Journal of Bridge Engineering

An efficient and robust Bayesian model updating is presented in this paper from the viewpoint of practical application by introducing a new objective function and a realistic parameterization of the mass and stiffness matrices. In this framework, the likelihood function for mode shapes is formulated based on the cosine of the angle between the analytical and measured mode shapes, which does not require any scaling or normalization. For the parameterization of the stiffness matrix, the framework uses element-level parameterization because it is evident from practical experience that different parts of the structure are subjected to different levels of deterioration as a result of corrosion and fatigue. The proposed updating method was validated experimentally by updating a finite-element model (FEM) of an existing steel truss bridge that utilized the vibration data obtained from a car-running test. The damage-detection capability of the proposed model-updating framework was then investigated by considering the data from a simulated damaged bridge and the experimental data from a damaged span of the same bridge with partial fractures on one of the diagonal members.

Corrosion damage is one of the main problems affecting the durability of concrete structures. Several corroded reinforced concrete (RC) railway bridges are located in regions of high seismic risk. Corroded bridge piers are often subjected to dynamic axial loads, such as the vertical pounding that occurs during earthquakes or due to railway trains. Repeated axial loading was used to simulate this vertical pounding effect. Therefore, the seismic performance of corroded RC structures under repeated axial and horizontal cyclic loading is an urgent issue. To investigate the influences of steel corrosion and repeated axial loading on the seismic performance of a column pier, eight RC column specimens were experimentally investigated. The results indicated that corrosion significantly influences the yield strength and load bearing capacity of a column. The load bearing capacities of the corroded specimens decreased by 18.27% compared with noncorroded specimens when the longitudinal loss of steel mass was 7.16%. Repeated axial loading did not significantly influence the mechanical properties of the corroded RC piers. Cyclic tests were performed to validate a finite-element model that was used to assess the effects of corrosion level on the seismic performance of columns. The level of steel corrosion ranged from 0 to 28%. According to the finite-element analysis, the yield strength (35%) and ultimate displacement (34%) decreased with increasing corrosion.

It is important to evaluate the amount of airborne sea salt adhering to the structural members of a bridge for effective maintenance. This study sought to develop a method to estimate salt conditions on individual road bridge girders. The estimation was based on airborne sea salt concentrations obtained by on-site observations using new equipment, a steady flow of wind around the bridge with a computational fluid dynamics (CFD) technique, and the washing-out effect (detachment of adhered particles) resulting from raindrops. The estimated salt amounts adhering to bridge girders showed the same tendency in distribution on the seaward surfaces of the webs but not on the cliff-side surfaces. Additionally, the relationship between the amounts on the upper and lower surfaces of the bottom flanges was better reproduced by considering the effect of gravity on the sea salt particles. Consideration of the spatial distribution and changes over time of airborne sea salt concentrations and wind is needed to improve the estimation accuracy. The significance of the washing-out effect on the salt amount was also clarified.

A new lightweight, low-profile composite deck system is presented that was fabricated using vacuum-assisted resin transfer molding. The deck in this system is composed of ultrahigh-performance concrete (UHPC) for high compressive strength and durability, carbon-fiber-reinforced polymer (CFRP) for high tensile strength, and glass-fiber-reinforced polymer (GFRP) for shear resistance. The high-performance modular deck panels are beneficial for applications such as movable bridges, where spans may be mechanically lifted, and deck repair or replacement, where transportation and installation assist in accelerated bridge construction. Seven single-unit deck specimens were fabricated with two different spans (1,220 and 864 mm) and tested under two different flexural load configurations (wheel-tire load and four-point load). The experimental results demonstrated that the target recommended strength demand for this deck was satisfied prior to failure as a result of delamination of the top UHPC plate from the core. Analysis of the results and corresponding finite-element models (FEMs) showed that the load-transfer mechanism was limited by the crushing of the UHPC plate and interfacial bond with the core.

Prestressing steel bars are damaged in the typical pattern of corrosion fatigue under the combined action of chloride corrosion and fatigue load, in which the two damage types are mutually promoting. This study experimentally investigates the promotion effect of fatigue on corrosion. Twelve prestressed concrete beam specimens with steel strands that bore the combined action of corrosion and fatigue for 20 days were prepared using four chloride concentrations and three fatigue stress ranges. Moreover, the specimens were subsequently broken to measure the size of the corrosion pits. Based on these measured sizes, the volume and stress intensification factor (SIF) of the pits were calculated and their volumes and SIFs were statistically analyzed. The results show that the steel strands corroded in the typical pitting corrosion pattern with approximately anticlastic or spheroid shapes. The parameters of the pit’s volume and SIF showed both normal and lognormal distributions. Thus, it was observed that the greater the action intensity of fatigue, the larger were the averages of the two parameters and the 95th fractile of the lognormal distribution of the SIF.

