Showing papers in "Journal of Bridge Engineering in 2012"

Optimal Resilience- and Cost-Based Postdisaster Intervention Prioritization for Bridges along a Highway Segment

Abstract: In this paper, a general framework for the optimal resilience- and cost-based prioritization of interventions on bridges distributed along a highway connection between two cities that have experienced a disruptive natural or man-made event is proposed. Given the structural damage levels after the extreme event and the bridge characteristics, the proposed computational procedure finds the best intervention schedules, defined as starting time and progress pace of the restoration. The possible intervention schedules are considered optimal when they maximize the resilience of the highway segment and minimize the total cost of interventions. Because the two objectives are conflicting, the procedure uses genetic algorithms (GAs) to automatically generate a Pareto front of optimal solutions. Numerical examples are presented and discussed.

Practical Formula for Cable Tension Estimation by Vibration Method

Abstract: The tension force of cables must be measured accurately during construction and maintenance stages for cable-supported bridge systems. On the basis of the transverse vibration equation of a cable and by using a curve-fitting technique to replace the numerical iterative process, a practical formula to estimate the cable tension is proposed in a simply explicit form, in which the bending stiffness of the cable is included, and the sag effect is neglected for simplicity by using the frequencies relative to antisymmetric or higher vibration modes of the cable. The capability of this formulation is verified through comparison with available experimental results and finite-element solutions, which indicate that the formula developed in this paper is sufficiently accurate and can be conveniently applied to field measurement for cable-supported bridge systems.

Instrumentation, Nondestructive Testing, and Finite-Element Model Updating for Bridge Evaluation Using Strain Measurements

Abstract: A baseline finite element model was developed for bridge management and calibration using nondestructive test data. The model calibration technique was evaluated on the Vernon Avenue Bridge over the Ware River in Barre, Massachusetts. This newly constructed bridgewas instrumented throughout its construction phases in preparation for a static truck load test performed before the bridge opening. The strain data collected during the load test was used to calibrate a detailed baseline finite element model in an effort to represent the 3D system behavior of the bridge. Three methods of load ratings were used and compared: (1) conventional method, (2) conventional method updated by using NDT data, and (3) finite element model calibrated with NDT data. DOI: 10.1061/(ASCE)BE.1943-5592.0000228. © 2012 American Society of Civil Engineers. CE Database subject headings: Bridges; Superstructures; Full-scale tests; Field tests; Nondestructive tests; Strain; Measurement; Finite element method; Load tests; Structural health monitoring. Author keywords: Bridge; Superstructure; Full scale; Field testing; Strain measurements; Finite elements; Model calibration; Load testing; Load rating; Structural health monitoring; SHM.

Behavior of Segmental Precast Posttensioned Bridge Piers under Lateral Loads

Abstract: A segmental precast posttensioned (SPPT) bridge pier is an economic recentering structural system. Understanding the seismic behavior of a SPPT system is an important step toward its application in high seismic zones. This paper presents a detailed three-dimensional finite-element (FE) model that was developed using the ABAQUS platform. A brief description and discussion of cyclic tests on eight large-scale SPPT piers is also presented. Four of the piers were constructed and tested to a predefined degree of damage. Then, these piers were retrofitted and retested. The FE models developed and presented in this paper predicted the backbone curves of the piers that were tested directly after construction with an average error of 7% for drift angles smaller than 2.5%. For drift angles greater than 2.5%, the average error reached 13%. For piers that were retrofitted and retested, the error in predicting the backbone curve depended on the state of damage before the retest. When preexistent microcracks we...

Nondestructive Bridge Deck Testing with Air-Coupled Impact-Echo and Infrared Thermography

Abstract: Two different nondestructive test (NDT) methods, air-coupled impact-echo (IE) and infrared (IR) thermography are evaluated on a full-scale simulated reinforced concrete bridge deck containing simulated delamination and cracking defects. The IE data are presented as two-dimensional frequency maps and spectral B-scan lines. The IR data are presented as temperature maps on the concrete surface. The lateral boundaries of the detected delaminations are also indicated in the images. The results obtained from each of the individual NDT methods show reasonably good agreement with most of the actual defects. The advantages and limitations of each method to characterize defects are discussed. The consistency and sensitivity of each method are also investigated. Finally, a simple data fusion technique is proposed to improve effectiveness of the individual test data. The findings from this study demonstrate that the combination of air-coupled IE and IR thermography tests is a practical option for consistent and rapid in situ evaluation of reinforced concrete bridge decks.

