MPC
Research Projects (2007-08)

Identifying Number

MPC-276

Project Title

Use of Salvaged Utility Poles in Roadway Bridges, Year 2

University

Colorado State University

Project Investigators

Richard M. Gutkowski and Jeno Balogh

Description of Project Abstract

Nationwide, many bridges are in a state of agedness, disrepair and/or structural or functional deficiency. In rural settings, county jurisdictions have numerous inventoried bridges in such condition but very limited funds for repair/replacement. Only a very small proportion can be addressed annually. Secondary roads and rural arterials are characterized by many short span bridges. Numerous bridges shorter than 20 ft long exist as well, especially over streams and ditches on agricultural land, or in state and national parks. Sub-20 ft bridges are not eligible for federal bridge infrastructure funds, so are frequently, if not commonly, neglected. Thus, innovative low material cost bridges which are readily built by unskilled labor are a boon to small rural jurisdictions and on park lands.

This project involves conceiving and configuring a composite bridge comprised of concrete and wood utility poles. The ease of construction will make the bridge a feasible alternative for use in short to medium span bridges in rural secondary road settings and off highway gravel roadways. The concept is to use of utility poles as either stringers or a solid deck beneath a conventional reinforced concrete bridge deck. Frequently, wood utility poles are replaced as part of secondary road reconstruction, such as widening roadways. Many of the removed poles are still sound structurally and usable. Instead of discarding these members it is worthwhile to consider viable alternatives uses. Since utility poles are commonly 30-60 ft long, sometimes longer, they can be a low cost recycled resource for short and medium span bridge construction. Conceiving such uses in which salvaged utility poles are used enables a large supply of poles to be re-used. Indeed, the PI readily accomplished a donation of the utility poles from the utility company for use in Year 1 of this project, suggesting a possible future low cost or no cost material source.

Project Objectives

The objective of this project is to develop the configuration of a roadway bridge using an innovative layered concrete-wood concept and test pertinent beam specimens under ramp loading, repeated loading and creep loading.

Two phases are anticipated:

• Year 1 – Develop the concept by preliminary configuration (via computer modeling) and construction of narrow beam specimens and subsequent laboratory load tests under ramp loading and repeated loading.
• Year 2 – Extend the concept to a wider (possibly up to full bridge width) specimens for laboratory (or possibly field) load testing under ramp and creep loading.

Year 1 is nearing completion. Year 2 is being proposed as a continuation project.

Project Approach/Methods

The laboratory work in Year 1 has been completed and consisted of the beam testing mentioned above. An M.S. thesis is in progress and a technical report will be then prepared.

Year 1 – To make the specimens (two were used), the tapered utility poles were placed in alternating directions at slight incline to incorporate camber and topped with a structural concrete layer. A 30 ft span was investigated. A solid layer of poles, i.e. several poles side by side, is the configuration being examined A degree of composite action of the layered system was anticipated from a) natural taper of the members leading to a sloped shear/bearing surface along the entire length, and b) addition of an interlayer connection. The initial trial load test program, specimens with an interlayer interconnection using a notch and dowel anchor were used but no lateral connection of the locks other than via the concrete layer. Elementary structural analysis was used to size the members, but a rigorous computer model is eventually needed and some work has been initiated on that aspect. Test results are still being processed, but it was generally evident that the system was considerably stiffer and stronger than expected. Failure was also progressive leading to a sort of ductile, not brittle, overall deflection behavior without collapse. One specimen maintained camber under dead load, one did not.

A literature review was conducted to assess other structural and cost-effective approaches for interconnection. Only work in Switzerland was found as related to use of round poles in wood-concrete bridge construction, with an actual bridge having been constructed. A notched shear key-anchor type of interlayer connection was incorporated. This detail has been examined in past CSU research on wood-concrete systems not involving utility poles, and it performs well. However, potential alternatives were also identified in work of other researchers included in the literature review. In Germany, researchers have examined notched shear key interconnection with and without mechanical devices to anchor the layers in the laboratory, but or floor systems, not bridges.

In a recent MPC supported workshop (apart from this project) held at CSU for county road and bridge engineers, international experts in wood-concrete floor and bridge construction gave summary presentations of their research and applied work. Researchers participated from Brazil (experience in use of low quality salvage material), New Zealand (rigorous computer modeling of long-term effects, such as creep and shrinkage, and Portugal (interconnection methods and computer models) and Sweden (prefabricated floor systems). Each of the researchers employs different inter-connection methods than each other, some examining a notched shear/key but without an anchor. Also, their applications are mostly not for bridges. Portuguese researchers have implemented a wood-concrete bridge construction in a successful pilot project on a forestry logging road of about 55 ft span. PI R. Gutkowski visited that bridge site to observe the completed bridge and discuss its performance with the research team. However, utility poles were not used and the wood layer was not a solid layer. Instead, spaced individual glue-laminated timber beams were used as the wood component.

Based on developments to date, the anticipated tasks in Year 2 are:

• Task 1 – Using elementary computer software developed in Year 1, initially determine trial dimensions for wide beam specimens in a shorter span, perhaps 25-27 ft, due to camber considerations. Specimens would have a solid wood layer of poles configuration and with interlayer connection.
• Task 2 – Develop a needed rigorous computer modeling for short term and long term effects of loading and exposure conditions (creep, shrinkage etc.) for wide beam specimens. This will be achieved by accessing available software from other researchers and adapting it to the problem at hand.
• Task 3 – Apply the rigorous software to the trial specimen and adjust configuration and dimensions if needed.
• Task 4 – Compare the performance of the various Specimen sets (2-3 beams per set) using load testing under short term and long term loading. Long term loading would be in exposed conditions for approximately 6-9 months, for purposes of this project. The specimens would likely be left in place for periodic monitoring beyond the term of this project.
• Task 5 – Develop an MPC research report on the findings.

Contributions/Potential Applications of Research

Much of rural America has low tax base communities dependent on agricultural economies and related freight and shipping industry. State and federal parks face tight budgets for daily operations and maintenance overall and especially for road and bridge maintenance and construction. Developing low cost, easily constructed bridge systems for short to medium span situations on secondary roads is helpful in these situations. As stated above, examples of recently constructed layered w/c bridges using round poles exist in Switzerland, including one with round poles. Also, the 55 ft span w/c stringer bridge was built with glue-laminated wood beams in Portugal. These successful overseas examples lend credibility to the above concept as being practically plausible, feasible and economical. Implementation of an actual field bridge project is envisioned, but as a task pursued subsequent to this project with either a local or county governmental jurisdiction or within the state or national park system. PI R. Gutkowski has achieved the former in past MPC projects on innovative bridge construction for rural/mountain roads by cooperation with a County entity. The USDA-Forest Service Rocky Mountain Research Station is situated on the CSU campus and offers links to possible parties interested a future field verification project.

Technology Transfer Activities

An innovative bridge concept will be configured. A written MPC report and TLN teleconference seminar are planned for dissemination of the results. A potential future pilot field bridge construction is envisioned (with presently undetermined timing) after this project concludes.

Time Duration

July 1, 2007 - June 30, 2008

Yearly and Total Project Cost

$42,976 Total $97,561

TRB Keywords

Bridges, concrete, highway, wood, utility poles