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Breaking Bridges

High School Engineers Compete in the 10th Annual National Bridge Contest



As national championships go, this one lacks hype. Only after I've found my way through the May 2 Saturday-noon drizzle to 3301 S. Dearborn do I see the signs. Two strips of paper are taped to the otherwise featureless glass-and-steel front of the Illinois Institute of Technology's Siegel Hall. They proclaim, "10th Annual National Bridge Contest."

The bridges in question have no problem fitting through the doors of the building. Most are little more than a hand span long and less than half as high, constructions of basswood and glue that look fragile but are designed to hold from 1,000 to 5,000 times their own weight.

Inside, the steeply sloping 350-seat auditorium is abuzz with high school students, parents, and teachers. The students -- each a regional champion or runner-up bridge-builder, some from as far away as New Hampshire and Washington state -- bring their models down to the front. Roy Coleman, a perpetually rumpled physics teacher from Chicago's Morgan Park High School, prevents mix-ups by taking an official quick-developing snapshot of each entrant with his or her name tag and bridge. Then the models are whisked into a side room for check-in.

In a lecture hall of this sort, attention normally centers on the black slab-topped table down front. But today the table is upstaged by two identical apparatuses flanking it: each six feet high, with one solid black surface at the top and another about halfway down, supported by green metal pillars. They look like transmogrified laboratory tables, which is what they are. Between the pillars, in the center of each "tabletop," is a circular hole about a foot in diameter, through which a metal rod (unattached now) runs from the top to the floor. The rod can hold as much as 450 kilograms (990 pounds). These 14 "testing stands" -- torture chambers for model bridges -- were crafted about nine years ago by IIT physics department mechanician John Benade. Before the afternoon ends, every one of the students' intricate and beautiful models will have been bent, twisted, snapped, and crushed on one stand or the other.

About the time this year's model builders were being born, Roy Coleman was diagraming forces on the blackboard of the new physics classroom at Morgan Park on the far south side. One of the kids asked, in that uppity way kids had in the late 60s, "What can we do with this?" And Coleman answered casually, "You could build a bridge."

The boy did. Says Coleman now, "He went home and built one and brought it in. I said, 'Well, it won't hold much.'

"So he set it between two lab tables and started piling bricks on it" -- the well-regulated physics classroom is full of useful objects -- "and my eyes started bugging out to see how much it would take. Then it broke, and the bricks crashed onto our tile floor. [The dents and cracks are still visible.] This building was pretty new, then and I was trying to keep it nice. I said, 'What have you done to my floor?' He said, 'Look how much my bridge held!'"

There was more. "Another kid said, 'Oh, I can build one that holds more weight than that,' and he brought one in. It went on like this for a couple of years before it dawned on me that this could be a good thing." In 1972, when a group of area physics teachers met at IIT, Coleman presented the idea of using model bridges to stimulate interest in physics. It stirred up enough excitement that the first Chicago regional bridge-building contest was held in 1974, and the first national contest in 1978.

"The bridge contest idea obviously promotes the study and application of the principles of statics," writes Joliet High School physics teacher Bill Blunk in a program note. "It also helps students develop 'hands on' laboratory skills through bridge construction. A third plus is that the competition confirms the idea that Physics is Phun!"

Contrary to what you might expect, today's winning bridge will not necessarily be the one that holds the most weight. Instead it will be the most efficient -- the one that supports the greatest load proportional to its own mass.

In order to qualify for that test, each model must first conform to strict specifications: it must be built from the official wood kit, be between 260 and 400 millimeters (10-16 inches) long, have at least a 40-millimeter (1 1/2-inch) square opening lengthwise, be symmetrical side-to-side and end-for-end, and have a mass no greater than 25 grams (0.88 ounces). ("Mass," by the way, refers to the amount of matter in an object, something it retains even in outer space, free from the influence of gravity; "weight" is what it acquires when gravity pulls on it. Those of us who are not physicists and who don't plan to go far from the earth's surface can regard mass and weight as equivalent: a nickel weighs about five grams; no model bridge can be heavier than five nickels.)

"We try to come up with standards so that the bridges can't hold more than about 100 kilograms [220 pounds]," says Earl Zwicker, physics professor at IIT, the contest's moving spirit, and coordinator of the National Bridge Building Committee, "but they usually outfox us some."

Three bridges fall by the wayside before they reach the testing stands. Two are disqualified for being over 25 grams, and one is asymmetrical: two tiny spars in its superstructure slant in opposite directions. Some of the remaining entries cut it close. One minute before the check-in deadline of one o'clock, Ed Yang of Marist High School in Chicago is still briskly rubbing his with sandpaper -- it was too heavy at first weigh-in. He gets it down to 24.56 grams. Ron Rygiel of Saint Viator in Prospect Heights weighs in his bridge at exactly 25 grams, one one-hundredth of a gram away from disqualification.

