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Research Projects (2009-10)

Identifying Number


Project Title

Field Application of Z-Spike Rejuvenation to Salvage Timber Railroad Bridges, Year 4


Colorado State University

Project Investigators

Richard Gutkowski, Don Radford, and Jeno Balogh

Description of Project Abstract

Numerous existing railroad bridges are old (five decades or more) timber trestle railroad bridges of the open deck timber trestle type. They are now encountering much higher trainloads than when they were initially constructed. Increased axle loads due to heavier single cars and double stack cars have significantly raised the needed stiffness and load capacity of the bridges. Open deck timber trestle bridges have multi-ply (multi-stringer) chords as their primary superstructure component. Stringers involved have short span distances, are relatively deep, and experience high magnitude moving point (axle) loads. Stringer stiffness largely depends on mid-depth horizontal shear stress integrity. Failed members can experience major shear cracking along the mid-depth and further crack elsewhere if loads continue to pass over. Others crack simply due to weathering over the years or from exposure to flood waters and then drying. To repair or rejuvenate such members, it is necessary to restore the shear transfer across cracked or split areas.

Fiber-reinforced plastic (FRP) and other such composites are extremely popular for infrastructure and in situ infrastructure repair, especially concrete members (columns and beams) and to a lesser extent, timber members. Common approaches are fiberglass wrap (bandages) or adding reinforcing plates (patches) to the sides of members. Material costs alone make these approaches relatively expensive and leave an unsightly appearance. These techniques can also require that the members be removed from the bridge for repair to be made, which is the case and is especially difficult for multi-ply chords of timber trestle railroad bridges. The FRP composites also degrade with time due to weather exposure. For timber, "shear spiking" (adapted from "Z-spiking," a construction method used in the aerospace industry) is emerging as a viable alternative to the above techniques for application to timber bridge members. Shear spikes are composite rods inserted from the top or bottom of the member into pre-drilled holes and injected adhesive bonds them to the wood. They tighten the member by restoring force transfer at material separations to restore overall stiffness and add horizontal shear resistance, among other benefits. Shear spiking does not require member removal and the repair is not exposed to weather. In timber railroad bridges, an added advantage is installation into the tops of the members, however methods can be developed for insertion from the bottom.

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 railroad 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 by Burgers et al.) shows significant recovery of stiffness is possible for intentionally badly damaged members of timber trestle member chord. Gutkowski and Forsling (see MPC Report No. 07-190) examined modest cycle repeated load on intentionally damaged individual chord members. 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, with cyclic loading showing modest to no effect on the stiffness.

In early 2008, the BNSF railroad contacted the researcher regarding the shear spiking studies. In Texas, their field engineers had been attempting repairs on in place, damaged stringers of trestle bridges by use of mechanical connectors. Initial indications were the method was not proving successful. Hence, they were interested in cooperating with CSU to explore the shear spike technology for some of these members and that proceeded. Members removed from actual field bridges were sent to CSU for laboratory tests after implementation of shear spiking. Shear spiking ensued on two badly damaged chord members, each having horizontal shear-type cracking. Each chord member was incrementally shear spiked and load tested after each increment to assess the increase in stiffness. The first chord member exhibited a 267% increase in flexural stiffness under an applied load, compared an initial load test before shear spiking. The stiffness of the second member increased 292%. This is consistent with (even surpasses) the work of Burgers et al. and Forsling et al. indicating that members in poor condition due to use and exposure can be significantly rejuvenated or repaired by shear spiking (see Miller at al. MPC Report No. 08-208). The shear spiking technology was also featured in the July issue of Railway Age magazine, which is distributed to the railroad industry nationwide.

