Structural Engineering

Notice that the Howe truss, one of the best designs, is similar to the mono-pitch truss.

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.

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.

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.

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

Beams can be constructed of many different materials. In this module, you'll make beams from balsa wood.

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.

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.

Famous truss designs are named for their inventor, such as the Howe truss, after William Howe. In the mid-19th century, designers came up with many fastening systems for wood and iron bridges.

By using a scissors truss, with its sloping bottom chords, a room's volume can be increased. This truss can span up to 40 feet across a room.

A prototype is a preliminary model of something from which future versions are further developed or formed. 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.

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 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.

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.

The earliest type of drawbridge was called a bascule. It was a hinged bridge made of timber and built over castle moats. This bridge was raised using chains and counterweights.

The London Tower Bridge, built in the 1830s across the Thames River, is probably the most famous example of a bascule. Do you remember the song "London Bridge Is Falling Down?

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.

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.

However, if the load becomes too heavy, deflection occurs. The bookshelf sags, or bends, in the middle. Because a bookshelf is thin, it has little material in the middle to handle the two forces. Compression is squeezing the top of the shelf, while tension is pulling at the bottom.

When a bookshelf is thicker, it can handle more weight without being bent by deflection. A beam, like this bookshelf, must be built thick enough to carry the load it needs to support without sagging.

Two opposing forces, tension and compression, are pulling and pushing all the time on the upper and lower surfaces of beams. In this example, the beam is an empty bookshelf. Will it be strong enough to hold the books we put on it?

When the load isn't too great and the opposing forces of compression and tension are balanced, the bookshelf will stay flat. We call this equilibrium.

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.

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?

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.

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.

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.

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.

There are four basic forces that act upon any structure, weakening its structural integrity. Tension is a force that pulls. Compression is a force that squeezes. Torsion is a force that twists. Shear is two opposing forces that try to cut or slide one piece over another. Every structural member is either in compression or tension.

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.

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.

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.

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.

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.

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.

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.

Throughout history people have built structures to protect themselves from the environment. Structures must be supported with a strong framework, or else they could fall down. A pueblo house (left) has mud walls and wood beams to support its flat roof. The Empire State Building (right) was completed in 1931 and is supported by a huge system of steel beams.

Architects and civil engineers are professionals who are trained to design structures so they'll be safe and sturdy. Many other people also work together to design structures so they won't fall down after they're built.

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.

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.

Structures must be built to maintain stability against the strongest forces on Earth. Architects and civil engineers worry that natural forces may destroy their structures. For example, hurricane winds blowing at 110 miles per hour have damaged hotels in Florida. Ocean waves 30 feet high have washed away homes in California. Strong earthquakes have knocked over highway bridges in Japan.

In 2011, Japan experienced a devastating earthquake that later triggered a powerful tsunami. The earthquake measured a record breaking 9.0 on the Richter scale. The Richter scale is a measurement of earthquake intensity. The tsunami waves reached heights of 100 feet and traveled up to 6 miles inland. Approximately 23,000 people were killed. Both the earthquake and tsunami caused extensive and severe structural damage, including heavy damage to roads, railways, buildings, and nuclear power plants. Do you think that bridges and buildings can be built to withstand earthquakes and tsunamis?

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.

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.

The first steel-arch bridge was designed by the American engineer James Buchanan Eads and was opened in 1874. It has three 500-foot arches spanning the Mississippi River at St. Louis, Missouri.

Opened in 1883 in New York City, the Brooklyn Bridge has a central span that stretches 486.2 meters (1,595 feet). It was built by John Roebling, a famous German-American engineer. In 1846 he also designed the first long-span wire cable suspension bridge in the world over the Ohio River.

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.

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.

The beams that you and your partner built are similar to the steel beams used in bridges and large buildings. These beams are made from one kind of material, such as wood or steel. Beams can also be made from two or more different materials. These are called composite beams. Composite beams have the best qualities of the different materials, making them stronger and lighter.

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. Tension web: the cross brace that resists pulling forces. Compression web: the cross brace that resists compression forces.

The first primitive roofs were flat, with beams spanning the walls. But large rooms needed posts, or else the beams would sag. If too much weight from snow or water fell onto the beams, the roof caved in!

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.

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.

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.

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.

Four months and seven days after this bridge was constructed in 1940 it collapsed. The bridge swayed violently in the strong winds that were funneled into the narrow canyon that it crossed. The engineers didn't take into consideration the effect the wind would have on the bridge.

They later built a bridge that had vents that allowed the wind to pass through it without causing it to sway.

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

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.

A beam is a horizontal member that spans a gap and has supports at both ends. Beams can be found in almost all structures. The first beams were probably cut from big trees. In large structures, steel or iron beams are also called girders. In house construction, ceiling beams are called rafters.

To span wider distances, a beam needs support underneath. Without support, the beam might sag in the middle. Ancient builders understood the limits of natural materials. They found ways to strengthen them. Greek architects in the 5th century B.C. used columns in the Parthenon, the temple built for Athena, goddess of wisdom. The architects placed the columns close together. In this way the columns could support the weight of the heavy marble.

