Institute for Transportation

About the research

The objective of this project was to demonstrate the field implementation of an innovative longitudinal joint design developed during a previous phase of research. To achieve this objective, a yet-to-be-constructed box girder bridge in Washington County, Iowa, was selected to demonstrate the construction and performance of the joint.

In order to evaluate the joint’s performance, a seven-day period of field monitoring was conducted shortly after construction was completed. In addition, long-term evaluation of the joint was performed through the completion of live load field tests and deck concrete crack inspections. The live load tests were performed every 12 months, and crack inspections of the bridge deck were performed every six months. During the field tests and monitoring, temperature, strain, and displacement data were collected at critical locations and analyzed to evaluate joint performance with respect to cracking resistance and load distribution.

The results indicate that the innovative joint is sufficient to resist early-age longitudinal joint cracking. Joint cracks that were seen on another box girder bridge with traditional narrow joints were not observed in this case. The innovative joint performed well with respect to load distribution. The whole bridge superstructure behaved as an integrated structure regardless of the transverse location of a passing truck. In addition, the box girder bridge was constructed using integral abutments, which added transverse restraint and positively affected the strain distribution at the joint ends.

About the research

Shrinkage and temperature forces are known to have short- and long-term effects on both the superstructures and substructures of bridges. In the substructure, such effects are more pronounced if frame piers are used, given their volumetric change is often restrained.

The main objective of this research was to investigate the forces developed in frame piers and their supporting foundations due to volumetric changes caused by thermal and shrinkage effects. For this purpose, a set of finite element (FE) models capable of simulating shrinkage strain, creep strain, thermal strain, strength development of concrete, and nonlinear behavior of concrete were developed and calibrated using experimental test results. Field data were then collected from bridges instrumented with vibrating wire strain gauges embedded in the frame piers at the time of construction. Further to obtaining firsthand information from the field, the FE models were validated using collected field data. Various frame pier geometries were then analyzed using the validated model to identify the most susceptible geometries.

The results of the study indicated that frame piers cast in Iowa on warm summer days, particularly in June and July, experience the most demand from temperature and shrinkage effects compared to frame piers cast at other times of the year. The most critical factors affecting frame pier susceptibility were found to be column stiffness, length of the cap beam, and flexural stiffness of the cap beam. Column stiffness was observed to be the most impactful factor on the susceptibility of frame piers to these effects. Basic susceptibility metrics, such as the length of the frame and the length-to-height ratio of the frame, were found to be not accurate enough to predict susceptibility, as accurate susceptibility metrics must account for column stiffness and column restraint factors. These results led to the development of two-dimensional linear elastic models that simplified the assessment process without losing accuracy. Overall, the requirements set by the Iowa DOT’s Bridge Design Manual were found to be adequate in capturing the performance of frame piers subjected to temperature and shrinkage forces.

About the research

Concrete diamond grinding on pavement projects generates a nonhazardous waste byproduct called concrete grinding residue (CGR). CGR has known cementitious characteristics that suggest a latent use as a soil-stabilizing amendment, especially for poor and problematic soils.

In this study, Western Iowa loess soil was amended with CGR and subjected to rainfall simulations and wind erosion tests to measure the erodibility of several soil mixtures. The results of the rainfall simulations showed that CGR-amended silty soil (loess) had only slightly different optimum moisture contents and maximum dry densities compared to untreated loess, while rainwater runoff samples of CGR-amended loess exhibited dramatically higher turbidity and total suspended solids. The results of the wind erosion tests showed that erosion was lower in more granular shoulder material and higher in shoulder material containing more organics. Wind erosion tests performed on CGR-amended Western Iowa loess showed modest improvement in this highly friable silty soil compared to untreated loess.

A field study conducted in Washington and Clinton Counties in Iowa compared CGR-stabilized and untreated sections to determine the effectiveness of CGR as a stabilizer for shoulder material. The CGR-stabilized sections in Washington County did not show significant improvement in strength, while the CGR-stabilized sections in Clinton County exhibited a 20% to 40% improvement in the composite elastic modulus and California bearing ratio values.

About the research

The Central Iowa Expo facility is located in Boone, Iowa. The Iowa DOT initiated a research project (IHRB Project TR-671) to implement foundation stabilization technologies (Phase I), construction of the pavement layers using intelligent compaction technology (Phase II), and non-destructive evaluation of pavement systems right after construction (Phase III).

Falling Weight Deflectometer (FWD) tests were performed on the pavement layer and ground penetrating radar tests were performed to evaluate thickness of the asphalt layer and moisture conditions of the base layer. This project includes an assessment of those tests.

About the research

Traffic signal structures are an integral part of the transportation infrastructure system, ensuring the safety of motorists and pedestrians. These structures, however, have been found to perform poorly due to fatigue-related issues in their connections. This mostly originates from the large-amplitude vibrations caused under galloping, vortex shedding, and natural wind and truck-induced gusts. The inherent dynamic properties of these structures, especially their low mechanical damping (0.1%-0.4%), is proven to be a key contributing factor, further exacerbating the fatigue-related issues. While most of investigations performed to date have been focused on the development of vibration mitigation strategies or the design of fatigue-rated connections, much less attention has been given to a more fundamental solution, stemming from the modification of the aerodynamic characteristics of this category of structures, addressing the issues at their roots.Considering the large number of traffic signal structures used for traffic control, their cost of repair and reinstallation can add up fast, while their potential failure can pose an immediate risk to the traveling public. This has led to a growing need to develop more cost-effective solutions to mitigate the large-amplitude vibrations of both new and existing traffic signal structures.

