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Table of Contents Chapter 1 – Bridge Overview History of Bridges...........................................................1 Modern Bridge Designs . 4 Chapter 2 – Engineering Types of Trusses............................................................6 Civil Engineering............................................................6 Education . 7 Chapter 3 – Bridge Design Factors in Bridge Design . .8 Considerations in Bridge Design ...............................................8 Designing Your Model Truss Bridge . .9 Design Steps ................................................................9 Step 1: Making Design Sketches . 11 Step 2: Completing a Three-View Sketch .......................................12 Step 2B: Drafting (optional) ..................................................13 Computer-Aided Drafting....................................................13 Chapter 4 – Building Your Model Truss Bridge The Purpose of Models . .15 Model Construction Methods . 15 Step 3: Constructing the Bridge...............................................17 Chapter 5 – Testing the Built Model Bridge Preparation for Testing......................................................19 Step 4: The Destructive Test . .19 Technology Student Association (TSA) Structural Challenge........................21 Other Competitions . .21 Bibliography . 22 Other Resources . 22 Chapter 1 – Bridge Overview History of Bridges Though they constructed many kinds of bridges such as wooden and beam bridges, the Roman stone arch When driving or riding from home to school, how bridges withstood heavy use, the elements, and time many bridges do you cross? Don’t know the answer? to become the notable bridge of that era. Many of the You probably haven’t noticed all the bridges over rail- stone arch bridges and aqueducts built by the Romans roads, rivers, creeks, and highways on the route. That’s can still be seen in Europe. the job of bridges – to make travel smooth. With the fall of the Roman Empire, Europe experi- Human travel has greatly improved due to bridges. enced an economic and social breakdown. Governments There was a time when to cross a river, people had to were small, local bodies that could not support new walk along its bank until they found a place where the development or even maintain existing structures very water was low enough to cross without being swept well. During the following five centuries – called the away by the current. A steep embankment or small Dark Ages by historians – bridge engineering came to a gorge had to be traveled around – unless you wanted to halt. climb down it and back out on the other side. However, other areas of the world continued to create new bridge forms during this time. There is writ- ten record – but no archeological findings of – a suspen- sion bridge built in India in the seventh century. Not long after that, suspension bridges made of iron chain were built in China. The simple clapper bridge led to the reemergence of bridge building in Europe, if not true bridge engineering. Though clapper bridges are considered by many to be a prehistoric style of bridge – the Tarr Steps in Somerset, England, for example, date back to 1,000 B.C. – most of the clapper bridges in Europe were built during the Middle Ages. These bridges feature large, flat slabs of stone placed across the top of stone piers. Clapper-style bridges were also built in China during the Middle Ages. European bridges built with engineering principles in mind, however, did not really return until the construction of the Pont d’Avignon in France. Similar to this bridge, primitive log bridges were often logs that fell across a stream. Photo courtesy of MorgueFile.com. The earliest bridges were primitive. Logs fall- ing across a stream are considered the earliest type of bridge. Following that was the practice of stringing large vines across the two areas needing to be bridged. People climbed across on this primitive cable bridge. Engineered arches originated in the Middle East approximately 4,000 B.C. They were also found a thou- Tarr Steps, the clapper bridge over the River Barle, is said to sand years later in Egypt. But the Romans applied the be the oldest bridge in Europe. Photo courtesy of MorgueFile. arch for bridges and aqueducts around 800 B.C. com. 1 According to legend, the Brothers of the Bridge In the late 18th century, monk Benezet built the bridge, Even though Europe in the late Middle Ages Frenchman Jean Perronet which featured more than 20 had more organization and funding than during the – sometimes called the father stone arches that together Dark Ages, governments still had difficulty creating of modern bridge building spanned nearly 3,000 feet. It and maintaining bridges – or they simply didn’t want – changed that. was a remarkable bridge for to bother. Perronet, the director 1187 A.D., the year it was com- In response to this, some individuals or religious of the first college of engi- pleted, and four of the arches orders would take it upon themselves to build and neering, was the