Institute for Transportation

About the research

Connected vehicle technologies are being developed to enable safe, interoperable networked wireless communications among vehicles (V2V), the infrastructure (V2I), and travelers’ personal communication devices (V2X). These technologies are intended to reduce highway crashes; provide data for assessing the performance of the transportation system; provide continual access to accurate information on the operation of the system to travelers; and reduce unnecessary stops, delays, and emissions.

Advances in the field of autonomous/self-driving vehicles has shown potential for new and innovative applications that could change how state departments of transportation (DOTs) and other public agencies maintain roadways and roadside vegetation, roadway and roadside construction, among other applications. Mowing of medians and the right-of-way is an important vegetation management practice for the California Department of Transportation (Caltrans), but it is labor intensive and requires expensive and specialized equipment. Autonomous vehicles have the potential to improve worker safety and efficiency.

With the advent of autonomous vehicles, it may be possible to reduce worker exposure and risk by utilizing driverless tractors for mowing operations. In addition, cost savings are possible by utilizing one operator to control more than one mower. The objective of this project is to assess ease of use, safety, and appropriateness for Caltrans operations of non-line-of-sight, remote control technology for Caltrans vehicles and operations. As a minimum, the technical literature will be reviewed to ascertain the state-of-the-art for autonomous vehicle technologies for highway mowing operations. Based on this review, a draft specification will be developed defining the minimum requirements a DOT expects. In addition, the specification will be shared with potential vendors to assess their capability to provide an implementable product.

About the research

Increased and heavier traffic loads and the effects of harsh environmental conditions contribute to significant deck distress in post-tensioned box-girder bridges in California. The deck in several of these bridges is expected to be in need of repair, rehabilitation, or complete replacement in the not too distant future due to concrete fatigue, freeze-thaw damage, and/or the potential for experiencing punching shear failure. Since the deck forms an integral part of the superstructure load resisting mechanism, a special approach is required for repair, rehabilitation, or replacement the deck in box-girder bridges.

However, to successfully develop such an approach, which involves localized partial deck concrete removal and replacement with UHPC that has thixotropic and rapid set properties, further investigation is needed to:

1. Determine, through detailed finite element modeling, the nature and magnitude of stresses that would develop following the removal and replacement of a thin layer in the deck of single span, two span, and/or multi-span continuous bridge structures.
2. Determine the maximum acceptable depth of removal and replacement of the existing deck concrete as a function of location and/or area such that the required structural section properties of the box in its final configuration is not adversely affected assuming no supplementary or temporary support requirements during construction.
3. Identify any special concerns that may develop from the changes of both deck and girder section properties during partial depth removal/replacement such as creep and shrinkage effects, shear transfer between old concrete and UHPC, positive/negative flexure, and resistance to punching shear.
4. Improve the understanding of and establish estimates for the fatigue and long-term effects on the bond between both old existing concrete and partial depth deck patch and the UHPC overlay, particularly under service loads, through testing of large-size box-girder bridge deck overlaid with UHPC.

The goal of this research is, therefore, to develop the knowledge needed to establish a suitable methodology for the rehabilitation of post-tensioned box-girder bridge decks on California using the UHPC overlay concept by:

• Numerically investigating the effects of rehabilitating the deck on post-tensioned box-girder bridges using UHPC layers that involve partial depth removal and replacement of deck concrete for different bridge configurations
• Determining the effects of a UHPC overlay used in a deck rehabilitation application on both local deck and global girder section properties of post tensioned box-girder bridges
• Investigate the long-term durability of bond interface between the old concrete and UHPC
• Developing design details, design guidelines with examples, construction specifications and quality control plan for application of UHPC overlays and proof-testing of a full-scale laboratory mockup with and without additional reinforcement in the UHPC layer, which will be suitable for use on a field trial pilot project to be conducted in a future study

About the research

Given their advantages over conventional construction techniques, Accelerated Bridge Construction (ABC) methods have been increasingly used not only for the rehabilitation/replacement of existing structures but also for the construction of new structures. Such methods can greatly reduce on-site construction time, improve safety of the traveling public and workers, improve bridge components quality, and enhance durability and longevity of the overall bridge structure. As a result, several Departments of Transportation (DOTs) have successfully developed and implemented ABC procedures for superstructures and to some extent for substructure systems when rehabilitating or replacing structurally deficient or functionally obsolete bridges.

