Response Of Superstructure Research Articles

Seismic reliability-based design of hardening and softening structures isolated by double concave sliding devices

This study proposes seismic reliability-based design relationships in terms of behavior factors and displacement demands for softening and hardening structures equipped with double concave sliding bearings (i.e., DFPS). An equivalent 3dof system is adopted, that is characterized by a hardening or softening post-yield slope, representative of the superstructure response, and by velocity-dependent laws to model the frictional responses of the two surfaces of the DFPS. The yielding characteristics of the superstructures are defined for increasing behavior factors, provided by the codes, in compliance with the seismic hazard of L'Aquila (Italian site) and with the life safety limit state as provided by NTC18. Considering several natural ground motions and different elastic and inelastic structural properties under the hypothesis of modelling the friction coefficients of the two surfaces of the DFPS as random variables, incremental dynamic analyses are developed to assess the seismic fragility. From the convolution integral of the fragility curves with the seismic hazard curves related to L'Aquila (Italian site), assuming a lifetime of 50 years, the corresponding reliability curves are computed. Precisely, seismic reliability-based linear and multi-linear regressions relating the displacement ductility demand to the behavior factors for the softening and hardening superstructures together with seismic reliability-based design (SRBD) curves for the two surfaces of the double concave sliding bearings are provided as the design relationships.

Dynamic analysis of railway with locally continuous supported superstructures

Purpose In this study, a railway superstructure is modeled with a new approach called locally continuous supporting, and its behavior under the effect of moving load is analyzed by using analytical and numerical techniques. The purpose of the study is to demonstrate the success of the new modeling technique. Design/methodology/approach In the railway superstructure, the support zones are not modeled with discrete spring-damping elements. Instead of this, it is considered to be a continuous viscoelastic structure in the local areas. To model this approach, the governing partial differential equations are derived by Hamilton’s principle and spatially discretized by the Galerkin’s method, and the time integration of the resulting ordinary differential equation system is carried out by the Newmark–Beta method. Findings Both the proposed model and the solution technique are verified against conventional one-dimensional and three-dimensional finite element models for a specific case, and a very good agreement between the results is observed. The effects of geometric, structural, and loading parameters such as rail-pad length, rail-pad stiffness, rail-pad damping ratio, the gap between rail pads and vehicle speed on the dynamic response of railway superstructure are investigated in detail. Originality/value There are mainly two approaches to the modeling of rail pads. The first approach considers them as a single spring-damper connected in parallel located at the centroid of the rail pad. The second one divides the rail pad into several parts, with each of part represented by an equivalent spring-damper system. To obtain realistic results with minimum CPU time for the dynamic response of railway superstructure, the rail pads are modeled as continuous linearly viscoelastic local supports. The mechanical model of viscoelastic material is considered as a spring and damper connected in parallel.

Optical response of electro-tuneable 3D superstructures of plasmonic nanoparticles self-assembling on transparent columnar electrodes.

Electrically tuneable, guided self-assembly of plasmonic nanoparticles (NPs) at polarized, patterned solid-liquid interfaces could enable numerous platforms for designing nanoplasmonic optical devices with new tuneable functionalities. Here, we propose a unique design of voltage-controlled guided 3D self-assembly of plasmonic NPs on transparent electrodes, patterned as columnar structures-arrays of vertical nanorods. NP assembly on the electrified surfaces of those columnar structures allows formation of a 3D superstructure of NPs, comprising stacking up of NPs in the voids between the columns, forming multiple NP-layers. A comprehensive theoretical model, based on quasi-static effective medium theory and multilayer Fresnel reflection scheme, is developed and verified against full-wave simulations for obtaining optical responses-reflectance, transmittance, and absorbance-from such systems of 3D self-assembled NPs. With a specific example of small gold nanospheres self-assembling on polarized zinc oxide columns, we show that the reflectance spectrum can be controlled by the number of stacked NP-layers. Numerical simulations show that peak reflectance can be enhanced up to ∼1.7 times, along with spectral broadening by a factor of ∼2-allowing wide-range tuning of optical reflectivity. Smaller NPs with superior mobility would be preferable over large NPs for realizing such devices for novel photonic and sensing applications.

