GeneralFirst order analysis assumes small deflection behavior; the resulting forces and moments take no account of the secondary effects due to the deformation of the structure under load.
Second order analysis combines two effects to reach a solution: - 1st order analysis & large displacement analysis. The large deformation analysis takes full account of the effects due to the deformed shape of the structure and its members. When structures become more slender and less resistant to deformation, consideration of the 2nd order effects is a must.
P–Delta analysisThe objective of this article is to provide engineers with a short introduction of P-Delta analysis currently available in commercially software packages.
P-Delta is a non-linear effect that occurs in every structure where elements are subject to axial load. P-Delta is actually only one of many second-order effects. It is a genuine “effect” that is associated with the magnitude of the applied axial load (P) and a displacement (delta).
There are two P-Delta effects:
- P-"BIG" delta (P-Ä) - a structure effect
- P-"little" delta (P-ä) - a member effect
Consider the pile foundation, as shown under the bridge pier in scourable cohesive soil, layout of piles in plan and the values of direct moments and lateral forces at the soffit of Pilecap, are as follows: