Journal of Bridge Engineering

Published by American Society of Civil Engineers
Print ISSN: 1084-0702
It is hopeful to detect damage in a fast and reliable way in order to increase the safety, extend the working life and reduce the maintenance cost of long-span bridges. Recently, more attention is being paid to dynamical damage detection techniques. The energy-based dynamical damage detection strategy is a novel topic in this field. In this paper, a damage detection strategy based on acceleration responses’ energy is proposed based on the relationship between the frequency response function (FRF) of acceleration responses and mode shapes. Numerical analysis on a long-span cable-stayed bridge is performed by using the proposed strategy and the traditional mode shape curvature strategy. Moreover, damage quantification analysis and robustness analysis for noise pollution are carried out. It can be shown from the analysis results that the acceleration responses’ energy-based damage detection strategy has not only accurate damage location ability but also excellent damage quantification ability and anti-noise pollution ability.
Representation of the crane passing over the bridge and sensor location.
Global monitoring of civil structures is a demanding challenge for engineers. Acoustic emission (AE) is one of the techniques that have the potential to inspect large volumes with transducers placed in strategic locations of the structure. In this paper, the AE technique is used to characterize the structural condition of a concrete bridge. The evaluation of AE activity leads to information about any specific part of the structure that requires attention. Consequently, more detailed examinations can be conducted once the target area is selected. In this case, wave propagation velocity was used as a means to evaluate, in more detail, the condition of the region indicated by the AE analysis.
The objective of the work of this paper was to investigate analytically the feasibility and advantages of applying various combinations of steel jacket retrofit measures developed for single-column bent bridges to multicolumn bent bridges. To achieve the objective, an existing nonlinear dynamic bridge analysis program with elastic–perfectly plastic column behavior and a conventional hysteresis model was modified in order to include softening behavior from column damage and a more realistic hysteresis rule for cyclic loading. A 2D structural model of an actual bridge was used to evaluate column retrofitting measures by applying a typical seismic record. Both partial and full column retrofit strategies were shown to result in decreased maximum earthquake response and decreased plastic deformation of columns for the bridge bent compared to the case without retrofitting, but to varying degrees. However, for some partial retrofit strategies, the plastic hinge rotation at the unretrofitted columns was deemed to be unacceptable. Therefore, it was concluded that partial column retrofit strategies are viable only if combined with an evaluation of the ductility capacity of the bridge.
Based on observed damage patterns from previous earthquakes and a rich history of analytical studies, asynchronous input motion has been identified as a major source of unfavorable response for long span structures, such as bridges. This study is aimed at quantifying the effect of geometric incoherence and wave arrival delay on complex straight and curved bridges using state-of-the-art methodologies and tools. Using fully parameterized computer codes combining expert geotechnical and earthquake structural engineering knowledge, suites of asynchronous accelerograms are produced for use in inelastic dynamic analysis of the bridge model. Two multi-degree-of-freedom (MDOF) analytical models are analyzed using 2,000 unique synthetic accelerograms. Results from this study indicate that response for the 344 meter study structure is amplified significantly by non-synchronous excitation, with displacement amplification factors between 1.6 and 3.4 for all levels of incoherence. This amplification was not constant or easily predicable, demonstrating the importance of inelastic dynamic analysis using asynchronous motion for assessment and design of this class of structure. Additionally, deck stiffness is shown to significantly affect response amplification, through response comparison between the curved and an equivalent straight bridge. Study results are used to suggest an appropriate domain for consideration of asynchronous excitation as well as an efficient methodology for analysis. National Science Foundation EEC-9701785 published or submitted for publication
Circular reinforced concrete highway bridge piers, designed in accordance with the requirements of the California Department of Transportation (Caltrans) in the U.S., New Zealand, and Japanese specifications, are experimentally investigated to assess their seismic performance. Pseudodynamic test procedures are developed to perform experiments on 30% scaled models of the three prototype bridge piers. Each specimen is subjected to a sequence of three different earthquake ground motions scaled appropriately to represent: (1) the design basis earthquake (DBE) with a 90% nonexceedance probability; (2) the maximum considered earthquake (MCE) with a 50% nonexceedance probability; and (3) the MCE with a 90% nonexceedance probability. Damage states after the earthquakes are assessed and mapped for seismic risk assessment. The damage outcomes and the corresponding seismic risks validate the objectives of the performance-based design codes of the three countries. The results show that when bridge piers are designed to the specifications of each of the three countries, satisfactory performance with only slight to moderate damage can be expected for DBE. For the MCE, severe damage without collapse is likely for the Caltrans and Japanese piers. However, the NZ pier may not be able to survive MCE motions with sufficient reliability to ensure the preservation of life-safety
In recent bridge construction in Connecticut involving heavy sections, galvanized coating thicknesses were in excess of 12 mils. The current American Association of State Highway and Transportation Officials specification is based on research conducted with coating thicknesses not greater than 6 mils. Since thicker coatings on steel can reduce shear capacity in high-strength bolted connections, there was concern that the thick galvanized coating could compromise the performance. In this research, tests were conducted to study the relaxation and the shear capacity of high-strength bolted connections with galvanized coating thicknesses up to 20 mils. Both normal and oversize holes were studied. The research shows that the shear capacity of connections with thick galvanized coatings is reduced due to the loss in the clamping force. The test results have been used to develop design guidelines.
