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Bridge Building Activities for the Reach for the Sky
After-School Program
October 2008
Designed by
S. Selcen Guzey, Tamara Moore, and Gillian Roehrig
2
Table of Contents
Objectives……………………………………...…………………………………………... 3
Standards Addressed by Activity………………………………………………………….. 3
Part I: Exploring Civil Engineering………………………………………………………..
4
Part II: Bridge Construction………………………………………………………………. Building your own paper bridge………………………………………………….. Building columns………………………………………………………………….
6 6 17
Part III: Types of Bridges………………………………………………………………….
22
Part IV: Designing the Least Expensive Bridge…………………………………………...
29
Part V: Bridge Model Eliciting Activity (MEA)…………………………………………. 33
Appendix…………………………………………………………………………………... 47 Pre-Post Test……………………………………………………………………….. Pre-Post Test Answer Key…………………………………………………………. Glossary……………………………………………………………………………. Resources…………………………………………………………………………...
48 52 56 57
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Bridge Building Activities for the Reach for the Sky After-School Program
Objectives:
Students will:
• Understand the benefits of a career in civil engineering and how civil engineers affect our lives.
• Expand their vocabulary of bridges, bridge structures and construction, and mathematic concepts such as geometry, algebra, and reasoning.
• Learn about material terminology such as stress, failure, compression, and tension.
• Define similarities and differences between different types of bridges (e.g. beam, truss, arch, suspension, and cable-stayed).
• Evaluate the strength and stability of each type of bridge.
• Design and build bridges.
• Present their bridges and test how strong they are.
• Create a procedure to decide on what type of bridge they should build in a particular area.
Assessment:
Students will be assessed using the following methods:
• Blogs posts
• Student activity worksheets
• Pre-post test
• Bridge designs (K’NEX and West Point Bridge 2007 Software)
• MEA procedure
Standards Addressed:
National Science Education Standards (NRC): Students will develop
Content Standard B: an understanding of motions and forces. Content Standard E: abilities of technological design and understanding about science
and technology. Content Standard F: an understanding of science and technology in society. Inquiry Standard: abilities to do scientific inquiry and an understanding about scientific inquiry.
National Educational Technology Standards: Students will Standard 6: employ technology in the development of strategies for solving problems in
the real world and use technology resources for solving problems and making informed decisions.
Standards for School Mathematics (NCTM): Students will
Geometry: use visualization, spatial reasoning, and geometric modeling to solve problems.
Data Analysis and probability: formulate questions that can be addressed with data and collect, organize, and display relevant data to answer them.
Problem solving: apply and adapt a variety of appropriate strategies to solve problems.
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Part I: Exploring Civil Engineering
Time requirement: 1 class period Materials needed: Computers with internet access (you may need a computer lab for this lesson) Rationale/Goal: Students will
• gain understanding of the engineering field.
• explore civil engineering. Suggested Procedure:
1) Introduce students to bridge building activities. 2) Distribute the pre assessment test, have students complete and return when finished 3) Ask students questions about their career choices. 4) Lead a discussion on career choices in engineering. You may ask any of the following
questions: a. What is engineering? b. What do engineers do? c. Do you think there are other types of engineers?
i. Goals: try to get students to come up with different types of engineers and understand that what makes engineering different than other fields is that they go through a design cycle
ii. A sample of engineering design process that engineers use to design something to solve a problem is: Ask, imagine, plan, create, and improve.
5) Introduce the field of civil engineering and tell students they will be viewing two short clips about civil engineering. http://www.youtube.com/watch?v=Wgrt4SXU2Ks (Introduction to civil engineering, 2:18) http://www.livevideo.com/video/B55D495429074D53AD06A10DDB524041/civil-engineering-jobs-jobs-.aspx (civil engineers job description, 1:19)
or go to http://reachforthesky0809.ning.org (videos are on the left side of the main page) 6) Hold a discussion of the videos. Ask questions such as what are the things that you
learned about civil engineering? What are some challenges of a career in civil engineering? What kind of project do you think civil engineers work on? What would you study to become a civil engineer? What are some examples of civil engineering projects found in our community?
7) Remind students their new 35W Bridge site trip in summer 2008. Ask questions such as where is the new bridge located? What kind of structure is it? What is the new bridge made of? What parts of it really makes the bridge stand up? What kind of challenges did civil engineers face when designing and building the bridge?
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Answer Key The new 35W bridge is located in Minneapolis. It is a 1,216-foot-long, 10-lane concrete bridge. The bridge has 3 piers (4 columns in each pier) and the main span is 504’ long. The engineers considered the safety issue while designing the bridge. They used concrete to provide superior durability. Pictures of the new 35W bridge:
Pictures are taken from: http://projects.dot.state.mn.us/35wbridge/index.html
Closing:
1) Lead the students in a discussion of what they have learned. 2) Tell students that they will continue to explore about the structure of the new and old
35W bridge in the following day.
Assessment: The students will write a short paragraph describing a career in civil engineering. Students will explain what a career in civil engineering would require, the description of the job and why this would be an interesting career choice. Ask students to upload their essays on their Blogs on Ning (http://reachforthesky0809.ning.com/). Lesson Extension:
Teachers may ask students to do an internet search on famous civil structures and make a short presentation on the following day.
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Part 2: Bridge Construction
-Activities are adapted from “Design it: Engineering in after school program” Curriculum-
Activity 1: Building your own paper bridge
Time requirement: 1 class period Rationale/Goal:
Students will
• experience bridge structure.
• learn about balance, forces (e.g. tension and compression) and beams. Materials:
Computers with internet access (you may need a computer lab for this lesson) Video on 35W bridge collapse (http://reachforthesky0809.ning.com) Student worksheet (p. 16) Copy paper Small drinking cup Clear tape Steel washer or nails Cardboard square (4 inches x 4 inches) Books or boxes Suggested Procedure:
Before the class: 1) Before the class, please read the newspaper article about 35W bridge collapse (p.10). In the class: 1) Ask questions about 35W bridge collapse. Lead a discussion on factors that might have
caused the bridge collapsed. 2) Show the video about 35W bridge collapse. 3) Lead a discussion on bridge construction and design. Ask any of the following questions:
• How can we design a structurally stable bridge?
• What factors do civil engineers take into consideration when designing a bridge? (i.e. work load)
4) Explain students parts of a bridge- beam and columns Beam is a compact horizontal piece of material that supports weight across a gap.