Air vents in bridge decks are considered one potential measure for mitigating risk of damage to coastal bridges caused by extreme storm surge because they may reduce hydrodynamic uplift loads significantly. This paper presents a systematic, two-dimensional, numerical study on physical phenomena and hydrodynamic loads involved during the impact of solitary waves on a bridge deck with vents. The effects of the opening size of vents and other prominent factors, including submergence of the deck, wave height, water depth, and number of girders, on hydrodynamic loads were investigated through the numerical study. It was found that, when the deck was submerged initially, the vertical loads on the bridge deck achieved their maximum values at a certain opening size of vents, and their magnitudes could be significantly higher than on a deck without vents. Formulas as functions of these factors were developed based on the computational results to estimate efficiency of air vents to reduce hydrodynamic loads on bridge decks.

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.

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.

Several concrete-filled steel tube (CFT) arch bridges have been built over the past few years around the world. Current design codes do not address the design of CFT arch bridges, particularly with consideration of concrete creep effects, which can be very important. This paper presents experimental results from tests conducted on 13 specimens to evaluate the creep behavior of CFT members. An experimental database was compiled using results from this paper and 35 additional tests from the literature. The comprehensive database was used to evaluate four commonly used creep models for predicting short-term (up to 730 days) creep strains of the concrete infill in CFT members. The selected models are the Comité Euro International du Béton–Fédération Internationale de la Précontrainte (CEB-FIP) MC90 model, fédération internationale du béton (fib) MC2010 model, American Concrete Institute (ACI) 209 R-92 model, and the B4 model. The evaluations indicate that the prediction quality varies by cases. Therefore, it is not possible to recommend a most-suitable model based on this study. Further investigations are required to evaluate the effects of factors such as the steel ratio. To evaluate the effects of creep on the time-dependent behavior of CFT arch bridges, creep analyses on 11 such bridges were conducted with the implemented ACI 209 R-92 creep model. Analytical results indicate that creep results in increases in the steel tube stresses and bridge deflections and relaxation of concrete stresses.

Louisiana has approximately 160 movable bridges, mostly in the southern part of the state. This places Louisiana among the states with the highest inventory of movable bridges in the nation. The typical deck systems in these movable bridges are steel grids. Records show that steel grids have had maintenance issues. An alternative ultrahigh-/high-performance concrete (UHPC/HPC) bridge deck system is proposed for Louisiana’s movable bridges. This system consists of precast waffle-slab deck panels, which are reinforced with glass-fiber-reinforced polymer (GFRP) bars as positive-moment reinforcement, and a two-way carbon-fiber-reinforced polymer (CFRP) mesh as top reinforcement. Several validated nonlinear finite-element analyses were performed to simulate the behavior of the precast panels from the onset of loading to failure. It is concluded that the precast concrete waffle slabs provide a viable alternative to steel grids by supplying load capacities that surpass service- and ultimate-level load demands and deflection capacities that are within code-specified limits.

Bridge scour has emerged as a significant concern worldwide, especially in the United States; approximately 60% of bridge failures are scour related. Because of the difficulty of bridge-scour inspection, scour-induced failures tend to occur suddenly without prior warning or signs of distress to the structures. A reliable, effective, and robust monitoring system is very desirable. Therefore, the present study aimed to develop an innovative scour monitoring system using fiber Bragg grating (FBG) sensors and water-swellable polymers. The polymer material swells to several times the original volume upon the absorption of water, and the expansion induces a measurable tension on the FBG sensor. The scour monitoring system is vertically embedded in soil, and the measured wavelength shifting of a particular sensor is able to indicate that the sensor is no longer covered with soil (i.e., the soil level has decreased to the elevation of that particular sensor). A detailed introduction of the sensor design was presented, including specially designed protection to prevent water from entering the sensor unit before the sensor system is in place. A prototype of the sensor system was fabricated, and several tests were conducted in the laboratory to verify the functionality of the device. The results indicate that the system is capable of monitoring the change of soil level. Furthermore, the repeatability of the polymer swelling implies the capability of monitoring the entire scour process in the long term. In addition, the proposed system concept could also be used for subsea pipeline scour monitoring and other types of chemical sensing by interchanging the polymer with materials sensitive to other measurands, such as oil.