Experimental and numerical studies on pseudo-negative-stiffness control of a base isolated building using magneto-rheological dampers

This article presents a series of experimental and numerical studies on the feasibility and effectiveness of pseudo-negative-stiffness (PNS) control system using magneto-rheological (MR) dampers. First, a MR damper with nominal force capacity of 10 kN was self-developed. A set of experiments was conducted to study the dynamic performance of the MR damper. Then, a PNS control system was established with NI Compact RIO as hardware platform and Labview as software platform. The displacement-based PNS (DPNS) control algorithm was employed to control the MR damper. Dynamic performance tests were performed to investigate the hysteretic behavior of DPNS control force under different excitation conditions and with different control parameters. Next, shaking table tests were conducted on a four-floor steel frame base isolated structure model employing the PNS control system. The seismic responses under uncontrolled case, passive off case, passive on case and DPNS control case were compared. For each control type, the control efficacy was verified for the El Centro, Ji Ji, Kobe_FN and Kobe_FP with increasing peak ground acceleration. The test results show that the DPNS control can further reduce the isolation displacement compared to the passive off case with no accompanying increase of superstructure responses under seismic excitation with different intensities and spectral characteristics. Finally, numerical studies were conducted to compare the effectiveness of DPNS and clipped-optimal control and investigate the effect of time delay of DPNS control. Results indicate that the DPNS control outperforms the clipped-optimal control and the time delay of the DPNS control leads to the adjustment of the DPNS control force at zero displacement, which is beneficial to control efficacy.

Modelling and in-situ measurement of dynamic behavior of asphalt supporting layer in slab track system

During the last decades, asphalt concrete has been introduced in both ballast and ballastless track (including but not limited to slab track) systems. The use of asphalt concrete provides better damping and waterproofing performance. For this reason, a supporting layer of asphalt concrete (ASL) was introduced to the latest Chinese slab track system. In this paper, an in-depth study of the dynamic behavior of ASL was presented using modelling and in-situ measurement approaches. In the FE model, the train load was simplified to be a time series of concentrated load on rail nodes, and asphalt concrete was modeled as viscoelastic material by Prony series. The FE model was validated against in-situ measurement on a test section, in which a monitoring system was setup during construction. A series of transient analysis were conducted to obtain the dynamic responses of ASL under moving train load. The parametric effects of thickness of ASL was also studied with respect to the dynamic responses of superstructure and substructure, as well as the stability and durability of ASL. The results showed that, under moving bogie load, the reach of the dynamic responses in ASL is about 7.5 m in the longitudinal direction, and the maximum values occur at the position beneath the rails. A thicker ASL is more favorable to ride comfort and structural stability of high-speed railway track system. However, considering the economic and construction factors, an optimal thickness range of 7–10 cm is suggested for ASL in CRTS III slab track.

Simulation analysis of TMD controlled building subjected to far- and near-fault records considering soil-structure interaction

This study aims to investigate the performance of a tuned mass damper (TMD) in mitigating the dynamic response of buildings to far- and near-fault earthquake records including soil–structure interaction (SSI) effects. The selected records ensure near-fault with forward directivity (FD) and near-fault with fling. The effects of certain parameters of the installed TMD, such as the mass, the frequency and the damping ratios have been investigated using a developed MATLAB code. Displacement, velocity, acceleration, and energy responses from the analysis of the building model subjected to each of the considered faults were numerically calculated. The obtained numerical simulation results for the cases without and with including the SSI effects are comparatively presented and evaluated for the building model with a TMD damper. The presented results clearly show that there is a more seismic demand on an induced response for buildings excited by near fault records with fling. In addition, the inclusion of SSI increases the induced responses and alters the role of TMD in reducing the superstructure responses.

