Performance of a Tied-Arch Reinforced Concrete Railway Bridge: Rating, Safety Assessment, and Bond Length Evaluation

This study presents investigations regarding visual inspection, dynamic testing, and finite-element modeling of an approximately 80-year old reinforced concrete tied-arch railway bridge that is still in service in Turkey. Investigations were conducted as part of a systematic periodic inspection along Ankara-Zonguldak railway line. The bridge is subject to heavy freight trains with increasing axle loads. Field tests such as material tests and dynamic tests were used to calibrate the finite-element model of the bridge. Detailed information regarding testing and model updating procedure is given. Based on test results, computer model was refined. The calibrated model of the bridge structure was then used for structural assessment and evaluation. Despite sufficient overall safety, local details were found to be problematic. Due to insufficient bond length in hanger-to-arch connection, a strengthening scheme using steel channel sections was proposed.     

Effect of Vehicle Velocity on the Dynamic Amplification of a Vehicle Crossing a Simply Supported Bridge

Many writers, using both experimental tests and complex numerical models, have examined the effect of vehicle velocity on a highway bridge’s dynamic amplification. Although these tests and models give valuable quantitative information on dynamic amplification, they give little insight into how amplification is affected by individual vehicle/bridge parameters. This paper uses relatively simple numerical models to investigate the effect of vehicle velocity on a bridge’s dynamic amplification. A single vehicle crossing a simply supported bridge is modeled as a constant point force. A set of critical velocities are determined associated with peaks of dynamic amplification for all beams. The reasons for these large amplifications are discussed. A more complex finite element model, validated with field tests, is used to test the applicability of the conclusions obtained from the simple models to a realistic bridge/vehicle system.     

Modal Testing, Finite-Element Model Updating, and Dynamic Analysis of an Arch Type Steel Footbridge

This paper describes an arch type steel footbridge, its analytical modeling, modal testing, finite-element model updating, and dynamic analysis. A modern steel footbridge which has an arch type structural system and is located on the Karadeniz coast road in Trabzon, Turkey is selected as an application. An analytical modal analysis is performed on the developed three-dimensional finite-element model of footbridge to provide analytical frequencies and mode shapes. Field ambient vibration tests on the footbridge deck under natural excitation such as human walking and traffic loads are conducted. The output-only modal parameter identification is carried out by using peak picking of the average normalized power spectral densities in the frequency domain and stochastic subspace identification in the time domain, and dynamic characteristics such as natural frequencies, mode shapes, and damping ratios are determined. The finite-element model of the footbridge is updated to minimize the differences between analytically and experimentally estimated modal properties by changing some uncertain modeling parameters such as material properties. Dynamic analyses of the footbridge before and after finite-element model updating are performed using the 1992 Erzincan earthquake record. At the end of the study, maximum differences in the natural frequencies are reduced from 22 to only 5% and good agreement is found between analytical and experimental dynamic characteristics such as natural frequencies and mode shapes by model updating. Also, maximum displacements and principal stresses before and after model updating are compared with each other.     

Analysis of Traffic-Induced Vibrations in a Cable-Stayed Bridge. Part II: Numerical Modeling and Stochastic Simulation

This paper describes the development of a numerical model to simulate the dynamic response of the bridge–vehicle system of Salgueiro Maia cable-stayed bridge, using the results from an extensive experimental investigation to calibrate this model. Further, a set of stochastic Monte Carlo simulations of the bridge–vehicle dynamic response is also presented, with the purpose of evaluating dynamic amplification factors, taking into account the randomness of different factors associated to characteristics of the pavement, of the vehicles and of the traffic flow.     

Experimental Assessment of Dynamic Responses Induced in Concrete Bridges by Permit Vehicles

Results from experimental testing of three permit vehicles are presented in the paper. The selected heavy vehicles, which require permits from state DOTs, included two tractor-trailer systems and a midsize crane. The vehicles were experimentally tested on popular existing speed bumps and on a representative highway bridge. The selected bridge was a reinforced-concrete structure constructed in 1999, located on the U.S. 90 in Northwest Florida. The bridge approach depression, combined with a distinct joint gap between the asphalt pavement and the concrete deck, triggered significant dynamic responses of the vehicle-bridge system. Similar dynamic vibrations were observed and recorded when the permit vehicles were driven over the speed bumps. Time histories of relative displacements, accelerations, and strains for selected locations on the vehicle-bridge system were recorded. The analysis of experimental data allowed for assessment of actual dynamic interactions between the vehicles and the speed bumps as well as dynamic load allowance factors for the selected bridge.     