Built-up steel girders were a primary fabrication method used for bridges until the early 1960s. Many bridges in the transportation inventory from this era consisted of built-up two-girder systems. Because built-up members are mechanically fastened instead of welded, there are discontinuities between individual components, preventing fracture propagation among components. There is ample evidence that suggests that these members have significant ability to resist crack propagation from one component to another and therefore are able to resist complete member fracture in the event that a single component suddenly fractures. However, because of the lack of experimental and analytical evidence, current regulations require that built-up members be conservatively considered susceptible to complete catastrophic failure in the event of a single component failure and prohibit member-level redundancy from being explicitly exploited in design or evaluation. Recent experimental testing on large-scale bridge girders showed that for members with typical proportioned components, failures of a single component do not propagate into adjacent components. Furthermore, guidance has been developed on how to evaluate built-up members to ensure appropriate application of member-level redundancy.

This research focuses on developing and measuring the mechanical behavior of ultrahigh-performance fiber-reinforced concrete (UHPFRC), transverse, field-cast connections between precast bridge deck elements. The connections had a closed shape, exposed aggregates, and lap splice length of 10 bar diameters (d_b). Three slab designs were considered: high-performance concrete (HPC), high- performance fiber-reinforced concrete (HPFRC), and hybrid HPFRC and UHPFRC. The first set of specimens was subjected to quasi-static loads up to failure, while the second set was subjected to cyclic fatigue loads prior to quasi-static loading to failure. Experimental results showed that all precast bridge decks with UHPFRC connections presented the same stiffness and ultimate strength as equivalent cast-in-place (CIP) slabs. Finite-elements models reproduced experimental results accurately and were used for predicting the mechanical behavior of continuous bridge slabs. Parametric studies demonstrated that, under various loading conditions, transverse UHPFRC field-cast connections do not modify the stiffness, ultimate strength, and failure mode of a slab differently than the equivalent CIP systems.

Past earthquakes have repeatedly demonstrated that skewed bridges are more vulnerable to earthquake-induced failure than straight bridges because of their complex, irregular geometries and unique load-transfer mechanisms. This study focused on analyzing the seismic performances of prestressed concrete box-girder highway bridges with seat-type abutments under bidirectional near-fault ground motions, especially with respect to abutment skew angle, gap size at the expansion joint between the superstructure and the abutment in the longitudinal direction, and initial gap size between the the superstructure and abutment shear keys in the transverse direction. Three dimensional models of single- and two-span bridges with seat-type abutments were developed considering nonlinear characteristics of skew-angled abutments, bridge key components, abutment-soil interaction, soil-pile interaction, and the pounding effect between the superstructure and the abutments. Nonlinear time-history analyses were performed for various skewed highway bridge models using seven sets of near-fault ground motions with two horizontal components. Results showed that the skew angle and gap size in longitudinal and transversal directions have significant impact on the seismic behavior of skewed highway bridges. The deck displacement in the longitudinal direction and rotation response will increase with the increase of the skew angle, but the transverse displacement response exhibits a more severe response after the skew angle reaches 30°. The longitudinal deck displacement and rotation of skewed bridges increase with decreasing gap size at the expansion joint in a longitudinal direction. Furthermore, the behavior of shear keys may have an important effect on the overall seismic response of skewed highway bridges, especially the probability of collapse due to excessive deck rotation.

Service lives can be extended for the aging steel girder bridge population, many of which are nominally simply spanning structures, by evaluating structural response and capacity, including system behavior, particularly in the presence of support restraint. Longitudinal shear restraint at steel girder bearings has been observed and documented in numerous studies and bridge tests. The restraint arises from various sources, such as friction restraint at older bearings in good condition, or frozen conditions at bearings with abutment deck joint corrosive deterioration. Longitudinal shear restraint at bearings induces arching action in the superstructure, redistributing and reducing moment demands at midspan. This study analytically investigated composite bridge superstructure system-based flexural behavior, including assessment of load levels to initiate yielding and the sequence of yielding initiations leading to ultimate capacity, considering a range of bearing longitudinal restraint conditions. The computational modeling was validated using two documented ultimate load tests on composite steel girder bridges. Nonlinear load-carrying capacity increased with bearing restraint and was accompanied by decreases in system ductility. Both ultimate load capacity and system ductility were observed to be sensitive to bearing restraint within a narrow range of low support stiffness only, relative to the stiffness required to achieve an effectively pinned response. The yield moment was sensitive to the exact restraint stiffness, but ultimate capacity was relatively insensitive and disproportionately benefitted by even slight support restraint.

