Earthquake-induced Structural Pounding Research Articles

Effect of Earthquake-Induced Structural Pounding on the Floor Accelerations and Floor Response Spectra of Adjacent Building Structures

The influence of earthquake-induced structural pounding among buildings is paramount in the seismic analysis and design of structures. The recognition of such a phenomenon has been growing in the last decades. The search for ways to understand and mitigate the consequences of these structural collisions in building structures is the primary goal of the investigation of earthquake-induced building pounding. This phenomenon is known for increasing the floor accelerations, mainly where pounding occurs, implying significant local damage. These collisions cause short-duration acceleration pulses that may compromise the building structure and the non-structural elements within the building’s stories. Non-structural elements supported by the structure’s floors under earthquake-induced pounding instances may present a risk to human lives and/or human activity. Hence, the influence of earthquake-induced pounding in the floor response spectra of two adjacent reinforced concrete structures with inelastic behavior is assessed by varying the number of stories and their separation distance. Pounding greatly influenced the floor acceleration spectra, increasing the spread of accelerations over a broader period range, particularly exciting low to moderate periods of vibration.

The Effect of Magnitude Mw and Distance Rrup on the Fragility Assessment of a Multistory RC Frame Due to Earthquake-Induced Structural Pounding

The effect of an intensity measure’s (IM’s) sufficiency property on the probabilistic assessment of reinforced concrete (RC) structures due to floor-to-floor structural pounding conditions is examined. In the first part of this investigation, efficiency and sufficiency properties of 23 scalar IMs are verified. Then, the magnitude Mw and the distance Rrup are examined as elements in a vector with an efficient scalar IM to evaluate whether they have any significant effect on the structural response. Subsequently, probabilistic seismic demand models (PSDMs) are developed using linear regression analyses based on a scalar IM and a vector-valued IM. Fragility curves are developed based on these PSDMs, and the influence of Mw and Rrup on the evaluation of the minimum required separation gap distance dg,min due to the pounding effect is examined. More than two hundred nonlinear time history analyses are performed based on the Cloud Analysis method. Seismic displacement demands that control of the global state of the structure, as well as the probability of structural pounding, are examined. The results of this research indicate that once Mw or Rrup is increased, fragility curves are shifted to greater values of IM, and the probability of the exceedance of a certain performance level is reduced. Also, the predictive power of Rrup seems to be greater than the one of Mw. On the other hand, it is revealed that Mw and Rrup induce variabilities in the demand solutions for adequate separation gap distance between the adjacent structures. Therefore, variation in Mw or Rrup may lead, in some cases, to unacceptable evaluations of the pounding effect in the capacity levels of structures.

The Effectiveness of Rubber Bumpers in Reducing the Effects of Earthquake-Induced Pounding between Base-Isolated Buildings

The methods for preventing earthquake-induced structural pounding between two adjacent buildings include ensuring a sufficient separation distance between them or decreasing their relative displacement during seismic excitation. Some equations or even specific values of such gap sizes between two buildings have been introduced so as to avoid collisions. Increasing the stiffness of buildings, using tuned mass dampers, applying liquid dampers, or decreasing the mass of the structures may reduce lateral displacements, and therefore pounding can be prevented. On the other hand, the application of base isolation systems may result in the elongation of the natural period of the building, thus increasing the probability of structural pounding. The aim of the present paper is to verify the effectiveness of using rubber bumpers to reduce the negative effects of earthquake-induced pounding between base-isolated buildings. The analysis was conducted for different gap sizes between buildings, as well as for various values of the thickness, number and stiffness of rubber bumpers. The results of the study show that the peak impact force decreases with increasing thickness, stiffness, and number of bumpers. Moreover, the peak impact forces are reduced with increasing gap size. The results of the investigation clearly indicate that the use of additional rubber bumpers can be considered an effective method for reducing the negative effects of earthquake-induced pounding between base-isolated buildings.