A few minutes after one, without flourish or announcement, Roy Coleman comes in the side door walking carefully, rather like a waiter bringing in an exotic dish. In each hand he carries a sheet of paper with a bridge on it. Other judges follow him with similar cargoes, and the central black lab table is soon covered with 28 weighed and tagged models whose teenaged creators -- 6 girls and 22 boys -- hail from California, Colorado, Illinois, Maryland, Missouri, Nebraska, New Hampshire, New York, Ohio, Kansas, Kentucky, Oregon, Pennsylvania, Tennessee, and Washington.

Now that the bridges are all together in one place for the first time, I see that however restrictive the rules, they haven't done much to limit the variety of designs. The standard trapezoid -- familiar to students of antique iron bridges on country roads, is common but not universal. It is often embellished, and perhaps strengthened, by graceful laminated arches. Several bridges have no tops or sides to speak of, and resemble ladders laid down flat. (These, it turns out, bend spectacularly under load before breaking; but without the benefit of weight-distributing superstructures, they can't support nearly as much as their counterparts.) The bridge built by sophomore David Buie (Somerset, Kentucky) has solid laminated sides and no top. But most have individual framing members, sticks glued at various angles to create the most stable and powerful collection of rigid triangles -- a first approximation at solving the classic engineering problem of how to accomplish the most with the least.

What makes a good bridge? "I look for simplicity of design, strength of the top beam, and neatness -- that is, good construction," says Norm Kerr, a senior at Morgan Park who will study civil engineering at Stanford University next year. At the Chicago regional competition in February, his bridge beat about 130 other entries by holding up 121.5 kilograms (267 pounds) before it cracked. (IIT electrical engineering professor emeritus Marvin Camras, inventor of the tape recorder, tested a bridge of his own making at that competition: it held 126 kilograms.)

"I have built the same bridge," says Kerr, "ever since my first school contest," but he has refined the design. He built some practice bridges to test, but more often he and fellow school winners William Buckner, Jose Carrillo, and Juan Garnett would build portions of bridges and test them. "We basically worked together, us four. We'd all have ideas, come to school and talk about them, and test them.

"At first I used a three-by-three for the top beam. Then I started thinking about a four-by-two," which would use only eight sticks of wood instead of nine. "I broke both: the four-by-two held more and weighed less. The legs I used first were two-by-two. Then I switched to a T-beam, three wide and one on the side in the middle -- so I got the strength of two going one way and three going the other, for the same weight."

But even the most devoted experimentation can fall victim to one small mistake -- Kerr's bridge for the national was disqualified for asymmetry. Bad luck also plays a role in a contest that can be decided by a matter of inches -- or centigrams. Kerr's schoolmate Garnett lost a squeaker at the regional: "If his bridge would have weighed one one-hundredth of a gram less, he would have gone." Ed Yang of Marist High, who did succeed in becoming the city's other representative, was surprised: "I've been in it since freshman year," he says, "and over the years I learned little hints. I expected to do pretty well, but I never expected to go to the national or anything." Yang will major in chemical engineering at the University of Illinois next year. "A lot of people build practice bridges, but I don't have that much time." His other activities include tae kwon do, Spanish club, and the school newspaper.

Jim Russo of Chicago Heights Bloom, who along with Ron Rygiel represents the suburbs in the national contest, took the time -- a lot of time. He also took up most of the family basement, spreading sawdust down there every night for two months, spending about 150 hours and $70 in the process. "When I started, it took me ten hours to build one -- this last one I got it down to four." When the bridge he designed for the regional held "only" 116 kilograms (255 pounds) and lost to Kerr's, "I knew I had to come up with a different design."

He thought about the contest rules. In order to simulate a moving load, they provide that the bridges may be tested at any one of seven possible points -- dead center and 20, 40, or 60 millimeters on either side -- the actual test point to be decided at random on the day of the competition. Russo flashes an infectious grin: "I decided to lay something at each position." The result was an elegant fan of supports rising from the center of the bottom beam to the seven critical points on the top beam. He tested the bridge on a homemade stand using a bucket of concrete for a weight. "Wherever it broke I'd always add wood." Russo's practice bridge breakings became a family spectator sport. At Easter, when his five nieces and nephews under age six were visiting, he gave a demonstration for them.