Column is a vertical support that designed to take vertical loadings. 5) Go to http://www.pbs.org/wgbh/buildingbig/lab/forces.html for the virtual lab on the
forces that act on the different parts of the bridge structure. Note: If you do not have internet access explain forces using copy papers.
Compression: A force that acts to squeeze the paper. Tension: A force that acts to stretch the paper. Torsion: A force that acts to twist the paper. Shear (sliding): A force that acts opposite directions against the paper. Flexure (bending): A force that acts to bend the paper.
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Figure 1: Compression (squeezing) Figure 2: Tension (stretching)
Figure 3: Torsion (twisting) Figure 4: Shear (sliding) Figure 5: Flexure (bending)
6) Ask each student to complete the worksheet (p.16). 7) When students finish their worksheets group students (groups of 2-3) for the “challenge.” 8) The challenge: students will make a bridge that spans an 8 ½ inch wide “river” using only
four sheets of paper. They will attempt to make the strongest bridge. Rules: The bridge must sit on the riverbanks without any extra help and no part of the bridge may touch the “water”.
9) While students work on their design ask any of the following questions:
• Why did you decide to place that piece of paper/tape in that position?
• Does it matter how tight/loose you roll the beams?
• What shapes can you make your paper into? Which are the strongest?
• Where is the strongest/weakest part of your bridge? 10) Table 1 (p. 9) includes a list of strategies that students may use in this activity. 11) When students finish building their bridges give each team a small square of cardboard, a
cup, and some washers (or small heavy metal pieces) to test their bridges. The following figure shows how to add load.
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Figure 6. Adding load
12) Have student teams participate in a small competition to find whose bridge structure is more structurally stable. To do this, have teams put increasing weight (in equal increments) in their cup and record the amount of weight the bridges held. If possible record the competition with a video camera and upload it into Ning (http://reachforthesky0809.ning.com/).
13) After students test their bridges ask them following questions:
• What part of your bridge is the strongest?
• How can you change your bridge design to make it stronger? 14) During the discussion, try to draw out the following points:
Beam is a compact horizontal piece of material that supports weight across a gap. Compression: A force that acts to squeeze a material. Tension: A force that acts to stretch a material Torsion: A force that acts to twist a material. Shear (sliding): A force that acts opposite directions against the paper. Flexure (bending): A force that acts to bend a material. - The paper is stronger in the form of a beam rather than a flat sheet or board. - A good shape of a beam is cylinder - The tighter the cylinder is rolled, the stronger it seems to become.
15) If time allows, have students make a second bridge that spans the length of the paper (11 inches). Use 6 sheets of paper this time.
9
Table 1: Building Strategies
Source: Design it! Engineering in after school program
Lesson Extension: You may find helpful for students to investigate more about bridge disasters. The following web sites provide information, pictures, and videos of famous bridge disasters. Ask students to visit any of these following web sites.
http://iti.acns.nwu.edu/links/bridges/disasters.html
http://eduspace.free.fr/bridging_uerope/disasters.html
http://www.engr.utexas.edu/wep/COOL/AcifRiver/allaboutbridges_Disasters.html
http://www.lib.washingtom.edu/specialcoll/tnb/
http://www.ketchum.org/brdigecollapse.html
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Newspaper Article on 35W Bridge Collapse
Source: http://www.startribune.com/local/11593606.html
4 dead, 79 injured, 20 missing after
dozens of vehicles plummet into river
By Paul Levy, Star Tribune
August 2, 2007
Emergency crews have resumed their
recovery and clean up efforts at the scene of
the Interstate 35W bridge that collapsed
during rush hour Wednesday evening.
Authorities lowered the number of
confirmed fatalities to four, but said they
expect the number to change throughout the
day.
Doctors at Hennepin County Medical Center
said at a news conference this morning that
79 people were injured in the disaster.
One of them died around midnight of blunt
force trauma, consistent with chest injuries
from falling 64 feet.
Fifty-five people were transported to area
hospitals including 24 to HCMC. Six of
those had life-threatening injuries, 10 were
listed in satisfactory condition and eight
were treated and released.
Twenty-four people made it to hospitals on
their own.
Dr. John Hick, who was one of the first
responders to the bridge collapse, said "It's
somewhat of a miracle that (the number of
injuries and fatalities) was that low."
Hick also praised work done by passersby
and people in area who jumped in to assist
police and paramedics with evacuating
injured.
Dr. William Heegaard, who operated on
some of the injured, said the hospital cleared
out 25 rooms in ICU to deal with the
expected flood of injuries.
He said at one point the hospital had 10
operating rooms available and that a number
of surgeries were performed. "They were in
shock, they were happy to be alive, but they
felt sad for all the people they had seen," he
said.
Doctors said the types of injuries dealt with
included head, arm, leg internal injuries
"They may make it, but some of the may
not, said Dr. Douglas Brunette.
Police Chief Tim Dolan said at a news
conference this morning that 20 to 30 people
were still missing.
Dolan said many vehicles were still in the
water.
"The recovery involving those vehicles and
the people who may be in those vehicles is
going to take a long time," Dolan said.
"We're dealing with the Mississippi River.
We're dealing with currents, and we're going
to have to do it slowly and safely."
Police Lt. Amelia Huffman said the number
of confirmed fatalities had been lowered
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from seven to four. "This morning, the
medical examiner's office only has four sets
of remains," she said.
Mayor R.T. Rybak said the police
department's number is based on the medical
examiner's information, but he still
considers there to be seven fatalities — and
he expects more.
"I think you can expect that to be a dynamic
situation for a while," he said.
Crews in boats were using sonar to search
the water, said Hennepin County Sheriff
Rick Stanek. The bridge is too unstable to
allow divers into the water, he said.
As the sun rose this morning at least two
patrol boats were visible on the river south
and east of the lock and dam and just
uptream from the collapsed bridge.
Many rescuers who'd been at scene as late as
2 a.m. were expected back at 6 a.m. for an
operations briefing. Then, they were going
to go back onto the water.
An hour before sunrise, nearly a dozen giant
lights mounted on the Cedar Avenue and
surviving parts of I-35W bridge illuminated
river surface.
The 1,907-foot bridge fell into the
Mississippi River and onto roadways below.
The span was packed with rush hour traffic,
and dozens of vehicles fell with the bridge
leaving scores of dazed commuters
scrambling for their lives.
Stanek told the Associated Press at about 1
a.m. today that all search efforts had been
called off for the night and that searchers did
not expect to find any survivors.
Wednesday night, Gov. Tim Pawlenty said
the bridge collapse "is a catastrophe of
historic proportions for Minnesota."
