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To proceed with this lesson, the learner should be conversant with the terms 'Tension' and 'Compression'

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By the end of the lesson however, the learner should be able to;

  • define the terms; Girders, Struts and Ties.
  • identify which girders are struts or ties in structures
  • give applications of struts and ties in daily life

A girder is a beam or straight part of a structure.
Types of girders;

  1. Struts
  2. Ties

Struts and Ties

Beams are categorised depending on the impact of the forces acting on a structure.

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  • Strut

A Strut is a girder under compression.

  • Tie

A Tie is a girder under tension

Identifying Struts and Ties

To identify ties and struts we look at the structure before us and imagine it with the girder in question removed. If the end points appear to move adrift (apart) then the girder is tie i.e it is in tension. If the points move towards each other,then the girder is a strut i.e it is compression.


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Portfolio Activity

Remove girders AB and CD observe what happens to the structure



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  1. If AB is removed point B moves away from A hence girder AB is a tie
  2. If CD is removed C moves away from D hence girder CD is a strut

Applications of Struts and Ties

In this section we shall try to link what we have studied in the previous sections to our daily life experiences.

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Tell us a story

Have you ever been near a telecommunication mast?If yes,try to describe to us the nature of the design of the mast.Make use of the diagram below

Telecommunication mast

Telecom site

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Why is it important for engineers to use the knowledge of ties and struts in designing a telecom mast?

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Stand up and walk to the nearest water tank on your school compound.Look carefully at the water tank stand

water tank

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Study the water tank stand below and try to identify which girders are struts and those that are ties

water tank stand


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In your free time find a bicycle and try to identify girders that are struts and the ties

Riding a bycycle

Roof of a house

Roofing a house

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  1. Define and give two examples of each of the following;

a) Strut
b) Tie