Diamagnetic response of a superconducting surface superstructure: Si(111)- √7×√3 -In

How does one detect the Meissner effect in ultrathin superconducting films that are usually extremely sensitive to air? Here, the authors succeed in observing the diamagnetic response of a superconducting surface superstructure by using an $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0.333em}{0ex}}s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ two-coil mutual inductance technique embedded in a specially designed scanning tunneling microscope. The diamagnetic measurement allows for the calculation of the penetration depth, which provides invaluable information about the nature of superconductivity and the symmetry of the underlying order parameter.

Dynamic Soil–Structure Interaction with a Flexible Foundation Embedded in a Half-Space: Closed-Form Analytical Solution for Incident Plane SH waves

ABSTRACT This paper presents a closed-form analytical solution of two-dimensional dynamic soil–structure interaction (SSI) with a flexible foundation in homogeneous half-space subjected to plane SH waves and verifies the verification of the solution by comparison with current results. This paper studies the effects of foundation stiffness and many more on the foundation effective input motion, the relative response of superstructure and the additional inner force in the superstructure. It shows that when the structure stiffness is relatively small, near the structural second self-vibration frequency, foundation effective input motion and relative response of superstructure will occur resonance phenomenon; when the stiffness and mass of superstructure are relative large, foundation cannot be treated as a rigid foundation even for the foundation stiffness many times larger than that of soil, and there is still significant additional inner force in superstructure, which should be considered in seismic design of superstructure. This paper is an attempt on SSI of nonrigid flexible foundations, and this model maybe helpful to obtain insight into the effects of foundation stiffness on dynamic SSI.

Variations in the dynamic response of structures founded on piles induced by obliquely incident SV waves

SummaryAlthough the seismic actions generally consist of a combination of waves, which propagates with an angle of incidence not necessarily vertical, the common practice when analyzing the dynamic behavior of pile groups is based on the assumption of vertically incident wave fields. The aim of this paper is to analyze how the angle of incidence of SV waves affects the dynamic response of pile foundations and piled structures. A three‐dimensional boundary element‐finite element coupling formulation is used to compute impedances and kinematic interaction factors corresponding to several configurations of vertical pile groups embedded in an isotropic homogeneous linear viscoelastic half‐space. These results, which are provided in ready‐to‐use dimensionless graphs, are used to determine the effective dynamic properties of an equivalent single‐degree‐of‐freedom oscillator that reproduces, within the range where the peak response occurs, the response of slender and nonslender superstructures through a procedure based on a substructuring model. Results are expressed in terms of effective flexible‐base period and damping as well as maximum shear force at the base of the structure. The relevance and main trends observed in the influence of the wavefront angle of incidence on the dynamic behavior of the superstructure are inferred from the presented results. It is found that effective damping is significantly affected by the variations of the wave angle of incidence. Furthermore, it comes out that the vertical incidence is not always the worst‐case scenario.

Soil-pile-structure interaction effects on high-rise building under seismic shaking

In this paper, study of the response (base shear, time period, storey drift, storey displacement) of a structure is done for the tall building including basement with fixed base and with pile foundation considering Soil Structure Interaction (SSI). Finite element based program ETABS2016 v16.1.0 is used for the analysis of the superstructure. Seismic analysis is done to get the dynamic response of superstructure for two types of model,one model is with fixed baseand second is Model with Winkler spring for Chhaya Center, Thamel, a high rise building with 14 story including double basements. Itisobserved with the consideration of Soil Structure Interaction (SSI). The soil is replaced by spring and assigned at joints. El Centro earthquake (1940) is used for time history analysis. The response obtained due to SSI effect is compared with fixed based model. Results of analysis presented include the comparison of natural periods, base shears, displacements and overturning moment. It is observed that the natural periods increase and the base shears decrease as the base become more flexible.