This study presents an evaluation of shear and moment live-load distribution factors for a new, prestressed concrete, spread box-girder bridge. The shear and moment distribution factors were measured under a live-load test using embedded fiber-optic sensors and used to verify a finite element model. The model was then loaded with the American Association of State Highway and Transportation (AASHTO) design truck. The resulting maximum girder distribution factors were compared to those calculated from both the AASHTO standard specifications and the AASHTO LRFD bridge design specifications. The LRFD specifications predictions of girder distribution factors were accurate to conservative when compared to the finite element model for all distribution factors. The standard specifications predictions of girder distribution factors ranged from highly unconservative to highly conservative when compared to the finite element model. For the study bridge, the LRFD specifications would result in a safe design, though exterior girders would be overdesigned. The standard Specifications, however, would result in an unsafe design for interior girders and overdesigned exterior girders.
A detailed finite-element (FE) modeling procedure is presented for evaluating the redundancy of twin steel box-girder bridges. For this study, it was assumed that the passage of a truck live load triggers the sudden fracture of one girder. Because of the possibility of localized damage in some bridge components, the proposed computational models incorporate material nonlinearity to represent cracking and crushing of concrete and steel yielding. In addition, the proposed FE models are capable of capturing deck haunch separation by adopting a stud connection failure model. This failure mode was first observed during testing of a full-scale bridge that included a girder with a full-depth fracture. Analysis results show that typical twin steel box-girder bridges likely have greater redundancy than the current provisions indicate and that stud connection failure could significantly affect the redundancy of steel box-girder bridges.
shows the average estimates
Schematic representation of the bridge with indication of the measurement sections used in the ambient vibration test The ambient vibration test was developed performing vibration measurements with six independent triaxial accelerographs, two of them being permanently installed at a given reference cross section (section 10, 1/3 span North), while the others were successively placed at 28 different mobile sections along the deck and towers (Figure 3). In all sections, the pairs of sensors were located laterally, upstream and downstream, always oriented according to the orthogonal referential xx (longitudinal direction), yy (transversal) and zz (vertical). These accelerographs were appropriately programmed before each sequence of measurements, in order to begin the acquisition simultaneously every twenty minutes, in principle. Taking into account the very low frequency range of interest (0-1Hz), the time of acquisition for each setup was always 16 minutes, with a sampling frequency of 50Hz, so as to obtain average spectral estimates with a frequency resolution inferior to 0.01Hz. The time left to change the position of the accelerographs between successive setups was of 4 minutes, except in the case of measurements along the towers, due to the necessity of climbing the stairs till the top, transporting the accelerographs in rockbags. Due to the relatively low level of signal captured, appropriate amplification factors were used, leading to a precision superior to 0.015mg (1g/2 16 ), in consequence of the use of 16 bit A/D converters.
Installation of accelerometers on stay cables 
This paper describes the dynamic tests performed on a large cable-stayed bridge, Vasco da Gama Bridge, on the basis of a non-conventional testing system, comprehending several independent accelerographs conveniently synchronised by a laptop, as well as a laser interferometry system for non-contact dynamic measurements in stay cables. This system showed to be rather portable, efficient and accurate, leading to the creation of a very large high quality data base concerning the dynamic behaviour of the bridge. Subsequent processing of the data permitted to identify accurately all the significant modal parameters of interest from the aerodynamic and seismic point of view, which present a very good correlation with the corresponding values provided by the 3-D numerical finite element model previously developed at the design stage
In general, state-of-the-art bridge management systems have adopted Markov-chain models to predict the future condition of bridge elements and networks in different environments when various maintenance actions are implemented. However, the categories used to describe the various possible environments for a bridge element are neither accurately defined nor explicitly linked to the external factors affecting the element deterioration. In this paper, a new approach is proposed to provide transportation agencies with an effective decision support tool to identify the categories that best define the environmental and operational conditions specific to their bridge structures. This approach is based on genetic algorithms to determine the combinations of deterioration parameters that best fit each environmental category. The proposed approach is applied to develop Markovian deterioration models for concrete bridge decks using actual data obtained from the Ministére des Transports du Québec. This application illustrates the ability of the proposed approach to correlate the definition of environmental categories to parameters, such as highway class, region, average daily traffic, and percentage of truck traffic, in an accurate and efficient manner.