Study on Earthquake-induced Structural Pounding Between Two Adjacent Building Structures with Unequal Heights

Structural pounding has been found to have a significant influence on the dynamic behavior of building structures under earthquake excitations. This phenomenon is more probable when the buildings have insufficient separation distance and substantial different dynamic properties. In large cities, it is more common for adjacent buildings to have unequal heights, leading to different demands in the structures’ stories under earthquake-induced pounding. Hence, in this study five different buildings’ configurations with equal or unequal heights and subjected to different ground motions are considered, to study how pounding influences the dynamic behavior of the involved structures. It was found, among other results, that the peak responses tend to suffer amplifications at the stories of the taller building above the height of the shorter building.

Highly Dissipative Materials for Damage Protection against Earthquake-Induced Structural Pounding.

It is a common situation that seismic excitations may lead to collisions between adjacent civil engineering structures. This phenomenon, called earthquake-induced structural pounding, may result in serious damage or even the total collapse of the colliding structures. Filling the gap between two buildings erected close to one another by using visco-elastic materials can be considered to be one of the most effective methods to avoid seismic pounding. In this paper, a new polymer–metal composite material made of polyurethane and closed-cell aluminum foam is proposed as a pounding energy absorber for protection against earthquake hazards. The composite was created in two versions, with and without an adhesive interface. A series of experiments which reflect the conditions of seismic collision were performed: quasi-static compression, dynamic uniaxial compression and low-cycle dynamic compression with 10 loops of unloading at 10% strain. The composite material’s behavior was observed and compared with respect to uniform material specimens: polymer and metal foam. The experimental results showed that the maximum energy absorption efficiency in the case of the new material with the bonding layer was improved by 34% and 49% in quasi-static and dynamic conditions, respectively, in comparison to a sole polymer bumper. Furthermore, the newly proposed composites dissipated from 35% to 44% of the energy absorbed in the cyclic procedure, whereas the polymer specimen dissipated 25%. The capacity of the maintenance of the dissipative properties throughout the complete low-cycle loading was also satisfactory: it achieved an additional 100% to 300% of the energy dissipated in the first loading–unloading loop.

An ANN-Based Approach for Prediction of Sufficient Seismic Gap between Adjacent Buildings Prone to Earthquake-Induced Pounding

Earthquake-induced structural pounding may cause major damages to structures, and therefore it should be prevented. This study is focused on using an artificial neural network (ANN) method to determine the sufficient seismic gap in order to avoid collisions between two adjacent buildings during seismic excitations. Six lumped mass models of structures with a different number of stories (from one to six) have been considered in the study. The earthquake characteristics and the parameters of buildings have been defined as inputs in the ANN analysis. The required seismic gap preventing pounding has been firstly determined for specified structural arrangements and earthquake records. In order to validate the method for other structural parameters, the study has been further extended for buildings with different values of height, mass, and stiffness of each story. Finally, the parametric analysis has been conducted for various earthquakes scaled to different values of the peak ground acceleration (PGA). The results of the verification and validation analyses indicate that the determined seismic gaps are large enough to prevent structural collisions, and they are just appropriate for all different structural arrangements, seismic excitations, and structural parameters. The results of the parametric analysis show that the increase in the PGA of earthquake records leads to a substantial, nearly uniform, increase in the required seismic gap between structures. The above conclusions clearly indicate that the ANN method can be successfully used to determine the minimal distance between two adjacent buildings preventing their collisions during different seismic excitations.

Seismic Pounding Between Bridge Segments: A State-of-the-Art Review

Earthquake-induced structural pounding in bridge structures has been observed in several previous seismic events. Collisions occur at the expansion joints provided between adjacent decks or between the deck and abutment. Pounding between the structural elements may lead to severe damages and even to the unseating of the bridge in certain cases. Several investigations have been performed to study pounding in bridges under uniform and non-uniform seismic excitations. Moreover, different mitigation measures have been suggested to overcome the drawbacks of this phenomenon. This work reviews previous research studies concerning earthquake-induced structural pounding in bridge structures, the factors that influence it and the recommended mitigation measures.

