Search

The Eddy Current Damper (ECD) is a velocity-based passive energy dissipation device that can be used for structural vibration control. This study aims to reveal the damper behavior and determine the optimal parameters of the ECDs applied to a suspension bridge suffering from bi-directional earthquakes. The influence of the bi-directional vibration interaction on the damping force is theoretically investigated. An optimization method is proposed combining the Sobol Sequence sampling method, the Coefficient of Variation (COV) method, and the Backpropagation neural network (BPNN) algorithm. A numerical model of a long-span suspension bridge with bi-directional ECDs is established and taken as a case study to verify the feasibility of the proposed optimization method. The results indicate that the ECD system with bi-directional interaction will produce a larger maximum force and less energy dissipation than one without bi-directional interaction. The proposed optimization method possesses the characteristics of objectivity, accuracy, and effectiveness. The obtained optimal bi-directional ECDs can significantly reduce the longitudinal and transverse vibration. Failing to consider bi-directional effects will lead to an overestimation of longitudinal damper parameters and an underestimation to transverse ones, as well as ignoring the influence of damper length on its mechanical performance. [ABSTRACT FROM AUTHOR]

Earthquake-induced poundings have been identified as a critical factor influencing bridge seismic behavior. However, most previous studies on this topic did not consider link-slabs in the continuous deck, which would influence the pounding occurrence and thus the subsequent seismic response. This paper uses a probabilistic method to evaluate the seismic vulnerability of a simply-supported bridge considering pounding and link-slabs. The damage states of girder ends due to poundings are proposed according to the cumulative damage. To analyze the seismic vulnerability of the whole bridge, both the joint probabilistic seismic demand model considering multiple engineering demand parameters and the joint damage state model considering the capability of each bridge component are established. Based on these models, the fragility curve of the whole bridge is obtained using the Monte Carlo method. The effects of gap sizes between pounding components and pier heights on the bridge seismic vulnerability are also investigated. The result reveals that the fragility of the whole bridge system is higher than that of any individual component. Ignoring the contribution of damage to each component to the whole system will lead to an overestimation of the seismic resistance of the overall bridge, which is detrimental to structural safety. [ABSTRACT FROM AUTHOR]

To mitigate longitudinal vibration of long-span railway suspension bridges, a Combined Viscous-Steel Damping System (CVSDS) is put forward in this paper. In the CVSDS, the viscous damper is expected to work under train braking and frequent earthquakes, while the steel damper can resist rare earthquakes. Moreover, a fuse-lock device is proposed to work as the switch between the aforementioned two dampers. The working mechanism of the CVSDS was introduced. The locking function was verified by static test, and the vibration reduction efficiency of the proposed system was validated through numerical method. The results show that the combined system is efficient. [ABSTRACT FROM AUTHOR]

China railway track system II (CRTS-II) slab ballastless track is usually constructed on high-speed railway (HSR) bridges to ensure the rail smoothness and the running safety of high-speed trains, but the use of the longitudinal continuous track system would significantly alter the dynamic characteristics of the bridges and therefore influence the bridge seismic responses. The pounding at shear keys has also been identified as one of the critical factors affecting the seismic behavior of bridges. To investigate the effects of shear keys and CRTS-II track system on the seismic behavior of HSR simply-supported bridges subjected to transverse earthquake excitations, detailed 3D finite element models are developed by using ABAQUS. The seismic responses calculated from the bridges with and without considering shear keys are firstly compared. The result shows that the shear keys can effectively limit the development of pier-girder relative displacement and thus decrease the potential of girder dislocation. However, large pounding forces would be generated between the shear keys and bearing pads and transferred to bridge piers, which will amplify the seismic responses of the bridge piers. The result of seismic analyses of multiple-span simply-supported bridges with and without considering the track system shows that the track system will significantly influence the distribution of seismic forces among the bridge spans. For a bridge with equal pier heights, considering the track system will reduce the seismic responses of side spans (close to subgrade) but will increase those of the middle spans. Whereas an opposite trend is found for bridges with high middle piers and short side piers. [ABSTRACT FROM AUTHOR]

