Report - PEER - University of California, Berkeley

distribution was then established for each set of simulations using the procedurediscussed in Section 3. In general, the viaduct performed extremely well, with closureprobabilities less than 1% in 50 years for all cases. The objective of the study,however, is to examine the consequences of model variations. The impact ofassumptions made during the modeling phase of the evaluation is discussed in theremainder of this section.4.1 Issues Related to ModelingIn this phase of the evaluation, the level of model detail is investigated. The medianpeak response of a critical bent (defined as the bent experiencing the maximum lateraldrift) using the three-frame model is compared to the same response when a singleframe model of the same bent is analyzed. Figure 6 indicates that the variation ofdemand with Intensity Measure (IM) is generally unaffected as is the probability ofclosure. When the hazard curve is integrated into the above distributions, the closureprobability in 50 years for the multiple bent model is 0.95% and 0.46% for the singlebent model. The difference appears to be significant but only because the maximumspectral acceleration for the 2%/50 year hazard is 1.4g which represents the initial tailof the distribution. The difference between the two closure probabilities is relativelyinsignificant for larger spectral magnitudes.EDP, Drift (%)43Multiple Bent ModelSingle Bent Model2100 1 2 3 4IM, S a (T), gP(Closure|IM)0.5Multiple Bent Model0.4Single Bent Model0.30.20.100 1 2 3 4IM, S a (T), gFigure 6. EDP-IM relationship and P(DV) for different system models.4.1.1 P-Delta EffectsThe single bent model was evaluated separately for P-delta effects. The difference inpeak response for the model with and without P-delta effects was insignificant, asshown on the left in Figure 7. Axial forces on bridge columns tend to be quite low andmost of the maximum drifts were 2% or less. Given this negligible variation, theclosure probabilities of the two models were not further investigated.72