Report - PEER - University of California, Berkeley

epresents moderate height buildings, designed for a base shear coefficient of 20percent. Elastic displacements are also calculated for comparison. It is notable toobserve in Figure 4 that even slight deterioration has a major influence on inelasticdisplacements. Moreover, the residual displacements, which are consistent indicatorsof permanent damage at the end of ground excitation, accumulate to values exceedingthe peak displacement of elastic system. When the level of deterioration is severe,both maximum and residual displacements reach values twice as much as those forthe slight and moderate deterioration levels. A severely deteriorating system hererepresents majority of existing buildings constructed with plain reinforcing bars andlacking confinement at the critical sections.Displacement (cm)12840ElasticSL (α = 0.9, β = 0.3)MD (α = 0.6, β = 0.5)SV (α = 0.3, β = 0.7)T = 0.5 sec, η = 0.2, ξ = 5%-40 50 100 150Time (sec)Figure 4. Displacement responses of a SDOF system with three levels ofperformance subjected to Marmara 1999 Earthquake, YPT Record, NSComponent (also compared with the elastic response).ENERGY BASED HYSTERESIS MODEL FOR DETERIORATINGSYSTEMSA simple piece-wise linear hysteresis model is developed for representing the forcedeformationresponse of deteriorating SDOF systems. It operates on a bilinearskeleton curve and based primarily on the stiffness degrading model (Clough, 1966),extended with an energy-based memory for simulating strength deterioration. Theenergy-based fatigue model given in Equation 1 is employed for calculating thereduction in the energy dissipation capacity under repeated inelastic displacementcycles. Once the reduced energy dissipation capacity at an equivalent cycle number ispredicted by the model, the force-displacement path is determined by reducing thestrength capacity of the deteriorating system accordingly. Pinching is not consideredexplicitly in the generated force-deformation reloading paths, however loss of energydissipation capacity due to pinching, or anchorage slip in reinforced concrete427