Seismic Pounding Research Articles

공유형 동조질량감쇠기를 이용한 인접건물의 지진응답제어

When adjacent tall buildings experience earthquake excitation, structural pounding may happen. In order to mitigate seismic pounding damage to adjacent structures, many studies have been done to date. Tuned mass dampers (TMD) are widely used for reduction of dynamic responses of building structures subjected to earthquake excitations. If a TMD is shared between adjacent buildings and it shows good control performance, it will be effective and economic means to reduce seismic responses of adjacent structures. In this study, control performance of a shared tuned mass damper (STMD) for seismic response reduction of adjacent buildings has been evaluated. For this purpose, two 8-story example buildings were used and multi-objective genetic algorithms has been employed for optimal design of the stiffness and damping parameters of the STMD. Based on numerical analyses, it has been shown that a STMD can effectively control dynamic responses and reduce the effect of pounding between adjacent buildings subjected to earthquake excitations in comparison with a traditional TMD.

SEISMIC POUNDING BETWEEN ADJACENT BUILDING STRUCTURES SUBJECTED TO NEAR FIELD GROUND MOTION

The pounding of adjacent structures during earthquakes has been receiving considerable attention in recent years. This is because adjacent structures with inadequate clear spacing between them have suffered considerable structural and nonstructural damage as a result of their collision during major earthquakes. The different dynamic characteristics of adjacent buildings make them vibrate out of phase, and pounding occurs if there is a lack of sufficient space between them. Pounding between closely spaced building structures can be a serious hazard in seismically active areas. Past seismic codes did not give definite guidelines to preclude pounding, because of this and due to economic considerations including maximum land usage requirements, especially in the high density populated areas of cities, there are many buildings worldwide which are already built in contact or extremely close to another that could suffer pounding damage in future earthquakes. The highly congested building system in many metropolitan cities constitutes a major concern for seismic pounding damage.

On the Seismic Response of Collided Structures

This study examines the inelastic behavior of adjacent planar reinforced concrete (R.C.) frames subjected to strong ground motions. The investigation focuses on the effects of vertical ground motion on the seismic pounding. The examined structures are modeled and analyzed by RUAUMOKO dynamic nonlinear analysis program using reliable hysteretic models for both structural members and contact elements. It is found that the vertical ground motion mildly affects the seismic response of adjacent buildings subjected to structural pounding and, for this reason, it can be ignored from the displacement and interstorey drifts assessment. However, the structural damage is moderately affected by the vertical component of earthquakes. Keywords—Nonlinear seismic behavior, reinforced concrete structures, structural pounding, vertical ground motions.

On the Seismic Response of Collided Structures

This study examines the inelastic behavior of adjacent planar reinforced concrete (R.C.) frames subjected to strong ground motions. The investigation focuses on the effects of vertical ground motion on the seismic pounding. The examined structures are modeled and analyzed by RUAUMOKO dynamic nonlinear analysis program using reliable hysteretic models for both structural members and contact elements. It is found that the vertical ground motion mildly affects the seismic response of adjacent buildings subjected to structural pounding and, for this reason, it can be ignored from the displacement and interstorey drifts assessment. However, the structural damage is moderately affected by the vertical component of earthquakes. Keywords—Nonlinear seismic behavior, reinforced concrete structures, structural pounding, vertical ground motions.

A STUDY OF SEISMIC POUNDING BETWEEN ADJACENT BUILDINGS

Seismic pounding between adjacent buildings can cause severe damage to the structures under earthquakes, when owing to their different dynamic characteristics. During earthquake, the buildings vibrate out of phase and at rest separation is deficient to accommodate their relative motions. Such buildings are usually separated by expansion joint which is insufficient to provide the lateral movements of the buildings during earthquakes. It can be prevented by providing safe separation distances, sometimes getting of required safe separations is not possible in metropolitan areas due to high land value and limited availability of land space. If building separations is found to be deficient to prevent pounding, then there should be some secure and cost effective methods to prevent structural pounding between adjacent buildings. There are many buildings which are constructed very nearly to one another in Metropolitan cities, because everyone wants to construct up to their property line due to high cost of land. This study covers the prevention techniques of pounding between adjacent buildings due to earthquakes. Constructing new RC walls, cross bracing system and combined RC wall & bracing, with proper placement are proposed as possible prevention techniques for pounding between adjacent buildings

