Hockaday Presentation

Slide 1: “ask the structure.” Hockaday Career Day By Amy Barr, EIT, Hockaday ‘00

Slide 3: What do I do? I’m a structural forensics engineer. I work for Wiss Janney Elstner, a company that investigates the situation whenever structures have problems.

Slide 4: What do you mean by “problems”?

Slide 5: BRIDGE COLLAPSE Tennessee River State Route 69 Bridge

Slide 6: WAREHOUSE FIRE New Orleans Warehouse

Slide 7: WORLD SEISMIC EVALUATION AND DAMAGE EVALUATION Earthquake - Turkey

Slide 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)

Slide 12: Two Unique Interview Questions: 1) Are you afraid of heights?

Slide 13: A Member of the WJE Difficult Access Team

Slide 14: 2) Are you afraid of enclosed spaces?

Slide 16: Education • Hockaday, Class of 2000 • BSCE Rice University, 2004 • MSCE University of Illinois, 2006

Slide 17: Career Choice • Always liked art • Always liked science • Anything to combine the two? • Working with people is a plus • Working outside is even better!

Slide 18: Getting into the Field • 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!

Slide 19: Things You Need • 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

Slide 20: Obstacles • 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

Slide 21: Overcoming Obstacles • 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!

Slide 22: Mentors • 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!

Slide 23: Balancing Act • 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 fiancé who is incredibly supportive of my career) • Organization, structure, diligence

Slide 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.

Slide 25: Case Study Best way to go over the sort of things I do is to take you through a representative investigation.

Slide 27: First job: Pedestrian bridge in North Carolina has collapsed. Pack your bags, we’re going to North Carolina.

Slide 28: Packing List • • Hard hat Sample bags • • Steel-toed boots Sample tags • • Safety glasses Ear protection • • Respirator Safety vest • • Camera Screwdriver • • Extra batteries Flashlight • • Pencil/clipboard Tape measure • • Hammer Business cards • • Gloves Any plans of the site

Slide 29: Packing List All of that equipment is really secondary to our engineering common sense.

Slide 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.

Slide 31: So… Take physics and calculus and chemistry, and keep your eyes open.

Slide 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

Slide 33: Photos sent via e-mail by your client, the NC Department of Transportation

Slide 34: Photos sent via e-mail by your client, the NC Department of Transportation

Slide 35: What could possibly have caused this?

Slide 36: Before we ask that question… Need to look at how this bridge was designed and built.

Slide 37: Before After

Slide 39: This is a double-tee beam.

Slide 42: What is prestressing, and why do we do it?

Slide 43: • Very, very cheap • Pretty durable • Very strong in compression (pushing, crushing) • Lousy in tension (pulling, snapping) (What do you mean by that?)

Slide 44: Look at a beam…

Slide 46: QuickTimeﾪ and a Animation decompressor are needed to see this picture.

Slide 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)

Slide 49: Steel is Stronger Steel is much stronger in 9 tension, and so the fact you 8 can’t break a steel bar like 7 you can break a concrete 6 block is because of the 5 Degree tension strength of steel. The 4 of Pain bottom of the steel bar would 3 not break, whereas when he 2 put the bottom of the bar of 1 0 concrete in tension, it broke Concrete Steel relatively easily.

Slide 50: How do we get a good, cheap construction material? It’d be great if we could take the average of the two…

Slide 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.

Slide 52: SIDE VIEW END VIEW

Slide 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.

Slide 59: How do we make prestressed beams?

Slide 60: Making Prestressed Beams

Slide 65: Making Prestressed Beams Tindall uses a quick-curing grout with calcium chloride in it.

Slide 66: So, what happened?

Slide 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…

Slide 68: Sifting through the concrete, you find this… What is it? What do you notice about it?

Slide 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.

Slide 70: What caused it to rust like that? (Remember that quick-curing grout that Tindall used to patch the pushdown hole?)

Slide 71: A bit about rust QuickTimeﾪ and a H.264 decompressor are needed to see this picture.

Slide 72: A Few Weeks Later

Slide 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.

Slide 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.

Slide 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.

Slide 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

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