Structural Pounding Research Articles

Linking of adjacent three-storey buildings for mitigation of structural pounding during earthquakes

The reports after major earthquakes indicate that the earthquake-induced pounding between insufficiently separated buildings may lead to significant damage or even total collapse of structures. An intensive study has recently been carried out on mitigation of pounding hazards so as to minimize the structural damages or prevent collisions at all. The aim of this paper is to investigate the effectiveness of the method when two adjacent three-storey buildings with different (substantially different) dynamic properties are connected at each storey level by link elements (springs, dashpots or viscoelastic elements). The results of the study indicate that connecting the structures by additional link elements can be very beneficial for the lighter and more flexible building. The largest decrease in the response of the structure has been obtained for links with large stiffness or damping values, which stands for the case when two buildings are fully connected and vibrate in-phase. Moreover, by comparing the effectiveness of different types of link elements, it has been confirmed that the use of viscoelastic elements reduces the peak displacement of the structure at lower stiffness and damping values comparing to the case when spring and dashpot elements are applied alone. On the other hand, the results of the study demonstrate that applying the additional link elements does not really change the response of the heavier and stiffer building. The final conclusion of the study indicates that linking two buildings allows us to reduce the in-between gap size substantially while structural pounding can be still prevented.

Effect of Planar Impact Modeling on the Pounding Response of Base-Isolated Buildings

During strong earthquake excitations, base-isolated buildings may collide, either with the surrounding moat wall or with adjacent buildings if the available clearance is exceeded. This undesirable possibility has been recently investigated by several researchers, adopting various types of force-based impact models. Evidently, an important issue that arises regarding such numerical studies is the way of taking into account potential impacts. This paper parametrically investigates the effects of impact modeling characteristics on the computed overall peak response of a base-isolated building that experiences structural pounding. Specifically, the Kelvin-Voigt impact model and various other modifications of this linear viscoelastic impact model are considered in the conducted analyses. In order to efficiently conduct this investigation a specially developed software is utilized. The results indicate that the excitation’s and isolator’s characteristics do not significantly influence the variation of the normalized peak response of the superstructure. In contrast, the impact parameters can have a significant effect on the superstructures’ peak accelerations with overestimations up to 70%. In general, the normalized peak response ratios of the inter-story drifts tend to increase as the available seismic gap clearance and the coefficient of restitution decrease, although the magnitude of the deviations is within 5%, which can be considered insignificant.

An optimization study for viscous dampers between adjacent buildings

This paper investigates optimum viscous damper capacity and number for prevention of one-sided structural pounding between two adjacent buildings under earthquake motion. The buildings assumed as shear-type structures are modeled by using lumped mass-stiffness technique. Impact forces due to pounding is simulated by nonlinear elastic spring approximation called Hertz model. A parametric study is conducted by varying storey number and stiffness of buildings in addition to the capacity of the viscous dampers. Pounding force and supplemental damping ratio for each case are presented based upon newly defined nondimensional natural frequency parameter ratio. An optimization procedure for determination of viscous damper capacity is developed based on modified supplemental damping ratio equation. Results are compared with each other to clarify the effect of variation in building parameters on pounding forces and viscous damper capacity.

A STUDY OF SEISMIC POUNDING EFFECT BETWEEN ADJACENT BUILDINGS AND ITS MITIGATION BY USING DIFFERENT TYPE OF BRACING SYSTEMS

Investigation of previous and recent earthquake damage have shown that the buildings are subjected to severe destruction or collapse during the earthquake ground motion. Among the probable structural damages, seismically induced pounding has been usually witnessed in most of the earthquakes. During the earthquake, Building vibrates out phase due there different dynamics characteristics. Such buildings are usually separated by expansion joint which is insufficient to accommodate the lateral movements of the buildings during the earthquake. Seismic pounding can be prevented by providing safe separation distances; sometimes availability of required safe separation gap is not possible in metropolitan cities due to high land value and limited availability of land. If building separation is found to be deficient to prevent pounding, then there should be some easy and cost-effective methods to prevent structural pounding between adjacent buildings. This study covers the effect of structural pounding on conventional beam column system adjacent to flat slab system .In order to observe pounding effect, Time history analysis is carried out by taking 1944 Elcentro earthquake data which is to be known as above average earthquake. This study also covers the prevention techniques of pounding by using retrofitting’s like introducing X cross bracings, Eccen forward and backward cross bracing, V cross bracing systems with proper placement are proposed as possible mitigation techniques for pounding between adjacent structures