Between 50 and 60 vehicles were on the
bridge when it went down shortly after 6
p.m., authorities said. Legions of rescue
workers and volunteers swarmed to the
scene and spent hours sifting through the
wreckage in a frantic search for survivors.
By late in the evening, officials said efforts
at the Mississippi had switched from rescue
to recovery.
Jay Danz, 45, of St. Paul, was on his way to
the Metrodome to watch the Twins play
Kansas City and had driven under W. River
Parkway, beneath the interstate bridge,
seconds before it fell.
"I heard it creaking and making all sorts of
noises it shouldn't make," Danz said. "And
then the bridge just started to fall apart."
In addition to the cars that went into the
water, a school bus carrying about 60
Minneapolis children fell from the bridge,
landing on all four of its tires and missing
the water as it came to rest near the
parkway.
Several of the children and at least two
adults were treated for injuries after the
group escaped through the back door of the
bus.
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"Some kids had blood on their faces, but
thank God everybody could move," Danz
said.
Bernie Toivonen of Minneapolis was
southbound on I-35 Wednesday when he
saw the bridge in front of him buckle.
"I knew it was going down," he said.
Toivonen scrambled out of his vehicle, and
helped others who were stranded among the
wreckage.
"I helped a lady get out of a minivan. She
was at a real steep angle. There were people
screaming."
Toivonen said that below him 40-50 feet
was a tabletop of concrete. He scrambled
down to the scene and found a man who he
said, "had a chunk of a beam on his arm and
a piece of concrete on his head."
The cause of the collapse wasn't known in
the hours afterward. It's too soon to know
what happened, said Catherine E. Wolfgram
French, a civil engineering professor at the
University of Minnesota.
"Things can happen with temperature, and
with construction, or a lot of other
confounding factors," French said.
This was a 40-year-old truss bridge, and
French did say that some early truss bridges
don't have as many structural redundancies -
- backups to carry the loads -- as is now
considered desirable.
Another engineer, Michael Ramerth, a
principal at MBJ Consulting Structural
Engineers in Minneapolis, said in the search
for answers "I would start at the
foundations."
On a typical weekday, more than 100,000
cars use the bridge.
Berndt Toivonen, 51, of Minneapolis, was
on his way home from a painting job when
the bridge collapsed beneath his car.
"The bridge started to buckle," Toivonen
said. "It went up and came down. I thought I
was going to die."
Bumper-to-bumper traffic
What people in the area of the collapse
experienced or saw at about 6:05 p.m.
unfolded as motorists crawled bumper to
bumper across I-35W toward the end of rush
hour.
Those on the bridge felt buckling and
swaying and heard a crunching.
Then came the unthinkable: The 40-year-old
bridge collapsed, dumping vehicles into the
water and onto land below. That was
followed by scenes of frantic, bloodied
motorists and rescuers who converged on
the scene.
Many vehicles, including at least one
semitrailer, were on fire. People were
reported to be floundering in the river.
Rescuers rushed to help people escape cars
trapped in the V-shaped hollow where the
bridge had caved in.
The school bus that fell was, returning from
a day-camp swimming trip sponsored by a
Waite House summer program.
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"We collapsed," said Ryan Watkins, one of
the children.
Crumpled wreckage lay on the east bank of
the river, and a huge section of concrete
roadway lay on the west bank. Down below
in the river gorge, rescue workers scrambled
to help people get out of the water.
Fire and black smoke rose from the
wreckage.
Memorial Blood Centers and the American
Red Cross put out immediate calls for blood
donors. A center for families of those who
are missing was set up at the Holiday Inn
Metrodome.
Homeland Security Secretary Michael
Chertoff issued a statement Wednesday
night saying there was no indication of
terrorism.
Transportation Secretary Mary Peters was
scheduled to fly to the Twin Cities early this
morning, along with Sens. Norm Coleman
and Amy Klobuchar.
Workers on the bridge
About 20 construction workers employed by
Progressive Contractors Inc. were about to
begin night shift work on the bridge when it
collapsed, company officials said.
The company has been working on a repair
project for about six weeks, said Mike
McGray, president of the company.
Progressive is based in St. Michael, Minn.,
and is one of the state's major road and
bridge repair contractors.
In 1990 a construction worker fell 90 feet to
his death when a concrete arch span on the
Lake Street-Marshall Avenue Bridge
collapsed into the Mississippi River. In 1960
a bridge over the Minnesota River at Hwy.
41 in Chaska collapsed during construction.
No one was killed in that incident.
Construction workers had been repairing the
bridge's surface as part of improvements
along that stretch of the interstate. There
were a large number of construction workers
who went into the water, said Maj. Michael
Asleson of the Minnesota State Patrol.
Most of the injured were taken to Hennepin
County Medical Center.
Nine people were taken to North Memorial
Medical Center in Robbinsdale and five
others arrived by ambulance at the
University of Minnesota Medical Center.
A staging area for the injured was set up
near the Stone Arch Bridge.
Marcelo Cruz, 26, of Crystal, who has used
a wheelchair since being paralyzed in a
shooting in South Carolina several years
ago, was driving his van across the bridge
toward downtown when he felt it began to
wave up and down.
He steered into the concrete railing to stop
himself from driving into the river, and saw
many cars on the bridge fall into the water.
His van came to rest steeply inclined toward
the river and several onlookers ran and told
him to get out. He said he needed help and
the onlookers carried him out of his van in
his wheelchair to safety on the riverbank.
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"I'm lucky to be alive," he said over and
over again.
Peter Siddons, a senior vice president at
Wells Fargo Home Mortgage, was heading
north over the bridge toward his home to
White Bear Lake when he heard
"crunching."I saw this rolling of the bridge,"
he said. "It kept collapsing, down, down,
down until it got to me."
Siddons' car dropped with the bridge, and its
nose rolled into the car in front of him and
stopped.
He got out of his car, jumped over the
crevice between the highway lanes and
crawled up the steeply tilted section of
bridge to land, where he jumped to the
ground.
"I thought I was dead," he said. "Honestly, I
honestly did. I thought it was over."
Ramon Houge of St. Paul was on his way
home from work and was on the bridge
when he heard a rumbling noise and cars in
front of him began to go down.
He said cars that could backed up, turned
around and drove toward safety.
Baseball game added to congestion
Danz said there were cars behind him on W.
River Parkway, but he didn't think any of
them were under the bridge when it fell.
