Journal of Bridge Engineering

Nowadays, AASHTO LRFD Bridge Design Specifications and the Canadian Highway Bridge Design Code contain flexural and shear provisions for the design of concrete bridge members reinforced with fiber-reinforced polymer (FRP) bars. Because of a lack of research, these standards do not recommend using FRP bars to resist compressive stresses in compression members. This paper reports on 14 full-scale circular RC columns tested under concentric axial load. The columns were reinforced with longitudinal FRP bars and confined with circular FRP spirals or hoops. Sand-coated glass-FRP (GFRP) and carbon-FRP (CFRP) reinforcement was used. The test parameters included configuration of the confinement reinforcement (spirals versus hoops), hoop lap length, volumetric ratio, and FRP reinforcement type (glass versus carbon). The test results indicate that the GFRP and CFRP RC columns behaved similarly to columns reinforced with steel. Using GFRP and CFRP spirals or hoops according to the provisions of the Canadian Standards Association S806-12 yielded sufficient restraint against the buckling of the longitudinal FRP bars and provided good confinement of the concrete core in the postpeak stages. The results of this study can be used as a fundamental step toward code provisions for using GFRP or CFRP spirals and hoops as internal confinement reinforcement in bridge pier and pile foundations.

Unlike straight bridges where cross frames and diaphragms are considered secondary members that predominantly stabilize the compression zones of noncomposite girders during construction, the interaction of bending and torsion in horizontally curved, steel, I-girder bridges renders these components primary load-carrying members. The effect of curvature on horizontally curved bridge behavior has been shown to be more critical during construction owing to a lack of a large, hardened, concrete deck that helps to stiffen and stabilize the entire system. Therefore, cross frames play important roles with respect to stabilizing the girders and distributing loads in curved bridges during construction. This work examined the effects of a bracing system that involved skewing cross frames relative to a normal to the girder’s web, termed skewed cross frames, on the construction behavior of horizontally curved, I-girder bridges having radially oriented substructure units (abutments and piers). The performance of this skewed cross-frame system was compared to that of more common bracing types, oriented normal to girder web, using three-dimensional, nonlinear, finite-element analyses. Preliminary studies of a single-span, small-radius bridge indicated more uniform load sharing among the girders during construction when a skewed cross-frame system was used. The current study aimed to expand these findings for bridges with other geometries and boundary conditions by investigating single-span and multispan plan geometries containing skewed cross frames at different spacings. In a fashion similar to the preliminary studies, for all cases examined, skewed cross frames were found to reduce deformations and rotations in critical superstructure members while generally requiring fewer intermediate cross frames compared to bracing placed normal to the girder web.

Instrumentation of bridge structures provides a stream of data representing operational structural response under loading. The authors define the term bridge signature as the expected response of a particular bridge under loading, as measured by different instruments. In this research, the authors propose a new method to develop and evaluate a bridge signature. The signature can be monitored over time and statistically evaluated to detect potential structural deterioration and damage. An instrumentation system was implemented on the Powder Mill Bridge in Barre, Massachusetts, as a research prototype for the development of a structural health monitoring (SHM) system. Heavy truck events due to daily traffic were collected using an automatic measurement system, which triggers above a given threshold of recorded strains. Using the measured strain data due to daily traffic, a bridge signature was created using nonparametric statistical techniques. Maximum experimental strain values from heavy truck events were used to establish a nonparametric probability distribution that describes the behavior of the undamaged bridge under normal operating conditions. Nonparametric prediction intervals were added to the bridge signature, which define where future distributions of strain data from the undamaged bridge should fall. To study the robustness of this method for use in damage detection, three damage scenarios were simulated using a calibrated finite-element model. Comparison of the prediction intervals of the undamaged bridge signature to the analytical damaged distributions showed that, for all three damage scenarios, the damaged distributions fell outside of those intervals, which indicates that this method can potentially identify the presence of structural damage. This study shows that the proposed method is robust and computationally efficient for operational bridge damage detection using only measured strain data from truck loadings.

In this paper, a beam-truss model is introduced for the design analysis of composite box-girder bridges. An integrated research program for beam-truss models, including modeling implementation, analysis, and application, has been performed to exploit this powerful research and design tool. First, beam-truss models of composite box-girder bridges are implemented, and then corresponding model strategies are formulated based on classical shear–flexible grillage analysis. The calculation accuracy of the beam-truss models is then verified through comparative studies on the structural behavior of straight and curved composite, simply supported, and continuous box-girder bridges obtained using elaborate beam-truss finite-element (FE) models. Numerical analyses include modal analysis; static analysis under gravity load, prestressing load, and lane live load; and whole-process analysis considering the construction method and the long-term behavior of concrete. Finally, beam-truss models are employed for the analysis of field tests on two actual composite box-girder bridges, one straight and the other curved. It is concluded that the beam-truss model provides a reliable and powerful tool for the design analysis of composite box-girder bridges.