Effective Formula for Impact Damping Ratio for Simulation of Earthquake-induced Structural Pounding

Structural pounding during earthquakes may cause substantial damage to colliding structures. The phenomenon is numerically studied using different models of collisions. The aim of the present paper is to propose an effective formula for the impact damping ratio, as a parameter of the impact force model used to study different problems of structural pounding under seismic excitations. Its accuracy has been verified by four various approaches. Firstly, for the case of collisions between two structural elements, the dissipated energy during impact has been compared to the loss of kinetic energy. In the second stage of verifications, the peak impact forces during single collision have been analyzed. Then, the accuracy of different equations have been verified by comparing the impact force time histories for the situation when a concrete ball is dropped on a rigid concrete surface. Finally, pounding between two structures during earthquakes has been studied. The results of the analysis focused on comparison between dissipated and kinetic energy show relatively low errors between calculated and assumed values of the coefficient of restitution when the proposed equation is used. In addition, the results of the comparison between experimentally and numerically determined peak impact forces during single collision confirm the effectiveness of the approach. The same conclusion has been obtained for the whole impact time history for collision between a ball and a rigid surface. Finally, the results of the comparative analysis, conducted for pounding between two structures during an earthquake, confirm the simulation accuracy when the proposed approach is used. The above conclusions indicate that the proposed formula for impact damping ratio, as a parameter of impact force model for simulation of earthquake-induced structural pounding, is very effective and accurate in numerical simulations in the case of different scenarios.

Verification of Formulas for Periods of Adjacent Buildings Used to Assess Minimum Separation Gap Preventing Structural Pounding during Earthquakes

Insufficient separation distance between adjacent buildings may lead to serious damages during earthquakes due to structural pounding. The best way to prevent collisions is to provide sufficiently large separation distance between structures. In this paper, the periods of two closely spaced linear and nonlinear buildings have been investigated so as to accurately assess the minimum in‐between separation gap. A new equation to calculate the effective periods of inelastic buildings has been proposed, and its effectiveness has been verified through numerical analysis. The results of the investigation conducted for inelastic buildings with different number of stories indicate that the proposed formula allows us to prevent earthquake‐induced structural pounding by ensuring an adequate value of seismic gap.

Preventing of earthquake-induced pounding between steel structures by using polymer elements – experimental study

Pounding between two, or more, adjacent buildings during earthquakes has been identified as one of the reasons for substantial damage or even total collapse of colliding structures, so it has been the subject of numerous studies in the recent years. A major reason leading to interactions between adjacent, insufficiently separated structures results from the differences in their dynamic properties. A number of different methods have been considered to mitigate earthquake-induced structural pounding. One of the techniques is linking structures which allow the forces to be transmitted between buildings and thus eliminate interactions. The aim of the present paper is to show the results of the experimental study focused on the application of polymer elements placed between the colliding members so as to mitigate earthquake-induced pounding between adjacent steel structures in series. In the study, three steel model towers with different dynamic parameters and various in-between distances were considered. The unidirectional shaking table was used in the experimental study. Models of steel towers were prepared and mounted to the platform of the shaking table. Additional mass was added at the top of each tower so as to obtain different dynamic characteristics of the structures. The results of the study indicate that earthquake-induced pounding may have a significant influence of the structural response. Moreover, the application of polymer elements between the structures can be an effective pounding mitigation technique. It allows us to prevent damaging collisions between adjacent structures during earthquakes. It also improves the structural behaviour leading to the reduction in vibrations under different seismic excitations.

Numerical Study on Pounding between Two Adjacent Buildings under Earthquake Excitation

Seismic excitation, which results in large horizontal relative displacements, may cause collisions between two adjacent structures due to insufficient separation distance between them. Such collisions, known as earthquake-induced structural pounding, may induce severe damage. In this paper, the case of pounding between two adjacent buildings is studied by the application of single degree-of-freedom structural models. Impact is numerically simulated with the use of a nonlinear viscoelastic model. Special attention is focused on calculating values of impact forces during collisions which have significant influence of pounding-involved response under ground motions. The results of the study indicate that the impact force time history is much dependent on the earthquake excitation analyzed. Moreover, the peak impact forces during collision depend substantially on such parameters as gap size, coefficient of restitution, impact velocity, and stiffness of impact spring element. The nonlinear viscoelastic model of impact force with the considered relation between the damping coefficient and the coefficient of restitution has also been found to be effective in simulating earthquake-induced structural pounding.

