available at: lesson 2.1, construct a truss tower construct a truss tower graphic retrieved from, ...

Available at: www.etcurr.com Lesson 2.1, Construct a Truss Tower

Construct a Truss Tower

Graphic retrieved from, http://www.world-city-photos.org/Paris/Eiffel_Tower/Pictures_of_Eiffel_Tower_black_and_white.jpg, on 5/11/2010

Graphic retrieved from, http://www.atlaso.com/images/bridge.jpg, on 4/09/2010


Construct a Truss Tower Performance Objective: Given VEX parts construct a truss tower

a minimum of 12” tall, and that will hold a weight ( > 5 lbs) without collapsing.

Enabling Objectives: define the following terms: force, compression, tension, and

shear identify the forces acting on an object explain how the geometric shape and orientation of an object

can affect the strength of that object or assembly explain the benefits of using certain geometric shapes over other

shapes in the construction of a structure design a truss bridge


Forces acting on a structure

Force is a pressure on a body or structure If the force is great enough it will produce a

change in movement or in shape of the body or structure

Conceptually, a force can be thought of as a push or a pull acting on a structure or system

In constructing a truss tower, the forces acting on members are compression, tension, and shear


Compression

Compression is a force or pressure that attempts to flatten or squeeze an object

Graphic retrieved from, http://library.thinkquest.org/06aug/02102/Forces%20acting%20on%20Bridges.html, on 3/27/2010


Tension

Tension is a force that attempts to pull apart or stretch an object



Shear

Shear force attempts to cause the internal material of an object to slide against itself



Interaction of forces

When weight is applied to the beam below it experiences compression, tension, and shear forces

compression

tensionshear

Graphic retrieved from, http://www.masstec.org/teched/mcasquestions.html, on 3/27/2010


Forces Applied to Structures

Various geometric shapes can be used in the construction of a structure Arcs, Rectangles, Triangles, etc.

Different shapes react to forces in different ways


Arches Arches have a keystone in the

middle, that allow the sides of the arch to lean inward, applying a force to the keystone

Graphic retrieved from, http://upload.wikimedia.org/wikipedia/en/7/79/Gateway_Arch.jpg, on 4/09/2010

The Gateway Arch, St. Louis, MO

Graphic retrieved from, http://www.dkandsons.com/images/arch%20with%20keystone.JPG, on 4/09/2010

keystone


Rectangles

Modular apartment buildings are constructed using rectangles

Graphic retrieved from, http://jouleconsultingengineers.co.uk/bigimages/640x480shed.jpg, on 4/09/2010


Triangles

Truss bridges use triangulation to support the weight or force Truss bridges

Graphic retrieved from, http://www.prhs.k12.ny.us/fac/HerskowitzM/images/cascade_teft_truss_bridge_476_1971_ampprn.jpg, on 4/09/2010

Graphic retrieved from, http://www.atlaso.com/images/bridge.jpg, on 4/09/2010


Combinations

What shapes are used in the Eiffel Tower?

Graphic retrieved from, http://www.thetravelpeach.com/europe-vacations/france/eiffel-tower.jpg, on 4/09/2010


Strength and orientation of geometric shapes

Which shape and orientation gives the most structural strength when a force is applied?

bar angle channel


Shape and Orientation

A beam placed vertically is stronger than if placed horizontally

horizontally the bar has very little strength when force is applied

vertically the bar has good strength when force is applied


Bends add support Notice how this bar

flexes or bends when force is applied

An angled shape has strength in two directions due to the bend in the material, minimizing flex as a force is applied.

bendin bar


Additional bends

Additional bends in the material create even more strength.

the strength is increased in this channel piece

bendin bar


Strength of Geometric Shapes in structures

Which shape gives the most structural strength when a force is applied?


Squares

What happens when you apply a force to the side of a square?

No Force Applied


Squares

The square collapses, because it has no strength from side to side.

Force Applied


Squares

What happens when your structure utilizes only square and rectangular shapes?

No Force Applied


Squares

The structure is not able to hold its shape, and it collapses.

Force Applied


Triangles

What happens when you apply a force to the side of a triangle?

No Force Applied


Triangles

When force is applied to the side, member A is in tension, while member B is in compression, this allows thetriangle to hold itsshape.

Force Applied

AB


Triangles

What happens when you use triangulation in your square structure?

No Force Applied


Triangles When a force is applied, the structure will be

able to hold its shape and not collapse.

Force Applied


Triangle vs. Square

Notice how the triangle did not lose its shape as the square did when force was applied to the side.

Using triangles in construction offers more structural support for an object than simple squares.


How does this apply to a robot?

Here is a robot that won a regional competition

What is good about the structural design? Why?

What could be improved? Why?


Robot design

Identify various shapes and structures used in this design.


Robot design

Here are four possible triangles

Here are various structures

Bar with bendChannel


The end

Now don’t get bent out of shape over building your truss tower!

available at: lesson 2.1, construct a truss tower construct a truss tower graphic retrieved from, ...

Documents

truss tower graphic

truss bridge available

truss towerforces

truss towerconstruct

truss towerarchesarches

truss towertensiontension

keystone available

object graphic