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MPC
Research Projects (2001-02)

Identifying Number

MPC-214

Project Title

Pultruded Composite Shear Spike for Repair of Large Timber Members

University

Colorado State University

Project Investigator

Don Radford, Professor
Dept. of Mechanical Engineering
Colorado State University
(970)491-8677 or Fax (970)491-2788
don@engr.colostate.edu

Bryan A. Hartnagel, Assistant Professor
Dept. of Civil Engineering
Colorado State University
(970)491-4660 or Fax (970)491-2788
bryanh@engr.colostate.edu

Dr. Richard M. Gutkowski, Professor
Dept. of Civil Engineering
Colorado State University
(970)491-8291 or Fax (970)491-2788
gutkowsk@engr.colostate.edu

External Project Contact

N/A

Project Objective

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

Project Abstract

In many installations, timber railroad bridge 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 recent MPC research project 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 2 x 2 and 2 x 4 sizes) and show promising results for application to full-size bridge members. 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 results. (See MPC Report No. 00-112, by D. Radford et al). In some cases repairs to split members resulted in strength and stiffness comparable to undamaged control specimens.

Task Descriptions

During this project the primary goal is to determine whether the level of shear spike rejuvenation achieved during testing of small, scale specimens, based on 2x4's, can be repeated at a larger scale. These larger scale tests will make use of timbers as used in railroad bridge construction. The most readily available timber is the railroad tie. (Nominal dimensions of 8"H x 7"W x 100"L allow a test aspect ratio (11:1) similar to that used in the small scale tests.) Therefore, it is planned to procure used ties in various states of degradation. All specimens will be tested for stiffness, in the as-received state, using a hydraulic test frame in CSU's Structures Laboratory. Specimens will be graded by stiffness relative to baseline, unused, specimens. Shear spike rejuvenation will be performed in a stepwise fashion similar to the approach used for the small scale specimens and described in MPC Report No. 00-112. Pultruded fiberglass shear spikes of a diameter of approximately 0.5" are presently planned. An approach to inserting this size shear spike will need to be developed, and in at least some cases, the shear spikes will be inserted using an instrumented hydraulic ram to determine the insertion force. Also, in this project, a preliminary evaluation of the effect of resin type and viscosity, on the beam performance and on the injection ability, will be undertaken. In the previous research, small scale specimen testing used epoxy resin; however, both polyester and vinylester resins are less expensive and are generally of lower viscosity. Thus, this project will generate insight into the practical aspects of implementing the fiberglass shear spike concept in the field.

  • Task 1 – Procure timber specimens
    1. 20 damaged specimens
    2. 5 undamaged specimens
  • Task 2 – Procure fiberglass pultruded rod for shear spikes.
  • Task 3 – Procure resin(s)
  • Task 4 – Assemble a 4-point bend test fixture of appropriate size.
  • Task 5 – Assess level/location of physical damage for each specimen.
  • Task 6 – Perform stiffness tests on unused and used specimens in the as-received condition to determine baseline values.
  • Task 7 – Perform stepwise rejuvenation and stiffness evaluation on damaged beams.
    1. ~ 8 - 10 specimens rejuvenated using shear spikes
    2. ~ 3 - 5 specimens repaired with only resin
  • Task 8 – At completion of rejuvenation, test specimens to failure, recording load and deflection to enable determination of strength and strain to failure.
  • Task 9 – Evaluate results of rejuvenation of scaled-up beams.
  • Task 10 – Compare findings with prior "small-scale" results (2x2's and 2x4's).
  • Task 11 – Report

Milestones, Dates

The milestones for this project relate directly to the tasks specified in the previous section.

  • Starting Date: July 1, 2001
  • Plan test setup: September 1, 2001
  • Test frame assembled and checked: November 1, 2001
  • Complete procurement of timber specimens: December 1, 2001
  • Complete procurement of pultruded fiberglass rod: December 1, 2001
  • Complete procurement of resin(s): January 1, 2002
  • Complete assessment of level/location of physical damage: January 15, 2002
  • Complete stiffness measurements in the as-received state: February 1, 2002
  • Complete rejuvenation and stiffness testing: May 15, 2002
  • Complete failure tests of rejuvenated specimens: June 1, 2002
  • Complete evaluation & reporting: June 30, 2002
  • Ending Date: June 30, 2002

Yearly and Total Budget

This is an annual project. The attached budget is for July 1, 2001-June 30, 2002. The amount requested is $25,218 USDOT and is augmented by $21,908 as a CSU match. The total budget is $47,126.

Student Involvement

Funds are included for support of a graduate research assistant for 6 months plus hourly student (graduate or undergraduate) student labor.

Relationship to Other Research Projects

The applicability of the innovative technology to small wood members was examined as a basic research study in a past Year 11 MPC project, namely MPC-161 Composite Repairs of Timber Structures. Successful results are an incentive to examine application to the larger members for practical application.

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 telecommunications network after completion of the project. Publicity about all of the MPC projects is available through the MPC web site maintained at NDSU.

If successful, as anticipated, there is a large inventory of deficient bridges available in Region 8 for possible field application. There are numerous railroad bridges, and the 2nd PI has conducted several timber trestle projects with the Association of American Railroads, 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, low cost alternative to presently limited repair methods based on fiber composites.

TRB Keywords

Fiber composites, timber, bridges, railroad, repair

NDSU Dept 2880P.O. Box 6050Fargo, ND 58108-6050
(701)231-7767ndsu.ugpti@ndsu.edu