Dennis R. Mertz

Bridge 1-351 over muddy run : Design, testing, and erection of an all-composite bridge

Bridge 1.351 on Business Route 896 in Glasgow, Delaware, was replaced with one of the first state-owned all-composite bridges in the nation. Composites are lightweight construction materials that do not corrode, which results in benefits such as ease of construction and reduced maintenance costs. A summary of the design, large-scale testing, fabrication, erection, and monitoring of this bridge is presented. The bridge was designed to AASHTO load and resistance factor design specifications. A methodology was developed to incorporate the engineering properties of these unique composite materials into the design. The bridge consists of two 13 × 32 ft (3.96 × 9.75 m) sections joined by a unique longitudinal joint. The sections have sandwich construction consisting of a core [28 in. (71.12 cm) deep] and facesheets [0.4 to 0.6 in. (10.16 to 15.24 mm) thick] that provide shear and flexural rigidity, respectively. The composite bridge was fabricated with E-glass preforms and vinyl-ester resin, which offers excellent structural performance and long-term durability. Each of the sections was fabricated to near-net shape in a single step by a vacuum-assisted resin transfer molding process. The overall structural behavior has been accurately predicted with simple design equations based on sandwich theory for anisotropic materials. Large-scale testing of full-sized subcomponents was conducted to prove that the design satisfied deflection, fatigue, and strength limit states. A redundant longitudinal joint was designed that consisted of both an adhesively bonded vertical joint between sections and splice plates. Assembly procedures were developed, and transverse testing of the full-sized joint was conducted. Final bridge sections were proof-tested to the strength limit state. The construction phase included section positioning, joint assembly, and application of a latex-modified concrete wear surface. The bridge was reopened to traffic on November 20, 1998. Results from the long-term monitoring effort will be documented.

Behavior of open steel grid decks for bridges

Abstract The life cycle of grid decks has come full circle from their introduction in the 1920s and 1930s, through their maturity in 1950s and 1960s, to their reintroduction in the 1980s. Many of these decks have been performing satisfactorily for 50 or more years of service. Open grid decks offer a lightweight deck alternative to reinforced concrete decks. Despite the good performance history of grid decks, some bridge owners are hesitant to utilize them, even in situations where weight savings is at a high premium. With a better understanding of grid deck behavior, the manufacturing process can be optimized, and design methods improved. Hence, poor details that may lead to fatigue problems can be avoided and design efficiency can be achieved. This paper presents results of research conducted with the goal of providing a better understanding of open steel grid deck behavior through experimental testing and numerical and analytical analyses. Four full-scale open grid decks were tested to experimentally quantify their structural behavior. Three-dimensional finite element models were developed for the grid decks and calibrated using the experimental results. Classic orthotropic thin plate theory and the theory for beams on elastic foundation were applied to the open decks and compared with the finite element (FE) results. Finally, parametric studies were conducted and used to quantify the effect of variations in the significant design parameters. The results of the parametric studies can be applied to optimize future grid deck designs.

Steel Girder Fracture on Delaware’s I-95 Bridge over the Brandywine River

A significant crack was recently discovered on an I-95 bridge over the Brandywine River in Delaware. The steel girder bridge carries six lanes of traffic just north of downtown Wilmington. The crack was located on the fascia girder at midspan of the bridge’s main span. The entire bottom flange was found to be fractured, with the crack extending upwards to within 0.3 meters of the upper flange. This paper will review the circumstances leading up to the crack, discuss the cause of the crack, review the repair strategy, and summarize the results of load tests performed prior to and during the repair.

Proposed Revisions to AASHTO-LRFD Bridge Design Specifications for Orthotropic Steel Deck Bridges

The orthotropic steel deck bridge is a structural system that has the potential to provide an extended service life and standardized modular design as compared to more conventional bridge construction. This paper summarizes proposed changes to the fifth edition of the AASHTO LRFD Bridge Design Specifications related to orthotropic deck bridges. The current version of AASHTO-LRFD contains provisions that provide limited guidance to complete the fatigue design. Contained within these proposed changes is a new framework for design verification, which may be based on different levels of design or physical testing. Criteria related to loads, load factors, limit states including fatigue in particular, resistance, and analysis requirements are covered in detail. Designs made according to these new provisions can be expected to perform very well and meet the design service life as per AASHTO-LRFD.

Framework for Simplified Live Load Distribution-Factor Computations

The live load distribution-factor (LLDF) equations in the AASHTO-LRFD specifications were developed under National Cooperative Highway Research Program (NCHRP) Project 12-26. These equations include limited ranges of applicability, and when these ranges are exceeded, a refined analysis must be used. Additionally, the multiple-presence factors, bias, and variability with respect to the rigorous estimates are obscurely embedded. Herein, a simplified LLDF framework is provided. The effects of analysis uncertainty, variability, and multiple presence are separated and distinctly defined. This separation provides specification writers with the opportunity to use different multiple-presence and variability models. LLDFs were calculated using several simplified methods and grillage analyses for over 1,500 bridges. Based on the comparison, two simplified methods were further studied: adjusted uniform distribution and adjusted lever rule methods. Calibration factors were used to their improve accuracy. Seventy-four...

