Summary
This paper addresses the effectiveness and optimal design of nonlinear viscous dampers for inelastic structures. First, a nonlinear damping index is derived by using the dimensional analysis ...to estimate the damping induced by supplemental nonlinear dampers on inelastic single degree of freedom (SDOF) structures. Subsequently, the effects of the added nonlinear damping on the seismic responses of inelastic SDOF systems are analyzed in dimensionless forms when subject to various near‐fault ground motions. The structure‐to‐motion frequency ratio, the motion characteristics, and the structural nonlinearity are the main factors that will affect the damping effectiveness. Especially, it is shown that adding nonlinear viscous dampers will decrease displacement demands yet sometimes lead to amplified acceleration responses. Furthermore, an equivalency procedure is developed to match the inelastic multi‐degree of freedom (MDOF) structure that is equipped with multiple nonlinear viscous dampers to its corresponding SDOF system. Such equivalency justifies that the analysis results for the viscous damping efficiency on SDOF systems can be congruously applied to realistic multi‐story structures. Finally, the optimal designs of nonlinear dampers for MDOF inelastic structures are identified by implementing a hybrid genetic optimization framework along with a robust performance index.
AbstractThis study investigates the effectiveness and optimal design of protective devices for the seismic protection of highway bridges. The Painter Street Overcrossing is seismically redesigned ...with protective devices. Component-level fragility functions are first derived by probabilistic seismic demand analysis using nonlinear time history analyses that include soil–structure interaction effects and ground motion uncertainties. The bridge repair cost ratios are then derived using a performance-based methodology and the associated component failure probability. Results of the comparison of two initial protection designs show that the bridge repair cost ratios provided an efficient evaluation of the protective devices. Subsequently, a multiobjective genetic optimization method utilizing the Pareto optimal concept is employed to identify the optimal design parameters of protective devices for six design cases with various combinations of isolation bearings and fluid dampers. Finally, the repair cost ratios of the bridge with optimally designed protective devices are evaluated. The results show that these optimal devices are able to minimize the overall damaging potential of the bridge, hence validating the optimal design procedure as a practical method for selecting protective devices.
Dynamic interaction between soil and structure group (SSGI) is of great significance to the seismic design and evaluation of structures in densely built areas. However, detailed three-dimensional ...parametric analysis of the SSGI effect using realistic modeling on both the superstructure and soil is still limited. This study develops a three-dimensional numerical method to account for the SSGI effect and validates it against the shaking table test result. Subsequently, parametric analyses are conducted to investigate the SSGI effect for a three-dimensional soil and structure group, where key parameters include the structure height, number, and spacing, material properties of the soil, and spectrum distributions of seismic records. Compared with the dynamic interaction between soil and a single structure, the SSGI can reduce the structural base shear and story drift (up to 17% and 24%, respectively) in most cases. However, the level of reduction is below 5% when (1) structure spacing is greater than 2.0 times the width of the structure foundation or (2) the shear wave velocity of soil is no less than 300 m/s. Essentially, the SSGI changes the seismic demand of the concerned structure mainly by altering its local ground acceleration input at the base. The SSGI effect is more significant when structure spacing is reduced, structure number is increased, or the height of the central structure equals those of the surrounding structures. In contrast, the influence of soil property on the SSGI effect is minor under medium-level earthquakes.
Multi-span reinforced concrete (RC) curved box-girder bridges are commonly designed to facilitate traffic flow at highway interchanges. The Aksemsettin Viaduct (henceforth, A Viaduct for brevity) in ...Istanbul, Turkey, is an eleven-span interchange bridge with a total length of 596.8 m. Located in a high seismicity zone, the A Viaduct is designed with a curved deck, multiple bearings that have different isolation mechanisms at different bents and directions, ten rectangular columns with unequal heights, and a mix of pile foundations and spread footings. The significant length of the viaduct crossed by eleven spans also makes it susceptible to varying ground motion excitations at different foundations. To evaluate the effects of the degree of modeling detail and analysis complexity on the estimated seismic performance, the present study conducts a comprehensive fragility assessment of the specimen viaduct under various ground motion excitation schemes. First, a three-dimensional finite element model is developed with detailed simulations for the deck, columns, bearings, foundations, and abutment components. To enable different ground motion excitations at each foundation, 57 sets of spatially varying ground motions are simulated by considering the realistic surface topography and soil stratigraphy at the bridge site. Cyclic pushover analyses are performed along multiple loading directions to develop the direction-dependent capacity limit state models for hollow rectangular columns. Subsequently, a demand-capacity ratio method is utilized to develop reliable fragility models for bridge columns. Component- and system-level fragilities of the A Viaduct are then assessed under uniform versus multi-support excitations, vertical motions, and ground motions with varying incidence angles. To further capture the seismic damage discrepancies of the same components at different locations, seismic repair cost ratios of the A Viaduct are assessed when subjected to uniform and multi-support excitations. This study highlights the significance of considering multi-support excitations to achieve more realistic seismic fragility and loss estimates for multi-span long curved highway bridges.