Dynamic Monitoring of Steel Girder Highway Bridge

Currently there are different monitoring techniques that have been considered for use in the structural evaluation of bridges. These include approaches based on both static and dynamic behavior. The use of dynamic properties has advantages over static properties, since components of the dynamic properties are only marginally influenced by variations in the loading. When dynamic properties are used, field studies have shown that it is not always sufficient to use only natural frequencies and modal displacements. Some research for structural evaluation of bridges indicates that techniques based on use of derivatives of the natural frequencies and the modal displacements may be more effectively used to generate effective diagnostic parameters for structural identification. This paper presents the results of applying one of these methods, the modal flexibility approach, to a field study of a bridge in which the bearings were partially restrained in colder weather. While others have used impact methods with the modal flexibility method, in this study the approach is modified so that excitation is provided by vehicular traffic. The results show that the modified modal flexibility method provides a clear indication that there have been changes in the bridge’s structural behavior.     

Dynamic Analysis of a Composite Cable-Stayed Bridge: Escaleritas Viaduct

This work describes some of the most important results of the experimental and numerical analyses of Escaleritas Viaduct, Spain. Before the inauguration of this composite cable-stayed bridge in 2006, the bridge authority required a dynamic load test identifying, for instance, the natural vibration modes, the dynamic magnification factor, and the maximum vertical acceleration. The dynamic test was accompanied by numerical simulation performed in two different three-dimensional finite-element models, one of them composed of 145,000 shell elements. The correlation of test and analysis data is good and allows several interesting general conclusions to be drawn. It is shown that Escaleritas Viaduct complies with the requirements on the dynamic structural behavior defined in the standards.     

Field Experiments and Numerical Models for the Condition Assessment of Historic Timber Bridges: Case Study

Covered wooden bridges and the principles of heavy timber framing by which they were built represent both a significant chapter in this country’s civil engineering heritage, and a subclass of bridges that are in immediate need of repair and rehabilitation. This work often falls on the shoulders of the municipalities who own the bridges or local consulting engineering companies, neither of which have the resources to perform state-of-the-art damage assessment analyses. This study presents two case studies in which a simplified approach to damage assessment is used. The writers explore the importance of proper condition assessments, including both field observations and load tests, to the creation of viable finite-element models that practicing engineers may use in their repair and rehabilitation of these unique structures. Experimental tests were performed on two covered bridges: Morgan Bridge in Belvidere, Vermont and Pine Grove Bridge, in Oxford, Pennsylvania, and comparisons were made to finite-element models created of those bridges. The combination of experimental and numerical tools led to the identification of several deteriorated components, including scarf joints, lapped brace joints, and retrofitted members within the bridges that may have otherwise gone undetected.     

Flexural Capacity of Compact Composite I-Girders in Positive Bending

Current American Association of State Highway and Transportation Officials (AASHTO) bridge specifications for compact composite steel girders in positive bending with adjacent compact pier sections limit the allowable maximum strength to a value between the full plastic moment and the hypothetical yield moment of the cross section as a function of the depth of web in compression. The strength prediction equations derived using these methods provide conservative values when compared to the results of the parametric studies used to develop the equations. Recent experimental tests coupled with finite-element analysis and mechanistic evaluations of the cross-section flexural capacity suggest that larger capacities may be achieved than those determined from AASHTO’s prediction equations. This paper presents an assessment of the behavior of composite positive bending specimens. A summary of a comprehensive literature review is provided coupled with results of the analytical and experimental evaluation of the nominal moment capacity of composite girders. Lastly, a less conservative design moment capacity expression developed from this assessment is provided.     

Refined Stick Model for Dynamic Analysis of Skew Highway Bridges

Stick models are widely employed in the dynamic analysis of bridges when only approximate results are desired or when detailed models are difficult or time-consuming to construct. Although the use of stick models for regular bridges has been validated by various researchers, the application of such models to skew highway bridges continues to present challenges. The conventional single-beam stick model used to represent the bridge deck often fails to capture certain predominant vibration modes that are important in obtaining the true dynamic response of the bridge. In this paper, a refined stick model is proposed for the preliminary dynamic analysis of skew bridges. The model utilizes a dual-beam stick representation of the bridge deck. The validity of the model is established by comparing results obtained from the proposed model with numerical solutions obtained for skew plates and a skew bridge. It is shown that this dual-beam stick model is superior to the conventional single-beam model in estimating the natural vibration frequencies and in predicting the predominant vibration modes of the bridge. Because of its simplicity and relative accuracy, this model is recommended for the preliminary dynamic analysis of skew highway bridges.     

Finite-Element Analysis and Vibration Testing of a Two-Span Masonry Arch Bridge

This paper presents the analytical modeling, modal testing, and finite-element model updating for a two-span masonry arch bridge. An Ottoman masonry arch bridge built in the 19th century and located at Camlihemsin, Rize, Turkey is selected as an example. Analytical modal analysis is performed on the developed 3D finite-element model of the bridge to obtain dynamic characteristics. The ambient vibration tests are conducted under natural excitation such as human walking. The operational modal analysis is carried out using peak picking method in the frequency domain and stochastic subspace identification method in the time domain, and dynamic characteristics (natural frequencies, mode shapes, and damping ratios) are determined experimentally. Finite-element model of the bridge is updated to minimize the differences between analytically and experimentally estimated dynamic characteristics by changing boundary conditions. At the end of the study, maximum differences in the natural frequencies are reduced on average from 18 to 7% and a good agreement is found between analytical and experimental dynamic characteristics after finite-element model updating.     