Seismic performance evaluation of soil-foundation-reinforced concrete frame systems by endurance time method

Endurance time (ET) method is a new approach for assessing the seismic performance of structures. This paper investigated the effectiveness and accuracy of employing ET method to predict the seismic response of soil-structure-interaction (SSI) system. The Chinese code-conforming endurance time acceleration functions (ETAFs) were firstly generated. Two 5- and 10-story reinforced concrete (RC) frame structures were employed as prototype structures. The finite element model of soil-foundation-structure was established based on nonlinear Beam-on-Nonlinear-Winkler-Foundation (BNWF) theory. Nonlinear dynamic analyses of the structural systems subjected to 3 ETAFs and 22 ground motions were carried out. The seismic response of superstructure and foundations, and different SSI models were compared. The results indicate the ET method can predict the seismic response of SSI structural systems, with a high efficiency and accepted accuracy.

Numerical Study of Alternative Seismic-Resisting Systems for CLT Buildings

Changes to building codes that enable use of materials such as cross-laminated timber (CLT) in mid- and high-rise construction are facilitating sustainable urban development in various parts of the world. Keys to this are the transition to multi-performance-based design approaches along with fewer limitations on heights or the number of storeys in superstructures constructed from combustible materials. Architects and engineers have increased freedom to apply new design and construction concepts and methods, as well as to combine timber with other structural materials. They also have started to develop wall arrangements that optimise interior space layouts and take advantage of the unique characteristics of CLT. This paper discusses the seismic response of multi-story buildings braced with a CLT core and perimeter shear walls anchored to foundations and floor platforms using modern high-capacity angle brackets and hold-downs, or X-Rad connectors. Linear dynamic finite element (FE) models of seismic responses of superstructures of various heights are presented, based on experimentally determined characteristics of wall anchor connections. Particular attention is given to fundamental vibration periods, base shear and uplift forces on walls, as well as inter-story drift. Discussion of FE model results focuses on structural engineering implications and advantages of using CLT to create shear walls, with emphasis on how choice of wall anchoring connections impacts the possible number of storeys and configurations of superstructures. Employing CLT shear walls with X-Rad or other types of high capacity anchoring connections makes possible the creation of building superstructures having eight and potentially more storeys even in high seismicity regions. However, it is important to emphasise that proper selection of suitable arrangements of shear walls for CLT buildings depends on accurate representation of the semi-rigid behaviors of anchoring connections. The linear dynamic analyses presented here demonstrates the need during engineering seismic design practices to avoid use of FE or other design models which do not explicitly incorporate connection flexibilities while estimating parameters like fundamental periods, base shear and uplift forces, as well as inter-story drift.

Influence of Near-Fault Ground Motions with Fling-Step and Forward-Directivity Characteristics on Seismic Response of Base-Isolated Buildings

ABSTRACT The behavior of base-isolated buildings under near-fault (NF) ground motions with fling-step and forward-directivity characteristics is investigated using three-dimensional nonlinear finite element models. Nonlinear response history analysis (NLRHA) is also carried out after removing the dominant pulse from the NF ground motion records. The results obtained for 10-story base-isolated buildings with and without shear walls, indicate that NF ground motions with fling-step and forward-directivity characteristics produce large inter-story drift ratios and floor accelerations, compared to the case when the dominant pulse is removed. Additional NLRHA carried out using artificial pulses shows that the isolator and superstructure responses are larger for pulses with fling-step characteristics, compared to pulses with forward-directivity characteristics.