Attempts at implementing ABC techniques for abutments in past projects by the California DOT (Caltrans) have been challenging. In a typical ABC methodology, the abutment is cast in pieces at a precast yard, transported to the project site and assembled using adequately detailed connections that generally require cast-in-place concrete closure pour. Limits imposed on individual precast pieces by the size and weight restrictions of the transportation routes and lifting equipment commonly available at project sites result in the need for several precast pieces and associated connections to achieve standard abutment sizes used in California. As a result, longer on-site construction time is required to connect the pieces, which negates some of the benefits associated with precast construction.

Moreover, the development of ABC for substructure systems, especially abutments, requires careful consideration of seismic performance and Soil-Foundation-Structure interaction (SFSI). In the current design philosophy, the abutment shear keys and backwall are frequently used seat-type abutments are sacrificial elements and part of the bridge energy dissipation system. They are designed to provide longitudinal and transverse resistance under service loads and small to moderate earthquakes, but fail under design level seismic events in order to limit the forces experienced by the abutment and its foundation elements. It is therefore important that the ABC methodology be developed to meet this design criterion and that the expected performance be verified through a comprehensive experimental testing.

To overcome the aforementioned challenges, this research aims to develop an improved ABC technique for abutments that will utilize hollow core prefabricated elements, which can be filled with concrete on-site to complete the system. The use of more efficient materials such as high strength concrete (HSC), ultra high-performance concrete (UHPC), and fiber reinforced polymer (FRP) will be investigated to increase the size of individual elements while minimizing their weights in order to facilitate transportation and assembly of the abutment system. In addition, any delays associated with curing of onsite concrete or grout will be minimized by using rapid set materials and/or temporary hardware that can be mounted to the prefabricated elements. The PI of the project has significant expertise in developing ABC techniques to successfully achieve the goal of the research.

The main objectives of this research include:

• Developing a cost-effective and lightweight prefabricated bridge abutment modular system that consists of light weight prefabricated hollow elements (shells) made from HSC, UHPC, and/or FRP that are infilled with concrete to form a complete abutment
• Developing simple and reliable details for the shell-to-footing, shell-to-pile, and shell-to-wingwall connections that minimize on-site working days, construction challenges and delays, and ensure adequate seismic performance of the overall system
• Developing analysis techniques that can quantify the expected performance of the abutment system with consideration of the developed connection details
• Verifying the performance of the system and its connections under service and seismic loading through scaled testing in real world conditions that will account for soil-abutment-pile interaction effects
• Developing construction techniques for quickly constructing abutments using the new concrete-filled shell system

About the research

Accelerated Bridge Construction (ABC) technologies have gained significant momentum in recent years. Besides their ability to deliver bridge projects (whether new or existing) rapidly and efficiently, these techniques can significantly improve safety of the traveling public and workers, enhance the quality and durability of bridge components and consequently those of the overall bridge structure. Given these advantages over conventional approaches to bridge construction, several Departments of Transportation (DOTs), in collaboration with research institutes, have successfully developed and implemented innovative ABC methods for various substructure and/or superstructure systems with the primary goal of reducing on-site construction time of existing or new structures and thus minimizing impacts on mobility and related traffic delays. Attempts at implementing ABC techniques for substructure systems in California and other states have been challenging owing to certain design practices, including the use of post-tensioning and cast-in-drilled-hole (CIDH) piles, and the necessity of in-situ concreting/grouting, which delays construction progress until the concrete/grout reaches adequate strengths. Moreover, the development of ABC for substructure systems requires careful consideration of seismic performance and soil-structure interaction.

The main objectives of this research include the following:

• Developing ABC concepts for column-footing-pile systems for use in California that will utilize lightweight precast modular sections
• Developing reliable connection details, which will ensure full mobilization of the system design strength and promote full development of the plastic hinge in the column adjacent to the footing
• Providing experimental evidence for the developed system with due consideration of soil-structure interaction
• Developing analysis techniques that can quantify the expected performance of the system with consideration of the developed connection details
• Developing construction specifications to ensure reliable performance of the system

About the research

A goal of the proposed work is to continue to improve the understanding of the true seismic behavior of a cap-to-girder connection that will facilitate ABC opportunities while mitigating the seismic hazard associated with bridge designs that utilize accelerated construction methods. To accomplish this purpose, we will design a prototype bridge and, using experimental and analysis methods, investigate the expected seismic performance of the girder-to-cap connection of the prototype.

Previous similar analytical work completed for the earlier inverted-tee project will be built upon to minimize the amount of analytical work associated with this investigation. The improved connection detail completed as part of the previous work will also be utilized again here to avoid unnecessary duplication of earlier work.