Evaluation of Commercially Available Remote Sensors for Highway Bridge Condition Assessment

Abstract: Improving transportation infrastructure inspection methods and the ability to assess conditions of bridges has become a priority in recent years as the transportation infrastructure continues to age. Current bridge inspection techniques consist largely of labor-intensive subjective measures for quantifying deterioration of various bridge elements. Some advanced nondestructive testing techniques, such as ground- penetrating radar, are being implemented; however, little attention has been given to remote sensing technologies. Remote sensing technologies can be used to assess and monitor the condition of bridge infrastructure and improve the efficiency of inspection, repair, and rehabilitation efforts. Most important, monitoring the condition of a bridge using remote sensors can eliminate the need for traffic disruption or total lane closure because remote sensors do not come in direct contact with the structure. The purpose of this paper is to evaluate 12 potential remote sensing technologies for assessing the bridge deck and superstructure condition. Each technology was rated for accuracy, commercial availability, cost of measurement, precollection preparation, complexity of analysis and interpretation, ease of data collection, stand-off distance, and traffic disruption. Results from this study demonstrate the capabilities of each technology and their ability to address bridge challenges.

Stress Analyses and Parametric Study on Full-Scale Fatigue Tests of Rib-to-Deck Welded Joints in Steel Orthotropic Decks

Abstract: Fatigue tests of full-scale orthotropic steel decks were recently conducted to evaluate the fatigue performance of rib-to-deck partial-joint-penetration (PJP) groove welded joints. The test results indicated that rib-to-deck joints are more prone to fatigue cracks in the deck plate than in the rib wall. A shallower weld penetration (for example, an 80% PJP) also appeared to have a slightly higher fatigue resistance than a deeper one (for example, a 100% weld penetration). These PJP welds were also more vulnerable to cracking initiated from the weld toe than from the weld root. Finite-element analyses of the test specimens, using the effective notch stress method, were performed to supplement the laboratory testing and provide additional information on the behavior of these welded joints. The analysis results showed a good correlation with the observed crack patterns. A parametric study also showed that the fatigue resistance of the PJP joint can be significantly influenced by the transverse loading location, deck plate thickness, and the weld penetration ratio. Increasing the deck plate thickness was effective in reducing the stresses, while the rib wall thickness had a little effect. A shallower weld penetration at the PJP joint appeared to have a positive effect in enhancing the fatigue resistance.

Vibration-Based Method and Sensor for Monitoring of Bridge Scour

Abstract: Scour is the major cause for many bridge failures and damage to piers and abutments. Scour is not easily discernible because it is hidden under the channel flow. Over the years, a number of sensors have been developed for detection of scour depth. Development, testing, and field implementation of a new and simple type of scour sensor is described in this paper. The scour depth detection concept is based on measuring the fundamental frequency of vibration of a rod embedded in the riverbed. The sensor uses a single fiber-optic Bragg grating (FBG) sensor for transduction of the vibration frequency. The inverse relationship between the fundamental frequency and the length of the sensor rod is used for detection of the scour depth. A computational approach is developed based on the Winkler spring reaction soil model for automated calibration of the scour sensor during installation in the riverbed. The scope of the research included development of the theoretical basis for the sensor, establishment of the computational methodology for detection of the riverbed foundation properties, proof-of-concept laboratory tests, small-scale field verification tests, and installation and remote monitoring of scour in a multispan scour critical bridge in Illinois. The results include laboratory test data from the measurements in soil, simulated scour tests in a hydraulic flume, and real-time data from remote monitoring of scour at the bridge site.

