The transient phase of a ductile beam under impact loading. Some issues about rigid-plastic analysis and first extension to masonry structures

This paper is aimed at defining such basic conditions as to apply the rigid-plastic analysis of ductile structures under impact loading to masonry structures. Thus, firstly the simple case of a fully clamped beam struck transversely by a mass at the mid-span is analysed by means of the classical rigid-plastic theory. Some issues about the transient phase are discussed with respect to other existing theoretical approaches. This phase is characterised by a stationary plastic hinge at the impact point and by two plastic hinges travelling continuously from a point close to the impact zone at the mid-span towards the supports. An iterative procedure is presented employing an interaction yield condition which combines the bending moment and transverse shear force required for plastic flow. Finally, a first application of dynamic rigid-plastic analysis to masonry structures is presented by means of a vertical column struck transversely by a mass at its top.