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In this module, you will be a student engineer and you will apply mathematical and scientific data to configure structural forms and meet hands-on challenges. After building and testing a variety of beam sections, stressed panels and trusses, you will design, engineer and construct a model bridge. The bridge is then stress tested on our computer-interfaced structural tester where you will observe and record the results of your construction techniques. - Answer In this module you will: Identify and strength test different types of beams and panels used in structures. Appropriately use hand-held cutting tools and safely operate a testing device. Identify and classify the portion of a structure's frame under tension, torsion, shear, and compression. Demonstrate, predict, and evaluate the behavior of loaded structural systems. Identify, describe, and clarify the major stresses and causes of structural failure on spanning structures. Design and build two different trusses then evaluate for strength. Here are the activities in this module: Activity: Building Beams Activity: Composite Beams Activity: Beam Testing Activity: Designing Trusses Activity: Truss Construction Activity: Test and Writing Assessment Activity: Testing the Trusses Activity: Video - Bridge Construction Activity: Design Brief
Activity: Internet Research - Bridge Construction Activity: Test, Writing Assessment, and Career Planning - Answer This Structural Engineering module is classified under the STEM Career Cluster. Individuals that work in the STEM Career Cluster demonstrate the following skills and knowledge: Apply engineering skills in a project that requires project management, process control and quality assurance. Use technology to acquire, manipulate, analyze and report data. Describe and follow safety, health and environmental standards related to science, technology, engineering and mathematics (STEM) workplaces. Understand the nature and scope of the Science, Technology, Engineering & Mathematics Career Cluster and the role of STEM in society and the economy. Demonstrate an understanding of the breadth of career opportunities and means to those opportunities in each of the Science, Technology, Engineering & Mathematics Career Pathways. Demonstrate technical skills needed in a chosen STEM field. There are hundreds of related careers in the STEM Career Cluster, some more similar than others. By classifying these similar careers into narrower categories called pathways, it helps individuals look at a range of options when it comes to employment in an area with similar skills and knowledge. Although this system of classifying careers into clusters and pathways is helpful in navigating career options, it is not the only way. This module is more specifically aligned with the Engineering and Technology Career Pathway. Individuals in this pathway share a set of skills and knowledge that expands on the skills and knowledge needed in the STEM Career Cluster. Individuals in the Engineering and Technology Career Pathway demonstrate the following skills and knowledge: Use STEM concepts and processes to solve problems involving design and/or production. Display and communicate STEM information. Apply processes and concepts for the use of technological tools in STEM.
A structure is made up of members, which spread out the weight of the forces acting on it. Horizontal members are identified as beams or girders. Vertical members are referred to as columns, studs, pillars, or posts. Diagonal members are called braces. Panels are walls that divide or form the surface of a structure. - Answer Members help to spread out the forces that push and pull on a structure. These forces are called loads. Usually, loads are measured in pounds or pounds per square inch. With the metric system, the measurements would be kilograms or kilograms per square centimeter. Static loads, also called dead loads, are forces that don't change. For example, a steel girder is strong but it's heavy. Its weight adds to the static load. Engineers need to consider static loads along with other factors in designing a structure. - Answer Dynamic loads, or live loads, include forces caused by: Man-made elements, such as traffic moving over a bridge Natural elements, such as snow, wind, waves, and earthquakes The strength of a structure also depends on the materials used to make it. Structures can be made of wood, stone, plastic, iron, steel, aluminum, and many other materials. Ancient peoples built beautiful stone structures that have lasted for many hundreds of years. Stone resists weather and fire. Yet it's very heavy and needs thick walls to support its weight. - Answer Architects and Civil Engineers must design structures to support forces much greater than those normally expected. If they don't, the structure could fall apart. They've developed Uniform Building Codes to include designs and materials that have worked well in the past. A building inspector reviews engineering plans and inspects construction for safety.
There are four basic forces that place stress upon any structure to weaken its structural integrity. Every structural member is either in compression or tension. Tension is a force that pulls. Compression is a force that squeezes. Torsion is a force that twists. Shear is two opposing forces that cut or slide one piece over another. - Answer All structures are designed around the idea of equilibrium. When the sum of all the forces bearing down on a structure is balanced by all the forces designed to make it stable, then equilibrium is reached. If the load from forces is more than a structure can handle, there is structural failure. But before this happens, engineers look for deflection, that is, bending or sagging under pressure. Engineers also know that over time, too much pressure can change a structure's size or shape. This will result in deformation. - Answer A beam is a horizontal member that spans a gap and has supports at both ends. In prehistoric times, a fallen tree lying across a stream probably acted as one of the first beam bridges. Later this design was improved. Several beams could be placed end to end on top of columns to cross a bigger river. How much weight a beam can handle depends on its design, as well as the material it's made of. There are five major beam shapes: Angle Channel Box Tee I-beam - Answer Beams can be constructed of many different materials. In this module, you'll make beams from balsa wood.
