1. Engineering Technology Program

2. OUTCOMES After completing the ENGINEERING SPOKE you will be able to:
Describe at least four different types of bridge structures.
Identify the forces of tension, compression, torsion, shear and bending.
Design and build a model engineering structure.
Evaluate the quality of bridge designs by using a stress test.

3. INTRODUCTION
Engineering is the practical application of science and math to find solutions to design problems. There are many types of engineering such as mechanical, civil, electrical and chemical. Civil engineers start with drawings and then build a prototype or model. After testing, they change their model until it works. When they are sure their model works, they construct a full scale project. In this spoke you will face the type of challenge a civil engineer would face. You will design and test a model bridge to its breaking point and then explain why your structure broke.

4. If you enjoy building things, you should look at engineering as a career. Both men and women work as engineers. Civil engineering is involved with building tunnels, roads, dams, and bridges to improve community environments.

5. LOAD
Dead loads – the weight of the structure itself.
Live loads – the weight of any load other than the structure itself, including earthquakes and wind.
LOAD is the amount of weight a structure must support. There are two types, LIVE and DEAD loads. Live loads are separate from the structure, such as cars and people. Dead loads refer to the weight distribution of the structure itself.

6. STRAIN AND STRESS
STRESS is the amount of force applied to a structure. It causes STRAIN which is the reaction or movement of a structure to forces or loads. There are five types of stress which affect the bridge structure you will design and build.

7. DANGER FIVE TYPES OF STRESS
These forces will cause your bridge to fail!
Tension – a pulling or
stretching action
Compression – a pushing or
crushing action
Bending – folding which results
from an applied force
Torsion – a twisting action
Shear – tearing or sliding
from opposing forces
DANGER

8. THRUST LINES
When designing structures, engineers must know about THRUST LINES. These are directions along which loads exert force. Put your elbows on a table with your hands together to form a triangle. Have a friend push down on your hands. You will feel your friend’s thrust on your elbows. Notice that the downward thrust forces your elbows sideways.

9. THRUST LINES
When thrust is not equal a rectangle is a poor shape.
A diagonal brace adds strength by opposing the direction of thrust.
When thrust is equal, a rectangle works well.
This shape is not in balance and will break.
This shape is in balance and will not break.
THRUST LINES carry the LOAD throughout a structure. The structure on the right has two triangles which work to oppose the direction of thrust as shown.

10. TRUST THOSE TRIANGLES
In any structure, the TRIANGLE gives excellent support.
If you apply force to any of the corners of a triangle, the opposite side will work in TENSION to provide support.

11. BEAMS AND TRUSSES BEAMS
Wooden beams are often LAMINATED or glued together, to make them stronger.
Wooden beams are the simplest type of bridge.
The strength of a beam depends upon the material composition, its length, and its depth.
A short beam will hold more than a long beam.
A deep beam will hold more than a shallow beam.

12. BEAMS AND TRUSSES BEAM TRUSSES
A beam with a LOAD like this boulder has COMPRESSION on the top and TENSION on the bottom.
BEAM
TRUSSES
The truss below uses the same amount of material as the beam above, yet the truss is many times stronger.
Trusses have been developed to increase the strength of beams. They are like beams that have been split and reinforced in their center.
TRUSS

13. TRUSS DESIGNS
Below are some truss designs which have stood the test of time.
All bridges use triangles, arches, or a combination of both. Look at the bridge and truss designs above. You will see many triangles. There are many other designs possible. See how creative you can be when you design your own bridge!

14. Arches
The Arch is a very strong structure. Many ancient arch bridges and buildings are still in use today. The arch supports loads by compression along a curved path. An arch can take a load at any place along its curve, while a triangle can only take a load at its top or APEX.

15. DECK ARCH BRIDGE
A deck arch bridge pushes outward against its abutment.
A deck arch bridge has the arch under the roadbed. The arch carries the load to the abutments and supports. The load forces the arch into COMPRESSION. The abutments prevent the arch from moving out and down.

16. BOWSTRING ARCH BRIDGE
In the bowstring arch bridge, the arch is held in TENSION like an archery bow. The arch is prevented from moving outward by the roadbed, which is like a bow string. The roadbed is suspended from the arch by wires. This type of bridge can be mounted on stone piers.

17. SUSPENSION BRIDGES
The deck in a suspension bridge is hung from wires attached to continuous steel cables. The cables are pulled over two towers and anchored beyond the ends of the bridge.
This structure is not suitable to build or test because you do not have steel cables.

18. CANTILEVER BRIDGE
Cantilever bridges have a center section set on top of two arms, or cantilevers, which hang over their piers. The arms are anchored at the ends of the bridge. This type of bridge is used to span great distances. The cantilever is not a suitable model bridge, because it requires anchors at both ends.

19. BRIDGE TERMINOLOGY
NOTE: Bridges are always LONGER
than their span

20. Last Card in Tour
You have completed the engineering technology tour. You can go over the information again and study it some more or if you feel you know the information well enough you can go and get the Engineering Quiz from Mr. Leidl. The quiz is worth 20 points.