The purpose of this paper is to develop new formulas for live load distribution in horizontally curved steel I-girder bridges. The formulas are developed by utilizing computer model results for a number of different horizontally curved steel I-girder bridges. The bridges used in this study are modeled as generalized grillage beam systems composed of horizontally curved beam elements for steel girders and substructure elements for lateral wind bracing and cross frames which consist of truss elements. Warping torsion is taken into consideration in the analysis. The effect of numerous parameters, including radius of curvature, girder spacing, overhang, etc., on the load distribution are studied. Key parameters affecting live load distribution are identified and simplified formulas are developed to predict positive moment, negative moment, and shear distribution for one-lane and multiple-lane loading. Comparisons of the formulas with finite element method and grillage analysis show that the proposed formulas have more accurate results than the various available American Association of State Highway and Transportation Officials specifications. The formulas developed in this study will assist bridge engineers and researchers in predicting the actual live load distribution in horizontally curved steel I-girder bridges.
This paper treats the dynamic effect of traffic actions on the deck slabs of concrete road bridges using the finite-element method. All the important parameters that influence bridge-vehicle interaction are studied with a systematic approach. An advanced numerical model is described and the results of a parametric study are presented. The results suggest that vehicle speed is less important than vehicle mass and that road roughness is the most important parameter affecting the dynamic behavior of deck slabs. The type of bridge cross section was not found to have a significant influence on deck slab behavior. The dynamic amplification factor varied between 1.0 and 1.55 for the bridges and vehicles studied. These results should be validated by further work.
Currently, estimations of the crack width in the deck slab of bridges given by codes of practice are based on either theoretical or empirical approaches considering mainly the monotonic loading behaviour. However, cracking in reinforced tensile members is highly influenced by the loading history (including both the loading and unloading processes). The irreversible non-linear behaviour of bond and the tensile response of concrete induce residual cracks of non negligible width. This paper investigates the influence of this phenomenon and presents a physical model describing it. An analytical model is developed and its results are compared to various tests with good agreement. Finally, a simple design formula is derived and recommendations for its application to practical cases are proposed.
Next generation bridge management systems will take into consideration multiple hazard scenarios and not only traffic loading and structural deterioration as they do now. The indirect costs used in these bridge management systems to determine optimal management strategies vary according to the hazard scenarios considered. The difference depends on whether or not the bridge failures are due to a common cause, such as a single flood or earthquake, or due to load events that may be considered statistically unrelated, such as truck loads. To illustrate the effect of common cause bridge failures on indirect costs, two examples are presented that treat the failures first as if they are due to statistically independent loading events and then as if they are due to a common cause. To examine the effect of bridge failures on indirect costs of the system, estimation is performed at the network level. The first example, on a simple network, shows the indirect cost estimate for all of the network condition states. The second example, on a complex network, shows the difference in the possible reduction of total indirect costs with a single bridge intervention as well as the change in intervention sequence. The main conclusions are that total indirect costs and optimal intervention sequences differ depending on whether or not bridge failures are due to a common cause, and that the largest changes in indirect cost estimation occur when simultaneously failed bridges affect the method of indirect cost incurrence.
Recent research studies have confirmed that curved I-girders are capable of developing substantial shear postbuckling resistance due to tension field action and have demonstrated that the AASHTO LRFD equations for the tension field resistance in straight I-girders may be applied to curved I-girders within specific limits. However, the corresponding demands on intermediate transverse stiffeners in curved I-girders are still largely unknown. Furthermore, a number of prior research studies have demonstrated that transverse stiffeners in straight I-girders are loaded predominantly by bending induced by their restraint of web lateral deflections at the shear strength limit state, not by in-plane tension field forces. This is at odds with present Specification approaches for the design of transverse stiffeners, which are based on (1) providing sufficient stiffener bending rigidity only to develop the shear buckling strength of the web and (2) providing sufficient stiffener area to resist the in-plane tension field forces. In this research, the behavior of one- and two-sided intermediate transverse stiffeners in straight and horizontally curved steel I-girders is investigated by refined full nonlinear finite element analysis. Variations in stiffener rigidity, panel aspect ratio, panel slenderness, and stiffener type are considered. New recommendations for design of transverse stiffeners in straight and curved I-girder bridges are developed by combining the solutions from the above FEA studies with the results from prior research. M.S. Committee Chair: Dr. Donald W. White; Committee Member: Dr. Kenneth M. Will; Committee Member: Dr. Rami M. Haj-Ali
Chapters 6–8 contains a clear discussion on how to carry out analytical design sensitivity analysis of eigenvalue–eigenvector, vibration, and flutter problems. It begins by considering the linear eigenvalue problem as occurs in undamped vibration or buckling; Nelson’s method is explained in detail. A rare-to-find adjoint technique is also discussed. Then, eigenvalue problems with damping are considered. These methods are applied to determining sensitivity coefficients of free-vibration bridge problems in Chapter 7. Worthy of mention is the treatment of design sensitivity analysis with a nonlinear geometric stiffness matrix. The authors discuss a code, ADISNOL3D, that they have developed for dynamic analysis and analytical design sensitivity analysis. A code with such capability is not available commercially. The results have been validated using divided differences. The authors have design data for various bridges, which enable them to produce the results. Chapter 8 treats the analytical design sensitivity analysis of flutter speeds. This derivation is not readily available in the literature and will be of great value for engineers working in dynamics and aeroelasticity. The details of finite elements and implementation that are presented will be of considerable value to scientists and professors as well. The derived expressions are then applied to bridges undergoing construction (Chapter 9) and completed bridges (Chapter 10).
