Torsional Irregularity in Structures — Why Buildings Rotate Under Earthquake Load

Why does a building rotate under earthquake load, even when the seismic force is applied in a perfectly straight direction? In this video, I explain exactly what causes torsional irregularity, show you how to deliberately recreate it and fix it in ETABS, and break down the structural mechanics behind it — from column and beam stiffness formulas to real frame behavior. We'll go through: ✅ Why stiffness differences between sides of a building cause rotation under seismic load ✅ A real ETABS demonstration — deliberately weakening one side, then the other, to see the rotation flip ✅ The two tools every engineer has to control this: section height and span length ✅ Column and beam stiffness formulas — from fixed-fixed to pinned supports — and how rigid diaphragms tie them together 0:00 What Is Torsional Irregularity 2:48 Why It Happens | Moment Frame Counts 7:09 Column & Beam Stiffness Formulas 15:10 Balancing the Structure in ETABS 📋 Want a free, step-by-step structural design checklist so you never miss a step in your projects? Get it here: https://forms.gle/naoaxVJCRcxZNSko6 If you found this helpful, subscribe for more videos on structural and earthquake engineering — theory, code, and real ETABS modeling, all in one place. #StructuralEngineering #ETABS #SeismicDesign #TorsionalIrregularity #CivilEngineering