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Research Projects (2004-05)

Identifying Number


Project Title

Pultruded Composite Shear Spike for Repair of Timber Bridge Members


Colorado State University

Project Investigator

Dr. Richard Gutkowski
Colorado State University

External Project Contact


Project Objective

The objective of the project is to examine the structural effectiveness and performance of pultruded composite shear spike reinforcement in full-size timber bridge members.

Project Abstract

In many installations, timber railroad bridges are 50-100 years old, but still necessary for daily operation. Numerous timber based highway bridges exist too, primarily of secondary roads. The latter are often in jurisdictions where new construction funds are very limited. Hence, economic repair of bridges is vital to the nation's infrastructure. Fiber reinforced composites are extremely popular for infrastructure and in situ infrastructure repair. Common approaches are fiberglass wrap (bandages) or adding reinforcing plates (patches) to the sides of members. These require that the members be removed from the bridge for the repair to be made. They also degrade with time due to exposure. Alternatives to these techniques that do not require member removal and are embedded in the member are invaluable to low cost, long lasting repair.

A prior MPC research project (MPC-161) explored an innovative alternative to fiberglass wrap and patch repair techniques. A "shear spike" insert approach was tried on small wood members (based on nominal 2x2 and 2x4 sizes). Shear spikes are composite rods inserted from the bottom to the top of the beam, in situ. Pre-drilled holes and an injected adhesive are used to bond the spikes to the wood. They are produced by pultrusion with principal fiber content being in the axial direction. They serve to tighten the member to restore overall stiffness and add horizontal shear resistance, among other benefits. Results of the study showed a substantial rejuvenation result. In some cases repairs to split members resulted in strength and stiffness comparable to undamaged control specimens.

Subsequent work in another MPC project (MPC-214) has shown the method to be highly effective on timber railroad cross-ties as an example of performance in larger members. Thirty five cross-ties were graded low, medium, and high quality sets on the basis of physical characteristics and original measured flexural stiffness. The average improvement in stiffness after shear spiking with cross-ties was 58 percent.

In a past MPC project (MPC-138), the researchers conducted laboratory load tests on full-size timber railroad chords used in open-deck timber trestle bridge construction. The material used was salvage material from the field. In this project, one of these bridge chords will be reconstructed and load tested before and after shear spiking the members. Comparison of the results will allow an assessment of the effectiveness of this method of repair. This work also related to a past MPC project (MPC-137) on field load testing and strengthening of open deck, timber trestle railroad bridges, done in cooperation with the railroad industry.

Task Descriptions

  1. Aquire the shear spike materials
  2. Reconstruct the laboratory bridge chord specimen
  3. Conduct a non-destructive load test and measure deflection performance
  4. Install the shear spikes in a pattern determined on the basis of the past work on cross-ties
  5. Repeat the non-destructive load test and measure deflection performance
  6. Compare the results and assess the benefit of the shear spiking repair
  7. Compile and MPC report
  8. Present the findings to interested parties

Milestones, Dates

Starting Date: July 1, 2004
Ending Date: June 30, 2005

Yearly and Total Budget


Student Involvement

Funds are included for support of a graduate research assistant for six months plus hourly student labor.

Relationship to Other Research Projects

The applicability of the innovative technology to small wood members was examine as a basic research study in a past MPC project, namely MPC-161 Composite Repairs of Timber Structures. Work was continued on railroad cross-ties in a subsequent MPC project, namely MPC-214. Successful results are an incentive to examine application to an actual bridge chord as a precedent to possible adoption in actual field practice.

Technology Transfer Activities

The shear spike concept itself is a tangible application idea resulting from the project and has immediate application possibilities. Technology transfer will be via an MPC final technical report, a technical journal and/or conference paper submittal and an MPC research seminar over the TEL8 network after completion of the project.

If successful, there is a large inventory of deficient bridges nationwide and in the nearby region for possible field application. There are numerous railroad bridges, and the PI has conducted several timber trestle projects with the AAR, including field strengthening and evaluation. Although not included in this project, the Pis will seek to arrange a pilot field application to either a highway or railroad bridge in the future.

Potential Benefits of the Project

It is critical to maintaining safety and economic vitality of rural areas that the transportation infrastructure be safe and long lasting after repairs. This project shows promise of leading to an invaluable technology for repairing aged timber bridges on short and main line railroads and on secondary roads. These vital links for the movement of commodities and other freight often depend on aging bridges and rail. The research effort will assist the bridge owners by providing a fundamentally new, more structurally effective, much lower cost alternative to presently used repair methods based on fiber composites.

TRB Keywords

Fiber composites, shear spike, timber, bridges, railroad, repair

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