"People always ask, if it will hold more than 200 pounds, can they stand on it? The answer is, no, they can't, because your foot doesn't distribute the weight evenly" -- any slight imbalance would twist and crush the structure -- "but you can hang from a chain underneath it. My brother got a picture of me doing that."

As Russo suggests, the original method of piling bricks on top of the structure has been refined. Instead, contestants hang weights from the bridge, piling them up on a bottom plate attached to the rod, which itself is attached to the bridge by a top plate. Roy Coleman briefs the contestants and judges (all volunteers) on the fine points: among them, "Take as long as you need to get your bridges set in place." The top plate is to be attached so that the weights will hang from a point 60 millimeters north of dead center. Each entrant will center his or her own bridge on the stand, hook the top plate onto the long metal rod, and then start building his or her own tower of weights.

That bottom plate hangs just a couple of inches off the floor, far enough so that there's a snap and a bang when the bridge is finally overloaded, but not so far that the weights pose any danger. The weights themselves are one-, two-, and five-kilogram metal cylinders labeled "IIT."

"Watch the sway," Coleman cautions. "It can be as deadly as anything," because the weight is at the end of a six-foot rod. A bridge that can bear 200 pounds of motionless load may be destroyed by a much smaller weight swinging gently from side to side. Audience participation is OK: anyone can tell you your weights are swaying, but only you can stop them. "But do not stick your hand under the bottom plate to stop the sway," Coleman adds with a touch of physics humor. "That leads to a real flat hand.

"You are the only one to put weights on your bridge." Obviously this doesn't apply to those contestants who mailed theirs in to be tested by proxy. "As you add weights, at some point it will break. The weight it held without breaking will be what it is judged on. If the bridge sags enough so that the bottom plate touches the board on the floor, then it will be considered broken. Obviously you could then pile hundreds of kilograms on there, and you wouldn't be testing the bridge, you'd be testing the floor.

"After it breaks, take your picture, name tag, and the remains and put them back on the table. It's often interesting to compare failure modes. Oh yes, and please bring the remains with you to the dinner."

I asked Earl Zwicker what is the record strongest model bridge in the ten-year history of the national competition. But there is no answer to the question, no such record. "The rules are never the same from one year to the next," he says, "because we don't want them to be able to copy winning designs from the past."

The national finals "oscillate across the country," says Zwicker, from Colorado to IIT to Brookhaven National Laboratory in New York and back to IIT -- Chicago thus hosting the nationals twice as often as any other site -- and the competition rules also change significantly with location.

The Chicago rules provide for testing bridges by P.H.D. (piling higher and deeper). The method is dramatic--"We want them to fall with a bang," says Zwicker--but imprecise. Complains Sean Hoess (whose New Hampshire contest used different rules for wood, testing points, and testing methods), "If you add a five-kilogram weight and your bridge breaks, how do you know whether it was the first or the fifth kilogram that broke it?" In the interest of precision, east and west coast rules usually provide for the model bridges to be crushed in some kind of hydraulic press, which also eliminates the problem of sway.

This dispute is professional as well as regional. The eastern and western contests tend to be run by engineers, the midwestern to be dominated by physics teachers. And as Zwicker points out, the contest makes more sense pedagogically if students and teachers can test practice bridges in the classroom. "We can get weights, sand, buckets -- that is, junk. We don't have hydraulic testing machines."

While Coleman briefs the contestants, a tall, slightly stooped man with a halo of gray hair and a benevolent, contemplative expression is slowly circling and recircling the table containing the 28 bridges soon to be broken. He's Marvin Goldsmith, a retired general partner of Skidmore, Owings & Merrill and a research professor of architecture at IIT (where he studied under Mies van der Rohe in 1938-39). Here and now he's judging the bridges on architectural merit. He makes notes, picks up bridges, sets them down sideways, confers briefly with Zwicker, and presently explains his criteria and decisions.

"One criterion was originality: something which was not a type well-known in structural engineering. Another was structural merit -- a good distribution of material, something that will perform well in structural testing. I can be surprised, though. Third was workmanship." He awards first place to Jim Russo's fanlike creation -- "a type new to me, looked like a good distribution of material and will probably test well" -- second to Darin Miller of Bellingham, Washington ("also a type I've never seen"), third to Adam Rutherford of Springfield, Oregon, and a runner-up award to Warren Kohm of Huntington, New York. "The ones I selected had a certain geometric order," adds Goldsmith, "and a certain clarity about how the loads go. There are some with beautiful workmanship" -- he picks up Sean Hoess's bridge -- "but less convincing structurally."

