This document discusses two methods for seismic retrofitting of steel bridge piers: 1) Concrete filling method, which involves partially filling hollow steel tubes with concrete to improve strength and ductility. 2) Corner reinforcement structure method, which involves adding reinforcing plates to corners to prevent cracks. This method has five restrictions on dimensions and properties of the reinforcing plates. The document provides details on each method and restrictions of the corner reinforcement method. It also includes figures illustrating concepts of seismic design and retrofitting and details of corner reinforcement.