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Highway Synthesis Reports

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Fragility Considerations in Highway Bridge Design

M. Shinozuka, S. Banerjee and S-H. Kim

MCEER-07-0023  | December 14, 2007

This report integrates statistical and analytical methods for the prediction of seismic performance of highway transportation networks. For this purpose, an integrated framework involving the structural engineering module of multilayer simulation scheme is developed. This module is a key component of the performance simulation of such spatially distributed systems. In the analysis, it is assumed that bridges are the only components of the network system vulnerable to earthquake ground motion. Bridge seismic damageability at various damage conditions is expressed in the form of fragility curves associated with the states of minor, moderate, major and collapse damage, mechanistically defined in terms of the extent of ductility rotation of bridge columns at the bottom and top. This report demonstrates the application of fragility curves in the performance-based seismic design of bridges. On the basis of statistical and analytical tools discussed here, a design acceptance criterion is suggested that can verify the target performance level of a newly designed bridge under a prescribed level of seismic hazard.

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Bridge Foundations: Modeling Large Pile Groups and Caissons for Seismic Design

I. Po Lam, H. Law and G.R. Martin (Coordinating Author)

MCEER-07-0018 | December 1, 2007

The report synthesizes and summarizes current FHWA-sponsored bridge research and related technical reports on the seismic design of large pile groups and caissons into one design-oriented guideline report on seismic design, suitable for applications to the retrofit of existing long span bridges or for new design. The characterization of ground motions for seismic soil-foundation-structure interaction analyses is an important component of the foundation modeling process, and is discussed in detail. Discussion includes methods for generating spectrum compatible time histories, spatial variations of ground motion and effects of local soil conditions on site response. Modeling approaches for large pile groups focus on the use of the substructuring approach, the use of p-y curves and associated pile group effects to develop linearized Winkler springs and the assembly of pile group stiffness matrices. The analysis approach is illustrated with several case history examples, including the San Francisco-Oakland Bay Bridge East Span project. The complexity of kinematic soil-pile interaction as related to modification of input ground motions is also described. Modeling approaches for large caisson foundations often employed as piers for large over-water bridges are discussed in detail, with an emphasis on the use of linear stiffness matrices, and nonlinear lumped spring and nonlinear distributed spring approaches. The influence of kinematic interaction on input ground motions is also described. Two case history examples are used to illustrate the modeling approaches, including one used for the new Tacoma Narrows Bridge.

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Liquefaction Remediation in Silty Soils Using Dynamic Compaction and Stone Columns

S. Thevanayagam, G.R. Martin, R. Nashed, T. Shenthan, T. Kanagalingam and N. Ecemis

MCEER-06-0009 | August 28, 2006

The objective of this report is to introduce a rational analysis procedure and design guidelines for liquefaction hazards mitigation in saturated sands and non-plastic silty sands using Dynamic Compaction (DC) and Vibro-Stone Columns (SC). A numerical model was developed to simulate the densification processes during both techniques through quantifying pore pressure generation due to vibrations caused by successive impacts on the ground surface or repeated insertions of a vibratory probe into the ground. The effects of site-specific conditions such as hydraulic conductivity, fines content, etc. were quantified for a range of energy contents delivered to the soil at specific spacing. In addition, the effects of field operational parameters such as energy per impact, number of impacts, time cycle between impacts, impact grid spacing, impact grid pattern, and wick drain spacing, in the case of DC, or area replacement ratio and wick drains spacing in the case of SC, on post-improvement resistance to liquefaction were included in the study. Based on the results, design charts and design guidelines for liquefaction mitigation in silty soils using DC and SC are provided. Design procedures and design examples are also provided.

Review of Current NDE Technologies for Post-earthquake Assessment of Retrofitted Bridge Columns

J.W. Song, Z. Liang and G.C. Lee

MCEER-06-0008  | August 21, 2006

The major objective of this report is to evaluate various nondestructive testing/evaluation (NDE) technologies for use on bridge columns that have been retrofitted with FRP-type jackets. Suitable and/or potentially suitable techniques for practical applications are identified, and promising techniques that could benefit from additional research prior to use in engineering applications are assessed. For each technology, the inherent physical principles and application characteristics are analyzed and their advantages and disadvantages are compared to determine whether each method could be used to detect damage and defects in the jacketed bridge columns. The most promising NDE methods (such as the impact echo method and electromagnetic method) are identified and corresponding application procedures are then presented. This report focuses solely on the application of NDE technologies to bridge columns, and therefore, recommendations and conclusions herein may differ from those discovered for other applications. Furthermore, this is a rapidly advancing field, so some applications and conclusions may change in the coming years.

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REDARS Validation Report

S. Cho, C.K. Huyck, S. Ghosh and R.T. Eguchi

MCEER-06-0007  | August 8, 2006

This report presents the results of an extensive review and evaluation of the Seismic Risk Assessment (SRA) methodology for highway systems, as documented in “A Risk-Based Methodology for Assessing the Seismic Performance of Highway Systems,” by S.D. Werner, C.E. Taylor, J.E. Moore II, J.S. Walton and S. Cho, MCEER-00-0014. The efficacy of all key modules in the REDARS (Risk of Earthquake Damage for Roadway Systems) software program were evaluated. The modules included: bridge damage or fragility module, post-earthquake traffic state module, transportation module and economic loss module. The results from this review were evaluated by the REDARS development team and subsequently used to update the REDARS software program. The REDARS methodology and software for seismic risk analysis of highway systems is presented in a companion MCEER special report, “REDARS 2 Methodology and Software for Seismic Risk Analysis of Highway Systems,” by S.D. Werner, C.E. Taylor, S. Cho, J.P. Lavoie, C.K. Huyck, C. Eitzel, H. Chung and R.T. Eguchi, MCEER-06-SP08.

 

 

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