Journal of Bridge Engineering

The experimental seismic response of two bridge columns built using highly flowable hybrid fiber-reinforced concrete under unidirectional static cyclic lateral loading is presented. The objective was to design bridge columns for use in regions of high seismic hazard that (1) sustain the seismic demands in a ductile manner; (2) minimize the concrete spalling that conventional RC bridge columns experience; and (3) avoid tension strain localization in the longitudinal steel bars observed in plastic hinge regions of fiber-reinforced concrete columns. The first column was designed to rock at its base. The second column was designed to form a flexural plastic hinge at its base and used stainless steel bars as longitudinal reinforcement. Both specimens experienced limited concrete spalling up to drift ratios of 4.8% and attained drift ratios of 11.3% without losing their vertical load resistance. The response of the specimens is compared with that of conventional RC columns.

In this paper, a model is proposed to evaluate vessel-bridge collision probability. A general mathematical model for navigation channels is suggested, which may be used for straight and meandering channels. The effects of waterway obstacles and water levels were taken into account in the proposed model. A definition and a judging criterion for an aberrant vessel to collide with a pier or an obstacle using geometry and kinematics were established. Finally, formulas were developed to estimate the vessel-bridge collision probability. The model proposed in this paper was applied to an existing bridge (Jiujiang Bridge) in China. The significances of meandering channels and waterway obstacles were noted.

Longitudinally stiffened plates with closed-section ribs are supposed to be an effective system for axially compressed members. However, current design specifications on closed-section ribs, particularly for the minimum required stiffness, are not sufficient, and thus, excessive designs are quite common because of the absence of suitable design guides. In this paper, simple closed-form formulas for the minimum required stiffness of compressively loaded isotropic plates braced by U-shaped longitudinal stiffeners (U-ribs) are derived. The effects of the sectional stiffness of U-ribs on the buckling modes and strengths of stiffened plates are examined by numerical analyses. Three-dimensional finite-element models of U-rib stiffened plates were obtained, and a series of eigenvalue analyses was conducted. By parametric study, thresholds of the sectional stiffness of U-ribs that may be adopted as the minimum requirement were collected, and these were used for regression analysis to obtain a simple and practical design equation for determining a suitable sectional stiffness after conducting a comparative study using a theoretically derived formula. The findings of this study would contribute to improving the optimum design of U-rib-stiffened plates.

For self-anchored suspension bridges having the fabrication camber subjected to live loads, a new deflection theory is formulated after an optimized initial state solution is found under dead loads. Its analytical solution for three-span continuous suspension bridges is consistently derived by considering tower effects compared with that derived by the conventional deflection theory for earth-anchored bridges. On the other hand, the unstrained length method (ULM), which keeps all element lengths constant in the nonlinear iteration process, is extended and applied to the nonlinear finite-element analysis of suspension bridges under live loads. Finally, an earth-anchored and self-anchored bridge examples are analytically and numerically solved using the two methods. The numerical results are compared to verify the accuracy and effectiveness of both the proposed deflection theory and the ULM.

Experimental and finite-element studies have shown that a significant correlation exists between the stress increment of unbonded prestressing tendons and the flexural load of prestressed concrete girders with corrugated steel webs. Key parameters, which dominate the ratio of the stress increment of unbonded prestressed tendons to that of bonded nonprestressed reinforcement, have been identified in this paper, including (1) strength and the cross-sectional reinforcement ratio of bonded nonprestressed reinforcement, (2) strength and the cross-sectional area of the steel flange, (3) concrete cubic strength, and (4) ratio of the concrete flange thickness to the girder depth. Other parameters, such as the strength and thickness of the corrugated webs, initial prestressing stress and cross-sectional area of prestressing tendons, and span-depth ratio, are demonstrated with less effect. With the understanding of the parametric analysis, an analytical model of the stress increment of unbonded prestressed tendons is established in this paper for the stress increment of unbonded prestressing tendons at the yielding load of the prestressed concrete girders with corrugated steel webs. This model is able to predict tendon stress increments with good comparison with the experimental results.

Structural health monitoring (SHM) of bridges by visual inspection is not necessarily reliable as many damages are not discovered during the periodic inspection of bridges. A technique to assist in visual inspection is vibration-based SHM. It is believed that structural damages lead to changes in stiffness and damping properties, and change the dynamic characteristics of structures, such as natural frequency, mode shape, and modal damping ratio. Although changes in the modal damping ratio can be used as damage indicators in the field of vibration-based SHM, the method’s accuracy remains concerning. This study investigated the analytical modal damping evaluation as a complementary method to the experimental SHM of bridges. An energy-based damping model was introduced to estimate the damping parameters of a steel arch bridge, such as the equivalent loss factors of structural components, and the modal damping ratios of the bridge were then analytically evaluated using the damping parameters. The results confirmed that the proposed methodology can identify the damping sources in steel bridges and their contributions to each modal damping ratio, and complements the experimental SHM of bridges.

This paper presents the shake-table tests of a damage-resistant posttensioned bridge column designed to rock at the interface with its foundation. It compares the response to that of a conventional bridge column detailed to conform with current California seismic design criteria. The lower portion of the rocking column was built using hybrid fiber-reinforced concrete (HYFRC) and was armored with headed rebars; these features enhanced the compression damage resistance at the column base. Unbonded rebars that crossed the rocking plane provided hysteretic energy dissipation. Both columns were subjected to a sequence of scaled historical triaxial earthquake ground motions including near-fault pulse-like motions. The conventional column formed a flexural plastic hinge with extensive spalling. It accumulated a 6.8% residual drift ratio after a sequence of seven ground motions, which caused a peak drift ratio of 10.8%. The posttensioned-HYFRC column sustained only light damage and accumulated only a 0.4% residual drift ratio after the same seven ground motions, which caused a peak drift ratio of 8.0%.