Seismic performance of a resilient low-damage base isolation system under combined vertical and horizontal excitations

Traditional base isolation systems focus on isolating the seismic response of a structure in the horizontal direction. However, in regions where the vertical earthquake excitation is significant (such as near-fault region), a traditional base-isolated building exhibits a significant vertical vibration. To eliminate this shortcoming, a rocking-isolated system named Telescopic Column (TC) is proposed in this paper. Detailed rocking and isolation mechanism of the TC system is presented. The seismic performance of the TC is compared with the traditional elastomeric bearing (EB) and friction pendulum (FP) base-isolated systems. A 4-storey reinforced concrete moment-resisting frame (RC-MRF) is selected as the reference superstructure. The seismic response of the reference superstructure in terms of column axial forces, base shears, floor accelerations, inter-storey drift ratios (IDR) and collapse margin ratios (CMRs) are evaluated using OpenSees. The results of the nonlinear dynamic analysis subjected to multi-directional earthquake excitations show that the superstructure equipped with the newly proposed TC is more resilient and exhibits a superior response with higher margin of safety against collapse when compared with the same superstructure with the traditional base-isolation (BI) system.

Nonlinear seismic response of a base isolated single pylon cable-stayed bridge

The vulnerability of single pylon cable-stayed bridges under strong ground motions are of great concern to both researchers and engineers. This paper investigates the seismic performance of reinforced concrete (RC) single pylon cable-stayed bridge equipped with friction sliding bearings under bi-directional earthquake excitations. Three-dimensional numerical models, consisting of the dynamic p-y elements, the fiber elements and the multi-layer shell elements, were developed in this study based on the prototype of a single pylon cable-stayed bridge in Guizhou Province, China, to investigate its seismic response. Three different types of friction sliding bearings were implemented between the base of the RC pier and the pile foundation to mitigate the dynamic response of the bridge superstructure under strong ground motions. The results of the nonlinear time history analyses indicate that friction sliding bearings can effectively reduce the base shear and the bending moment of the RC pier, as well as the seismic responses of substructure, at the cost of increasing the absolute displacement of the deck. To reduce the deck displacement, viscous dampers were implemented in parallel to the friction sliding bearings. Parametric studies and optimization analyses were performed on the critical parameters of the viscous dampers with the target of minimizing the absolute displacement of the deck and reducing the base shear of the RC pier to an acceptable level. The numerical results show that implementation of friction sliding bearings together with the viscous dampers is an effective seismic control approach to mitigate the seismic damage of the single pylon cable-stayed bridge.

Fire resistance of composite steel & concrete highway bridges

In this paper, the effects of geometric skewness and abutment restraint on the fire resistance of a real highway bridge have been studied. Four finite element models have been investigated using rectangular and skew shapes with and without modelling the abutment. The investigation has been carried out in three steps: 1) heat transfer analysis under a specified hydrocarbon fire; 2) simulation of the thermo-mechanical response of the bridge superstructure over the entire duration of the fire using beam and shell elements to represent the structural components; 3) detailed processing and interpretation of the simulation results to understand and illustrate the global response of the structure by comparing all the models. Results indicate that a skew bridge may possess greater inherent resistance to fire. For the two-span highway bridge model, restraint from the abutment does not affect the estimated failure time significantly.

ОСОБЕННОСТИ ДИНАМИЧЕСКОГО ВЗАИМОДЕЙСТВИЯ МАГНИТОЛЕВИТАЦИОННОГО ВЫСОКОСКОРОСТНОГО ТРАНСПОРТА И МОСТОВЫХ СООРУЖЕНИЙ

Objective: To determine key parameters for calculating dynamic effect of magnetic-levitation highspeed transport on bridge structures, carry out a dynamic analysis, and check the obtained results against experimental data and compare them with similar results on high-speed railways. Methods: In the course of the study, the method of direct integration of the dynamic problem of mo ving a mobile load along the bridge superstructure was used. Results: Computational model of a magnetic-levitation high-speed train was developed. A set of dynamic calculations was performed. Data on the magnitude of dynamic reaction of the bridge superstructure during the movement of a magnetic-levitation train were obtained. Values of the dynamic coefficient for mobile load in the speed range of up to 1000 km/h were calculated. Practical importance: Results obtained in the course of the study and the comparison made with similar data for high-speed rail transport have confirmed a significant decrease in the dynamic response of bridge superstructures when magnetic-levitation technologies are deployed. The calculation model thus developed opens up broad prospects for further research.