A New Formula of Impact Stiffness in Linear Viscoelastic Model for Pounding Simulation

The phenomenon of earthquake-induced structural pounding was extensively studied by some researchers using different models for the impact force. The aim of this paper is to provide a new formula of impact stiffness in the linear viscoelastic contact model, based on the assumption that the maximum impact deformation from the distributed mass model should be equal to that from the equivalent lumped mass model. The correctness and accuracy of the proposed formula have been confirmed by comparing the pounding simulation using the present formula of impact stiffness with those using the existing formulae.

Pounding Between Superstructure Segments in Multi-Supported Elevated Bridge with Three-Span Continuous Deck Under 3D Non-Uniform Earthquake Excitation

Reports after severe ground motions show that the earthquake-induced structural pounding may lead to significant damage in elevated bridges. The aim of this paper is to analyze pounding between superstructure segments of a highway elevated bridge with three-span continuous deck under 3D non-uniform earthquake excitation, which is induced by spatial seismic effects related to the propagation of seismic wave. The conditional stochastic approach has been applied to generate the earthquake records for different support locations along the structure. The analysis has been conducted with the help of FEM taking into account the influence of rotation of superstructure segments due to corner collisions. The detailed non-linear strain-rate-dependent model has been applied to simulate the behavior of bearings under earthquake excitation. The results of the study confirm that pounding has considerable influence on the behavior of the analyzed bridge and may lead to the substantial increase in the structural response. They show that the structural response depends much on the gap size between adjacent superstructure segments. Moreover, the results clearly indicate that the incorporation of the non-uniform earthquake excitation may lead to considerable changes in the structural behavior. The application of the method of conditional stochastic modeling for generation of earthquake records has also been proved to be useful for practical purposes of modeling the spatial seismic effects for long multi-supported elevated bridges.

Inelastic Damage-Involved Response of Colliding Buildings during Earthquakes

Interactions between adjacent, insufficiently separated buildings have been repeatedly observed during major earthquakes. This phenomenon, known as the earthquake-induced structural pounding, may be the reason of local damage at the contact points as well as may lead to the extensive damage at the base of the colliding structure or even initiate its total collapse. In this paper, we examine the importance of inelastic modelling of structural behaviour as the result of damage due to earthquake excitation and structural pounding. The study concerns two adjacent four-storey buildings with different dynamic properties. In the numerical simulations, the nonlinear viscoelastic model is used to model the pounding force during collisions at different storey levels of the structures. The model allows us to take into consideration the dissipation of energy due to damage taking place at the time of collision. Three different ground motion records with different peak ground acceleration levels are used in the study. The comparison between elastic and inelastic damage-involved structural behaviour is investigated. The results of the study show significant changes in the dynamic responses of the inelastic systems as compared to those of elastic ones. The results clearly indicate that modelling the colliding buildings to behave inelastically is really essential in order to obtain accurate damage-involved structural response under earthquake excitation.

Experimental study on earthquake‐induced pounding between structural elements made of different building materials

AbstractThe phenomenon of earthquake‐induced structural pounding has attracted the researchers' attention for several years now. The aim of this paper is to show the results of two experiments concerning interactions between elements made of different building materials, such as steel, concrete, timber and ceramic. The first experiment was conducted by dropping balls from different height levels onto a rigid surface, whereas the second one was focused on pounding‐involved response of two tower models excited on a shaking table. The results of the impact experiment show that the value of the coefficient of restitution depends substantially on the prior‐impact velocity as well as on the material used. Based on these results, the appropriate formulations have been suggested to be applied in the numerical simulations. The results of the shaking table tests show a considerable influence of the material used for colliding elements on the behaviour of structures during earthquakes. Copyright © 2009 John Wiley & Sons, Ltd.

