Pounding Effect Research Articles

Pounding Effects on the Earthquake Response of Adjacent Reinforced Concrete Structures Strengthened by Cable Elements

Abstract A numerical approach for estimating the effects of pounding (seismic interaction) on the response of adjacent Civil Engineering structures is presented. Emphasis is given to reinforced concrete (RC) frames of existing buildings which are seismically strengthened by cable-elements. A double discretization, in space by the Finite Element Method and in time by a direct incremental approach is used. The unilateral behaviours of both, the cable-elements and the interfaces contact-constraints, are taken strictly into account and result to inequality constitutive conditions. So, in each time-step, a non-convex linear complementarity problem is solved. It is found that pounding and cable strengthening have significant effects on the earthquake response and, hence, on the seismic upgrading of existing adjacent RC structures.

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.

Earthquake Induced Pounding-Involved Response of Base-Isolated Buildings Incorporating Soil Flexibility

This research aims to get some insight into the influence of supporting soil on the seismic response of base-isolated buildings impacting with the neighbouring retaining wall. Two ground motion records from two different regions are used as excitations. A nonlinear impact model is incorporated to capture the pounding force. In addition, an efficient discrete-element model is applied to represent the rotational and horizontal movements of the soil. The dynamic response of the isolated building resting on different flexible base soils and hits the adjacent abutment and the corresponding response of the building resting on a rigid base soil are presented. Analysis of the results expressed in the form of time-history and peak response for various values of structural natural periods, gap sizes, and base-isolated periods is carried out. The results show a considerable influence of the simultaneous effect of base-isolated pounding and base soil flexibility on the dynamic response of isolated buildings during earthquakes.

SEISMIC POUNDING OF MULTISTOREYED BUILDINGS

The investigations made by past and present earthqu ake seismologist have shown that during earthquake, the building structures are vulnerable to severe damages. The adjacent building s collide and collapse during moderate to strong gr ound vibrations caused by earthquakes. Actually, the separation distance of m any buildings is n adequate to accommodate their re lative motions, so building vibrate out of phase and collapse. Among the possib le structural damages the seismic induced pounding has been commonly observed phenomenon. In this paper, a systematic study regar ding pounding of building response as well as seism ic hazard mitigation practices like effect of different separation distances and e ffect of addition of shear walls are investigated inonlinear software. The results were obtained in the form of pounding force and point displacements. As the pounding effect va ries inversely with separation distance so by increasing separation distance pound ing effect is reduced greatly and hence damage to n eighboring buildings is minimized. Also, the provision of shear wall reduce s effect of pounding.

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.

Non-linear FEM analysis of seismic induced pounding between neighbouring multi-storey structures

Pounding of neighbouring construction of structures due to seismic excitation increases the damage of structural components or even causes collapse of structures. Among the possible building damages, earthquake induced pounding has been commonly observed in several earthquakes. Therefore it is imperative to consider pounding effect for structures. This study aims to understand the response behaviour of adjacent buildings with dissimilar heights under earthquake induced pounding. Effects of different separation distances between structures are also investigated. Nonlinear finite element analysis in time domain has been carried out for pounding of neighbouring structures having varying heights. To show the importance of avoiding pounding in structures the results obtained were compared with model having no pounding phenomena. The results were obtained in the form of storey shear, pounding force, storey drift, point displacement and acceleration. The acceleration at pounding level significantly increases during collision of building. The generated extra pounding force may cause severe damage to structural members of structures. Pounding produces shear at various story levels, which are greater than those obtained from no pounding case. Building with more height suffers greater damage than shorter building when pounding occurs. Increasing gap distance tends to reduce story shear in consistent manner. The results also show that the conventional modelling of building considering only beams and columns underestimates pounding effects. More realistic modelling such as beams, columns and slabs shall be adopted to accurately understand the pounding phenomenon.

