[Design and Technology] SolidWorks Bridge Design Project

Thu Sep 6 11:43:44 EST 2012

Hello,

Below is a brief overview of the bridge design project  curriculum I wanted to share with everybody. The Bridge Design Project is set up to teach students how to design, build and analyse simple trussed wooden bridge. The bridge design project is split into 9 different lessons- below is a brief overview of what the students will learn. The lessons are design to take the student through every step of the design process- students are given basic background knowledge, then taught how to design the structure and finally, once the design is completed, they will build, test and report on their final results.

Visit the Courseware Video Library to see a video clip about SolidWorks Bridge Design Project<http://blogs.solidworks.com/teacher/2010/05/solidworks-bridge-design-project.html>

Bridge Design Project
Using SolidWorks and SolidWorks Simulation to design, test and build structures

What are Trusses?

Trusses are simple structures used as bridges for railroads, auto and foot traffic; capable of carrying large loads across spans. They consist of a road or rail surface, 2 walls and sometimes bracing between the walls.

[cid:image004.png at 01CD8C24.DD819220]
[cid:image008.png at 01CD8C24.DD819220]

Longer Spans

For longer spans, the truss structure can be repeated several times.

[cid:image012.png at 01CD8C24.DD819220]

Truss Types

The Warren truss, shown at right, is one of the simplest and most economical types. It can even be used upside down, in this case with added vertical members.

[cid:image016.png at 01CD8C24.DD819220][cid:image020.png at 01CD8C24.DD819220]

The Pratt(left) and Howe(right) are other common types. We will look at a truss similar to the Pratt truss.

[cid:image022.png at 01CD8C24.DD819220][cid:image024.png at 01CD8C24.DD819220]

Truss Walls

The side walls of the truss are much more than walls that keep the trains or cars from falling off the truss. They are used to absorb and direct the loads placed on the truss such as trains cars.

[cid:image026.png at 01CD8C24.DD819220]

Beams
Trusses are made up of beams that are held together by bolts, welds or rivets. A common example of a beam is a closet rod used to hang clothes.
Beams have the same cross section.

[cid:image028.png at 01CD8C24.DD819220]

External Loads

External Loads are forces that are applied to the beam. A common load on a beam would be weight, such as a train car. Loads are usually applied over an area of the beam.

[cid:image030.png at 01CD8C24.DD819220]

Bending and Deflection

Bending is caused by a load that is applied to a beam. The load causes the beam to bend and move in the direction of the load. The deflection is how far the beam moves from it’s original position. The larger the load, the larger the deflection. The “worst case” deflection occurs when the load is at the centre of the beam.

[cid:image040.png at 01CD8C24.DD819220]

Tension and Compression

While the beam is bending, things are happening within the beam. The top portion of the beam (the face the load is applied) compresses(pushing ends together) while the opposite face sees tension(pulling ends apart).

[cid:image041.png at 01CD8C24.DD819220]

Stress

Stress measures what happens inside the beam when forces are applied. It is defined as force divided by area, common units being Pascals(Pa), Megapascals(Mpa) or pounds per square inch (psi).

Stress can cause the beam to break under high loads. Analysis provides maps that show areas of high and low stress.
[cid:image042.png at 01CD8C24.DD819220]
Yield Strength

·        How much can the beam take before it breaks? We use the Yield Strength as the limit of the beam’s strength based on stress.

·        Actually it measures the point where a beam bends and remains in the bent shape.

·        Both the material and beam section contribute to the strength.
[cid:image043.png at 01CD8C24.DD819220]
Strength of Beams

·        The cross sectional shape influences the strength.

·        Using a stronger material (steel rather than wood) makes the beam stronger.

Cross Section Shape
Stacking two or three beams as shown in the image makes the beam harder to bend and stronger against a load.

[cid:image044.png at 01CD8C24.DD819220]

Section Depth

The deeper the section (left) the stronger the material. Wider sections (right) help a little but not that much.

The reason that deeper beams are stronger is the area moment of inertia. This is calculated using the width (b) and height (h) dimensions of the section.
[cid:image048.png at 01CD8C24.DD819220]
Materials

·        The material used to create the beam has a great impact on its strength. Although there are many varieties of wood and alloys of metals, generally metal is stronger then wood.

