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Stress and Strain TUTORIAL 6 to answer just click on the button or image related to the answer.

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Presentation on theme: "Stress and Strain TUTORIAL 6 to answer just click on the button or image related to the answer."— Presentation transcript:

1 Stress and Strain TUTORIAL 6 to answer just click on the button or image related to the answer

2 what is stress? Question 1a internal force intensity a force per unit area c internal force b a or c d

3 what are the units of stress? Question 1b kN, MN a kPa, MPa c kN / m, MN /m b kNm 2, MNm 2 d

4 what is strain? Question 2a a bad back ache a change in size or shape c response to stress b b and d e change in size or shape relative to original state d b and c f

5 what are the units of strain? Question 2b mm, cm, m a no units c kN / m b kNm d

6 what is the strain in the cable? Question 3a 4 mm a 8 x b 50 kN 5 m 20 mm a 20mm ø high-strength steel cable 5 m long has a weight of 50 kN at its end. Neglecting the self-weight of the cable and Given that the cable lengthens by 4mm 8 x mm c

7 what is the stress in the cable? Question 3b kPa a MPa b 50 kN 5 m 20 mm a 20mm ø high-strength steel cable 5 m long has a weight of 50 kN at its end. Neglecting the self-weight of the cable and Given that the cable lengthens by 4mm 0.15 kPa c

8 is the cable strong enough? Question 3c no a yes b 50 kN 5 m 20 mm a 20mm ø high-strength steel cable 5 m long has a weight of 50 kN at its end. Neglecting the self-weight of the cable and Given that the cable lengthens by 4mm Given that the maximum allowable tensile stress for high-strength steel is 1000 MPa

9 what factors do we have to take Into consideration? Question 4a strength of the column a slenderness of the column b when a column is under load a and b c

10 what is the first means of failure we should check for? Question 4b column breaking under compression a buckling b when a column is under load

11 what is the stress in the column? Question 5a 1 MPa a 4 kPa b a reinforced concrete column, 400 x 400 mm and 3.5 m high is subject to a load of 160 kN Given that the column shortens by 0.07 mm 1 kPa c 160 kN 3.5 m 400 mm

12 what is the strain in the column? Question 5b 50 a 2 x b a reinforced concrete column, 400 x 400 mm and 3.5 m high is subject to a load of 160 kN Given that the column shortens by 0.07 mm mm c 160 kN 3.5 m 400 mm

13 is the column strong enough? Question 5c yes a no b a reinforced concrete column, 400 x 400 mm and 3.5 m high is subject to a load of 160 kN Given that the column shortens by 0.07 mm Given that the maximum allowable stress for the concrete is 20 MPa 160 kN 3.5 m 400 mm

14 could you reduce the area of the column? Question 5d yes a no b a reinforced concrete column, 400 x 400 mm and 3.5 m high is subject to a load of 160 kN Given that the column shortens by 0.07 mm Given that the column is understressed 160 kN 3.5 m 400 mm maybe c

15 to what size could you theoretically reduce the area of the column? Question 5e 90 mm x 90 mm a 400 mm x 200 mm b a reinforced concrete column, 400 x 400 mm and 3.5 m high is subject to a load of 160 kN Given that the column shortens by 0.07 mm 160 kN 3.5 m 400 mm 200 mm x 40 mm c

16 what would be the problem with that? Question 5f none a it would buckle b Given that you want to reduce the column to 90 mm x 90mm 160 kN 3.5 m 400 mm it would be difficult to build c b and c d

17 next question enough ! f = F /A – so its force distributed over an area that means its the intensity of the force, not the force itself

18 let me try again let me out of here partly correct

19 let me try again let me out of here a thousand times NO! a force is a force – not stress

20 next question enough ! f = F /A – so its force distributed over an area 1 kN/m 2 = 1 kPa

21 let me try again let me out of here thats force units

22 let me try again let me out of here go back to the formula f = F / A

23 next question enough ! strain is a response to stress and is a relative concept

24 let me try again let me out of here No? Then you are the pain

25 let me try again let me out of here

26 let me try again let me out of here I dont like that the change is just the deformation – not the strain

27 next question enough ! length over length means strain is dimensionless

28 let me try again let me out of here e = ΔL / L this is length over length

29 let me try again let me out of here wheres the force in e = ΔL / L ?

30 next question enough ! is also correct but 8 x gives a better feel

31 let me try again let me out of here e = ΔL / L whats ΔL, whats L, what are the units for strain?

32 let me try again let me out of here what are the units for strain ?

33 next question enough ! Well done !

34 let me try again let me out of here f = F / A check your calculations and units (its good practice to keep everything to Newtons and mm 1 N/mm 2 = 1 MPa = 1MN/m 2 )

35 next question enough ! actual stress of 159 MPa is much less than max allowable stress of 1000 MPa

36 and then think again let me try again let me out of here Whats the actual stress? Whats the maximum allowable stress? Is the actual stress less or more than the max allowable stress?

37 next question enough ! both are important

38 let me try again let me out of here

39 next question enough ! we always check to see if a column is slender and would buckle first

40 let me try again let me out of here

41 next question enough ! Right on ! f = F / A

42 let me try again let me out of here How did you get that? f = F / A Whats the force? Whats the area?

43 let me try again let me out of here check your calculations and your units? Its good practice to keep everything to Newtons and mms 1 N/mm 2 = 1 MPa = 1 MN/m 2

44 next question enough ! is also correct but 2 x is easier to follow

45 Check your calculations? Whats ΔL? Whats L? let me try again let me out of here e = ΔL / L

46 let me try again let me out of here What are the units of strain ?? e = ΔL / L

47 next question enough ! actual stress of 1 MPa is much less than max allowable stress of 20 MPa

48 Whats the actual stress? Whats the maximum allowable stress? Is the actual stress less than or greater than the max allowable stress? SO ? let me try again let me out of here

49 next question enough ! it depends on how much we reduce it by

50 let me try again let me out of here

51 If its understressed that means the area is greater than needs be let me try again let me out of here

52 next question enough ! according to calculations A = F / f Minimum required area = 8000 mm 2

53 let me try again let me out of here not according to the theoretical calculations f = F / A A = F / f

54 the end ! Yes its much too slender. It would buckle immediately Also, how could you pour concrete into such a small area?

55 let me try again let me out of here think again !

56 let me try again let me out of here

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