Attending Presentations in Week-10

Dr. Primerano asked me to clarify that we want you to attend three presentations by students in other sections.  You’ll have an excellent opportunity to see the wide variety of projects undertaken by your classmates.

We elected not to require presentations in our sections, substituting the bridge testing in Week-9 in its stead.  However, becoming familiar with presentations as both an observer and a presenter is an important skill for all engineers.

Week-10 Presentations - Why We're Not Making Them

Question:

Why don't we have a presentation time for our project? I don't mind that we don't have to do that extra work, but I'm curious about your reasoning on this decision.

Response:

My belief when putting together this course was that the week-10 presentations didn't make sense for our sections for the following reasons:

• Everybody is doing the same thing in our sections, whereas other sections have more varied projects.  I felt it would become boring to everyone to hear the same issues addressed many times.
• I asked a considerable effort of you in putting together the weekly posts as well as the assignments.  Making the last week a lighter load seemed like a good idea.

I'd be glad to hear from the class if you think adding the presentations another time would be beneficial.

Jim Mitchell

COMP2 - Final Results

See the following link for the comp 2 results: https://docs.google.com/spreadsheet/ccc?key=0Aq9AvRYJR07tdFpoRExuUlpGcVZMa2VONm8zZjdxemc

Group highlighted in Red had the lowest cost-to-strength ratio.

Group highlighted in orange had the smallest deviation between predicted and actual failure.

Comp-2 Corrections

Question 1

I believe there is an error in the COMP2 description where it says "When you have completed your initial WPBD design you'll submit the results to an online spreadsheet including....". I believe it should say Knex instead of WPBD, correct?

Response

You are correct.  I have corrected the page to reflect that.

 

Question 2

… only one person per group needs to turn in the COMP2 right? Or do all the members of the group have to complete/submit it?

Response

Yes.  Only one person per group needs to submit Comp-2

Refining Bridge Design

I've had two good questions about refining your bridge designs that may be of general interest.

Q1 - Why does an "X" type arrangement fail when using the Hopkins "Bridge Designer".

Response:

Probably the best answer is that you have created a "redundant" structure with an "X".  You can test that by removing one leg of the X and probably it will work as in the example above.  If you add the member from the lower left to the center of square so you have a complete "X" Bridge Designer won't calculate it because you have an unnecessary or "redundant" member.

Q2 - Additional Analysis

Throughout the project, I have been replicating the Knex bridge on WPBD as an extra load test. But thinking about what you said today after lab, I realize that's not the best way to test our truss. What at-home methods do you suggest would be best to see if the truss is stable?

Response:

Unfortunately you're running up against the limits of the tools you will understand in your first year.  There are indeed many tools for additional analysis and testing, but to use them effectively you need the knowledge that you'll gain in your more advanced courses.  WPBD and Bridge Designer have to make simplifying assumptions that your real bridges violate.  Let's hope this is your incentive to continue learning.

Units for Results

At 10:47pm the day before the assignment was due I was asked the following question.

“Is it ok if we converted pounds to newtons and feet to meters to do the calculations?”

Response

You may work internally in any units you wish, but results should always be shown in the units of the country in which you work unless told otherwise.  If I were working in almost anyplace other than the US then newtons and meters would be the appropriate units.  In our backward (in terms of units) country we still use feet, inches and pound-force and expect to see them in the results.

A3 - Part-5 Clarification

Question:

Did you say that only one group member needed to complete task 5 for Assignment 3? It asks us to use Bridge Designer to model our Knex Truss, and right now only one member of our group has the bridge with them.

Response:

You only have to perform the "Bridge Designer" analysis once in each group.  Each member, however, is to include the results of the analysis (part #1) and perform part #2 of Task 5 individually, though you're welcome to coordinate with your team members.