•A numerical model is developed for a multi-span irregular curved bridge.•The DCR approach quantifies the seismic fragilities of hollow rectangular columns.•Ground motions with different incidence angles affect the column fragility.•The multi-support excitation scheme outperforms uniform excitations.•Vulnerability assessment is suggested for multi-span bridges with many components.
Aiming at disclosing a general research landscape of structural engineering in the twenty-first century, this study applies the latent Dirichlet allocation (LDA), a topic modeling approach, to ...analyze 51,346 article abstracts from 23 prestigious journals in structural engineering with a publication period from 2000 to 2020. The LDA analyzes the literature inventory by extracting 50 distinguishable wordclouds, each centered around one distinct research theme and assigned a unique topic name. Subsequently, various measures have been proposed to integrate the posterior distributions of these research topics with article information such as publication year, journal name, and correspondence address. The increase index identifies five cold and hot topics, which reflect the shift of research interests in the community. Emerging research topics such as seismic risk assessment and composite material have received much more attention in recent years. Moreover, advanced metrics have been proposed to analyze the research similarity and evolution across different journals and countries/regions. As discussed in the paper, analysis findings would enable community stakeholders (e.g., students, engineers, researchers, conference organizers, journal editors, funding agencies) to explore the state of the research and develop viable strategies to further foster the healthy growth of the community. Such strategies can be (1) researchers submitting a paper to the most appropriate journal; (2) journal editors adjusting the journal focus to enhance its impact; and (3) funding agencies prioritizing research supports that best fit regional needs and circumstances, among others.
•Shake table tests verify the capability of USRBs to roll over during earthquakes.•The rollover deformation of USRBs effectively controls bearings’ unstable sliding.•USRBs are seismically more ...efficient in isolating the bridge deck than ULNRs.•Seismic performance of USBRs can be captured through a hardening material model.
Previous earthquakes in China have caused significant seismic damage in short-to-medium span highway bridges due to the uncontrollable sliding of unbonded laminated rubber bearings (ULNRs). This paper investigates the soundness of replacing the ULNRs in these bridges with novel unbonded steel mesh reinforced rubber bearings (USRBs). Distinct from ULNRs that use rigid steel plates, USRBs are reinforced by flexible high-strength steel meshes to enable large and stable rollover deformations when subjected to strong earthquakes. To this end, shake table tests have been carried out for a two-span steel girder bridge that is isolated by ULNRs and USRBs, respectively. The test bridge was designed with a scale factor of 1/15 by maintaining the similarity of the deck mass, pier longitudinal stiffness, and bearing lateral stiffness for a typical prototype bridge in high seismic zones in China. Various types of sensors were used to monitor the dynamic responses of the bridge when excited by four different sets of earthquake motions. Test results show that USRBs not only exhibit a higher isolation efficiency in limiting the deck inertia force, but also outperform ULNRs in controlling the sliding of the bearings. Moreover, a phenomenological material model is utilized to simulate the hysteretic behavior of the USRBs, where the bridge’s time-history responses have been validated against the experimental outcomes. This paper illustrates that the use of USRBs can be a cost-effective, robust, and reliable substitute for the ULNRs to enhance the seismic resilience of the transportation infrastructure in China.
This study develops the first-of-its-kind seismic fragility models for estimation of approach backfill differential settlement for statewide bridges in California. Seismic compression analysis is ...carried out through a multi-step framework that estimates seismic-induced shear strain profiles for backfills, converts them to volumetric strains, and computes soil settlement through depth integration. As a crucial step, three independent methods are advanced on a uniform basis to estimate soil shear strains under earthquake loading: a simplified one-dimensional (1D) Static approach, a 1D Dynamic method from site response analysis, and a two-dimensional (2D) Dynamic method that accounts for the trapezoidal shape of the bridge embankment. Subsequently, seismic fragility models are derived using the multiple-stripe analysis (MSA) approach that convolves the seismic demands of backfill settlement with capacity models for several broad groupings of approach-slab designs having different abutment and abutment-foundation types, and abutment-connection details. A survey of California's bridge inventory provides stochastic data inputs that quantify various sources of uncertainties in backfill profile, embankment geometry, and both approach slab and abutment designs. Finally, a combined fragility model is developed by considering an equal methodological contribution from each mentioned approach. The final fragility models suggest that the lowest differential-settlement fragility is achieved by combining regular abutments on spread footings with long-length approach slabs connected to the bridge abutment, while the worst case occurs where bridge abutments on deep foundations are not connected with abutting pavements. The proposed seismic fragility models offer a sound basis for first-order estimation of approach-fill differential settlement which may lead to reduced ride quality, traffic speed reductions, and in extreme cases, temporary roadway closure. These represent one of many seismic fragility models for the full range of bridge components needed for prioritizing seismic retrofit measures, facilitating post-hazard inspections and repair actions, as well as assessing the network mobility for resilience quantification.
