Hurricane Break–Keep Working

As you’re undoubtedly aware, Drexel is closed on Monday and Tuesday due to Hurricane Sandy.

Discussion Due Date Extended to Wednesday

I’ve extended the due date for the discussion until Wednesday morning.

Review Dr. Block’s Slides Planned for Monday

I’ve mounted in the Lecture Notes folder the slides from our planned speaker for Monday, Dr. Paul Block.  Please review them for Wednesday.

Location of Web Plates–Bridge Lab

I’m responding to this late query because the deadline was extended to noon Saturday. Otherwise it would have been too late.

Question

“I have a question regarding the cross-sectional area sketch for the top chord of the bridge. Since the cross sectional area has two sets of different web plates (two are 24x5/8 and the other two are 24x11/16), would that mean that I'd have to sketch four web plates total? If so, how would I arrange these web plates in the sketch (i.e would the inner web plates be the 24x5/8 plates or the 24x11/16 plates)?”

Response

In practice there’s no difference – we’ll take either location.  The difference of 1/16 of an inch matters to the total area resisting the force, but otherwise does not.

Bridge Lab–Sign of Strain

Question

“Because the strain values are negative, does this mean that we keep it as a negative value? For example, when calculating the force in the top chord, if the max measure strain is left negative, the force will then be a negative value. Or, instead, do we put this number as a positive value?”

Response

Exactly what sign you use doesn’t matter so long as you’re consistent.  You’d like to understand what it means.  I suggest that you review Dr. Moon’s lecture notes to understand whether you expect the top chord to be in tension or compression.  The sign will mean one or the other of those.

Dimensions for Bridge Lab

Question:

“If I'm looking at the dimensions given directly about the 85' marker, it would appear that these are not for the top chord since there is no cover plate dimension. Am I supposed to then pick set of top chord dimensions nearby - such as between U3-L4 or U5-L6? Also, for the image, will it end up looking like the example on the blog (the cross-sectional view of the top chord), except with different dimensions?”

Response:

The Tacony (PA) and Palmyra (NJ) spans are symmetrical.  You can therefore look, as you suggest, at the U5-6 information to determine the top chord.
Yes that section of the chord will look like the cross section that I posted.

10/26/2012 Correction on the location reference.  85' should put you between U4-U5.  The member section information for this is the different than for what I sepcified above originally for U5-U6.  I am asking the graders to accept either sets of information so that you are not penalized.

Bridge Lab–Extension + Report Ingredients

Due Date Extension

Because we’ve had late-flowing information I have extended the due date for Dr. Moon’s bridge analysis lab until noon on Saturday (10/27).

Report Ingredients & Grading Weights

Neha Sunger provides the following summary information about the expected report ingredients and grading weights.

1) No memo is required for the LAB-4 (T-P Bridge visit lab submission).

2) Submit 2-sketches (properly labeled, Gauge location on the truss span and cross-section of the top chord identifying all the members and sensors). (20 points).

3) Cross sectional area calculation (20 points)

4) Maximum strain value calculation (15 points)

5) BONUS -Comment on maximum strain reading being negative (5 points)

6) Show the input values for Force calculation, the equation used and the result (correct units, conversion and scientific notation) . (10 points)

4) Distribution factor value.(5-points)

5) Moment calculation - (equation used, input values, units) - (30 points)

Bridge Lab–Lane Location

Question:

“I was just wondering what lane the truck was in for the given picture and readings? Is it lane 1 or lane 3? I know we will need this to figure out the distribution factor.”

Neha Sunger’s Response

If students look at the "read me" document it shows that side walk is on right side of sensor 1. Truck image shows the side walk on right of truck. So this indicates truck in lane 1 ( adjacent to sensor location)

Units of Strain - Bridge Lab

Question:

"after doing the "Force on the Chord" calculation, I got a value of 1.17E11 pounds. I am thinking my 33.72 (in/in) strain measurement should be much lower."

Response:

The units of strain are MICRO-inches/inch.  That should help.

Jim Mitchell

Bridge Lab–Solution Steps Suggestion

A number of students have asked for more instructions on the method to address the Tacony-Palmyra bridge lab prepared by Dr. Moon.  Neha Sunger, one of our TA’s, has most kindly prepared the following notes.