Analysis and mitigation of seismic pounding of a slender R/C bell tower

Pounding is one of the greatest sources of seismic vulnerability of slender R/C structures, including civic or bell towers. An emblematic case study falling in this class of structures, i.e. a modern heritage R/C bell tower constructed in the early 1960s to replace the former 19th century tower of the Chiesa del Sacro Cuore in Florence, is analyzed in this paper. In order to assess the effects of pounding, a special multi-link viscoelastic finite element contact model was devised and calibrated in this study to reproduce Jankowski’s non-linear viscoelastic analytical model. Indeed, the damping coefficient of the latter is defined as a non-linear function of time, and thus it cannot be directly implemented in commercial calculus programs, because the damping coefficient of the damper elements included in their basic libraries is assumed to be a constant. The non-linear dynamic enquiry carried out by the finite element model of the bell tower and the church incorporating the multi-link viscoelastic contact elements shows that pounding affects the seismic response of the two buildings as early as an input seismic action scaled at the amplitude of the normative basic design earthquake level. Furthermore, unsafe stress states are highlighted for the columns of the tower under seismic action scaled at the maximum considered earthquake level. A damped-interconnection retrofit solution consisting in linking the two structures by means of a pair of pressurized fluid-viscous dissipaters is proposed to prevent pounding. The technical implementation details of this rehabilitation strategy are illustrated, and the benefits induced are discussed by comparison with the response in original conditions and in the hypothesis of a conventional rigid-connection retrofit intervention between the bell tower and the church.

Performance of base‐isolated reinforced concrete buildings under bidirectional seismic excitation considering pounding with retaining walls including friction effects

SUMMARYSeismic pounding of base‐isolated buildings has been mostly studied in the past assuming unidirectional excitation. Therefore, in this study, the effects of seismic pounding on the response of base‐isolated reinforced concrete buildings under bidirectional excitation are investigated. For this purpose, a three‐dimensional finite element model of a code‐compliant four‐story building is considered, where a newly developed contact element that accounts for friction and is capable of simulating pounding with retaining walls at the base, is used. Nonlinear behavior of the superstructure as well as the isolation system is considered. The performance of the building is evaluated separately for far‐fault non‐pulse‐like ground motions and near‐fault pulse‐like ground motions, which are weighted scaled to represent two levels of shaking viz. the design earthquake (DE) level and the risk‐targeted maximum considered earthquake (MCER) level. Nonlinear time‐history analyses are carried out considering lower bound as well as upper bound properties of isolators. The influence of separation distance between the building and the retaining walls at the base is also investigated. It is found that if pounding is avoided, the performance of the building is satisfactory in terms of limiting structural and nonstructural damage, under DE‐level motions and MCER‐level far‐fault motions, whereas unacceptably large demands are imposed by MCER‐level near‐fault motions. In the case of seismic pounding, MCER‐level near‐fault motions are found to be detrimental, where the effect of pounding is mostly concentrated at the first story. In addition, it is determined that considering unidirectional excitation instead of bidirectional excitation for MCER‐level near‐fault motions provides highly unconservative estimates of superstructure demands. Copyright © 2014 John Wiley & Sons, Ltd.

Influence of bi-directional seismic pounding on the inelastic demand distribution of three adjacent multi-storey R/C buildings

