Examine the following statements : i) Factor of safety for steel should be based on its yield stress, ii) Factor of safety for steel should be based on its ultimate stress, iii) Factor of safety for concrete should be based on its yield stress, iv) Factor of safety for concrete should be based on its ultimate stress. The correct statements are A. (i) and (iii) B. (i) and (iv) C. (ii) and (iii) D. (ii) and (iv)

The correct answer is A. (i) and (iii).

A factor of safety is a number greater than 1 that is used to design structures and machines to account for uncertainties in the loading, material properties, and manufacturing processes. The factor of safety is typically chosen based on the consequences of failure. For example, a structure that supports human life would have a higher factor of safety than a structure that does not.

The yield stress of a material is the stress at which it begins to deform plastically. The ultimate stress of a material is the maximum stress that it can withstand before it fails.

For steel, the yield stress is typically lower than the ultimate stress. Therefore, the factor of safety for steel should be based on its yield stress. This will ensure that the steel does not deform plastically under normal loads.

For concrete, the ultimate stress is typically higher than the yield stress. Therefore, the factor of safety for concrete should be based on its ultimate stress. This will ensure that the concrete does not fail under normal loads.

Statements (i) and (iii) are correct because they state that the factor of safety for steel should be based on its yield stress and the factor of safety for concrete should be based on its ultimate stress. Statements (ii) and (iv) are incorrect because they state that the factor of safety for steel should be based on its ultimate stress and the factor of safety for concrete should be based on its yield stress.