---

1) Look at the “Truss Spans Stress Sheet” drawing at pg-12 of Tacony-Palmyra Drawings document.

a. There are 3 “truss span” sketches and two “cross-section” sketches.

b. Look at the third sketch from top and locate pier F.

c. Locate the position of strain gauges. They are 85’ east of pier F on the New Jersey Truss span.

i. For this, roughly estimate the 85’ distance from pier F to pier G (shown that the total distance between two piers is 244.87’).

d. Submit a sketch showing this location (You can copy –paste the given drawing and mark the location on it OR you can draw it yourself but make sure to label beams and spans appropriately).

e. Look the second sketch from top on the same page and find the details of the members of the top truss chord at the gauge location.

f. Submit a sketch of the cross-sectional view of the top chord highlighting the cover plates, angles, webs and plates. (A sample of this sketch is provided by Dr Mitchell, check the blog post at- http://caee-201ay121.blogspot.com/2012/10/top-chord-tacony-palmyra-bridge.html).

2) Calculate the cross-sectional area of the top chord following the example calculation given in the “T-P Lab description 20121018.docx” document.

3) Now calculate the top chord force using the following expression:

F = ε E A

Where,

F = force in the top chord (lb)

ε = maximum measure strain (in/in) (given in the excel sheet)

E = elastic modulus of steel (29,000,000 psi)

A = cross-sectional area of the top chord (calculated in step 3 above)

a. Value of ε should be the maximum strain recorded in the member.

i. Either identify the minimum strain gauge data reading for each sensor and take an average.

ii. Or pick any one strain gauge but justify the criteria for the selection.

b. BONUS: Answer to the question- Why are the maximum readings negative?

4) Check the truck picture and locate if it’s in lane 1, 2 or 3.

5) Assign a ‘distribution’ factor based on which lane the truck was in when it crossed the bridge.

γ = distribution factor:

0.75 for Lane 1

0.5 for Lane 2

0.25 for Lane 3

6) Now apply moment equilibrium (see the forces shown below in Figure 1) and calculate the weight of the truck using equation:

ΣM_o = 0

F (H) - γ W (L) = 0

W = [F (H)] / [γ (L)]

Where,

L= truss span (given 85’)

H= distance between chords (get from the pg-12 drawing)

F= calculated in step 4.

Fig. 1

Top Chord - Tacony-Palmyra Bridge

The drawings of the Tacony-Palmyra bridge do not explicitly show a section of the the top chord of the truss on which the strain gauges are mounted.  The above image may help you understand the locations of the various pieces that are specified in the notation described in the lab problem  e.g.  "1-Cov. 28x1/2" is the brown top piece is this image.  The location of the four strain gauges are shown in red.

Note that what matters for the calculations you're doing is the total area of the steel, not the specific locations.

Strain Gauge Location for Week-4 Lab

Question

“It is given that the strain gauge is located approximately at 35.0 [%] of the span of the bridge. I have checked the diagrams provided on bblearn, though I am still uncertain about which measurement this is. My question is: Is it 35 [%] of the linear distance, or, since the bridge has a parabolic like shape, is it 35 [%] of the generally parabolic distance? “

Response

This is an good question that made us realize we hadn’t shown you the strain gauge location on the bridge as we had intended – the result of the rain disruption last Friday.

John Devitis provided the following information that will help you, in conjunction with the drawings, to locate the place they are applied.

The strain gauges are located 85’ east of Pier F on the New Jersey Truss span.  You can ignore the information about the percent location since this is more precise.

Each member of the truss is straight so the overall shape of the bridge doesn’t matter.  For your purposes you can assume the truss member is horizontal (it’s close enough).

Week 3 Discussion Feedback

Hey class,

Week 3 discussion posts looked better than last week on the average. It was good to see the enthusiasm a lot of students put into their discussion, and it's clear the majority of you really endeavored to learn something new from the assignment. Still a couple technical details to clear up:

• When you're asked to discuss the most confusing aspects of the article, this is not an opportunity to critique the author's writing style. Even if there are grammatical errors in the text, that's not what you should be focusing on. We want you to pick out a certain concept or detail that confused you or made you think, "hmm. I want to know more about this," and then describe how you could have understood it better.
• Week Specific Question: a number of you are still not making it clear what part of your discussion responds to the week specific question. Be sure to look at this each week and answer it with specific details or examples from your chosen articles.

