BUILD A STRAW BRIDGE
• Plan, design, build and test a model truss bridge made with paper straws.
• Identify effective geometric shapes used in bridge design and the force distribution these create.
• Identify several factors that engineers consider when designing bridges, including budgets.
L_A_U_N_C_H
Using the LAUNCH cycle design, build and work together in small groups to create a straw bridge that can carry weight. There are restrictions on the types of materials you can use. They include:
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LOOK, LISTEN AND LEARN
We take bridges for granted in our daily lives. We regularly cross bridges of various types and lengths without even thinking about it. Watch this clip about the Sydney Harbour Bridge. Imagine what a difference this crossing provided for people living either side of the harbour. The easy 5 minute drive or leisurely half hour walk linked two parts of the city that were previously divided by an immense stretch of water.
Sydney Harbour Bridge, NSW. It required 6m hand-driven rivets, 53,000 tonnes of steel, 1,400 workers and eight years of long, hard labour, but on 1932 the Sydney Harbour Bridge was finally opened by the then NSW premier, Jack Lang. Since then millions of people have crossed it, climbed it and, of course, photographed it. Photograph: Nikki Short/AAP
Making History in Tathra
By Vanessa Milton (ABC Open Producer, South East NSW)
Think of all the bridges in our local area, including Hancock Bridge at Mogareeka. It was built in the 1960s but before that, a punt run by the Preo family was the only way people could travel from one side to the other.
Long-time Tathra local Betty Koellner tells her story of growing up in the days of the ferry punt, training the surf lifesavers, and helping to save Tathra wharf from demolition.
Betty Koellner is a Tathra local whose history is closely entwined with the history of the town. The Preo family were early settlers in the Bega Valley, and Betty's grandfather Jim operated the ferry punt at Mogareeka. Hancock Bridge replaced the ferry in the late 1960s, but there are many locals who remember the days of the punt, and the reserve near the boat ramp at the northern end of the bridge is named after Jim. Read more... |
Our First People
This item is reproduced with kind permission from Mannum Aboriginal Community Association and shows two Aboriginal people in a bark canoe close to the river bank on the Murray, in the Moorundie area. The man standing is dressed in a fur cloak made of possum skins and is propelling the canoe with a long pole. The photo is thought to be created around 1870.
Our indigenous people in this region lived in one of the most populated areas of the continent and relied on rivers as transport networks for trade and travelling. The rivers acted as roads and they may not have relied on bridges as much as society does now with the advent of the car. Transport changes heralded the need for bridges. Can you think of other changes this has brought? |
Types of Bridges
1. Suspension Bridges
A suspension bridge is easily recognised by its defining characteristic of a bridge deck suspended from cables (or ropes or chains).
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Simple rope or vine bridges allow people to climb across gorges or rivers, More complex rope bridges made up of many ropes fixed together, eventually with decking make it easier for people to walk across. However rope bridges are not long-lasting, and not suitable for heavier vehicular traffic. Watch this clip about how a new bridge is woven every year at Q'eswachaka. What techniques used here can you use in designing and building a bridge? |
Reference: https://www.teachengineering.org/lessons/view/cub_brid_lesson01
Conventional suspension bridges are recognized by the elongated M shape. In these bridges, parallel sets of large cables are suspended between at least two towers (with smaller cables hung vertically from the large cable) and anchor into the earth at their end points. The smaller cables support the roadway. The weight of the bridge deck and any additional load push down on the bridge deck and create a force of tension in the cables. The cables then transfer their force to the towers. The force induced in the towers is compressive; the towers dissipate this force to the earth.
A second type of suspension bridge is a cable-stayed bridge, recognized by its A shape(s). In cable-stayed suspension bridges, the small cables are attached directly to the tower, and they splay out in rows "like the strings of a harp."