John Joachim of Taylors Falls, Minn., took
I-35W to the Twins game and said traffic
suddenly "slammed to a stop" as he neared
University Avenue.
"I didn't know what was going on but a huge
cloud of dust rose in front of us," he said.
After the game, traffic were being rerouted
away from the collapse, routes that also
were being used by theater patrons leaving
the Guthrie.
This afternoon's Twins game has been
postponed, along with scheduled
groundbreaking ceremonies for the new
baseball park that had been scheduled for
this evening.
'Five feet from the edge'
Louis Rogers, 28, of Roseville was driving
home from work listening to music in his
Chevy Blazer when the bridge gave way just
feet in front of him.
"It just disappeared; it made no sound
whatsoever," he said. "It was pretty much
like a thud, not too loud of a thud. The next
thing I know, cars were dropping and there
was smoke. My car was no more than five
feet from the edge."
Rogers tried to help some of the people in
cars that had fallen into the river and
stopped on the bridge.
"I saw a lady in a car and I screamed, but I
got no response," he said. "I grabbed my bag
and started signaling cars to get out of
there."
Ryan Murphey, 30, of Minneapolis, went to
the scene to see if he could help out.
"It looked like a terrorist attack, a complete
catastrophe," Murphey said. "But everyone
there was very calm and organized."
15
He helped remove two victims from the east
side of the bridge on stretchers, including a
woman in her late 50s with a "bloody face."
The Twins decided to play Wednesday
night's game, but only after the public
address announcer alerted the crowd at 7:08
p.m. of the bridge's collapse. A moment of
prayer followed. It was then announced that
the game would go on so emergency crews
could perform their duties without the added
pressure of having 20,000 to 25,000 people
scrambling in swarms from the Dome area.
Area law enforcement, including the
Hennepin County Sheriff's Office, had
launched at least three boats to help with the
rescues.
"Unbelievable," said Audrey Glassman of
Minneapolis, who left her work shift at
nearby Spoonriver restaurant to survey the
scene. "You'll never cross a bridge again
without thinking about this."
Red Cross volunteer Eric Pone guessed 100
people came through the Holiday Inn
Metrodome Wednesday searching for word
on loved ones. "For some folks they're
dealing with a sense of relief because they're
loved ones are OK. Others haven't heard
anything."
Ian Anderson rode his bike to the Holiday
Inn to look for his girlfriend, Allysa
Rocklitz, 24, of Burnsville, a waitress at the
Fine Line club in downtown Minneapolis. "I
can't remember a single instance when I
called her and wasn't able to instantly talk to
her," he said. "She calls me all the time and
all of a sudden she's not there.
"Hopefully, I'll get a call tonight. I'll be up
all night, I'm sure of that."
--The Associated Press contributed.
Staff writers Curt Brown, Tim Campbell,
Joe Christensen, Terry Collins, H.J.
Cummins, Pat Doyle, Kevin Duchschere,
Tom Ford, Kevin Giles, Pat Lopez, Maura
Lerner, Bill McAuliffe, Pamela Miller,
Claude Peck, Joy Powell, James Shiffer, Jim
Foti and Doug Tice contributed to this story,
which was written by Paul Levy.
© 2008 Star Tribune. All rights reserved.
Source: http://www.startribune.com/local/11593606.html
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Student Worksheet-Forces
Student’s Name: ………………………… Date: Please write down the forces that are shown in the following drawings. Note: Arrows indicate the forces that act on the materials. 1)
This force is called ……………………………… 2)
This force is called……………………………..
3) This force is called……………………………..
4) This force is called…………………………….
5)
This force is called…………………………………………
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Activity 2: Building Columns
Time requirement: 1 class period Rationale/Goal: students will
• learn about columns
• learn about buckling Materials: One empty toilet paper-towel tube and one empty paper-towel tube for the demonstration Student worksheet (p. 21) Copy paper Clear tape Rubber bands Washers 2 cardboard squares (4inches by 4 inches) Suggested Procedure:
1) Show an empty toilet paper-towel tube and an empty paper-towel tube to students and ask them what happens if any of them put weight on them or stand on them.
2) When students make their predictions have one of the student stand on them 3) Ask them how they can make them stronger (e.g. filling the tube with sand, covering tube
with tape).
Buckling occurs when compressive stresses are too great for the material. Columns are the vertical supports of a bridge and they may buckle if they cannot support the load. How a column behaves depends on the strength of the material it is made from. Generally, a short, wide column can support a greater load than a long, thin one.
Figure 1: Buckling
4) Show students some pictures of long bridges that have columns. You can show the following pictures.
18
George P. Coleman Bridge, Yorktown, Virginia
Brooklyn Bridge, New York
19
Sunshine Skyway Bridge, Tampa, Florida
George Washington, New York
20
5) Have a discussion on bridges and their columns. Ask any of the following questions:
• What is the best way to place a column under the bridge?
• What is the best shape for bridge columns?
• Where are the strongest and weakest parts of the bridges in the pictures?
• Are tall columns stronger than short columns? 6) Group students for the challenge (2 students in each group). The challenge: Students
make a structure at least 4 inches high with only 4 sheets of paper. They then test and record how much load it can carry.
7) Ask students make their columns. (Students can make columns round, square, or triangular. They can make them narrow or wide)
8) Give students their data sheets (on next page). 9) To test how much load a column can carry, students should place one cardboard on the
top of the table and place their columns on it. Put the second cardboard on top of the columns and place the smallest load on the top square. Record the load and continue to add more load. Textbooks can be used for load. Allow students to take pictures while testing their designs. Note: Students will post these pictures on Ning later.
10) Ask students write down the loads on their worksheet (p.21) 11) Lead a discussion using any of the following questions:
• What makes some columns stronger than others?
• What is the best shape for the columns? (round, square, etc.)
• Which one is better? Long columns or short columns?
21
Student Data Sheet:
Team members: Date: ……………………………………………….
Each time you test your structure, one team member should write down the predictions and the largest actual load it carried without breaking and collapsing.
Trial# #Columns Height Diameter Shape Predicted load (ounces)
Actual load (ounces)
1
2
3
4
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Part III: Types of Bridges
Time requirement: 2 to 3 class periods Rationale/Goal: Students will learn the five main types of bridges (beam, truss, arch, suspension, and cable-stayed bridges) Materials:
Pictures of well-known bridges (See page 26, 27, and 28)
K’NEX (each group of students need one set of K’NEX) Weights measured in designated amounts (actual weights: 10-1000 grams, books etc.) Suggested Procedure: Before the class: 1) Please read the below information regarding the five main types of bridges.
i: Beam bridges are the simplest kind of bridges. They have one horizontal beam with two columns. It is typically used to span short distances. However, several beams can be linked together to build beam bridges to span long distances as in the case of Chesapeake Bay Bridge-Tunnel (The length of this bridge is 79,200 feet). Wood, concrete, steel, and stone can be used to build beam bridges.