Probabilistic seismic demand model for pounding risk assessment

SummaryEarthquake‐induced pounding of adjacent structures can cause severe structural damage, and advanced probabilistic approaches are needed to obtain a reliable estimate of the risk of impact. This study aims to develop an efficient and accurate probabilistic seismic demand model (PSDM) for pounding risk assessment between adjacent buildings, which is suitable for use within modern performance‐based engineering frameworks. In developing a PSDM, different choices can be made regarding the intensity measures (IMs) to be used, the record selection, the analysis technique applied for estimating the system response at increasing IM levels, and the model to be employed for describing the response statistics given the IM. In the present paper, some of these choices are analyzed and evaluated first by performing an extensive parametric study for the adjacent buildings modeled as linear single‐degree‐of‐freedom systems, and successively by considering more complex nonlinear multi‐degree‐of‐freedom building models. An efficient and accurate PSDM is defined using advanced intensity measures and a bilinear regression model for the response samples obtained by cloud analysis. The results of the study demonstrate that the proposed PSDM allows accurate estimates of the risk of pounding to be obtained while limiting the number of simulations required. Copyright © 2016 John Wiley & Sons, Ltd.

Comparative Life Cycle Analysis of Conventional and Base-Isolated Buildings

This paper presents a case study life cycle analysis of a conventional and base isolated steel braced frame office building. The case study focuses particularly on the effects of moat wall pounding and business interruption using the FEMA P-58 methodology. Analytical results suggest that the overall performance of the base isolated building is far superior to the conventional building but that expected financial losses in the isolated building become significant if structural pounding occurs. The cost-effectiveness of the isolation is found to be particularly sensitive to the ability of businesses to relocate quickly and effectively after a large earthquake.

Historical Origin and Recent Development on Normal Directional Impact Models for Rigid Body Contact Simulation: A Critical Review

The impact is one of the most abundant phenomena in the field of multi-body dynamics when two or more bodies come in close vicinity and depending on the interaction properties and geometry, all the interacting bodies experience certain impulsive force for an infinitesimal duration. Nowadays, impact modelling becomes an intrinsic part in the modelling of structural pounding, granular materials, crash and machinery analysis, robotics and bio-mechatronics applications. Since the time of Newton, numerous literatures have been published on the modelling of both normal and oblique contact phenomena. The scope of this critical review is limited to consolidate the existing knowledge on the computational model of normal directional impact on rigid bodies. The literature related to modelling of oblique impact, soft body impact, impact damage in composites and associated stress wave propagation are excluded from the scope of this critical review. Smooth and non-smooth mechanics are two schools of thought in simulating the normal directional impact. In this review, the shortcomings of all the classes of compliance and non-smooth models are analysed in the unified dimensionless frame-work to compare their response output with the conventional stereo-mechanical model. This review opens a new avenue for future researchers in selecting a proper contact formulation for specific application.

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.

An Updated Analytical Structural Pounding Force Model Based on Viscoelasticity of Materials

Based on the summary of existing pounding force analytical models, an updated pounding force analysis method is proposed by introducing viscoelastic constitutive model and contact mechanics method. Traditional Kelvin viscoelastic pounding force model can be expanded to 3-parameter linear viscoelastic model by separating classic pounding model parameters into geometry parameters and viscoelastic material parameters. Two existing pounding examples, the poundings of steel-to-steel and concrete-to-concrete, are recalculated by utilizing the proposed method. Afterwards, the calculation results are compared with other pounding force models. The results show certain accuracy in proposed model. The relative normalized errors of steel-to-steel and concrete-to-concrete experiments are 19.8% and 12.5%, respectively. Furthermore, a steel-to-polymer pounding example is calculated, and the application of the proposed method in vibration control analysis for pounding tuned mass damper (TMD) is simulated consequently. However, due to insufficient experiment details, the proposed model can only give a rough trend for both single pounding process and vibration control process. Regardless of the cheerful prospect, the study in this paper is only the first step of pounding force calculation. It still needs a more careful assessment of the model performance, especially in the presence of inelastic response.