Interaction between closely-spaced buildings subject to earthquake induced strong ground motions, termed in the literature as “seismic pounding”, occurs commonly during major seismic events in contemporary congested urban environments. This influence is not taken into account by current codes of practice and is rarely considered in practice at the design stage of new buildings constructed “in contact” with existing ones. Thus far, limited research work has been devoted to quantify the influence of slab-to-slab pounding on the inelastic seismic demands at critical locations of structural members in adjacent structures that are not aligned in series. In this respect, this paper considers a typical case study of a “new” reinforced concrete (R/C) EC8-compliant, torsionally sensitive, 7-story corner building constructed within a block, in bi-lateral contact with two existing R/C 5-story structures with same height floors. A non-linear local plasticity numerical model is developed and a series of non-linear time-history analyses is undertaken considering the corner building “in isolation” from the existing ones (no-pounding case), and in combination with the existing ones (pounding case). Numerical results are reported in terms of averages of ratios of peak inelastic rotation demands at all structural elements (beams, columns, shear walls) at each storey. It is shown that seismic pounding reduces on average the inelastic demands of the structural members at the lower floors of the 7-story building. However, the discrepancy in structural response of the entire block due to torsion-induced, bi-directionally seismic pounding is substantial as a result of the complex nonlinear dynamics of the coupled building block system.

隣接建築物の適切な棟間距離算定のための棟間衝突解析

隣接建築物の適切な棟間距離算定のための棟間衝突解析

New Equivalent Linear Impact Model for Simulation of Seismic Isolated Structure Pounding against Moat Wall

Base-isolated buildings subjected to extreme earthquakes or near-fault pulse-like earthquakes can exceed their design gap distance and impact against the surrounding moat wall. Based on equating energy dissipation and maximum collision compression deformation of isolated structure with the Hertz-damp model and Kevin-Voigt model in the process of collision, an equivalent linear impact model (ELIM) is proposed to better predict impact response of seismic isolated structure. The formula of the equivalent linear stiffness of ELIM is theoretically derived. The effectiveness of ELIM is verified by comparing the results of numerical analyses with the results of pounding experiments. Four near-fault earthquakes are selected to validate rationality and accuracy of the proposed model using numerical analysis. The results indicate that the proposed linear model can nearly capture impact behavior of isolated structure in simulating the pounding-involved structural response.

Influence of Near-Fault Ground Motions on the Response of Base-Isolated Reinforced Concrete Buildings considering Seismic Pounding

Performance of base-isolated buildings subjected to near-fault ground motions containing long-period pulses is of increasing concern, because these ground motions have the potential to impose large seismic demands on structures. A review of previous studies on the performance evaluation of base-isolated reinforced concrete (RC) buildings under near-fault ground motions shows that these studies lack in the consideration of seismic pounding and the use of lower bound and upper bound values of isolator properties according to the current state of practice. Accordingly, in this study the performance of a typical four-story base-isolated RC building is evaluated using a three-dimensional nonlinear finite element model, considering bounding values of isolator properties, to investigate the influences of (i) pulse-like nature of near-fault ground motions and (ii) seismic pounding with retaining walls at the base. Two sets of ground motions containing 14 far-fault non-pulse-like ground motions and 14 near-fault pulse-like ground motions, representing the risk-targeted maximum considered earthquake (MCER), are used. It is found that the response indicators of the building under near-fault motions are significantly larger than those under far-fault motions. Analysis results reveal that the building response indicators are significantly increased due to seismic pounding. Nonetheless, if a bounding analysis is conducted, consideration of seismic pounding in the analysis does not have appreciable consequences on the prediction of damage to structural elements and drift-sensitive nonstructural components, while dramatic increase in floor accelerations due to pounding is critical for acceleration-sensitive nonstructural components.

Evaluation of numerical pounding models with experimental validation

Pounding damage in major earthquakes has been observed frequently in the form of aesthetic, minor or major structural cracks and collapse of buildings. These observations have attracted many numerical and experimental studies that led to analytical models for simulating seismic pounding. This study considers pounding between two steel portal frames without a seismic gap. The first frame has a constant natural period while the second frame has variable stiffness and mass values. Five different ground motions are applied to eight combinations of adjacent frames using a shake table. Numerical simulations for the same configurations are carried out with five pounding force models, viz. linear viscoelastic model, modified linear viscoelastic model, nonlinear viscoelastic model, Hertzdamp model and modified Hertzdamp model. The contact element stiffness and coefficient of restitution for numerical models are determined experimentally. The amplification of maximum displacement of the first frame predicted by the numerical simulations is compared with the shake table results. It was found that the Hertzdamp model always overestimated the responses while the other four models also frequently overestimated the amplifications. The predictions from the four models were not significantly different. Since the linear viscoelastic model requires substantially less computation, compared with the other models this model is more suitable for numerical modelling of pounding responses. However, more study is required to refine the numerical models before building pounding can be modelled with enough confidence.

