Guidelines - Design Institute of Australia No 9.pdf5.1.4 Innovation & Aesthetics Prize The...

The CIT Bridge Challenge

Guidelines The 2016 Bridge Challenge

1. The Challenge Welcome to the Canberra Institute of Technology Construction and Engineering Bridge Challenge. Proudly supported by the CIT, Training Fund Authority (TFA), Project Coordination (Australia) Pty Ltd, Construction Industry Training Council. This year, CIT is looking at potential bridge/truss designs to support static loads.

It is open to teams of students currently enrolled in years 9 and 10 at high school. The competition is also open to those enrolled in a certificate I or certificate II from a relevant area (building, construction, etc.).

As a team, your goal is to design and construct a bridge to support the test load. Strength-to-weight and outright strength will be determined.

The materials used for the bridge construction will be supplied by CIT. There is to be no additional materials used for the bridge.

Note that your bridge will tested to destruction; therefore your bridge will be broken during testing.

We are looking for bridge designs that are able to showcase construction, efficiency, strength and creativity. There is not a standard bridge design so there are many designs to choose from for your bridge, refer to appendix for examples of styles.

Note that terms in blue and italicised text have a definition in the glossary (Appendix 2).

Canberra Institute of Technology | GPO Box 826, Canberra, 2601 Australia | T +(61) 02 6207 3188 | cit.edu.au CIT Bruce | CIT Fyshwick | CIT Gungahlin | CIT Tuggeranong | CIT Woden | ABN 432 737 96 990 | CRICOS No. 00001K

The 2016 CIT Bridge Challenge

2. Specifications 2.1 Before you start

Plan and sketch your bridge on paper before cutting your materials to ensure you have enough material to achieve your design (see Appendix 4). You will be provided with 18 linear metres of timber (6mmx12mm).

Think about the most efficient use of materials supplied. Remember that you can only use the materials supplied. One of the aims is to support the maximum amount of weight with the lightest bridge weight.

Think about where the forces are going to be applied (refer to Appendix 3), and how much this might affect your design and construction method (refer to Appendix 5).

Be as accurate as possible keeping symmetry in your bridge design. Ensure your bridge design distributes load evenly to prevent twisting of the bridge whilst maintaining stability.

It is important to plan and draw/sketch your bridge before you begin building it. This will ensure you don’t run out of materials.

The bridge will be tested on a purpose built rig (Appendix 1).

2.2 Bridge Specifications Your bridge must be built to fit the testing rig within the following constraints:

Bridge width 150mm (max.)

Bridge height above roadway no limit

Bridge depth below roadway 250mm (max.)

Bridge length 1000mm (max.)

Roadway width 100mm (min.)

Ensure that your bridge fits the testing rig otherwise it will not be tested on competition day.

Canberra Institute of Technology | GPO Box 826, Canberra, 2601 Australia | T +(61) 02 6207 3188 | cit.edu.au of 24 CIT Bruce | CIT Fyshwick | CIT Gungahlin | CIT Tuggeranong | CIT Woden | ABN 432 737 96 990 | CRICOS No. 00001K


2.2.1 Span

Your bridge must be no longer than 1000mm and bridge across the 900mm clear span between both supports. Your bridge will rest on the abutment support pad.

2.2.2 End supports Your bridge foot pads can be up to 50mm in length and 150mm in width.

Your bridge cannot rely on the testing support frame for lateral support. Side thrust onto the vertical faces of the frame is not permitted.

The bridge abutment pad has dimensions of 50mm x 150mm.

Your bridge must be self-supporting.

2.2.3 Width Your bridge must be no wider than 150mm at any point along its length.

2.2.4 Depth The maximum allowable depth of the bridge below the roadway is 250mm.

Canberra Institute of Technology | GPO Box 826, Canberra, 2601 Australia | T +(61) 02 6207 3188 | cit.edu.au CIT Bruce | CIT Fyshwick | CIT Gungahlin | CIT Tuggeranong | CIT Woden | ABN 432 737 96 990 | CRICOS No. 00001K of 24


2.2.5 Load hanger clearance The load beam requires two (2) gaps in the roadway that will accommodate the two (2) load hangers. The minimum hole size required is 12mm in diameter. The distribution beam will be centrally placed both laterally and longitudinally. The hanger rods are 300mm apart.

The load will be distributed through a 500mm long load beam.

The load bars and hanger assembly must be able to fit within the central region of the bridge span.



2.2.6 Roadway and vehicle Your bridge will be required to support a roadway (5mm x 100mm x 1000mm) and to allow a vehicle to pass through unimpeded. The vehicle dimensions are 90mm wide x 80mm high.



2.3 Design guide The bridge will flex under the weight during testing so make sure there is consistency in flexibility across all members so all members flex cohesively.

Take into account the design and remember if you do not triangulate the design you will introduce raking and premature failure.

• Designs other than that of a triangle (for example a square) are unstable and can be easily pushed out of shape (raking) – triangles on the other hand are more rigid and less likely to be pushed or raked out of shape.

