MPC
Research Projects (2008-09)

Identifying Number

MPC-275

Project Title

Field Application of Z-Spike Rejuvenation to Salvage Timber Railroad Bridges, Year 3

University

Colorado State University

Project Investigators

Richard Gutkowski, Don Radford, and Jeno Balogh

Description of Project Abstract

The U.S inventory of railroad bridges includes many long existing timber trestle railroad bridges of the open deck timber trestle type. As many are five decades old or older, 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. 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 top of the member but 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 similar or higher recovery of stiffness is possible for intentionally badly damaged members of timber trestle member chord. More recently, Forsling at al. (an MPC Report has been submitted but is not yet in print) 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.

The Burlington Northern-Sante Fe (BNSF) railroad recently contacted the CSU researchers. In Texas, their field engineers have 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 and that work is ongoing. Shear spiking has ensued on the first of six four-ply chord members, each having varying degree of significant damage such as shear type horizontal shear-type cracking. The first chord member has been partially spiked (about ¼ of the full spiking plan) and already exhibits a 140% increase in flexural stiffness under applied load, compared an initial load test before shear spiking. This is consistent with (even surpasses) the work of Burgers et al. and Forsling et al. indicating that members in poor condition can be significantly rejuvenated or repaired by shear spiking. Based on the prior MPC reports and verbal information on this most recent development the Association of American Railroads has keen interest in this technology, particularly as applicable to bridges on short line railroad lines.

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 Approach/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 chords of selected bridges will be load and retested in the field for stiffness levels before and after adding the shear spikes, likely in sequential increments.

Tentatively, the work plan consists of:

• Task 1 - TTIC will work with various railroads to identify candidate bridges for shear spiking. Candidate bridges will be based on degree of degradation and location on short line railroad sites where interest and need appears to be prevalent.
• Task 2 - One or two sites or possibly two nearby bridges at the same location are the target, but depends upon the circumstances encountered. A low number of spans is desired, as one factor.
• Task 3 - The bridges will be instrumented for automatic, electronic displacement data acquisition, e.g. by an in place data logger with sufficient acquisition rate and total time capability connected to potentiometers.
• Task 4 - Prior to shear spiking, an attempt will be made to record data for periodic, selected actual trains passing over the bridge. Trainloads would need to be somewhat consistent, such as in the case of coal cars, which more or less have very narrowly varying total weight. The AAR can assist in determining when such trains (not necessarily coal cars) will be passing over the bridge.
• Task 5 - A controlled test under a fixed known car load, likely a locomotive positioned on the bridge, will then be conducted, before any shear spiking.
• Task 6 - The controlled test loading will then be repeated at selected stages of the shear spiking process, to be determined by the extent and sequence of shear spiking involved, not known until the bridges are selected and extent and dispersion of deterioration/damage is observed, and the time element to cure the adhesive after each spiking increment. A balance between the overall time duration needed and repeated availability of a load car or locomotive is a main consideration.
• Task 7 - Displacement data will then be collected automatically over time, for actual trains passing over the bridge.
• Task 8 - Results of the before and after loadings will be examined to assess the effectiveness of the shear spiking on overall chord/bridge stiffness.

NOTE: Likely sites could include a BNSF site in Texas and/or a short line location within Colorado, proximate to either the TTIC or CSU or both.

MPC Critical Issues Addressed by teh 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 Research

The applicability of the shear spike methodology in the filed 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, long lasting, 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. 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-reinforced composites. It is evident that an alternative methodology being used by the BNSF railroad is not proving highly viable. If, as anticipated, field load tests using the shear spike approach continue to show the highly successful outcomes seen in the laboratory, there is clear interest to expand the field studies to other sites in a future project.

Technology Transfer Benefits

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. attending. An MPC technical report will be produced on the conduct and outcomes of the work.

Time Duration

July 1, 2008 - June 30, 2009

Total Project Cost

$41,196

MPC Funds Requested

$32,771

TRB Keywords

Fiber reinforced composites, field load tests, railroad bridges, rejuvenate, shear spike, timber

References

MPC Reports mentioned in the proposal, plus:

• Radford, D., D. Vangoethem, R. Gutkowski, and M. Peterson. “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, “Composite repair of timber structures.” Construction and Building Materials, Elsevier Publications, 16 (2002) 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, Repirs 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.
• R. M. Gutkowski, TJ Schilling, J. Balogh and D. W. Radford. “FRP Z-Spike Repairing of Wood Railroad Crossties.” Accepted for publication, Journal of Structural Engineering, ASCE, Reston, VA.
• T. A. Burgers, R.M. Gutkowski, J. Balogh, and 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.
• Travis A Burgers, Richard M Gutkowski, Jeno Balogh and Donald W. Radford, “Repair of Full-Scale Timber Bridge Chord Members by Shear Spiking.” Accepted for publication, Journal of Bridge Engineering, ASCE, Reston, VA.