What is progressive collapse and how is it analyzed and prevented?

Progressive collapse is a chain reaction failure where local damage spreads to cause disproportionate structural collapse (like WTC buildings). Analysis methods include: linear/nonlinear static alternate path method (remove critical members and check if structure survives), dynamic analysis for impact effects, and risk-based approaches. Prevention strategies include: structural redundancy and alternate load paths, connection design for ductility and catenary action, compartmentalization to limit damage spread, and specific local resistance for key elements.