The Roebling Legacy, a new book by Princeton-based historian Clifford W. Zink, chronicles the story of the Roeblings and their remarkable engineering legacy over two centuries. John A. Roebling was born in Prussia in 1806, and Napoleon’s conquest of the kingdom just 4 months later prompted educational reforms that greatly benefited Roebling’s development as an engineer. He learned basic mathematics, physics, and drafting at the free gymnasium school in his town, studied advanced mathematics and geometry at a small private institute under a renowned mathematician, and then studied drawing, architecture, and engineering with Prussia’s premier technical educators at the Royal Building Academy in Berlin, Germany.
Both aerostatic torsional divergence and flutter are challenging for the wind-resistant performance of long-span cable-stayed bridges. Aiming at a cable-stayed bridge with double main spans of 1,500 m each and a typical twin-box bridge girder, a combination of wind tunnel tests and nonlinear aerostatic analysis was used to investigate the wind-induced stability of the bridge as well as the effects of central grids with 0% installed on the upper surface of the bridge girder for the wind-induced stability of the bridge. Aerostatic torsional divergence was observed both at initial attack angles of +3° and 0° for the twin-box section and the initial attack angle of 0° for the revised section with central grids with 0%, whereas flutter was observed at the initial attack angle of +3°. Therefore, there are clear competitive relationships between aerostatic torsional divergence and flutter for a revised section with central grids with 0%, depending on the initial attack angle. Furthermore, the addition of central grids with 0% led to deteriorated wind-induced stability, including aerostatic torsional divergence and flutter. Then synchronous evolutionary relationships between structural stiffness and displacements in the instability process are presented. It was found that the downstream cable stress at the center node of the main span decreased prior to the twin-box section when central grids with 0% were added, and the upstream cable stress decreased faster than that of the twin-box section, resulting in the deterioration of aerostatic stability at the initial attack angles of +3° and 0°.
This paper addresses the determination of the 18 flutter derivatives of bridge decks from three degrees-of-freedom (3DOF) free vibration data using an improved stochastic search algorithm (ISSA) combined with the unified least-squares (ULS) method. The ISSA is capable of circumventing the local optimum dilemma in pursuing the optimal solution experienced in the traditional ULS method. The validity and accuracy of the ISSA are demonstrated by one numerical example and two long-span, cable-stayed, bridge deck sections. The attractive merit of using different lengths of vertical, torsional, and lateral vibration data in flutter derivatives identification is investigated. The identification error and modal participations in flutter are easily examined through a decomposition of modal components from the original vibration data. The underlying complexities in aeroelastic parameter identification are studied, and the causes of low accuracy of some flutter derivatives are unveiled. Based on the comparative investigation on the aerodynamic characteristics of typical streamlined and bluff bridge decks, an improved understanding of the coupled bridge flutter is achieved. DOI: 10.1061/(ASCE)BE.1943-5592.0000295. (C) 2012 American Society of Civil Engineers.
Navier's 1823 Memoire (C. L. Navier. 1823. Rapport à Monsieur Becquey, Conseiller d'État, Directeur Général des Ponts et Chaussées et des Mines; et mémoire sur les ponts suspendus. Paris: L'Imprimerie Royale) is the seminal analytical study on displacements, stiffness, and vibration of suspension bridges. Navier derived a linearized formula for the vertical displacement at midspan of an unstiffened cable caused by a small change in cable length or span length. He predicted the vertical displacement caused by a concentrated midspan load on a cable with a dominant, uniformly distributed load on its horizontal projection. He thus quantified the geometric stiffness of a cable with a large axial force. Navier also examined the effects of different bearings on displacements of multispan suspension cables subject to unequal vertical loads on adjacent spans. To assess the accuracy of Navier's quantitative results and to provide insights on structural behavior, geometrically nonlinear models were defined and solved. Navier's analyses of the vibration of cables and the later contributions of Edward Routh, Hans Reissner, and David Steinman were assessed by geometrically nonlinear OpenSees models of unstiffened and deck-stiffened suspension cables. The influence of Navier's work on the designs of Charles Ellet and John Roebling was revealed.
