Božidar Stojadinović

Comparison of Incremental Dynamic, Cloud, and Stripe Methods for Computing Probabilistic Seismic Demand Models

Probabilistic seismic demand models (PSDMs) are mathematical relations between measures of earthquake intensity and measures of structural response. The models include best estimates as well as considerations of uncertainty. Three methods for obtaining the demand models are compared in this paper: cloud, incremental dynamic, and stripe. A PSDM is derived using each method for a sample reinforced concrete bridge using a single IM (first-mode spectral acceleration) and EDP (column drift ratio). Merits and drawbacks of each method are discussed. For the structure considered, cloud and incremental dynamic analyses yield interchangeable PSDMs for the same amount of computational effort. Stripe analysis should be used only for individual intensity levels, not as a means of generating complete PSDMs.

Nonlinear Modeling of Bridge Structures in California

This paper presents a collection of practical and readily implementable recommendations for the modeling of highway bridges and overpasses subjected to earthquake ground motions. The specifications were developed particularly for Ordinary Standard Bridges in California as defined according to the Caltrans Seismic Design Criteria. Bridge components that require special modeling considerations and nonlinear characterization are identified in this paper, establishing specific criteria for the level of sophistication required. To reduce possible errors that arise during modeling and analysis of bridge structures using a particular structural analysis program, a comparison between bridge models using SAP2000 and OpenSees analysis packages was carried out to assess sensitivities and characterize important modeling parameters. Comparisons were made between the two software packages using modal, pushover and nonlinear time history analyses. A total of six typical reinforced concrete bridges in California with box-girder superstructure and different geometries and cross sections were considered. Inconsistencies between the two analysis packages were found for peak displacements obtained through nonlinear time history analysis. Two methods of obtaining response estimate bias factors between the two programs are illustrated for the six bridges analyzed under three seismic hazard levels (50%-, 10%-, and 2%-in-50-year probabilities of exceedance).

I-Shaped Unreinforced Masonry Wallettes with a Soft-Layer Bed Joint: Behavior under Static-Cyclic Shear

AbstractIn order to extend the latest findings on the in-plane shear behavior of rectangular unreinforced masonry (URM) wallettes with soft-layer bed joints and gain insight into the possible influ...

Performance-Based Post-Earthquake Repair Metrics for RC Bridges

Post-earthquake repair costs and repair times are important for evaluating the performance of new bridge designs and existing bridges in regions where bridges are subject to seismic hazards. Hazard and structural demand models describe the probabilistic structural response during earthquakes. Damage and decision models link the structural response to decisions on bridge repair actions and repair costs. A step-by-step probabilistic repair cost and repair time methodology is proposed in this paper to probabilistically evaluate repair metrics for different bridge components and the bridge as a system, corresponding to varying degrees of damage. Repair actions, quantities, times, and costs are input into spreadsheet templates, and a numerical tool evaluates the expected value and variance of both repair costs and repair times for a range of earthquake intensities. This methodology uses the concept of performance groups—groups defined to account for bridge components that are repaired together. Spreadsheets are used to track all the necessary data: bridge information, structural response, component damage states, repair methods and repair quantities, and unit costs or production rates. Data can be customized for repair methods and bridge types particular to different regions. A multi-span, reinforced concrete highway overpass bridge in California is used to illustrate the methodology.