• The taller the triangle and shorter the base of the triangle the stronger it is. This also means that more material will be used the taller it becomes.

• The more triangles used the stronger the construction will be if chosen appropriately.

Tension on butt joints will cause a failure at the joint – minimise the tension on these joints where possible.

Minimise compression force of long members to reduce buckling.

2.4 Pre-testing Any practice builds and/or pre-testing are at the expense of the design team. You will only be given one (1) bridge pack.



3. Kit and Equipment

3.1 Kit contents Your bridge building kit will contain the following items. Only materials supplied in the kit may be used in the construction of your bridge:

• 18 linear metres timber (6mmx12mm) - 15 x 1.2m lengths • 12mm panel pins • 1 road base template (card) • 1 tube PVA glue

3.2 Extra equipment • Safety goggles and gloves • Pencil and paper for planning and drawing bridge before it is

constructed • A tape measure and a ruler • A saw for cutting timber • Hammer for panel pins • Pegs, clips or masking tape for temporarily holding timber together

whilst glue is drying • Sandpaper for finishing edges for a better build quality

3.3 Decorating your bridge To allow the joins to be inspected, no decoration of bridge, such as paint or vanish, is allowed.

3.4 Safety precautions • All construction work must be supervised by a teacher at all times. • Wear safety goggles and gloves while creating your bridge • Ensure workplace is well ventilated at all times especially while gluing. • When working with sharp tools, cut on a clean, flat and stable surface. • Read and carefully observe all glue instructions. • Protect the surfaces you will be working on from glue and accidental

cutting.

Only one (1) kit will be supplied to each team



4. Judging and Testing

4.1 Judging On judging day, your team(s) will be called before a panel of judges consisting of CIT teachers from construction, engineering and design who will engage in discussions with the team about approaches and techniques used in your bridge design. The judges will assess your bridges in the following categories:

Workmanship (10 points)

• Joints with good contact between members • Robust feel • Compliance with dimension requirements

Innovation (10 points)

• Structural form • Creative techniques at joints • Use of building techniques

Aesthetics (10 points)

• Visual appeal • Proportion • Neat finish

Functionality (10 points)

• Ability to support a roadway • Ability to pass traffic across the bridge

The design score is the sum of the four categories. A maximum of 40 points is available.

Design score = Workmanship + Innovation + Aesthetics + Functionality



4.2 Load testing The load testing will be done by the CIT staff.

On the day, you will be required to wear safety goggles.

Your bridge will be tested in the bridge testing zone, as indicated on testing day. Bridges are tested by progressively increasing the load on the hanger attached to the bridge.

Your bridge is considered to have failed if any member or joint breaks or the bridge fails to carry any additional load. The load will be recorded in the judging spreadsheet. Using this data an efficiency (strength-to-weight) score will be determined by the ratio between the mass supported by the bridge and the mass of the bridge itself.

Efficiency score= Load mass (kg)

Bridge mass (kg)



5. Final scoring 5.1 Award Categories Based on your team’s bridge design, you can take home one of the following award titles. These will be awarded on the day of the event based on your team’s performance.

5.1.1 All-Rounder Award The All- Rounder award is won by teams with the highest combined score (judges’ score and 25% of efficiency score).

5.1.2 Efficiency (strength-to-weight) Award The efficiency award is given to the team whose bridge design has the best strength-to-weight ratio, that is, the maximum amount of mass it can carry/support without collapsing compared to the mass of the structure. This bridge must be able to carry/support a minimum 40kg.

5.1.3 Strength Award The strength award is offered to teams whose bridge carries the maximum load recorded on the day.

5.1.4 Innovation & Aesthetics Prize The innovation and aesthetics prize will be assigned by the judging panel on the day of the competition. This is a combination of creativity and innovation – how do you stand out from the crowd. This bridge must be able to carry/support 40kg.

All rounder score =Total design score + Efficiency score

4∗

* This value may be adjusted on the day to maintain a balance between strength efficiency and the total design score.

Score = Innovation + Aesthetics



6. Appendix 1 – Test rig



Detail of bridge support



Bridge test rig template.

1. Print/copy and cut out this template twice (it is drawn to scale when printed on A4 paper).

2. On a flat and horizontal surface, layout the cut-outs so the side edges of the shaded areas are aligned and the far edges are 1000mm apart.

3. Use the template to ensure your bridge will fit the test rig. The bridge ends must fit within the shaded area.

Top view of bridge test rig pad

Scale: 1 : 1 (when printed at A4

size)

Bridge end must fit within the shaded area.

100 mm

1000 mm between

150

mm



7. Appendix 2 - Glossary Term Definition

Beam A member that supports loads.

Bracing A structural member used to stabilise or stiffen a framework.

Buckle The bending, warping, or collapse under force. It occurs when compression overcomes an object’s ability to endure that force.

Capacity The maximum load the bridge can successfully carry.