Forces that act on beam bridges: Load Note: The arrows that point together represent compression and the arrows that point apart represent tension.
ii: Truss bridges are a type of beam bridge in which the beam is constructed from triangle sections. This type of bridge is usually made from steel. The longest steel truss bridges are around 500 m long.
Forces that act on truss bridge:
Compression
Load
Compression
Compression
Tension
23
iii: Arch bridges are very strong bridges. Wide range of materials (i.e. stone, metal) can be used to build arch bridges. Arch bridges can be built for both short and long distances.
Forces that act on arch bridge:
iv: Suspension bridges span long distances. However, it is very expensive and very challenging to build suspension bridges. The need for large amount of material and labor intention increase the cost.
Forces that act on suspension bridge:
v: Cable-stayed bridges span medium distances. These bridges are visually appealing. However, cable-stayed bridges are very expensive to build as in the case of suspension bridges. Labor intention increases the cost.
Compression
Tension
Load
Compression
Load
Compression
Compression
Tension
Compression
Load
Tension Tension
24
Forces that act on cable-stayed bridge: In the class:
1) Have a discussion about different types of bridges that students have seen. 2) Show pictures of well-know bridges (see page 26, 27, and 28). And then ask students any
of the following questions.
• Are they long or short?
• What factors might engineers consider while designing these bridges? (i.e. river, traffic)
• What do you think they were designed to transport? (i.e. pedestrian, vehicles, train)
Answer Key:
The beam bridge: The Eagle County Road Bridge is a short bridge. Engineers focused on the length of the span while designing this bridge, because the forces acting on a beam bridge tend to compress the top of the bridge. If the bridge is long and heavy piers become under compression. This bridge was built as functional walkway. The truss bridge: The Smithfield Street Bridge span medium distance (less than 300 feet).The engineers considered the river traffic while designing the bridge. There are a couple piers on the river and the bridge has a short clearance. The bridge was designed to transport vehicles. The arch bridges: The Rogue River Bridge spans a long distance. The engineers considered the weight of vehicles since the bridge itself apply large forces at the base of the arch. This bridge was designed to transport vehicles. The suspension bridge: The Golden Gate Bridge spans a very long distance. The engineers considered earthquake and wind while designing this particular bridge. This bridge was designed to transport pedestrian and vehicles. The cable-stayed bridge: The Sunshine Skyway Bridge spans a long distance. The engineers considered the weight of the material that structure is made of. The bridge was built to transport vehicles.
Compression
Load
Tension Tension
25
3) Discuss about the similarities and differences among different types of bridges. 4) Group students (2 to 3 students in each group). Provide each group the K’NEX education
kit (Note: The booklet in the kit shows how to connect different pieces). 5) Each group of students should build all 5 types of bridges in an order starting with beam
bridge (Beam bridge, truss bridge, arch bridge, suspension bridge, and cable-stayed bridge). Give 20-30 minutes for each group of student to build each type of bridge. After they build a bridge ask them to test how strong the bridge is. Provide them the weights (10-1000 grams or books). Allow students take pictures or videos when they testing their bridges. Note: Students will upload these pictures and videos on their personal Blog.
6) Lead a discussion on the strengths and weakness of each type of bridge. Possible answers can be found in the following table.
Bridge Type
Advantages
Disadvantages
Beam bridge -Easy to build -Inexpensive
-Short span range -Not aesthetic
Truss bridge -Strong and rigid framework -Work well with most applications
-Cannot be use in curves -Expensive materials needed
Arch bridge -Aesthetic -Used for longer bridges with curves -Long life time
-Abutments are under compression -Long span arches are most difficult to construct
Suspension
bridge
-Light and flexible -Aesthetic
-Wind is always a concern -Expensive to build
Cable-stayed
bridge
-Cables are economical -Fast to build -Aesthetic
-Stability of cables need to be considered for long span bridges
7) Ask students to upload pictures and videos that they took while testing their bridges to
their Blogs. Also, ask them to answer the following questions on their Blogs.
• How strong were the bridges that you built?
• How did you test your bridges?
26
Pictures of Famous Bridges
Beam Bridge:
Eagle County Road Bridge, Colorado
Truss Bridge:
Smithfield Street Bridge, Pittsburg, PA
27
Arch Bridge:
Rogue River Bridge, Gold Beach, Oregon
Suspension Bridge:
Golden Gate Bridge, San Francisco, California
28
Cable-Stayed Bridge:
Sunshine Skyway Bridge, Tampa, Florida
29
Part IV- Designing the Least Expensive Bridge
Time requirement: 3 class periods
Rationale/Goal: Students will use the West Point Bridge Design 2007 software to design the least expensive truss bridge. Materials: Computers with West Point Bridge Design 2007 Software Information about Truss Bridges for teachers (see below)
Truss Bridges
There are more than a half million bridges in the United States. This number includes all
the bridges greater than 20 foot and carry roadways on it. Thousand of us cross bridges everyday. While crossing a bridge, how many of us think about how engineers design a bridge or how engineers decide which bridge to build. When we think of a bridge, many of us remember only the Truss bridges because these bridges are very common in the United States.
Truss bridges’ frames consist of a series of triangle shapes. The triangles transfer the load
from the deck to the piers (bold words are defined in the glossary at the end). The truss bridge deals with two types of forces called tension and compression. While compression acts to compress or shorten the parts of structure of the bridge, tension acts to expend or lengthen the structure. The design of the bridge should handle these two forces. To deal with these forces, engineers use various materials and strengthen the structure of the bridge. For example, truss bridges are commonly made from cast iron, steel, or combination of these materials.
There are two main types of truss bridges: through trusses and deck trusses (see figure 1 on p.31). In a truss bridge, the deck can be located over or within the bridge structure. In a through truss bridge, the deck is located through, or in the middle of, the bridge structure. In a deck truss bridge, the bridge structure is under the deck.