A disastrous earthquake struck Wenchuan in China's Sichuan province in 2008 and caused heavy casualties and structural damage to bridges and buildings. One of the two severely earthquake-damaged curved bridges in China, the Huilan interchange, had been carefully studied, including postearthquake investigation and identification of the cause of failure for this bridge. The Huilan interchange, constructed in 2004 in Mianzhu City, consisted of a viaduct and four horizontally circular ramp bridges with continuous box girders. Field investigations found that the seismic damage to the ramp bridges was especially heavy, one or two short piers in all, but one of the ramp bridges experienced severe failure, and the box girders over the failed piers were fractured. Other piers of the ramp bridges suffered minor-to-moderate damage, including concrete cover spalling, concrete cracking, and slippage damage of the rubber bearings. The viaduct suffered only slight damage, including slippage damage of the rubber bearings and pounding damage of the superstructure. The seismic performance of the bridge was evaluated by finite-element modeling and compared with field observations. It was found that the bearing on top of the shortest pier, Pier 1, was damaged first. Then, the seismic action was concentrated on the next shortest pier, Pier 2, which had the largest flexural stiffness. Pier 2 first yielded in flexure, and, as the lateral displacement increased, the ultimate response of this pier was dominated by its shear capacity, and it eventually failed in flexure-shear mode. DOI: 10.1061/(ASCE)BE.1943-5592.0000210. (C) 2012 American Society of Civil Engineers.
Since 2006, the number of M3.0 and larger earthquakes occurring in Oklahoma has increased dramatically. Four M5.0 and larger events have caused damage to residential structures, which raises a concern about the potential for damage to Oklahoma's highway bridges and their components. This study evaluates the potential for damage by assessing the seismic response of the most common bridge class in Oklahoma. The Oklahoma DOT bridge inventory is used to determine the most typical bridge class, and a representative bridge is modeled using nonlinear finite elements. A series of transient analyses were conducted to assess its performance under a suite of recorded bidirectional ground motions (GMs) from the September 3, 2016, M5.8 Pawnee earthquake (the largest event to date). Transient time history analyses were performed and responses (bearing deformation and column curvature) were recorded and presented. Slightly nonlinear responses were observed for the measured GMs. An incremental dynamic analysis was performed to assess the response of the typical highway bridge under higher intensity shaking closer to the epicenter in which seismic stations were not present. The measured GMs from seismic station GS.OK005 were incrementally scaled to AASHTO design levels (S1 = 0.10g) and to intensities derived by a USGS GM mapping product near the epicenter (S1 = 0.20g). Bearing responses indicative of slight damage, such as failure of anchor bolts and sliding of bearings, were predicted, and maximum column curvatures reached 80% of their yield curvature. This study has shown that future earthquakes with comparable or higher levels of shaking may well damage bridges, especially close to the epicenter in which shaking intensities are higher.
Structural analysis methods for steel I-girder bridges can be grouped in three categories: 1D line-girder, 2D-grid, and 3D finite-element analysis. This paper discusses the qualities and limitations of these techniques, and it focuses on improvements that may be implemented to 2D-grid methods to capture horizontal curvature and support skew effects effectively at little or no additional computational cost compared to traditional 2D-grid methods. The paper focuses predominantly on the problem of analyzing the noncomposite response of the structure during construction, which is of essential importance for setting girder cambers and controlling the constructed geometry. The proposed modeling techniques also can be applied to the analysis of partially composite structures during staged deck placement and to the analysis of a structure in final composite condition. Analysis results for several example bridges with challenging geometries are presented to demonstrate the application and show the impact of the proposed modeling improvements.
This study explored the application of two-dimensional digital image correlation (2D-DIC) for measuring deflections of in-service bridges. Within the emerging area of image-based structural health monitoring, this work builds from previous efforts to deploy vision-based sensing techniques for describing the operational behavior of structures. Whereas the literature includes deflection measurement systems using cameras mounted on fixed ground near the bridge span at maximum distances of approximately 300 m, this work proposes an innovative setup that enables deflection measurement in remote, offshore, and complex environments. This paper first describes a laboratory study aimed at evaluating the system performance and identifying the sources of measurement error, thus determining the level of confidence in the results and the range of applicability. The laboratory study demonstrated that the setup, designed using an inexpensive consumer-grade imaging system, had an average error consistently less than 0.2 mm (0.0075 in.). In addition, the system was deployed during a field test on a high-profile bridge structure nearly 1 mile offshore. The test program and results are presented to assess the logistics and performance of the system during load testing. Results from the study indicate the feasibility of the proposed setup for measuring deflections without a fixed ground reference.
The paper describes how two-dimensional (2D) digital image correlation (DIC) is used on underneath surfaces of concrete bridges with a wide-angle-lens camera during load testing, and how it has potential as a stop criterion in proof loadings. A method is proposed for correction of out-of-plane deflection including rotation of the surface. The method is applied to laboratory tests, using well-defined circular speckle patterns, as well as to a field-tested bridge (on raw concrete). The proposed correction corresponds to the level of pseudo strain but is very sensitive to precise surface deflection measurements. In the laboratory tests, a strain precision of the wide-angle-lens camera is compared to a regular-lens camera. The parametric study concludes that a pattern pixel relation (PPR), in the interval from four to nine pixels per pattern circle diameter, provides the optimal precision regardless of the camera type. The field-tested bridge has less good precision compared to most parameter combinations of the laboratory tests. Nevertheless, the field strain precision has potential for improvement based on results from the laboratory tests.
