New Eurocode-3 (2005) & HK Steel Code (2005) disallow the use of effective length method for complex, long-span and slender structures because of uncertainty in effective length and stability checks.

Effective length is unknown for many structural members including those in roof arch structures and slender frames of unusual shape.

Second-order analysis goes beyond the scope for effective length which is inapplicable in many scenarios like structures under fire and in plastic range. Linear analysis with effective length gives no indication on stability in an analysis.

Modern design codes including LRFD in USA and Eurocode-3 pushes engineers to use second-order analysis with imperfections.