Assignment 3 6504

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Engineering Education Studies 1

DATESTAMPHERE

Insert

this

way

Donald

E D U C 6 5 0 4

HEATHER

Intro to University

1700

A B C D 1 2 3 4

http://www.newcastle.edu.au/policylibrary/000608.html

D. HEATHER - C2008809

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CONTENTS PAGE

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RESEARCH

Current pylon technology-P3

Types of trusses-P3

Types of pylons-P5

Forces on pylons-P6

Why use a truss-P6

Joining methods-P7

Test methods-P7

Design and development-P8

Results and conclusion-P17

Bibliograpthy-P18


RESEARCH

Current Pylon Technology

Pylon is the Greek term for monumental gateway of an Egyptian temple. A pylon is usually

tapered from bottom to top to support something like power lines. A transmission tower is a tall

structure used to support power lines usually made out of steel lattice. The four main functions of

towers are suspension, terminal, tension and transposition towers. The towers have prototypes

tested at tower-testing stations. The towers can be assembled on the ground and then erected using

push pull cables. Assembled vertically helicopters can be utilised as aerial cranes.

Pylons can also be used to support bridges, and can reach heights that rival some of the tallest

buildings. They are used in suspension bridges and cable staged bridges. The use of the pylon, as

a simple tower structure, has also been used to build rail road bridges.

TYPES OF TRUSSES

Warren Truss

The warren truss was patented by James Warren in 1948. It is one of the most popular designs

which use equilateral triangles to spread out the load on the bridge. The forces on the members

are minimalised due to the triangles being in compression and tension. As a load moves over the

bridge sometimes the forces switch in the members from compression to tension. This happens

especially to the members near the centre of the bridge.

.

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Pratt Truss

Pratt trusses have the vertical compression members and diagonal tension members. The end

members are the only ones that do not slope towards the centre of the truss configuration. The

diagonal members are subjected to tension forces only so they can be thinner allowing for a more

economical design.

Howe Truss

The Howe Truss is the opposite of the Pratt Truss with the diagonal members slanting towards the

closest bridge end. These members are subjected to compressive forces which necessitate large

steel members. This makes this type of truss uneconomical for steel construction.

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TYPES OF PYLONS

Pylons are tower-like structures that support antennas or electrical cables, or used as the vertical

support for a bridge or a tower.

Lattice Tower

These towers are made from steel and are a very practical type of pylon. They can be climbed by

hand to be serviced or modified and are easy to maintain. Different types of pylons do not allow

for climbing so the need to service the pylon must be done by crane or by lifts.

Monopole.

A monopole pylon is a single tall pole with an antenna on the top.

Wired Pylons

If a single pole pylon becomes extremely tall then supporting cables are connected in each

direction around the pole to stabilise it. Wired pylons are also called guyed towers.

Electric Pylon

Electric pylons are designed on the lattice tower model, with two or three sets of vertical arms to

hold the wires.

Bridge Pylons

Suspension bridges use the pylons as tall supports that hold up the cables of the bridge. They are

constructed deep into the ground, with large concrete foundations. Pylons may be positioned at

either side of the bridge providing a formal entrance.

Egyptian Pylons

Pylons in Egypt were large structures that marked the entrance to temples. They were strong

enough and high enough to provide a defensive barrier.

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PYLONS IN CIVIL STRUCTURES

Pylons are utilised on civil structures to support a variety of needs.

Bridges: used to support the base of the bridge or be utilised to hold cables to support the bridge.

Power Lines: used to support power lines in different configurations and quantities of lines.

Aeronautics: used to support structures on aircraft such as navigation equipment.

Telecommunication: used for many types of electronic communication including radio, EMS

services, cellular and global positioning satellite technology.

FORCES ON PYLONS

Axial force – is the tension or compression force acting on a member. The axial force acts

through the centroid of the member and is called concentric loading. If the force does not act

through the centroid it is called eccentric loading. Eccentric loading produces a moment in the

beam because the load is a distance away from the centroid.

Radial Forces-This is a force that is exerted perpendicular to the centreline, or axis of an object.

WHY USE A TRUSS

A truss is a frame made up of a number of members, generally arranged in triangular units,

through which forces are transmitted to the joints called nodes. (Rochford, 2011)

Truss members need to be long and slender, the moments transmitted to these joints are negligible

and the nodes can be considered as hinges. Trusses are stronger than other structures because

nearly every material is much stronger in compression and tension than shear, torsion or bending.

