Scott A. Civjan

Evaluation of a Noncomposite Steel Girder Bridge through Live-Load Field Testing

This paper presents the field evaluation of a damaged noncomposite steel girder bridge that is part of the interstate highway system in Vermont. This bridge is typical of late 1960s construction and spans over a two-lane state highway near the town of Weathersfield, Vermont. The superstructure contains three-span continuous girders supported on abutments at the ends and on RC multicolumn interior bents. Strains were measured during live-load testing that was conducted to better understand the bridge behavior. The field results were compared with results from finite-element models created using common engineering assumptions. In addition, the load-distribution characteristics of girders that were damaged by an overheight truck traveling on the state highway under the bridge were evaluated. The results indicate that alternate load paths were developed within the bridge superstructure as a result of damage from the truck impact. For the loading magnitude applied during the load tests, evidence of composite action was observed and participation of curbs on the response of the bridge was noticed. Bridge skew and partial restraint generated at the supports also contributed to differences in the observed and calculated responses. These nondestructive load testing results were used to provide confidence on the load-carrying capacity of the bridge and to avoid costly bridge closures and detours.

Load Testing and Modeling of Two Integral Abutment Bridges in Vermont, US

Abstract Load testing of two instrumented single-span integral abutment bridges (IABs) in Vermont, US, was conducted using loaded multiple tandem dump trucks. Data was used to validate finite element (FE) models of each structure. Field data and FE model results were compared to gain an understanding of the distribution of live load on completed integral bridges and resulting stresses and deformations in structural components. The superstructure of the two bridges consists of a concrete deck supported on steel I-girders that are cast integrally into concrete abutments at the bridge ends. Abutments are supported on H-piles oriented with their weak axis resisting deformations in the direction of bridge alignment. The spans of the two bridges are 43 and 37 m, with girders connected to the abutments perpendicularly and with a skew angle of 15°. Correlation of measured data, such as girder strains, pile strains and deflections, abutment displacements, and backfill pressures, with FE model values are presented. Important considerations in the interpretation of field data are presented, including evaluations of the degree of composite action in girders, effects of thermal fluctuations over the course of testing and challenges faced when using field data directly to compute live load distribution factors.

Influence of daily and annual thermal variations on integral abutment bridge performance

The increased use of integral abutment bridges in recent decades has preceded fundamental understanding of system behavior and development of design methods that appropriately account for controlling parameters. Due to its integral design, the influence of factors such as thermal expansion/contraction must be revisited as they have a dominant role in behavior. This paper summarizes the soil-structure interaction aspects of the south abutment performance of a 270-ft three-span integral abutment bridge in central Massachusetts. Continuous performance monitoring with an instrumentation array of 85 sensors is ongoing. A site investigation of the abutment backfill was performed to estimate the lateral earth pressures. The influence of thermal effects on the south abutment performance over one 12-month cycle that included temperature variations between -18 and 38 degrees centigrade are presented.

Field monitoring of integral abutment bridge in Massachusetts

Integral abutment bridges are increasingly being used to eliminate undesirable bridge joint effects on the long-term performance of bridges. Although many states use this type of construction, common design guidelines are lacking, and nonuniform limitations on integral abutment design are imposed by different agencies. Data from the field monitoring of an existing three-span integral abutment bridge in central Massachusetts are presented. Resulting data are valuable in evaluating existing design provisions and understanding structural behavior. The results presented for a 16-month period of monitoring include recorded ambient temperature from -4°F to 99°F (-20°C to 37°C). Longitudinal movements induced by thermal expansion and contraction of the bridge are consistent with temperature changes. However, earth pressure cell data indicate that the maximum pressures generated behind the abutment walls occur in early spring. Lower pressures measured in the summer indicate some dissipation of soil pressures with time. Longitudinal displacement measurements taken during 2-week periods included variations that approached the magnitude of seasonal changes. Although fairly significant abutment movement has been recorded to date, there is no clear indication that the abutment piles have yielded. Field monitoring will continue, and the results from this study will be used to calibrate a detailed finite element model of the bridge to validate current integral abutment bridge design practices.

