Seismic performance of quasi-isolated highway bridges in Illinois.

PDFTech ReportFHWA-ICT-13-015UILU-ENG-2013-2019SeismicityEarthquake resistant designHighway bridgesBridge bearingsBase isolationBridge designFinite element methodDislocation (Geology)IllinoisIllinois. Dept. of Transportation. Bureau of Materials and Physical ResearchLaFave, JamesFahnestock, LarryFoutch, DouglasSteelman, JoshuaRevell, JessicaFilipov, EvgueniHajjar, JeromeIllinois Center for TransportationUniversity of Illinois at Urbana-Champaign. Dept. of Civil and Environmental EngineeringUnited States. Federal Highway AdministrationUS Transportation CollectionThe Illinois Department of Transportation (IDOT) commonly uses elastomeric bearings to accommodatethermal deformations in bridges, and these bearings have potential utility in seismic events. IDOT has developedan Earthquake Resisting System (ERS) using the displacement capacity of typical bearings to achieve astructural response similar to isolation. Project R27-70 was conducted to validate and calibrate the quasi-isolatedERS based on full-scale laboratory tests of bearings and computational models capturing full-bridge seismicresponse. The overall report is divided into two volumes. Volume 1 discussed the experimental program. Thissecond volume focuses on the analytical program but also contains retainer design recommendations. Resultsfrom the experimental testing program were used to develop constitutive bearing models, which wereincorporated into the finite element model of a three-span bridge with simply supported abutments and fixedbearings at one pier. A suite of 48 bridges was created to represent the most common highway bridgeconfigurations in Illinois. Variables included superstructure type, pier type, pier height, elastomeric bearing type,and foundation flexibility. Two sets of ten synthetic ground motions from the New Madrid Seismic Zone werescaled to match the AASHTO seismic design spectra for Cairo, Illinois, and applied in the longitudinal andtransverse directions. A total of 12,000 nonlinear dynamic analyses were conducted in OpenSees at six scalefactors from 0.5 to 1.75 and used to create coarse incremental dynamic analyses. On the basis of the findings ofthe parametric study, most bridges in Illinois would not experience severe damage during a 75-year design life,and bearing unseating or span loss are not likely to occur in regions with moderate seismic hazard. Piers withfixed bearings commonly yielded for small earthquakes, but future calibration of fuse capacities may improve thisbehavior