Most previous studies investigating how transverse poundings at shear keys affect the seismic behavior of bridges were conducted numerically. Few laboratory investigations were reported, especially for isolated bridges. This study investigates the effect of transverse poundings on a bridge isolated by friction pendulum bearings (FPB) using 1:6 large-scale shake table tests. To evaluate the seismic isolation effectiveness of FPB in the cases of no pounding and pounding, bridges with ordinary spherical steel bearings (SSB) are also tested and regarded as reference cases. Results indicate that FPB has a better ability to reduce the acceleration of girder and the bending moment at pier base than SSB in the case of no pounding. However, poundings significantly increase the seismic forces developed in the bridge super- and substructure, especially for the bridge using FPB, which would considerably reduce the isolation effectiveness. The findings highlight the importance of considering transverse poundings when designing an isolated bridge. • The seismic performance of bridges with spherical steel bearings and friction pendulum bearings is investigated. • The consequence of poundings at shear keys for the transmission of seismic force in bridges is analyzed. • The seismic isolation effectiveness of friction pendulum bearings is evaluated with and without poundings. • The friction pendulum bearings show an excellent isolation effectiveness in the case of no pounding. • Introducing poundings will significantly reduce the isolation effectiveness of friction pendulum bearings. [ABSTRACT FROM AUTHOR]

This article proposes a seismic optimization strategy to reduce the cost of piers of simply-supported bridges for high-speed railway (HSR) in China. The dimension and reinforcement ratio of piers are defined as variables. The running safety of high-speed trains during normal operation is considered by novelly setting the vibration amplitude of running trains to satisfy the corresponding constraint condition. Other constraint conditions include the structural fundamental frequency, buckling stability, and longitudinal stiffness, as well as the stress and crack width of piers during earthquakes. An improved genetic algorithm with a double-filter strategy is proposed to increase the efficiency of the optimization calculation. Six HSR simply-supported bridges with different pier heights are selected as examples to verify the effectiveness and applicability of the proposed optimization method. The result shows that for the example bridges, the cost of the optimised piers that are not higher than 30 m can be reduced by 33.38% to 50.65%. The optimised piers can ensure the integrity of the HSR bridges subjected to the considered earthquakes and can provide sufficient stiffness to ensure the running safety and stationarity of high-speed trains. [ABSTRACT FROM AUTHOR]

• Transverse poundings on seismic responses of a 1:6 large-scale bridge model are studied using a shake table. • The interaction between the bridge pier and the girder with friction pendulum bearings is analysed. • Consequence of shear keys for load transfer from the bridge support to the girder is investigated. • Pounding increases the girder acceleration and the bending moment at pier supports. • A suitable gap is determined for the overall seismic performance of the bridge. To reduce the seismic force transmitted between piers and girders, friction pendulum bearings have been widely used in bridge structures. However, the bearings will lead to large relative displacements between the girder and the pier and thus increase the pounding potential of adjacent bridge structures. In the transverse direction, the girder movement can only be limited by shear keys. In this study, a series of shake table experiments were performed on a 1/6-scaled bridge model. To evaluate the consequences of poundings for isolated bridges, the wavelet transform (WT) is applied in addition to the fast Fourier transform (FFT). WT transform is used to capture the change in frequency content at the time of impact, while FFT is used to visualise the change in the frequency content of the entire response. Four different gap sizes and El-Centro earthquake with two different peak ground accelerations were considered. The results show that the selected gap size is relevant to the overall performance of the bridge. [ABSTRACT FROM AUTHOR]

This paper introduces a new integrated Horizontal Bidirectional Hybrid Damping System (HBHDS) incorporating eddy current dampers, metallic yielding dampers, fuse-lock device with a spherical steel bearing, for controlling the longitudinal and transverse vibrations of long-span bridges under near-fault pulse-like earthquakes. Based on the nonlinear time history analysis, the seismic response of a long-span bridge with HBHDS is investigated under different near-fault pulse-like earthquakes and compared to the installed damping system on the as-built bridge. The numerical results indicate that the HBHDS is an effective damping system against the near-fault earthquakes and exhibits a common tendency with similar or even better reductions of structural responses in comparison to installed damping system. Besides, a series of robustness investigations for HBHDS are carried out considering the out-of-service different HBHDS' components. It is found that HBHDS presents superior robustness to considering out-of-service dampers in terms of response reduction and energy dissipation capacity. • A new integrated hybrid damping system for vibration control of long-span bridges. • Advanced finite model assessment considering near-fault pulse-like earthquakes. • Horizontal bidirectional control effectiveness of the new system and comparison. • Robustness of the proposed system under near-fault pulse-like earthquakes. [ABSTRACT FROM AUTHOR]

