Lecture 5

Question 1

18. What information would you require to check whether or not a limit state had been reached

Answer 1

To check if the limit state had been reached the following information should be provided. This may be defined by code of practice or be arrived at by the designer from his own knowledge of the purpose of the structure:
* Limits of acceptable behaviour
* Design leading under which criteria should be checked
* Design material properties
* A model of behaviour, with calculations where the load and material is assumed.

Question 2

19. Explain the difference between the two groups of limit states known as Ultimate Limit States (ULS) and Serviceability Limit States (SLS)

Answer 2

• Ultimate limit state(ULS) is where the structure is unable to support the load and then fails. This can either be the whole structure or parts
• Serviceability limit states (SLS) issue of excessive deflections. The structure can not fulfil its purpose satisfactorily.

Question 3

20. State which of the following actions are classified as Permanent actions (G), Variable actions (Q), or Accidental actions (A)

Answer 3

Self-weight = G
Fire = A
Imposed floor loads = Q
Wind loads = Q
Water and earth pressure = G
Explosions = A

Question 4

21. In the design of reinforced concrete structures why is M for concrete (M = 1.5) higher than for steel rebars (M = 1.15)

Answer 4

The values are the probability of not being attained in a hypothetical unlimited test series. The value corresponds to a specified tractile of the material. The moduli of elasticity E are mean values.