SummaryStudents learn about the types of possible loads, how to calculate ultimate load combinations, and investigate the different sizes for the beams (girders) and columns (piers) of simple bridge design. They learn the steps that engineers use to design bridges by conducting their own hands on associated activity to prototype their own structure. Students will begin to understand the problem, and learn how to determine the potential bridge loads, calculate the highest possible load, and calculate the amount of material needed to resist the loads.This engineering curriculum meets Next Generation Science Standards.Engineering ConnectionEngineers who design structures must completely understand the problem to be solved, which includes the complexities of the site and the customer needs. To design for safety and longevity, engineers consider the different types of loads, how they are applied and where. Engineers often aim for a design that is strongest and lightest possible—one with the highest strength-to-weight ratio.Learning ObjectivesAfter this lesson, students should be able to:.

• What Engineers Know And How They Know It Pdf File Format

List several examples of loads that could affect a bridge. Explain why knowledge about various loads or forces is important in bridge design. Describe the process that an engineer uses to design a bridge, including determining loads, calculating the highest load, and calculating the amount of material to resist the loads.Educational Standards. Each TeachEngineering lesson or activity is correlated to one or more K-12 science,technology, engineering or math (STEM) educational standards.All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN),a project of D2L (www.achievementstandards.org).In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics;within type by subtype, then by grade, etc. Middle SchoolLessonPre-Req KnowledgeThe students should have a familiarity with bridge types, as introduced in the first lesson of the Bridges unit, including area, and compressive and tensile forces.Introduction/MotivationWe know that bridges play an important part in our daily lives.

We know they are essential components of cities and the roadways between populations of people. Some bridges are simple and straightforward; others are amazingly complex. What are some bridges that you know that might be called simple bridges? (Possible answers: Log over a creek, bridges over streams.) What are some bridges you know that might be considered more complicated? (Possible answers: Golden Gate Bridge, other large bridges, bridges that carry both highway traffic and train traffic.) What makes some bridges simple and other complex? (Possible answers: Their size, multiple purposes, environmental conditions, environmental forces, material maintenance requirements, etc.)One amazing example of a bridge's contribution to connecting people to other populations and places for both social and commerce reasons is the Sky Gate Bridge connecting people to Japan's Kansai International Airport, located in Osaka Bay.It all started when the nearby Osaka and Tokyo airports were unable to meet demand, nor be expanded.

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To solve the problem, the people of Japan took on one of the most challenging engineering projects the world has ever seen. Since they had no land for a new airport, they decided to create the Kansai International Airport by constructing an entire island! On this new, artificial island, they built the airport terminal and runways. Then, they needed a bridge to access it. Spanning 3.7 km from the mainland in Osaka to the airport in an ocean bay, the Sky Gate Bridge is one of the longest truss bridges in the world and has an upper deck for auto transport and a lower, internal deck for rail lines.Satellite image of Sky Gate Bridge to Kansai Airport in Osaka Bay, Japan. Copyright © 2003 Earth Observatory, NASA a modern engineering marvel, the airport and bridge opened in 1994.

Four months later, it survived a magnitude 6.7 earthquake with only minor damage. Because the airport site is built on compact soil, it sinks 2-4 cm per year — another condition for engineers to consider in the ongoing safety and maintenance of the airport and bridge.It is not easy to create a bridge the size of the Sky Gate Bridge.

Have you ever wondered how engineers actually go about designing an entire bridge? Bridges are often designed one piece at a time. Each pier (columns) and girder (beams) has to meet certain criteria for the success of the whole bridge.

Structural engineers go through several steps before even coming up with ideas for their final designs. First and foremost, engineers must understand the problem completely. To do this, they ask a lot of questions. What are some questions the engineers might ask? (Possible answers: How strong would you need to make the bridge? What materials would you use? How would you anchor the pier foundations?

