Alternative to Double-Tee Bridges for Local Roads 

Sponsors:  

South Dakota Department of Transportation and Mountain-Plains Consortium (MPC) – University Transportation Center (UTC) 

Project Funds:  $160,000 ($85,000 from SDDOT and $75,000 from MPC)

Year:  2015-2017

Personnel:  

PI:  Nadim Wehbe, PhD, PE

Co-PI:  Mostafa Tazarv, PhD, PE

Graduate Research Assistant:  Michael Mingo and Zachary Carnahan

Industry Collaborators/Donors:  Gage Brothers Concrete Products,  Gruen-Wald Engineered Laminates, Inc.,  Headed Reinforcement Corp., and Journey Group Construction.

Project Summary:

The South Dakota Department of Transportation (SDDOT) allows the use of precast double-tee bridges in counties because they are economical and fast in construction.  Alternative durable prefabricated bridge systems are needed to provide more options to local governments.  The present study was carried out to investigate the feasibility of alternative prefabricated bridge systems that can be incorporated in South Dakota.  The project technical panel approved testing of two superstructure bridge systems: (1) precast full-depth deck panels on prestressed inverted bulb-tee girders, and (2) glulam timber bridges.  The present report includes the design, construction, testing methods, and the recommendations for the selected bridge alternatives.

Three full-scale bridges, one fully precast and two glulam timber, were tested under fatigue and ultimate loading.  The precast bridge specimen was 50-ft long by 9.5-ft wide.  No significant damage beyond the prior-to-testing shrinkage cracks was observed throughout the fatigue test, and the overall bridge stiffness did not deteriorate.  The ultimate testing showed that the load at the first crack was higher than the loads equivalent AASHTO Service and Strength I limit states, indicting sufficient performance.  Based on the construction, testing, and cost analysis, it was concluded that that the precast bridge is a viable alternative to the double-tee girder bridges.  The full-scale glulam girder bridge test model was 50-ft long and 9.25-ft wide.  The full-scale glulam slab bridge was 16.5-ft long and 8-ft wide.  Both timber bridge types showed minimal damage during the fatigue testing.  The only damage of the girder timber bridge was cracking of male-to-female deck-to-deck connections, which can be eliminated using flat-end panels.  Ultimate testing of the two bridge systems confirmed that the AASHTO method of the design for timber bridges is adequate.  Girders of glulam girder bridges should be designed as fully non-composite members.  Based on the construction, testing, and cost analysis, it was concluded that both types of glulam timber bridges are viable alternatives to the double-tee girder bridges. 

Project Work Plan:

Task 1:  Meet with the technical panel to review project scope and work plan.

Task 2:  Perform literature review of bridge system alternatives to the double tee girder system that are low cost, single span less than 70 feet, applicable for use on local roads with service life of at least 75 years.

Task 3:  Provide the technical panel with a technical memorandum explaining the results of the literature review from task 2. 

Task 4:  Meet with technical panel to discuss results of literature review and technical memorandum. Based on discussion, technical panel will decide which option(s), if any, will require structural testing.

Task 5:  If directed by the technical panel, prepare a technical memorandum describing a complete instrumentation, construction, and testing plan for technical panel review.

Task 6:  Upon approval of the plan by the technical panel, proceed with instrumentation and construction of test girders. Notify the technical panel of construction schedule to give the option to be present at time of construction.

Task 7:  Perform and provide the technical panel opportunity to observe ultimate and fatigue loading of selected structure type. 

Task 8:  Compare results of testing to the results from SD2013-01 project to understand the construction and load capacity differences between bridge systems.

Task 9:  Develop a recommendation to the SDDOT based on cost and performance of the alternative bridge system compared to the revised double tee section from SD2013-01.

Task 10:  Meet with technical panel to review and accept results of investigation and proposed recommendations

Task 11:  Prepare a final report and executive summary of the research methodology, findings, conclusions, and recommendations.

Task 12:  Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.

Publications:

1. Tazarv, M., Carnahan, Z., Wehbe, N. (2019). “Glulam Timber Bridges for Local Roads,” Engineering Structures, DOI: 10.1016/j.engstruct.2019.03.012, Vol. 188, pp. 11-23 (Link).

2. Tazarv, M., Mingo, M., Wehbe, N. (2019). “System Performance of a Precast Bridge Incorporating Full-Depth Deck Panels and Prestressed Inverted Bulb-Tee Girders,” Journal of Bridge Engineering, ASCE, Accepted for Publication.

3. Carnahan, Z., Mingo, M., Tazarv, M., Wehbe, N. (2019). “Development of Alternative Bridge Superstructures for South Dakota Local Roads.” North Dakota State University - Upper Great Plains Transportation Institute, Fargo: Mountain-Plains Consortium (MPC), MPC Report No. 19-373, 140 pp (Link).

4. Mingo, Michael James, "Precast Full-Depth Deck Panels Supported on Inverted Bulb-Tee Bridge Girders" (2016). MS Thesis, South Dakota State University, 177 pp (Link).

5. Carnahan, Zachary Charles, "Glulam Timber Bridges for Local Roads" (2017). MS Thesis, South Dakota State University, 182 pp (Link).