Parametric Evaluation of Stiffness Distribution on Drift Amplification and First Three Modes in Frame Tube Buildings with P–Δ Effects

This paper presents a parametric evaluation of stiffness distribution on lateral drift amplification and modal response (first three modes) of frame tube tall buildings incorporating geometric nonlinearity (P–Δ effects). Three stiffness distribution schemes uniform stiffness, soft lower stories, and stiff perimeter tube are compared through nonlinear static and dynamic analyses. Results reveal that stiffness distribution significantly alters inter-story drift demands and modal properties when P–Δ effects are included. The study highlights the interaction between gravity load–induced P–Δ moments and stiffness gradients, with implications for design optimization of tall structures under wind and seismic forces.