Weight Materials Area of load Some shapes make stronger beams because they combine horizontal and vertical shapes. Some of the best beam shapes are channel design, box design, and I-beam design. Structural engineers choose shapes appropriate for different structure. - Answer A bigger beam is thicker and can carry more weight than a smaller one. The size of the beam for a structure is often determined by how big the structure is and how much weight it will be bearing. The wider the span is, the weaker it becomes in the middle. To make sure the beams can hold up the structure's weight, the structural engineers must have longer beams supported to prevent deflection. - Answer If a beam is heavy, it has its own weight to bear, in addition to the weight placed upon it. A heavy beam places more weight on its ends, so stronger columns are needed to support it. Iron is a stronger material than wood. Carbon fiber is even stronger! Iron beams were invented in the 1800s. Iron allowed architects to design taller buildings than they could using wood beams. - Answer If the load on the beam is centered in one spot, the beam may need more support at that point. A beam can bear more weight if the weight is spaced evenly along the length of the beam. Some beams are made with a slight upward curve or arc called camber. When weight is set on the beam, the weight deflects the beam into a straight position. - Answer Another important structural member is the panel. Panels divide spaces in a structure or form the outer surfaces. You also know them as walls! Jet planes and race cars have curved panels on the outside. This gives them a smooth outer skin for better aerodynamics.
As aircraft became faster, aircraft designers needed to make wing panels stronger. But thicker panels would also make planes too heavy. The problem was solved with the invention of stressed-skin and composite construction. - Answer These new stressed-skin panels called sandwich panels weren't solid. Instead, they had a rigid foam or honeycomb-like center. This center was sandwiched between two thin outer layers. These layers were made of a different material, usually aluminum. They were something like a bologna sandwich! Gluing two different materials together is called composite construction. The stressed-skin panel construction method is used when strength is needed on curved surfaces. Blocks of material such as balsa wood are placed between fiberglass and held together with epoxy glue. For even greater stiffness, airplane wings are made with an aluminum core. This core looks like a honeycomb sandwiched between carbon-fiber skin. - Answer Curved surfaces are needed to build smooth shapes for jet planes, racecars and power boats. To make a curved panel, the materials that make up the composite must be shaped over a curved mold. The panels will be very strong, stiff and light. Stressed skin panels can be molded to fit the design of a plane, racecar or boat. They create a strong, stiff and light surface. Composite construction needs strong, high-tech adhesives, or glues, to hold the outer skin to the inner materials. Chemical Engineers have invented new materials that hold together with heat. New epoxy glues cause a chemical reaction when the two components of the glue are mixed together and the glue becomes solid. - Answer Structural Engineers help to make decisions on how to construct a building. They make sure that the building plan and the materials are safe and can function appropriately. In this activity, you will construct four composite beams called stress-skinned panels. Stress-skinned panels consist of an insulting core sandwiched between two thin layers of board. Two of your beams will have foam cores and two will have cores made of laminated (stacked) strips of corrugated cardboard. Poster board will be used for the outer skins of your composite beams. - Answer The beams that
A scale model is a physical representation of a real structure or object, except much smaller. A scale model must maintain an accurate relationship between all of the important aspects of the object as well as meet the same general requirements to be functional. For example, if a scale model is made so that 1 inch equals 20 feet, the scale is written as 1:20 or 1/20. A one-twentieth scale model of a 400-foot ship would be 20 inches long. - Answer Model tests, or simulations, will only work if the forces placed on the model can be perfectly controlled. If this happens, then the results should tell what will take place after the structure is really built. Putting weights on a model bridge suggests how a real bridge will handle real load forces. The structural tester you will use can create a downward force of 125 pounds. This simulates the force of a heavy object on a real bridge. - Answer Special equipment is used to test prototypes and building materials. Some machines put huge pressure on concrete samples to test them. The concrete must be strong enough to pass industry standards. If the concrete breaks too soon, it can't be used for construction. Other testing instruments include water tanks to test ship models. Aircraft models are tested inside a wind tunnel. The structure of a plane must be designed for shape and lightness. Many prototypes are tested until everything is proven to work. - Answer CAD stands for Computer-Aided Design. A CAD operator uses software tools to recreate the way the design looks in 3-D. Then the design can be rotated to view it from any angle. Before a new car is sold it must be tested for safety and pass government codes. Car companies use formulas to measure the force of a crash. In this way they can test different designs to see if passengers will be protected. - Answer Computer simulation and CAD also played a big role in designing the Boeing 777 jet airplane. Once the tests were finished, the final computer designs could be used to build the panels and beams accurately.
