Let’s talk about P-delta effect today. This prevalent in tall buildings, tall bridge piers😁.
In simple words, a deflection Delta occurs as shown in figure due to geometry configuration, this extra Delta combined with the axial load causes secondary moments in addition to primary loads, which is equal to P multiplied by Delta.
Does that stop there? 😁not really, this Delta value will increase with time, cause again additional moments. An iterative method is to be done to arrive at final moments and iteration is continued till the increase in moment due to sway is negligible.