Arrival in Panama part two of two

I left off in my previous post at the point that I was on a deployment in Chirique Province. I talked about the helicopter rides, but I did not talk about the countryside rides. I worked with Smith and Woldridge (Woolridge? I can't remember for sure). Smith was red headed and funny in a confident country boy kind of way. Woolridge was funny in a Christian Slater kind of way (and he looked a lot like him).

We had to drive down these little crappy roads to get to our sites. On one road was a stream that had banks that dropped down about 10'. The stream wasn't too far across, maybe 12' or 15'. There was a cut in the bank and a water crossing, or you could take the bridge. This was not a bridge that for one minute I considered taking. It was a suspension bridge, with the support towers visibly leaning into the center. I was for going through the stream. Smith was driving and didn't want to go through the stream because then he would have to wash the blazer. This funny exchange went on, with Smith telling me we should do it and me telling him he was nuts. Finally, Woolridge and I got out of the Blazer and stood on the bank while he went across. I must have gone over the bridge first on foot, because I remember watching Smith's face as he went over. Smith went very slowly over the bridge, and I watched, expecting the whole thing to come crashing down. I think Smith knew that's what I was thinking because he was driving with his neck craned up, looking over the side until he got in the middle, where he stopped and his eyes went wide. I had just enough time to wonder what was wrong when he started bouncing up and down in his seat. I'm sure I did a frantic "Don't do that, you crazy person!" look or gesture, because he was laughing his ass off shortly. I can't believe the truck made it over that crappy little bridge.

There was a stretch of road we were making that was getting the most attention. We could not find a good local natural supply of rock, much less crushed rock to make the roadbed with. While we searched, construction on the road continued and we worked around the frequent heavy rains in the area. We knew that if you graded everything smooth at the end of the day and ran the vibratory roller over the road last, that the smooth hard dirt surface would drain off the rain and dry out in about an hour. The road was so smooth and slick that kids were going down it in skateboards. I never questioned what a kid in the jungle with no paved surfaces in site was doing with a skateboard.

The road went through a coffee plantation, and the coffee was harvested by hand and spread out on tarps or small slabs to dry in the sun. It was swept up and put into bags, and these little old ladies would sling great big sacks of coffee beans over their backs and walk for miles to the processing buildings.

The leader of the platoon working on the road was Lieutenant Gonzales, a Puerto Rican officer with little engineering abilities or experience. He did speak spanish fluently, though, so he could sure talk to the locals. Lt. Gonzles started to wear these big sunglasses one day, and I could see he was trying to cover up a black eye. I spoke to Sergeant (SFC) Parks, his Platoon Sergeant, but he would not tell me what was going on. SFC Parks was a wizard with equipment, a really good yet friendly Platoon Sergeant with a ready smile and a southern accent. I found out that Lt. Gonzales had tried to take advantage of a local girl, and SFC Parks had caught him in the act before he could do anything to the girl. SFC Parks had torn Lt. Gonzales off of the girl and beat the hell out of him. Now you have to understand that in the military it is very much against the rules to strike a superior officer. The penalty for that would have been very severe. Lt. Gonzales couldn't turn him in without people discovering what he was doing when he got caught, and SFC Parks wasn't going to say anything about it either. It was one of those rare cases when justice was served.

The other main thing I remember about the deployment, besides the cheery red and white color that they painted all the little schools in the area was the fruits. There was fruit trees everywhere with these lemon looking fruits in them. They called them limones (lee'-moan-ays), but they were really limes. You could make a really nice drink with them if you squeezed them and cut them with water, but they were way too tart to drink. There was something funky about the oranges, too, and you could not eat them either.

I didn't make any lifelong friends or accomplish anything noteworthy on the deployment, but I did enjoy myself and learn a lot.

When the deployment finished, I had to go back to Panama and get a house and meet my wife coming down from the states. But that is another story.

Impact

Jake Brown was competing in the X-Games this week and fell 50 feet to the floor after a mishap with this skateboard. He walked away from the fall. You can check out the video at http://www.youtube.com/watch?v=KBvCrSjpx9I

Apparently, the only injuries he has are a minor fracture on a vertebra, a broken bone in his wrist, and some liver damage. Watch the video, that's amazingly light damage for the fall that he took.

At the same time this week, reporters were talking about how a lot of people in the Minneapolis bridge collapse fell 65 feet and not only survived, but walked away uninjured. Many of them went to the hospital 2 or 3 days later, finally complaining about their aches and pains, but still, a 65 foot fall is supposed to be fatal.

So how did these people walk away for falls that are supposed to kill you?

Jake Brown actually had time to think about it and was able to twist around to control his landing to minimize the impact. They interviewed him and he claims he thought about the fall of a friend of his while he was falling. His friend fell from a lesser height than Jake, but broke both legs. So he probably thought it through before he was in trouble. He said in an interview after the accident that he planned to fall the way he did. I heard that Army Airborne parachutists hit with the impact of someone jumping off a 2 story building. The way they are trained to survive the fall is to hit on their feet, crumple by collapsing their legs, and roll out across their side, taking up the rest of the force. I think Jake did somthing similar to this. He hit on his feet and that probably took a great deal of the impact. I still wonder why the legs didn't snap under him.

The people that were in cars on the bridge when it fell claim that there were a series of jolts rather than one long fall. Even though the bridge looks like it drops pretty fast, it wasn't freefall, it was getting hung up on the way down, slowing the fall.

Americans used to drive around without seat belts. Car accidents used to kill around 65,000 people a year in the 60s, and I believe we're down to around 40,000 a year. That's with something like twice the total miles travelled for cars, so I'm guessing we've reduced the fatality rate to 1/4 what it was. We finally decided that enough was enough back then and started developing safety features in cars, starting with the seatbelt.

The way the seatbelt works is by making you part of the car. Before seatbelts, accidents were a series of 2 collisions. Your car hit an object and then you flew forward in the car and hit the windshield or steering column. The second little mini collision between the person and the car is what injures the people inside. When you strap yourself in, you become a part of the car, and it takes the brunt of the impact.

A moving object requires energy to stop. In a collision, that energy is used to deform the car. Think of crushing a soda can with your foot. In an accident the car gets hurt, not the person. When engineers started understanding this, they started designing "crumple zones" into the car. Those are places that the car is designed to smash down safely and not smash the people inside. In most cases, this is the frame in the front, below the engine. They also reinforced the cab so that the area where the people are is less likely to crumple. Two other features they designed were a seat that supported your head and airbags to cushion your forward motion. This impact is supposed to be like being smashed between pillows.

In the case of the Minneapolis bridge collapse, the cars are falling straight down while upright. This is not the way a car is designed to impact, but it is the way a car, and the driver in the car, are designed to be supported. I suspect that many of the cars on the bridge would have flat tires (quite a cushion there, like 4 air bags)and probably snapped axles. That would take a lot of the energy out, and then the people are sitting upright in cushioned seats that would take up the rest.

That's just my theory. This is not something you ever want to really test.

Bridging the Gap

The news in Minneapolis this week was unreal. A highway bridge collapsed over the Mississippi during rush hour with vehicles going over the bridge. This tragedy is a rare event that is making many people think about bridges and wonder about how you know if they are safe.

I started doing this in college. My sophomore curriculum in Mechanical Engineering included a Statics course. This is where you learn about the forces in structures, how things want to bend, and how weights and levers affect bodies at rest. The Statics textbook authors loved to use little bridges to illustrate the principles it was teaching. I loved the little bridge designs. The ME's would go on to take this information and use it to design tools and machines. The Civil (Structural) Engineers would actually design bridges. Every freshman engineer is taught about a phenomenon called resonance with the example of the Tacoma Narrows Bridge, a structure that tore itself to pieces because of wind induced harmonics. You want engineers in training to be very worried about the consequences of failure.

After school I entered the Army, in their Corps of Engineers. Some of the things we were supposed to know was how to inspect and rate existing bridges, how to design and construct bridges, and how to destroy them. Can you guess why we needed to know this? Army Engineers are there to make sure that the rest of the forces can get where they need to get and that the bad guys can't. A river is called a "water obstacle" and the thinking is to either erect that line as an obstacle for the enemies movement and at the same time, to breach that line to facilitate your own movement. So we learn about the breach points, the bridges.

