ABSTRACT
In a severe earthquake two different types of plastic hinge zone may form in the beams of frame structures. These are referred to as reversing and uni-directional plastic hinges and they exhibit very different load deflection characteristics. Beams which form reversing plastic hinge zones are generally more ductile but they undergo greater stiffness degradation under cyclic loading than those that develop uni-directional hinges. With both types of plastic hinge the tensile yielding of the flexural reinforcement causes the beams to elongate to a much greater extent than would be intuitively expected. This largely neglected aspect of behaviour can have a major influence on the seismic performance of a structure and it should be taken into account in the design of the supports for precast floors, cladding and in the detailing of columns.
