Model Making Workshop — Structure of Tall Buildings and ...

Model Making Workshop — Structure of Tall Buildings and Towers

Science Teaching Kit for Senior Secondary Curriculum

[Teacher notes]

Force and Motion

Organizer Sponsor Research Team

ContentsPreamble

Teaching plan i

DisclaimerCreate Hong Kong of the Government of the Hong Kong Special Administrative Region provides funding support to the project only, and does not otherwise take part in the project. Any opinions, findings, conclusions or recommendations expressed in these materials/events (or by members of the project team) do not reflect the views of the Government of the Hong Kong Special Administrative Region.© 2012 Hong Kong Institute of Architects

Lesson 1 : Model Making Workshop - Structure of Tall Buildings and Towers

1.1 Introduction to Tall Buildings

1.2 Loads and Forces on Buildings

1.2.1 Vertical Forces

1.2.2 Horizontal Forces

1.2.3 Internal Forces

Exercise: Forces on the Structure

1.3 Typical Structural Systems in Tall Buildings

Project Brief on Tower-Making Workshop

Summary, Key words and Further reading

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Structure of Tall Buildings and Towers

Topic 03Model Making Workshop — Structure of Tall Buildings and Towers

Major teaching areasPhysics: Chapter II Force and Motion• Force and motion

Related teaching areasPhysics: Chapter X Investigative Study in Physics

Learning objectives• To understand the forces acting on a stable structure

• To learn the major structural systems for buildings

• To apply new knowledge in a hands-on exercise

Teaching planLesson ContentsLesson 1

Model Making Workshop — Structure of Tall Buildings and Towers

• 1.1

• 1.2

• Exercise

• 1.3

• Project

Introduction to tall buildings

Explanation of the forces that act on buildings

Understanding of internal and shear forces, structural elements, and the relationship between action and reaction

Examples of typical structural systems for high-rise buildings

Brief and assessment methods for tower-making workshop

Interdisciplinary teaching areas Design and Applied Technology• Strand 1 Design and Innovation • Strand 2 Technological Principles

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Structure of Tall Buildings and Towers

Lesson 1 Model Making Workshop — Structure of Tall Buildings and Towers

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Structure of Tall Buildings and Towers

Lesson 1Model Making Workshop — Structure of Tall Buildings and Towers1.1 Introduction to Tall BuildingsTall buildings are symbolic elements within any city, carrying significant political, social, cultural and even religious meanings. Today cities compete to produce the tallest building in the world as a way of showcasing financial and economic power. Understanding the structures of these buildings, and how they support themselves as well as the loads imposed on them by the environment, is a fascinating way to see the real-life applications of physics.

p The Leaning Tower of Pisa (55.86 m) was built in 1372, using marble stone in a Romanesque style. Its current leaning appearance is due to sub-soil settlement.

q The Eiffel Tower is a 320-m-high steel structure that was completed in 1889 as the entrance arch for that year’s World’s Fair.

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t The 90-m-high Royal Liver Building in Liverpool was one of the first concrete buildings in the world. It was completed in 1911 after a Neoclassical design by Walter A. Thomas. © Chowells - Wikipedia User

In the early 20th century, cities became bigger and denser. Urban populations were growing but land supply was limited. High-rise buildings became an essential solution to the problem. New technologies and building materials, such as industrial reinforced concrete, steel and elevators, made high-rise structures feasible and drove innovation.

p The modernist Wainwright Building in St. Louis was completed in 1891 by architects Dankmar Adler & Louis Sullivan. Its 10 storeys are supported by an early steel framing system.

p Equitable Life Assurance Building in New York was completed in 1890. It was the first building equipped with elevators. It was destroyed by the fire in 1912. The 36-storey Equitable Building in New York was completed in 1915. Its architect, Ernest R. Graham, used a Neoclassical style despite the building’s modernity. It triggered the implementation of height limits and setbacks for tall buildings to allow sunlight to reach street level.

