Journal of Bridge Engineering

Abstract

Additional damping provided by a viscous damper (VD) may not be sufficient to mitigate the wind-induced vibration of long cables. In this paper, the damping properties of the hybrid application of a VD and a tuned mass damper (TMD) on a taut cable are studied. The VD-TMD-cable system’s characteristic equation is formulated by using complex modal analysis. The modal properties of the VD-TMD-cable system are subsequently discussed. Then, a damper optimization principle is introduced. When optimizing the cable single mode, based on the damper optimization principle, the effects of the damper parameters of the VD and TMD on the damping ratio of the optimized cable mode are investigated. Furthermore, a damper optimization method for cable multimode vibration mitigation is proposed. Finally, case studies are presented to verify the effectiveness of the damper optimization method. It is shown that the hybrid application of the VD and TMD can significantly improve the damping ratios of the cable multimode. The hybrid application approximates the superposition of separate applications if cable lower modes are optimized and outperforms the superposition of separate applications for cable higher modes if cable higher modes are optimized. The optimum modal damping ratios can be obtained efficiently by the proposed damper optimization method for cable multimode vibration mitigation to satisfy the damping requirement.

Practical Applications

This paper proposes a damper optimization method of the hybrid application of a viscous damper and a tuned mass damper for a bridge taut cable multimode vibration mitigation. To overcome the difficulty involved in the actual implementation of the hybrid application, the authors provide a practical solution based on the findings of this paper, which is to set the optimum conditions of the viscous damper and tuned mass damper for the longest cables of each group, while setting the suboptimum conditions of the viscous damper and tuned mass damper’s for the other cables of each group as long as the modal damping ratios meet the target damping ratio. To achieve this, the following steps are required to be taken: First, select adjacent cables with the similar properties as one group. Second, optimize viscous damper and tuned mass damper parameters for the lower and higher modes of the longest cable in one group, respectively. Third, set the viscous damper and tuned mass damper’s configuration parameters of the other cables in the group equal to the optimum viscous damper and tuned mass damper’s configuration parameters of the longest cable. Check whether the damping ratios of the considered modes of the other cables in the group meet the target damping ratio; if not, just try adjusting the cable modes optimized by the viscous damper and tuned mass damper, which means actually adjusting the viscous damper and tuned mass damper’s installation locations of these dampers to meet the target damping ratio.

This paper introduces a novel, cost-effective deployable tool for the construction of highly skewed and curved steel girder bridges that will provide the necessary geometrical adjustments to the adjacent girders for the fit-up and installation of cross-frames. This tool consists of two cables and one hydraulic jack and would be deployed near the location where a cross-frame needs to be installed. The jack would be extended or contracted to rotate the girders such that they are approximately parallel to one another to achieve the desired geometry for the installation of the cross-frame without requiring force-fitting. After the cross-frame is installed, the deployable tool would be released and reused elsewhere. This paper presents a numerical investigation of the efficacy of this deployable tool in facilitating the installation of cross-frames for two prototype bridges: a highly skewed and a curved steel girder prototype bridge. Three-dimensional (3D) finite-element (FE) analyses of the prototype bridges under steel dead load at the construction increment just before the cross-frames would be installed were performed to first understand the challenges in cross-frame fit-up. The deployable tool was then incorporated into the developed FE model to determine the forces in the system throughout its deployment and the installation of the cross-frames. A control sequence for the deployment was developed and evaluated. For the prototype bridges considered in this research, the peak force in the hydraulic jack was 26.6 kN (5.97 k), meaning that off-the-shelf technologies could be used. The peak von Mises stress in the installed cross-frame was 22.4 MPa (3.25 ksi), indicating that the procedure is not overstressing the system. Overall, this research demonstrates the promise of a new tool to facilitate cross-frame installation in highly skewed and curved steel girder bridges and culminates in recommendations on the use of this technology in the field.

The stress response behaviors of steel wires at the anchorage part of bridge cables under tension and bending coupling loads play a predominant role in determining their fatigue life and failure modes. The inherent complexity of the spiral geometry and the large diameter of actual bridge cables made the stress response behaviors of steel wires at the anchorage part unclear up to now. An analytical method was proposed for spiral steel wires at the anchorage part of semiparallel steel wire cables under tension and bending coupling loads. The corresponding refined numerical modeling method was also developed for studying the local anchorage part. Both the analytical formulation and numerical model agree well with the related experimental results in the literature. The presented analytical and numerical methods are thereby efficient and accurate to simulate bridge cables under tension and bending coupling loads. The critical slip curvature of steel wires increases linearly with the tensile strain of the bridge cable. The axial stresses of the steel wires of the bridge cable at a given longitudinal location display a linear relation with the angular change at the anchorage end. For steel wires located at the guide deviator part of the bridge cable, the axial stress behavior differs between the stick and slip states. It changes to a chord curve in the longitudinal direction in the stick state, while it follows an exponential function with respect to the polar angle in the slip state. The axial stress range of the outermost steel wire of the bridge cable increases linearly with the harmonic tension load range and the bending load range, separately. Regarding the phase difference between harmonic tension and bending coupling loads, a phase difference of 0 represents the most unfavorable combination for the bridge cable. By contrast, when the phase difference falls between 0 and π/2, the two harmonic loads tend to mutually inhibit each other’s effects on the cable’s behavior.