Dynamic and Mitigation Analysis of Seismic Pounding Effect on Multi-Span Highway Bridges Subjected to Spatial Earthquakes

The main girder and the piers of bridges are generally linked with sliding bearings. Under seismic excitation, pounding effects between the main girder and the abutment, the adjacent girder and the blocking device caused by excessive relative displacements between piers, abutments and the girder are highly probable. The effects can not only damage the structure but also lead to collapsing. Based on a continuous viaduct, the paper studied the disciplines of the pounding response under uniform seismic excitation and the spatial seismic excitation, then put forward that the composite metal damper may reduce the effect of pounding. The research shows that under same seismic intensity, the results, including pounding force, the shear force of the fixed bearings and the plastic hinge on the piers, are amplified under multi-point excitation than under uniform excitation. And composite metal dampers can reduce the seismic responds under frequent earthquakes and prevent or largely reduce the pounding effect under severe earthquakes. Therefore the effect of pounding on the dynamic performance can be lessened. The seismic reduction is widely and well-adapted under both uniform excitation and multi-point excitation.

Shaking Table Test on Seismic Pounding Response of Reinforced Concrete Bridge

To investigate the response of the bridge pounding, shaking table test was performed using 1/10 scaled reinforced concrete rigid frame bridge specimen. The influence of traveling effect on pounding and the anti-impact capability using dampers were discussed. The experimental results demonstrate that the acceleration responses of the girder and bridge piers, the frequency and the impact force are increased when the traveling wave excitation is considered. Moreover, relatively displacement of the adjacent bridge frames increased magnitudely. Dynamic responses, the frequency and the impact force are decrease when the dampers are installed.Therefore, installation of the dampers is a sustainable and effective way to improve the anti-impact capability.

Seismic Pounding and Protection Measures of Simply-Supported Beams Considering Interaction between Continuously Welded Rail and Bridge

The pounding effect between neighboring simply-supported beams can damage a bridge and even cause collapse of a beam. However, previous pounding studies did not consider the influence of the continuously welded rail (CWR) during earthquakes, thus overestimating the seismic response of the railway bridge, yielding uneconomic design and neglecting the influence of seismic pounding on track forces. Therefore, the main focus of this paper is to investigate the influence of CWR on bridge pounding through numerical modeling. In the simulation, nonlinear bar element was used to model longitudinal resistance of the track. Large-mass method was used to obtain multi-support excitation and the Kelvin model was applied to simulate the beam pounding. In addition, a number of detailed effects were taken into account, including the nonlinear behavior of the bearing, the moment–curvature relationship of the pier and the interaction of the piles and soil. Taking the three-span 32 m simply-supported box beams on the Shanghai–Kunming line as an example, this paper also studies the influence of temperature loads, train braking load, traveling wave effect, line resistance, track expansion device, buffer device and beam connection device on the bridge pounding effect an d the pier force. The numerical results showed that the track can significantly mitigate the pounding effect of the bridge. The traveling wave effect could significantly increase the force in track and bridge, which can result in pounding. If the high-speed railway train brakes on the bridge during an earthquake, the rail may be destroyed near the location of abutment. The use of track expansion devices and small resistance fasteners could result in the poundi ng effect between the neighboring beams while the use of buffer device and beam connection device can mitigate the pounding effect and eventually reduce force on the pier.

Influence of Seismic Pounding on RC Buildings with and without Base Isolation System Subject to Near-Fault Ground Motions

Building pounding occurs between two adjacent buildings with small gap or without sufficient separation distance. It leads to damage buildings during earthquake due to impact. Many researchers have investigated building pounding based on impact force reduction and energy dissipation increase, when two buildings collide with each other. In numerical investigations, using specific link element, impact force is calculated in order to get the proper evaluation of damage for preventing failure of structural elements. In this paper, focusing on numerical investigation, the effectiveness of impact and energy dissipation is studied. For this challenge, two RC structural models are considered to evaluate the pounding to calculate the impact force and finally, to compare the effectiveness of Base Isolation (BI) support against fixed support. A link element is located at the connection level between two studied dynamic models.

