In any engineering structure or mechanism the individual components will be subjected to
external forces arising from the service conditions or environment in which the component
works. If the component or member is in equilibrium, the resultant of the external forces will
be zero but, nevertheless, they together place a load on the member which tends to deform
that member and which must be reacted by internal forces which are set up within the
If a cylindrical bar is subjected to a direct pull or push along its axis as shown in Fig. 1.1,
then it is said to be subjected to tension or compression. Typical examples of tension are the
forces present in towing ropes or lifting hoists, whilst compression occurs in the legs of your
chair as you sit on it or in the support pillars of buildings.

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