MPC
Research Projects (2005-06)

Identifying Number

MPC-262

Project Title

Cambering of Wood-Concrete Highway Bridges

University

Colorado State University

Project Investigators

Dr. Richard Gutkowski
Colorado State University
(970)491-8291
gutkowsk@engr.colostate.edu

Dr. Jeno Balogh
Colorado State University
(970)257-7278
jbalogh@engr.colostate.edu

External Project Contact

N/A

Project Objective

The objective of this project is to develop methods to incorporate camber in short-to-medium span roadway bridges involving an innovative composite concrete-wood construction and test lab specimens under dead load and creep loading.

Project Abstract

Low cost, easily constructed bridge systems are essential for short to medium span situations in rural jurisdictions. One approach previously investigated a composite wood-concrete desk bridge system in which the concrete deck layer was interconnected to the wood deck. A notched shear key/anchor detail is used between the layers. However, the wood members must be cambered to avoid the dead load deflection and creep causing an undesirable sag. The problem worsens as the span was increased because deeper members (more concrete in particular) increased the dead weight significantly. A need exists to solve this problem to be able to foster implementation of such bridges. This project included experimental creep tests on laboratory beam specimens which will be configured to include camber to a degree estimated to be sufficient to avoid sag under dead load.

Task Descriptions

Incorporation of camber will be investigated via two potential techniques. For short span application, an end taper oriented upward toward mid span will be provided in the wood layer at both ends of the specimen. This will be made via an appropriate diagonal cut piece glued and/or screwed in place at one end of the member. For medium span application, camber will be achieved by using tapered utility poles instead of modified straight solid wood members. These will be placed in alternate directions at slight incline to accomplish some degree of leveling, then structural modeling will be employed to configure the bridge and produce camber required. A set of beams made of this construction will be used to trouble shoot the concept and examine the success of the camber technique under the dead load creep load of about 6 months. A load test to failure will then be done to examine the load capacity. If successful, and extension to full bridge construction is anticipated as a future project.

Milestones, Dates

Starting Date: July 1, 2005
Ending Date: June 30, 2006

Yearly and Total Budget

$42,970

Student Involvement

Two graduate research assistants, one undergraduate student

Relationship to Other Research Projects

Prior MPC laboratory projects showed the mixed wood concrete composite construction to be successful for stresses and short term absolute deflection. This project continues that work.

Technology Transfer Activities

Outcomes will be presented via the TLN videoconference system in its technology transfer programming.

Potential Benefits of the Project

Much of rural America has low tax based communities dependent on agricultural economies and related freight and shipping industry. Upgraded or improved bridge construction improves safety of travel in such rural areas. Commonly, many short span bridges are in use to cross narrow streams and irrigation ditches. Cost effective design practices lead to lower bridge costs. This is especially important for sub -20' bridges, which are not eligible for federal aid monies, and for which repairs are often neglected. The envisioned composite wood concrete concept also has potential short span access bridges into related recreational areas and tourist attractions along secondary roads, adjacent to major highways. These place much more structural burden on bridges in these communities than most rural secondary roads.

Examples of recently constructed medium span, wood-concrete bridges comprised of round poles exist in Europe, and led the PI to consider the concept as practically plausible. The utility poles to be used will constitute a recycling feature. Existing, including structurally sound utility poles are commonly removed when roads are widened. The used utility poles are normally discarded. This actually was occurring for the secondary roadway leading to the research facility where this research is to be performed. The PI readily accomplished a donation of the utility poles from the utility company for use in this project, suggesting a possible future low-cost material source.

Techniques for achieving sufficient camber are anticipated. An MPC technical report will be developed to detail the research and its outcomes.

TRB Keywords

Bridges, composite, wood-concrete, short- to medium-span