Later on I ask Goldsmith what keeps him coming back to examine and judge miniature wooden bridges built by high school kids. "It's just absolutely fascinating," he says, "because they do it by intuition in large part. And some bridges are amazing in what they will support. You're finding a fantastic intuitive process here; they don't have the mathematical skills. And this intuitive process, I think, must be how the great cathedrals and early structures were designed -- trial and error, using models."

Earl Zwicker says he used to be a chalk-and-blackboard physics teacher. But that was before he met Harald Jensen of Lake Forest College and a group of high school physics teachers involved in the Illinois State Physics Project, funded by the National Science Foundation in the late 1960s. "Already back then physics enrollments were going down," he says, and the project was an attempt to perk them up. "Other people gave a great deal of support, but in Chicago, Harald was the physics person the rest of us took as a model. He took a phenomenological approach: no lecture, start with live phenomena. The class becomes a very exciting on-the-spot investigation.

"The idea is that you develop strategies to make the students curious to understand what they're seeing. Curiosity is just creating an emotional need to satisfy the intellect. Usually people operate on two different modes, emotional and intellectual. If you can win emotions to the side of intellect, essentially you've won.

"The point is that physics is something live and living -- the classroom should be more like the laboratory. Sure, some of these things have been discovered long ago. But that doesn't matter. The student doesn't have to discover something new. It's not the published new, it's the personal new."

The physics teachers' group survived the eventual curtailment of NSF funding and Jensen's retirement to San Diego. The freshness of the ideas the unpredictability of each meeting, and the welcome support of colleagues keep the group and similar groups around the city and country meeting.

"You know, something happens to teachers," says Zwicker. "After two or three years, a new teacher becomes better skilled, but he also begins to make assumptions. He uses the same tricks, and he begins to think it's getting stale.

"He assumes that those brand-new fresh minds coming into his classroom every year have all seen it before, just because he has! That's the great mistake." Zwicker's voice drops to an urgent whisper. "Be excited! Think back to the first time you saw that demonstration! That's how it is to your students! That's what we keep reminding each other of." It was this group to which Roy Coleman brought his bridge-building notion in 1972.

Word has it that this approach can pack 'em in to physics classrooms where teachers take it seriously -- Norm Kerr remembers that the bridge contest he saw at Morgan Park when he was in eighth grade helped him decide to attend the school -- but the excitement hasn't caught on at enough schools, and physics enrollment overall has continued to drop. Worse, Zwicker says the teacher pipeline is empty. As experienced teachers retire -- or quit to receive twice the pay for half the hassles in private industry -- school administrators have great difficulty in finding qualified replacements. The less qualified or unqualified instructors available often communicate their own unease with the subject, further discouraging student enrollment. It's a vicious circle, leading in some schools to physics courses being offered only every other year, or not at all.

The remaining physics teachers, of course, enjoy the silver lining to this cloud. Ann Brandon, one of the volunteer judges and a National Bridge Building Committee stalwart, says she quit her suburban physics teaching job, after a dispute with her superintendent, in late August of last year. Even though the school year was about to start, within six hours she had her pick of three job offers from the city.

Bridge breaking will never be a great action sport, but the tension never leaves the air once the first contestant (selected at random) is called up to test his or her model to destruction. Outfitted in a black Billy Joel T-shirt, Ken Hutchings of Ardmore, Pennsylvania, picks up his bridge from the table, carefully centers it both ways at the top of the stand, and screws in the metal plate from which the rod hangs to hold the weights. His bridge is a nice clean-looking arch I haven't picked from the crowd before. Since he's the first one to test his model (another one is getting ready on the other stand), he'll be in first place for a little while no matter what, but looking at the bridge I realize I'm in the same boat as the most "intuitive" of Professor Goldsmith's acolytes: for all I know, this could be the one.

Hutchings adds the weights carefully -- each one is slotted through to the center, and the wise contestant aims the slots of successive weights in opposite directions so that if one should fall off, all the rest will not follow. He's up to 33 kilograms (73 pounds), adds another 5. His bridge is bending visibly. Someone in the audience says, "Put on a couple of little ones." He does. At 40 kilograms, he puts on 2 more, there is a sharp snap, and suddenly his bridge is in two pieces and the weights are resting on the floor. The overhead projector soon displays the first results: Hutchings's bridge weighed 24.98 grams, and held 40 kilograms. Its efficiency is officially calculated at 15,700 (40 kilograms times the acceleration of gravity equals the force, in newtons, that the bridge resisted just prior to breaking; this amount divided by the bridge's mass in kilograms gives the efficiency).

