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Research Projects (2006-07)

Identifying Number


Project Title

Safety Factor Increase to Fatigue Limit States through Shear Spiking for Timber Railroad Bridge Rehabilitation


Colorado State University

Project Investigator:

John van de Lindt, CSU

External Project Contact


Project Objective

The research objectives for the proposed project are to (1) develop a realistic loading sequence along the length of timber bridge stringers using the spatio-temporal load equipment recently procured at CSU, (2) compute the change in safety factor for long-term realistic fatigue loading (e.g. 100,000 cycles) when shear spiking is used as a rehabilitation technique, and (3) compute the change in safety factor based on ultimate capacity using static tests.

Project Abstract

This project will demonstrate the effectiveness of shear spiking (technique already developed through a previous project). Many timber railroad bridges are deficient but it is too costly to replace them, hence inexpensive repair techniques are needed. The proposed project will provide the necessary documentation of the effectiveness of this newly developed mitigation technique under realistic loads using new equipment available from a National Science Foundation grant to Colorado State University. This will be accomplished through a series of spatio-temporal fatigue tests on stringers for both non-repaired and repaired. The timing and locations of the loading will be determined from influence line analysis of a typical freight train(s). The results will be used as leverage and/or proof-of-concept to approach the American Railway Association for additional funding.

Task Descriptions

There are numerous timber railroad bridges still in use across the United States, many of them in need of various levels of repair or replacement. Unfortunately, replacement is too costly considering the vast number of bridges in use. Many of these bridges are suffering from decay which significantly reduces their shear capacity. Bending moment is typically less of a problem because of the multiple supports of the stringers. Over the last several years, CSU has developed and demonstrated a shear spiking technique using 1 inch diameter FRP spikes inserted into the top of beams and secured with high strength epoxy. The system was tested under static load and found to be quite effective, increasing the strength beyond the design capacity. As with most new techniques, in order to apply the technique in-situ, a great deal of proof is needed to convince bridge owners (i.e. railroad) that shear spiking is not only an economically viable, but safe option in lieu of costly stringer replacement. Replacement not only results in significant construction costs but there is down time to consider. The investigators believe the necessary proof lies in demonstrating the increase in the safety factor under realistic loading conditions for both ultimate capacity and fatigue limit states. Thus, the work tasks include:

  1. Selection of stringer orientation for installation into the existing spatio-temporal load frame at CSU. This frame has seven dynamic actuators which will be oriented and used in load control to simulate the load effects (moment and shear) experienced by the stringer.
  2. Influence line analyses using train weight data to determine the load control signals to each actuator. This is the spatial portion of the loading.
  3. Development of the numerical algorithm to control the actuators. This will be based on tasks 1 and 2 above and requires the introduction of the trains speed. This is the temporal portion of the loading.
  4. Testing damaged-unrepaired and damaged-repaired bridge stringers in a spatio-temporal fatigue test, and testeing damaged-unrepaired and damaged-repaired bridge stringers under more significant loads (e.g. ~200 kips) to numerically estimate the safety factor to ultimate load for each based on codified levels. (This is primarily a year 2 activity, but is included for completeness).

The structural engineering laboratory at CSU is in a unique position to be able to perform spatio-temporal loading on bridge test specimens using a suite of seven dynamic actuators in a 30 ft x 20 ft x 18 ft steel test frame. This equipment was recently awarded to CSU in the form of a major research instrumentation (MRI) grant from the National Science Foundation and will be used during the experimental portion of the project.

Milestones, Dates

Starting Date: July 1, 2006
Ending Date: June 30, 2007

Yearly and Total Budget


Student Involvement

One graduate and one undergraduate research assistant

Relationship to Other Research Projects

Several MPC projects have been executed by Dr. Gutkowski and served to develop the specific technique and confirm the spiking technique for static loading. In addition, the spatio-temporal test frame is being built using funds from a major research instrumentation grant from the National Science Foundation.

Technology Transfer Activities

Outcomes will be presented in a seminar via the TLN videoconference system in its technology exchange series with regional transportation agencies. Publicity about all of the MPC projects is available through the MPC website at mountain-plains.org. Results will be presented at the 2008 meeting of the TRB and conventional academic information dissemination mechanisms (journal papers) will be used. In order to provide dissemination worldwide and showcase the MPC, a project website will be developed and updated monthly to allow interested parties to follow this research project as it progresses. There will be a mechanism for website visitors to sign up for special project announcements including viewing videos of portions of the testing. This may be able to serve as an example of a virtual discussion template for other projects.

Potential Benefits of the Project

The potential benefits of this research project are extensive. Shear spiking could be used on deteriorating bridges throughout the U.S. to provide a level of safety consistent with new and rehabilitated bridges, thus becoming a new, well-accepted, rehabilitation technique that is economically viable and proven. The deliverable for this project will be a final report detailing the increase in safety factor when shear spiking is utilized versus when it is not.

TRB Keywords

Fatigue strength, Fatigue tests, Trains, Shear Capacity, Shear Strength

NDSU Dept 2880P.O. Box 6050Fargo, ND 58108-6050