•Develop seismic fragility models of backfill settlements for California bridges.•Integrate three methods to estimate soil shear strains under earthquake loading.•A survey provides stochastic data that quantify various sources of uncertainties.•The fragility models are sensitive to abutment foundation and approach slab design.
•FEMs predict accurate backfill backbone curves against full-scale abutment tests.•Probabilistic backfill models capture soil uncertainty from field investigation.•Height adjustment factors bear ...matching backbone curves at different heights.•The models capture temporal evolution of backfill behaviors in California bridges.•The models affect the longitudinal demand estimates of various bridge components.
Seismic responses of ordinary highway bridges that feature stiff superstructures have been shown to be strongly affected by abutment-backfill interactions. Seismic risk assessment of these bridges at the regional scale faces the added challenge of having to deal with the large uncertainty in backfill properties. In this regard, the study develops probabilistic backfill models to better quantify the uncertainties in modeling the abutment. First, efforts to establish the validity of the numerical method in predicting the pushover response of backfills are described. Advanced plasticity materials are used in finite element models (FEMs) to simulate sandy and clayey soils that yield consistent backfill force-displacement relationships against full-scale test results. Second, a probabilistic analysis framework is constructed to incorporate soil uncertainties that are identified from field investigations. Statistical moments are extracted from the resultant pushover curves to fully define the probabilistic backfill models, which are verified to bear appropriate uncertainty treatment and reasonable height adjustment factors. Further, statistical analysis tools are used to investigate the influences of different backfill models on the bridge demand estimates of two common bridge classes. The study reveals that backfill models will affect the response estimates of different bridge components in both diaphragm and seat-type abutment bridges. However, probabilistic models shall be especially considered on backfills for the bridge components that are expected to have dominant responses in the longitudinal direction. The proposed backfill models appear to outperform previous deterministic models in predicting realistic bridge responses. The models can be employed in the task of regional seismic assessment of various bridge classes.
A replaceable rotational viscoelastic damper (RRVD) which has the potential for replacing the existing steel beam-column connections is proposed for steel frame buildings subject to dynamic ...vibrations. The RRVD is used with a sacrificial fuse segment to protect the structure at large inter-story drifts. A low-damage solution for the floor diaphragm with the RRVDs is also proposed. The test result confirms that the failure of the new connection is governed by fuse damage. Moreover, the RRVDs improve the system damping and reduces the earthquake-induced roof acceleration and the peak inter-story drift by up to 30%.
Quantifying the influence of seismic interaction between soil and structure group (SSGI) is of great significance to seismic design, retrofit, and damage assessment of structures in densely built ...urban areas. To this end, this study proposes a one-dimensional convolutional neural network (1D-CNN) model to rapidly predict the influence of adjacent structures on the maximum inter-story drifts and base shears of RC frame structures. Based on an experimentally validated three-dimensional finite element method, 890 pairs of soil-single structure versus soil-structure group systems under different earthquake loadings are simulated. The dataset comprising 890 groups of input (i.e., soil and structure group parameters, ground motion acceleration) and output data (i.e., changes in maximum inter-story drift and base shear) is constructed to train the machine learning model. Subsequently, sensitivity analysis is performed to identify optimal hyperparameters for training the 1D-CNN model, whereas a back propagation artificial neural network (BP-ANN) model is established to compare the model performance. Results indicate that compared with the BP-ANN model, the 1D-CNN model has a more stable and robust architecture and features superior prediction accuracy. In particular, the developed 1D-CNN model has a mean absolute error of less than 2.3% and an absolute error of less than 5.4% for 90% of cases in the testing set. The superior performance of the 1D-CNN model makes it an effective and efficient tool to be applied to predict the seismic responses of RC frame buildings under the SSGI effect.
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