This study aims at developing appropriate multilevel performance classification of tall RC bridge piers for seismic design. A new performance classification toward postearthquake rehabilitation requirements is presented. It considers damage states of the local environmental conditions and accessibility of the potentially damaged part. To reduce postearthquake rehabilitation requirements, higher performance levels allowing only minor and moderate damages are advised for tall bridge piers. Two RC columns with high aspect ratios were designed, fabricated, and tested under static cyclic loading, focusing primarily on minor and moderate damage states such as residual concrete cracking and onset of visible concrete crushing. The experimental results show that the zero-tip-displacement crack width measured after the column returned to zero tip displacement significantly underestimated residual-cracking damage, while the zero-lateral-force crack width can be taken as an approximate estimation for the residual cracking on the safe side. An improved model is proposed to evaluate the cracking behavior beyond steel yielding. In this model, the expected residual-crack width is expressed as a function of the maximum crack width. The results obtained using the model show good agreement with the experimental results. For the onset of concrete crushing, 24 cantilever test columns in total were analyzed, with aspect ratios equal to or greater than 3.0 and axial-load ratios ranging from 0.05 to 0.25. The results indicate that a higher aspect ratio and lower axial-load ratio lead to a higher drift ratio corresponding to the onset of visible concrete crushing.
The demand for the construction of infrastructure is being transferred to the West of China. To ensure the seismic safety of new long-span bridges in the area of high seismic activity, the state of the art earthquake-resisting systems for long-span bridges are investigated and further developed. The common issues of the isolation mechanism, advantages and disadvantages, and influence of practical earthquake resisting systems are summarized. During the recent development of practical applications of long-span bridges, many approaches and techniques have been developed for such bridges with moderate seismic risks. However, there are few studies (as well as the corresponding design theory and specifications) on earthquake-resisting systems for appropriate long-span bridges with extremely high seismic risks (e.g., near-fault or cross-fault conditions).
Summary The collapse of long‐span cable‐stayed bridges under strong earthquakes will not only result in severe casualties and loss of property but also significantly delay the rehabilitation of the affected area. It is therefore essential to study the failure progress and potential collapse mechanisms of these bridges under strong earthquakes for assisting their inspection and maintenance and helping them survive an earthquake. Collapse simulations in existing studies are commonly conducted with design‐document‐based finite element (FE) models, which usually neglect the actual damage state of the bridges. The influences of modelling uncertainties on the simulated responses cannot be addressed. This study proposes a nonlinear FE model updating‐based collapse prognosis method for long‐span cable‐stayed bridges, which includes (1) a correlated‐updating‐parameter‐based nonlinear FE model updating algorithm, (2) a restarted time history analysis‐based seismic response prediction method and (3) an elemental deactivation‐based collapse simulation algorithm. The shake table test of a scaled Sutong cable‐stayed bridge in China is adopted to illustrate the proposed earthquake‐induced collapse prognosis method. A refined FE model of the bridge is first established and nonlinearly updated using the measurement data. The collapse prognosis of the bridge under a subsequent strong ground motion is then performed based on the updated model. The predicted structural responses and final failure mechanisms are compared with the measured responses and experimental observations with good agreement, indicating that the proposed method is feasible and accurate for evaluating the seismic performance and failure mechanisms of long‐span cable‐stayed bridges.
The collapses of curved bridges are mainly caused by the damaged columns, subjected to the combined loadings of axial load, shear force, flexural moment and torsional moment, under earthquakes. However, these combined loadings have not been fully investigated. This paper firstly investigated the mechanical characteristics of the bending-torsion coupling effects, based on the seismic response spectrum analysis of 24 curved bridge models. And then 9 reinforced concrete (RC) and circular column specimens were tested, by changing the bending-tortion ratio (M/T), axial compression ratio, longitudinal reinforcement ratio and spiral reinforcement ratio, respectively. The results show that the bending-torsion coupling effects of piers are more significant, along with the decrease of girder curvature and the increase of pier height. The M/T ratio ranges from 6 to 15 for common cases, and influences the crack distribution, plastic zone and hysteretic curve of piers. And these seismic characteristics are also influenced by the compression ratio, longitudinal reinforcement ratio and spiral reinforcement ratios of piers.