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1.2 Loads and Forces on Buildings

The statics of a building deal with its structural stability. When an object is in equilibrium, the sum of all forces equals zero. Various forces from the environment, the weight of the building elements, furniture and equipment installations, users and other sources act on the building structure. There are three types of loads generally:

Dead LoadDead loads are the loads of the structure and fixed components. It is a permanent force that is relatively constant for a extended period of time. The force is gravitational.

Live LoadLive load is a changing force generated by mobile objects inside the building, such as people within the building or stock in a warehouse. The force is gravitational.

Environmental LoadEnvironmental loads are forces acting on the building from its environment and may include wind, rain, earthquakes and temperature changes. The forces created can be either horizontal or vertical, positive or negative.

1.2.1 Vertical Forces

Dead loads and live loads contribute to the vertical forces on the structure of buildings. Vertical loads are transferred from the floors to the columns and walls, and eventually to the soil or bedrock. At times, environmental loads also act vertically.

1.2.2 Horizontal Forces

Environmental loads contribute most of the horizontal forces acting on the structure of a building, with loads from wind being the most common. Architects refer to these horizontal forces as shear force. Adding cross bracing or shear walls can improve structural resistance to shear forces.

1.2.3 Internal Forces

The internal strength of the entire structure must be equal to or larger than the total forces applied on the building in order to stay in equilibrium. The ability to withstand all forces depends on the structural component’s dimensions and the solidity and elasticity of the material. Internal forces include compressive force, tensile force and torque.

Compressive and Tensile ForcesAccording to Newton’s Third Law, forces act in pairs. In structural terms, tensile force pulls a structural element apart while compressive force compresses it.

TorqueIf opposing forces are applied at different points, a structural element may become twisted. This is called torque in the building industry.

Dead loads e.g. Weight of the building

Environmental Loads e.g. Wind

Live loads e.g. Weight of people at the building

p Live loads, dead loads and environmental loads are the three major types of forces on the Bank of China Tower. The loads are transferred to the ground via columns and pilings.

p Internal forces in a structural element

Compressive force

Tensile force

Torque

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Possible perspectivesThe horizontal structural block is supported at two points. When a force is applied on the member between the two points, the upper surface of the member is in compression where the lower surface is in tension. On the other hand, vertical structural blocks are in compression mainly. The loads are then transferred to the earth.

This shows the difference between the load-supporting behaviours of vertical members (e.g. columns and wall) and horizontal members (e.g. floor and ceiling). When the internal strength of a structural member cannot withstand the loads imposed on it, it will buckle or even break at the most stressed point.

Possible perspectivesCross bracing can be added at the joints of the horizontal and vertical block.

Cross bracing is usually constructed of diagonal supports between structural members. It can resist both compression and tension forces, depending on the direction of the shear forces acting on the building.

2 Can you identify the internal forces acting on each piece of the structure? What paths do they take?

3 How would you modify the below structure to resist shear force?

Shear Force

1 Illustrate the action and reaction pairs, and distinguish dead loads and live loads acting on the following structure. Assume the weight of the mass is FA and the weight of each building block is FB , and the structure is in equilibrium.

Possible perspectivesThe weight of mass ( FA ) is the live load and the total weight of the structural blocks ( 3FB ) is the dead load.

1. Action by the mass on the block = FAReaction by the block on the mass = FA

2. Action by the horizontal block on each vertical block = 0.5 (FA + FB)Reaction by each vertical block on the horizontal block = 0.5 (FA + FB)

3. Action by each vertical block on the ground = 0.5 (FA + FB) + FBReaction by the ground on each vertical block = 0.5 (FA + FB) + FB

Loads

CompressionTension

Stress points

[Exercise]Forces on the Structure

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SteelSteel is a common construction material for tall buildings because it has good performance in withstanding compressive and tensile forces, as opposed to concrete’s low tensile strength in compression. Steel bars can be used to reinforce concrete to add extra structural performance. However, steel is relatively weak in fire-resistance. An extra layer of fire-resisting coating is often put onto the steel surface.

