Newsletters and Summaries

The Southern Plains Transportation Center compiles periodic newsletters to communicate the impact of the center in the areas of research, outreach, workforce development and more.

Bridge Timber Pile Treatment, repair and assessment techniques

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OVERVIEW: Oklahoma is rated first in the Nation in the percentage of bridges that are structurally deficient or functionally obsolete (OkTC 2013).  According to Federal Highway Administration data, Oklahoma has approximately 23,250 bridges maintained by state, County, City, and Tribal governments.  The Oklahoma Department of Transportation estimated that it would cost $3.4 billion to replace these bridges (OkTC 2013).  As funds for replacing bridges decline and construction costs increase, effective rehabilitation and strengthening techniques for extending the life of the timber substructures in bridges with structurally sound superstructures has become even more important (Iowa 2012). These techniques can facilitate county, tribal, and local government officials in prioritizing and wisely spending bridge and road maintenance resources. Implementation can also result in successfully extending the life of bridges and enhancing stewardship and safety (OkTC 2013).

CURRENT TECHNIQUES: There are a number of timber pile treatment, repair and assessment techniques being used across the country today (Iowa 2012). Preservative treatments are generally oil-borne or water-borne preservatives and are applied to timber to enhance its longevity or service life and will depend upon a range of factors including type of preservative, treatment quality, construction practices, type of exposure, and climate (Iowa 2012). Copper naphthenate, either in liquid or paste form, is the most commonly used preservative treatment indicated in a national survey (Iowa 2012). The American Wood Protection Association (AWPA) has produced standards for treatment and care of timber products for use in bridge applications.

Available repair methods for timber piles can be categorized by the stage of biological or physical deterioration in which they are best applied: preventive maintenance, remedial maintenance and major maintenance (Iowa 2012). Preventive maintenance is applied when no deterioration is observed, but conditions are favorable for decay. This type of maintenance is associated with the best cost savings over the long term because it reduces the greater costs of major rehabilitation due to maintenance deferment (Iowa 2012). Techniques include moisture control, in-place treatments (e.g. surface treatments, paste, fumigants) and minor crack repair (e.g. epoxy grouting) (Iowa 2012).

Remedial maintenance is used when non-structural deterioration is observed. It serves to protect the strength and environmental resilience of piles. It does this by repairing the pile and inhibiting the exponentially-increasing decay and includes the following techniques (Iowa 2012):

  • Posting/splicing – removing and replacing the damaged portion of timber at or above-ground level (OkTC 2013)
    • connecting the new portion via concrete jacket or fishplates (shown right; White et al. 2007)
    • connecting the new portion via fiber reinforced polymers (FRP) sheets or composites
    • mechanical splicing – lap splices secured with metal screws
    • posting and epoxy grouting procedure
  • Concrete jacketing – encasing pile with reinforced concrete or concrete-filled corrugated pipe
  • Polyvinyl Chloride (PVC) Wrap - flexible plastic wrap tightly drawn/attached to pile
  • Epoxy-Injected Piles (OkTC 2013),
  • Installing steel H-pile sections or mild-steel reinforcement (e.g. angles, channels, W shapes), and
  • FRP composite shell - FRP jacket, an underwater epoxy or grout fill, or carbon fiber reinforcement between the FRP jacket and the timber pile (shown below; SPTC 2017, Lopez-Anido et al. 2005).

Design tables and installation procedures of splice repair have been developed by an Oklahoma study to assist county management in choosing a replacement shape that will safely take the load from the bridge deck to the old pile underground (OkTC 2013). The final design specifies the details in all welds, including types of weld and sizes of weld.  The guidance also includes details of splice connections.  Diagrams are provided to assist in the installation process (shown right). These types of repairs can adequately restore strength and stiffness and transfer loads from the super structure to the foundation. 

Major maintenance, which is considered to be the most costly type of maintenance due to the extent of damage, is applied to correct and restore the strength of the pile structure and includes adding supplemental piles for support.

Studies also noted techniques for assessing timber pile condition, which include visual assessment, probing and picking, moisture measurement, sounding, stress wave devices, drill resistance devices, core boring and preservative retention analysis. However, any single method may give an incomplete or inaccurate assessment of the given substructure element; therefore, using multiple assessment methods to evaluate a given structure is recommended (Iowa 2012).

ABOUT THIS SUMMARY Implementation of effective timber pile treatment, repair and assessment techniques can support the protection and strengthening of structures and extend their life expectancy, enhance user safety and reduce costs. The Final Reports referenced throughout this summary are available upon request.  Please send inquiries to sptc@ou.edu.

The Southern Plains Transportation Center is a consortium of eight universities in U.S. Department of Transportation Region VI: the University of Oklahoma, Oklahoma State University, Langston University, University of Arkansas, University of New Mexico, Louisiana Tech University, University of Texas at El Paso and Texas Tech University.

The SPTC provides a unique opportunity through multi-institutional initiatives to develop comprehensive, cost-effective, and implementable solutions to critical infrastructure issues facing the transportation systems of the region and the nation, and to prepare transportation professionals for leadership roles through Research, Leadership, Collaboration, Education, Outreach, Tech Transfer and Workforce Development activities.

 

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Other Publications  

University Transportation Center Program, Design of Integral Abutment Bridges for Extreme Climates - September 2015

OU School of Civil Engineering and Environmental Science, Communique - Summer 2014 (see pg. 14)