12.07.2015 Views

Report - PEER - University of California, Berkeley

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The collapse capacities <strong>of</strong> the brick wall with and without constructional columns aretaken as 90% and 85% <strong>of</strong> ultimate strength, respectively. The capacity for the severedamage is related to the ultimate strength. The capacity for the initial crackingdamage is related to the cracking strength. The capacities for slight damage andmoderate damage are taken as the values at 1/5 and 3/5 points between the capacitiesfor the initial cracking damage and severe damage, respectively. The median andlogarithmic standard deviation <strong>of</strong> story capacity <strong>of</strong> the brick buildings are obtained bycomposing the mean and standard deviation <strong>of</strong> the brick wall with and withoutconstructional columns according to their cross section ratio.5.3 Probabilistic Response <strong>of</strong> Earthquake Load-Structure SystemThe hysteretic model used in nonlinear seismic response analysis includes a negativestiffness branch. In order to avoid the probable unstable phenomenon in the iterationmethod and probable non-definite abnormal matrix in the variable stiffness matrixmethod during dealing with the negative stiffness, we use the method <strong>of</strong> nonlineardynamic response analysis based on pattern <strong>of</strong> self-equilibrating stresses (Zhang1998, Zhang 1997b) to analyze the response <strong>of</strong> multistory brick buildings.For each earthquake load-structure system, the nonlinear seismic responseanalysis is carried out. The i-th story ductility ratio is:U max,iµ i =U(7)c,iwhere U max,i is the maximum absolute inter-story deformation <strong>of</strong> the i-th story and U c,iis the cracking deformation <strong>of</strong> the i-th story.For the results <strong>of</strong> 81 samples, statistical analysis is utilized to determine mean,standard deviation and distribution function <strong>of</strong> the maximum response. According toZhang (2002), the maximum structural response can be modeled by a lognormaldistribution.5.4 Reliability AnalysisThe structural seismic reliability analysis is used to determine the limit stateprobability PF with respect to a particular limit state during the structure’s servicelife. It can be expressed as:10PF = ∑ λ I ⋅ Pj=6jf(Ij)where j=6, 7, 8, 9, 10, is the number <strong>of</strong> intensity. The structural reliability index withrespect to a particular limit state is:−1β = −Φ (PF)(8)(9)415

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