A3 - Yilei

• Free Body Diagram & Calculations

     By using the "Method of Joints", the analysis of the truss bridge is showed below. The bridge has a span of 24", a height of 8" and a load of 15 lb at point C.

• The overall forces can be seen below.

• The  same results of analysis in The Bridge Designer's version. 

       The online Bridge Designer is a program allows to design a virtual truss, and then put a load on it. It will calculate the tensions and compressions of each members itself. 

       When I did this program, I had to use the same scale of all members and angles to correspond the results of my hand analysis.  I made each grid be 2"so that the length should be 12 grids. And the height should be 4 grids. Then I picked up the middle node of the length to put a load on, which was 15 pound in this case. Consequently, I got the most approximating forces equaling the ones calculated by hand.   

• The results of analysis of our two foot span bridge in Bridge Designer program.

        Might because of our design, it was hard to computed via the Bridge Designer program. Our two foot span bridge has a bottom truss. So when I completed the adding process and pressed the calculate button, there's an error came out. It said that we had to followed stable structure is M + 3 = 2*N , where M is the number of members and N is the number of nodes. The simulation will not calculate forces unless this condition is met. Thus, we changed our K'Nex design a lot. Besides, we did looked the K'Nex joint test page and it showed the tension would increase if the bridge is symmetrical. So we did the bridge symmetrically.

        That type analysis of the K'Nex truss bridge can find out the strong and weak parts of the bridge by using the average strength of each joint. So we can change our design to reach the proper number. That can make the bridge more stronger.