A3-Truss Analysis: Amanda Ngov

By using the Method of Joint, calculations for an analysis of a bridge was possible. Figure 1 shows the calculations of a bridge that has a span of 24", a height of 8", and a load of 15 lb at the middle joint.

Figure 1

The diagram and table of all the forces can be seen in figure 2 and figure 3 below.

Figure 2

Figure 3

A computer program called Bridge Designer has the abilities to create a similar type of analysis of the bridge with similar values as seen below in figure 4. The advantage of this program is that it has the ability to scale the values of the length, width or load of any type of truss bridge. With this in mind, the bridge in figure 1 can be drawn twice as small or large. The only needed adjustment would be to multiple or divide the results outputted by the program. For example, if my bridge had a span of 48", height of 16", and a load of 30lb then all the forces would simply need to be multiplied by a factor of two. The F_AB would be approximately -18 lb instead of -9 lb. This basic concept can be applied to a number of different designs. In addition, the bridge in figure 5 has similar features of the previous truss design but with extra beam members. When the design was drawn in Bridge Designer, an error occurred because certain nodes were not attached by members. This resulted in an indeterminate bridge, which forced my group to adjust the design in Bridge Designer. In reality, the changes would allow a shift and more even distribution of the forces onto the other members. The overall forces are symmetrically and evenly distributed, but the forces in my group's design allows more even distributions.The advantage with recreating the design in Bridge Designer is simple scaling of the weight load or the length of the members to different proportions.

Figure 4

Figure 5

The knowledge of the "Testing Information About Knex Joints" gives knowledge on the average, median and minimum force (in pounds) a member would pull out from a joint given the amount of members that were connected. It appears that as the number of beams connected to a gusset increased, the load capacity increased. The reasoning and logic behind the results is the force can be displaced more evenly throughout the entire bridge as opposed to a few weaker beams. In addition, if a member got pulled out of the gusset, then other members have the ability to allow a longer period of time for the collapse of the bridge. A more graceful collapse will occur instead of a catastrophic collapse. In real life, a catastrophic collapse could result in many casualties dying. The process of this analysis has shown a more even distribution of forces is preferable for n efficient bridge.