Journal of Bridge Engineering

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.

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.

The main objectives of this study were to: (1) study the response of bridge decks to blast effects resulting from an explosion on the deck; and (2) develop efficient technologies and systems that can be used in design and construction of bridges to enable them to survive blast attacks without collapse. To understand the actual behavior of orthotropic decks subjected to blast loads, typical steel orthotropic decks used in long-span, cable-supported bridges were modeled using MSC/Dytran nonlinear finite-element analysis software, and the models were subjected to simulated explosions occurring on the deck. The parameters that varied in the analyses were the size of the explosive device in terms of equivalent TNT, the axial compressive force present in the deck, and the high-strain-rate mechanical properties of the material of the steel used in the orthotropic decks. Through dynamic analyses, the behavior of the orthotropic decks under blast loads was established and their failure modes were identified. Also, implementation of a new and effective blast-resistant technology, the “fuse system,” was simulated. In this system, to limit the effect of a blast to a localized area of the bridge and to prevent catastrophic progressive collapse of the span, special “fuses” (comparatively weaker structural elements) are placed between two deck segments.

Four finite-element models of ships with deadweight tonnage varying from 3,000 to 50,000 t are developed for numerical collision simulation. The time histories of ship collisions against rigid walls are obtained using the software LS-DYNA. Equivalent static loading is determined, and simplified formulas are developed through a fitting procedure as indicated by the data from the numerical simulations. Codified formulations from AASHTO and other design specifications are compared with the simplified formulas. The geometric effects of the bridge foundation on the ship impact force are investigated with an example pile cap. A geometric modification factor is proposed for an ideal rectangular block to modify ship impact forces estimated by code formulas.

The AASHTO standard bridge specifications require that nominal reinforcement should be placed to enclose prestressing steel at girder ends for at least a distance equal to the girder’s height. The AASHTO LRFD bridge specifications state that the minimum requirements for this confinement reinforcement is No. 10 (#3) bars at a maximum spacing of 150 mm (6 in.) for at least 1.5 times the girder’s height. Neither standard nor LRFD specifications justify the need for such reinforcement. The main objective of this study is to investigate the effect of confinement reinforcement on the performance of prestressed concrete bridge girders. Of particular interest is the effect on transfer and development length of prestressing steel and on the shear capacity of prestressed girders. The experimental investigation includes testing the flexural and shear capacities of 610 mm (24 in.) deep T-girders and 1,100 mm (43.3 in.) I-girders. The results indicate that (1) neither the amount or distribution of confinement reinforcement has a significant effect on the transfer length of prestress strands; (2) at the AASHTO calculated development length, the amount of confinement reinforcement does not have significant impact on either the nominal flexural capacity of bridge girders or bond capacity of the prestressing steel, however, the distribution of confinement reinforcement along the entire length of the girder results in improved ductility and reduced cracking under extreme loading conditions; and (3) confinement reinforcement improves the anchorage of strands at girder ends, and consequently, the shear capacity of prestressed girders.

The design of skewed bridges is becoming more customary in the engineering community. In this paper, the effect of the skew angle on continuous composite girder bridges is presented using three-dimensional finite-element analysis. Seventy-two models of two-span bridges with various span ratios ($N=1$, 1.55, and 1.82), skew angles (0–60°), and various arrangements of intermediate transverse diaphragms are analyzed. All models were subjected to AASHTO HS20-44 loading. Results for skewed bridges are compared with the reference nonskewed bridge, as well as to the AASHTO standard specifications and AASHTO LRFD specifications. The results show that as the skew angle increases, the support moment in interior and exterior girders rapidly decreases. It decreases about 10% when the skew angle is less than 20° and reaches 33% for a 45° skew angle. The shear force increases in the pier support at the exterior girders and decreases at the interior ones with increasing skew angle. For exterior girders, the ratio of shear force increases up to 1.3 for a skew angle of 45°. The AASHTO standard specifications overestimate the maximum bending moment by 20% for a skew angle of 30° and $N=1$ and by 50% for a skew angle of 45°. The overestimation of shear force is about 10% for a skew angle of 45°. The AASHTO LRFD specifications overestimate the longitudinal bending moment and shear force. This overestimation increases with an increase of the skew angle and reaches 12% for a skew angle of 20° and 45% for a skew angle of 45°. The results show that transverse diaphragms perpendicular to the longitudinal girders of the bridges are the best arrangement for load distribution. Comparing the results of the simplified relationships of the skewed decks with the finite-element analysis shows that the results of the proposed equations are conservative for continuous-skewed bridges. It is noted that the results pertain to those bridges with specific configurations and the results may change if the presumed conditions vary, although the tendency should be similar.

