What makes bridges

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. In Figure 1, the area is unknown and hence the stress is unknown.

Fy can be the tensile strength or compressive strength of the material. Typically, engineers assume that the tensile strength of concrete is zero. The area is easily solved for and is measured in square inches in 2. Figure 2. Force acting on a beam. To 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. 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. Figure 3. Example beam shape cross sections: left to right a solid rectangle, an I-shape, and a hollow rectangle. Every 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. Watch this activity on YouTube. Take 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. To create for a particular purpose or effect. Design a bridge. Pairs Drawing : Divide the class into teams of three students each. Have each engineering team sketch a bridge to carry a train across a river that is meters wide. Have them describe the type of bridge and where the compressive and tensile forces are acting on it.

Have them draw in the loads and the direction that they would act on the bridge. What do they think the highest load combination would be how many of these loads could actually happen at the same time? Then, ask for one or two engineering teams to volunteer to present the details of their bridge design to the class. 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.

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. My 9 year old son, Cody, made a folded bridge with 4 pillar supports. That bridge held coins! How fun!

I ran out of coins for some of the paper bridges. I extended this with making human bridges. They loved experiencing the weight, pulls and pushes of the structures. They really got creative within their groups.

I wish I could show you the great pictures I got!! Building, re-designing, learning from our failures- all of it was great! They worked together building bridges and testing their ideas, then trying out a different method or way learning from their mistakes. A great activity. I learned much myself. He had fun building bridges out of paper. The lesson is very entertaining! Students discovered which bridge supported the most weight.

So much fun! They ended up using the weights for our balances instead of pennies and that gave us math review too! My students had such great conversations with the prompts in the video. I love this program. Even though they had done an experiment similar to the paper bridge activity, your visuals gave it deeper depth and made them excited to try it with more effort in their attempts.

It was a great way to extend their thinking in building a challenge for the local roborave. We also loved the live action videos; we felt like we were there! Giving the students time to discuss their ideas is a great feature, too. Thanks for such a great product.

Our PTO is purchasing a subscription for us next year because we enjoyed our free trial! It's interesting too! They even started taking pictures of bridges on their time to make comparisons to what they built during the exploration. I enjoyed how they had to build upon each bridge to make it better.

It really brought up our topic of Growth Mindset. Best part of ALL lessons And did I mention they have readily available supplies? The kids loved it! The kids tried different ideas and once they failed, they thought about what they should do next time.

One team was very successful on their second bridge and then I noticed other bridges were similar. We had a great discussion about how engineers will consult each other and share ideas. They just need to give credit to the person who helped. Thank you for making this. We will be watching the video about the Tacoma Bridge and doing the assessment soon.

It is very educational, and it seems like it is taught from a teacher's perspective. Can't wait to do 3!!! These lessons make my life SO easy! Students and staff loved building the bridges.

It was fun to watch them "fail" and figure out what they could do to hold more coins. They didn't want to go to their next class! My students are begging for more. They're obsessed now and keep trying out different shapes.

Makes me so happy. I love the way the experiments make the science lessons really come to life. I loved that the students had to use critical thinking skills in order to build the bridge and determine which type of bridge would be the strongest!

The students enjoyed testing the bridge, reading about the Tacoma bridge, and watching the video about the Tacoma bridge! You have set this up so user-friendly! Can't wait to try more! My kids most enjoyed building their own bridges with paper. My 6 year old built one that held all the coins in the house- more than 60! Plus a bag of centimeter cubes, plastic tiles, toy cars, and a metal harmonica. He wanted me to "take a picture and send it to Doug!

My students were so engaged in building bridges! To walk around my classroom as they worked and hear the science talk and the vocabulary used by my students was amazing! Thank you for helping me provide my students with meaningful lessons! Seeing my ELL student come up with one of the top designs that held the second most pennies.

The students were really into it. We went back to it the next day to see if they could improve their design. They applied what they had learned through the video session to build structures that held more than pennies! They loved the bridge building activity to go along with the lesson. I stretched this lesson even further because they enjoyed it so much! Watching science in action is so much better than just reading about it Thanks so much for this program!

Bridge members The bridge members are divided into two major categories: the superstructure and the substructure. Superstructure The superstructure is the upper portion of the bridge above the beam seats where you drive or walk.

Substructure The substructure is under the superstructure and supports all of the bridge loads. Bridge materials Some of the main materials found on a bridge are steel, concrete, stone and asphalt. Other materials include iron, timber, aluminum, rubber and other joint materials. Below is a description of some typical uses for these materials in a bridge. Concrete Concrete is commonly used for many bridge superstructure members such as decks, pre-stressed concrete beams, curbs, sidewalks and parapets side traffic barrier walls.

It is used extensively in new construction for the entire abutment, including the footings, stem main front wall , wingwalls, cheek walls, backwalls, endwalls for traffic barrier connection , beam seats, and the piers with similar members.

It can also be used for cast-in-place or precast concrete piles to support the abutments and piers. Steel Steel is commonly used in the bridge superstructure for armoring expansion joints, beams, bearings, floor beams, girders, reinforcing bars in concrete, traffic barriers and trusses. It is used in the substructure for the reinforcing bars in concrete, armoring for expansion joints, anchor bolts, etc.

It is also used for piles to support the abutments and piers.