What natural phenomena might your bridge need to be capable of withstanding?). Next, engineers must determine what types of loads or forces they expect the bridge to carry. Loads might include traffic such as trains, trucks, bikes, people and cars. Other loads might be from the natural environment. For example, bridges in Florida must be able to withstand hurricane forces. So, engineers consider loads such as winds, hurricanes, tornadoes, snow, earthquakes, rushing river water, and sometimes standing water. Can you think of any other loads that may act on a bridge of any kind?.

The next step is to determine if these loads can occur at the same time and what combination of loads provides the highest possible force (stress) on the bridge. For example, a train crossing a bridge and an earthquake in the vicinity of the bridge could occur at the same time.

However, many vehicles crossing a bridge and a tornado passing close to the bridge probably would not occur at the same time. After having calculated the largest anticipated force from all the possible load combinations, engineers use mathematical equations to calculate the amount of material required to resist the loads in that design. (For simplicity, we will not consider how these forces act on the bridge; just knowing that they do act on the bridge is sufficient.).

After they have considered all of these calculations, engineers brainstorm different design ideas that would accommodate the anticipated loads and amount of material needed. Copyright © 2007 ITL Program, College of Engineering, University of Colorado BoulderAfter an engineer determines the highest or most critical load combination, s/he determines the size of the members. A bridge member is any individual main piece of the bridge structure, such as columns (piers) or beams (girders).

Column and beam sizes are calculated independently.To solve for the size of a column, engineers perform calculations using strengths of materials that have been pre-determined through testing. The Figure 1 sketch shows a load acting on a column. This force represents the highest or most critical load combination from above. This load acts on the cross-sectional area of the column.The stress due to this load is σ = Force ÷ Area. In Figure 1, the area is unknown and hence the stress is unknown. Therefore, the use of the tensile and compressive strength of the material is used to size the member and the equation becomes Force = Fy x Area, where force is the highest or most critical load combination.

Fy can be the tensile strength or compressive strength of the material. For common building steel, this value is typically 50,000 lb/in 2. For concrete, this value is typically in the range of 3,500 lb/in 2 to 5,000 lb/in 2 for compression. Typically, engineers assume that the tensile strength of concrete is zero.

Therefore, solving for the Area, Area = Force ÷ Fy. Keeping the units consistent is important: Force is measured in pounds (lbs) and Fy in pounds per square inches (lb/in 2). The area is easily solved for and is measured in square inches (in 2).Figure 2. Force acting on a beam. Copyright © 2007 ITL Program, College of Engineering, University of Colorado BoulderTo solve for the size of a beam, engineers perform more calculations. The sketch in Figure 2 shows a beam with a load acting on it. This load is the highest or most critical load combination acting on the top of the beam at mid-span.

Compressive forces usually act on the top of the beam and tensile forces act on the bottom of the beam due to this particular loading. For this example, the equation for calculating the area becomes a bit more complicated than for the size of a column.

With a single load acting at the mid-span of a beam, the equation is Force x Length ÷ 4 = F y x Z x. As before, force equals the highest or most critical load combination pounds (lbs). Length is the total length of the beam that is usually known. Usually, units of length are given in feet (ft) and often converted to inches. F y is the tensile strength or compressive strength of the material as described above. Z x is a coefficient that involves the dimensions of the cross-sectional area of the member.

Therefore, Z x = (Force x Length) ÷ (F y x 4), where Z x has units of cubed inches (in 3).Figure 3. Example beam shape cross sections: (left to right) a solid rectangle, an I-shape, and a hollow rectangle. Copyright © 2007 Denise W. Carlson, ITL Program, College of Engineering, University of Colorado BoulderEvery beam shape has its own cross sectional area calculations.

Most beams actually have rectangular cross sections in reinforced concrete buildings, but the best cross-section design is an I-shaped beam for one direction of bending (up and down). For two directions of movement, a box, or hollow rectangular beam, works well (see Figure 3).Associated Activities.- Students take a hands-on look at the design of bridge piers (columns).