Corrosion and Embrittlement in High-Strength Wires of Suspension Bridge Cables

An in-depth analysis of the deterioration mechanisms in high-strength wires of suspension bridge cables is presented. Accelerated cyclic corrosion tests were conducted to assess the relative effect of corrosion on galvanized and ungalvanized wires. Samples were corroded under various levels of sustained loads in a cabinet that cyclically applied an acidic salt spray, dry conditions, and 100% relative humidity at elevated temperature, and mass loss, hydrogen concentration, ultimate load, and elongation at failure were measured. Elongation measurements indicated a significant embrittlement of the wires that could not be explained solely by the presence of absorbed hydrogen (hydrogen embrittlement). The main cause of reduction of wire elongation was found to be the surface irregularities induced by the corrosion process. The experimental results were validated through a numerical analysis using a finite-element method model of the corroded steel wire and through a series of scanning electron microscope analyses of the fracture surfaces.     

Experimental Evaluation of Dynamic Effects for a Selected Highway Bridge

The paper presents an experimental study of the actual dynamic effects for a preselected typical highway bridge. Knowledge of the dynamic impact factors is important for accurate determination of the ultimate load capacity and performance assessment of constructed bridges. Static and dynamic field tests were performed on a two-lane concrete highway bridge built in 1999 on U.S. 90 in northwest Florida. During the tests, one or two fully loaded trucks crossed over the bridge, which was instrumented with strain gauges, accelerometers, and displacement transducers. A wooden plank was placed across the lanes for some runs to trigger extensive dynamic vibration and to simulate poor road surface conditions. Data collected from the tests were used for comprehensive assessment of the bridge under dynamic loading. Impact factors obtained from the tests with higher speeds were found larger than corresponding values recommended by bridge codes. Analysis revealed that stiff vehicle suspension, road surface imperfection, and “bouncing” of the truck loading contributed to the high impact factors. Experimental data were also used for validation of the finite-element models developed for the vehicle–bridge system.     

Vibration Control of Stay Cables of the Shandong Binzhou Yellow River Highway Bridge Using Magnetorheological Fluid Dampers

The Shandong Binzhou Yellow River Highway Bridge is a three-tower, cable-stayed bridge in Shandong Province, China. Because the stay cables are prone to vibration, 40 magnetorheological (MR) fluid dampers were attached to the 20 longest cables of this bridge to suppress possible vibration. An innovative control algorithm for active and semiactive control of mass-distributed dynamic systems, e.g., stay cables, was proposed. The frequencies and modal damping ratios of the unimpeded tested cable were identified through an ambient vibration test and free vibration tests, respectively. Subsequently, a series of field tests were carried out to investigate the control efficacy of the free cable vibrations achieved by semiactive MR dampers, “Passive-off” MR dampers and “Passive-on” MR dampers. The first three modal damping ratios of the cable incorporated with the MR dampers were also identified from the in situ experiments. The field experiment results indicated that the semiactive MR dampers can provide significantly greater supplemental damping for the cable than either the Passive-off or the Passive-on MR dampers because of the pseudonegative stiffness generated by the semiactive MR dampers.     

Influence of Foundation Scour on the Dynamic Response of an Existing Bridge

Foundation scour is a major issue affecting the structural safety of existing bridges, hence its monitoring is of paramount importance. This paper reports a case history of assessment and monitoring with dynamic tests for a bridge affected by scouring and subjected to retrofitting. Two different approaches measuring traffic-induced vibrations are applied as potential tools for monitoring foundation scour. The modal identification of bridge spans is one approach, and the observation of the dynamic response of pier foundations is the other approach. A finite-element model is used to choose the parameters for scour monitoring. Both approaches are applied to the experimental data collected about the structure prior to and after retrofitting to show their effectiveness.     

Dynamic and Static Behavior of a Curved-Girder Bridge with Varying Boundary Conditions

A curved, three-span continuous, steel I-girder bridge in Salt Lake City was tested in order to determine its dynamic and static load carrying properties for three boundary condition states. For each of the three boundary condition states, two dynamic forced vibration methods were applied to the bridge as well as a static live-load test. The first forced vibration method used an eccentric mass shaker. The second method involved striking the side of the bridge with an impact hammer. The live-load test was performed by slowly driving a truck at a crawl speed across the bridge. Velocity transducers, accelerometers, and strain gauges were utilized to record the response of the bridge. The analysis and compilation of recorded dynamic response of the bridge enabled the preparation of mode shapes and natural frequencies for each boundary condition. This paper discusses the resulting changes in relevant dynamic properties and compares them with the changes in the static properties that were determined from the bridge response recorded from the live-load tests.     