first bridge remain today. maintain bridges (though it is more accurate to say builder to understand the The next notable bridge they raised the funds to hire craftsmen to build and structural importance of the of the medieval period was maintain the bridges) as well as to assist travelers. arch. During the late 18th the old London Bridge, which One of these religious orders was called the century, he designed bridges was a massive stone bridge Brothers of the Bridge. Some believe the monk with flattened arches and that replaced an older wooden Benezet, credited with building the Pont d’Avignon slender piers that could still bridge. Built by yet another re- in France, founded this order. But even without the support considerable weight. ligious man, Peter Colechurch, Brothers of the Bridge, Benezet inspired quite a lot His last bridge, the London Bridge was completed of folklore. In some stories, he was divinely inspired Pont de la Concorde in Paris, in 1209 A.D. It featured 19 to build the bridge and received divine assistance. France, was not only graceful arches. Legend has it that Benezet was able to move a stone but also blocked just 35 Though this bridge lasted that 30 men could not and also thwarted the Devil, percent of the water flow more than 600 years (it was who was trying to kill him. Benezet eventually be- with its piers. replaced in 1823), it needed came a patron saint – of bridges, of course. The next big innovation frequent repair that makes in bridge engineering was the clear the logic behind the iron bridge. nursery rhyme “London Bridge is Falling Down.” The first built was a cast iron arch bridge at Coal- London Bridge was also an example of a popular brookdale, England. Completed in 1779, it still stands development of the late Middle Ages: inhabited bridges. today. As the Industrial Revolution progressed, many of Not only did these large bridges serve as crossings over these iron bridges were built. water, but also as building foundations. Homes and shops Wooden bridges were also popular at this time. But were built right on the bridges. The Ponte Vecchio in the wooden truss bridge really took shape in the United Florence, Italy, is another famous inhabited bridge. Built States during the early 19th century, namely because the in 1333 A.D., it is still in use today. young country had the large timber needed as materi- During the next several centuries, stone arch als for these bridges. Truss designs use the structural bridges continued to be massive objects with heavy strength inherent in triangles and later were made with stone piers with a variety of arch shapes. However, these iron. hefty bridges blocked 50 to 65 percent of the water flow. But with the spread of railroads carrying heavy trains, the wooden and iron bridges did not always have the strength to support the weight. Additionally, many builders untrained in engineering were building bridges during the mid-to-late 1800s. The resulting large-scale bridge failure caused many deaths both in Europe and America. From these failures came both the use of a stronger material – steel – and the acceptance of bridge building as a professional engineering endeavor. The remainder of the 19th century and early 20th ushered in an era when many impressive and landmark bridges were con- structed. One of the first of these was the Eads Bridge in St. Louis. Designed and built by James B. Eads, the bridge Ponte Vecchio in Florence, Italy, was one of the many was an innovative construction that was key to bridging inhabited bridges built in the Middle Ages. Photo courtesy of the east and west sides of the country and to helping MorgueFile.com. secure St. Louis’ position of importance. Eads, who had 2 Chapter 3 – Bridge Design Factors in Bridge Design After considering these and other factors, including A number of factors must be taken into account the aesthetics (attractiveness) of the bridge, the engineer when an engineer is designing a bridge. Earlier, several is ready to begin the design. bridge designs were described. In addition to these, an engineer must consider the following when designing a Considerations in Bridge Design bridge: The number of design possibilities for a bridge is • What is the span of the bridge? Span means the almost limitless. However, certain facts about the design length of the bridge from one side (bank) of the river to of a bridge are necessary for the engineer to design a the other. strong, durable bridge. Terms for bridges are shown be- • What will be the load on the bridge? Load means low (Figure 2). Some of these basic facts and terms are how much weight will be on the bridge. described and discussed as follows. • What type of load will the bridge have? Engineers The terms load, compression, and tension are the consider two types of load: live load, which is the weight words commonly used in the design of a bridge. When of the vehicles and people expected on the bridge, and the load is placed in the middle of a beam, it presses on dead load, which is weight of the bridge itself.

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