Nilay's Assignments

A3- KANTARIA

Method of Joints showing the calculations done by hand to calculate the forces acting on each member as shown in the last diagram.

Results of replicating the analysis using the Bridge Designer software.

In order to have the hand results of the analysis match the one computed by the Bridge Designer we would have to make sure we’re using the same scale for all the members and the angles. Since I did the hand analysis first, I tried to have the Bridge Analysis design match the one drawn by hand. For this I used the same ratio for the lengths of members while keeping the design symmetric. Not surprisingly, I got the resulting forces approximately equaling the ones computed by hand. 

Results of the analysis of our team bridge using the Bridge Designer software.

The load applied during the Bridge Designer analysis to our custom bridge was 10 pounds as shown in the picture. In order to calculate the forces acting on each member of the bridge based on the given load of 15 pounds, we would simply multiply the forces by a factor of 1.5. Since 15/10 = 1.5, all the tension and compression forces acting on the bridge would be multiplied by 1.5. This would change the magnitude without changing the angles.


The method of joints analysis is one way that enables us to determine the magnitude of tension and compression forces acting on each member with a given load. The pull-out force date provided by the chart can be used to determine the force under which the bridge would fail at the corresponding connectors. We can notice that the gusset plates with more members connecting to it have a higher pull out force associated with it. The three, two and one member joints have the average pull-out force of 35.6, 26.5, and 20.7 respectively. This tells us that we would have a stronger bridge if we have the maximum number of connections at the gusset plates. We can also use this information to design our bridge such that the forces acting on each member would be under the given values of the pull-out force while maximizing the applied load. This s similar to how we designed our bridge in WPBD by setting our goal to reach the tension/ compression ratio to 1 while having a functioning bridge with the cheapest cost. 

A2- KANTARIA

Since the bridge will be suspended with the supported only by the gusset plates at the bottom corner, I decided to design a bridge that would have majority of its construction on the sides. I wanted the force coming down on the center of the bridge to be distributed to the sides, so I ended up with the shape shown in the figure.

Figure 1: Elevation 

Figure 2: Plan

Figure 3: Truss Bill of Materials

At first I started out with a rectangular bridge with alternating triangles. However I decided to have more support on the sides than the center and so I came up with a design that was similar to the final once illustrated above, but it was much thinner at the center. I later learned that if the bridge is too narrow in the center then there is a greater chance of it “splitting” apart when the force is applied at the top. So I ended up modifying that design by reinforcing support in the middle portion. There will be two identical sides as shown in figure one, connected by 7.5" chords.

One thing I learned from designing the bridge is that you have to work with 45 degree angles. This is part of the constraint, limiting you with design choices. I also learned that sometimes it would be worth spending more money on the bridge if the design seems to be much stronger. 

A1 -KANTARIA

I based my general bridge design on the predefined Pratt template with right triangles running along the sides. I wanted to have a triangular shape for the upper chord but due to one of the design constraints, the deck elevation had to be 24 meters which only allowed the bridge to be certain height.

Figure 1: 2-D Image of Design

Figure 2: 3-D Animation Image with Truck 

Figure 3: Load Test Results

Initially the design had square ends, with all of the bars made of 140x140 carbon steel. However the design had several errors in it which were fixed upon multiple trials with the truck animation. I changed the material and the dimension of the bars which had the most amount of force exerted on them. Once it was a functioning bridge, I further reduced the dimensions of the rest of the bars in order to reduce the overall cost of the bridge. The final cost came out to be $358,795.65. With further time and knowledge while using the same design, I think the cost could be reduced by about $5000.00.

By designing this bridge, I learned a couple of things. The most important thing is that sometimes we don’t need some of the members to make bridge look symmetrical. The weight and the cost of these members seem to outdo the support that they provide. Through the trial and error design process, I noticed that rectangular shapes don’t function well if they function at all. I also came to realize that not all the beams and members have to be the same material with the same dimensions. Having different materials depending on how much weight/ force they bear can function better as well as reduce the expenditure.