Units for Bridge Lab–Sources for Calculation Problems–Dimensions and Micro-Strain

There are two potential sources of error on the bridge lab, one of which is probably not as obvious as it ought to be.

#1 Consistent Units

It’s easy to forget to convert your lengths into consistent units – usually inches.  That often introduces big errors.

 

#2 Micro-Strain

The data for the lab are marked “ue”.   It is probably not obvious that this means the real strain is 10^6 times smaller than shown in the excel spreadsheet.  It’s shown that way in the spreadsheet to avoid showing many, many zeroes before the significant digits.

So: a strain shown on the spreadsheet as –1.23 ue  is really –1.23/10^6 = 0.00000123

Lab-9 T-P Bridge Questions

 

Questions

Are these problems that need to be done for the lab? 

(2) Monitor the strain gage data under traffic and inform the engineer operating the data acquisition system when a truck approaches so they can record the strain time-history.

(3) Take a photograph of the truck that caused the measured strain in the top chord and note the lane (upstream, downstream or center) it occupied. 

      (8) Is the computed truck weight less than the legal limit?   (Where are we to find the legal limit?) 

Added Later

And is the max stress level the values in the one in the -30 range or in the 4-5 in/in range

 

Response

#2 & #3 – We provided the strain gauge data and the truck photograph this time

#8 – As Dr. Moon said in his lecture and I said in class today you can find this by a Google Search looking for Federal truck weight load limit or something similar.

Max Stress Level – It’s up to you to determine the max stress level.  Usually a maximum (in absolute terms) is the greatest departure from the average.

About the Online Final Assessment

Where Do I Find It?

• Click on the “Quizzes and Exams” menu item in the course website in BbLearn

When It’s Available

• Opens – Midnight Thursday Morning  6/5 
• Closes – 11:59PM Sunday Evening 6/8

How Much Does It Count?

• 18% of the total grade

What is on it?

• 75% Multiple Choice + True/False + Multiple Answers (more than one answer per question possible)
  • These are drawn from the lectures and the labs in the course.
  • A few require you to be careful in your thinking, but most are straightforward.
• 15% – Calculation Questions based on the labs
  • The description and logic for calculating the answer are the same, but each student will see different numbers
• 10% – 200 words or more on the Best or Worst (or Both) Aspects of CAEE-201 – graded on being specific, not on your opinions.

May I take It More than Once?

• Yes, you may take it up to three times – each time you have 3 hours
• You will not receive your score after taking the assessment– not until I have graded the essays after the assessment closes
• You may not save and resume during one instance of the test.
• Each time you take it the numbers for the calculations and the order of the questions will probably be different.
• You should assume that we will use the grade from the last instance that you take the assessment.

Lab-9–Tacony-Palmyra Bridge Questions

Questions

#1 What files do we submit to Bb Learn for this assignment? If it is a singular Excel workbook, then are we to create the Memo sheet from scratch? If not, what other files are we to complete?

#2 When analyzing the strain values from the sensors, I noticed that a lot of them, including the largest ones, are negative. Does this imply that the strain is in compression? Are we to use these larger negative values in our calculations and disregard the negative sign?

#3 Which distribution factor are we supposed to use? Are we to use just one? Or do we calculate the weight of the truck three separate times for all three scenarios?

 

Responses

#1 – As in any work situation you are to submit what is required to address the problem.  We left it more open.   If it were me, I’d submit a single Excel sheet using what I’d learned from the other labs.

#2 – Think about the truss and how it bends.  The bottom wants to stretch and the top wants to compress.  Negative values indicate compression.

#3 – You are to look at the information provided and decide which lane the truck is in and thus which distribution factor is appropriate.

Lab-1 - Help with Question 5b

Question

“would the first blank where it asks for the Air BTU/CF-DegF be solved by dividing the air specific heat by the air density?”

Response

There are several ways to address this kind of problem where you’re facing new material.

1) Check the units.  Given the information available what combination produces the units of the desired answer.  In this case that’s BTU/CF-DegF.

2) Think about the physical reality – the more meaningful approach.  I suggest thinking about one cubic foot of air. 

• What do we know about it? 
• It has a mass, which we can calculate with the given information
• It will take a amount of heat to raise it one degF
• We can calculate that if we know the mass because of the other given information
• With those two you have the answer
• The same approach will give you answers to the other parts.

Discussions–How Many Other Students to Review?

Question

If we posted first in our thread, do you still want us to reference other students' posts?

Response

I’ve revised the discussion page to address this question explicitly.  Here’s what it now says.

Each week you are to prepare for the week by reading two professional-level sources that give material related to the topic for the week.

You are to answer some standard questions about it and give some opinions.

You will enter that into one of the discussion "topics" for that week in BbLearn. You are also to read the entries of other students who have read the same primary source material and react to those entries in an appropriate way by editing what you've written to react to what those before you in your topic have entered.

We expect you to comment in some way in your discussion post on the work of at least two other students.

• If you're the first to post in your thread you do not need to comment on other student's work - but you do need to state that you were the first to post.
• If you're the second to post you comment on only one.
• We'll check and deduct points if we find suspicious claims.

Discussion Posts–Addressing Other Student’s Work

Question:

I would like some clarification about how you and/or the graders would like us to respond to other students posts. Should we use the "Reply" button underneath another students post, or should we include our responses in the body of our own post?

Response:

You want to make sure the grader knows that you have read and considered other people’s work.  The best way to do so is incorporate references to other people’s posts in your own post.

• e.g…… I agree with Jonathan Doe’s opinion about the importance of Geotextiles in Geotech, but am concerned that we don’t have good data on how they will deteriorate over time…………