299301804-balsa-wood-bridge.docx

Balsa wood Bridge Engineering Report

By Alvin Wong 10Eng1 Mr Wallace August 2015

Abstract In this report, I will explain how to design and construct the most efficient Balsa Bridge by using limited material in a limited time period. I need to find an engineering process which allows me to design and construct a Balsa bridge when I do not have any constraints on how the Balsa Bridge must be manufactured.

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Contents Abstract ................................................................................................................................................... 2 Introduction ............................................................................................................................................ 4 Design Brief ............................................................................................................................................. 5 Work Breakdown Structure .................................................................................................................... 6 Balsa Wood Bridge Design ...................................................................................................................... 7 Production plan - sequence of proposed steps ...................................................................................... 8 Bridge specifications ............................................................................................................................... 9 Equipment ............................................................................................................................................. 10 Evaluation ............................................................................................................................................. 12 Final Evaluation ................................................................................................................................. 12 Recommendations ................................................................................................................................ 14 Appendix ............................................................................................................................................... 15 Appendix 1: Rules and Guidance ...................................................................................................... 15 Appendix 2: Construction Rules ........................................................................................................ 16 Appendix 3: Important tips ............................................................................................................... 17 Appendix 4: Further tips for bridge construction ............................................................................. 18 Appendix 5: Safety precautions and hazards .................................................................................... 19 Appendix 6: Types of bridges ............................................................................................................ 20 Appendix 7: Types of force ............................................................................................................... 23 Appendix 8: Live Load and Dead Load .............................................................................................. 24 Glossary ................................................................................................................................................. 25 Bibliography .......................................................................................................................................... 26

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Introduction The year 10 engineering class received a project known as the Balsa bridge where we were given a set amount of materials to design and construct a bridge which could hold the most weight and have the best weight to load ratio. We must solve many problems in this Balsa bridge before constructing the most efficient Balsa bridge. Some problems are the availability of each materials and time constraint. In the end, it is up to us, the engineers to solve the question of ‘how best to make the bridge?’ This project involves planning, decision making, creative thinking and innovation.

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Design Brief For this Balsa wood bridge project, we had to complete these things: 1. 2. 3.

Bridge draft Balsa wood bridge model Progressed folio

Aim: to understand the characteristics of the balsa wood bridge, to develop skills on bridge building, forces, technical terminology, how to use a certain equipment and how to make a wood balsa bridge efficiently.

For my balsa wood bridge model, I had specifications to follow to comply with the bridge specifications. Some examples of these were  The length of the bridge  The width of the bridge  The amount of materials provided

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Work Breakdown Structure Balsa Bridge Project

Research

Design

Make

Test

Evaluate

Similar Designs

First sketch

Cutting Balsa

Weight

Evaluation

Final test

Final Evaluation

Award winning designs

Westpoint Bridge Designer

Drafts

Final Design

File to the right measurement

Gluing

Add on decking

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Balsa Wood Bridge Design

Figure 1 My Balsa wood bridge

Figure 2 My Balsa wood bridge's side drawn to scale

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Production plan - sequence of proposed steps 1. Research and evaluate designs 2. See pros and cons 3. Choose the designs I want 4. Come up with the final design I want using research 5. Draw the final design (pencil, ruler, A3 paper) 6. Cut balsa wood into pieces to a length of 50mm (Stanley knife) 7. Draw design to scale on the A3 paper 8. Cut out gusset pieces 9. Glue pieces together with gusset pieces (hot glue) 10.Cut balsa wood into pieces to a length of 60mm (Stanley knife) 11.Glue pieces together with pieces glued together in step 9 to complete one side of the bridge 12.Repeat step 6-11 13.Cut out pieces of balsa woods of 50mm in length 14.Put the pieces from step 13 at the bottom of the 2 bridge sides 15.Glue them together 16.Cut out pieces of balsa woods of 50mm in length 17.Glue them on top of the bridge 18.Put on decking 19.Glue on decking 20.Smoothen the edges with file or sandpaper 21.Weight the bridge 22.Test the bridge

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Bridge specifications  Truss Bridge or whatever  Bridge must be 300mm in length  50mm wide (block of 50mm x 50mm x 50mm can pass along the whole length)  Maximum height of bridge is 60mm  Cannot use more than the material provided  One decking sheet (balsa) which is 50mm x 300mm x 1.5mm  4x915mm lengths of 5mm square balsa  Only hot glue (or PVA wood glue)

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Equipment Stanley knife- a retractable-blade knife that is used for utility purposes. This was used when cutting the balsa wood. (See figure 3)

Figure 3 A Stanley Knife

Hot glue- a type of glue typically used for crafting. This was used when gluing the bridge together. (See figure 4)

Figure 4 Hot glue sticks

Hot glue gun- a gun designed to melt hot glue in order for it to stick. This was used when melting the hot glue. (See figure 5)