Demolitions of bridges was a fascinating study. You learn that it is surprisingly hard to knock most bridges down. The trick is to find the weak key point and blast away at it, hoping it would take down the rest of the bridge. There are examples of people that drop a center span of a bridge, but not the approaches, so you could easily rebuild the gap and restore the bridge. There are lots of examples of artillery cutting the wires out to the charges and the demolition failing, or charges badly placed that did nothing. Most bridges have a lot of redundancy built into them. Another note about bridge failure, again involving resonance. We were taught that when large formations of soldiers cross bridges, you go to "route step", which is a marching term meaning you break step, or stop having everyone slam their foot down at the exact same time. Supposedly, the combined force of all those footfalls happening simultaneously is enough to sometimes collapse a bridge.

We also had to inspect bridges and rate their load carrying capability and their integrity. This was surprisingly hard to do, because most of the bridges I looked at were made of wood, and most of the guide was about steel bridges. We had to make sure that bridges could handle heavy construction equipment, and most of the guides rated bridges in terms of main battle tanks. I guess a bulldozer is pretty close. This process of inspecting bridges always bothered me. We learned in materials that steel fails by a mechanism called cyclic fatigue. This is like when you bend a metal hanger enough times and eventually it breaks. You can't see cyclic fatigue, usually. The other mechanism that occurs is stress fracture propagation. Many people believe that tiny cracks on the surface of the metal eventually propagate into the center of the structure and widen, weakening the metal. The problem is that you don't know to what degree metal has weakened, and it's not often evident from a visual inspection. You could see these fractures and indications of fatigue with x-rays, but you can't x-ray a whole bridge. So often, we'd inspect and rate a bridge and I would wonder if we missed something or if our estimate was even in the ball park. One time, I was driving with 2 surveyors in the back country in Panama and we came to a tiny sagging suspension bridge in the country. I didn't think we would ever be able to put a pickup truck across it without breaking the bridge. I barely trusted it for foot traffic. The driver insisted, and as I got out and watched from the safety of the road, he slowly drove over the bridge. Stopping in the middle, he looked up and made eye contact with me, smiling, and started bouncing up and down in his seat. It was very funny. He made it across, but I still wonder how that nasty little bridge held him. Another bridge I remember was an ancient suspension bridge 100' over a river in Ecuador. The wooden floor of the bridge was very old and crumbling and several boards were missing. The first time I went over it, my knees were shaking so bad, I could barely walk. After watching a man drive a herd of cattle over the bridge one day, I stopped worrying about it as much. Later, I always stopped in the middle and got the bridge swaying, because by then it was like a fun amusement park ride.

By far, the most fun was building bridges. At school, they always get students to make a span with popsicle sticks or toothpicks, then add weight until it failed. Calvin and Hobbes had a great cartoon where the father explains to Calvin that the way they made highway bridges in a similar way, overloading and breaking it first and then rebuilding it. The Army uses a bridge called the Bailey bridge, which is the tinker toy method of constructing bridges. You use these truss panel sections, and just stack them up differently for different lengths and weight classes. It was in a manual like a book of recipes for bridges. I got to work on building two of them and also found a few already in place that had been in service for years.

When I got to Panama, I got to see one of the coolest bridges in the world, the Bridge of the Americas. This structure, shown in the picture above, spans the mouth of the Panama canal. It is beautiful, but has a strange feature. There are 4 lanes on the bridge. You go up to and over the bridge on two lanes, then it necks down to one lane. So there's only 3 lanes on the approaches (the ones that are still on the bridge, just not the central span). It's harrowing during rush hour traffic, because you rush across the bridge, speeding for placement at the other end, and then you merge dangerously before the lanes come together, honking your horn the whole time. That was the way you drove in Panama. I crossed the bridge every day to go to work.

Sharon, one of my coworkers, read that people's fear of crossing bridges is second only to public speaking of the biggest fears there are. This week's collapse in Minneapolis is probably not going to help that.