Truss DEsign
Materials testing
We spent a couple of weeks doing some initial materials testing. The reason for this is to have a ballpark range of the weight that our material can hold, and to choose a member design. We were using basal wood for our trusses. We built three standard, and similarly dimensioned triangle trusses. One of these used a single piece of wood for each member. The second used two pieces laminated together horizontally to form each member. The third truss used two pieces laminated together vertically together to form each member. After building each of these three trusses, we put them in a load tester and applied a load until they broke. The single piece was the weakest, withstanding 12 pounds of pressure. The horizontally laminated was the second strongest, it was able to hold 22 pounds. The only real advantage of horizontal lamination is that it reduces side to side sway, and that is the only reason that it is able to hold a higher load than a single-piece member. The vertically laminated member held the highest load, at 47 pounds. The vertical arrangement of two pieces per member more than double the amount of weight that the member can withstand. This was the obvious choice to use for each member, and was the choice of almost the entire class, including myself. Now I knew that the truss I designed had to put no more than 47 pounds of pressure on each member of the truss I was going to be designing.
designing the truss
The next part of the project was to design and build a truss that could hold 100 pounds and be as light as possible. I did some preliminary sketching and then designed and tested those in a program called MD solids to determine if they would be able to hold 100 lbs without putting more than 47 lbs. on each member.
In the end I decided to go with a simpler design that was much easier to construct and light. My idea was to design the most efficient truss possible, and if it was constructed well enough it might hold the 100 lbs.
Testing the truss
After I constructed my truss and let the glue set, it was time to test. Testing is a fairly simple process, you just have to position the truss into the tester and push start. We had the tester set up to stop at 100 lbs. My truss held up no problem at all. The only indication that a load was actually put on it is an indent on top of the truss.
reflection
Overall, I am very pleased, if not a little bit surprised at how well my truss actually held up. Given more time for construction, I'd have liked to construct on the more complicated truss' that I designed. They would have been much stronger and I am curious as to how much they would be able to support. I would also have liked to pushed the one I did end up building to its breaking point just to see what it is capable of sporting, but we didn't have time for that.
I believe that my truss withheld 100 pounds of pressure without breaking because of construction. When I constructed this truss I took it more seriously than when constructing my materials testing trusses. That leads to my error in the material trusses, they just weren't constructed as well as my final truss and therefore I was unable to get an accurate reading to base my truss design on. Because of that, I may have over engineered my truss. Looking back, I should have taken more care when building my test trusses. However, it was rather inconsequential in this situation, because my truss held the weight. Also, on the final truss I designed and printed out little wooden gussets on a laser cutter/printer. I believe that these added rigidity to the joints in my truss.
I believe that my truss withheld 100 pounds of pressure without breaking because of construction. When I constructed this truss I took it more seriously than when constructing my materials testing trusses. That leads to my error in the material trusses, they just weren't constructed as well as my final truss and therefore I was unable to get an accurate reading to base my truss design on. Because of that, I may have over engineered my truss. Looking back, I should have taken more care when building my test trusses. However, it was rather inconsequential in this situation, because my truss held the weight. Also, on the final truss I designed and printed out little wooden gussets on a laser cutter/printer. I believe that these added rigidity to the joints in my truss.