Conventional suspension bridges are recognized by the elongated M shape. In these bridges, parallel sets of large cables are suspended between at least two towers (with smaller cables hung vertically from the large cable) and anchor into the earth at their end points. The smaller cables support the roadway. The weight of the bridge deck and any additional load push down on the bridge deck and create a force of tension in the cables. The cables then transfer their force to the towers. The force induced in the towers is compressive; the towers dissipate this force to the earth.
A second type of suspension bridge is a cable-stayed bridge, recognized by its A shape(s). In cable-stayed suspension bridges, the small cables are attached directly to the tower, and they splay out in rows "like the strings of a harp."
Anzac Bridge, NSW. The sun sets behind the Anzac Bridge. It replaced the Glebe Island Bridge in 1995 and in 1998 was named in honour of the men and women of the Australian and New Zealand Army, by the then premier of NSW, Bob Carr. It is best seen at night when the lights are twinkling, or just before evening sets inPhotograph: Melanie Campbell/AAP
2. Arch Bridge
How strong are arches?
There are Ancient Roman bridges still in use today. What's the secret of their longevity? The Arch!
Reference: https://www.teachengineering.org/lessons/view/cub_brid_lesson01
An arch bridge is easily recognized with its defining characteristic of a semicircular structure. Not as easily recognized but extremely important are the abutments at each end of the semicircular arch.
The weight of the bridge and any additional load is dissipated by the abutments of the arch through the semicircular design. The force of compression is pushed outward along the curve of the arch and into the abutments . The tensile forces are small in most arches and usually negligible. However, when the degree of curvature or the semicircular arch gets larger, the force of tension becomes larger and must be considered in the design.
Arch bridges have little variability in the overall design, however most arch bridges do vary cosmetically. Some examples include the Roman, Baroque and Renaissance arches. Romans built arch bridges for transportation and aqueducts; many are still standing and are structurally sound. These bridges and aqueducts are excellent examples of the natural effectiveness of the arch shape as a bridge structure.
An arch bridge is easily recognized with its defining characteristic of a semicircular structure. Not as easily recognized but extremely important are the abutments at each end of the semicircular arch.
The weight of the bridge and any additional load is dissipated by the abutments of the arch through the semicircular design. The force of compression is pushed outward along the curve of the arch and into the abutments . The tensile forces are small in most arches and usually negligible. However, when the degree of curvature or the semicircular arch gets larger, the force of tension becomes larger and must be considered in the design.
Arch bridges have little variability in the overall design, however most arch bridges do vary cosmetically. Some examples include the Roman, Baroque and Renaissance arches. Romans built arch bridges for transportation and aqueducts; many are still standing and are structurally sound. These bridges and aqueducts are excellent examples of the natural effectiveness of the arch shape as a bridge structure.
Stone arch bridges continued to be built for many centuries. There are some classic examples of these still surviving from early Australian convict times, particularly in Tasmania. However, the emergence of structural steel as a building material during the industrial age allowed the design and construction of bridges on a scale never before contemplated.
Closer to home...
Ross Bridge, Tasmania. Completed in 1836, the Ross Bridge is just one of many historic bridges in Tasmania and is the third oldest sandstone bridge in Australia. Its design features more than 180 Celtic-style carvings and was constructed with the blood and sweat of convicts – including stonemasons Daniel Herbert and James ColebeckPhotograph: James Lane/AAP
Gladesville Bridge, NSW. With a 300m arch span, the Gladesville Bridge opened on 2 October 1964 and, according to the Sydney Morning Herald, ‘engineers declared its impressive arches, then the longest concrete arch span in the world, would stand for 2,000 years’ Photograph: Roads and Maritime Services
3. Beam (or Truss) Bridge
Reference: https://www.teachengineering.org/lessons/view/cub_brid_lesson01
A beam bridge is typically a simple structure made of horizontal, rigid beams. The beam ends rest on piers or columns. The weight of the beams (and any other load) is supported by the piers or columns. Compression force acts on the top portion of the beam and bridge deck, shortening these two elements. Tension force acts on the bottom portion of the beam, stretching this element.
