Bidirectional Motions Research Articles

Seismic demand of base-isolated irregular structures subjected to pulse-type earthquakes

Base-isolated structures may be subjected to severe seismic demand in the superstructure and/or in the isolation system at sites located near an active fault. Forward directivity effects with long-period horizontal pulses in the fault-normal velocity signals are the main cause of this behaviour. However, recent studies have identified pulses in arbitrary orientations along with false-positive classification of pulse-type ground motions. The aim of the present work is to evaluate the reliability of elastomeric (i.e. high-damping-laminated-rubber bearings, HDLRBs) and sliding (i.e. curved surface sliding bearings, CSSBs) base-isolation systems for the seismic retrofitting of in-plan irregular buildings located in the near-fault area. To this end, a five-storey reinforced concrete (r.c.) framed structure, with an asymmetric-plan and bays of different length, is chosen from benchmark structures of the Re.L.U.I.S. project. Attention is focused on the pulse-type and non-pulse-type nature of near-fault earthquakes and moderately-soft and soft subsoil conditions. First, a comparison between algorithms based on wavelet signal processing, that can identify pulses at a single (e.g. fault-normal) or arbitrary orientation in multicomponent near-fault ground motions, is carried out to classify records of recent events in central Italy and worldwide. Then, nonlinear seismic analysis of the fixed-base and base-isolated test structures is performed by using a lumped plasticity model to describe the inelastic behaviour of the r.c. frame members. Nonlinear force-displacement laws are considered for the HDLRBs and CSSBs, including coupled bi-directional motions in the horizontal directions and coupling of vertical and horizontal motions.

An adaptive modal pushover analysis procedure (VMPA-A) for buildings subjected to bi-directional ground motions

A new modal pushover analysis procedure (VMPA-A) is developed and implemented in MATLAB code for three-dimensional buildings subjected to bidirectional ground motions. VMPA-A uses stepwise force patterns to represent changes in the dynamic characteristics because of the accumulated structural damages. The hybrid-spectrum concept is introduced to account for the bidirectional ground motion effects. Due to enactments of the equal displacement rule and the secant stiffness-based linearization process, nonlinear analysis is performed for specific displacement targets without stipulation of full modal capacity curves for each mode. Horizontal components of an earthquake record are considered simultaneously, and the consistency between the force and displacement vectors for each mode is provided. These are the main advantages of the proposed procedure against modal pushover analysis (MPA). An existing 21-story reinforced concrete building is analyzed to exemplify VMPA-A. The response parameters such as displacements, story drifts, internal forces, strains, etc. are discussed by comparing the results of VMPA-A with nonlinear time history analyses, which is accepted as the “exact solution”. Though consistent demand estimations are obtained for story drifts, displacements and deformations, some conservative results are obtained for story shears.

Bidirectional shake table testing of RC columns retrofitted and repaired with shape memory alloy spirals

Under the extreme threats of strong earthquakes, bridge columns are required to remain functional to ensure the safety and structural integrity of the entire bridge system. However, many existing bridges designed according to old seismic design provisions lack flexural ductility due to insufficient concrete confinement. Lack of confinement in old bridges is often addressed through providing supplementary external passive confinement. Recently, an active confinement technique using Shape Memory Alloys (SMAs) has been proposed as a more effective alternative to conventional passive confinement methods. In this study, the application of SMA confinement in seismic retrofitting and emergency repair of RC bridge columns is examined experimentally through a series of shake table tests. Two 1/6-scale RC columns, retrofitted and repaired with SMA spirals, are tested simultaneously under bidirectional test motions with varying intensity. Test results show that SMA confinement is highly effective in mitigating the seismic damage and improving the seismic performance of retrofitted and repaired RC columns subjected to strong earthquakes.

Currents on the continental shelf adjacent to the Laje de Santos (SP, Brazil)

Abstract Analysis of current meter data permitted the elaboration of a description of the hydrodynamic characteristics of the continental shelf adjacent to Laje de Santos, a rocky islet located in the inner part of the São Paulo Continental Shelf (SPCS). The currents in the region are mainly driven by the synoptic winds, presenting bidirectional motions approximately parallel to the local isobaths at all levels, depending on the wind direction but with the predominance of those that leave the isobaths to the left. The tidal currents in this sector of the SPCS are more energetic in the direction perpendicular to the isobaths in comparison with the along isobath component and have the predominance of the semidiurnal oscillations.