Damped Interconnection-Based Mitigation of Seismic Pounding between Adjacent R/C Buildings

viscoelastic model for the numerical time-history analysis of the dynamic impact problem is proposed and implemented in the finite element model of the buildings. The results of the assessment enquiries carried out in current conditions, and a damped interconnection-based mitigation solution based on the incorporation of pressurized fluid-viscous dissipaters across the inadequate separation gaps, are presented. Evaluations of the benefits provided by the retrofit intervention, and some of its technical installation details, are finally offered.

A probabilistic performance‐based approach for mitigating the seismic pounding risk between adjacent buildings

ABSTRACTExisting design procedures for determining the separation distance between adjacent buildings subjected to seismic pounding risk are based on approximations of the buildings' peak relative displacement. These procedures are characterized by unknown safety levels and thus are not suitable for use within a performance‐based earthquake engineering framework.This paper introduces an innovative reliability‐based methodology for the design of the separation distance between adjacent buildings. The proposed methodology, which is naturally integrated into modern performance‐based design procedures, provides the value of the separation distance corresponding to a target probability of pounding during the design life of the buildings. It recasts the inverse reliability problem of the determination of the design separation distance as a zero‐finding problem and involves the use of analytical techniques in order to evaluate the statistics of the dynamic response of the buildings. Both uncertainty in the seismic intensity and record‐to‐record variability are taken into account.The proposed methodology is applied to several different buildings modeled as linear elastic single‐degree‐of‐freedom (SDOF) and multi‐degree‐of‐freedom (MDOF) systems, as well as SDOF nonlinear hysteretic systems. The design separation distances obtained are compared with the corresponding estimates that are based on several response combination rules suggested in the seismic design codes and in the literature. In contrast to current seismic code design procedures, the newly proposed methodology provides consistent safety levels for different building properties and different seismic hazard conditions. Copyright © 2012 John Wiley & Sons, Ltd.

Reduction of seismic pounding effects of base-isolated RC highway bridges using MR damper

Significant structural damages due to pounding between adjacent superstructures of multi-span reinforced concrete (RC) highway bridges have been observed in past earthquakes. Different methods have been proposed in the literature to mitigate the adverse seismic pounding effects. This paper presents an analytical investigation on the use of magnetorheological (MR) dampers in reducing seismic pounding effects of base-isolated multi-span RC highway bridges. It has been observed that MR damper can effectively reduce the seismic pounding effect. Three control strategies (passive off, passive on, and bang bang control) of MR damper have been investigated. Although all the control strategies are found to be effective, bang bang control has been observed to be the most effective.

A probabilistic performance-based risk assessment approach for seismic pounding with efficient application to linear systems

Earthquake ground motion excitation can induce pounding in adjacent buildings with inadequate separation distance. The corresponding risk is particularly relevant in densely inhabited metropolitan areas, due to the usually limited separation distance between adjacent buildings.Existing procedures to determine a minimum separation distance needed to avoid seismic pounding are based on approximations of the peak relative horizontal displacement between adjacent buildings, and are characterized by unknown safety levels. The present study proposes a probabilistic performance-based procedure for assessing the mean annual frequency of pounding between adjacent buildings. An efficient combination of analytical and simulation techniques is defined for the calculation of the pounding risk under the assumptions of linear elastic behavior for the buildings and of non-stationary Gaussian input ground motion.The proposed methodology is illustrated by estimating the probability of pounding between linear single-degree-of-freedom systems with deterministic and uncertain properties. Furthermore, the capabilities of the proposed method are demonstrated by assessing the effectiveness of the use of viscous dampers, according to different retrofit schemes, in reducing the pounding probability of adjacent buildings modeled as linear elastic multi-degree-of-freedom systems. The results obtained based on the proposed methodology are validated against purely numerical simulation results.