Experimental evaluation of aerostatic properties of a typical streamlined bridge deck under different conditions is conducted using wind-tunnel tests. The influences of aerodynamic modification factors (including stacking loads, crash barriers, vehicles, and central slotting) on the aerostatic force coefficients are investigated in this study. These factors increase the drag force, and their influences on the lift force and torsional moment are comparatively minor. The installation eccentricities of test models in both the lateral and vertical orientations have a noticeable influence on the torsional moment. These eccentricities are measured and the effects are eliminated to improve test accuracy. The aerodynamic steady and unsteady behavior, stall angles, and Gaussian and non-Gaussian characteristics at typical attack angles and extremely large attack angles are elaborated. The unsteady fluctuations and non-Gaussian performance of the aerodynamic forces are experimentally verified to be almost negligible at small attack angles. The experimental and analytical framework presented herein provides an effective analysis tool for study of the different aerostatic characteristics of bridge decks. It sheds light on the experimental details and further the potential issues involved in characterizing actual aerostatic performance in the wind-resistant design of flexible long-span bridges.

Cable inspections revealed that severe corrosion of steel wires is one of the main failure mechanisms of cables. Accelerated corrosion experiments were conducted to evaluate the variation in the uniform and pitting corrosion depths of high-strength steel wires over time. The measured uniform corrosion depth followed a lognormal distribution with time-dependent corrosion variables at both the zinc coating corrosion stage and the steel corrosion stage. The block’s maximum pitting factors from a different exposure time were proven to be drawn from the same underlying continuous population and followed Gumbel distribution. The regression models of the scale and location parameter with increased surface area were obtained based on the experimental block’s maximum pitting factors. The extreme value distribution of the pit depth of corroding steel wires could be predicted by the developed statistical uniform and pitting factor models.

Pretensioned members such as AASHTO I-girders and bulb tees (BTs) are widely used in the construction of bridges. In response to the challenges of longer bridge spans and more application of high-strength concrete in future girder design, high-capacity strands (HCSs) have recently been introduced in the construction of pretensioned concrete girders. These HCSs, such as 18-mm (0.7-in.) diameter Grade 270 (1,860 MPa) strands and 16-mm (0.62-in.) diameter Grade 330 (2,275 MPa) strands, can provide large prestressing forces and lead to increased bridge spans without switching from AASHTO I-girders and BTs to other girders. Currently, there is limited research concerning the application of these HCSs in AASHTO I-girders and BTs; therefore, this study focuses on the transfer length and strand spacing of the HCSs in these girder sections. The research results from this study indicate that the transfer length of these HCSs from experimental tests is considerably smaller than that predicted by several codes. On the basis of the concrete used in this study, the 50-mm (2.0-in.) strand spacing is applicable to the HCSs. Finally, this paper discusses the splitting effect within anchorage zones. Tractable equations are suggested to calculate the splitting forces in AASHTO I-girders and BTs prestressed by the HCSs.

The measurement of dynamic deflection is an important component of bridge loading experiments for high-speed railway bridges, but it is difficult to do directly for some long high-speed railway bridges. The deflection curve of the bridge in theory can be obtained by integrating the inclination curve of the bridge. This may be a good indirect method for dynamic deflection measurements of high-speed railway bridges if it meets two conditions: first, it must use a high-precision inclinometer to get a high-precision inclination curve of the bridge, and second, it must have a reliable integration method to calculate the deflection curve from the inclination curve. Based on this theory, the authors propose a new indirect dynamic deflection measurement method that uses precision inclinometers and a reliable integration method to measure the dynamic deflection curves of high-speed railway bridges. First, the authors designed a precision inclinometer called the QY inclinometer; second, the authors propose an inclinometer placement optimization method and a reliable integration method; last, two comparison experiments are conducted to prove this method on the Baima River Bridge. Test results indicate that this method can achieve the same accuracy as the method that uses cable-displacement sensors to test deflection and can achieve 0.01-mm accuracy. These experiments also prove indirectly that QY inclinometers have high precision and a response that is rapid enough to produce a dynamic intimation curve of a beam bridge when a train runs across it at high speed; the integration method proposed in this paper is also reliable. Compared with other methods of dynamic deflection measurement, this indirect measurement method is very easy to execute and does not need a static reference point to install inclinometers, and it can measure the static and dynamic deflection of any long- or short-beam bridge.

The Maanshan Bridge over the Yangtze River in China is a new long-span suspension bridge with double main spans of $2\times \mathrm{1,080}\hspace{0.17em}\text{m}$ and a closed streamlined cross section of single box deck. The flutter performance of the bridge was investigated via a wind tunnel test of a full bridge aeroelastic model at a geometric scale of 1:211. The test was conducted in both smooth and simulated boundary layer wind fields with various combinations of wind yaw and inclination angles. A unique and interesting flutter-mode transition behavior was observed in smooth flow. As wind speed approaches the flutter threshold, the model oscillation with the first antisymmetric torsional mode (A-T-1) transfers to alternate torsional oscillation between double spans, then transfers to oscillation with the first symmetric torsional mode (S-T-1), and then violent oscillation occurs. The mechanism of the phenomenon is unknown, and there may be no numerical method to simulate it to date. One possible reason for the flutter-mode transition is that a nonlinear aerodynamic self-excited force acting on the middle pylon dragged the full aeroelastic model into soft-type flutter. The other inference is that internal resonance occurred, in which energy transforms between two spans and between modes A-T-1 and S-T-1 at the same time.