About the research

Changes in technology have an impact on standard practice, materials, and equipment. The traffic signal industry is constantly producing more energy-efficient and durable equipment, better communications, and more sophisticated detection and monitoring capabilities. Accordingly, this project provides an update to the traffic signal content within the Statewide Urban Design and Specifications (SUDAS) Design Manual and Standard Specifications.

This work was completed through a technical advisory committee with a variety of participants representing contractors, the Iowa Department of Transportation, cities, consultants, vendors, and university research and support staff.

About the research

The primary goal for this project was to evaluate the efficacy of A709 Grade QST 65 steel for use in Iowa bridge projects. The objectives of the project were as follows:

• Identify the current state of use of A709 Grade QST 65 steel in bridge projects
• Identify the ductility and strength characteristics of A709 Grade QST 65 steel through full-scale laboratory testing
• Identify the fatigue characteristics of A709 Grade QST 65 steel through cyclic fatigue testing
• Observe and compare bridge construction similarities and differences to conventional steel construction using a new bridge planned over Sand Creek in Buchanan County, Iowa
• Compare relative costs of using A709 Grade QST 65 steel versus conventional steel
• Measure the live load response at various points in time on the Sand Creek Bridge, which was constructed using A709 Grade QST 65 steel

The ductility and strength of the steel was observed through the various laboratory tests completed for this project as well as the testing performed by others. Minimum requirements for this steel grade have been established, and the results of this study indicate that the requirements were met and surpassed.

The modified design of this first-in-the-nation bridge using Grade QST 65 steel over Sand Creek allowed for a reduction in beam size for this relatively short-span, low-traveled bridge due to the increased strength of the steel beams. The total steel cost for these beams resulted in a 20% material cost savings.

The results should give confidence to engineers considering use of this steel grade on bridge construction projects with longer spans and higher traffic counts.

About the research

Cape seals, which have been applied in several countries as well as the United States for many years, have never before been used by counties in the State of Iowa. As part of the Clinton County Pilot Demonstration Project of Cape Seals endorsed by the Iowa Highway Research Board (IHRB) serving as Iowa’s State Transportation Innovation Council (STIC), this study will (1) perform data collection and monitoring activities at the Cape Seal Pilot Demonstration Project site in Clinton County and (2) collect before and after stakeholder input to measure perceptions about the project and cape seal performance. This will be achieved through the execution of the following primary tasks: (1) documenting construction activities and executing a showcase/open house during project construction, (2) monitoring and evaluating pavement performance regarding the effectiveness of the innovations, (3) executing subsequent technology transfer and information dissemination activities and developing implementation plans with recommendations, and (4) publishing final research project documents. This research project would be highly helpful in scientifically documenting the performance of cape seal application over its service life and in providing the necessary data for the Iowa Department of Transportation (DOT) and Iowa counties who are considering deploying cape seals as standard pavement preservation practices (if the deployment is successful).

About the research

Conventional culverts are mainly designed to transport water underneath roadways with minimal headwater buildup, resulting in low to moderate peak flow attenuation. On-road structures (ORS) offer an alternative by using the roadway embankment as a dam, restricting flow into the culvert to provide flood storage during large precipitation events.

In this project, statewide geographic information system (GIS) analyses were conducted that identified approximately 250,000 potential ORS locations with a combined storage capacity of 2 million acre-feet and a pool area covering 900,000 acres, representing about 2.7% of Iowa. A methodology was developed to automate the hydrologic design of individual ORS, enhancing the identification of those that offer significant peak flow reduction benefits. In addition, the peak flow reduction benefits were quantified at the HUC12 watershed scale for ORS systems. For a 50-year storm event, peak flows at watershed outlets were reduced by approximately 18%.

The research outcomes are accessible through a web portal named the Iowa Department of Transportation (DOT) On-Road Structures (IDOT-ORS) information platform. This platform facilitates the dissemination of results, allowing various stakeholders to view information on ORS locations, expected pool and drainage areas, structure designs, and inflow and outflow hydrographs for several return periods. The platform can be accessed at https://hydroinformatics.uiowa.edu/lab/idot-ors/.

About the research

Accelerated bridge construction (ABC) is widely used by departments of transportation (DOTs) because of the reductions in traffic disruption, social cost, environmental impact, and lost time. ABC is also known to improve work-zone safety, on-site constructability, and project completion time.

A common ABC technique is the use of prefabricated bridge elements and systems (PBES). Bridge components are built outside of the construction area, transported to the site, and then rapidly installed. Time lost due to concrete placement, curing in the construction zone, and formwork erection/removal is reduced. Another benefit to using prefabricated structural elements is improved quality control. Damage due to weather is also minimized because elements are built in a controlled environment.

Considering the advantages of PBES, a number of research projects have been conducted on the prefabrication and installation of the main structural elements of bridges. However, there is a gap in the literature regarding how to address the long-term performance and durability concerns associated with the joints that connect high-quality bridge elements. One approach that has gained significant attention is to eliminate these joints through revised design strategies. While such strategies have been successfully developed for integral abutments used for ABC applications, no systematic study on removing the expansion joints between bridge girders has been undertaken.

To address this issue, this research project investigated the use of a flexible link slab through a comprehensive set of experimental tests and numerical simulations. The outcome of this project is design guidelines and practical recommendations for properly implementing a link slab in jointless bridges constructed using ABC and conventional techniques.