Experimental and Numerical Study of the Fatigue Properties of Corroded Parallel Wire Cables

Abstract: Corroded cables from a cable-stayed bridge in China that had been in service for 18 years were employed to investigate the basic mechanical properties and residual fatigue life of wires and cables. First, the wires were randomly selected from the cables near the bottom anchorages and cut into segments as test specimens. The extent of corrosion of the wires was experimentally investigated. A tensile loading test was conducted on the wires to obtain the mechanical properties of the corroded single wires. The fatigue life of the corroded single wires was experimentally studied, and a dramatic degradation in fatigue life was observed. This phenomenon was interpreted using SEM images. Fatigue tests on two corroded cables were also conducted, and the test results indicated that the fatigue life of the cables had also decreased dramatically. A Monte Carlo simulation was conducted to obtain the fatigue life of cables. The simulation results indicated that the fatigue life of a cable was controlled by the small fraction of wires in the cable with the shortest fatigue lives. The fatigue life of a cable at a certain failure probability was dependent on the number of wires in the cable, but the mean fatigue life of a cable was not affected by the number of wires in the cable. DOI: 10.1061/(ASCE)BE.1943-5592.0000235. © 2012 American Society of Civil Engineers. CE Database subject headings: Cable-stayed bridges; Fatigue; Corrosion; Monte Carlo method; Simulation; Experimentation. Author keywords: Stay cable; Corrosion; Fatigue; Monte Carlo simulation.

Fatigue Reliability Assessment for Existing Bridges Considering Vehicle Speed and Road Surface Conditions

Abstract: During the life cycle of a bridge, dynamic impacts due to random traffic loads and deteriorated road surface conditions can induce serious fatigue issues for bridge components. It is necessary, and more realistic than the deterministic approach, to use reliability methods and treat the input parameters as random variables for the vehicle-bridge dynamic system. This paper presents a framework of fatigue reliability assessment for existing bridges in lifetime serviceability considering the random effects of vehicle speed and road-roughness condition. Since each truck passage might generate multiple stress ranges, revised equivalent stress-range is introduced to include fatigue damage accumulations for one truck passage. Therefore, the two variables, i.e., the stress-range numbers and equivalent stress ranges per truck passage, are coalesced in the newly defined variable based on equivalent fatigue damage. The revised equivalent stress-range is obtained through a fully-computerized approach toward so...

In-service condition assessment of bridge deck using long-term monitoring data of strain response

Abstract: Continuous awareness of the evolution of the structural condition of bridge structures is of great value for bridge owners, as it allows them to make informed decisions regarding the maintenance and management of these public facilities. Structural condition assessment via monitoring has gained in popularity in recent years, because it can provide structural engineers with plentiful information on the structural condition through various sensors. A key issue for successful application of monitoring technologies for condition assessment is how to realize meaningful interpretations of monitoring data. In this study, an approach to structural condition assessment of in-service bridge deck making use of long-term monitoring data of strain response is proposed and applied to the instrumented Tsing Ma Bridge. The proposed method consists of structural assessment at two levels: (1) deck truss component level and (2) deck cross-section level. As long-term monitoring data of dynamic strain under the in-ser...

Modeling Structural Performance of Ultrahigh Performance Concrete I-Girders

Abstract: Ultrahigh performance concrete (UHPC) is an advanced cementitious composite material that has been developed in recent decades. When compared with more conventional cement-based concrete materials, UHPC tends to exhibit superior properties such as increased durability, strength, and long-term stability. This computational investigation focused on modeling the structural behaviors of UHPC components including prestressed UHPC AASHTO Type II girders. The concrete damaged plasticity model was tailored to model UHPC within a commercially available finite-element analysis package. This manuscript focuses on modeling three UHPC I-girders tested under flexural or shear loading configurations. The concrete damaged plasticity model was demonstrated to replicate both linear and nonlinear structural responses of I-girders reasonably well. A set of UHPC constitutive properties were developed that facilitate the model replication of the local and global responses observed in the series of physical tests.

Investigation of Extreme Environmental Conditions and Design Thermal Gradients during Construction for Prestressed Concrete Bridge Girders

Abstract: Current AASHTO specifications provide engineers with a temperature gradient across the depth of the cross section to predict the vertical thermal behavior of bridges. This gradient is based on one-dimensional heat flow and does not account for change in the cross section, as found in prestressed concrete girders, nor does it account for thermal effects on the sides of the girder. Furthermore, the current specifications do not provide the transverse temperature gradient that is needed to predict the lateral thermal behavior of the girders, especially during construction, before the placement of the bridge decks. To determine the transverse and vertical temperature gradients in prestressed concrete girders, experimental and analytical studies were conducted on a prestressed BT-63 concrete girder segment. The analytical results were found to be in good agreement with experimental measurements. The analytical model was then used to determine the seasonal temperature gradients in four standard PCI girder sections at selected cities in the United States. On the basis of these findings, vertical and transverse temperature gradients were developed to aid engineers in predicting the thermal behavior of prestressed girders during construction.