Estimation of Seismic Loss for a Portfolio of Buildings under Bidirectional Horizontal Ground Motions due to a Scenario Cascadia Event

Earthquake ground motions induced by a scenario event are spatially (partially) correlated and (partially) coherent. Simulated ground motion records can be used to carry out nonlinear inelastic time history analysis for a portfolio of buildings to estimate the seismic loss, which is advantageous as there is no need to develop and apply empirical ground motion prediction equations and the ductility demand rules, or to search the scenario compatible recorded records at selected sites that may not exist. Further, if the structures being considered are sensitive to the orientation of the excitation, multiple-component ground motion records are needed. For the simulation of such ground motion records, previous studies have shown that correlation and coherency between any pair of ground motion components need to be incorporated. In this study, the seismic loss of a portfolio of hypothetical buildings in downtown Vancouver under bidirectional horizontal ground motions due to a scenario Cascadia event is estimated by using simulated bidirectional ground motion records that include realistic correlation and coherency characteristics. The hysteretic behaviours of the buildings are described by bidirectional Bouc-Wen model. The results show that the use of unidirectional ground motions and single-degree-of-freedom (SDOF) system structural model may underestimate the aggregated seismic loss.

Effect of pounding on nonlinear seismic response of skewed highway bridges

Skewed bridges are more vulnerable to earthquake-induced failure than straight bridges due to pounding at expansion joints between the bridge superstructure and abutments. This study focuses on analyzing pounding effect and rotation mechanism of highway bridges with prestressed concrete box girder and seat-type abutments when subjected to bi-directional near-fault ground motions, especially seismic response with respect to abutment skew angle. These analytical models include nonlinear characteristics of skewed bridge components, especially pounding effect between the superstructure and abutment in both longitudinal and transverse directions. Nonlinear time history analyses were performed to predict the pounding force and its effect on the seismic response of skewed highway bridges using the Kelvin model. The analytical results indicate that the pounding of skewed bridge causes significant seismic displacement response and local damage of superstructure. In addition, the pounding in the transverse initial gap reduced the rotation response of the skewed bridge, and the skew angle has significant effect on the seismic behavior of skewed highway bridges. The pounding force and back-fill response decreased with an increasing skew angle, but deck displacement in longitudinal direction and torsion response increased apparently. Bridges with skew angle increased demand on shear keys under the strong earthquake excitation.

Influence of ground motion duration on damage index-based fragility assessment of a plan-asymmetric non-ductile reinforced concrete building

The role of ground motion duration on the seismic performance of building structures remains unclear. This paper presents results on the effects of ground motion duration on the seismic behaviour of a 3-D plan-asymmetric reinforced concrete building. A three-story reinforced concrete building tested in Europe is used asa case study. A nonlinear model of the building with fibre-section distributed inelasticity displacement-based beam-column elements is subjected to two ground motion sets: (1) long-duration bi-directional earthquake ground motions, and (2) short-duration bi-directional earthquake ground motions. A new ground motion selection procedure is proposed to isolate the effect of duration on the structural response and on damage assessment. For comparative studies, long- and short-duration ground motions are selected so that they have similar response spectra. The damage assessment is performed analysing global and local responses. Global responses of the structure are evaluated in terms of peak roof drift ratios, peak interstory drift ratios (IDRs), IDR envelopes, normalized roof displacements relative to motion of the centre of gravity of the roof, and dissipated energy. Local responses assessed include moment-curvature or moment-rotation response in beams and columns as well as the hysteretic energy dissipated at selected sections of the structure. Two damage indices available in the literature are used to characterize the level of damage that the structure experiences, through damage index-based fragility curves that are developed as part of the work. For the short-duration motions, fragility curves developed independently from interstory responses and from the damage indices are similar, thus providing confidence into the use of the damages indices for fragility curve development. In addition, results indicate that for the vintage plan-asymmetric building analysed, the ground motion duration plays a role in the damage predicted using the two damage indices.

Nonlinear Seismic Response of Skewed Highway Bridges Subjected to Bidirectional Near-Fault Ground Motions

Nonlinear Seismic Response of Skewed Highway Bridges Subjected to Bidirectional Near-Fault Ground Motions

Seismic Fragility Analysis of the Smithsonian Institute Museum Support Center

This paper presents the seismic fragility assessment of the Smithsonian Institute Museum Support Center (MSC), which sustained appreciable damage during the 2011 Virginia earthquake. A three-dimensional (3-D) finite element model (FEM) for the building was created and validated using measured dynamic characteristics determined from field vibration test data. Two suites of bidirectional ground motions at different hazard levels were applied to the FEM to generate fragility curves for structural as well as nonstructural (storage cabinets) damage. The effect of brace yielding strength on structural and nonstructural damage is also investigated to provide recommendations for future retrofit. The fragility curves show that the spectral acceleration to cause structural damage to the building is not high. Due to low seismicity, however, the probability for the structure to be damaged at the design basis earthquake is small. Nevertheless, the probability for nonstructural damage is considerable, which is an important issue related to the seismic performance of the building.