Based on the prior MPC reports and a meeting about the outcomes with bridge engineering and safety staff, the Association of American Railroads has keen interest in this technology, particularly as applicable to bridges on short line railroad lines. A four span bridge on the Kyle Railroad in Colorado has been identified for potential pilot testing of the effectiveness of shear spiking under actual train loads. Determination of the logistics needs of the experimental program has been initiated. This bridge is longer than and requires more material, time and effort than initially anticipated. It was also indentified by the railroad staff toward the end of the current project necessitating more time to arrange and conduct the shear spiking and load test. Lastly, all aspects of the project and its timing must be approved by the railroad agencies and owner involved and conducted with their cooperation and presence on site

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 in actual in place bridges.

Project Approaches/Methods

In the continuation phase of the project, the PIs will work jointly with Transportation Technology Center, Inc. (TTIC) of the Association of American Railroads (AAR), located in Pueblo, Colorado, to proceed to pilot studies concerning the application of shear spiking in the field. The damaged chord members of the bridge will be load tested in the field for stiffness levels before and after adding the shear spikes.

The anticipated work plan consists of:

  1. A reconnaissance site visit will be made to assess the condition of damaged members of and make a tentative plan for the extent of shear spiking needed.
  2. A work and time plan will be developed for the field activities of shear spiking, instrumentation and data collection for needed shear spiking will be determined.
  3. The bridges will be instrumented with potentiometers for displacement data acquisition by an appropriate data logger (with sufficient acquisition rate and total time capability) connected to potentiometers.
  4. Loading will be actual trains passing over the bridge, and are known to be a locomotive and a stream of grain cars, which more or less have very narrowly varying total weight. The AAR and TTCI will assist in determining when such trains will be passing over the bridge.
  5. A controlled test under a passing line of locomotive and cars load will then be conducted, before any shear spiking.
  6. The controlled test loading will then be repeated at planned stages of the shear spiking process, to be determined by the extent and sequence of shear spiking involved, the time element to cure the adhesive after each spiking increment and the scheduled times of passing trains.
  7. Results of the before and after loadings will be examined to assess the effectiveness of the shear spiking on overall chord/bridge stiffness.

MPC Critical Issues Addressed by the Research

This work addresses USDOT Strategic Goal - Infrastructure Management (and Environmental Stewardship): (1) Improved Infrastructure Design, (2) Infrastructure Longevity, and (3) Infrastructure that Minimizes Environmental Impacts. It addresses CSU Critical Research Areas: (5 Low-Cost Safety Improvements, (16) Infrastructure Longevity, and (17) Environmental Impacts of Infrastructure

Contributions/Potential Applications of the Research

The applicability of the shear spike methodology in the field is a tangible result of the project. As the shear spikes are made from commercially available rods, are easily installed and imbedded in the member, they are invaluable as a very low cost, repair. In many installations, timber trestle 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. 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-reinforced composites. It is evident that an alternative methodology being used by the BNSF railroad is not proving highly viable. If successful, as is anticipated, the project will demonstrate the effectiveness on an actual railroad bridge leading to invaluable, affordable technology for repairing aged timber bridges on short line railroads. It should then drive the interest to expand the field studies to other sites.

Technology Transfer Activities

The rejuvenated bridge itself is a direct applied product of the R&D done to this point. A detailed technical report will be prepared for submittal to the AAR. This work is of value to the timber roadway bridges as well. A TLN teleconference about the field study will be conducted with interested railroads, State DOTS, County Engineers, Municipal Public Works Directors, etc. invited to attend. An MPC technical report will be produced on the conduct and outcomes of the work.

Time Duration

July 1, 2009 through June 30, 2010

Total Project Cost


MPC Funds Requested


TRB Keywords

Fiber Reinforced Composites, Field Load Tests, Railroad Bridges, Rejuvenate, Shear Spike, Timber


MPC Reports mentioned in the proposal plus pertinent other publications.

