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11.4

Making Structures Strong: The Truss, Arch, and Dome

Key Question: How do trusses, arches, and domes support structures?

Beams are not the only way to make structures stronger. Trusses, arches, and domes can strengthen structures and make them look more interesting.

THE TRUSS

truss a network of beams arranged in triangles

A truss is a network of beams that form triangles. You can see trusses in construction cranes, bridges, and even the International Space Station. Figure 1 shows a truss that will support the roof of a house.

Figure 1 Houses often have trusses to support their roofs.

Trusses use the strength of triangles to make structures strong. The sides of the triangle distribute forces so the structure can support more weight. Trusses can be bent or curved and still be strong. For example, a Ferris wheel uses a circular truss. The truss supports the weight of the wheel and the passengers.

252 Chapter 11 Worksheet 11.4-1

Copyright © 2010 by Nelson Education Ltd.

THE ARCH

arch a curved structure used to span a space while supporting a load

An arch is a curved structure that supports loads. The curve of an arch transfers compression force downward (Figure 2).

load

keystone compression force

Figure 2 The arch transfers compression force downward.

Arches can be used to span spaces. They may be used to support greater loads than beams could support. Arches may also be used to give structures a more appealing design. Many doorways, windows, and bridges use arches. The Romans used arches to build structures over 2000 years ago. Some of these structures are still standing.

dome a shell structure that looks like the top half of a sphere Hint A plane is a surface with only two dimensions. Planes are often used in geometry and architecture.

THE DOME

A dome is a structure that looks like the top half of a sphere. Domes and arches work in similar ways. An arch transfers compression force downward in one plane of application (Figure 3).

plane of application of force

Figure 3 The arch directs the force downward in a single plane.

Copyright © 2010 by Nelson Education Ltd.

Chapter 11 Worksheet 11.4-1 253

TURN

Name:

_________________________________________

Date: ________________________

A dome transfers compression force downward in many planes of application (Figure 4). A dome is like a series of arches connected at a centre point.

Figure 4 The dome directs the force downward in many places at once.

Domes are strong and can enclose a large volume of space. Many churches and stadiums have domes.

CHECK YOUR UNDERSTANDING

1. How do trusses help support structures?

2. Name three structures that use trusses.

3. (a) How are arches and domes similar?

(b) How are they different?

4. Think back to the Key Question. Why might an engineer choose to use an arch instead of a beam?

254 Chapter 11 Worksheet 11.4-1

END

Copyright © 2010 by Nelson Education Ltd.

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