A wind tunnel test method on aerodynamic characteristics of moving vehicles under crosswinds

A new experimental investigation approach of a moving vehicle device is proposed to investigate the aerodynamic characteristics of moving vehicles on bridges under crosswinds. The new moving vehicle device, which can adjust the incoming wind directions and wind attack angles, consists of a vehicle, bridge segment, and motion system etc. The motion system includes a linear module propelled by a servo motor and it can realize bidirectional motions and rapid acceleration and deceleration. The five-component coefficients of the moving vehicle model were tested with the force balance equipment, and the sensitivity of some parameters on the aerodynamic characteristics of moving vehicles is studied. The results show that the proposed moving vehicle device can provide a rather smooth guideway. The measured time histories of aerodynamic force and moment are stable after filtering and the identified aerodynamic characteristics of moving vehicles have a good consistency over different wind speeds.

The visual kinetic depth effect is altered with Parkinson's disease

BackgroundPeople with Parkinson's disease (PD) often have visual-perceptual disorders. The goal of this study was to learn if they can develop a three dimensional (3D) percept that depends on the kinetic depth effect; that is, the viewer's ability to spatially integrate over time images that are moving along many trajectories. MethodsSixteen patients with PD and 12 healthy matched controls were presented with stimuli that were comprised of a circular region of randomly placed dots that moved as orthographic projections of a sphere. With a normal kinetic depth effect, the Training stimuli appear as an opaque rotating ball and the Test stimuli appear as a rotating transparent ball. ResultsWhereas all controls and all PD patients reported seeing the Training stimuli as a rotating ball, the patients with PD were significantly less likely to report the Test stimuli appearing as a 3D “ball” than were the healthy participants. Instead, seven PD patients often reported these bidirectional stimuli appeared “flat.” ConclusionsThis study has revealed that some patients with PD have impaired spatio-temporal integration of bidirectional visual motions, but the mechanism accounting for this loss, as well as why only some patients had this deficit, needs further study. When the driver of a moving vehicle fixates upon a stationary target in the surroundings, bidirectional retinal image motions may occur. Failure to perceive 3D structure in such moving scenes can be plausibly suspected to contribute to adverse events such as auto accidents.

Characterization of radial and circumferential mechanical energy components in bi-directional nonlinear seismic response of steel bridge piers

In this study, the bi-directional nonlinear elaso-plastic seismic response of steel bridge piers subjected to bi-directional ground motions is analyzed with a particular interest in the role of the radial and circumferential components of mechanical energy. In order to explore the influencing factors to the maximum bi-directional seismic response, dynamic characteristics of a circular steel bridge pier are expressed by two modeling techniques: the multiple shear spring (MSS) model, and the fiber model. The calculated bi-directional dynamic responses of the steel bridge pier models under artificially generated bi-directional ground motions are characterized by introducing a technique to divide the strain and kinetic energies to the radial and circumferential components. The analysis result indicates that the level of circumferential strain energy that effectively contributes to dissipation of the total kinetic energy is of great importance in assessing the maximum bi-directional response. When the two models are subjected to the identical bi-directional ground motion, the circumferential strain energy induced in the fiber model is higher than that obtained by the multiple shear spring model, resulting in smaller radial displacement. Also, the analyses of the fiber model for various cases of directivity property of the input bi-directional seismic ground motion show that the bi-directional response is smaller than the unidirectional response in some cases. The reason can be explained by higher circumferential strain energy which can be related to the reduction of radial displacement in those cases.