Non-linear FEM analysis of earthquake-induced pounding between the main building and the stairway tower of the Olive View Hospital

The reports after major ground motions indicate that earthquake-induced pounding between buildings may lead to substantial damage or even collapse of colliding structures. The research on structural pounding during earthquakes has been recently much advanced, although most of the studies were conducted on much simplified discrete lumped mass models of buildings. In the present paper, a detailed three-dimensional pounding-involved response analysis of two adjacent structures has been conducted using the FEM with the non-linear model of material behaviour, including stiffness degradation of concrete under cyclic loading. The study concerns pounding between the Olive View Hospital main building and one of its independently standing stairway towers, which was observed during the San Fernando earthquake of 1971. The results of the study show that collisions may lead to a significant increase of the response of the lighter stairway tower as well as may result in a substantial increase of the range and intensity of damage at the base of the structure, whereas the behaviour of the heavier main building has been found to be only slightly influenced by structural interactions. The results clearly confirm that special attention should be paid to appropriate design of a weaker building, for which earthquake-induced structural pounding can be catastrophic.

Earthquake-induced pounding between equal height buildings with substantially different dynamic properties

Earthquake-induced structural pounding may result in considerable damage or even collapse of colliding structures during severe ground motions. The aim of the paper is to conduct a detailed investigation on pounding-involved response of two equal height buildings with substantially different dynamic properties, paying a special attention to modelling the non-linear effects taking place during impact as well as observed in the structural behaviour as the result of ground motion excitation. The three-dimensional non-linear response analysis as well as the parametric study have been conducted for earthquake-induced pounding of structures modelled as elastoplastic multi-degree-of-freedom lumped mass systems. The results of the response analysis show that collisions have a significant influence on the behaviour of the lighter and more flexible building causing substantial amplification of the response and leading to considerable permanent deformation due to yielding. On the other hand, it has been found that the behaviour of the heavier and stiffer building is nearly unaffected by collisions between structures. The parametric investigation has led to the conclusion that the peak displacement of the lighter and more flexible building is very sensitive to a change of structural parameters considered (gap size, storey mass, structural stiffness and yield strength), whereas the response of the heavier and stiffer structure can be influenced only negligibly.

Impact Force Spectrum for Damage Assessment of Earthquake-Induced Structural Pounding

Past earthquakes indicate that pounding between inadequately separated structures may cause considerable damage or even lead to collapse of colliding structures. Intensive study has been recently carried out on mitigation of pounding hazards. The assessment of damage due to structural pounding, or its prediction under a particular ground motion, requires the knowledge of the maximum impact force value expected during the time of earthquake. The aim of the present paper is to consider the concept of impact force response spectrum for two closely-spaced structures, which shows the plot of the peak value of pounding force as a function of the natural structural vibration period. The spectrum can be used as a practical tool to assess the magnitude of the expected pounding-induced damage and, if necessary, to apply some damage reduction techniques. In the analysis, both interacting structures have been modelled by single-degree-of-freedom systems and pounding has been simulated by the non-linear viscoelastic model, which accounts for the energy dissipation during impact. The examples of response spectra show that the appropriate selection of the separation gap between structures as well as the dynamic structural parameters, such as the natural vibration period, mass and damping, might have a significant influence on the intensity of damage due to earthquake-induced pounding.

Non-linear viscoelastic modelling of earthquake-induced structural pounding

Past severe earthquakes indicate that structural pounding may cause considerable damage or even lead to collapse of colliding structures if the separation distance between them is not sufficient. Because of its complexity, modelling of impact is an extremely difficult task, however, the precise numerical model of pounding is essential if an accurate structural response is to be simulated. The aim of this paper is to analyse a non-linear viscoelastic model of collisions which allows more precise simulation of the structural pounding during earthquakes. The effectiveness of the model is verified by comparing the results of numerical analyses with the results of experiments conducted on pounding between different types of structures. The results of the study indicate that, compared to other models, the proposed non-linear viscoelastic model is the most precise one in simulating the pounding-involved structural response. Copyright © 2005 John Wiley & Sons, Ltd.