SUMMARYEnergy dissipation characteristics of structural members which exhibit both strength and sti ness deterioration under imposed displacement reversals are investigated. In the experimental part, 17 reinforced concrete beam specimens were tested under constant and variable amplitude inelastic displacement cycles. The constant-amplitude tests were employed to determine the low-cycle fatigue behaviour of specimens where the imposed displacement amplitude was the major variable. A two-parameter fatigue model was developed in order to express the variation of dissipated energy with the number of displacement cycles. This model was then used to predict the energy dissipation of test specimens subjected to variable-amplitude displacement cycles simulating severe seismic excitations. It has been demonstrated that the remaining energy dissipation capacity in a forthcoming displacement cycle is dependent on the energy dissipated along the completed displacement path. Moreover, it is observed that total energy dissipation is dependent on the length of the displacement path.

SUMMARYThe low-cycle fatigue model presented in the companion paper is employed for developing hysteresis and damage models for deteriorating systems. The hysteresis model performs strength reduction at a current displacement cycle by evaluating the loss in the energy dissipation capacity along the completed displacement path. Hence it is completely memory dependent. Pinching is accounted for implicitly by a reduced energy dissipation capacity in a displacement cycle. The model predicts the experimental results obtained from variable-amplitude tests reasonably well. Response analysis under earthquake excitations reveals that both the maximum displacements and the number of large-amplitude displacement response cycles increase signiÿcantly with the reduction in energy dissipation capacity, resulting in higher damage. Damage is deÿned as the deterioration in the e ective sti ness of a displacement cycle, which is in turn related to the reduction in the energy dissipation capacity. A simple damage function is developed accordingly, consisting of displacement and fatigue components. It is observed that the fatigue component of damage is more signiÿcant than the displacement component for deteriorating systems under ground motions with signiÿcant e ective durations.

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SUMMARYSeismic performance of a three-storey unreinforced masonry building which survived the 1992 Erzincan earthquake without damage is evaluated. Mechanical properties of the masonry walls have been determined experimentally by using identical brick and mortar used in construction. An accurate material model is developed for masonry and employed in a computer program for the non-linear dynamic analysis of masonry buildings. The analytical results based on measured material properties indicated that masonry buildings which satisfy basic seismic code requirements possess remarkable lateral strength, stiffness and energy dissipation capacity. Accordingly, a simple elastic design approach is rendered suitable for unreinforced masonry under seismic excitations, provided that realistic material properties are employed in design.