In addition, a truss bridge can involve various types of frame structures. The most
representative truss bridges are Pratt truss, Howe truss, and Warren truss (see figure 1). A Pratt truss has vertical compression members and diagonal tension members. Except the very end members, all the diagonal members slant down toward the center of the span. The diagonals are in tension and the verticals in compression. This structure allows using thin diagonal members located near the center. The Pratt truss can be used with spans up to 250 feet. In a Howe truss, the vertical members are in tension and the diagonal members are in compression, the opposite structure of a Pratt truss. The diagonal members of the Howe truss slant toward the bridge end. The need to use thick steel to support the diagonal members makes it uneconomical design. Warren bridges are the simplest truss bridges. They usually do not have any vertical members, but to strengthen the bridge, vertical members can be used.
30
Glossary:
Abutments: supports of the each end of the bridge Deck: the structure that caries the road, path, or the railway. Members: connected elements (verticals and diagonals) that form truss bridge Pier: an upright support of the span of a bridge Span: a part of a bridge that extends between two supports
31
Student instructions: Select one type of bridge and build it according to the illustrations below using West Point Bridge Designer 2007. After building the bridge, identify the characteristics of the bridge. Share your findings with others who build different type of truss bridge.
Through Truss Warren Through Truss
Pratt Through Truss
Howe Through Truss
Deck Truss
Warren Deck Truss
Pratt Deck Truss
Howe Deck Truss
Figure 1. Images demonstrating through and deck trusses, as well as Warren, Pratt, and Howe trusses. All images were generated with West Point Bridge Designer 2005.
32
Suggested Procedure: Before the class:
• Please complete tutorial from http://bridgecontest.usma.edu/tutorial.htm to get experience with the West Point Bridge Software. In this tutorial you'll use the West Point Bridge Designer 2005 to design a steel truss bridge.
• Please install the West Point Bridge Designer 2007 software to the student computers. The software work only on PCs. There is no Macintosh version of this software.
• Students do not need to register for the bridge contest! In the class:
1) Give students information about truss bridges. You can use the above article for information.
2) Discuss about the structure of truss bridges. Ask any of the following questions:
• What are the advantages and disadvantages of truss bridges?
• What kind of materials can be used to build truss bridges?
• What are the basic types of truss bridges?
3) Group students for the challenge (max 2 students in each group). The challenge: Students will try to design the least expensive truss bridge using West Point Bridge 2007 software.
4) Give information about the West Point Bridge software. You can use the following information which is taken from the web site (http://bridgecontest.usma.edu/)
The software provides students with the tools to model, test, and optimize a steel highway bridge, based on realistic specifications, constraints, and performance criteria. The software allows students to:
• Learn about engineering through a realistic, hands-on problem-solving experience.
• Learn about the engineering design process--the application of math, science, and technology to create devices and systems that meet human needs.
• Learn about truss bridges and how they work.
• Learn how engineers use the computer as a problem-solving tool.
5) Ask students design their bridges using West Point Bridge software 6) Save students’ bridge designs. 7) Ask students to Blog about their bridge design. Students need to find answers to the
following questions and Blog about them.
• How did you design your bridge?
• What did you consider while designing your bridge?
• How did it go?
• How did the structure of your truss bridge look like?
• Which parts of your truss bridge stress from tension and compression?
33
Part V: Bridge MEA
Time requirement: 2 class periods Rationale/Goal: Students will create a model to build a bridge in a particular location. Material: Bridge MEA (see below) Pictures of bridges (see p.39-46) Suggested Procedure:
Students individually read the article to extent their knowledge on 35W bridge collapse. This article is on page 34. Students then watch a short clip on bridge collapse and then individually answer the guiding questions. These questions are also on page 34. Once students finish their responses give students the Internal Memo and ask them to read the Internal Memo individually. The Internal Memo is on page 35. Afterwards, place the students in teams of three to four. After students choose a name for their team, present the problem. The problem is on page 36 (You may want to give at least one hard copy of the problem to each group).
In teams, students work on the problem for 90 minutes. Each team needs to write their
solution in a letter to Mn/Dot. Then, they present their solutions to the class. You may give five minutes to each group to present their solution. At the end of the class presentation, students upload their letters to Mn/Dot into their Blogs. When Blogging is over collect student teams’ memos.
34
Model Eliciting Activity-Part A Bridge Design-Individual Activity
Read the following information and individually answer the questions that follow.
35W Bridge Collapse
Background material adapted from Mn/Dot Bridge website (http://www.dot.state.mn.us/bridge/ )
The Interstate 35W Mississippi River Bridge in Minneapolis collapsed on August 1, 2007. The eight lane bridge was Minnesota’s busiest, carrying 140,000 vehicles a day. This deck steel truss bridge was 1,907 feet long and had 14 spans. It was open to traffic in 1967 and expected to be reconstructed in 2020-2025. The bridge was inspected every two years until 1993; after that it was inspected every year.
Starting in 1997, deficiencies were demonstrated in inspection reports. Mn/Dot attempted to improve the condition of the bridge through bridge span rehabilitations. Furthermore, in 2001 Mn/Dot worked with civil engineers from University of Minnesota to evaluate the fatigue stress within the truss. Following the field tests, the civil engineers recommended that fatigue cracking was not expected to be a problem in the truss but reported that some critical locations of the trusses had high stress and some girders were distorted. The bridge’s last inspection was completed in June 15, 2006. As a result of comprehensive analysis on fatigue and fracture structure recommended supporting the critical 52 truss members.
During the 35W bridge collapse, 13 people were killed and more than 100 injured. The investigations on the collapsed bridge continue. Mn/Dot has investigated every single detail to find what caused the bridge collapse. It has been considered that gusset plates in the center span and the extra weight from construction may have contributed to the tragedy. The gusset plates are steel plates that tie steel beams together on a bridge. These are a very important structural component of truss bridges. However, it should be also considered that gusset plates are not the only structural components in truss bridges; other critical parts of the bridge might have deficiencies. In addition, extra weight may not be a main factor for the bridge collapse since the bridge had less than its usual traffic at the time of the collapse. Half of the lanes were closed for the repair when the bridge failed.
Individually:
• Watch the video of 35 W bridge collapse from http://www.youtube.com/watch?v=osocGiofdvc Or go to http://reachforthesky0809.ning.com
• Generate a list of factors you believe are involved in the 35W bridge collapse.
• Generate a list of factors that you need to consider when designing a bridge.
• Once you have finished your individual response, request the memo from Mn/Dot. Read the memo individually and then let your instructor know that you are ready to proceed.