The effect of multiple tuned mass dampers on response control of base isolated multi-storey space frame structure

Dynamic response of base isolated multi-storey symmetrical and asymmetrical space frame structures with multiple tuned mass dampers (MTMD), subjected to bi-directional harmonic and Mexico earthquake ground motions are studied. A four-storey space frame structure having six degrees of freedom (three translations along x, y, z-axes and three rotations about these axes) at each node is considered for study. Each tuned mass damper (TMD) is modelled using a two-noded element having two translational degrees of freedom at each node. MTMD with uniformly distributed frequencies are considered for this purpose. The effectiveness of MTMD in suppressing the structural response is determined by comparing the response of corresponding structure without MTMD. It is found that the MTMD can be used effectively to suppress the responses of the symmetrical and asymmetrical base isolated space frame structures. The effect of important parameters on the effectiveness of the MTMD is also studied. The parameters include the fundamental characteristics of the MTMD such as damping, total number of MTMD, tuning frequency ratio and frequency spacing of the dampers. It is shown that these parameters have considerable influence on the effectiveness of the MTMD in reducing the dynamic response of the base isolated structure.

Spatial seismic modeling of base‐isolated buildings pounding against moat walls: effects of ground motion directionality and mass eccentricity

SummaryStructural impact between adjacent buildings may induce local and, in some extreme cases, severe damage, especially in the case of seismically isolated buildings. This study parametrically investigates in the three‐dimensional domain the effect of pounding on the peak response of base‐isolated buildings, which are simulated as nonlinear three‐dimensional multi‐degree‐of‐freedom systems. Firstly, it is shown that considering unidirectional, instead of bidirectional, excitations may lead to underestimation of the base drift demands. Subsequently, the peak responses of seismically isolated buildings utilizing lead rubber bearings are studied while varying important parameters, such as the incidence angle of seismic excitations, the available seismic clearance, and mass eccentricities, under the action of bidirectional horizontal excitations. A large number of numerical simulations are performed using a specially developed software that implements an efficient approach to model impacts, taking into account arbitrary locations of contact points. It is found that the peak interstory drift ratio is significantly influenced by the directionality of the ground motion. Therefore, the seismic performance of structures should ideally be assessed examining the peak structural response while bidirectional ground motions are imposed at various incident angles. Furthermore, it is also observed that the interstory drift ratios increase while decreasing the available gap size, up to a certain value. Finally, the parametric analyses indicate that the effects of impact are more severe for structures with mass eccentricities, and in which case, the estimation of the critical incidence angle becomes more laborious. Copyright © 2016 John Wiley & Sons, Ltd.

Redundantly piezo-actuated XYθz compliant mechanism for nano-positioning featuring simple kinematics, bi-directional motion and enlarged workspace

This paper presents a novel redundantly piezo-actuated three-degree-of-freedom XYθz compliant mechanism for nano-positioning, driven by four mirror-symmetrically configured piezoelectric actuators (PEAs). By means of differential motion principle, linearized kinematics and physically bi-directional motions in all the three directions are achieved. Meanwhile, the decoupled delivering of three-directional independent motions at the output end is accessible, and the essential parallel and mirror symmetric configuration guarantees large output stiffness, high natural frequencies, high accuracy as well as high structural compactness of the mechanism. Accurate kinematics analysis with consideration of input coupling indicates that the proposed redundantly actuated compliant mechanism can generate three-dimensional (3D) symmetric polyhedral workspace envelope with enlarged reachable workspace, as compared with the most common parallel XYθz mechanism driven by three PEAs. Keeping a high consistence with both analytical and numerical models, the experimental results show the working ranges of ±6.21 μm and ±12.41 μm in X- and Y-directions, and that of ±873.2 μrad in θz-direction with nano-positioning capability can be realized. The superior performances and easily achievable structure well facilitate practical applications of the proposed XYθz compliant mechanism in nano-positioning systems.

Efficient Seismic Design of 3D Asymmetric and Setback RC Frame Buildings for Drift and Strain Limitation

AbstractThis paper presents an analysis–redesign-type approach for the efficient seismic design of three-dimensional (3D) irregular RC frame structures for bidirectional ground motions. The designs...

Structural Demand on Bridges Subjected to Bidirectional Ground Motions

AbstractBridge design spectra in the current design specifications are geometric mean based. In other words, the underlying research on which ground motion data are based predicts the geometric mean spectral acceleration of two horizontal components. This is, perhaps, transparent to many engineers performing bridge design in regions subject to extreme seismic loading. For response spectrum analyses, this does prove problematic when estimating structural response to bidirectional ground motions. Prevailing combination rules rely on the assumption that, when one component produces the maximum structural response, the second component produces 30% of the corresponding maximum. The purpose of this paper is to assess the validity of this prevalent rule for sites characterized by large magnitude earthquakes (MW = ±7.7) and Site Class D/E subsurface conditions. This study further provides estimates of maximum-to-geometric mean displacement ratios for various levels of ductility and provides estimates of dispersi...