Permanent metal deck forms (PMDFs) are often used in the bridge industry to support wet concrete and other loads during construction. Although metal formwork in the building industry is routinely relied on for stability bracing, the forms are not permitted for bracing in the bridge industry, despite the large in-plane stiffness. The forms in bridge applications are typically supported on cold-formed angles, which allow the contractor to adjust the form elevation to account for changes in flange thickness and differential camber between adjacent girders. Although the support angles are beneficial toward the constructability of the bridge, they lead to eccentric connections that substantially reduce the in-plane stiffness of the PMDF systems, which is one of the reasons the forms are not relied on for bracing in bridge applications. This paper documents the results of an investigation focused on improving the bracing potential of bridge deck forms. Modifications to the connection details were developed to improve the stiffness and strength of the forming system. Research included buckling tests on a 15-m (50-ft) long, twin-girder system with PMDFs for bracing. In addition, twin-girder tests were also used to validate computer models of the bracing systems that were used for parametric finite-element analytical studies. The buckling test results demonstrated that modified connection details make PMDF systems a viable bracing alternative in steel bridges, which can significantly reduce the number of cross-frames or diaphragms required for stability bracing of steel bridge I-girders during construction.

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 structural components.

This paper presents an evaluation of flexural live-load distribution factors for cast-in-place box-girder bridges. The response of a typical box-girder bridge was recorded during a static live-load test. This test involved driving two heavily loaded trucks across the instrumented bridge on selected load paths. The instruments used to record the response of the bridge were strain gauges, displacement transducers, and tilt sensors. The measured data were then used to calibrate a finite-element modeling scheme using solid elements. From this finite-element model, the theoretical live-load distribution factors and load ratings for the test bridge were determined and compared with the factors and ratings predicted in the AASHTO LRFD specifications. A parametric study of cast-in-place, box-girder bridges using the calibrated finite-element modeling scheme was then used to investigate how various parameters such as span length, girder spacing, parapets, skew, and deck thickness affect the flexural live-load distribution factors. Based on the results of the parametric study, a new equation, which more accurately predicts the exterior girder distribution factor, is proposed.

This paper presents a new, practical methodology with simple analysis methods coupled with rapid experimental tests to identify distribution factors (DFs) for existing highway bridges. This approach is demonstrated on a reinforced concrete T-beam bridge population. It is shown that the moment DFs of single-span T-beam bridges can be determined by using skew angle, modal frequency, and the flexibility coefficient, where the frequency and the flexibility coefficient can be identified by means of rapid impact testing that can be conducted using an impactor, such as a falling weight deflectometer (FWD). This approach is first demonstrated using finite-element model (FEM) simulations. Moment approximation to FEM results with the new approach is 6%, whereas this approximation is on the order of 30% compared with the conventional beamline analysis given in the AASHTO code. This new approach is then demonstrated by using experimental data from four real-life bridges for the computation of moment values as well as the load ratings. It is shown that this new approach can conservatively approximate live load increases for the four existing bridges.

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.

A parametric study was carried out to provide criteria for structural regularity on reinforced concrete (RC) or precast reinforced concrete (PRC) multispan continuous bridges, assessing whether an equivalent single degree-of-freedom (ESDOF) system represents a multiple degree-of-freedom (MDOF) system correctly. The ESDOF system, determined by means of a nonlinear static analysis, is compared, in terms of displacements, with the original MDOF through a nonlinear dynamic analysis. To this end, a sample of 32 bridges was considered, taking into account the effect of the stiffness ratio between various piers and between piers and decks. Together with the the evaluation of the reliability of the regularity indexes found in the literature, a comparative analysis was carried out. The results showed that the simplified system is representative of the bridge global behavior when the deck is stiff enough to control pier displacements and deformations and when the pier distribution is symmetric.

Spatial arch bridges have significant out-of-plane behavior that must be controlled even under vertical loads. In some designs, the centerline of the arch may not lie within a plane. This study focuses on the structural behavior and the effect of the geometrical configurations of inferior-deck arch bridges with imposed curvature. In this type of spatial arch bridge, the arch and the deck centroid lines are both contained in the same vertical cylinder. The aim of this study is to propose the most appropriate design for controlling the out-of-plane response. A simple analytical model representing the stiffness of the arch, the deck, and a hanger allowed us to determine the main variables that control the behavior of the system. We also analyzed a series of linear three-dimensional-frame finite-element models of the complete bridge. This study demonstrates that nonplanar arches can be approximated by inclined planar arches. These parametric analyses have led to a set of recommended relevant design criteria for such bridges.