Skew bridges consisting of simply supported girders, continuous decks, and laminated‐rubber bearings are widely used in western China; however, they are highly vulnerable to strong earthquakes. To investigate the seismic performance of skew bridges considering the sliding behavior of laminated‐rubber bearings, the Duxiufeng Bridge located in Sichuan, China, was used as a prototype bridge. This bridge is a skew bridge that suffered seismic damage during the 2008 Wenchuan earthquake. The possible seismic response of this skew bridge under the Wenchuan earthquake was simulated, and the postearthquake repair methods were analyzed considering the effects of bearing types and cable restrainers. Parametric studies, using the finite element method, were also performed to investigate the effects of the skew angle and friction coefficient of the bearings on the seismic response of the skew bridge. The results indicate that pin‐free bearings could effectively control the seismic displacement of the bridge, and the cable restrainers with an appropriate stiffness could significantly reduce the longitudinal residual displacements. The effect of skew angles is less significant on skew bridges with laminated‐rubber bearings than on rigid‐frame skew bridges because of the sliding between the girders and bearings. The residual displacements of the bearings were more sensitive to the variation in the friction coefficient between the laminated‐rubber bearings and the girders compared to the maximum seismic displacements.
In this paper, the incremental dynamic analysis (IDA) is used to investigate the effect of higher vibration modes on the displacement ductility capacity of a tall pier. The results show that if the conventional method is used to evaluate the displacement ductility capacity of tall piers, there will be large error. The contribution of higher vibration modes to response has a significant effect on the yield, ultimate displacement and displacement ductility capacity for a tall pier.
Numerous bridges in the mountainous areas of southwest China are constructed with tall reinforced-concrete (RC) piers. This paper presents the influence of higher-mode effects of pier columns on seismic performance in a quantitative manner for, to our knowledge, the first time, while the impact of excitation intensity and the frequency content of input motion, which do not appear to be considered in any previous study, are incorporated as well. Numerical models are developed for three bridges with different pier heights, considering higher-mode effects by comparing the seismic responses computed from multi-degree-of-freedom and single-degree-of-freedom systems. An incremental dynamic analysis method is used to investigate the influence of input intensity, and motions matching different target spectra are employed, showing the effects of frequency components. The analytical results show that when the tall piers remain elastic or experience substantial nonlinearity approaching the ultimate state, the higher-order modes contribute more significantly to the seismic responses, while input excitations with more low-frequency components could generally suppress the effects of higher-order modes. Based on the analysis, seismic design strategies for tall piers are discussed and a novel design scheme using preset plastic region length is proposed, which is demonstrated to be able to limit the range of damage with a negligible increase in maximum curvature demand.
Elastomeric pad bearings are widely applied in short- to medium-span girder bridges in China, with the superstructure restrained by reinforced concrete (RC) shear keys in the transverse direction. Field investigations after the 2008 Wenchuan earthquake reveal that bearing systems had suffered the most serious damage, such as span falling, bearing displaced, and shear key failure, while the piers and foundations underwent minor damage. As part of a major study on damage mechanism and displacement control method for short- to medium-span bridges suffered in Wenchuan earthquake, a 1:4 scale, two-span bridge model supported on elastomeric pad bearings were recently tested on shake tables at Tongji University, Shanghai. The bridge model was subjected to increasing levels of four seismic excitations possessing different spectral characteristics. Two restraint systems with and without the restraint of RC shear keys were tested. A comprehensive analytical modeling of the test systems was also performed using OpenSees. The experimental results confirmed that for the typical bridges on elastomeric pad bearings without RC shear keys, the sliding effect of the elastomeric pad bearings plays an important role in isolation of ground motions and, however, lead to lager bearing displacement that consequently increases the seismic risk of fall of span, especially under earthquakes that contain significant mid-period contents or velocity pulse components. It is suggested from the test results that RC shear keys should be elaborately designed in order to achieve a balance between isolation efficiency and bearing displacement. Good correlation between the analytical and the experimental data indicates that the analytical models for the bearing and RC shear key as well as other modeling assumptions were appropriate.
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