Using clay, marshmallows or foam, they design and test model columns to resist predetermined loads and perform calculations to determine the columns' cross-sectional areas.Lesson ClosureTake a moment and think of all the bridges you know around your home and community. Maybe you see them on roadways, bike paths or walking paths. Think of those that have piers (columns) and girders (beams). What do they look like? Can you remember the sizes of the piers and girders? (Discussion point: Students may recall noticing that piers and girders for pedestrian and bicycle bridges are much smaller than those for highway or railway traffic.)What are examples of load types?

(Possible answers: Vehicles, people, snow, rain, wind, the weight of the bridge and its railings and signs, etc.) Why would the loads make a difference in how an engineer designed a bridge? (Answer: Engineers must figure out all of the loads that might affect bridges before they design them.) If you were an engineer, how would you go about designing a bridge to make sure it was safe? (Discussion points: First, fully understand the problem to be solved with the bridge, its requirements and purpose.

Then figure out all the possible types of loads forces that the bridge might need to withstand. Then calculate the highest possible load the bridge might have to withstand at one time.

Then figure out the amount of construction material required that can resist that projected load.)Vocabulary/DefinitionsA method of shared problem solving in which all members of a group quickly and spontaneously contribute many ideas.The amount of compressive stress that a material can resist before failing.A 'slice' or top-view of a shape (such as a girder or pier).(verb) To plan out in systematic, often graphic form. To create for a particular purpose or effect. Design a bridge. (noun) A well thought-out plan.A person who applies her/his understanding of science and mathematics to creating things for the benefit of humanity and our world.Applying scientific and mathematical principles to practical ends such as the design, manufacture and operation of efficient and economical structures, machines, processes and systems.The process of devising a system, component or process to meet desired needs.

What Engineers Know And How They Know It Pdf File Format

Copyright © 2004 Microsoft Corporation, One Microsoft Way, Redmond, WA USA. All rights reserved.Human Bridge: Have students use themselves as the raw construction material to create a bridge that spans the classroom and is strong enough that a cat could walk across it. Encourage them to be creative and design it however they want, with the requirement that each person must be in direct contact with another class member. How many places can you identify tension and compression? How would you change the design if the human bridge had to be strong enough for a child to walk across it? What other loads might act upon your bridge?Concluding Discussion: Wrap up the lesson and gauge students' comprehension of the learning objectives by leading a class discussion using the questions provided in the Lesson Closure section.HomeworkMath Worksheet: Assign students the attached as homework.

After using the five UBC load combinations to calculate the highest or most critical load on the first page, they use that information to solve three problems on subsequent pages, determining the required size of bridge members of specified shapes and materials. The three problem questions increase in difficulty: younger students should complete only problem 1; older students should complete problems 1 and 2; advanced math students should complete all three problems.Lesson Extension ActivitiesHave students build and test the load-carrying capacity of balsa wood bridges. Begin by looking at Peter L.

Vogel's website on his Balsa Bridge Building Contest at happen! Assign students to investigate and report on what went wrong when a steel beam from a highway viaduct fell onto a moving vehicle. Read the May 2004 National Transportation Safety Board highway accident brief with photos.

See NTSB Abstract HAB-06/01, Passenger Vehicle Collision with a Fallen Overhead Bridge Girder at: the class participate in the yearly West Point Bridge Design Contest. Access excellent and free downloadable bridge design software and other educational resources at the US Military Academy at West Point website: bridgecontest.usma.edu/Additional Multimedia SupportUse the online Bridge Designer software (no downloading required!) provided by Virtual Laboratories, Whiting School of Engineering, Johns Hopkins University:References. Uniform Building Code. International Conference of Building Officials: Whittier, CA, 1991.ContributorsJonathan S. Goode; Joe Friedrichsen; Natalie Mach; Christopher Valenti; Denali Lander; Denise W. Carlson; Malinda Schaefer ZarskeCopyright© 2007 by Regents of the University of ColoradoSupporting ProgramIntegrated Teaching and Learning Program and Laboratory, University of Colorado BoulderAcknowledgementsThe contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and the National Science Foundation (GK-12 grant no.

However, these contents do not necessarily represent the policies of the DOE or NSF, and you should not assume endorsement by the federal government.Last modified: May 31, 2019.