Plastic Behavior of Structures was organized under the auspices of the Pressure Vessel Research Committee of the Welding Research Council. The group was organized because of the need for unified and standardized methods for limit analysis or plastic collapse determinations. A variety of different methods were being used to determine limit loads and there were questions as to the acceptability of all these different methods.

During 1975-1976, three preliminary studies (1.1-1.3) were carried out by the Task Group in three different areas related to three geometries, (plates, shells, and piping and branch connections), where work had been done by other subcommittees of PVRC. After these three summary reports had been prepared, this author was employed in 1976-1978, to review these reports and to prepare the following comprehensive interpretative report on determining limit loads and plastic collapse loads in general.

Four objectives were agreed upon:

1. To review definitions of limit loads and plastic collapse loads as used in both theoretical and experimental analyses, as well as in the ASME code; and to recommend a unified definition of plastic (collapse) load. These definitions were to be treated on two levels: rigid-plastic definitions, and elasticplastic definitions.
2. To check the definitions and compare theory and experiment in a variety of conditions and on a variety of configurations. The configurations were: beams (as illustrations of basic behavior), pressure vessel heads, unperforated and perforated plates, straight piping, curved piping, nozzles in vessels, and branch connections in pipes. The loadings to be considered were: pressure only, concentrated loads only, moments only and combinations of loadings. The analysis was to be restricted to single monotonic loadings; overloads not cyclic loadings.
3. To assess strain limits, ductility requirements, and shakedown. The range of applicability of limit analysis versus fracture mechanics was to be discussed.
4. To recommend critical tests and research needed to fill in gaps in theory and experiment.

This report covers the above four objectives of the investigation. In this introduction, some basic definitions are first given before considering the theory and application of limit analysis and elastic plastic analysis to different geometries.