Effect of foundation embedment on the response of a multi-story building to earthquake excitation

During an earthquake, the behaviour of any structure is affected not only by the superstructure response, but also by the response of the soil beneath. Recent structural failure patterns have indicated the significance of soil-structure interaction (SSI) effects. The present study focuses on SSI analysis considering the embedment depth of the foundation of a symmetric six stories reinforced concrete (RC)space bare frame building resting on stiff soil and subjected to seismic loading. The finite element analysis software ANSYS v17.2 is used. Time history (TH) analysis has been adopted. The Response in terms of lateral displacements, base shear forces, base moments and variation in natural time periods are calculated from the analysis of the soil foundation structure interaction (SFSI) model. Results are compared with that obtained from conventional method assuming rigid support at the base (fixed base) of the structure. The results show that the SFSI considering different embedment depths are significant in altering the seismic response of the multi-story building (MSB).

Soil-dependent optimum design of a new passive vibration control system combining seismic base isolation with tuned inerter damper

The papers addresses a novel passive vibration control system combining seismic base isolation with a tuned inerter damper (TID) system. The latter, by analogy with the tuned mass damper (TMD), is a dynamic vibration absorber in which the physical mass of the TMD is partly or entirely replaced by an apparent mass, also called inertance, created by a particular arrangement of mechanical gearings—the inerter. By attaching a TID to the isolation floor, not only the displacement demand of base-isolated structures can be significantly reduced, but also the superstructure response (e.g. interstory drift, base shear) is effectively controlled. Optimum parameters of this system are found based on a simplified three degree-of-freedom model that reflects the dynamic properties of both the isolation system and the TID while accounting for the flexibility of the base-isolated superstructure. Within a probabilistic framework, the influence of soil conditions is investigated by modeling the seismic ground motion as a filtered Gaussian random process. Different filter parameters are considered that may be associated with firm, medium or soft soil conditions depending on the frequency content of the power spectral density function. A wide parametric study is performed in order to detect the optimal TID parameters depending on the soil conditions for a variety of isolation ratios, mass ratios and damping ratios of both the superstructure and the isolation system. Finally, a multi-story building equipped with the proposed passive vibration control system is examined. Effectiveness of the proposed system is assessed via the evaluation of the structural response in the time domain. Detuning effects are investigated via a sensitivity analysis. Comparison with alternative passive vibration control systems proposed in the literature and based on different arrangements of TMD and inerter-based device is discussed.

SOIL-STRUCTURE INTERACTION ANALYSES OF PILE SUPPORTED BUILDING FRAME

The effect of the soil-structure interaction on the simple single storeyed and two bayed space frame resting on pile group of two piles with flexible cap is examined in this paper by resorting to more rational approach and realistic assumptions. Initially, 3-D FEA is carried out independently for the frame on the premised of fixed column bases. Later, pile foundation is worked out separately. The stiffness so obtained for foundation is used in the interactive analysis of frame to quantify the effect of soil- structure interaction on the response of the superstructure. For modeling the foundation system two approaches of finite element analysis are used. In the first approach complete three dimensional finite element analysis is resorted to wherein pile, pile cap along with the soil are discretized into 20 noded isoparametric continnum elements and interface between pile and soil is idealized as 6 noded isoparametric interface elements. In the second approach simplified finite element analysis procedure is used wherein beam element, plate element and spring elements are used to model pile, pile cap and soil respectively. The salient feature of the investigation is that the interaction between pile cap and soil underlying it is considered. In the parametric study presented here, effect of pile spacing and pile configuration is evaluated on the response of superstructure in the form top displacement in frame and bending moment at top as well as bottom of the superstructure columns. Results obtained by either analysis are compared.