For the successful implementation of long-term monitoring strategies of prestressed concrete structures, the expected behavior of the structure must be accurately quantified before anomalous or damage-related readings can be properly identified. In situ structures may be subject to large variations in temperature, which can have a significant impact on measured deformations, and continued creep and shrinkage of the concrete further complicate long-term predictions. The goals of this and a companion paper are to present the methodology for extracting the time-dependent behavior of a posttensioned concrete box girder bridge from structural monitoring data in the presence of changing temperatures (this paper) and to compare predictions of long-term time-dependent deformations computed using finite-element analysis with the extracted time-dependent monitoring data (the companion paper). To investigate the interactions between temperature and time-dependent behavior for in situ monitoring data, strains and expansion joint deflections from the St. Anthony Falls Bridge, a posttensioned concrete box girder bridge on I-35W in Minneapolis, Minnesota, were collected over a period of 5 years. A methodology based on linear regression was used to separate the time-dependent deformations from the temperature-related deformations given a variable coefficient of thermal expansion (CTE). The total temperature-related deformations were captured by functions based on the average bridge temperature, the thermal gradient through the depth of the superstructure, and the average squared temperature of the bridge, which was proposed because the CTE was observed to vary with temperature. On examination of the extracted time-dependent readings, the deformation rates were found to decelerate during the winter and accelerate during the summer. To enable direct comparison between the measured results and the creep and shrinkage predictions from finite-element models assuming constant temperature, an Arrhenius-adjusted time formulation was used, which normalized the measured deformations under varying temperatures to those expected from a constant reference temperature. This procedure for processing the time-dependent measured data enables a comparison with time-dependent finite-element model results conducted at constant temperature.
Thermal gradients were measured through the section of the I-35W St. Anthony Falls Bridge, a posttensioned concrete box girder bridge in Minneapolis, Minnesota, over the course of 3 years. The magnitudes and shapes of the measured thermal gradients were compared with various design gradients, and a fifth-order curve was found to best approximate the shape of the gradients. The responses of the structure to the largest measured thermal gradients were compared with stresses and deformations predicted by finite-element modeling given applied design gradients. The measured structural response was found to be best predicted when the finite-element model of the bridge was subjected to a fifth-order design thermal gradient scaled to match maximum top surface temperature values proposed by AASHTO LRFD Bridge Design Specifications for the region. Stresses and deformations predicted by finite-element modeling using the AASHTO LRFD bilinear design gradients were found to be considerably lower than those derived from measured results. Recommendations for design thermal gradients are proposed.
The I-35W St. Anthony Falls Bridge was constructed to replace the steel truss bridge that collapsed on August 1, 2007. The design of the replacement bridge featured a smart-bridge system. The smart-bridge concept included instrumentation for long-term monitoring of the structural behavior of the bridge. Truck-load tests were conducted prior to opening the bridge and 26 months later to measure the response of the structure under controlled loading. The measurements were used to validate a FEM model of the bridge constructed to further investigate the behavior of the structure. The correlation between computed and measured results was found to be good. This paper describes the bridge, the instrumentation installed within the bridge, the FEM model, and validation of the model with respect to the truck-load tests. Recommendations are provided for static instrumentation plans of concrete box-girder structures. (C) 2013 American Society of Civil Engineers.
Data collected from the monitoring system installed in the St. Anthony Falls Bridge, a posttensioned concrete box girder bridge in Minneapolis, Minnesota, represented a combination of temperature-dependent effects due to daily and seasonal temperature changes and time-dependent effects related to creep and shrinkage of the concrete. In the companion paper of this study, the time-dependent creep and shrinkage effects were isolated from the data, and the rates of the creep and shrinkage were adjusted according to the Arrhenius equation. In this paper, results from finite-element models incorporating a variety of time-dependent provisions were compared with the measured time-dependent behavior. The modeling methodology is discussed extensively, including the procedures for incorporating the segmental construction staging sequence and midspan closure pour. Each of the models provided different predictions, and none were found to provide reliable estimates of the measured results throughout the entire 5-year period of investigation, although this was not unexpected due to the uncertainty inherent in the long-term predictions of the time-dependent behavior of concrete structures. Provisions from several standards with asymptotic creep models underestimated the longitudinal deformations and were found to approach asymptotic creep and shrinkage values before any indication of asymptotic behavior was observed in the measured data, although early-age behavior was accurately captured by these provisions. The shape of available logarithmic creep models appeared to be consistent with the measured data, although these models overestimated the longitudinal deformations of the bridge. The best predictions of the measured data were given by the provisions of a previous model code with an asymptotic creep model that properly accounted for the large volume-to-surface ratio of the bridge. Investigation of the computed vertical deflections showed that for all models the direction of the deflections reversed after completion of the structure, and that this bridge was not in danger of failure from excessive deflections. This was believed to be due to how continuity of the structure was achieved and the balance between the posttensioning forces and the gravity loading. Finally, Bayesian regression was proposed to update the finite-element model predictions to better match measured data. This technique could be used in structural monitoring applications to detect when time-dependent deformations fall outside expected bounds.