35
INTERNAL MEMO
To: White Earth Engineering Team From: Mn/Dot Re: Bridge Design
After the I-35 W bridge collapse, Mn/Dot has focused attention on the condition of other
bridges in Minnesota. Mn/Dot conducted recent inspections on bridges in the Minnesota and
found that there are 1,907 bridges that are structurally deficient. As a result of recent inspections,
Mn/Dot shut down another bridge in March 2008. Originally, the bridge was scheduled for
replacement in 2015, but Mn/Dot inspectors found critical deficiencies during the inspection. The
bridge has a similar design configuration as 35W Bridge and it is located over the Mississippi
River in St Cloud. Mn/Dot plans to replace the bridge soon. The new bridge will be located in
the same place as the old one. It will carry a highway and run east-west. The length of the bridge
will be approximately 900 feet. The bridge deck should have two lanes and should also have 5 ft
wide sidewalks along both sides of the bridge.
Starting with the St Cloud Bridge, Mn/Dot will replace many of the bridges that have been
found to be structurally deficient. Because so many bridges are going to be replaced, Mn/Dot
needs a procedure for comparing different type of bridges and choosing the right type of bridge to
build across each span. Mn/Dot is asking you to create this procedure. First, your team should
decide on the least expensive and safest bridge to replace the St. Cloud Bridge. Pay attention to
how you made this decision because we also need you to create a procedure to make the same
type of decision in other locations around Minnesota. Mn/Dot will use your procedure to replace
the St Cloud Bridge and then other bridges. Please find the enclosed information regarding the
types of bridges that Mn/Dot plans to build―truss bridge, arch bridge, suspension bridge, and
cable-stayed bridge. In addition to the information about the major types of bridges, Mn/Dot also
has provided you two examples of four types of bridge in the U.S. You may need to use this
information as a starting point to determine your procedure for selecting the new bridge design.
Please respond in a letter to Mn/Dot explaining which bridge is right for the St. Cloud span and
why you chose it, and provide them with a method to make the decision of which type of bridge
to use to replace any bridge in Minnesota.
Thank you.
Peggy Abrams
Hwy. 23 bridge in St. Cloud, MN.
36
Model Eliciting Activity- Part B Bridge Design- Team Activity
• Read each team member’s individual list of factors that need to be considered when designing a bridge.
• Reread the Memo as a team.
• Write the body of a memo to Peggy Abrams at Mn/Dot that includes: o A clear explanation of what type of bridge you decided to build in St. Cloud and
why you made that decision. o A detailed explanation of your team’s general procedure for choosing the best
bridge type to build across any span and indicate how Mn/Dot can use this procedure to replace other bridges in Minnesota.
37
Table 1: Different Types of Bridges
Bridge Type
Advantages
Disadvantages
Span range
Material
Design
Effort
Truss bridge
-Strong and rigid
framework
-Work well with most
applications
-Cannot be used in curves
-Expensive materials needed
Short to medium
Iron, steel, concrete
Low
Arch bridge
-Aesthetic
-Used for longer bridges
with curves
-Long life time
-Very strong
-Abutments are under compression
-Long span arches are most difficult to
construct
-Relatively expensive
Short to long
Stone, cast iron,
timber, steel
Medium
Suspension
bridge
-Light and flexible
-Aesthetic
-Wind is always a concern
-Expensive to build
Long (up to
7,000 feet)
Steel rope and
concrete
High
Cable-stayed
bridge
-Fast to build
-Aesthetic
-Stability of cables need to be considered
for long span bridges
Medium (500-
2,800 feet)
Steel rope and
concrete
High
38
Table 2: Examples of four major types of bridges
Bridge Name
Location
Bridge Type
Total
length
Clearance
below
Lanes
Constructability Life
time
Cost
(Present
value)
Hennepin Ave
Bridge
Over Mississippi
(Metro area)
Suspension
bridge
1037
feet
37 feet
6
Easy
Fairly
long
(Built in
1990)
$100
million
Golden Gate
Bridge
San Francisco, CA
Suspension
bridge
8,981
feet
220 feet
6
Difficult
Fairly
long
(Built in
1937)
$212
million
10th Ave Bridge
Over Mississippi
(Metro area)
Arch bridge
2175
feet
101 feet
4
Difficult
Long
(Built in
1929)
$ 9 million
Stone Arch
Bridge
Over Mississippi
(Metro Area)
Arch bridge
2100
feet
24.4 feet
Bike and
pedestrian trials
Difficult
Long
(Built in
1883)
$15
million
Greenway
Bridge
Minneapolis, MN-
55, Light Rail Line
Cable-stayed
bridge
2,200
feet
20 to 27
feet
Bike and
pedestrian trials
Easy
Fairly
long
(Built in
2007)
$5.2
million
Arthur Ravenel
Jr. Bridge
South Carolina,
crosses
Cooper River
Cable-stayed
bridge
13,200
feet
186 feet
8
Easy
Fairly
long
(Built in
1929)
$ 62
million
John E.
Mathews
Bridge
Florida,
crosses St. Johns
River
Truss bridge
7736
feet
152 feet
4
Difficult
Short
(Built in
1953)
$ 65
million
Eagle Point
Bridge
Iowa
Truss bridge
2,000
feet
70 feet
2
Difficult
Short
(Built in
1902)
$2.5
million
39
Hennepin Ave Bridge, Minneapolis, MN (Suspension Bridge)
40
Golden Gate Bridge, San Francisco, CA (Suspension Bridge)
41
10th Ave Bridge, Minneapolis, MN (Arch Bridge)
42
Stone Arch Bridge, Minneapolis, MN (Arch Bridge)
43
Greenway Bridge, Minneapolis, MN (Cable-stayed Bridge)
44
Arthur Ravenel Jr. Bridge, Charleston, SC (Cable-stayed Bridge)
45
John E. Mathews Bridge, Jacksonville, FL (Truss Bridge)
46
Eagle Point Bridge, Dubuque, IA (Truss Bridge)
47
Appendix
48
Pre-Post Test for Bridge Activities
Source: KNEX Teacher Guide
Student Name:…………………………………………………..
Date:
1. Answer the following questions.
• What is engineering?
• What do civil engineers do?
2. Match the words with their correct definitions. Draw a line from the word to its matching
definition.
Beam Vertical support that hold up the bridge
Piers Foundation on which roadway/walkway is built on top of the beam.
Span: Distance between the piers
Deck: Horizontal framework that rests on piers
49
3. Match the pictures of different bridges with their names. Draw a line form the name of the
bridge to its matching diagram.