The Bank of China Tower is a steel trussed-tube structure. The whole building acts as a single tubular truss, with the diagonals wrapping the building to transfer loads.

Core and Outrigger structure The International Commerce Centre is built using a ‘Core and Outrigger’ concept. The core at the centre of the building bears most of the vertical load, while columns at the perimeter carry less weight and are thus smaller in dimension. Loads are transferred to the core through steel outriggers that balance the lateral forces on the whole building.

1.3 Typical Structural Systems in Tall Buildings

p Plan of International Commerce Centre

p Bank of China Tower

Core

Columns

Outrigger

p Outrigger connecting the core and the columns s

Outriggers help balancing lateral forces.

Weight is centralised to the core.

Columns at the perimeter carry less weight.

p Installation of outriggers at the International Commerce Centre © Raymond Wong

Teaching TipsField trips to Central can be organized to facilitate the learning of high-rise structure, can refer to Science Topic 02: ‘VISIT: Central - Structure of Skyscrapers ’.

Teaching TipsMore information on the construction process, can refer to Design and Applied Technology Topic 02: ‘Construction Process - Victoria Park Swimming Pool Complex ’.

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TrussTrusses are a very common structural element in architecture. Steel members are joined together into triangular shapes, which are very strong and able to resist external forces. When joined together, these triangles can form large truss systems that can span long distances.

External force

External force

External force

External force

result

resultCompression

Tension

Compres

sion

q Common types of truss © Structural Building Components Association

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Project Model Making Workshop — Tower

Divide the class into groups of four to five students. Each group is required to build a tower that should be: • structurally stable and aesthetically pleasing• tall• lightweight• resistant to horizontal forces• able to support a heavy loadSubmit a laboratory group report after the workshop.

Tools needed• Sketching papers and pencil• Scissors, cutters, tape, glue• Different weights (10 g/ 50 g/ 100 g/ 500 g/ 1 kg)• Weight scale• Measuring tape• Electric fans

Suggested materials• Cardboard• Bamboo sticks• Recycled cans• Recycled plastic bottles• Fishing line

Assessment criterias:

Tests Descriptions Score

Structural stability The tower should be free-standing without external supports. 20

Aesthetics The teacher will judge the beauty of the tower and will give a score. 0 - 10

Height Measure the height of the tower from the ground to the highest point. The tallest tower gets the highest score.

10 - 20

Weight-height ratio Weigh the tower and find out the weight-height ratio. The tower with the smallest ratio will get the highest score.

R =

10 - 20

Resistance to wind Blow the tower from the side with an electric fan. The tower that does not fall will get the highest score.

10

Load supporting Test the maximum weight that the tower can support. The weight needs to be placed above the ground. Students should be able to explain how load is transferred to the ground.

10 -20

Total score 100

Teacher tips: To make the workshop more informative, teachers are recommended to summarize critical factors for a light-weight and stable tower. Evaluations are useful to point out the reasons for structural failure.

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ProjectModel Making Workshop — Tower

p Using rope to join the components

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1. Foster, Jack Stroud, Raymond Harington, and Roger Greeno. Structure and Fabric. 7th ed. Harlow: Pearson Prentice Hall, 2007.

2. Brotrueck, Tanja, Basic: Roof construction. Basel: Birhaeuser, 2007.

1. Although humans have long attempted to build tall structures, skyscrapers began to appear in our cities in the late 19th century as a result of technological breakthroughs in building materials and methods, including reinforced concrete, steel and elevators.

2. Buildings bear three types of loads: dead loads, live loads and environmental loads.3. All loads are resolved into vertical and horizontal forces on the structure.4. Typical structural systems used in tall buildings include core and outrigger structures, steel frames

and trusses.

High-rise buildingsSkyscraperTowerStructureForceEquilibrium

Key words

Summary

Further reading

Organizer Sponsor Research Team

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Structure of Tall Buildings and Towers