Predicting Erosion Impact on Highway and Railway Bridge Substructures

Detailed finite element analysis is performed to characterize the dynamic characteristics of two bridges identified in the study area. The two bridges lie in different geologic formations such that one was designed with a deep foundation system and the other with a shallow one. Fixed base models highlight the significant difference in fundamental frequencies for the two structural systems even when the different foundations are not considered. Soil-structure interaction models are developed to incorporate the soil and foundation elements and account for scour conditions. The deep foundation or flexible system is used to characterize the effect of soil-structure interaction and the influence of scour, first on the dynamic characteristics and then on the response to a simulated earthquake event. Changes in dynamic characteristics are evaluated for a symmetric scour scenario in which the stream bed depends to a depth justified by current conditions observed in the field projected to a depth likely in the operational life of the bridge. Vibration modes involving horizontal movement of the deck mass exhibit a noticeable reduction in frequency which would make them more excitable under significant excitations. An earthquake scenario of the type used in emergency management plans for the study region is used to assess the effect of scour on vulnerability to ground motion. An asymmetric scour scenario is used in which the footings of one of the two piers closest to the stream is left completely exposed. Simulated time history response is computed for the flexible system with and without scour. Acceleration response time histories are presented that show a significant increase in the transverse acceleration which tends to increase the instability of the system. The supporting erosion/scour studies identified substantial erosion resulting from the negative consequences of channelization, easily erodible geologic materials, and inadequate erosion mitigation measures. Past practices have ignored the “under-bridge” stream which is the primary agent of erosion. Stream geometry should be recorded on design plans and monitored as part of standard bridge inspection practices.

• Record URL:
  http://www.ncitec.msstate.edu/wp-content/uploads/2013-25FR.pdf
• 
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/39950
• Supplemental Notes:
  • This research was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
• Corporate Authors:

  University of Mississippi, University

  Department of Civil Engineering
  University, MS  United States  38677

  National Center for Intermodal Transportation for Economic Competitiveness

  Mississippi State University
  479-2 Hardy Road 260 McCain Hall
  Mississippi State, MS  United States  39762

  Research and Innovative Technology Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Swann, Charles
  • Mullen, Chris
• Publication Date: 2016-6

Language

• English

Media Info

• Media Type: Digital/other
• Features: Figures; Maps; Photos; References; Tables;
• Pagination: 62p

Subject/Index Terms

• TRT Terms: Bridge foundations; Bridge substructures; Earthquakes; Erosion; Finite element method; Highway bridges; Railroad bridges; Scour; Soil structure interaction
• Subject Areas: Bridges and other structures; Geotechnology; Highways; Railroads;

Filing Info

• Accession Number: 01604930
• Record Type: Publication
• Report/Paper Numbers: NCITEC Project No. UM 2013-25
• Files: UTC, NTL, TRIS, RITA, ATRI, USDOT
• Created Date: Jul 25 2016 6:32PM