The seismic behavior of horizontally curved steel bridges is more complex than straight bridges because of their curvature and other parameters. Studies that attempt to develop methods to efficiently predict their seismic response have been somewhat limited to date. A computational modeling approach was examined to assist with understanding the seismic behavior of these bridges. The computational, three-dimensional (3D) bridge models consisting of the concrete deck, steel girders, cross-frames, pier columns and caps, and abutments and footings were created in OpenSees and examined for accuracy via application to a representative, three-span continuous curved steel plate girder bridge in Pennsylvania. Sensitivity studies in the form of tornado analyses were also carried out to investigate the influence of critical curved bridge parameters on the seismic response using a group of representative bridges. Each representative bridge was subjected to an ensemble of synthetic ground motions, and seismic response was examined. Results from the sensitivity study indicated a 17-22% variation in maximum bearing and abutment deformations, column curvature ductility, and cross-frame axial forces parameters for the range of bridge radii and span numbers that were investigated.
Ultrahigh performance concrete (UHPC) presents many superior properties, such as advanced strength, durability, and long-term stability. The use of existing cross section geometries for materials with advanced properties results in inefficient designs and less cost-effective solutions. This study focused on developing a series of finite-element optimized sections of pi-girders to effectively utilize the superior mechanical properties of UHPC over span lengths of up to 41 m (135 ft). The research was performed using a finite-element model that has been calibrated and verified against experimental results. The optimization was progressively conducted at local, element, and structural levels. At the local level, the focus of the investigation was to find the optimal deck thickness and prevent transverse bending failure of the deck. At the element level, sectional parameters, including girder height, bulb size, web thickness, and strand layouts, were investigated to find the minimal sectional size that accommodates standard loads for a span length of 23m(75 ft) or above. At the structural level, deflection under a live load was checked such that the bridge system using the proposed sections can meet the deflection requirements specified in guidelines. Four cross sections based on the second generation pi-girder were proposed, and a design chart was provided to facilitate preliminary design for bridge engineers. (C) 2014 American Society of Civil Engineers.
This paper describes the experimental testing of 48-year-old concrete bridge girders that were fabricated using lightweight concrete. After the bridge was decommissioned, three girders were transported to the Systems, Material, and Structural Health (SMASH) Laboratory at Utah State University (USU). The double-tee girders were tested to quantify the effective prestress, flexural capacity, and deck punching shear strength. The experimental results were compared with calculated values based on recommended procedures in the AASHTO LRFD bridge design specifications. The AASHTO refined method underestimated the loss of prestress of the three girders by an average of 17.6%. The calculated flexural capacities were overestimated by an average of 34.0% when compared with the measured values. This unconservative result is believed to be a result of the deck deterioration. The average calculated punching shear capacity was within 3.0% of the measured values. The experimental results were also compared with analytical values using computer software. These nonlinear finite-element analyses (FEAs) were found to replicate the behavior of the flexural and punching shear experiments in terms of both the failure mechanism and magnitude.
In the days of the AASHTO standard bridge design specifications, engineers used simple equations for calculating the HS-20 live-load moment for a simple span bridge. Engineers computed and compared the lane load moments to the truck load moments. The larger moment controlled the design. The second axle of the design truck was not placed at midspan but rather at a 2 ft 4 in. (0.711 m) offset from midspan. The correct orientation of the offset required that the truck's resultant force reside on the opposite side of the midspan from the second axle. As an example, for a 50 ft (15.240 m) span, this 2 ft 4 in. (0.711 m) offset yielded a 628 kip-ft/lane (851 kN-m/lane) truck moment compared with a 620 kip-ft/lane (841 kN-m/lane) truck moment without an offset. By the 1990s, a new AASHTO specification was introduced based on LRFD. The old HS-20 live-load model was modified to combine its component lane load and truck load cases into a single load case called HL-93. This combined load case impacted the traditional 2 ft 4 in. (0.711 m) offset and made it vary according to span length. This paper proposes to derive an equation for determining the correct truck offset to produce maximum moment using HL-93 loading on simple spans greater than 40 ft (12.192 m). The scope of this paper does not include the tandem vehicle, because it does not govern spans greater than 40 ft (12.192 m) in length.
Details of the single-lane sites in WIM database.
Mid-span bending moment in the girder where lanes meet in a 30 m girder bridge at 
Proposed variable UDL single-lane load model (UDL= 0.014L 2 – 1.73L + 76.4 
Single-lane characteristic load effects, normalized with respect to proposed variable UDL load model (mean of site standard deviations is 0.064).
