Reliability-based Calibration of Bridge Design Code


Professor Andrzej S. Nowak, University of Nebraska


Thursday, May 3, 2012 - 11:15am to 12:30pm


Room 102D, Engineering Bldg. 1



The presentation deals with the development of a design code for bridges. It is focused on the calibration process with the objective to determine load and resistance factors for AASHTO. The major steps in the code calibration procedure include the development of load and resistance models, reliability analysis procedure, selection of the target reliability and selection of the load and resistance factors. Bridge live load is based on the available extensive weigh-in-motion (WIM) data. The weight of vehicles and traffic volume is strongly site-specific. The WIM trucks were run over the influence lines to determine the load effects such as moments and shears. The parameters of the dynamic load are derived from the field measurements. A considerable database is gathered on material strength: concrete, reinforcing steel, and prestressing steel. The test results were provided by industry and they are analyzed to determine the cumulative distribution functions and other statistical parameters. The statistical parameters of concrete strength depends on fc’. A very small coefficient of variation is observed for reinforcing steel and even smaller for prestressing strands. The reliability analysis is performed to determine the reliability indices for components designed according to the AASHTO Code prior to calibration and after calibration. The results confirmed that the reliability-based calibration results in a consistent design, with reliability indices being close to the target value.

About the speaker: 

Dr. Nowak is Robert W. Brightfelt Professor of Engineering in the Department of Civil Engineering at the University of Nebraska since 2005, after 25 years at the University of Michigan. He received his MS and Ph.D. from the Warsaw University of Technology in Poland. His area of expertise is structural reliability and bridge engineering, and major research accomplishments include the development of a reliability-based calibration procedure for calculate ion of load and resistance factors. The procedure was successfully applied on calibration of AASHTO LRFD design code for bridges, ACI 318 Code for Concrete Buildings, Canadian Highway Bridge Design Code, and British Standard BS-5400. He made important contributions in the area of bridge diagnostics and evaluation, including analytical load models used for prediction of extreme load events for bridges and buildings and the development of efficient experimental procedures for weigh-in-motion measurement of truck loads, dynamic loads on bridges and fatigue load spectra. In the area of materials, Dr. Nowak has developed a design guide for self-consolidating concrete (SCC), including field applications. Dr. Nowak has authored over 450 technical publications, and chaired a number of committees associated with professional organizations such as: ASCE, ACI, TRB IABSE and IABMAS. He is an Honorary Professor of the Warsaw University of Technology and Krakow University of Technology, and a Fellow of ASCE, ACI and IABSE. Prof. Nowak received the ASCE Moisseiff Award, IFIP WG 7.5 Award, Bene Merentibus Medal, and Kasimir Gzowski Medal from the Canadian Society of Civil Engineers.