Truss design pylons can be constructed on the ground and then lifted into position which is cost

effective.

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JOINING METHODS OF TRUSSES

Gussit plate-A gusset plate is a steel sheet that is used to connect beams and girders to a column or

to connect truss members to the top or bottom plate. They can be fastened to a permanent member

by rivets, bolts or welding. They serve to join the members together and strengthen the joint in the

process.

Gang nails-Roof trusses can have gang nails in the nodes. These are made out of galvanised steel

to resist rusting and are hammered into members at the join.

TEST METHOD

I used a piece of steel clamped to the table with a long range dial indicator. The dial had a

magnetic base to secure it in position. I placed a piece of wood on the moveable jaw of the vice to

give me some height to allow indicators to rest up against. I then fitted the pylon, set the dial on

both zeros. The dial was set on zero and the clock dial was also on zero. As the vice was wound

in I could measure how far and feel the pressure needed to overcome the initial resistance, the

flexibility of the structure and finally failure length in mm. When I was winding I could feel the

resistance in the pylon, when the pylon members began to bent I could feel the pressure needed on

the vice handle decrease until the structure finally fractured. I had time to stop winding the vice

and read the measurement on the dial indicator at these three points in the exercise.

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Vice with dial set up to take reading.

DESIGN AND DEVELOPMENT

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DESIGN 1

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I tried to construct a simple design

to complete the task. Difficult to

assemble with little room left in the

top of the caps. The result was a

very sturdy structure. Materials

were 10 Popsicle sticks, 2 caps and

5 pins. I am concerned about the

pins splitting the sticks which

would weaken the structure.

When the vice was tightened it

became hard to compress the pylon.

With extra force the members

cracked below the pins. There was

little flexibility in this pylon as it

was sturdy up until fracture.


DESIGN 2

When the vice was tightened it was hard to compress, then the structure began to fail with less

pressure needed. This was compressing the structure resulting in bowing of vertical members in

an outwards direction. Continued winding of the vice resulted in fracture in middle of exposed

vertical member.

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The 3 sets of sticks were easy to assemble. The result was a sturdy

structure which I was hoping the axial force could be centred

between the 3 vertical pairs. Materials were 10 Popsicle sticks and

2 caps.


DESIGN 3

Attempted to construct a pylon design which utilised four vertical members. This made it difficult

to add supporting members between verticals because of a lack of material. This was difficult to

assemble as the four joint members had to be exactly a square to fit into cap. Materials used were

10 Popsicle sticks and glue.

When the vice was tightened it was hard to compress, then the structure began to fail with less

pressure needed. The structure continued to bow until failure in the middle of vertical member.

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RESULTS AND CONCLUSIONS

DESIGN 1 DESIGN 2 DESIGN 2

INITIAL RESISTANCE 3mm 2mm 2mm

FLEXABILITY 3mm-5mm 2mm-11mm 2mm-8mm

COMPRESION FRACTURE 5mm 11mm 8mm

These results allow me to work out the percentage distance each design allowed before fracture.

Strain=compression length x 100

original length 1

Design 1

5/120 x 100/1=4.16%

Design 2

11/120 x 100/1= 9.16%

Design 3

8/120 x 100/1=6.66%

The construction of the 3 pylons in different configurations led me to believe Design 1 would be

the best. Design 2 and 3 were similar and I believed they would be less stable. The results were

design 1 was the hardest to wind in, resisted more force, however, it had no flexibility and

fractured quickly with no allowance to absorb the axial force. Designs 2 & 3 resisted at first then

allowed the vice to be wound in with less effort. This was absorbed by the members in

compression which resulted in the members bending until failure. The design 3 four member

pylon bowed in and out where the 3 member pylon all members bowed out from the centre which

allowed more travel on the axial plane.

In conclusion I can see a use for all types for different reasons. Design 1 could resist a greater

force and Design 2 & 3 could absorb forces that could be calculated so the pylon would be elastic

and return to original condition.

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BIBLIOGRAPTHY

Rochford. J. (2011). Stage 6 Engineering Studies. [ed 2011]. Tumbi Umbi; KJS Publications.

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Assignment 3 6504

Education

Transcript of Assignment 3 6504