Continuous, Long-Term Monitoring of Two Advanced Polymer Composite Bridges

Continuous, long-term monitoring systems have been designed for two polymer composite bridges recently built in Delaware. The Magazine Ditch bridge has been continuously monitored for more than a year. The monitoring system provides data to investigate the effects of sustained load, environmental factors and live load on the bridge. Early results show that daily and seasonal temperature changes can induce strains in the bridge that are equal in magnitude to the maximum live load strains. A similar system has been designed for the first State owned composite bridge in Delaware. The monitoring system for bridge 1-351 is expected to be on-line by the summer 2000. Presented in the paper is a brief overview of the systems and sample results from the data collected for the Magazine Ditch bridge.

Performance of Uncoated Weathering Steel Highway Bridges Throughout the United States

Because uncoated weathering steel (UWS) bridges have been in use in the United States for nearly 50 years, the long-term performance of these structures can now be assessed. An assessment was completed by surveying the varied experiences of 52 U.S. transportation agencies and analyzing the data on all UWS bridges known within these and other agencies, which totaled nearly 10,000 structures. It was established that the superstructure condition ratings system (based on a standard national rating system) of these structures was a valid means of assessing UWS performance in a quantitative manner on the basis of a comparison of these ratings to qualitative information received from bridge owners in the 52 agencies surveyed. Of the most significant findings from the analysis, first, was that the superstructure condition ratings of the majority of UWS bridges were classified as excellent or very good, on the basis of the national criteria for these qualitative descriptors. Second, a comparison of the ratings of UWS bridges and other steel bridges within representative agencies while accounting for differences in ages of the various populations indicated that UWS displays increased or similar performance relative to other steel. UWS bridges performed quite well in most cases. Considering their economic and environmental benefits, continued or increased use of UWS bridges is regarded as sound engineering practice.

Strength behavior of filled steel grid decks for bridges

The life cycle of grid decks has come full circle from their introduction in the 1920s and 1930s through their maturity in 1950s and 1960s to their reintroduction in the 1980s. Many of these decks have been performing satisfactorily over 50 or more years of service. Filled grid decks offer a lightweight and high strength deck alternative to reinforced concrete decks. Despite the good performance history of grid decks, some bridge owners are hesitant to utilize them. With a better understanding of grid deck behavior, the manufacturing process can be optimized, and design method improved. Hence, poor details can be avoided and design efficiency can be achieved. This paper presents results of research conducted with the goal of providing a better understanding of filled steel grid deck behavior through experimental testing and numerical analyses. Three full-scale filled grid decks were tested to experimentally quantify their structural behavior. Three-dimensional finite element (FE) models were developed for...

Performance of Uncoated Weathering Steel Bridge Inventories: Methodology and Gulf Coast Region Evaluation

AbstractAlthough the majority of uncoated weathering steel (UWS) structures are performing well when designed and maintained in accordance with existing recommendations, exceptions to this trend exist. Additionally, the guidance on UWS use is largely qualitative. For these reasons, a data-driven method for assessing deterioration of a large sample of bridges as a function of environment was formulated, piloted, assessed, and validated. Key aspects of the methodology include the development of a database that uses graphical information systems to quantify the climate of hundreds of structures, a statistically driven process for selecting a representative sample of bridges for further evaluation, and a review of bridge performance based on owners’ evaluations and independent field evaluations. As a result of applying this methodology to UWS bridges with proximity to the Gulf Coast, environments consistently resulting in satisfactory performance were quantified; a rare combination of severe proximity to the ...

National Review on Use and Performance of Uncoated Weathering Steel Highway Bridges

Uncoated weathering steel (UWS) bridges have been in use in the United States for nearly 50 years, now enabling the long-term performance of these structures to be assessed. This was accomplished by surveying the varied experiences of 52 U.S. transportation agencies, along with data analysis on all UWS bridges known within these and other agencies, which total nearly 10,000 structures. Climate and age were key considerations in this data analysis. Contrary to previous, more limited research, this analysis showed that there is not a strong trend in UWS bridge performance as a function of climate. A similar climate analysis for non-UWS bridges also showed a counterintuitive relationship between some climate types and these bridges. This suggests that design and maintenance practices may be more influential to UWS performance than climate, and further research to cultivate current best practices in this regard is recommended. Comparison between the UWS and non-UWS data sets also reveals that UWS bridges generally perform well in relation to non-UWS bridges.