Issues and Methods for Transdisciplinary Planning of Combined Wildlife and Pedestrian Highway Crossings

Highways are increasingly understood as barriers to wildlife and pedestrian movement and as significant causes of landscape fragmentation–-especially in suburban and periurban areas. FHWAs Transportation, Community, and System Preservation (TCSP) Program encourages innovative solutions to reduce the impact of highways on the communities they link and traverse. This paper is based on research and public participation as part of an FHWA–TCSP sponsored feasibility study for a combined wildlife and pedestrian crossing to mitigate highway impacts on wildlife and recreation, and on the communities of Concord and Lincoln, Massachusetts. The interdisciplinary study team included representatives from landscape architecture, urban planning, wildlife biology, civil engineering, and landscape history. The study included diverse public participation and collaboration throughout the project. The paper defines significant planning issues likely to pertain to similar projects and offers a transdisciplinary method for conducting planning or feasibility studies for combined wildlife–pedestrian crossings. The method is innovative for its interdisciplinary integration and its inclusion of public officials, nongovernmental representatives, citizens, and other stakeholders. The study is being considered for further research and possible implementation by FHWA with support from the host communities and a private conservation organization.

CURVED INTEGRAL ABUTMENT BRIDGES - THERMAL RESPONSE PREDICTIONS THROUGH FINITE ELEMENT ANALYSIS

Integral abutment bridges (IAB) are common types of bridges that are designed to avoid maintenance problems occurring due to corrosion, creep and fatigue at connection elements such as expansion joints, bearings and roller supports. Deterioration of these connection elements may cause corrosion in structural elements and higher bridge maintenance costs. Performance of IABs is primarily governed by seasonal thermal changes, which subject abutments and piles to large deformations. These thermal movements are dependent on the superstructure material and geometry. Past research on this type of bridge has included real time field monitoring and finite element analyses on straight bridges with and without skew. Outcomes of these research studies have been used to form the basis for several guidelines on IAB design developed by state departments of transportation (DOT). Contrastingly, research on curved IABs are scarce and since, by virtue of their geometry response of the curved integral bridges to thermal loadings are complicated, most DOTs have restricted the design of curved girders for IABs. This paper presents results from finite element modeling of curved integral abutment bridges using the structural characteristics of a curved IAB in Vermont. The bridge models differed by varying the degree of curvature of the superstructure and backfill material properties. The influence of these two parameters on IAB thermal response were quantified through comparison of longitudinal and vertical deformations of the bridge deck, abutment displacements and rotations, weak and strong axis pile moments, and backfill pressures behind abutments. The models included five different degrees of curvature ranging from 0° (straight bridge) to 50°. For each model two different backfill properties (loose sand and dense sand) were used.

Bat Roosting in Bridges: Pros and Cons of Assessment Methods from a New England Regional Study

A research project was undertaken to assess bats’ use of bridges for roosting in New England. The project included rapid visual assessments of 191 bridges and more extensive evaluation of 18 of these bridges. Full evaluations included acoustic monitoring, detailed inspections, and emergence studies during early, mid-, and late summer roosting seasons in summer 2015, summer 2016, or both. During this project, 13 bridges were documented and positively identified as bat roosting sites in New England, and an additional two were highly likely (six of them were monitored in the project; 11 were identified by state departments of transportation), with possible roosting at several other sites. The project evaluated monitoring technologies including acoustic methods, infrared imaging, borescope inspection, and visual inspection. To identify bat species, both full-spectrum and zero-crossing acoustic monitoring software programs were used. These programs’ results differed significantly in species identification of identical call sequences; the range agreed with wide discrepancies between automated acoustic bat identification software program results previously reported in the literature. A new bridge inspection survey has been developed for the project to supplement FHWA-FRA survey forms. Recommendations for bridge surveys, training of inspection personnel, interpretation of data, and information to request from consultants have been developed through the project. Final project findings can be used as guidance for transportation agencies developing protocol for construction at potential roosting sites, which will be especially useful if federal listing of bat species and associated 4(d) rulings are modified in the future.