Figure 5 A hot got gun

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File- a tool to fine amounts of materials in workplace. This was used when smoothing the balsa wood bridge’s edges. (See figure 6)

Figure 6 A file

Sand paper- another tool to fine amounts of materials when crafting. This was also used when smoothing the balsa wood bridge’s edges. (See figure 7)

Figure 7 Sandpapers

Ruler- an instrument used to measure distances or draw straight lines. This was used to measure the length of balsa wood pieces and to draw the draft of my bridge on the A3 paper. (See figure 8)

Figure 8 A metal ruler

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Evaluation Final Evaluation

I did the balsa wood bridge after finishing the spaghetti bridge project. They are both quite similar but the spaghetti bridge project only allowed very limited materials and it was more challenging than the balsa wood bridge because spaghettis are easier to break. My balsa wood bridge met the specifications that I was given. My bridge was 300mm in length, 50mm in width and 60mm in height. (See figure 1 and 2). My bridge was above average, it reached a load to weight ratio as 787.815 which was the 4th strongest bridge in my class. My bridge was 19.04 grams which was relatively light if you compare it with other bridges and it handled 15 Kilograms of weights which was quite a lot. The strongest bridge was built by James Wong, his bridge was not only the strongest, and it was the lightest as well with 14.58 grams only. I was amazed at his result as his bridge handled 14 Kilograms with such a light weight. My bridge was poorly built due to lack of time and experience, especially most of the edges were not glued properly and not all the members were exact 50mm in length. This was resulted in failing early in the weight test. This also caused the bridge to look uneven on both sides and made the bridge unbalanced. The reason that I did not apply that much glue on my balsa wood bridge is that I believed that it would make the bridge much lighter and the hot glue would spread very well, I also thought the hot glue we were using was very strong.

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I missed out a couple of lessons due to illness and other activities such as peer support, these are some reasons that I had to rush in order to finish my balsa wood bridge. I was also distracted by my friends easier during class which made me spend less time on building the bridge. I did not spend my time efficiently because I was spending too much on one particular area of the project, such as researching on bridges. Another problem that led to my failure was forgetting to use the Westpoint bridge program, this program would allow me to test my bridge virtually first. I believe I should have done a lot better if I had spent more time on this project. Even though I did my research on bridges, I did not put good uses of them. Some strengths about my bridge are it reached the 700-1000 weight to load ratio which are the main focus of the project, it looked quite aesthetic even thought it was unbalanced, it was relatively light comparing to other bridges and it was quite successful. I have learnt a lot from this balsa wood bridge project and I think I would definitely improve if I do this project again.

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Recommendations After finishing the balsa wood bridge project, I have learnt a lot knowledge about building bridges, forces and many technical terminologies. There would be many changes to how I handle this project if I was given a 2nd chance. Some things I would do are making a Gnatt chart which is timeline for project, it would allow me to show the steps of each stage that fit into the weeks available for researching, analysing, production and evaluation. Making a project milestones chart would allow me to write down the deliverables for each week with a comment. A better structured work breakdown structure which would have helped my project significantly as it would be able to counter the time constraints and the things need to be done. Spending more time on building the balsa wood bridge itself is another thing I would definitely do. My bridge did not achieve the best result in the class due to lack of time on making the bridge. Gluing and cutting balsa members are the two most significant jobs in the production section. I did not spend a lot time on these two areas, I would take my bridge home and spend more time on it next time. This would make my bridge more stable and possibly result in a better weight to load ratio. More researching would give me more knowledge on building bridges. Using the Westpoint bridge program would allow me to test the bridge virtually and possibly make changes to my design. I need to know more about my tools and materials, so I can construct my bridge with the correct techniques. If the recommendations above are used, the balsa wood bridge would definitely have a better weight to load ratio and improved significantly.

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Appendix Appendix 1: Rules and Guidance

 Bridge must be made with only of the balsa wood and glue supplied in class  Bridge must be 300mm in length  Bridge must be 50mm in width  Bridge’s maximum height is 60mm  There must be 1 decking sheet on top on the bridge which is 50mm*300mm*1.5mm  Only allow 4 of the 915mm lengths of 5mm square balsa  Only allow hot glue or PVA wood glue  No part of the bridge may touch anything except the top surface of the chair within 50mm of the edge of the gap, and the equipment used to test the bridge  Bridge must rest freely on the table tops. It cannot be attached to the table tops with glue or screws, for example  Bridges will be designed and built by 1 person only.  Each person must submit a photo of their bridge and video of the test to the teacher

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Appendix 2: Construction Rules

The bridge must rest simply on top of the supports at each side and not rely on the testing support frame of lateral support. Side thrust onto the vertical faces of the frame is not permitted. (See figure 9)

Figure 9 Bridge on top of the support

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Appendix 3: Important tips

 Plan and sketch the bridge on paper before cutting balsa wood to ensure the availability of material to achieve the design.  Pay attention to the joints between the balsa wood elements.  Lack of glue or inadequate contact between the two surfaces may lead to bridge failures.  Cut small notches to connect bridge components  Fewer pieces mean fewer problems  Design for strength at the load application point  Most bridges bend inwards  Double-check the length of the bridge. It should be 300mm.  Do not cover the bridge with any material. Glue should be used only to join components.  Use sandpaper to clean the bridge and remove excess glue.  Align connections carefully so that you structure is straight when finished.  Balsa is unlikely to be same strength throughout its entire length.