Sensor Networks, Computer Imaging, and Unit Influence Lines for Structural Health Monitoring: Case Study for Bridge Load Rating

Abstract: In this paper, a novel methodology for structural health monitoring of a bridge is presented with implementations for bridge load rating using sensor and video image data from operating traffic. With this methodology, video images are analyzed by means of computer vision techniques to detect and track vehicles crossing the bridge. Traditional sensor data are correlated with computer images to extract unit influence lines (UILs). Based on laboratory studies, UILs can be extracted for a critical section with different vehicles by means of synchronized video and sensor data. The synchronized computer vision and strain measurements can be obtained for bridge load rating under operational traffic. For this, the following are presented: a real life bridge is instrumented and monitored, and the real-life data are processed under a moving load. A detailed finite-element model (FEM) of the bridge is also developed and presented along with the experimental measurements to support the applicability of the approach for load rating using UILs extracted from operating traffic. The load rating of the bridges using operational traffic in real life was validated with the FEM results of the bridge and the simulation of the operational traffic on the bridge. This approach is further proven with different vehicles captured with video and measurements. The UILs are used for load rating by multiplying the UIL vector of the critical section with the load vector from the HL-93 design truck. The load rating based on the UIL is compared with the FEM results and indicates good agreement. With this method, it is possible to extract UILs of bridges under regular traffic and obtain load rating efficiently.

Modeling Structural Performance of Second-Generation Ultrahigh-Performance Concrete Pi-Girders

Abstract: The concrete-damaged plasticity (CDP) model with proposed material properties replicated the observed deflection and strain responses of three experimentally tested I-girders and was determined to be consistent for different spans under both flexural and shear tests. In this study, the CDP model was further tested in modeling the behaviors of a prestressed second-generation ultrahigh-performance concrete (UHPC) pi-girder. The computational aspects include discussion of the various parameters that influenced the accuracy of the model and investigation of the scenarios regarding the limits that are useful for further optimization of the girder. The CDP model was reconfirmed to be consistent and reliable in replicating the observed structural response of both the UHPC pi-girder and a modified structural configuration referred to as the “UHPC pi-girder-with-joint.” The finite-element analysis modeling techniques developed herein are expected to be valuable in the future development of additional UHPC ...

Bridge Piers with Structural Fuses and Bi-Steel Columns. I: Experimental Testing

Abstract: Structural fuses, easily replaceable sacrificial elements to dissipate seismic energy while preventing damage to the gravity load-resisting structural system, are proposed as part of a multicolumn accelerated bridge construction (ABC) pier concept. Different types of structural fuses are investigated to compare the effect of each on ABC bridge bents. The piers of a three span-continuous bridge prototypes having two twin-column pier bents were designed using double-composite rectangular columns and structural fuses. Two corresponding 2/3-scale models were developed and were subjected to cyclic quasi-static tests. For the first specimen, steel-plate shear links (SPSLs) were installed between the columns as a series of structural fuses. Testing was performed, first up to a drift corresponding to the onset of columns yielding to investigate the effectiveness of adding the fuses in dissipating the seismic energy, then up to failure of the composite columns. The second tested specimen has buckling restrained braces (BRBs) as a series of structural fuses between the columns. The BRBs were then removed, and a cyclic test of the composite bent continued until failure of the columns. Both specimens exhibited stable hysteretic behavior, with the structural fuses also increasing stiffness and strength of the bent. Individual testing results for the SPSLs with various geometries and boundary conditions are then presented.

Cable-Stayed Bridges: Case Study for Ambient Vibration-Based Cable Tension Estimation

Abstract: A cable-stayed bridge recently constructed by the Ohio Department of Transportation incorporates measures put forth by a Federal Highway Administration study to mitigate stay motion. In following recent trends, the stays at this bridge are built without the use of grout for the purposes of inspection and, if necessary, replacement. Several experiments were performed to determine the viability of using traditional vibration techniques, which assume an integral sheath, to estimate cable tension with this new configuration.