Previous research has shown that the transient and partial footing separation is one of the effective methods to reduce the impact of earthquakes on bridge structures. The separation will not only temporarily stop the transfer of seismic load to structures, but also activate rigid-like body motions of the bridge piers. Most of current investigations involving footing uplift only focused on straight bridges. The influence of skew angle is rarely considered. Even though skewed bridges are common and more vulnerable to seismic load. This work reveals the simultaneous influence of skew angle and footing uplift on soil on seismic response of bridges. A bridge with a 30∘ or 45∘ skew angle, in addition to a straight bridge, was excited using a large-scale shake table. The ground excitations were stochastically simulated based on design spectrum of New Zealand standard. The result revealed that with increasing skew angle bridges will have frequent footing uplifts. In the case of a straight bridge, although allowing footing uplift is beneficial in reducing the bending moment at the pier support, it increases the longitudinal girder displacement. In contrast, in the case of 30∘ and 45∘ skewed bridges, uplifts increase the bending moments of piers and the displacements of the girder, especially in the transverse direction. [ABSTRACT FROM AUTHOR]

• A series of shake-table tests are conducted on a 1:6 scale single-span bridge model. • The effects of pounding and rubber bumpers on seismic responses are investigated. • The pounding reduction mechanism of bumpers is analyzed by FFT of seismic responses. • The pounding evidently increases the high frequency responses of the bridge model. • Bumpers can weaken the high frequency responses, thus mitigating pounding effects. The pounding between shear keys and bearing padstones has been identified as one of critical factors affecting transverse seismic responses of bridges. It is inevitable since the role of shear keys is to limit the excessive displacement of girders during earthquakes. Therefore, it is necessary to perform investigations on reducing the adverse transverse pounding effects on bridges. This paper presents an experimental study on the transverse pounding reduction of a high-speed railway (HSR) simply-supported girder bridge using rubber dampers. A series of shaking table tests were performed on a 1/6-scaled bridge model to investigate the influence of pounding on transverse seismic responses of the bridge model and the pounding reduction effects of rubber bumpers. The fast Fourier transform (FFT) of seismic responses was performed to further discuss the pounding reduction mechanism of rubber bumpers. The experimental results showed that the rubber bumpers are effective on reducing the transverse seismic responses. The pounding between shear keys and bearing padstones evidently increases the high frequency seismic responses of the bridge model. However, the presence of the rubber bumpers can significantly weaken the high frequency responses, and thus mitigates the adverse seismic responses caused by the pounding. In addition, a numerical model incorporating the pounding and rubber bumpers was developed to verify the validity and the accuracy of the numerical modeling. A good agreement between the calculated results and the experimental ones was found. [ABSTRACT FROM AUTHOR]

This study develops a novel Horizontal Bidirectional Hybrid Damping System (HBHDS) for mitigating the vibration of long-span bridges. It consists of eddy current dampers (ECDs), metallic yielding dampers (MYDs), fuse-lock device (FLD), and a spherical steel bearing (SSB). The ECD and MYD are connected in series through the FLD along the longitudinal direction to form an integrated passive control system together with the SSB. This system can not only mitigate the vibrations caused by service and seismic loads in the longitudinal direction, but also reduce the bridge seismic response when experiencing an earthquake in the transverse direction. The mechanical model of the HBHDS is introduced, and the method for determining the parameters of the HBHDS is given. To verify the superiority of the proposed HBHDS, a case study is performed on a long-span cable-stayed bridge. The numerical results confirm that the HBHDS has an excellent multi-level vibration control capacity, i.e., it can effectively mitigate structural vibrations caused by moving vehicle as well as earthquakes. • A novel hybrid damping system for mitigating vibration of long-span bridges is proposed. • The method for determining the parameters of the damping system is introduced. • The system is capable of mitigating structural vibrations caused by both the service and seismic loads. [ABSTRACT FROM AUTHOR]