Did you know that a skyscraper moves in the wind? The John Hancock Insurance Building in Boston moved so much that people on the top floors felt seasick. The glass windows even fell out! To find a solution, engineers tested a model skyscraper in a wind tunnel. Fixing the building after it was already finished was a very expensive mistake. - Answer Another important person involved in making a building or bridge safe is the Surveyor. The surveyor looks over the land and determines the best location for the structure. He or she later makes sure the structure is built where the plan designates. In this lesson, you'll study different kinds of trusses. You'll see how trusses are used in construction. You'll probably want to use trusses when you build your bridge prototype. A truss is a structure made from one or more triangles. A triangle always has three sides, but the sides don't always have to be equal. - Answer A truss offers one of the best ways to build a structure. It's much better than a beam, which sags in the middle if the span is too large. A roof truss can span distances up to 40 feet without a column underneath it. This means rooms can be larger and more open. The triangle is the basic shape found in trusses. It's the only geometric figure that cannot change shape without shortening or stretching at least one side. A Fink truss has five triangles that all share sides. The downward pressure is spaced across all of the linked triangles. - Answer Compared to triangles, squares easily change their geometric shape. Just push on a corner and a square falls over! It becomes a diamond. A square can be strengthened with a diagonal cross brace. But notice how it becomes a square with two internal triangles! A truss that holds the roof over your head has the following parts: Upper/bottom chord: the sides and base of the truss. The bottom chord is also called a tie. Gang-nail plate: the joint at the roof peak.
You might see this truss in your school gym or cafeteria. The simplest truss is a king-post truss, which can span about 25 feet. - Answer A mono-pitch truss, used for shed roofs, spans about 25 feet. Notice that the Howe truss, one of the best designs, is similar to the mono-pitch truss. - Answer The Pratt truss uses simple construction and a more logical spacing of stresses. It was patented in 1844. When iron became less expensive, the Pratt truss became a popular choice for building bridges. The engineer's job is to follow the architect's plans and figure out the load capacity for the roof trusses. The drawings are given to the Building Inspector for approval. The trusses will probably be made at a factory and trucked to the home site. Before the trusses leave the factory, workers must follow the plans for their construction and test them. - Answer The General Contractor watches over the entire construction process. He or she must follow the architect's approved plans. The Construction Carpenters install the trusses at the construction site. Bridges have been very important throughout history. For instance, they played a significant role in the exploration of the West, the outcome of World War II, and the growth of many cities. - Answer A bridge provides a pathway over an obstacle. The obstacle might be a body of water, a roadway, or a valley. The bridge carries a load, for example, a footpath, a road, train tracks, power lines, pipelines, or even a city water supply. Other types of bridges include aqueducts (which carry water), causeways (a road over a shallow lake), and overpasses (highway bridges). The history of bridges shows how technology has changed. Bridges reflect the materials and needs of the time in which they were built. The beam bridge is the simplest type of bridge. It's ideal for short spans or places where columns won't get in the way. Beam bridges are still commonly used for
railroad and highway overpasses. - Answer The ancient Romans built arch bridges out of stone and brick. Now such bridges are made using steel and concrete. Arch bridges need temporary structures in place until the arch is completed. Patented truss railroad bridge designs were quick and inexpensive to build. They were often made from wood and later, from iron. American settlers needed lots of bridges to travel west after the 1850s. - Answer The suspension bridge is one of the most beautiful designs. Yet this type of bridge is one of the most costly to build. So it's used only to cross long spans. The Brooklyn Bridge opened in 1883. The roadway for a truss bridge can either be placed on the bottom, through the middle, or on top of the trusses. This makes a truss design practical for many different situations. - Answer When the original Clark Bridge was built, the people of Alton, Illinois, were pleased. However, in the early 1990s, the bridge no longer had the capacity for the cars crossing it. The Clark Bridge was rebuilt and reopened in 1994, in order to handle all the traffic and allow the city to grow. What did the engineers think about when choosing a new bridge design? Two hundred years ago, you would have had to swim or float across the Mississippi River. There were no bridges across the river then. Early peoples were smart bridge builders. The Incas knew how to make suspension footbridges out of simple natural materials. They braided grass together to make big ropes that lasted for years. - Answer In the 1st century B.C., Romans built an aqueduct at Pont du Gard in France. It still spans 855 feet today. The Roman army also built semicircular arch bridges wherever it defeated people. One at Martorell, near Barcelona, Spain, was built around 219 B.C. and is still standing.
