The correct answer is: B. Equilibrium and plastic moment conditions
The mechanism method of plastic analysis is a method of determining the collapse load of a structure by considering the formation of a mechanism. A mechanism is a kinematically admissible collapse mode, which means that it satisfies the equilibrium and compatibility conditions. The plastic moment condition is a condition that states that the plastic moment of resistance of each member must be greater than or equal to the bending moment at that member due to the applied loads.
The mechanism method of plastic analysis is a powerful tool for analyzing the collapse load of structures. However, it is important to note that it is only valid for structures that are statically determinate. For statically indeterminate structures, the equilibrium and compatibility conditions are not sufficient to determine the collapse load, and other methods, such as the energy method, must be used.
Here is a brief explanation of each option:
- Option A: Equilibrium and mechanism conditions. This is the correct answer. The mechanism method of plastic analysis satisfies both the equilibrium and mechanism conditions.
- Option B: Equilibrium and plastic moment conditions. This is not the correct answer. The mechanism method of plastic analysis satisfies the equilibrium and mechanism conditions, but it does not necessarily satisfy the plastic moment condition.
- Option C: Mechanism and plastic moment conditions. This is not the correct answer. The mechanism method of plastic analysis satisfies the mechanism condition, but it does not necessarily satisfy the equilibrium and plastic moment conditions.
- Option D: Equilibrium condition only. This is not the correct answer. The mechanism method of plastic analysis satisfies the equilibrium condition, but it does not necessarily satisfy the mechanism and plastic moment conditions.