This paper proposes a theoretical solution for multi-span continuous sliding cable structures, which were usually analyzed by numerical simulations. Firstly, the analytical equation for the unstressed length of single-span cable based on the undeformed configuration is derived, in which the tension forces at the ends can be accurately calculated. Then, according to the tension balance condition at sliding joints and the assumption of invariant total unstressed cable length (ITUL method), multivariate transcendental equations for the sliding analysis of multi-span cable structures with and without considering friction are established and solved by multiple Newton-Raphson iterations. Moreover, a theoretical method based on the assumption of invariant total cable length (ITL method) is also proposed and the applicability of the ITL method is investigated. Finally, four typical examples are analyzed by the ITUL method, and the accuracy of the ITL method as well as some existing numerical simulations is evaluated. The result shows that the ITUL method proposed in this paper is more accurate and reliable than the ITL method. The ITUL method can provide a theoretical basis for the design and analysis of multi-span sliding cable structures. [ABSTRACT FROM AUTHOR]

• This paper presents a numerical method for predicting the nucleation and propagation of multiple cracks based on XFEM. • The proposed competitive criterion can accurately judge the sequence of new-crack nucleation and existing-crack propagation. • The implementation of modified XFEM is introduced and verified to be effective. In practical engineering, structures will inevitably suffer from multiple cracks and require accurate numerical methods to calculate the structural behavior. Regarding the multi-crack problems, the nucleation of new cracks and the development of existing cracks will affect the subsequent structural responses. Therefore, the criterion for calculating crack nucleation and development is a critical factor influencing the numerical results. This paper presents a modified Extended Finite Element Method (XFEM) to predict the nucleation and development of multiple cracks in plane members focusing on the interaction of multiple cracks. In the proposed method, the crack competition criterion is based on the minimum total energy principle, which can ensure that the nucleation and development of cracks can achieve a maximum energy dissipation per unit length. The effectiveness and robustness of the presented method are verified by comparing the numerical results with experimental and/or other numerical simulations. The result shows that the proposed competition criterion can accurately judge the sequence of new-crack nucleation and existing-crack propagation. [ABSTRACT FROM AUTHOR]

This paper investigated the flexural behavior of large-scale damaged reinforced concrete (RC) bridge slab strengthened with the ultra-high performance concrete (UHPC) layer at the tensile side. The RC slabs were preloaded under flexure to introduce cracks. The pre-damage degree was evaluated using the crack width at the highest load. Then, two types of interface technique of the RC substrate were conducted before strengthening of the UHPC layer. The first technique was a combination of embedded studs and rough surface (S-R) on the RC substrate. The second technique was rough surface (R) only. Experimental results indicated that the UHPC layer enhanced the flexural capacity and stiffness of the damaged RC slab. The UHPC layer also restrained and delayed the crack development in the RC and UHPC layers. It should be highlighted that the strengthened slab with the S-R interface technique exhibited significant mechanical performance compared with the interface treated using the R technique only. Therefore, the enhanced flexural performance of the UHPC-RC slab using the S-R technique may have an impact on the analysis and design of strengthening large-scale damaged RC bridge slab. [ABSTRACT FROM AUTHOR]

• Damaged RC slabs strengthened with UHPC layer were tested in laboratory and applied in field. • Two different load patterns: negative bending moment and positive bending moment. • Two different curing conditions: normal temperature curing and high temperature steam curing. • Calculated flexure capacity by analytical models developed theoretically agreed well with experimental values. Based on strengthening a damaged bridge deck in the field, this paper conducted flexural experiments on a scaled damaged bridge deck strengthened by reinforced ultrahigh performance concrete (UHPC) layer with high temperature steam and normal temperature curing; this paper investigates cracking capacity, ultimate capacity, deformation features and failure mode of RC-UHPC composites under positive bending moment and negative bending moment, respectively. Experimental results indicate that cracking and ultimate capacity of composites increased by about 2.5 and 2 times respectively with UHPC located at tension face comparing with intact RC slab; while for UHPC at compression face, no change in cracking capacity was observed and ultimate capacity was 30% higher than that of intact RC slab. Meanwhile, stiffness also obviously increased with tensile stress in steel reinforcement in RC slabs, decreasing after strengthening for all strengthened slabs; and propagation of cracks in RC slabs was restrained and delayed due to ultrahigh ductility and behavior of strain hardening of UHPC. Based on experimental results and failure mode, analytical equations for cracking and ultimate flexure capacity of UHPC-RC slabs were constructed, and applicability of equations was validated by some experimental results in this paper and other literature with good accuracy by predicted equations. Finally, the research achievements of this paper were effectively applied on the reinforcement design of damaged deck of main girder in a cable-stayed bridge. [ABSTRACT FROM AUTHOR]