Hockaday Presentation
- 1. “ ask the structure.” Hockaday Career Day By Amy Barr, EIT, Hockaday ‘00
- 3. I’m a structural forensics engineer. I work for Wiss Janney Elstner, a company that investigates the situation whenever structures have problems. What do I do?
- 4. What do you mean by “problems”?
- 5. Tennessee River State Route 69 Bridge BRIDGE COLLAPSE
- 6. New Orleans Warehouse WAREHOUSE FIRE
- 7. Earthquake - Turkey WORLD SEISMIC EVALUATION AND DAMAGE EVALUATION
- 8. What does a structural failure analyst do? Building design Expert witness work Blast protection analysis Structural failure analysis Analysis of existing structures Seismic retrofit (making buildings safer in case of earthquakes)
- 12. Two Unique Interview Questions: 1) Are you afraid of heights?
- 13. A Member of the WJE Difficult Access Team
- 14. 2) Are you afraid of enclosed spaces?
- 16. Hockaday, Class of 2000 BSCE Rice University, 2004 MSCE University of Illinois, 2006 Education
- 17. Always liked art Always liked science Anything to combine the two? Working with people is a plus Working outside is even better! Career Choice
- 18. Hockaday Senior Project College: majored in civil engineering Grad school: structural engineering, research Applied for lots of jobs, got several offers Ended up at WJE! Getting into the Field
- 19. Education (4 years of college plus about 2 years grad school in civil engineering) Aptitude in math, interest in physics (mechanics, rather than electrical) Don’t necessarily need to have a history of obsessively taking things apart to see how they work, just need a curiosity about the world Certain amount of intellectual courage and a sense of adventure Things You Need
- 20. Aren’t structural engineers usually guys…? Idiots/Naysayers Lots think they’re “not smart enough” I was always my own biggest obstacle: overcoming self-doubt Obstacles
- 21. Gender ratio: most of the guys are really nice, and they’re pretty easy to work with. Naysayers: Don’t listen to idiots. Life’s too short! Not smart enough: Work hard, plan well, work with others! You’re smart enough. Dealing with self-doubt: Everyone is struggling, but nobody talks about it. You aren’t alone! Overcoming Obstacles
- 22. Older Daisies are a great place to look for resources, especially with the Internet, FB, etc. Many alumnae in science fields now Let me know! Mentors
- 23. No family yet! It’ll be a challenge… Lots of travel, long hours sometimes Tough to be Supermom, might have to go with a Supermom/dad combo (I’m lucky to have a great fianc é who is incredibly supportive of my career) Organization, structure, diligence Balancing Act
- 24. If there is a career out there that you want to pursue, you just have to decide to pursue it and work hard. It is yours for the taking. Hockaday grads can do ANYTHING.
- 25. Case Study Best way to go over the sort of things I do is to take you through a representative investigation.
- 27. First job: Pedestrian bridge in North Carolina has collapsed. Pack your bags, we’re going to North Carolina.
- 28. Packing List Hard hat Steel-toed boots Safety glasses Respirator Camera Extra batteries Pencil/clipboard Hammer Gloves Sample bags Sample tags Ear protection Safety vest Screwdriver Flashlight Tape measure Business cards Any plans of the site
- 29. Packing List All of that equipment is really secondary to our engineering common sense.
- 30. How do you get engineering common sense? Experience To get experience, you need a good job To get a good job, you need a good technical background To get a good technical background, you need a good technical foundation.
- 31. So… Take physics and calculus and chemistry, and keep your eyes open.
- 32. The Details Lowe’s Motor Speedway in Concord, NC 11:15 PM on a warm evening 17-foot high concrete pedestrian bridge Bridge length is 80 feet, constructed of a prestressed concrete double-tee beam designed and produced by the Tindall Corp. Goes from the track to the parking lot, passes over US 29 Over 100 people were walking on the bridge Two loud cracks heard, then the whole thing collapsed 107 people received medical treatment
- 33. Photos sent via e-mail by your client, the NC Department of Transportation
- 34. Photos sent via e-mail by your client, the NC Department of Transportation
- 35. What could possibly have caused this?
- 36. Before we ask that question… Need to look at how this bridge was designed and built.
- 37. Before After
- 39. This is a double-tee beam.
- 42. What is prestressing, and why do we do it? Material Properties!
- 43. Very, very cheap Pretty durable Very strong in compression (pushing, crushing) Lousy in tension (pulling, snapping) CONCRETE (What do you mean by that?)
- 44. Look at a beam…
- 47. Very expensive in comparison to concrete If you get it wet, it rusts Very strong in compression (pushing, crushing) Very strong in tension (pulling, snapping) STEEL
- 49. Steel is Stronger Steel is much stronger in tension, and so the fact you can’t break a steel bar like you can break a concrete block is because of the tension strength of steel. The bottom of the steel bar would not break, whereas when he put the bottom of the bar of concrete in tension, it broke relatively easily.
- 50. How do we get a good, cheap construction material? It’d be great if we could take the average of the two…
- 51. Solution: Reinforced Concrete Uses concrete for the bulk of the material Where the material’s going to try to pull apart, we embed steel rods in the concrete. These steel rods are called “reinforcing bars,” or “rebar” for short.
- 52. SIDE VIEW END VIEW
- 53. How do we get the most use out of these steel strands? It’s called “prestressing”. We use steel as though it were a rubber band.
- 59. How do we make prestressed beams?
- 65. Making Prestressed Beams Tindall uses a quick-curing grout with calcium chloride in it.
- 67. What happened? Broke in the middle Must’ve had something to do with the beam itself What’s different about the beam in the middle? Let’s look around to find more evidence…
- 68. What is it? What do you notice about it? Sifting through the concrete, you find this…
- 69. That is a RUSTED PRESTRESSING TENDON. Rust is a BIG problem The process of rusting changes the nice, strong, flexible steel into brittle, weak, nasty iron oxide. Rust doesn’t act like a rubber band at all.
- 70. What caused it to rust like that? (Remember that quick-curing grout that Tindall used to patch the pushdown hole?)
- 71. A bit about rust
- 72. A Few Weeks Later
- 73. What Happened? Look at the other similar double-tees. Hammer-sounding reveals concrete spalling around the grout patches So what actually happened, given all that we know? We must now draw a conclusion and report back to our client.
- 74. What Happened? Chlorides in the grout, in addition to the presence of moisture and the normal cracking that’s typical of concrete structures, sped up the corrosion of the critical prestressing tendons. When the demand required of the tendons exceeded the capacity of the rusting tendons, the pedestrian bridge failed.
- 75. What Happened? You present this to your client, who repairs the bridges. Lawsuits also ensue… Tindall is still around, but they don’t manufacture prestressed beams anymore. Further, the industry has learned a lesson and is now more careful, as a result of what you’ve discovered.
- 76. Questions? Business cards up front… Take one if you’d like to be in contact with me! Can also get in touch with me through the alumnae office, Mrs. O’Reilly, Mrs. Laffitte