing.
So I went to my favorite store and bought a hundred feet of ¾ inch EMT pipe. (Electrical Metallic Tubing) I had to cut them into the proper lengths and then flatten out the ends for about 2.5 inches, then cut out ¾ inch holes in the ends, put in the proper angles so they would match the axle pins to stiffen things up. This is not an easy build but it had to be able to be taken apart and then reassembled.
The Warren Truss Design is based on Equilateral Triangles. I made the sides of the triangles 4 ft long, 3 inches wide and a half inch thick. I drilled ¾ inch concentric holes with the rounded corners ends in order to accept the axle pins as shown here as the basic concept.
In this next picture I am trying to show you the lattice work of bracing I used to stop the desert winds from toppling this bridge over. Most of the time I had to lay it down on its side. It is higher than the wall which is slightly over 6 feet high. Yes, my neighbors think I am crazy.
This bridge is supposed to span a distance of 5.715 meters or 18.75 feet.
I used EMT compression pipe couplings cut in half to use as my axle locks. Only a pair of channel locks pliers and a crescent wrench are needed to tighten them.
Seemingly with the braces added the wind is no longer a threat to collapse it
¾ inch PVC was cut and sleeved over the ½ inch axles to prevent the bridge from collapsing in on itself. Some assembly required here.
Very flexible wood struts but they were painted in order to make assembly easier. Red to red, Blue to blue, Green to green, etc…
Only some minor adjustments are left to do along with some marking and numbering on the braces. Maybe electrical marking tapes will work to identify like members to make the selections from the pile of materials more sensible.
The young girls have been surprisingly talented, cooperative and when given something like this to tackle, they meet the challenge and have never disappointed me yet. A last pictures of the bridge is down below. That is 160 lbs (me) at mid-span. See any sagging?
Remember the Wright Brothers with their invention? I say, “Well gee whiz why not?” That attitude, some planning, and a willingness to experiment can lead to remarkable results.
This is Corporal Willy saying believe in your ideas and projects when you work. Bye for now.