A2: Ngov

The essential reasoning of the design of a truss bridge with a Knex kit is to allow a hands on experience with a realistic approach for a creative design to be physically tested. Consequently, the pieces of Knex are being used. The design in Figure 1 and Figure 2 show the elevation and plan view of a specific designed truss bridge. The reasoning of this particular creation came about because the most cost effective and stable bridge created must be built for a competition. A limited amount of members and gussets were used because an excess amount of material will increase the cost dramatically; as a result, there were not a great number of Knex pieces used. In addition, the use of the triangular pattern and shape allows for maximum load bearing capacity compared to squares and circles.

A design of a bridge shown below is an example of a CAD drawing version of Knex of the elevation view.

Figure 1

The plan view of the design is shown below.

 

Figure 2

The spread sheet seen below shows the cost and materials used for the design. 

As the spread sheet shows, the cost of the bridge design should total to be approximately $189000. Only three main pieces were used. 46 3.375" long chords, 12 5.0" long chords, and 48 180 degree grooved gusset plates that were later connected were used to create the Knex bridge.

The original design of the bridge was hand drawn and needed to be completely redesign due to the limited amount of member sizes. In addition, the intended design began with more triangles intersecting the middle to reduce the amount of deformation of the squares because the geometry of squares will force the squares to become trapezoids under compression and tension. The amount of triangles was reduced because the cost of the bridge project was too extravagant. Consequently, the design seen in Figure 1 and Figure 2 were drawn up.

Throughout the process of designing this bridge, a number of things were taught. For example, the pieces are similar to real life were some pieces are readily available and made in industrial plants, while the customization of new pieces would have an extravagant cost. This showed that not every piece of member will be constantly available for the erection of a bridge. In addition, the planning and drawing of the bridge on a computer is a similar process to professional because real engineers and construction managers must have a clear understanding of other trades to complete a bridge. If a designer or any member of the project is unorganized or unable to communicate effectively, then misinterpretations will occur and the project will be prolonged; consequently, the cost of the project will increase while the productivity decreases.

Week 5: Amanda Ngov Knex Design

 The previous week had a number of questions answered because the Engineering librarian from Drexel University came to show a few resources that could be utilized for future references in the course project and future research papers for other classes. The navigation of the Drexel University library website was also shown for further understanding. In addition, the majority of the class allowed students to experiment and creatively design new ideas for a truss bridge with a kit called Knex. Though a final design has not been agreed upon, the progress of communicating ideas to other team members in a specific group is improving. Suggestions are constantly being offered and not enforced independently. For the upcoming week, the specific group hopes to accomplish a possible finalized design as a back up while creating new designs to improve on in the future with Knex. The main and only issue that the group is encountering is the inability to use or physically have more Knex pieces to experiment and design an efficient bridge. Permission was allowed to borrow pieces but only a few were taken. Next week, more pieces will be taken to create a great bridge. 

The use of the program West Point Bridge Design and Knex certainly showed a few similarities and differences. Firstly, the computer program allowed a stimulation of a load being suspended on the bridge that was recently designed to show the compression and tension forces in each member, while the Knex allowed a literal hands-on experience. The computer program also allowed for a number of variety and changes of the member's material and size, but the Knex does not allow a change because the alterations of the pieces will result in a break of the material. The West Point Bridge Design seems to be more realistic and suitable for the project occurring due to the additional amounts of benefits than the Knex pieces.

Week 4: Corey Duane

In the previous week, the groups were shown different designs of truss bridges.  The idea of changing the kinds of materials used in the design was also introduced.  The groups spent the lab designing different kinds of truss bridges through trial and error.  A final design for a truss bridge was not determined and further research should be done before making the final design is decided on.

The bridges are designed using a program called West Point Bridge Design.  This program allows the user to design a bridge using different kinds of materials.  The program determines the total cost of the design.  It also provides information such as the maximum compression force / strength, maximum tension force / strength, and the length of each beam used.  In the program, the user can choose between using carbon steel tubes, or hollow tubes.  Changing the type of material being used can decrease the overall cost of the bridge, but this also make the bridge less stable.  I think the program is pretty realistic.  It is able to calculate the cost of the bridge and some of the forces on it.  However, the program does not account for other factors.  When testing, one truck drives over the bridge, when in reality there could numerous trucks on the bridge at once.  Weather such as warm or cold temperatures, rain, snow, ice, and wind may not have an immediate effect on the bridge, but over time they do.  The program does not account for these factors as well.

