FORCE, DEFORMATION AND FAILURE PROFESSIONAL ENGLISH IN USE FOR ENGINEERING

 

PROFESSIONAL ENGLISH IN USE FOR ENGINEERING UNIT 31. FORCE, DEFORMATION AND FAILURE

 

A Types of force and deformation Bending comprises two opposite stresses: tension and compression. This is shown in the diagram of a simply supported beam. As a result of the bending force, the lower half of the beam is in tension and the upper half is in compression. These opposite stresses reach their maximum at the upper and lower surfaces of the beam, and progressively decrease to zero at the neutral axis – an imaginary line along the centre of the beam which is free from stress. B Types of failure The ultimate failure of a component or structural member depends on the type of force: ·       in tension – it will fracture ·       in compression – if it is thick, it will crush (squash). If it is slender (long and thin), it will bucle, bending out of shape. EXERCISES 31.1 Complete the word puzzle and find the word going down the page. Look at A and B opposite to help you. 1. bend downwards 2. a twisting force 3. take a force without breaking 31.2 The question below, which was posted on a forum on a construction website, contains a mistake about a technical fact. Can you find the mistake? Look at A opposite to help you. Post 1 I was under the impression that concrete and steel bars were used together in reinforced concrete (RC) because concrete is good at resisting compression and poor at resisting tension, whereas steel is strong in tension. I also thought the steel always went at the bottom of an RC beam because that’s the part that’s in tension, whereas the top of the beam is free from stress. But if that’s the case, when you see reinforcement being fixed in big RC beams, why are there bars both at the bottom and at the top? 31.3 Now complete a structural engineer’s answer to the question in 31.2 using the words in the box. Look at A and B opposite and 31.2 above to help you. bending compressive deflect fracturing neutral tensile compression crushing deflection hog sag tension Replies to post 1: Let me start by clarifying something. When a beam is subjected to (1)__________ stress, the bottom part is generally in tension, as you rightly say. But the top part is not ‘free from stress’, as you suggest. It’s in (2)__________. Only the horizontal centreline

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