Research Projects (2001-02)
Experimental Thick-Deck Wood-Concrete Highway Bridge Construction
Colorado State University
Dr. Richard M. Gutkowski, Professor
Department of Civil Engineering
Colorado State University
(970)491-8291 or Fax (970)491-2788
Jeno Balogh, Visiting Scientist
Department of Civil Engineering
Colorado State University
(970)491-8524 or Fax (970)491-2788
External Project Contact
The objective is to configure and construct a prototype "thick deck" wood-concrete highway bridge and test it to failure in the laboratory.
Commonly, deteriorating wood bridge decks are completely replaced without consideration of a possible retrofit. This is likely due to lack of potential approaches to strengthen such decks. One approach to strengthening a wood bridge deck is to add a concrete deck layer and interconnect it to the wood deck. A prior MPC project showed this to be successful using a notched shear key/anchor detail tested in the laboratory under static loads. A need exists to examine field application.
A concrete overlay technique recently developed in Europe is used. It involves a unique, but readily done, interlayer connection method. While a mechanical connector is involved, it is not relied upon for interlayer shear transfer needed to affect the desired composite behavior. Instead, a notched shear key is utilized to rely on wood to concrete shear and bearing to achieve the interlayer force transfer. The mechanical connector serves to tighten the concrete to wood bearing surfaces after hydration drying of the concrete has taken place. It is not affected itself by curing of the concrete, as it is anchored into the wood by gluing or grouting.
A popular tourist community in Colorado has expressed interest in such new experimental bridge construction to achieve a significant traffic rerouting to improve mobility and relieve congestion. The low cost, ease of construction and "fit" of the bridge's appearance to the community character are motivations. However, the load capacity needed greatly exceeds that of the shorter span applications envisioned in the prior study, resulting in a "thick deck". Mechanically, ordinary decks and slabs are usually governed by "thin plate theory" (Kirchoff plate theory) because their depth/span ratio is such that only flexural deformations are pertinent. The depth/span ratio of the envisioned prototype is such that shear deformation is important, too. Thus, the system may be controlled by Mindlin plate theory, which accounts for shear deformation.
To proceed to any envisioned pilot field application it is imperative to examine ultimate strength for a "thick deck" as compared to the more slender decks previously examined. Fundamentally, the thick deck mechanics differ from a thin deck in mathematical modeling, too. Extrapolation of the findings for a thin deck specimen to the loads required in the field application (HS-20 loading) is high risk without a study of the underlying mechanics differences.
A bridge deck specimen is needed in each year of the two-year study. Computer based structural modeling based on applicable commercial software will be employed to configure the bridge specimens and predict capacity. Some non-destructive service load investigations of thicker beams (not decks) is ongoing as a pilot study, without MPC or other funding. A thick deck wood-concrete bridge can possibly be assembled from these salvaged beams specimens. Otherwise, a layered wood-concrete deck bridge will be constructed from new materials for the first deck specimen. The second specimen must and will be made from original materials.
Preliminary approximate analysis and the ongoing beam tests show the available test frame must be modified to sufficiently and safely apply the high failure loads required. This includes strengthening the test frame and actuator load restraint system. Static ramp load tests will be augmented to further assess structural behavior under low cycle repeated loading and to failure (Year 1) and high cycle repeated loading long term loading (creep) (Year 2) in the laboratory. These tests will permit verification of the computer simulation for the "thick deck" bridge.
- Starting Date: July 1, 2001: October 1, 2001
- Completion of computer modeling: December 1, 2001
- Completion of physical test set-up: March 1, 2002
- Completion of load testing: April 15, 2002
- Comparison of analytical and test results: June 15, 2002
- Technical paper prepared/submitted: June 30, 2002
- Recommendations for Year 2
- Ending Date: June 30, 2002
Yearly and Total Budget
This is a two year project. The attached budget is for Year 1 of the project (July 1, 2001-June 30, 2002). The amount requested from the USDOT is $36,312 and is augmented by $37,745 anticipated CSU match. The total budget for Year 1 of the project is $74,057. It is expected a total budget of about $50,000 will be requested for Year 2 of the project.
Funds are included for about 6 months of support for a graduate research assistant and part-time student hourly labor (graduate or undergraduate).
Relationship to Other Research Projects
A prior MPC project conducted at CSU by the first PI showed this to be mechanically successful using a notched shear key/anchor detail tested in the laboratory under static loads for thin deck systems. This, it is promising for the thick deck system needed for repetitive HS-20 capacity bridge loadings.
Technology Transfer Activities
Technology transfer will be via an MPC final technical report, a technical journal and/or conference paper submittal each year 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 the study is successful, as anticipated, there is a large inventory of deficient bridges available in Region 8 for possible field application. Although not included in this project, the PI will seek to arrange a pilot field test bridge in the future.
Potential Benefits of the Project
As stated above, an historic community in Colorado needs to reroute traffic to solve environmental and safety issues. Bridge construction at a critical juncture would alleviate much of the problem. Interest exists in possibility utilizing a layered wood-concrete deck type bridge for a new short span roadway bridge. This cost effective concept also has potential short span access bridges into recreational areas and tourist attractions along secondary and access roads, adjacent to major highways. This project is imperative on a safety basis, to confidently proceed to such possible applications.
In region of the MPC universities, State and local bridges are predominately on secondary roads and are critical to the movement of the vast agricultural and mineral production of the region. The dispersed rural area and low tax base makes saving every possible bridge repair and replacement dollar a critical need. Numerous highway bridges (about 20% nationwide, and higher percentages in Region 8) on secondary roads involve the use of timber decking on either steel or wood stringers. Typically, decks in older bridges are the first component to wear and exhibit reduced load capacity. As stated above, the usual consequence is the deck is completely replaced with a new one. Otherwise, the bridge using the deck would have to be either posted for lower load limits or closed.
The technology being examined in this project has the potential to not only save existing deteriorated wood decks, but to increase the overall bridge load capacity considerably. If the proposed research is successful, a method for new construction would also result. The resulting additional strength would enable bridge owners to avoid posting and closures in many cases. The number of deficient bridges in the nation is very high (nearly half of the nation's bridges) and funds to effect repair and replacements are very limited. Thus methods to avoid costly deck replacements and strengthen bridges for today's (and tomorrow's higher) truck loads are economically beneficial.
Bridges, decks, computer modeling, load tests, wood-concrete