Elastic and Inelastic Response of Structural Systems in Seismic Pounding

The present paper addresses the comparative study of three adjacent single-degree-of freedom structures for elastic and inelastic system with and without pounding under seismic excitations. For the gap between three adjacent structures, the simulation is done by using linear spring element without damping. The entire numerical simulation is done in time domain by considering the inputs of four real ground motions. The results of the study show that the response of elastic system is much different to that of response of inelastic system in the absence and presence of pounding, especially in lighter or more flexible structures. Elastic structures show much severe pounding response than inelastic structures. Modeling of colliding structures behaving inelastically is really needed in order to obtain the accurate structural pounding involved response under seismic excitation.

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.

Pounding between Inelastic Three-Storey Buildings under Seismic Excitations

Structural interactions between adjacent, insufficiently separated buildings have been repeatedly observed during damaging ground motions. This phenomenon, known as the structural pounding, may result in substantial damage or even total collapse of structures. The aim of the present paper is to show the results of the nonlinear numerical analysis focused on pounding between inelastic three-storey buildings under seismic excitations. The discrete lumped-mass numerical models of two building have been used in the analysis. The results of the study indicate that the response of the lighter and more flexible inelastic building can be substantially influenced by structural interactions, and collisions may even lead to the permanent deformation of the structure. On the other hand, the behaviour of the heavier and stiffer building does not really change considerably during the earthquake. The results of the study also indicate that incorporation of the inelastic behaviour of colliding buildings with different dynamic characteristics is very important for the purposes of accurate numerical modelling of pounding-involved structural response under damaging seismic excitations.

Building damage due to structural pounding during earthquakes

Earthquake-induced pounding between adjacent buildings has been identified as one of the reasons for substantial damage or even total collapse of colliding structures. A major reason leading to interactions in buildings results from the differences in their dynamic parameters and also from insufficient distance between the structures. Although the research on structural pounding has been much advanced, the studies have mainly been conducted for concrete structures. The aim of this paper is to show the results of the non-linear numerical analysis focuses on damage due to pounding between two steel buildings under earthquake excitation. The numerical analysis has been performed using models of steel asymmetric structures with different number of storeys which makes them vibrate out-of-phase. Pounding between buildings has been controlled using three-dimensional gap-friction elements which become active when contact is detected. In order to identify the dynamic characteristics of analyzed structures, the modal analysis has been first conducted. Then, the detailed non-linear dynamic analysis of colliding structures has been performed. The acceleration time histories of the El Centro earthquake have been used in the numerical analysis. The results of the study clearly indicate that pounding may substantially influence the response of steel buildings intensifying their damage during earthquakes.

Effect of the seismic excitation angle on the dynamic response of adjacent buildings during pounding

The excitation angle or angle of incidence is the angle in which the horizontal seismic components are applied with respect to the principal structural axes during a time history analysis. In this study, numerical simulations and parametric studies are performed for the investigation of the effect of the angle of seismic incidence on the response of adjacent buildings, which may experience structural pounding during strong earthquakes due to insufficient or no separation distance between them. A specially developed software application has been used that implements a simple and efficient methodology, according to which buildings are modelled in three dimensions and potential impacts are simulated using a novel impact model that takes into account the arbitrary location of impacts and the geometry at the point of impact. Two typical multi-storey buildings and a set of earthquake records have been used in the performed analyses. The results of the conducted parametric studies reveal that it is very important to consider the arbitrary direction of the ground motion with respect to the structural axes of the simulated buildings, especially during pounding, since, in many cases, the detrimental effects of pounding become more pronounced for an excitation angle different from the commonly examined 0 or 90 degrees.

Evaluation and refinement of closely spaced buildings’ performance under near-fault ground motions