Seismic Fragility of Retrofitted Multispan Continuous Steel Bridges in New York

Abstract: Various retrofit measures, such as elastomeric bearings, lead-rubber bearings, viscous dampers, and jacketing with carbon fibers, are commonly used to improve the seismic performance of multispan continuous steel highway bridges. In this paper, we have investigated the effectiveness of these retrofit measures through comparisons of seismic fragility of as-built and retrofitted multispan continuous steel bridges. Both elastomeric and lead-rubber bearings reduce the fragility of bridge piers significantly through isolation effects. Wrapping of piers with fiber-reinforced polymer (FRP) increases the effective ductility of piers through confinement and shifts the failure mode of a FRP wrapped pier to rupture of the FRP at much higher peak ground acceleration. The use of viscous dampers in combination with elastomeric bearings is effective in reducing fragilities because of both pier ductilities and bearing displacements. Hence, all four seismic retrofit strategies are effective in improving the safety of bridge components during earthquakes.

Probabilistic Fatigue Life Estimation of Steel Bridges by Using a Bilinear S-N Approach

Abstract: This paper focuses on estimating the fatigue life below the constant amplitude fatigue threshold (CAFT) of steel bridges by using a probabilistic approach on the basis of a bilinear stress life (i.e., the S-N approach). The current AASHTO S-N approach uses a single S-N line for predicting the fatigue life. However, because of the variation of actual applied live-load stress cycles, this approach very often results in a severe underestimation of the useful life of structures. It implies that fatigue damage in respective structural steel details may be overestimated. To improve fatigue life estimation, a bilinear S-N approach is integrated into a probabilistic framework that can model the uncertainties associated with the fatigue deterioration process. In this approach, the equivalent stress range is computed by using two S-N slopes and several probability density functions associated with stress ranges. These probabilistic functions are determined on the basis of stress-range bin histograms from long-term ...

Effect of Temperature on Daily Modal Variability of a Steel-Concrete Composite Bridge

Abstract: Vibration-based damage detection techniques typically use changes of modal characteristics of bridges as a possible indication of damage. However, structural damages are not the only cause of these changes. This study investigates the effect of temperature variations on modal characteristics of a two span steel-concrete composite bridge in North Carolina, and addresses the extent and reason of the daily changes observed in its dynamic properties. The field testing included measuring vibration responses, deflections, and temperatures of the bridge throughout a summer day. The dynamic characteristics of the bridge, derived from measurements at different times of the day, were compared with each other. Recorded temperatures and deflections of the bridge deck were used to address the observed changes in the natural frequencies of the bridge. Results of the field testing showed that temperature variations can induce modal variability on a daily cycle. A primary reason for this observation can be attributed to the temperature gradients measured on the bridge deck from night to noon.

Dynamic Analysis of Multihazard-Resistant Bridge Piers Having Concrete-Filled Steel Tube under Blast Loading

Abstract: Research was conducted to analytically investigate the blast-response and behavior of multihazard-resistant bridge piers having circular-shaped, concrete-filled steel tube (CFST) columns. Two different analysis methods, namely a single-degree-of-freedom (SDOF) dynamic analysis and a fiber-based dynamic analysis, were used for this purpose and calibrated with the maximum residual deformations obtained from 1=4 scale blast tests of CFST columns. It was noted that the structural response of SDOF dynamic analyses is sensitive to assumptions made in the load-mass factors needed to model structural components as an equivalent SDOF system. Fiber-based dynamic analyses showed that high-frequency modes of vibration have some influence on the structural response when subjected to blast loading. This study shows that different values of the shape factors, β (which reduces blast pressures when applied to a circular column), must be used with different analytical methods, along with assumptions and conditions behind these different analytical methods. DOI: 10.1061/(ASCE)BE .1943-5592.0000270. © 2012 American Society of Civil Engineers. CE Database subject headings: Blast loads; Bridges; Piers; Columns; Steel; Dynamic analysis. Author keywords: Blast loads; Bridges; Piers; Columns; Steel; Concrete-filled steel tube; Dynamic analyses; Multi-hazard.