  • Radford, D.W., Peterson, M.L. and VanGoethem, D. "Composite Repair of Timber Structures", Report No. 00-112, Mountain Plains Consortium, North Dakota State University, Fargo, ND.
  • Schilling, TJ T., Gutkowski, R.M. and Radford, D.W. (2004)"Composite Repair of Railroad Crossties through the Process of Shear Spiking", Report No, 04-163, Mountain Plains Consortium, North Dakota State University, Fargo, ND.
  • Burgers, T.A., Gutkowski, R.M., Radford, D.W. and Balogh, J .(2005) "Composite Repair of Full-Scale Timber Bridge Chord Members through the Process of Shear Spiking", Report No. 05-173, Mountain Plains Consortium, North Dakota State University, Fargo, ND.
  • Gutkowski,R.M. and Forsling, H. (2007) "Durability and Ultimate Flexural Loading of Shear Spike Repaired Large-Scale Timber Railroad Members" , Report No. 07-190, Mountain Plains Consortium, North Dakota State University, Fargo, ND.
  • Miller, N.J, Gutkowski,R.M., Balogh, J., Radford, D.W. (2008) "Z-Spike Rejuvenation to Salvage Timber Railroad Bridge Members", Report No. 08-208, Mountain Plains Consortium, North Dakota State University, Fargo, ND.
  • Radford, D., D. Van Goethem, R. Gutkowski, and M. Peterson. (2001) "Composite Repair of Timber Bridges," Proceedings, 9th International Conference and Exhibition in Structural Faults and Repair - 2001, ASCE, London, UK.
  • D.W. Radford, D. Van Goethem, R.M. Gutkowski and M.L. Peterson, (2002) "Composite repair of timber structures." Construction and Building Materials, Elsevier Publications, Vol. 16 417-425
  • D. Radford, R. Gutkowski, D. Van Goethem, M. Peterson. (2003) Pultruded composite shear spike for repair of timber members. STREMAH 2003, Eighth International Conference on Structural Studies, Repairs and Maintenance of Heritage Architecture, Halkidiki, Greece, Wessex Institute of Technology, UK. pp. 737-750
  • R. Gutkowski, J. Balogh, M. Wieligmann, C. Rogers and P. Haller. (2003) "Analysis and Testing of Composite Wood-Concrete Floor/Deck Systems". Proceedings of CMEM 2003, Eleventh International Conference on Computational Methods and Experimental Measurements, Halkidiki, Greece, WIT Press, Wessex Institute of Technology, UK.
  • R.M. Gutkowski, D. Radford, and T. Shilling. (2006)"Composite Repair of Railroad Cross-Ties by Shear Spiking." Proceedings, 11th International Conference and Exhibition in Structural Faults and Repair -2006, Edinburgh, Scotland.
  • T. Burgers, R.M. Gutkowski, J. Balogh, D. Radford, 2006, Shear Spike Repair of Timber Railroad Bridge Chord Members, Proceedings, IABSE Symposium on Responding to Tomorrow's Challenges in Structural Engineering, Budapest, Hungary.
  • R. M. Gutkowski, TJ Schilling, J. Balogh and D. W. Radford. (2008) "FRP Z-Spike Repairing of Wood Railroad Crossties." Journal of Structural Engineering, ASCE, Reston, VA., Vol. 134, No. 2, pp. 248-257.
  • Burgers, T.A., R.M. Gutkowski, J. Balogh, and D.W. Radford, 2008. Repair of Full Scale Timber Bridge Chord Members by Shear Spiking, Journal of Bridge Engineering, ASCE, Vol. 13, No.4. Reston, VA.
  • R.M. Gutkowski, TJ T. Schilling, J. Balogh, and D.W. Radford, 2008. FRP Z-Spike Repairing of Wood Crossties, Journal of Structural Engineering, ASCE. Vol. 134, No. 2, pp. 248-257.
  • H. Forsling, R. M. Gutkowski, J. Balogh, D. Radford, In Review, Load Tests of Damaged Railroad Timber Stringers Repaired by Shear Spiking, Journal of Bridge Engineering. ASCE. Reston VA.
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