Connections between prefabricated concrete panels (PCPs) are susceptible to cracking and damage, attracting the attention of bridge engineers. Curved bolt connections have ideal flexural performance when they have an appropriate anchorage distance. High-performance materials, such as ultrahigh-performance concrete (UHPC) and carbon fiber‒reinforced polymer (CFRP) bars, bring solutions to further reduce construction resources on-site and improve the durability and mechanical properties of curved bolt connections. In this paper, curved bolt connections with UHPC grout and CFRP tendons (UHPC–CFRP connections) for PCPs were proposed. Prediction models for the flexural capacity, cracking moment, and deflection of UHPC–CFRP connections were proposed. Full-scale flexural tests were carried out to study their working mechanism, and their flexural performances were compared with those of ordinary curved bolt connections. Three-dimensional finite-element numerical models were developed, and the influences of important design factors on flexural capacity were discussed. Both experimental and numerical results showed that the flexural behavior of the PCPs with UHPC–CFRP connections is more desirable than that of curved bolt connections with ordinary materials. The improved models are effective for predicting the flexural response of PCPs with UHPC–CFRP connections.

A key component of infrastructure seismic risk assessment is the execution of nonlinear time-history analyses with a suite of selected ground motions scaled to site-specific spectra. When interested in the evaluation of distributed systems residing near major active faults, such an approach is challenged by the scarcity of records adequately incorporating region and site-specific features known to impact the nonlinear response of distributed infrastructure substantially (pulses, spectral shape, spatial variability). This paper assesses the differences in the seismic demand posed to a suspension bridge as obtained from real ground motions selected based on state-of-the-art methods and arrays of site-specific simulated ground motions generated from physics-based wave-propagation models. The objective is to characterize the biases in structural response estimates introduced by the use of real ground motions in code-compliant approaches. A total of 15 realizations of an M7 Hayward fault earthquake and a detailed nonlinear simulation model representative of the West San Francisco–Oakland Bay Bridge are utilized as a case study. Damage limit states associated with structural drifts are defined for each bridge component as a function of the spread of plasticity. The results indicate that the median and variability of the demands posed by the simulated motions and real ground motions scaled to the same site-specific spectra are markedly different. Evidence from this study highlights the sensitivity of complex structures to multiple characteristics of the ground motions that might be biased by current scaling methods. Finally, fundamental characteristics of the scaled records leading to differences in the bridge response are discussed providing the basis to inform current ground motion selection and scaling procedures.

This study presents a seismic design methodology for precast concrete column-to-pile shaft member socket connections. In designing such connections, the intent was to ensure that the plastic hinge occurs in columns while minimizing the damage to the pile shaft. To achieve this, a strut-and-tie model was developed to represent the force transfer mechanism within the connection region; this model served as the basis for efficient seismic design details, including shaft transverse reinforcement, column embedment length, and shaft size. The predictive accuracy of the strut-and-tie model was validated against both the experimental and finite-element analysis results for a wide variety of connection features. Upon validation, the strut-and-tie model was integrated into a step-by-step seismic design procedure and a case study was conducted to demonstrate the effectiveness of these procedures for determining suitable connection design details. Finally, a computer application with a graphical user interface was developed for the ease of implementation of the strut-and-tie model and reliable interpretation of its analysis results, making it possible to be used routinely in seismic design practice for precast column-to-pile shaft assemblies.

Assembly of precast elements is a widely adopted technology for achieving accelerated bridge construction (ABC) owing to the increased construction speed and quality. Connection methods between precast structural members, if designed properly, can facilitate a convenient postearthquake replacement of damaged members and hence enable rapid function recovery of bridges. This study proposes a new precast bridge pier–footing connection using external sockets. The external sockets are prefabricated on the top of bridge footings and the precast piers can be directly inserted into the sockets with postgrouting. Quasi-static cyclic loading tests were conducted on four 1/4-scale pier–footing specimens, including three external socket pier specimens and a cast-in-place (CIP) specimen for comparison purposes. The experimental results show that the external sockets with normal design sizes are effective precast pier–footing connection methods, ensuring that plastic hinges are formed in the piers without damaging the external sockets and footings. Because of the shortened effective pier height, the socket piers show increased lateral stiffness and strength but decreased displacement capacity compared with the CIP pier. The measured peak horizontal forces for the precast socket pier specimens PCS-1, PCS-2, and PCS-3 are increased by 7.5%, 34.5%, and 51.4%, respectively. However, the ultimate displacements are reduced by 11.1%–22.0% compared with the CIP pier. The hysteretic energy dissipation of the socket piers is compared with that of the CIP pier, with a difference less than 20%. Postexperiment replacement of a tested precast pier was carried out, which demonstrates the feasibility of rapidly replacing damaged bridge piers when using the proposed external socket connections. A subsequent experiment reveals that the newly replaced pier specimen could show an equivalent seismic performance to the previous specimen. The maximum differences of the peak force and initial stiffness between the two piers are within 6.7%, and the difference of the dissipated energy is only 3.8%. The experimental results verified the effectiveness of the rapid replacement.

