Truss Construction Portfolio
If you haven’t already, check out my webpage for solving a truss:
http://alexanderrt.weebly.com/truss-calculations.html
Performance Objectives:
1. Calculate the forces that each member was under at the breaking point.
2. Design a truss to hold a specified amount of weight.
3. Discuss the results of your experiment, positive or negative. Discuss any ideas as to how you got your results.
The specified amount of weight for this experiment is 100lbs. If my truss design breaks before that weight is reached, then my experiment is a failure.
Before I started designing a truss, I had to understand a basic one. I made a few trusses to see how much weight they can hold. Here are my basic trusses:
http://alexanderrt.weebly.com/truss-calculations.html
Performance Objectives:
1. Calculate the forces that each member was under at the breaking point.
2. Design a truss to hold a specified amount of weight.
3. Discuss the results of your experiment, positive or negative. Discuss any ideas as to how you got your results.
The specified amount of weight for this experiment is 100lbs. If my truss design breaks before that weight is reached, then my experiment is a failure.
Before I started designing a truss, I had to understand a basic one. I made a few trusses to see how much weight they can hold. Here are my basic trusses:
This truss one piece of wood thick, the smaller pieces are there so the truss can fit inside the machine.
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The members for the trusses above consist of two pieces of wood.
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The members for this truss consist of two members like the other truss; except for this truss they’re stacked on top of each other.
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After Construction
After I built the trusses, I simply tested them.
Here are the trusses being tested and destroyed:
Here are the trusses being tested and destroyed:
Here is the simplest truss breaking.
In this photograph, you can see where the double-thick truss broke.
This is the double-stacked truss breaking.
After testing the three trusses, I solved the three trusses using MDSolids. Here are the three trusses:
The simple truss broke at 5lbs. The height of this truss was 3.25” and the width was 6.75”. The member was under 3.6lbs compression when it broke (red line).
For the double-thick truss, it broke at 35lbs. The height for this truss was 3.75” and the width was 6.5”. The member broke at 23.16lbs of compression.
The double-stacked truss did the best out of all of the trusses, it broke at 61lbs. The height for truss was 4” and the width was 7”. The member was at 40.53lbs of compression before it broke.
All of the trusses that I tested had the same member forces on both sides and same y-direction reaction forces too. The horizontal member for every truss tested was under tension, and didn’t break.
Why did the double-stacked truss perform the best in this test? Well the answer is simple; the double-stacked truss had a greater moment of inertia for its member forces. The shape of the members had a greater resistance to deformation; therefore it took more force to break them.
For more about the moment of inertia, look at my other webpage:
http://alexanderrt.weebly.com/deflection-lab.html
I decided to design my truss after the double-stacked truss. I liked the triangle design because it split force equally between the two member forces. But how would I improve the original design?
What I did was added a member to the design, and this is what I discovered:
Why did the double-stacked truss perform the best in this test? Well the answer is simple; the double-stacked truss had a greater moment of inertia for its member forces. The shape of the members had a greater resistance to deformation; therefore it took more force to break them.
For more about the moment of inertia, look at my other webpage:
http://alexanderrt.weebly.com/deflection-lab.html
I decided to design my truss after the double-stacked truss. I liked the triangle design because it split force equally between the two member forces. But how would I improve the original design?
What I did was added a member to the design, and this is what I discovered:
Adding a vertical member in the middle of the truss does nothing! You might be asking yourself, "Does the member really do nothing?" Well, the answer is that the member actually does.
You see, adding the member in the middle of the design does this:
You see, adding the member in the middle of the design does this:
The vertical member forces the horizontal member to bow, making the horizontal or vertical member break before the other two members would. So in a sense, the member doesn’t do anything statically, but it does.
My design had to be at least 6.75” wide, and at the most 4” tall. In my design I wanted to make it the tallest that I possibly could, so I made mine 4” tall and 6.75” wide. I started placing members around where the double-stacked truss broke, and I arrived to this statically determinant design:
My design had to be at least 6.75” wide, and at the most 4” tall. In my design I wanted to make it the tallest that I possibly could, so I made mine 4” tall and 6.75” wide. I started placing members around where the double-stacked truss broke, and I arrived to this statically determinant design:
As you can see, one side of the truss design has more members than the other side has. I did this to see if the truss would break in the same area as the double-stacked truss. The obvious flaw to my design, is that all of the inside member forces are 0lbs. I did this on purpose; I wanted to see what the inside members would do. In my hypothesis; the members would stick together because of all of the joints I had to glue together, and the member attached to the least amount of other members would break. According to this design, the two sides would experience 65.42lbs of compression…the double-stacked member broke at 40.53lbs of compression!
When I built my truss, I used wood glue and laminated all of it. I made my gusset plates mostly triangles; I had two squares on the top and bottom. Here is my truss design:
When I built my truss, I used wood glue and laminated all of it. I made my gusset plates mostly triangles; I had two squares on the top and bottom. Here is my truss design:
After I finished testing my truss, I examined the results of the experiment. My truss broke at 138lbs, 38lbs above the goal. The experiment was a success, but why?
I predicted that the member attached to the least amount of other members would break, and the member that broke was the diagonal side with five joints, and it fractured near the top, or the area with the least amount of joints. Here is the fracture:
I predicted that the member attached to the least amount of other members would break, and the member that broke was the diagonal side with five joints, and it fractured near the top, or the area with the least amount of joints. Here is the fracture:
Member forces are very important in understanding trusses, but understanding the purpose of gusset plates and the joints of a truss are also important. On August 1st, 2007, the I35-W Mississippi bridge collapsed because of improper gusset plates. More than 145 people were injured and 13 were killed because of the sudden collapse.
Understanding trusses and the significance of proper gusset plates can make sure bridge collapses, like in the video above, won't happen in the future.