wind would have on the bridge. - Answer They later built a bridge that had vents that allowed the wind to pass through it without causing it to sway. Bridges have progressed a lot. The Incas made simple suspension bridges for people hundreds of years ago. Now we have mechanical draw bridges, long steel suspension bridges, and bridges that have many levels for high traffic areas. - Answer Building a big bridge takes years of hard labor by skillful workers in many construction trades. Steelworkers weld and bolt together the tower sections and pull miles of wire cables. Masonry workers pour tons of concrete to hold the bridge to its foundations. It is very dangerous work. Eleven men were killed building the Golden Gate Bridge in San Francisco. Surrounding any bridge will be roads and other infrastructure. Opened in May 1998, the Ting Kau Bridge and its highways connect Hong Kong and China. The Ting Kau Bridge is part of a large new roadway linking factories in China to ships in Hong Kong Harbor. Toll fees will eventually pay back the private investors. - Answer Opened in 1998, the Akashi Kaikyo Bridge in Japan holds the record as the longest suspension bridge in the world. The bridge links the city of Kobe and Awaji Island. The center span is 1,990 meters. One of the longest fixed steel-rib arch bridges in the world crosses the Niagara River between Queenston, Ontario, and Lewiston, New York. It opened in 1965, and and its span is 304.8 meters. - Answer The Astoria Bridge, completed in 1966, spans the Columbia River in Oregon. It is the longest continuous truss bridge in North America, with a 375.5-meter (1,232-foot) span. The Lake Pontchartrain Causeways, two parallel roadways, are the longest bridges in the U.S., measuring 38.6 kilometers (nearly 24 miles). The bridges connect New Orleans and Covington, Louisiana.
The longest bridge of any kind in the world, can be found in China. - Answer The highest suspension bridge in the U.S.crosses the Royal Gorge of the Arkansas River in Colorado. It rises 321 meters (1,053 feet) above the water. The highest suspension bridge in the world is the Baluarte Bridge in Mexico. When designing your bridge make sure to consider all you have seen and learned in this module. There are many different possibilities. Choose the one that best suits your purposes. - Answer The structural strength of the triangle is the secret used by skyscraper architects. The Willis Tower, formerly the Sears Tower, is really a bundle of triangular tubes that support each other. Only one of those tubes is a full 110 stories tall. Look for triangles in the structure of one of the world's tallest skyscrapers, the Bank of China Tower in Hong Kong. These towers are among the tallest skyscrapers in the world. The twin 88-story towers are 1,483 feet tall. Completed in 1996, they are located in Kuala Lumpur, Malaysia. - Answer In 2013, the One World Trade Center building officially became the tallest building in the United States. Prior to this, the Willis Tower in Chicago, Illinois, had held that title for 40 years. One World Trade is third tallest in the world. There are 104 floors within One World Trade Center. Completed in 1931, the Empire State Building was the tallest skyscraper for a long time. It still serves as a symbol for New York City. - Answer On August 27, 1997, construction began on the Shanghai World Financial Center in China. After its completion in 2008, the 101-story, 492-meter-high skyscraper became one of the world's tallest buildings Ancient builders used materials they found in nature to make structures. For example, they used grass, vines, wood, stone, mud, and animal skins. This lesson shows how structures are made today with man-made materials. - Answer
Shear is two opposing forces that try to cut or slide one piece over another. Every structural member is either in compression or tension. - Answer All structures are designed around the idea of equilibrium. In other words, a state of balance exists when the sum of all the forces trying to weaken the structure equals the sum of all the forces that have been designed to strengthen it and make it stable. A beam's load capacity depends on its design, as well as the material from which it is made. There are five major beam shapes: Angle Channel Box Tee I-beam - Answer Six variables determine a beam's load capacity. Shape Size Span Weight Materials Area of load A truss that holds the roof over your head is made up of the following members: Upper/bottom chord: the sides and base of the truss. The bottom chord is also called a tie. Gang-nail plate: the joint at the roof peak.
Tension web: works against pulling forces. Compression web: works against compression forces. - Answer Truss bridges were first built out of wood, then iron. Popular designs were patented and named after their inventors. 1806: The Burr-arch, the first patented bridge system 1820: The Towne truss, the first with standard sizes and no arch 1840: The Howe truss, simple and easy to build 1841: The Squire Whipple, an iron bowstring, using the first scientific analysis of loads 1844: The Pratt truss, a logical design The structural strength of the triangle is the secret used by skyscraper architects. The Willis Tower, formerly the Sears Tower, (left) is really a bundle of triangular tubes that support each other. Only one of those tubes is a full 110 stories tall. Look for triangles in the structure of the Bank of China Tower in Hong Kong (right). - Answer