A general assumption reported in the literature is that the structural response of a stress-laminated-timber (SLT) bridge deck is linear until failure. However, few studies of ultimate-load tests (ULTs) on timber bridges have been reported. A full-scale test of a SLT deck (span, 4.9 m; thickness, 270 mm) was performed to obtain the deformations at various prestress levels as well as at the ultimate-load capacity of such a structure. Prior to the ULT, nondestructive tests (NDT) were performed at three different prestress levels. The load was applied as an axle load positioned both centrically and eccentrically. The deflections were about 10% larger at a prestress level of 300 kPa compared with a prestress level of 600 and 900 kPa. For applied loads larger than 150–250 kN, the deflection of the deck was nonlinear at certain positions. This was most likely owing to large concentrated shear forces that resulted in interlaminar slip between the laminates. The limit for linearity seems to be dependent on the applied prestress. A prestress of 600 kPa and an eccentrically positioned load was used for the ULT. Failure occurred at a load level of 900 kN. The existing design codes and new procedures in development may be verified and calibrated against the results in this paper.

This study evaluates the load rating procedure that is currently used in rating timber piles supporting multiple-span simply supported bridges. For simplicity, these piles are often rated under concentric loads and the effect of bending in the piles is neglected. Recent studies have shown, however, that under highly eccentric live loads, the effect of bending moments in the piles are of great importance and could have a dramatic effect on the load rating of the piles. This paper proposes an alternative structural load rating method for timber piles based on the National Design Specifications, which takes the effect of combined compression-flexure behavior of piles into consideration. This method is used to conduct a parametric study to investigate the effect of several geometric and structural parameters on the load rating of bridge timber piles using three-dimensional finite element models of concrete-deck bridges supported on group of timber piles. The results show that the proposed load rating method produces significantly less ratings for piles with moderate-to-high levels of deterioration, as compared with that obtained by the conventional approach. Among the studied parameters, the pile length is found to have the most significant impact on the pile load rating.

By in situ measurements, the real distribution of stress ranges caused by service loads can be recorded. Inherent effects in the measured response as disturbance can, however, create puzzles in the interpretation of the result. In large monitoring campaigns, it is not possible to examine the result from every gauge over the whole measured period by visual control. An approach for a quality assurance of the measured response is presented here based on established statistical methods. The stress range spectra, the product of the monitoring program intended for fatigue assessment, are analyzed. The aim is to find deviant spectra and identify corrupt gauges. An additional aspect is the length of the monitoring period, which is the required duration for obtaining a stable result. A case study of a monitored Swedish steel railway bridge is incorporated to exemplify the approaches. Some statistical distributions for the monitored stress ranges are also presented and incorporated in a fatigue assessment.

The cables and hangers of old suspension bridges and the stays of cable-stayed bridges often suffer from steel corrosion. It is important to repair them by proper methods to prevent the further progression of corrosion. In this paper six repair methods were proposed and applied to cable specimens. Then, the specimens were exposed to severe corrosion environments and the effectiveness of the proposed repair methods was compared. Two different types of test cables were used in this study: parallel wire strands and spiral strands. The first test group used parallel wire strand cables consisting of 19 nongalvanized steel wires. This test was aimed at the main cables of the suspension bridges. Six repair methods were applied to these cable specimens: coating with zinc-rich paint, coating with epoxy resin paint, coating with zinc powder paste, filling with epoxy resin, filling with oil, and a dehumidification method. Then, the specimens were accelerated to corrode in a laboratory for 15 months. By investigating the mass loss owing to corrosion and appearance during this period, the effectiveness of the six repair methods was compared. For the surface wires, the dehumidification method was the most effective followed by the epoxy resin paint and filling, the zinc powder paste, and the zinc and epoxy resin paint on the surface. The oil filling was not very effective compared with other repair methods. The corrosion of the inside wires was much less than for the surface wires. The second group test used spiral strand cables consisting of seven galvanized steel wires. This test was aimed at the hangers of suspension bridges and the stays of cable-stayed bridges. The same repair methods and corrosion acceleration methods were used. By investigating the mass loss owing to corrosion and the appearance of both inside and surface wires during the 16-month period, most of the proposed repair methods were very effective compared with those of unrepaired strands. This study proves that even if cables are corroded proper repair work is effective in preventing further corrosion.

A large portion of highway bridges in the United States are reaching or have reached their intended design lives. To avoid replacing a large number of bridges simultaneously, methodologies to safely extend their lives are important to help avoid high replacement costs and to schedule bridge replacement over a longer time window. This paper proposes an approach to extend the fatigue life of vulnerable steel bridges through a response modification apparatus, consisting of a mechanical amplifier and a response modification device, which provides supplemental stiffness and damping to the bridge. Because of the relatively small deflections encountered under typical service loads, the use of a mechanical amplifier allows for a smaller apparatus and enables a more efficient device to provide adequate response modification forces to the bridge. Herein, the use of a scissor jack as the mechanical amplifier is proposed for use in bridge applications, and its utility in concert with a passive stiffness device is demonstrated by application to a simple beam structure. Reductions in moment ranges of 37% and safe life extensions of 300% are achieved on a simple beam model with the proposed response modification apparatus.