Many beam bridges are constructed of steel, concrete, and (in some cases) wood. The beam size directly influences the maximum span capability of the beam. A very large solid beam must be strong enough to support itself (it is very heavy) plus any other load on the beam. Therefore, as the span gets longer the beam must be able to support more "self-weight."
Beam bridges come in a variety of different styles. For example, a beam bridge might be made of solid beams of steel, concrete, wood or other rigid material. Or, beams might be made with a hollow-center (reducing their weight). Beam bridges can also be composed of a truss system, which is a combination of triangular units that use fewer materials and are simple to build. A truss is a structural form based on the geometric rigidity of the triangle and composed of straight members. Many truss systems originated in the mid-1800s and are still in use today. One example is a truss designed in 1840 — the Howe Truss — that combined diagonal and vertical members to create impressive strength over long spans; which contributed to its overwhelming popularity as a railroad bridge.
A beam bridge is typically a simple structure made of horizontal, rigid beams. The beam ends rest on piers or columns. The weight of the beams (and any other load) is supported by the piers or columns. Compression force acts on the top portion of the beam and bridge deck, shortening these two elements. Tension force acts on the bottom portion of the beam, stretching this element.
Many beam bridges are constructed of steel, concrete, and (in some cases) wood. The beam size directly influences the maximum span capability of the beam. A very large solid beam must be strong enough to support itself (it is very heavy) plus any other load on the beam. Therefore, as the span gets longer the beam must be able to support more "self-weight."
Beam bridges come in a variety of different styles. For example, a beam bridge might be made of solid beams of steel, concrete, wood or other rigid material. Or, beams might be made with a hollow-center (reducing their weight). Beam bridges can also be composed of a truss system, which is a combination of triangular units that use fewer materials and are simple to build. A truss is a structural form based on the geometric rigidity of the triangle and composed of straight members. Many truss systems originated in the mid-1800s and are still in use today. One example is a truss designed in 1840 — the Howe Truss — that combined diagonal and vertical members to create impressive strength over long spans; which contributed to its overwhelming popularity as a railroad bridge.
Sea Cliff Bridge, NSW. Proving true the phrase ‘location, location, location’, the appeal of the Sea Cliff Bridge is in its dramatic placement rather than the bridge itself. The construction of the bridge was no small, technical feat, chief among its challenges being the balanced curved bridge design Photograph: AAP/Prancing Horse
It's time to ASK TONS OF QUESTIONS
Write down in your STEM notebook all the questions you are thinking about. They might include:
What forces are acting on bridges? Which one is the strongest?
What materials are available for bridges?
Are there plastic bridges?
What happens to bridges when nobody uses them?
What is the oldest bridge in the world? How do we know it is?
Write down your questions.
What forces are acting on bridges? Which one is the strongest?
What materials are available for bridges?
Are there plastic bridges?
What happens to bridges when nobody uses them?
What is the oldest bridge in the world? How do we know it is?
Write down your questions.
UNDERSTAND THE PROBLEM
• work as part of a team, each playing a particular role;
• design, make, test and critique a straw bridge;
• gain hands-on experience in design and construction;
• discover how to best record all observations, planned modifications and observed results in a journal; and
• build on your speaking and listening skills by sharing the straw bridges.
• design, make, test and critique a straw bridge;
• gain hands-on experience in design and construction;
• discover how to best record all observations, planned modifications and observed results in a journal; and
• build on your speaking and listening skills by sharing the straw bridges.
NAVIGATE IDEAS
What will your bridge look like?
How will it carry weight?
Where will it be weakest?
How will it stand alone?
How will it carry weight?
Where will it be weakest?
How will it stand alone?
Try out this app and build a bridge. Watch what happens when you change the design and the load and the forces have the last word. |
CREATE A PROTOTYPE
Here's some ideas for different bridge building prototypes. See if you can build one of these.
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HIGHLIGHT AND FIX
STEM is about changing up. Learn from your mistakes and after testing, go back as a team and build again.