This paper investigates the seismic behaviour of closely spaced fixed-base and isolated building structures in near-fault (NF) zones. Seismic pounding of fixed-base structures is considered at different heights, being from one or both opposite sides and at different seismic gap width. The response evaluation results of fixed-base buildings drive towards providing limited, but adequate, seismic gaps to perform seismic isolation. This aims at reducing structural responses with no seismic pounding under limited gaps, minimising the possible damage repair and diminishing the needed maintenance works due to strong NF earthquakes. To achieve that untraditionally, the paper presents a recently proposed seismic isolation system, named roll-in-cage (RNC) isolator, as a non-traditional solution to avoid direct seismic pounding of isolated buildings with their surrounding adjacent structures. It was found that the RNC isolator’s buffer mechanism is able to draw down any possible pounding of the isolated superstructure to be within the isolator solid limits. This entirely prevents direct structure-to-structure pounding but on the account of amplifying its acceleration and drift responses. However, such amplified responses might lead to only minor or moderate structural damage under sever NF earthquakes with 1.20g peak ground acceleration. Nevertheless, such damage could be avoided entirely using stiffer RNC isolators to achieve reduction of seismic response up to 69.0% under the same severe loading conditions and limited seismic gaps with no seismic pounding. Consequently, the RNC isolator could be an efficient solution for aseismic design in NF zones considering limited seismic gaps.

Optimum tuned mass damper approaches for adjacent structures

Pounding of adjacent structures are always a notable reason for damages after strong ground motions, but it is already unforeseen detail in newly constructed structures. Thus, several approaches have been proposed in order to prevent the pounding of structures. By using optimally tuned mass dampers, it is possible to decrease the displacement vibrations of structures. But in adjacent structures, the response of both structures must be considered in the objective function of optimization process. In this paper, two different designs of Tuned Mass Dampers (TMD) are investigated. The first design covers independent TMDs on both structures. In the second design, adjacent structures are coupled by a TMD on the top of the structures. Optimum TMD parameters are found by using the developed optimization methodology employing harmony search algorithm. The proposed method is presented with single degree of freedom and multiple degree of freedom structures. Results show that the coupled design is not effective on multiple degree of freedom adjacent structures. The coupled design is only effective for rigid structures with a single degree of freedom while the use of independent TMDs are effective on both rigid and flexural structures.

Passive and hybrid mitigation of potential near-fault inner pounding of a self-braking seismic isolator

A seismic isolated structure is usually a long-period structural system, which may encounter a low-frequency resonance problem when subjected to a near-fault earthquake that usually has a long-period pulse-like waveform. This long-period wave component may result in an enlargement of the base displacement and a decrease of the isolation efficiency. To overcome this problem, a rolling-based seismic isolator, referred to as roll-n-cage (RNC) isolator, has been recently proposed. The RNC isolator has a built-in buffer (braking) mechanism that limits the peak isolator displacements under severe earthquakes and prevents adjacent structural pounding. This paper addresses the problem of passive and hybrid mitigation of the potential inner pounding of the self-braking RNC isolator under near-fault earthquakes. Numerical results show that the RNC isolator can intrinsically limit the isolator displacements under near-fault earthquakes with less severe inner pounding using additional hysteretic damping and active control forces.

An isolation system for limited seismic gaps in near‐fault zones

SummaryThe ability of a recently proposed seismic isolation system, with inherent self‐stopping mechanism, to mitigate or even eliminate seismic pounding of adjacent structures is investigated under severe near‐fault earthquakes. The isolation system is referred to as roll‐in‐cage (RNC) isolator. It is a rolling‐based isolator that provides in one unit the necessary functions of vertical rigid support, horizontal flexibility with enhanced stability, hysteretic energy dissipation, and resistance to minor vibration loads. In addition, the RNC isolator is distinguished by a self‐stopping (buffer) mechanism to limit the bearing displacement under excitations stronger than a design earthquake or at limited seismic gaps, and a linear gravity‐based self‐recentering mechanism to prevent permanent bearing displacement without causing vertical fluctuation of the isolated structure. A previously developed multifeature SAP2000 model of the RNC isolator is improved in this paper to account for the inherent buffer mechanism's damping. Then, the effectiveness of the isolator's buffer mechanism in limiting peak bearing displacements is studied together with its possibly arising negative influence on the isolation efficiency. After that, the study investigates how to alleviate or even eliminate those possibly arising drawbacks, due to the developed RNC isolator's inner pounding as a result of its buffer activation, to achieve efficient seismic isolation with no direct structure‐to‐structure pounding, considering limited seismic gaps with adjacent structures and near‐fault earthquakes. The results show that the RNC isolator could be an efficient solution for aseismic design in near‐fault zones considering limited seismic gaps. Earthquake Engineering and Structural Dynamics. Copyright © 2014 John Wiley & Sons, Ltd.

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.