Bridge Piers with Structural Fuses and Bi-Steel Columns. II: Analytical Investigation

Abstract: This paper presents the results of an analytical investigation conducted to replicate experimentally obtained behavior, and better understand the behavior of the proposed structural fuse concept for bridges that is presented in a companion paper. First, a steel plate shear link (SPSL) proposed as a new type of structural fuse is described. Equations are derived to define its shear-moment interaction equation, to determine some of its critical design parameters, and to quantify the link ductility, lateral stiffness and strength. Strengths and stiffnesses equations are developed using free-body diagrams (FBDs) for the tested systems as a convenient simple design tool. Finite-element models (FEM) are developed by using the finite-element software package ABAQUS/explicit to validate the proposed SPSL concept, and then to replicate the full range of results obtained from the experiments. Comparisons between the analytical and experimental results are conducted to highlight the differences in behavior among all tested specimens. The simple numerical equations correctly represent the expected strengths and stiffnesses of the fuse systems. Further, the results obtained from the ABAQUS model accurately captured the global behavior of the system, and provided valuable insight into individual fuse behavior.

Detection of the Presence of Broken Wires in Cables by Acoustic Emission Inspection

Abstract: Safety of suspension or stay cable bridges depends on the durability of their cables; stay cable bridges may present a healthy aspect on observable lengths but may be damaged in the nonvisible parts (anchorages). It is important to be able to detect as early as possible the defects affecting them. In this study, the acoustic emission (AE) technique is employed to detect the presence and location of broken wires in anchorage. Allowing a cable to vibrate can induce AE from interwire fretting. The study of the behavior of a broken wire during bending contributed to the understanding of the origin of the AE, that is, interwire fretting and the definition of the most suited bending conditions. For the identification of interwire friction, the main parameters of the acoustic signals are the number of events, their energy, and frequency distribution. These parameters are very dependent of roughness, lubrication, contact strength between wires, and recovery length. Several cables were studied with various surface conditions including corroded, dry, and oiled.

Fatigue Evaluation of Transverse U-Bar Joint Details for Accelerated Bridge Construction

Abstract: When precast full-depth deck panels and/or decked bulb-Ts (DBTs) are used for accelerated bridge construction, transverse joints exist. In this study, continuous transverse U-bar joint details, which can provide negative moment continuity in multispan bridges, have been investigated. Four full-scale specimens connected by the developed U-bar detail together with the selected closure-pour (CP) materials, overnight cure and seven-day cure, were tested. Static and fatigue tests under tension loading were conducted. The loading demand necessary in the testing was determined based on the maximum forces in the transverse joint from an analytical study. Test results were evaluated based on tension capacity, cracking, and steel strain. Based on these test results, the developed transverse U-bar joint detail is a promising connection system.

Approach to Reduce the Limitations of Modal Identification in Damage Detection Using Limited Field Data for Nondestructive Structural Health Monitoring of a Cable-Stayed Concrete Bridge

Abstract: The objective of the study was to propose a technique to reduce the limitations of modal identification in damage detection using reduced field data for nondestructive structural health monitoring of a cable-stayed concrete bridge. Simply supported bridge models were constructed with predetermined damage at the midspan of the bridge. The technique necessitated the performance of linear and eigen analyses on the control beam and nonlinear analysis on the bridge with damage. Residuals from regression of the mode shape using the Chebyshev rational series on the modal frequencies and transformation and application into the fourth-order centered finite-divided-difference formula were shown. The use of the regressed-mode shapes for the RC bridge model showed very large residuals around the areas of the damage. The results showed that the method was successful in assisting to reduce the limitations of modal identification in locating damage on a bridge model with limited field data and was comparable to other techniques proposed by other researchers in terms of its simplicity.

Effects of Temperature Variations on the In-Plane Stability of Steel Arch Bridges

Abstract: The in-plane stability of shallow parabolic arches subjected to a central concentrated load and temperature variations was in- vestigated in this paper. The virtual work principle method was used to establish the non-linear equilibrium and buckling equations. Analytical solutions for the non-linear in-plane symmetric snap-through and antisymmetric bifurcation buckling loads were obtained. Then, the effects of temperature changes on the in-plane stability for arches with supports that stiffen under compression were studied. The results show that the influence of temperature variations on the critical loads for both buckling modes (symmetric snap-through and anti symmetric bifurcation) is significant. The critical loads for the two buckling modes are more than those only under external loads without thermal loading. Moreover, the critical loads increase with an increase of the thermal loadings. It can also be found that the effects of applying a temperature field increase when either initial stiffness coefficient α or the stiffening rate β is raised. Furthermore, the effect of thermal loading on the critical load increases with the span-rise ratio m for arches with any initial stiffness coefficient α and the stiffening rate β. DOI: 10.1061/(ASCE)BE.1943-5592.0000208. © 2012 American Society of Civil Engineers. CE Database subject headings: Arch bridges; Steel bridges; Buckling; Temperature effects; Structural stability; Support structures. Author keywords: Bridges; Arch; Steel; Buckling; Temperature effects; Structural stability; Supports.