States may allow vehicles to exceed US federal weight limits off the interstate system, but state-specific load rating vehicles are developed to ensure that bridges can carry such vehicles safely. However, if the load effects of state rating vehicles are not similar to those of the vehicles operating in the state, the load factors required for the safety of some bridges may be too large for others, resulting in unnecessary remediation that may include retrofitting, posting, or even closure. In this study, a quantifiable measure of load rating efficiency is used to analyze the load effects of rating and operating vehicles on a wide range of bridges. Using this measure of efficiency, a novel heuristic approach is used to identify nearly optimal rating loads that envelope the load effects of state operating vehicles, potentially reducing the need for remedial action. To illustrate, the approach is used to develop new rating loads proposed for the state of Indiana. This approach may be combined with further analyses to assess the potential economic impact of new rating vehicles.

To optimally use the excellent mechanical properties of ultrahigh performance concrete (UHPC), this study experimentally investigated the flexural behavior of 10 lightweight steel-UHPC composite beams constructed using thin UHPC slabs and ultrashort studs. The influences of stud spacing, slab thickness, stud aspect ratio (height-to-diameter ratio), and shear span ratio on moment capacities, postcracking and postyielding strength, and deflection increments were investigated, along with the observations of failure modes, crack patterns, strain distributions, slip/uplift behavior, and unloading response after failure. Experimental results indicated a 9% decrease in the moment capacity with a 22% larger ultimate deflection as the full shear connection degree decreased to 0.5. A decrease in the stud aspect ratio from 1.5 to 1.0 caused similar loads but 45% larger ultimate deflections due to the uplifting and splitting behavior of the composite beams. An increase in the thickness of the UHPC slabs from 35 to 55 mm increased the postyielding strength and deformability by relieving the local UHPC crushing failure. With only half and one-third the thickness of normal concrete slabs, the 35- and 55-mm-thick slabs provided an elastic flexural stiffness similar to and 26% higher than that of the composite sections, respectively, with higher ductility. The current design code accurately predicts the bearing capacity of ultrathin UHPC–steel composite beams. In future research, the coupling effects of both interfacial slip and uplift on the overall deflection of such composite systems should be investigated.

The incorporation of high-strength steel wire mesh and polyurethane cement (HSSWM–PUC) has been identified as an effective approach for enhancing existing reinforced structures. This study comprehensively examined the flexural performance of reinforced concrete (RC) T-beams fortified with HSSWM–PUC composite material, proposing an accurate formula to calculate flexural capacity. This formula took into account various factors such as the strengthening ratio of HSSWM, laminate thickness, the type of bonding anchorage material, the presence of end anchorage, and the degree of initial damage. Flexural tests were conducted on one contrast beam and six reinforced beams within the scope of this research. Subsequent analyses revealed that the application of HSSWM–PUC significantly elevates the flexural capacity of both damaged and undamaged beams. This indicates that the load-bearing capacity correspondingly improves as the PUC thickness increases. With an increase in PUC thickness from 20 to 30 mm, the reinforced beam showed a 34% improvement in ultimate load and a 31.7% increase in yield load. Compared under similar parameters, beams strengthened with HSSWM–PUC showed a 43% higher cracking load than HSSWM–PM, especially with eight longitudinal high-strength steel wire ropes and a 20-mm-thick PUC layer. Additionally, using a U-shaped anchorage at the end provided a 20% advantage. A further merit of the HSSWM–PUC approach lies in its capability to both restrain the formation of concrete cracks and retard the progression of such defects, thereby fortifying the structural integrity. The observed failure mode was predominantly flexural, distinctly avoiding the common peeling failure witnessed between strengthening laminates and concrete. This suggests that HSSWM–PUC stands as a credible solution for amplifying the durability and lifespan of RC structures.

In the design of conventional steel and concrete highway girder bridges, the amount of live load carried by a single girder is quantified through distribution factors (DFs). However, moment DFs for the recently developed fiber-reinforced polymer (FRP) composite tub (CT) girders are not defined in current design codes, leaving questions as to these bridges’ live load distribution. To address this, two diagnostic live load tests were performed on an in-service CT girder bridge under heavy truck loads. The measured strains from each test were analyzed and compared with predictions from a calibrated, high-fidelity finite-element (FE) model, which was shown to accurately predict the live load distribution. Then, a simplified FE model was developed that was also shown to accurately predict the live load distribution at a significant computational discount. The simplified model was subsequently used in a parametric study to assess current CT girder design practices, which were found to be consistently conservative. One conclusion was that unintended end restraint of the girder significantly impacted the maximum measured flexural strains, and the high-fidelity FE model required modification and calibration to capture this effect. However, simplified FE models that were not calibrated to the field data were shown to reasonably accurately predict the live load distribution to the most heavily loaded, interior girders. Ultimately, the results of this study show that live load moment DFs should be developed that are specific to the CT girder to ensure efficient future designs with this new technology.