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Research Projects (2007-08)

Identifying Number


Project Title

Z-Spike Rejuvenation to Salvage Timber Railroad Bridge Members, Year 2


Colorado State University

Project Investigators

Richard Gutkowski, Don Radford, and Jeno Balogh

Description of Project Abstract

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 techniques require that the members be removed from the bridge for repair to be made. They also degrade with time due to weather exposure. "Shear Spiking" (adapted from "Z-spiking," a construction method used in the aerospace industry) is a viable alternative to the above techniques for application to timber bridge members. Shear spikes are composite rods normally inserted from the bottom of the member into pre-drilled holes and an injected adhesive bonds them to the wood. They tighten the member to restore overall stiffness and add horizontal shear resistance, among other benefits. This method does not require member removal and the repair is not exposed to weather. In timber railroad bridges, an added advantage is installation into the top of the members.

Researchers at Colorado Sate University (CSU) have been very active in pursuing this adaptation in the setting of rehabilitation of timber railroad bridge members. A past MPC research project ( see MPC Report No. 00-112, by D. Radford et al) explored an innovative alternative to fiberglass wrap and patch repair techniques. A "shear spike" insert approach was tried on small wood members (based on 2 x 4 nominal sizes) and show promising results. Results of the study show substantial rejuvenation. In some cases repairs to split members resulted in strength and stiffness comparable to undamaged control specimens. A subsequent completed laboratory project (see MPC Report No. by TJ Schilling et al) addressed application to larger timbers (using rail road ties as a medium with similar encouraging results). Repairs improve stiffness by an average of 58%. A recent project (see MPC Report No. 05-173) shows significant recovery of stiffness is possible for intentionally badly damaged members of timber trestle member chord. These members were newly fabricated members donated by the Transportation Technology Center, Inc. of the Association of American Railroads for a past MPC project. Additional new members with different types of intentional severe inflicted damage were load tested under initial ramp, repeated loading and failure loading with indications of similar high degree of success. An MPC Report has been submitted but is not yet in print. The Burlington Northern-Sante Fe (BNSF) railroad recently contacted the researchers. In Texas, their engineers have been attempting repairs on in place damaged stringers of trestle bridges by use of mechanical connectors. Initial indications are the method is not proving successful. Hence, they are interested in cooperating with CSU to explore the shear spike technology for some of these members. Members are to be removed from actual field bridges and sent to CSU for laboratory tests after implementation of shear spiking.

Project Objectives

The objective is to examine the effectiveness and performance of installing composite shear spikes to salvage damaged and/or deteriorated full size timber trestle bridge chord members.

Project Approach/Methods

Past research in related projects involved load testing tested for flexural stiffness improvement as shear spikes were added and proved highly successful. In the current phase of the project flexural tests are being conducted on a limited number of actual aged or deteriorated timber stringer members obtained from rail yards in Colorado and Wyoming. Some of these are 50+ years old. As a continuation, additional damaged, but potentially salvageable, stringer members will be acquired via the BNSF railroad. This is augmentation of the original scope in terms of numbers of specimens involve. Each of these stringer will be incrementally reinforced with shear spikes and load tested after each increment of spiking. Effect on stiffness will be observed and once benefits taper off for added shear spikes a load test to destruction will be conducted to determine ultimate load capacity. The number of members is potentially large. Thus the potential exist to compare non-reinforced members vs. mechanically reinforced members vs. shear spike reinforced members. Also, some members may have already been repaired by the mechanical connector approach. These specimens will be retested for stiffness before and after adding the shear spikes and then loaded for stiffness measurements and then to failure.

Technology Transfer Activities

A TLN teleconference seminar on all past work will be conducted to disseminate the results of the work. An MPC technical report will be produced on the conduct and outcomes of the work.

Contributions/Potential Applications of Research

The shear spike methodology is a tangible result of the project. As the shear spikes are made from commercially available rods, easily installed and imbedded in the member, they are invaluable as a low cost, long lasting, repair. In many installations, timber railroad bridges are 50+ years old but still necessary for daily operation. It is increasingly difficult to obtain large size timber members needed for repair and upgrading such bridges. Hence, economic repair of bridges is vital as an alternative to replacement of members. This project shows promise of leading to invaluable, affordable technology for repairing aged timber bridges on short and main line railroads and on secondary roads. It is particularly critical to maintain safety and economic vitality of the nation's railroad infrastructure in rural areas. These vital links for the movement of agricultural commodities and other freight often depend on aging bridges. The research effort will assist the bridge owners by providing a fundamentally new, more structurally effective, substantially low cost alternative to presently limited repair methods based on fiber composites. It is evident that an alternative methodology being used by the BNSF railroad is not proving highly viable. If laboratory tests comparing with the shear spike approach continue to be successful, there is clear interest to try it in the field in a future project with the BNSF railroad. The PIs will continue to foster such a field pilot project, albeit not included as a known aspect at this time.

Time Duration

July 1, 2007 - June 30, 2008

Yearly and Total Project Cost

$26,047 Total $80,340

TRB Keywords

Fiber reinforced composites, railroad bridges, rejuvenate, shear spike, timber

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