HL-93, the current bridge traffic load model used in the United States is examined here. Weigh-in-motion (WIM) data from 17 sites in 16 states containing 74 million truck records are used to assess the level of consistency in the characteristic load effects (LEs) implied by the HL-93 model. The LEs of positive and negative bending moments and shear force are considered on single- and two-lane same-direction slab and girder bridges with a range of spans. It is found that the ratio of WIM-implied LE to HL-93 LE varies considerably from one LE to another. An alternative model is proposed that achieves improvements in consistency in this ratio for the LEs examined, especially for the single-lane case. The proposed model consists of a uniformly distributed load whose intensity varies with bridge length.
With the institution of AASHTO HL-93 loading, calculating the maximum live-load moment on simple spans became more complex than it had been previously. In the past, to find the maximum live-load moment from the HS-20 design truck, the middle axle was offset from midspan by 0.711 m (2 ft 4 in.), and the moment under that axle was the maximum moment on the beam. However, with the combination of the design vehicle and the distributed design lane load, this general approach became obsolete. The purpose of this study was to develop a new generalized approach to determine the location and value of the maximum moment under HL-93 loading on simple spans. This was accomplished by creating moment envelopes and studying their extremum. Subsequently, equations, charts, and tables were developed that describe the location and value of the maximum moment on a beam under HL-93 loading, consisting of design truck or design tandem loading in combination with the design lane load for a simple span of any length.
This study investigates the mechanical properties of ASTM A1010 steel plates and assesses their cost efficiency through life cycle cost (LCC) analyses when used in bridge construction. First, tensile tests were conducted on specimens with different plate thicknesses and rolling direction orientations. The overall stress-strain response and tensile properties of the A1010 steel were evaluated. In addition, failure zones of fractured specimens were analyzed using a scanning electron microscope to reveal the fracture morphology and failure type. Then, to assess the competitiveness of this relatively new steel in bridge construction, a series of LCC analyses were conducted. The first analytical investigation focused on the comparative LCC performance of two case study bridges located at different atmospheric environments and constructed using either A1010 steel or painted conventional carbon steel. The second analytical study explored the major factors impacting the A1010 payoff time. Results indicated that the use of A1010 steel can be most beneficial in bridges located in aggressive environmental conditions with heavy traffic volumes.
This experimental study was the first to evaluate the galvanic corrosion risk of using galvanized ASTM A325 Type I bolts with ASTM A1010 steel girders in the construction of A1010 steel bridges. The emerging construction of A1010 steel bridges is intended to extend the service life of bridges and reduce the need for maintenance under atmospheric corrosion attack, particularly in regions subject to severe saline exposure. However, combining high-corrosion-resistant A1010 steel with connection bolts that have a lower corrosion-resistance rating can lead to galvanic corrosion that accelerates the metal dissolution of bolts after installation and while in service. The results of this study indicate that under light saline exposure, the galvanic corrosion rate of galvanized ASTM A325 bolts used with A1010 steel was similar to the corrosion rate of A325 bolts used with ASTM A588 weathering steel. Under heavy saline exposure, however, the galvanic corrosion rate of A325 bolts was significantly higher when used with A1010 steel than when used with A588 weathering steel. Reducing the galvanic corrosion rate can be achieved by painting the joints of the steel girders, thereby reducing the cathode-to-anode area ratio. The results of this study suggest that the corrosion compatibility of the bolt and steel materials must be considered when designing corrosion-resistant A1010 steel bridges, and that the compatibility must be confirmed with an experimental validation.
Steel H-piles (HP shapes) are most commonly available as ASTM A572 Grade 50 material, having a nominal yield strength of Fy = 50 ksi (345 MPa). However, until fairly recently, HP shapes were typically available as ASTM A36 shapes, for which Fy = 36 ksi (248 MPa). Many state DOT provisions for driven piles continue to base design structural capacity calculations on the lower yield stress. In this paper, a parametric study investigating the impact of increasing the yield capacity from Fy = 36 ksi to Fy = 50 ksi on design structural capacity and driving analysis of steel H-piles is presented. Results of the parametric study indicate that the AASHTO-permitted pile capacity of 0.5 AgFy is not achievable without a reduction in the required overstrength factor of 2 (based on assessing driveability by wave analysis only), and even then, this capacity may only be achievable for smaller pile sections. Driving piles to the maximum permitted driving stress of 0.90 Fy = 45 ksi (310 MPa) resulted in pile capacities at refusal ranging from 0.64 to 0.76 AgFy, with smaller pile sections having marginally higher achievable capacities. A representative cost analysis led to the conclusion that increasing the design capacity of a pile results in a decrease in cost per driven pile capacity, although, because of the need for larger hammers and cranes, permitting design capacities greater than 16.5 ksi (114 MPa) results in only marginal additional savings.
Top-cited authors
C. S. Cai
  • Louisiana State University
Dan Frangopol
  • Lehigh University
Anil Agrawal
  • City College of New York
Lu Deng
  • Hunan University
Brahim Benmokrane
  • Université de Sherbrooke