a) to calculate external force equilibrium in deformed geometry of structure

b) to calculate internal force equilibrium in deformed geometry of structure
c) to calculate external force equilibrium in undeformed geometry of structure
d) to calculate internal force equilibrium in undeformed geometry of structure

Answer: b
Explanation: Basic objective of second order elastic analysis is to calculate internal force equilibrium in deformed geometry of structure. In this P-Δ effect is also considered.