Week 4

     In the past week, our team examined the three different bridge designs we came up with and designed a new bridge that minimized the cost.  The technique we used was to make a bridge that had a low number of members and that is low in relation to the surface of the road.  Originally, we all had designs that were very tall, by making a design that was short, the price was cut down tremendously.  The lowest we have been able cut the cost down to is $226,559.12.  We experimented with using hollow tubes versus solid bars.  The hollow tubes have to be much thicker than the solid bars but they are significantly less expensive than the solid bars.  Another interesting thing we found was just because the size of the members is smaller doesn't directly relate to the cost decreasing.  Sometimes we would decrease the thickness of the members and the cost would go up because it is not a standard size.  This was a minimal problem because then we had to check if the price decreases or increases as the size changes for each member.  We also found that every bridge design seems to have a minimum cost, there is a point where you cannot do much more to decrease the cost of the bridge.  We had many designs that we could not get the cost low enough to use.   Our major accomplishment was coming up with a bridge design that is very cost efficient however we still continue to look for ways to minimize the cost.  In the coming week, our goals are to start converting our design to knex to build a physical model to test and possibly changing the design as we progress.

     Now that we have been using West Point Bridge Designer for several weeks, we are beginning to see how realistic this program is for designing a real bridge.  It is a very realistic program for the intentions of introducing the structural design process, it is very simplified program that emphasizes the design process, not the detailed technical aspects of design.  It gives us the freedom to design whatever shapes we desire.  The program limits the design in ways like limiting span length and support configurations and the choices of material and member size are limited.  It also allows us to evaluate alternative designs and materials.  We can test the alternatives to see what is the best option.  When experimenting with changing one area it usually affects another area.  In the real world, there are codes that must be followed to make sure engineering is practiced with consistency and safety throughout the country, WPBD takes some of these codes into account.  Safety is always the most important factor, the cost is important but if the bridge is not safe and functional then the cost is irrelevant.  Cost reductions cannot be made if the safety of the bridge is compromised.  The cost calculation is also realistic because WPBD takes into account the cost for fabrication and assembly.  A degree of standardization in the selection of structural elements can cause the price to be reduced because there are not many unique pieces that need to be made, everything is consistent.  West Point Bridge Designer takes a lot of necessary elements into consideration when designing and testing our bridge designs.  It is also unrealistic in some ways.  When engineers design actual bridges, they are required to develop very detailed designs and cost estimates for the piers, roadways, and decks.  WPBD only allows us to develop very simplified designs and calculates the cost estimate for us.  It has us design the main trusses and the design is two-dimensional as opposed to three-dimensional that actual engineers work with.  Engineers also consider the environmental impact of the bridge, they examine its impact on water and ice in the body of water it is crossing and take fatigue into consideration.  WPBD does not take many different types of loading into consideration.  The program does not look at different forms of wind, snow, collision by vehicles and ships, or earthquakes.  Deflections are also a limitation that engineers have to consider, WPBD calculated deflections but does not use them as design criteria.  WPBD only tests truck movement from left to right.  In the design of an actual bridge, the movement in both directions must be considered.  The cost estimation is not accurate in WPBD, the concepts are taken into account but they actual cost estimation is not accurate.  Overall, West Point Bridge Designer introduces us to the design process but it is nothing like designing a real bridge.