Thermal performance analysis of long-span bridges is important for structural design and safety evaluation; however, its experimental investigation using measured field test data is still insufficient. In this article, 1-year monitoring data of a long-span suspension bridge have been processed to study the thermal effects on structural performance under operating conditions. First, long-term temperature and structural response data, including strain, displacements, and suspender frequency/force, were analyzed statistically for evaluating their correlations. Temperature distribution along the main girder in the longitudinal direction and the temperature gradient in the vertical direction were also analyzed. Statistical analysis results show that the temperature distribution along the girder in the longitudinal direction is nonuniform. The strain change of the lower deck is greater than that of the upper deck in a day. Second, a theoretical study regarding the thermal performance analysis was conducted to calculate structural vertical/longitudinal displacements and thermal-induced internal forces by using measured strains. The estimated displacements are comparable with those measured directly from displacement transducers installed on expansion joints and the global positioning system (GPS) installed on four sections of the girder under normal operating conditions.

This paper studies the vibration characteristics and damping properties of a newly developed fiber-reinforced polymer (FRP) cable with a self-damping function using a model vibration experiment. To verify the self-damping effect of the designed FRP cable, the scaled model vibration test of the FRP cable was designed according to the real cables of the Su-tong Bridge. The damping properties of the FRP cable with self-damping were studied by excitation with small amplitude, middle amplitude, and high amplitude, respectively. The experimental results show that the model vibration test, designed based on similarity criteria, could effectively simulate the vibration characteristics of the real cable according to the experimental results of the natural frequencies. The properties of the energy dissipation of the self-damping FRP cable were superior to those of the FRP cable without self-damping based on the comparison of the modal damping ratios. Furthermore, the modal damping ratios of the FRP cable with self-damping increase with the vibration amplitude of the cable, indicating that the designed FRP cable can efficiently dissipate vibration energy with respect to the vibration amplitude.

The serviceability response of ultrahigh strength self-consolidating concrete (UHSSCC) in strengthened and nonstrengthened unbonded posttensioned indeterminate members is crucial, because little research has been conducted on such continuous members composed of this relatively new type of concrete. Moreover, most studies on continuous beams mainly focused on ultimate response prediction, because the results are not applicable to the serviceability response, and the design of these members is mostly governed by the serviceability limit state. Therefore, for evaluation of the serviceability response, flexural testing of unbonded posttensioned UHSSCC continuous nonstrengthened and strengthened I-beams, reinforced with one unbonded tendon of variable eccentricity and different area of tensile and compressive reinforcement bars, was conducted. One layer of unidirectional carbon-fiber-reinforced polymer sheet (CFRP) (ply) at sagging and hogging regions was externally applied to strengthened beams. To determine the service loads, materials stress and strain (tendon, concrete, steel rebar, and CFRP sheets), the flexural crack width and deflection of test beams were monitored at different stages of loading. Different standards were used to specify the permissible stress and strain of materials and flexural crack widths (0.1 and 0.2 mm) under the serviceability limit state. The end of the serviceability level was determined for beams with a new flexural crack width limitation of 0.3 mm. Considering this aspect, it was found that for the test beams, an average load capacity enhancement of 20% was pronounced at the serviceability state. An increase in propagation length and number of cracks with a decrease in crack spacing was monitored for strengthened beams compared with nonstrengthened ones. This was primarily caused by lower values of effective prestressing stress ($f_{\mathrm{p}\mathrm{e}}$) and strengthening technique. Maximum flexural crack width equations were proposed and compared with experimental and theoretical values. The performances of the proposed equations were as good as that for the American Concrete Institute (ACI), but were superior to those recommended by the Eurocode 2 and Canadian Prestressed Concrete Institute standards. The ACI equation was more versatile because it was applicable to both nonstrengthened and strengthened beams. The predicted values for immediate deflection of the beams at the service limit state based on the simplified method were compared with the experimental deflection values, and the results showed good agreement up to the yielding of nonprestressed steel. The discrepancies between the predicted and experimental deflections were within ±20%.