The plastic method has been used extensively by engineers for the design of steel structures, including simple beams, continuous beams, and simple portal frames. Traditionally, the analysis is based on the rigidplastic theory whereby the plastic collapse load is evaluated through virtual work formulation in which elastic deflection is ignored. For more complex frames, specialist computer packages for elastoplastic analysis are usually employed. Current publications on plastic design method provide means of analysis based on either virtual work formulation or sophisticated plastic theory contained in specialist computer packages. This book aims to bridge this gap.