Week 4: Bridget Breslin

In the previous week, the West Point Bridge Designer was used by the team, again. We had tested many different types of bridges in the program observing different factors. Designing a bridge that was as safe as it possibly could be was very important to us. Another factor we looked at was the cost. We designed many different types of trusses to try and make it as safe as possible at the lowest price. After many trials and errors, we then played around with using different types of materials for different components of the bridge. Doing this brought down the cost of the bridge substantially, however was more of a task choosing which pieces would be made of what material.  

After using the West Point Bridge Designer for several weeks now, I have noticed some qualities of the program that are not realistic. Although the program helps to facilitate the thought and design process, some designs would never work in real life. When the design for the bridge is completed, a test run is done, which is one of the problems in the software. No matter what the design of the bridge looks like, as long as it does not break or deform into so strange shape, the truck will pass over it. This is a huge problem because although the bridge is safe in the program, in real life it would be anything but safe. The program does not account for the proper amount of bending that should be allowed. Also, the program does not consider nature’s effects on the bridge. Finally, the West Point Bridge Designer does not drawn into account the fatigue on the bridge and how long it is supposed to last based on environmental conditions and usages. All of these factors need to be considered in real life, otherwise many lives will be at stake.

Week 4: Amanda Ngov

The previous week showed different types of truss bridge designs to further stimulate the create flow of ideas to incorporate into the final design or further development of a bridge. In addition, the experience and process of editing and changing a particular design was seen through the testing of a bridge design to lower the cost but improve the efficiency and stability. Though it did not appear that the following design shown below in figure 1 was the most efficient, the process allowed the further education of the field and subject. Failure to notice or explore different ideas was experienced due to the lack of experience in the field and limited amount of time to recognize various designs. The exploration for new designs for a truss bridge is still being examined; consequently, a final design has yet to be finalized. The upcoming week requires more research on differing designs on truss bridges and further perfection on the cost and capacity ratio.

Figure 1: Design submitted of the truss bridge

Throughout the process of the bridge design, the program called West Point Bridge Design (also WPBD) was in constant use and utilized in many ways. For example, the stability of the structure, amount of weight a point load that could be tolerated and the compression and tension force amount was recorded. In addition, the program offered a hands-on experience of the civil engineering field. Also, WPBD allowed constant changes and edits because the design process is an ongoing process that constantly is not definitive. It is similar to the real-world problems where natural occurrences or damages created must be taken into consideration for the most efficient design. Another real-world problem that must be taken into awareness would be the balance between the height, weight and cost. With this in mind, the program also allowed changes in differing materials and lengths of bars and tubes for beams. Unfortunately, the unrealistic or unaffected features were also present within the program. For example, the program did not consider the three dimensional analysis of the design along with the environmental factors, such as earthquakes, water and rain, traffic, erosion and wind, because it focused on the two dimensional analysis. In addition, the program did not factor the amount of deflection the bridge passed. The deflection point of a bridge should not be significant because the program only considered the level of tension and compression recorded in the steal beams. Finally, WPBD did not care for the aesthetics values of the bridge design. In the real world community members also value the appearance of the bridge if it is in sight. The program WPBD has a number of benefits but also has many flaws and disadvantages. 

Week 4: Team Update

The previous week included a competition to create the lowest costing bridge design that was capable of allowing the transport of vehicles successfully. Groups were required to create one single design of a truss bridge to submit and allow that one design to be seen and critiqued by other students. The trial, error and stimulation in the WPBD program allowed students to become more knowledgeable of how to interpret the reading of the compression and tension forces applied on the beams. If there was a beam that exceeded a force greater than 1, the bridge would become nonfunctional and the truss bridge would be a failure. With this in mind a strategy was discovered to allow unexplored areas of designing below and above the middle beam body of the bridge. The lowest costing design that was created cost $253087.61 and can be seen below. The amount of deflection the bridge experienced was not significant and is reasonable for the safety of objects being transported.

The following week will consist of the further changes to improve the ratio for the bridge. Computer analysis and calculations will be to improve the design are also planned to be included in the next week's goals.

Difficulties that will be needed to be overcome will consist of the need to manage and multitask the design, ratio improvements, research on an overall completion of a bridge process and frequent updates on the designs of teams.