·        Note that wood, unlike metals, has a grain that makes its strength different in different directions.

Steel Beams
The deeper beam starts to look like the steel beams used in construction of trusses, and buildings, channels, I-beams and tubes.

[cid:image050.png at 01CD8C24.DD819220]

Cross Bracing

Cross bracing stiffens the structure by preventing rotation at the joints. Using drinking straws pinned at the ends shows the difference that a brace can make.
[cid:image062.png at 01CD8C24.DD819220] [cid:image063.png at 01CD8C24.DD819220]  [cid:image064.png at 01CD8C24.DD819220]

Beam Calculator

The Beam Calculator can be used to get an estimate of the displacement. This can be used to make sure that the analysis is within expectations.

[cid:image065.png at 01CD8C24.DD819220]

Analysis Stages

A Structural Analysis has several stages that are followed in order.

·        In SolidWorks: Model is where the geometry is created.

·        Using Solid Works Simulation Xpress:

o   Pre-Processing is used to add materials, fixtures and loads.

o   Analysis is where the input is “run” through the analyser.

o   Post-Processing allows you to see the results.
[cid:image066.png at 01CD8C24.DD819220]

Design Cycle

The Design Cycle is used to “iterate” changes by returning to the original design to change the model. The changes alter the results of the analysis.

[cid:image097.png at 01CD8C24.DD819220]

Fixtures and External Loads

Fixtures prevent movement of portions of the structure.

External Loads apply forces to the structure.
[cid:image098.png at 01CD8C24.DD819220]
Material

The material selected supplies data to the analysis in the form of numeric properties.

[cid:image099.png at 01CD8C24.DD819220]

Joints

Joints are automatically created at the intersections of the beam centrelines.
[cid:image100.png at 01CD8C24.DD819220]

Fixtures

The fixtures are applied by selecting joints in the model.

[cid:image101.png at 01CD8C24.DD819220] [cid:image102.png at 01CD8C24.DD819220]

Loads

The External Loads are applied by selecting joints in the model.

[cid:image103.png at 01CD8C24.DD819220] [cid:image104.png at 01CD8C24.DD819220]

Mesh and Run

Meshing creates beam elements and nodes that represent the model shape.

[cid:image105.png at 01CD8C24.DD819220] [cid:image106.png at 01CD8C24.DD819220]

Making Design Changes

Using different models, follow the changes in the model and the changes in capacity of the structure.
[cid:image107.png at 01CD8C24.DD819220]

Using an Assembly

Collision Detection

In an assembly, components can be checked for collision, interference or clash.
[cid:image108.png at 01CD8C24.DD819220]

Changing Dimensions

The dimensions that define the shape of the model can also be used to change the size of the model.
[cid:image109.png at 01CD8C24.DD819220]

Making Drawings of the Structure

The drawing includes a view of the model, a cut list and balloons.
[cid:image110.png at 01CD8C24.DD819220]

Building and Testing the Structure

The PDF files Measuring Chart and Construction Guide can be used to make construction easier.

[cid:image112.png at 01CD8C24.DD819220] [cid:image114.png at 01CD8C24.DD819220]

Building the Structure
Distribute 1/8" x 1/8" x 24" balsa sticks, glue and cutters.
Cut, glue and assemble structure per instructions.

[cid:image116.png at 01CD8C24.DD819220]

Testing the Structure

1.Set up sawhorses or tables to represent the 350mm span.

2.Place the bridge and load plate across the sawhorses or tables.

[cid:image118.png at 01CD8C24.DD819220] [cid:image120.png at 01CD8C24.DD819220]

Testing the Structure (test weight)

3.Use a drawstring bag or bucket with wire attached.

4.Pass drawstring or wire through hole in load plate and pin in place.

5.Load bag or bucket with weighted objects until breakage occurs.

[cid:image122.png at 01CD8C24.DD819220] [cid:image124.png at 01CD8C24.DD819220]

[cid:image125.jpg at 01CD8C24.DD819220]Radmila Mrkobrad
Education Manager | ANZ
www.intercad.com.au<http://www.intercad.com.au/>

Phone:

(+612) 9454 4429

Fax:

(+612) 9454 4455

Mobile:

(+61) 402 900 361

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