Analysis Process

Last week in class, I worked with the other members in my group to analyze our Knex bridge design using online bridge designer software created by Johns Hopkins University. It was difficult for us to put our exact bridge design into the software because of a special restraint the program called for: "Members + 3 equal twice the nodes." Basically the problem was that our bridge is symmetrical about a single node--not about a single member. This caused our bridge to have an even number of members. When you add 3 to any even number, you come up with an odd number which, when divided by, is a decimal. But for our bridge, we cannot have a fraction of a node, so we needed to change our bridge design in order to use the online design program. The fact that this program wouldn't accept a bridge whose exact center point was a node rather than a member, led me to question our bridge's strength. This week in class, I will discuss with my group mates ways we can modify our current bridge design so that it follows the "members + 3 = 2*nodes" rule.

As far as analysis goes, I do think this method of analysis is efficient for a real bridge if additional factors are considered. On a real bridge, the weight of each bridge component needs to be taken into consideration when determining the tension and compression on chords. The steal beams, metal bolts, thick plates, and even the paint, all add to the total dead weight of a bridge which is a factor significant in determining the forces on each bridge member. If this dead weight is not accounted for, the bridge would fail before reaching its calculated load capacity. After thinking about this, I decided that I'd like to analyze the twisting of truss bridges. One bridge design that my group mates and I tested ended up twisting and snapping. I think it is important to know how strong and, as a result, heavy, a cross beam needs to be so that it is not adding to the bridge's dead weight, nor decreasing the bridge's weight capacity.