Report - PEER - University of California, Berkeley

Examples of moderate deterioration (MD) behavior belong to test specimensWS3, WS6, SO2 and PJ1-5 with parameter α ranging between 0.45-0.65 andparameter β ranging between 0.2-1.2. The observed behavior for “MD” type ofstructural members is gradual deterioration in strength with increasing cycle number,and slight pinching. However the specimen can still dissipate a considerable amountof energy after a significant number of cycles. Such a behavior is presented in Figure2.b for the specimen WS6.(a)400F (kN)(b)100F (kN)(c)150F (kN)0-100 0"100u (mm)0-40 0 40u (mm)0-40 0 40u (mm)-400-100Figure 2. Force-displacement relationships for specimens (a) SO4, (b) WS6,(c) WS1.Severely deteriorating (SV) structural members include test specimens WS1-2,SO1 and ES1-6. These specimens either have plain longitudinal bars, or lowconfinement ratio. When plain bars are used as longitudinal reinforcement, excessivebar slip occurs even in the early stages of displacement reversals leading to pinchingand strength deterioration, which reduces the energy dissipation capacitysignificantly. The curves given in Figure 2.c for specimen WS1 validate this behavior.For seismic performance evaluation of deteriorating structures, three differentclasses of structural systems are defined based on the experimental database. Theseclasses are defined as slightly deteriorating (SL) systems, moderately deteriorating(MD) systems and severely deteriorating (SV) systems; a different pair of low cyclefatigue parameters (α, β) is assigned to each class. For SL systems, α=0.9 and β=0.3are assigned as the low cycle fatigue parameters. Considering the experimentalresults, the values of the parameters α and β for MD systems are taken as 0.6 and 0.5respectively. Finally the low-cycle fatigue parameters for SV systems are taken asα=0.3 and β=0.7, respectively.Figure 3 presents the normalized dissipated energy per cycle (Ē h,n ) versus cyclenumber (n) relationship for each specimen in Table 1, obtained by substituting α andβ parameters into Equation 1. Three different levels of performance can be clearlydistinguished from the grouping of the curves, each group corresponding to a class ofstructural system defined as SL, MD or SV. The sensitivity of the parameter α, whichdescribes the ultimate level of deterioration in the energy dissipation capacity, toseveral structural characteristics has been evaluated by employing the experimentaldata base summarized in Table 1. It is observed that three fundamental characteristicsof concrete members have a significant influence on the level of strength-150425