# ISU Civil Engineering Integrated Curriculum ISU CCEE

# The Golden Section

– its origin and usefulness in engineering

## The Fibonacci Series

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Fibonacci Series 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55,… ( add the last two to get the next ) What is the next number?

Ratio between numbers

Leonardo Fibonacci c1175-1250.

### Fibonacci and plant growth

Plant branches could be modeled to grow such that they can branch into two every month once they are two months old.

This leads to a Fibonacci series for branch counts

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Fibonacci’s rabbits

Rabbits could be modeled to conceive at 1 month of age and have two offspring every month thereafter.

This leads to a Fibonacci series for rabbit counts for each subsequent month

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### Petals on flowers

3 petals (or sepals) : lily, iris Lilies often have 6 petals formed from two sets of 3 4 petals Very few plants show 4 e.g. fuchsia 5 petals: buttercup, wild rose, larkspur, columbine (aquilegia), orchid 8 petals: delphiniums

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Petals on flowers 13 petals: ragwort, corn marigold, cineraria, some daisies 21 petals: aster, black-eyed susan, chicory 34 petals: plantain, pyrethrum 55, 89 petals: michaelmas daisies, Asteraceae family

Ratio of Fibonacci numbers

Divide each number by the number before it, we will find the following series of numbers:

1 / 1 = 1, 2 / 1 = 2, 3 / 2 = 1·5, 5 / 3 = 1·666..., 8 / 5 = 1·6, 13 / 8 = 1·625, 21 / 13 = 1·61538...

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These values converge to a constant value, 1.61803 39887……, the golden section,

Dividing a number by the number behind it: 0·61803 39887..... 1/

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The golden section in geometry

  

The occurrence of the ratio,

The meaning of the ratio

The use of

in engineering

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Constructing the golden section

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Geometric ratios involving

:

### Pentagon

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Geometric ratios involving

:

### Decagon

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Golden Spiral Construction Start with a golden rectangle Construct a square inside Construct squares in the remaining rectangles in a rotational sequence Construct a spiral through the corners of the squares

Golden Spiral Shortcut

http://powerretouche.com/Divine_ proportion_tutorial.htm

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Golden Triangle and Spirals

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1

1/ 

1 1

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Golden proportions in humans

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Echinacea – the Midwest Coneflower

Note the spirals originating from the center. These can be seen moving out both clockwise and anti-clockwise.

These spirals are no mirror images and have different curvatures. These can be shown to be square spirals based on series of golden rectangle constructions.

Cauliflower and Romanesque (or Romanesco) BrocolliXCauliflower

Note the spiral formation in the florets as well as in the total layout

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The spirals are, once again, golden section based

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Pine cone spiral arrangements

The arrangement here can once more be shown to be spirals based on golden section ratios.

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Pine cone spirals

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Fibonacci Rectangles and Shell Spirals

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Construction: Brick patterns

The number of patterns possible in brickwork Increases in a Fibonacci series as the width increases

Phi in Ancient Architecture

A number of lengths can be shown to be related in ratio to each other by Phi

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Golden Ratio in Architecture

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The Dome of St. Paul, London.

Windsor Castle

Golden Ratio in Architecture

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Baghdad City Gate The Great Wall of China

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Modern Architecture: Eden project The Eden Project's new Education Building

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Modern Architecture: California Polytechnic Engineering Plaza

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More examples of golden sections

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Mathematical Relationships for Phi

The Number Phive

5 0.5

x .5 + .5 = 1.61803399 = phi phive to the power of point phive times point phive plus point phive = phi 1.61803399 2 = 2.61803399 = phi +1 1 / 1.61803399 (the reciprocal) = 0.61803399 = phi - 1 .61803399

2 + .61803399 = 1

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Golden Ratio in the Arts

Aztec Ornament

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Golden Ratio in the Arts

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Golden Ratio in the Arts Piet Mondrian’s Rectangles

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Design Applications of Phi

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Design Applications of Phi

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### Phi in Design

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Three-dimensional symmetry: the Platonic solids

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Octahedron 8-sided solid

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## Dodecahedron

This 12-sided regular solid is the 4 th Platonian figure

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Icosahedron 20-sided solid Note the three mutually orthogonal golden rectangles that could be constructed

Three-dimensional near-symmetry

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http://www.mathconsult.ch/showroom/unipoly/list-graph.html