Beam Bridge
Truss Bridge
Arch Bridge
Suspension Bridge
Cable-Stayed Bridge
50
4. Here are some statements about beam, truss, arch, suspension, and cable-stayed bridges. Determine if they are true or false.
--------------- 1. All suspension bridges have three things in common: two very tall towers; strong anchorages; cables made of many wires.
--------------- 2. Cable-stayed bridges easily spans distances under 3000 feet (1000 meters).
-------------- 3. The longer the suspension bridge, the shorter the towers need to be.
--------------- 4. Beam bridges easily span short distances.
--------------- 5. Beam bridges allow large ships to pass underneath.
---------------- 6. Truss bridges span long distances.
---------------- 7. The force that has the most impact on arch bridges is compression.
51
5. Below are facts about the different types of bridges you have investigated. Match the fact with the name of a bridge from the list provided. You may use the bridge names more than once.
ARCH BEAM TRUSS SUSPENSION CABLE-STAYED
1. Because bridges like me are long, light in weight, and high in the air, our greatest enemy is the wind. _____________________________________________
2. Builders made the original versions of me out of wedge shaped stones that fit snugly
together. They were held in place with the pressure of the weight of the bridge.
3. My bridge design is popular when the span is less than 3,000 feet (1,000 meters), mainly
because I do not need anchorages or many piers. _______________________________
4. In the past I was commonly used to cross narrow distances like small streams or rivers. _______________________________________________
5. The strength of my design lies in the use of triangles. ____________________________
6. I am a new bridge design that includes elements from a suspension bridge, I am easier to build than either of those but I am limited to spanning shorter distances. ______________________________________________________
7. Two bridges that are like me are the Brooklyn Bridge and the Golden Gate Bridge. They
both have decks that hang from cables made of hundreds of steel wires. ____________________________
8. I am one of the oldest and simplest bridge designs. Today I can be quite a complex
bridge, but like my ancestors, I support my own weight and the loads I have to bear, on vertical piers. ________________________________________
52
Pre-Post Test for Bridge Activities Answer Key
1. Answer the following questions.
• What is engineer/engineering?
Engineer/Engineering: A person who uses his/her creativity and understanding of
materials, tools, mathematics, and science to design things that solve problems for
people.
• What do civil engineers do?
Civil engineering is a branch of engineering that concern with design of bridges,
highways, buildings, airports, factories, and so on.
2. Match the words with their correct definitions. Draw a line from the word to its matching
definition.
Beam Vertical support that hold up the bridge
Piers Foundation on which roadway/walkway is built on top of the beam.
Span: Distance between the piers
Deck: Horizontal framework that rests on piers
53
3. Match the pictures of different bridges with their names. Draw a line form the name of
the bridge to its matching diagram.
Beam Bridge
Truss Bridge
Arch Bridge
Suspension Bridge
Cable-Stayed Bridge
54
4. Here are some statements about beam, truss, arch, suspension, and cable-stayed bridges. Determine if they are true or false.
----------T---- 1. All suspension bridges have three things in common: two very tall towers; strong anchorages; cables made of many wires.
------------T--- 2. Cable-stayed bridges easily spans distances under 3000 feet (1000 meters).
-----------F--- 3. The longer the suspension bridge, the shorter the towers need to be.
-------------T-- 4. Beam bridges easily span short distances.
------------F--- 5. Beam bridges allow large ships to pass underneath.
-------------F--- 6. Truss bridges span long distances.
--------------T-- 7. The force that has the most impact on arch bridges is compression.
55
5. Below are facts about the different types of bridges you have investigated. Match the fact with the name of a bridge from the list provided. You may use the bridge names more than once.
ARCH BEAM TRUSS SUSPENSION CABLE-STAYED
1. Because bridges like me are long, light in weight, and high in the air, our greatest enemy is the wind. __________________SUSPENSION______________
2. Builders made the original versions of me out of wedge shaped stones that fit snugly
together. They were held in place with the pressure of the weight of the bridge. ARCH
3. My bridge design is popular when the span is less than 3,000 feet (1,000 meters), mainly
because I do not need anchorages or many piers. _CABLE-STAYED________________
4. In the past I was commonly used to cross narrow distances like small streams or rivers. _______________________________BEAM________________
5. The strength of my design lies in the use of triangles. __TRUSS____________________
6. I am a new bridge design that includes elements from a suspension bridge, I am easier to build than either of those but I am limited to spanning shorter distances. ______________ CABLE-STAYED __________________________
7. Two bridges that are like me are the Brooklyn Bridge and the Golden Gate Bridge. They
both have decks that hang from cables made of hundreds of steel wires. __________SUSPENSION_________________
8. I am one of the oldest and simplest bridge designs. Today I can be quite a complex
bridge, but like my ancestors, I support my own weight and the loads I have to bear, on vertical piers. ___________BEAM_____________________________
56
Glossary
Source: www.dot.state.mn.us/
Abutment: Earth-retaining structures supporting the superstructure at each end of the structure. Deck: The bridge floor; the surface that supports the vehicular traffic. Main span: The center or primary span of the bridge over the river, typically the longest span of the bridge. Pier: A vertical structure that supports the bridge superstructure. Piers transfer forces from the superstructure to the foundations. Span: Section of superstructure between supports. The span is the length between supports. Substructure: All portions of the structure below the bearings (pylon, piers, columns, and foundations) that support the superstructure. Superstructure: The top portion of the structure that vehicles drive over, which is supported by the substructure. Tendon: Steel strands used for post tensioning. Tension: A force that is used to stretch (stress) tendons. Transverse: Used to describe the axis of a bridge that lies perpendicular or radial to the longitudinal axis. Vertical Curve: Curvature of the roadway or bridge in the vertical plane.
57
Reference Materials
Books:
Design it! Engineering in after school program (2002), Kelvin, Education Development Center, Inc., NY. K’NEX Education, Teachers’ Guide, Bridges (2007), PA. Internet Resources:
Minnesota Department of Transportation http://www.dot.state.mn.us/ Building Big http://www.pbs.org/wgbh/buildingbig/bridge K’NEX http://www.knex.com/ West Point Bridge Designer www.bridgecontest.usma.edu
http://iti.acns.nwu.edu/links/bridges/disasters.html
http://eduspace.free.fr/bridging_uerope/disasters.html
http://www.engr.utexas.edu/wep/COOL/AcifRiver/allaboutbridges_Disasters.html
http://www.lib.washingtom.edu/specialcoll/tnb/
http://www.ketchum.org/brdigecollapse.html