I-70 Pavement Structure Evaluation

Roadway structural properties on 463 lane-miles of Interstate 70 between Kansas City and St. Louis were determined using deflection, surface condition, and three-dimensional ground penetrating radar (3DGPR) data collected with the ARRB iPAVE Traffic Speed Deflectometer (TSD). Data was collected in the right wheel path of the travel lane in both the eastbound and westbound directions. The TSD data are collected at the posted speed limited (typically, no more than 60 mph) and results are averaged and reported at 0.01-mile intervals. The 3DGPR data was analyzed to determine the thickness of the pavement layers at each reported TSD test point. The data was analyzed to determine pavement structural properties, to evaluate the load transfer of the underlying transverse joints and cracks, and to identify areas of potential asphalt stripping.

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Report number: cmr 24-006
Published: June 2024

Project number: TR202419

Performing organization: Infrasense and NCE 

Design Coefficients of Friction for MoDOT PTFE Bearings

This report evaluates the design coefficients of friction for polytetrafluoroethylene (PTFE) bearings, identifying key influencing parameters through a literature review and a detailed test program. Seven parameters were studied: PTFE material and surface types, size, contact pressure, temperature, sliding speed, and surface contamination. The analysis presented in the report showed that unfilled dimpled lubricated PTFE and filled flat PTFE exhibited the lowest and highest coefficients of friction, respectively. The coefficients of friction for unfilled flat and filled dimpled PTFE fell in between. The study found that coefficients of friction increased with higher sliding speeds and surface contamination but decreased with increased contact pressure. No consistent changes in the coefficients were observed with variations in specimen size or at low temperatures. Notably, surface contamination drastically increased friction coefficients—light dust levels increased friction tenfold, while heavier contamination prevented sliding altogether. Based on these findings, updated design coefficients of friction are proposed for the four main PTFE bearing types: flat (both unfilled and filled) and dimpled lubricated (both unfilled and filled). The report also discusses various preventative measures and underscores the importance of regular maintenance and the adoption of protective strategies to enhance bearing longevity and functionality.

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Report number: cmr 24-005
Published: June 2024

Project number: TR202204
Authors: Saeed Nejad, Jonathan C. McGormley

Performing organization: Wiss, Janney, Elstner Associates, Inc. (WJE) 

Intermediate Bents – Calculation of Restraint Factor

This report investigates the restraint at the top of the column of non-integral intermediate bents with closed diaphragms, a common connection configuration utilized by the MoDOT. Although closed diaphragms inherently possess some level of rotational restraint, the current design approach considers this type of connection as free, resulting in the use of design k-factors of 2.1. However, rotational restraint significantly influences the k-factor. Utilizing an integration of experimental and numerical analyses, the study determined the approximate level of restraint of these types of intermediate bents. The main source of rotational flexibility was in the diaphragm to bent cap connection. A parametric analysis showed that the dowel bar area, diaphragm width, and skew angle were all parameters that needed to be considered in the simplified equation to predict the rotational restraint developed as part of this study. A comparison of the simplified equation to predict rotational restraint showed at most a 10% difference compared to that found in the FE models. Calculations of the k-factors, using a simplified bilinear equation, showed k-factors less than the assumed 2.0 theoretical value for fixed-free columns (on average 1.5), and in the case of the steel column bridge a k-factor of only 1.2. A procedure for analyzing telescoping columns was also formulated in which an effective moment of inertia can be used to treat the column as a uniform diameter. Three examples showed that the use of rotational restraint increased the buckling capacity of the concrete column by 24% to 40%. However, for steel HP columns this increase was most significant at 62%, which changed the controlling buckling mode to the weak axis direction. If buckling capacity controls the design of the column this could result in a potential cost savings of 20 to 30% of the column cost. The work culminates in a suggested design procedure to use rotational restraint in the design of intermediate bent bridge columns.

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Report number: cmr 24-004
Published: June 2024

Project number: TR202203
Authors: Sarah Orton, Alaaeldin Elsisi, David Barrett, Cory Imhoff, Narek Galustanian, Mohamed Elshazli, and Olivia Bommelje

Performing organization: University of Missouri-Columbia, Missouri Center for Transportation Innovation