identify the forces that act on structures Forces Next > In this presentation you will:

Structures are exposed to all physical forces. Technology is used to enable structures to withstand the forces acting on them. Next > Introduction Knowing how forces act on structures can help to ensure the structure is adequate for its intended purpose.

All structures are subject to forces. A bridge or office block can weigh hundreds of tons. The structure has to withstand this weight, as well as carry the loads due to weather and the people using it. Next > Forces

Which of the following causes force to act on a structure? A)The weight of the structure B)The weather C)The people using it D)All of the above Next > Question 1

Which of the following causes force to act on a structure? A)The weight of the structure B)The weather C)The people using it D)All of the above Next > Question 1

As the brick is squashed, it exerts a force back up on the wall equal and opposite to the force acting on it. Imagine a brick in the base of a wall. The brick has to resist a load due to the weight of the bricks above it. Next > Forces on Structures

If the load is too great, the brick will fail and be crushed. In reality, bricks and other masonry can withstand these large forces so they rarely fail in this way. Next > Forces on Structures

Many construction materials, such as stone, steel, and concrete are extremely good at resisting compression forces. A force that acts to squash part of a structure is called compression. Next > Compression

Arches are built from materials that are strong in compression. Arches are used in many structures, including bridges and dams. Some arches have survived for hundreds of years. The arch is an extremely old design for a structure that carries a compression force. The shape of the arch is such that the whole structure is in compression. Next > Arches

A force that acts to stretch part of a structure is called tension. When an elastic band is stretched, a tension force is applied to it. Next > Tension

Materials such as steel and wood can be strong under tension. Stone and concrete are weak under tension. In a suspension bridge, the deck hangs from two towers by many steel cables under tension. Next > Tension

Compression Tension If someone walks across a plank of wood, the plank bends. The top of the plank is under compression and the bottom is under tension. Materials used to carry bending forces must be strong in tension and compression. Steel is a good example of this. When a force acts to bend an object, it is a bending force. However, bending is really a combination of compression and tension forces. Next > Bending

Some bridges have to resist torsion forces created by the wind trying to twist them. A force that causes twisting is called torsion. Fabric structures such as tents have to be resistant to shearing forces. A force that causes tearing of the material is called shearing. Next > Other Forces

The Tacoma Narrows bridge collapsed due to torsion and shearing forces produced by the wind. Bridge Example of Forces in Nature Next >

A load is applied to a column causing it to be squashed slightly. What is this force called? A)Compression B)Tension C)Torsion D)Shearing Next > Question 2

A load is applied to a column causing it to be squashed slightly. What is this force called? A)Compression B)Tension C)Torsion D)Shearing When an object is squashed the force applied is a compressive force. Next > Question 2

A load is applied to a cable causing it to be stretched. What is this force called? A)Compression B)Tension C)Torsion D)Shearing Next > Question 3

A load is applied to a cable causing it to be stretched. What is this force called? A)Compression B)Tension C)Torsion D)Shearing A cable under load that is being stretched will be under the force of tension. Next > Question 3

A load is applied to the deck of a bridge causing it to twist. What is this force called? A)Compression B)Tension C)Torsion D)Shearing Next > Question 4

A load is applied to the deck of a bridge causing it to twist. What is this force called? A)Compression B)Tension C)Torsion D)Shearing A twisting action is caused by torsion. Next > Question 4

A structure in this diagram is subject to bending by a force. Where is the tension force greatest? A)Point A B)Point B C)Point C D)Point D Next > A B C D Question 5

Tension will be greatest on the bottom surface of the beam. Next > A B C D Question 5 A)Point A B)Point B C)Point C D)Point D A structure in this diagram is subject to bending by a force. Where is the tension force greatest?

End In this presentation you have: identified the forces that act on structures Summary