Determination of Bridge Design Parameters through Field Evaluation of the Route 601 Bridge Utilizing Fiber-Reinforced Polymer Girders

The Route 601 Bridge in Sugar Grove, Virginia, spans 11.89?m (39?ft) over Dickey Creek. The bridge is the first to use the Strongwell 91.4?cm (36?in.) deep fiber-reinforced polymer double web beam in a vehicular bridge superstructure. Construction of the new bridge was completed in October 2001 and field testing was undertaken shortly thereafter, as well as in June of 2002, to assess any potential changes in structural performance. This paper details the field evaluation of the Route 601 Bridge. Using midspan deflection and strain data from the October 2001 and June 2002 field tests, AASHTO bridge design parameters were determined—namely, wheel load distribution factor g, dynamic load allowance IM, and maximum deflection. The wheel load distribution factor was determined to be S/4, a dynamic load allowance was determined to be 0.36, and the maximum deflection of the bridge was L/1,110. Deflection results were lower than the AASHTO L/800 limit. This discrepancy is attributed to partial composite action of the deck-to-girder connections, bearing restraint at the supports, and contribution of guardrail stiffness. It was found that diaphragm removal had a small effect on the wheel load distribution factor.     

Static and Dynamic Behavior of High- and Ultrahigh-Performance Fiber-Reinforced Concrete Precast Bridge Parapets

New designs of precast bridge parapets made with fiber-reinforced concrete (FRC) were developed using nonlinear finite-element calculations. Specific properties of high- and ultrahigh-performance FRC were exploited in these designs. The conventional reinforcement required in the FRC precast parapets varied from 0 to 50% when compared with a reference built-on-site parapet. An extensive experimental program was carried out to verify the performance of the FRC precast parapets. The parapet mechanical behavior was established under quasi-static tests and under dynamic loading replicating a vehicle impact. The results of the quasi-static tests indicate that precast FRC parapets possess the required strength and have ductility comparable to reference parapets. Quasi-static tests carried out after the dynamic tests indicate that the residual strength of the parapets corresponds to 75 to 100% of their original capacity. The finite-element model adopted in the project satisfactorily reproduced the strength, stiffness, and failure mode of the parapets. Finally, the system efficiency of precast FRC parapets was established for their application in a typical urban bridge project, considering the mechanical performance, the fabrication costs, and the required installation time.     

Development and Implementation of a Continuous Strain Monitoring System on a Multi-Girder Composite Steel Bridge

This paper describes the implementation and evaluation of a long-term strain monitoring system on a three-span, multisteel girder composite bridge located on the interstate system. The bridge is part of a network of bridges that are currently being monitored in Connecticut. The three steel girders are simply supported, whereas the concrete slab is continuous over the interior supports. The bridge has been analyzed using the standard AASHTO Specifications and the analytical predictions have been compared with the field monitoring results. The study has included determination of the location of the neutral axes and the evaluation of the load distributions to the different girders when large trucks cross the bridge. A finite-element analysis of the bridge has been carried out to further study the distribution of live load stresses in the steel girders and to study how continuity of the slabs at the interior joints would influence the overall behavior. The results of the continuous data collection are being used to evaluate the influence of truck traffic on the bridge and to establish a baseline for long-term monitoring.     

Development of FRP Short-Span Deployable Bridge—Experimental Results

For military and civilian applications, there exists a need for lightweight, inexpensive, short-span bridges that can be easily transported and erected with minimal equipment. Owing to its favorable properties, fiber-reinforced polymer (FRP) has been shown to be feasible for the construction of such bridges. Investigations into the behavior of a short-span bridge structural concept, adapted to the material properties of commercially available glass FRP (GFRP) pultruded products, are presented. A 4.8-m span prototype was built from GFRP sections, bonded throughout to form a tapered box beam, with a width of 1.2?m and a height at midspan of approximately 0.5?m. The box beam represents a single trackway of a double-trackway bridge, whose trackways could be connected by light structural elements. The quasi-static and dynamic behavior of the prototype box beam was investigated in ambient laboratory and field conditions to assess the design and construction techniques used, with a view to designing a full-scale 10-m GFRP bridge. Laboratory testing of the prototype box beam used single and pairs of patch loads to simulate wheel loading. These tests confirmed that the box beam had sufficient stiffness and strength to function effectively as a single trackway of a small span bridge. Field testing of the structure was undertaken using a Bison vehicle (13,000?kg), driven at varying speeds over the structure to establish its response to realistic vehicle loads and the effects of their movement across the span.