Overall, everybody is doing a great job finding articles and contributing interesting ideas to the discussion.

Keep up the good work!

~Mitch and Taylor

Tacony-Palmyra Bridge Visit – Friday 10/19/2012

This coming Friday we’ll visit the Tacony-Palmyra Bridge. 

• The visit will take the entire lab period for each lab section
• We’ll be traveling by Drexel bus, walking across the bridge making observations, and then returning to Drexel, all within the two hour lab period. 
• Below are the key facts for this visit.

Our Hosts

• Dr. Franklin Moon of our department has arranged the visit for us.  Some of his graduate students will join us and conduct tour groups.
• We are there through the courtesy of the Burlington County Bridge Commission, which owns the bridge.

Preparation

• Download and bring the appropriate materials from the Week-4 Lab assignment.
• Follow Dr. Moon’s instructions in his Wednesday lecture.

Timing

• We will leave PMOMPTLY on the hour at the start of each lab - 10:00 and 12:00.  We really will leave on time.
• To ensure that the bus has sufficient capacity stick with your assigned lab section.
• We expect to be back by 11:50 and 1:50 respectively.  If there’s a traffic problem we could be delayed, but at that time of day it should be OK>

Location

• The bus will leave from in front of the main building on Chestnut street, probably on the south side of the street.
  • Sometimes for traffic reasons the bus goes to Market street.  If that’s the case we’ll alert you by having someone on Chestnut to direct you.  That person will leave Chestnut at 10:00 or 12:00
• If you’re a commuter you can meet us at the Tacony Palmyra bridge.
  • The easiest parking lot is on the NJ side
  • We’ll be starting our walk from the PA side so you’ll want to walk across the bridge to meet us.
  • We’ll probably start walking from the PA side about 10:25 or 12:25

Wearing Apparel

• Wear a windbreaker (raingear if the weather threatens)
  • The bridge is always markedly cooler and windier than on the ground
• Wear flat shoes – heels will be a problem on some of the sidewalks.

Safety

• The bridge is a dangerous place, particularly if you lean into the traffic lanes – it’s extraordinarily tight.
• LISTEN TO THE SAFETY INSTRUCTIONS WHEN WE’RE THERE

Week 2 Discussion Feedback

Hey all, I just wanted to give back some feedback after grading the first set of discussion posts.  Overall, students did a great job at responding to articles pertaining to geotechnical engineering.  Posts were engaging and thought was put into writing each section of the posts. Here are some bullet points on improving the posts:

• Add more content about what you thought was interesting/confusing.  Often, students only wrote a couple of sentences for each part that pertains to the articles.  Students also summarized the articles instead of answering the questions required for the posts.
• Focus on the week specific question. This week's question was: One aspect of geotechnical engineering they thought was interesting.  I know this question was already one of the deliverables  needed to write the discussion post (one interesting part about the article), but we were  looking for more than a couple sentences that pertained to this aspect.
• Please make sure to post your discussions on time!  This was the one and only time that you received credit for a late discussion post.  The following weeks will be recorded as a zero if submitted late.

Please let us know if you have any questions!
-Taylor & Mitch

Lab Location & Times for Friday 10/5/2012

The CAEE-201 labs for this Friday, and most successive Fridays unless announced otherwise, is the space listed by Banner – Randell-121.

We are NOT dividing the lab sections in half. 

• All 060 students come at 10:00. 
• All 061 students come at 12:00

 

• You may leave once you sign in to the lab, but are advised to stay and work through the lab while the TA’s are available to assist you. 
• Bring a laptop if possible.

Instructor’s Name for the Lab

Question

I am confused what to put for "faculty member for lab" for the CAEE201 Lab 1. Do I put your name? Or the lab instructor. If I am supposed to put her name, could you please inform me of what it is? All I have written down is her last name and her email address.

Response

The intention was that you supply the name of the faculty member who prepared the lab, usually the individual who spoke to the class on Wednesday explaining the lab.  For week-1 that would be Prof. Mitchell.  For week-2 it is Dr. Sjoblom.

Jim Mitchell