A large-scale bridge component test will be designed to replicate a portion of the prototype superstructure consisting of several precast I-girders and an inverted-tee pier cap using the girder-to-cap connection developed in the previous work. The model will be subjected to the seismic effects resulting from horizontal and vertical accelerations and fully quantify the elastic and plastic behavior of the connection. Using the test data, the accuracy of the analysis models will be evaluated.

The results of the experimental and analytical work will be used to create design guidelines, details, and examples that will enable increased use of accelerated bridge construction methods and increased understanding of how precast girder to cap connection should be detailed to address the concerns resulting from vertical ground acceleration. The research team will play a proactive role in disseminating project findings to Caltrans engineers and other interested designers and organizations and will also assist with rapidly deploying the research results into practice.

The inverted-tee test also revealed that use of untensioned, grouted tendons in the girder-to-cap might provide sufficient seismic resistance. The research team plans to develop individual component tests to compare the behavior of grouted tendons with different level of initial stresses and provide experimental behavior comparisons of the different options.

The research team is aware that in addition to the I-girder, Caltrans has utilized bulb-tee girders and perhaps even more commonly the California wide-flange (or super) girder. It is believed that experimental results established by using the I-girder configuration can also be applied to bulb-tee girders and the California Wide Flange Girder configuration. If needed, the experimental program could be altered to accommodate one of these girder types.

About the research

About the research

State highway agencies are increasingly intersted in using recycled asphalt shingles (RAS) in hot mix asphalt (HMA) applications, yet many agencies share common questions about the effect of RAS on the performance of HMA. Previous research has allowed for only limited laboratory testing and field surveys. The complexity of RAS materials and lack of past experiences led to the creation of Transportation Pooled Fund (TPF) Program TPF-5(213). The primary goal of this study is to address research needs of state DOT and environmental officials to determine the best practices for the use of recycled asphalt shingles in hot-mix asphalt applications.Agencies participating in the study include Missouri (lead state), California, Colorado, Illinois, Indiana, Iowa, Minnesota, Wisconsin, and the Federal Highway Administration. The agencies conducted demonstration projects that focused on evaluating different aspects (factors) of RAS that include RAS grind size, RAS percentage, RAS source (post-consumer versus post-manufactured), RAS in combination with warm mix asphalt technology, RAS as a fiber replacement for stone matrix asphalt, and RAS in combination with ground tire rubber. Field mixes from each demonstration project were sampled for conducting the following tests: dynamic modulus, flow number, four-point beam fatigue, semi-circular bending, and binder extraction and recovery with subsequent binder characterization. Pavement condition surveys were then conducted for each project after completion.

The demonstration projects showed that pavements using RAS alone or in combination with other cost saving technologies (e.g., WMA, RAP, GTR, SMA) can be successfully produced and meet state agency quality assurance requirements. The RAS mixes have very promising prospects since laboratory test results indicate good rutting and fatigue cracking resistance with low temperature cracking resistance similar to the mixes without RAS. The pavement condition of the mixes in the field after two years corroborated the laboratory test results. No signs of rutting, wheel path fatigue cracking, or thermal cracking were exhibited in the pavements. However, transverse reflective cracking from the underlying jointed concrete pavement was measured in the Missouri, Colorado, Iowa, Indiana, and Minnesota projects.

About the research

The goal of this project was to understand the true seismic behavior of the cap-to-girder connection as currently used and to mitigate the potential seismic hazard associated with these bridges.

About the research

• Develop risk assessment procedures to identify critical bridges in a bridge network
• Develop bridge vulnerability assessment guide
• Develop concepts for mitigation and structural protection of bridges

Soon after the attacks of September 11, 2001, the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO) assembled a Blue-Ribbon Panel of experts to develop strategies and provide guidance to improve the safety and security of bridge and tunnel infrastructure. This effort led to recognizing that the threat is real and can be devastating, risk assessment is necessary, and engineering guidance are needed based on research. Building on current and past efforts, the goal of this project is develop procedures to assist professionals and bridge owners identify critical bridges and to develop procedures to assess their vulnerability to explosions (terrorist’s bomb attacks). Potential Benefits of the Project The procedures and design guides developed in this project will benefit the bridge owners, designers, inspectors, and professionals nationwide.

Funding Sources:
California Department of Transportation
Midwest Transportation Consortium
University of Missouri – Columbia