Operator-Based Robust Nonlinear Control Design of a Robot Arm with Micro-Hand

[abstFig src='/00280004/14.jpg' width='300' text='Robot arm with micro-hand system' ] This work focuses on a robust nonlinear control design of a robot arm with micro-hand (RAMH) by using operator-based robust right coprime factorization (RRCF) approach. In the proposed control system, we can control the endpoint position of robot arm and obtain the desired force of micro-hand to perform a task, and a miniature pneumatic curling soft (MPCS) actuator which can generate bidirectional curling motions in different positive and negative pressures is used to develop the fingers of micro-hand. In detail, to control successively the precise position of robot arm and the desired force of three fingers according to the external environment or task involved, this paper proposes a double-loop feedback control architecture using operator-based RRCF approach. First, the inner-loop feedback control scheme is designed to control the angular position of the robot arm, the operator controllers and the tracking controller are designed, and the robust stability and tracking conditions are derived. Second, the complex stable inner-loop and micro-hand with three fingers are viewed as two right factorizations separately, a robust control scheme using operator-based RRCF approach is presented to control the fingers forces, and the robust tracking conditions are also discussed. Finally, the effectiveness of the proposed control system is verified by experimental and simulation results.

Nonlinear dynamic analysis for multi-storey RC structures with hybrid base isolation systems in presence of bi-directional ground motions

Multi-storey reinforced concrete (RC) structures may experience a weak structural behavior when subject to seismic and dynamic actions. In such cases the base isolation techniques are innovative strategies to protect the structures from seismic and dynamic loadings. In the present work three different hybrid base isolation systems are analyzed in order to protect reinforced concrete structures with regards to bi-directional ground motions. The three considered hybrid base isolation systems are the Elastomeric Spring Dampers operated in parallel with Friction Sliders, the Lead Rubber Bearings operated in parallel with Friction Sliders and the High Damping Rubber Bearings also operated in parallel with Friction Sliders. The analyzed base isolation systems have been designed in compliance to the European seismic codes EC2 and EC8. The base isolation devices are realized by elastomeric materials and steel-teflon bearings. The highly nonlinear behavior of the composite sliding isolation systems is investigated. A detailed analysis is reported of the hysteretic cycles of the friction slider bearings and the hysteretic cycles of the composite rubber bearing isolators. Bi-directional ground motions corresponding to recorded accelerograms have been considered as seismic actions. A spectrum compatibility analysis has been performed for the chosen recorded sets of accelerograms. A comparative analysis is illustrated for the three base isolated composite structures by reporting the time history of the base acceleration, the time history of the base shear, the time history of the base displacements and of the inter-storey drifts and the peak values of the base shear. The seismic and dynamic response of the considered base isolated structure is illustrated and a comparative analysis is finally presented between the base isolated structure with the three considered base isolation systems and the fixed base structure.

Effects of seismic isolation on the seismic response of a California high‐speed rail prototype bridge with soil‐structure and track‐structure interactions

SummaryWith the launch of the high‐speed train project in California, the seismic risk is a crucial concern to the stakeholders. To investigate the seismic behavior of future California High‐Speed Rail (CHSR) bridge structures, a 3D nonlinear finite‐element model of a CHSR prototype bridge is developed. Soil‐structure and track‐structure interactions are accounted for in this comprehensive numerical model used to simulate the seismic response of the bridge and track system. This paper focuses on examining potential benefits and possible drawbacks of the a priori promising application of seismic isolation in CHSR bridges. Nonlinear time history analyses are performed for this prototype bridge subjected to two bidirectional horizontal historical earthquake ground motions each scaled to two different seismic hazard levels. The effect of seismic isolation on the seismic performance of the bridge is investigated through a detailed comparison of the seismic response of the bridge with and without seismic isolation. It is found that seismic isolation significantly reduces the deck acceleration and the force demand in the bridge substructure (i.e., piers and foundations), especially for high‐intensity earthquakes. However, seismic isolation increases the deck displacement (relative to the pile cap) and the stresses in the rails. These findings imply that seismic isolation can be promisingly applied to CHSR bridges with due consideration of balancing its beneficial and detrimental effects through using appropriate isolators design. The optimum seismic isolator properties can be sought by solving a performance‐based optimum seismic design problem using the nonlinear finite‐element model presented herein. Copyright © 2016 John Wiley & Sons, Ltd.