Report - PEER - University of California, Berkeley

where ν ( DV ) is the probabilistic description of the decision variable (for example,the annual rate of exceeding a certain repair cost), DM represents the damagemeasure, EDP represents the engineering demand parameter (drift, plastic rotation,etc.) and IM represents the intensity measure (characterizing the hazard). Theexpression of the form P(A|B) is essentially a cumulative distribution function or theconditional probability that A exceeds a specified limit for a given value of B. Theterms that appear in the above equation can be deaggregated using the totalprobability theorem that assumes that each operation is mutually independent. Oneuseful application of Equation (1) is to derive the mean annual probability ofexceeding a DV given an IM.While probabilistic methods offer distinct advantages over deterministicapproaches, it is important to be cognizant of the assumptions that underlie theframework. A closer look at the PEER methodology indicates that the resultingevaluation is a function of four separate modeling tasks: hazard, demand, damage anddecision-making. Suppositions and simplifications are often introduced at variousmodeling phases that can impact the final outcome of the assessment. This paperattempts to investigate the sensitivity of modeling assumptions introduced at differentstages of a performance-based evaluation using the PEER framework.2. APPLICATION OF THE PEER METHODOLOGY TO AN EXISTINGVIADUCT IN CALIFORNIAThe expected seismic performance of a section of the I-880 viaduct constructed in themid-1990s as part of the California Department of Transportations (CALTRANS)Cypress Replacement Project in Oakland, California, is evaluated using the PEERPBSE framework. The specific issues investigated include: modeling of the sitehazard and issues related to scaling the ground motions; modeling of the system, thelevel of detail that is needed to establish reliable estimates of performance, and issuesrelated to soil-foundation-structure interaction (SFSI) and P-delta effects;considerations in damage modeling; and finally, the significance of subjectivedecisions made by bridge inspectors in post-earthquake reconnaissance.2.1 Description of the ViaductThe rebuilt segment of the I-880 (Figure 1) is a seven-frame structure consisting of 26spans and a total length of approximately 1140 m. The site is located within 7-8 kmof the Hayward Fault. The soils on the site near the San Francisco Bay consist ofdense fill, Bay mud and sand, covering deep clay deposits. The superstructure iscomposed of 7 cast-in place reinforced concrete box girders, approximately 21.8 mwide, 2.0 m tall and 0.3 m in depth. All columns of the viaduct have rectangularcross-sections with circular reinforcement. While a majority of the columns havecontinuous moment connections at the column-deck and column-pile-cap region,some bents have pinned connections at either the column-pile-cap or column-deck66