Detection of Initial Yield and Onset of Failure in Bonded Posttensioned Concrete Beams

Abstract: This paper discusses monitoring of bonded posttensioned (PT) concrete elements using the acoustic emission technique. In particular, a statistical pattern recognition technique based on a multivariate outlier analysis is presented to identify initial yielding and the onset of failure. Experimental tests on large-scale single-tendon bonded PT concrete beams, subjected to multiple load cycles, will be presented to validate the proposed monitoring system.

Evaluation of a Permit Vehicle Model Using Weigh-in-Motion Truck Records

Abstract: Permit truck models are used to consider local truck traffic in addition to national live load models in bridge design and rating practices. Weigh-in-motion (WIM) systems installed in the United States provide millions of truck records that can be used for evaluating such truck models. In this study, the standard permit vehicle in Wisconsin was evaluated by using six million WIM truck records collected in 2007. The evaluation was on the basis of statistical analyses of the maximum moments and shear in simply supported, 2-span, and 3-span continuous girders in the selected heaviest 5% of trucks in each vehicle class/group. The comparisons showed that 5-axle, short, single-unit trucks may cause larger moment/shear in bridge girders than the standard permit vehicle, and a 5-axle truck model was proposed to supplement the standard permit vehicle for possible use in bridge design and rating in Wisconsin.

Measurement System Configuration for Damage Identification of Continuously Monitored Structures

Abstract: Measurement system configuration is an important task in structural health monitoring in that decisions influence the performance of monitoring systems. This task is generally performed using only engineering judgment and experience. Such approach may result in either a large amount of redundant data and high data‐interpretation costs, or insufficient data leading to ambiguous interpretations. This paper presents a systematic approach to configure measurement systems where static measurement data are interpreted for damage detection using model‐free (non‐physics‐based) methods. The proposed approach provides decision support for two tasks: (1) determining the appropriate number of sensors to be employed and (2) placing the sensors at the most informative locations. The first task involves evaluating the performance of measurement systems in terms of the number of sensors. Using a given number of sensors, the second task involves configuring a measurement system by identifying the most informative sensor locations. The locations are identified based on three criteria: the number of non‐detectable damage scenarios, the average time to detection and the damage detectability. A multi‐objective optimization is thus carried out leading to a set of non‐dominated solutions. To select the best compromise solution in this set, two multi criteria decision making methods, Pareto‐Edgeworth‐Grierson multi‐criteria decision making (PEG‐MCDM) and Preference Ranking Organization METhod for Enrichment Evaluation (PROMETHEE), are employed. A railway truss bridge in Zangenberg (Germany) is used as a case study to illustrate the applicability of the proposed approach. Measurement systems are configured for situations where measurement data are interpreted using two model‐free methods: Moving Principal Component Analysis (MPCA) and Robust Regression Analysis (RRA). Results demonstrate that the proposed approach is able to provide engineers with decision support for configuring measurement systems based on the data‐interpretation methods used for damage detection. The approach is also able to accommodate the simultaneous use of several model‐free data‐interpretation methods. It is also concluded that the number of non‐detectable scenarios, the average time to detection and the damage detectability are useful metrics for evaluating the performance of measurement systems when data are interpreted using model‐free methods.

Analysis and Design of Straight and Skewed Slab Bridges

Abstract: Results of an investigation aimed at determining bending moments and shear forces, required to design skewed concrete slab bridges using the equivalent-beam method are presented in this paper Straight and skewed slab bridges were modeled using grillage and finite-element models to characterize their behavior under uniform and moving loads with the objective of determining the most appropriate modeling approach for design A parametric study was carried out on 390 simply supported slabs with geometries covering one to four lane bridges of 3- to 20-m spans and with skew angles ranging from 0 to 60° The analyses showed that nonorthogonal grillages satisfactorily predict the amplitude and the transverse distribution of longitudinal bending moments and shear forces, and can be used for the analysis of skewed slab bridges Results of the parametric study indicated that shear forces and secondary bending moments increase with increasing skew angle while longitudinal bending moments diminish Equations are prop