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.

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 simplest solution was to make the roof slope, as shown in the diagram. But this also caused downward forces to punch out the supporting walls at the tops. To solve this, engineers connected the two sloping members with another member laid across the bottom. This is called a tie.

Trusses have many advantages. These include strength, efficient use of material, and longer span. For this reason, they're often used in building structures.

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.

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 simplest truss is a king-post truss, which can span about 25 feet.

A mono-pitch truss, used for shed roofs, spans about 25 feet.

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.

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.

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. Apply the elements of the design process. Apply the knowledge learned in STEM to solve problems. Apply the knowledge learned in the study of STEM to provide solutions to human and societal problems in an ethical and legal manner.

By working through this module you will begin your journey on developing the skills and knowledge to be successfully employed in this pathway. By taking your experience and building on it by applying these skills in different scenarios you will be better prepared to take the next step in your educational path. At the end of this module you will select two of the related careers and describe the means to achieve those opportunities. These are the careers you will explore in this module: Architect Civil Engineer Chemical Engineer Surveyor Building Inspector General Contractor Construction Carpenter

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.

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!

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.

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.

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.

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.

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.

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.

Throughout the ages, the problem of how to cross over a river or valley has been solved by some type of bridge construction.

It took brilliant engineers to solve the problem the first time. They created structures that are still seen today as marvels of technology.

Although beams and arches came first, we know the Romans built bridges using trusses. Julius Caesar wrote about one in detail. There was a big problem after trains were invented. Railroad companies needed quick, low-cost bridges so trains could cross over valleys and rivers. The solution was the truss bridge. Today, thousands of both wood and iron-truss bridges are still standing.

Look up at the ceiling next time you're in the school gym or cafeteria. Were parallel-chord truss girders used? Truss girders support many flat roofs in schools, factories, and office buildings.

High-tech plastics are actually composites. That is, two unlike materials are bonded together. For example, carbon fibers and plastic resins are sandwiched together in molded panels for airplanes, cars, and boats. However, chemists first had to discover new resins to hold the layers together. Otherwise, they would split apart.

Natural glues come from animal or petroleum substances. Natural plant resins and gums become sticky or solid after they're exposed to air. Natural rubber comes from trees. Man-made glues don't need air to harden. One type of man-made glue is called epoxy. It becomes solid when two materials are mixed together.

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.

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

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.

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.

Fink and fan trusses are common designs found in many homes. The Fink truss spans more than 40 feet, allowing large, open rooms. The fan truss adds one more vertical tension web.

Parallel-chord trusses are used for flat roofs. Standard spans are up to 30 feet. You might see this truss in your school gym or cafeteria.

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.

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 name of the ancient engineer who built the first arch bridge is not known. But he was probably Chinese or Babylonian. The best example of a 1st century B.C. Roman aqueduct is the Pont du Gard in France. It measures 260.6 meters (855 feet) in length. There are three tiers of arches rising 47.2 meters (155 feet) above the Gard River.

The British engineer John Rennie built the Tweed River Arch Bridge in Kelso, Scotland, in 1803. It was the first semielliptical arch bridge. This design improved upon the semicircular arch bridges, which weren't wide enough for easy travel underneath.

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.

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.

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.

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.

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.

Ancient builders made their own concrete from a mixture of lime paste, water, fine and coarse particles, and air. Some Egyptian concrete columns are still standing after 3,600 years! Concrete is poured into forms. Wire and steel bars are buried inside to make it stronger. The big advantages of concrete are that it is strong and that it lasts for a long time.

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.

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.

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.

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.

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

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.

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.

In 1981, an accident happened due to bad engineering design and construction. In Kansas City, a Hyatt Hotel walkway fell four floors, killing 113 people. The movement of dancing people had caused some of the bolts to fail.

How can civil engineers and architects know if their designs are safe? Before actual construction begins, a model must be tested. This helps engineers to find the weaknesses in the structure. This step is especially important when using new materials or building structures that aren't covered by the Uniform Building Code.

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.

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.

Plastic was invented by chemists in the 1920s. Nylon, Rayon, and Lucite are brand names of the DuPont Company, not chemical names. DuPont's slogan was "Better Living Through Chemistry."

Radical new inventions don't happen very frequently. More often, engineers discover small ways to improve the designs for existing technology. They improve the little details in a structure. For example, modern materials can make structures stronger, lighter, or easier and less expensive to build. But the basic forms such as trusses, beams, and panels seem to remain the same.

Remember these five beam shapes from Day One? Look at the I-beam. You could say the I-beam combines two horizontal bookshelves with a vertical member between them. The I-beam balances the tension and compression forces with a good combination of horizontal and vertical widths.

Six variables affect how much a beam can hold, also known as its load capacity: Shape Size Span Weight Materials Area of load

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

Six variables determine a beam's load capacity. Shape Size Span Weight Materials Area of load

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.

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.