Compression Compression is a force which squeezes objects together.

Cross section The plane made by cutting across something at 90° to its length.

Deflection The movement of a structure or member as a result of stress.

Force Flow Path The path an external force takes to reach the supports through your structure.

Joints A connection point.

Lateral support A type of support to help prevent sideways movement.

Member An element that forms part of a truss or bridge, such as a beam, bracing or a support.

Raking A force which will cause twisting or torsion in the structure.

Span The clear distance between the support points.

Tension Tension is the force that stretches or pulls objects apart.



8. Appendix 3 - Forces When constructing your bridge, pay attention to how the load is being distributed amongst the members. Is your bridge symmetrical? Is the force being distributed evenly?

The two major forces you will be working with are compression and tension.

8.1 Compressive forces Compressive forces will crush or buckle the truss members whereas the tensile forces tend to stretch the truss members. Member failure will be through buckling or material collapse.

Take a ruler and push it inwards from both ends, this is applying a compressive force. Because the ruler’s section is thin in one direction it will buckle (bend) under the force in that direction.

If a compressive force is applied to a shorter and thicker member (squat member) the material will not buckle. The material will fail through crushing or fracture.

Compressive force Compressive force

Compressive force

Compressive force



8.2 Tensile forces Tensile forces will stretch the truss members whereas the tensile forces tend to stretch the truss members.

Member failure will often be through failure of the connection (especially if pinned or bolted).

8.3 Bending forces These forces occur in a truss frame when the load is between the connections and/or when the connection is fixed (i.e. welded or glued). When a truss member has a bending load, one side will be under compression while the other side is under tension.

Tensile force Tensile force Tensile force



8.4 Torsional forces These forces will twist the members. If the bridge is symmetric and evenly loaded torsional failure will be unlikely.



9. Appendix 4– Planning & sketching

9.1 Why Sketch? Sketching is important before designing a structure. It allows you to visualise what your bridge will look like, before you start the building process. Sketching gives you a better idea of how much material you might be using, allowing you to better delegate building tasks within the team and plan your bridge.

Sketching can be utilised throughout your building process to develop your bridge, make changes to it, or clarify what you are building.

Below are some sketches of initial bridge planning.

9.2 3D Sketching Sketching can also be 3-dimensional. Sketching in 3D can often be the next phase of planning a structure. Using 3D digital modelling software allows you to view your model in #D, as well as make 1:1 plans and templates. Below are several 3D modelling software that are free to students:

TinkerCAD – browser based 3D modelling program

https://www.tinkercad.com/

Sketchup Make – 3D modelling program

https://www.sketchup.com/products/sketchup-make

3DTin – browser based 3D modelling program

http://www.3dtin.com/

Lego Digital Designer - 3D modelling program by Lego

http://ldd.lego.com/en-us/

Autodesk 123D – 3D modelling app

http://www.123dapp.com/design

FreeCAD – open source 3D parametric modeller

http://www.freecadweb.org/


https://www.tinkercad.com/

https://www.sketchup.com/products/sketchup-make

http://www.3dtin.com/

http://ldd.lego.com/en-us/

http://www.123dapp.com/design

http://www.freecadweb.org/


9.3 Bridge Modelling Each year the American Society of Civil Engineers (ASCE) sponsors a competition on bridge design using a bridge design software program. The software is available for download and can be used by anyone. Why not download it and try your hand at bridge building. This software may help with your design decisions.

Bridge Designer 2016

https://bridgecontest.org/resources/download/





10. Appendix 5 - Construction Tips

10.1 Joints Pay close attention to how you line up your joints. The more material overlayed the more critical this section of your bridge will be.

Ensure you construct your connections adequately. This is critical to the bridge achieving its capacity Bridges most often fail here due to lack of pins, glue or inadequate contact between surfaces.

The two types of joints you will consider for your bridge will be fixed or flexible.

Fixed joints will be glued or pinned and glued. These joints allow for no rotation of the members around the joint and introduce torsional loads onto the members.

Flexible joints will be only pinned. These joints allow rotation around the pin, therefore the loading on the members is axial and no torsional loads are induced.

The graphics below show the different deflections from the two types of joint.

Figure 1 Pinned Joint Figure 2 Pinned and Glued Joint

10.2 Members Think about the forces in each member. Will it be in tension or compression? In other words, are the members being stretched or crushed? Picture how the bridge will deflect/bend. Where the members bend the most, these require the most strengthening.



Longer members in compression tend to buckle and therefore fail more easily than a shorter member of the same cross-section. Consider reducing unsupported lengths by connecting them to cross members, or providing bracing.

A member that is in tension will most likely fail at its joints. Consider providing extra support at these joints.

Refer to appendix 6 for examples of truss design.



11. Appendix 6 – Examples of truss types

Through Howe Truss

Through Pratt Truss

Through Warren Truss



Deck Howe Truss

Deck Pratt Truss

Deck Warren Truss


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