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Appendix 4: Further tips for bridge construction

Connections are typically the weakest part of Balsa Bridge. Strong connections have a lot of surface area for the glued connection. Using gusset plates when constructing can strengthen the bridge. The connection on the left below can use only one gusset plate because the widths of the two members are different. The connection on the right can use two gusset plates because the bottom member is rotated flat-wise. (See figure 10 & 11)

Figure 11 Gusset plates

Figure 10 Gusset plates

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Appendix 5: Safety precautions and hazards

 All construction and decoration work must be done within the workshop supervised by a teacher at all times.  Wear safety goggles while creating your bridge.  Ensure the workspace is well ventilated at all times, particularly while gluing your bridge.  Take great care when carrying out cutting on a clean, flat and stable surface when working with sharp tools.  Be extremely careful when handling hot glue as it is very hot and a strong adhesive, so avoid contact with skin, eyes and clothing.  Protect the surfaces you will be working on from both glue and accident cutting.  Need to clean up work area after each bridge building lesson.  Keep your hands away from the bridges during testing.

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Appendix 6: Types of bridges

Type of Bridge Beam Bridge

Truss Bridge

Illustration

Description/example s Simplest bridge structure supported by a pier at each end. Can be made with timber, iron, steel, reinforced concrete, prestressed concrete.  Manchac Swamp Bridge  Tianjin Grand Bridge  Lake pontchartrain Causeway  Donghai Bridge  King Fahd causeway A bridge of connected elements forming triangles, maybe stressed from tension, compression or both. Can be made with timber, iron, steel, reinforced concrete, prestressed concrete.  Ikitsuki Bridge  Astoria-Megler Bridge  Francis Scott Key Bridge 20 of 26

Arch Bridge

A bridge with abutments at each end, shaped like a curved arch. Can be made with masonry, concrete, wrought iron, cast iron, timber, structural steel.  Halfpenny footbridge  York Millennium footbridge

Suspensio n Bridge

Bridge with deck hung below the suspension cables on vertical suspenders. Can be made with steel rope, steel wire strand cables or forged or cast chain links  Verraganonarrows bridge  Golden Gate bridge  Mackinac Bridge

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Cablestayed Bridge

Bridge has 1 or more pylons from which cables support the bridge deck. Can be made with steel rope, steel wire stranded cables or forged or cast chain links  Sutong Bridge  Stonecutters Bridge

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Appendix 7: Types of force

There are 2 types of force, they are compression and tension. Tension force is a force that is exerted equally on both sides of an object, such as a rope or a cable and is transmitted between the ends of the object. (See figure 12)

Compression force is the force generated from squeezing an object. An example of this would be placing an object on a spring, when the spring is compressed and then released, the object is ejected into the air. (See figure 12)

Figure 12 Compression and Tension force

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Appendix 8: Live Load and Dead Load

Bridges must be able to support 2 types of forces, called loads or they will collapse. Dead load (See figure 13) is the weight of bridge itself, such as its columns, beams, nuts, bolts, trusses, cables, etc. Live load (See figure 14) is the weight or force of temporary external elements acting on the bridge, such as people, vehicles, wind, etc. Environmental factors such as temperature, earthquakes and wind also contribute the loads on bridges. Hot and cold temperatures cause parts of the bridge to change.

Figure 14 Dead load

Figure 13 Live load

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Glossary  Span- Distance between 2 bridge supports whether they are columns towers or the wall of a canyon  Force- Any action that tends to maintain or after the position of a structure  Compression- a force which acts to compress or shorten the thing it is acting on  Tension- a force which acts to expand or lengthen the thing it is acting on  Dynamic forces- force that make something accelerate.  Static forces- a constant force applied to a stationary object.  Beam- a rigid, usually horizontal, structural element  Pier-a vertical supporting structure, such as a pillar  Cantilever- a projecting structure supported only at an end, like a shelf bracket or a diving board  Load- weight distribution throughout a structure  Truss- a rigid frame composed of short, straight pieces joined to form a series of triangles or other stable shapes  Stable- ability to resist collapse and deformation or characteristic that is able to carry a realistic load without collapsing or deforming significantly  Deform- to change shape  Buckling- is what happens when the force of compression over comes an objects ability to handle compression.  Snapping- is what happens when tension overcomes an object’s ability to handle tension  Dissipate forces- to spread forces out over a greater area  Transfer forces- to move the forces from an area of weakness to an area of strength, an area designed to handle the forces

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