With two tests going on almost all the time, there's a fair amount of scurrying back and forth, from one test stand to the other, in the audience of 100 or so. Emcee Bob Novinsky of the Illinois Society of Professional Engineers speaks into his lapel mike now and then to alert us: "Right now, on the right test stand we've got 63 kilograms for Darin Miller." Miller placed second in the architectural judging, and I cross the auditorium, anxious to see if his model holds up structurally as well as aesthetically.

"73." (The numbers are odd because the rod and top and bottom plates themselves weigh three kilograms.)

Miller is working as fast as he can without dropping anything or causing any sway. I see that, like several other of the more serious competitors, he piled the five-kilogram weights ready to hand before starting.


"93," and the bridge cracks just before he can put on a two-kilogrammer. The auditorium breaks out in applause (each model gets this posthumous accolade). Miller's bridge comes in at 37,200, and holds a comfortable lead over the field for a few minutes.

Half a dozen contestants later, Ron Rygiel of Saint Viator -- a tall, solid football player with slicked-back blond hair -- is called to the right stand. His bridge, with double laminated arches, looks formidable to me. But Jim Russo, seated across the aisle, gestures to where a horizontal member projects out beyond the curve of the arch at each end -- right where the load will be -- and confides, "There's not enough beef at that corner above the arch."

While Rygiel is centering his bridge, the emcee again directs our attention to the left stand, where Sean Hoess -- who finished his model the night before in New Hampshire and flew to Chicago by himself -- is stacking weights on like Dagwood loading a Sandwich. "73 kilograms for Sean Hoess." "78." The almost-rhythmic play-by-play goes on; his bridge shows no signs of bending, but then some of them go to pieces all at once, like the wonderful one-hoss shay in Oliver Wendell Holmes's poem.

"93 kilograms" -- Darin Miller's standing record -- brings whistles and scattered applause from the crowd. "98." "103." And snap!

Meanwhile, Rygiel has a new method to minimize the sway: he wants to set extra weights on either side of the bottom plate. The judges say it's OK as long as they don't touch the weights being loaded on. Hoess sits back down after unloading his tall stack of weights and offers a first-glance postmortem: "It broke at a glue joint and along this tension member." He's copped first place with 41,200, but it won't last long.

Rygiel piles on the weights -- 63, 68, 73. "This guy's scaring me," mutters Hoess. "103, 108, 109," crack, and a cloud of dust flies up. Rygiel -- hands on hips, shaking his head with a puzzled expression -- spends almost as much time examining the broken bridge as he did centering it at first. Sure enough, that top corner was the first to fail, but not before Rygiel edged out Hoess with an efficiency ratio of 42,700.

When Jim Russo is called over to the left testing stand, both Rygiel and Hoess -- one-two at the moment -- cross the auditorium to get a close-up view of the bridge Goldsmith said would "probably test well." Russo takes plenty of time centering, piling up weights conveniently nearby, and placing weights at the sides to control the sway. Tom Jensen, who teaches physics at Bloom, tells me, "He broke one at school that was just slightly over the weight limit at 150 kilograms."

The emcee takes up the chant at 63 kilograms. Sean Hoess stands up. "68." "73." At "113" there is applause. Someone calls, "Jim, put a two on." He is oblivious, concentrating. The stack of weights has grown so high that he has to lift them shoulder-high to add more. "118." "123." "128." He brings up two more like a weight lifter, and his bridge breaks. The applause is vigorous and prolonged.

"I'm not disappointed," Russo insists later, even though his practice bridge of the same design did better. There's no reason he should be, since he finished in a convincing first place, ahead of Rygiel at 51,400.

At the dinner that evening, the National Bridge Building Committee gives out certificates to every student, trophies to every school, fancy plotting calculators to the second- and third-place winners, and a half-tuition scholarship to IIT to the builder of the most efficient bridge. Russo is delighted, as are his parents: the scholarship, renewable based on academic performance, will be worth about $4,000 a year. Over four years, that would put the value of his winning model at just over $655 per gram.

After the meal, product engineer Mike Ploof -- an expert in the manufacture and maintenance of fans for food and chemical processing -- gives a slide show on the greatest engineering innovations of the last 50 years: nylon, computers, transistors, pacemakers, satellite communications, the Apollo moon program, lasers, jet airplanes, nuclear energy . . .

It dawns on me that elegant wooden model bridges are the least of it. This is what it's all about in the real world, where these bright and eager young people will soon be at large. I think about how absorbing it's been to spend the day thinking about which bridge would prove strongest, without once having to consider what it might be used for.

Art accompanying story in printed newspaper (not available in this archive): photos/Mike Tappin.

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