Deterioration of Terrazzo

Terrazzo installation is often perceived as an art, left to individual contractors and craftsmen to implement tried-and-true application and repair methods. In this context, architects and engineers often relegate themselves to a minimal supervisory role during construction and planning. The writers have found several recurring instances of terrazzo cracking problems during construction as well as deterioration that could be prevented or minimized with attention to the responsibilities of all parties to communicate throughout the design process. Causes are often related to shrinkage of terrazzo, concentrated stresses attributable to configuration of divider strips, and impact loads. To objectively minimize deterioration rates of terrazzo, an experimental program was initiated to evaluate performance. Testing consisted of compressive strength and linear shrinkage tests on cementitious terrazzo under varying curing conditions and a durability test that applied a cyclic gravity wheel load to gaps at the edge of terrazzo tiles. The latter test used metal wheels and considered parameters of material type, gap size between terrazzo edge and adjacent steel plate, wheel diameter, vertical offset of tile, and vertical load being applied. Results indicated that proper curing of cementitious terrazzo is critical to achieving compressive strength and minimizing early shrinkage. For the durability test performed, epoxy terrazzo exhibited significantly less deterioration. Durability of terrazzo is affected primarily by gap size, upward vertical offset, and weight applied. Small wheel size and direction of loading can also contribute to deterioration. It is important that architects, engineers, and contractors understand methods that ensure material properties, minimize stress concentrations, and use appropriate divider strip spacing to minimize deterioration attributable to cracking and impact load. These steps will ensure the visual appearance and durability expected by the project team.

Assessment of Bridge Joint Performance in the Northeastern States

The University of Massachusetts, Amherst conducted a research project to determine the best practices for bridge expansion joints and headers in the northeastern United States. This research included understanding how joints and headers are used and maintained, and what factors and practices have affected joint and header performance positively and negatively. The initial research included reviewing the literature on previous joint research and compiling information on the existing bridge joint inventory in Massachusetts. Next, information was collected on bridge joints, headers, and practices within the Massachusetts Department of Transportation (DOT), by meeting with and interviewing personnel from each of the six district offices. These meetings identified significant variation in joint preferences and performance between districts within a single DOT. A survey on the use and performance of joints and headers that included questions specific to installation, repair, maintenance, and overall practice was created and distributed to transportation agencies in Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont. The 26 survey responses were compiled and summarized. This paper describes regional practice in the northeastern United States based on the results of this research.

Field and Analytical Studies of the First Folded-Plate Girder Bridge

An innovative Folded Plate Girder (FPG) system bridge was constructed in Uxbridge, Massachusetts. The University of Massachusetts at Amherst collaborated with the Massachusetts Department of Transportation (MassDOT) Accelerated Bridge Construction Program to instrument the bridge with a total of 93 gages (strain gages, pressure cells, tiltmeters, displacement transducers, and convergence gages). Data was collected during construction, static live load testing, and long-term for twenty months. This paper presents data and comparisons to analysis (3-D bridge and girder modeling in SAP-2000 and ANSYS and 2-D hand calculations) to present an independent evaluation of the performance of this innovative bridge. Stresses in concrete and steel components are well below allowable design values through construction, long term data collection and truck load testing. Live-load test data indicate that the elastic neutral axis of the girders is higher than calculated, with measured strains being much lower than estimated from hand calculations and finite element (FE) results. This was partially explained by non-linearity of strains in the bottom flanges of the FPG due to shear lag when truck axles were positioned near instrumented locations, as confirmed through analysis. Through the first two years of service no signs of distress have been noted and readings are within the expected range of bridge behavior. Based on this study the FPG is an effective system for accelerated construction of short span bridges.