Nonlinear analysis of pounding between decks of multi-span bridge subjected to multi-support and multi-dimensional earthquake excitation

The nonlinear analysis of pounding between bridge deck segments subjected to multi-support excitations and multi-dimensional earthquake motion was performed. A novel bottom rigid element (BRE) method of the current displacement input model for structural seismic analysis under the multi-support excitations was used to calculate structural dynamic response. In the analysis, pounding between adjacent deck segments was considered. The seismic response of a multi-span bridge subjected to the multi-support excitation, considering not only the traveling-wave effect and partial coherence effect, but also the seismic non-stationary characteristics of multi-support earthquake motion, was simulated using finite element method (FEM). Meanwhile, the seismic response of the bridge under uniform earthquake was also analyzed. Finally, comparative analysis was conducted and some calculation results were shown for pounding effect, under multi-dimensional and multi-support earthquake motion, when performing seismic response analysis of multi-span bridge. Compared with the case of uniform/multi-support/multi-support and multi-dimensional earthquake input, the maximum values of pounding force in the case of multi-support and multi-dimensional earthquake input increase by about 5–8 times; the absolute value of bottom moment and shear force of piers increase by about 50%–600% and 23.1%–900%, respectively. A conclusion can be given that it is very necessary to consider the pounding effect under multi-dimensional and multi-support earthquake motion while performing seismic response analysis of multi-span bridge.

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.

Effect of Eccentric Pounding on Elasto-Plastic Behavior of a Simply Supported Bridge under Transverse Earthquake

An increasing number of bridges have been built in earthquake zones, alonged with rapid development of high-speed railway. Their seismic behaviors attract researchers’ attention now. The steel shear keys as falling-off prevention measures have been used widely in 32m simply-supported box girder bridges on high-speed railways in China. To allow for transverse temperature movement, the shear keys are placed with a slight gap from the girders. However, out-of-phase vibrations between superstructures and substructures result in nonlinear eccentric pounding between bearing base and steel shear keys if the relative displacements exceed their initial gaps. The aim of this paper is to analyze the effect of eccentric pounding on elasto-plastic behavior of a simply-supported concrete box girder bridge under transverse earthquake, and evaluate the seismic performance of falling-off prevention measures. The effect of cushion block on seismic response has been studied. The results of the study indicate that a bridge column occur plastic deformation and suffer residual displacements due to eccentric pounding, and simple analysis in elastic range may result in nonconservative results. The lateral shear keys play a key role in limiting girder displacements. By setting hardwood blocks between steel shear keys and bearing base, the pounding forces can be appropriately reduced, and the lateral seismic performance of bridge can be effectively improved

Pounding of San Francisco-Type Soft-Story Corner Buildings

We investigated 1920s-era four-story wood-frame corner buildings common to San Francisco, many of which were damaged in the city's Marina District during the 1989 Loma Prieta earthquake. Such buildings can have relatively weak and flexible first stories and are referred to as soft-story buildings. We calibrated two building computer models to simulate actual earthquake response. We then performed computer analysis to assess collapse performance under 22 hypothetical pounding situations of both as-built and retrofitted soft-story buildings. For this building type, we found that a typical pounding situation increased the collapse rate by 14%, and for retrofitted versions, pounding slightly decreased the collapse rate. However, there were factors that appear to significantly increase the rate, especially in combination: negligible building separations and multiple adjacent buildings having low effective damping and large mass. Based on the results, we outline an approximate way to account for pounding within the context of current design procedures. An upper bound on the pounding effect was found to be equivalent to about a 30% increase in demand.

Experimental study of variable-frequency rocking bearings for near-fault seismic isolation

Near-fault earthquakes, which usually have a long-period pulse-like component, may result in excessive isolator displacement for a conventional isolation system, and consequently lead to an oversized isolator design or increase the risk of an isolation pounding effect. To alleviate these problems, seismic isolation using variable-frequency rocking bearings (VFRBs), which have variable mechanical property, are investigated experimentally in this study. A general VFRB has an axially symmetric rocking surface with variable curvature. By properly selecting the geometry of the rocking surface, the VFRB isolation frequency, which is independent of the super-structural mass, becomes variable and can be designed to meet the required specifications. To experimentally verify the VFRB isolation theory, a full-scale steel frame isolated by several prototype bearings is tested in this work by using a shaking table. To fabricate these bearings, a six-order polynomial function is proposed to define their rocking surface, so the bearings possess a relatively higher initial stiffness followed by softening mechanical behavior. The experimental results, which have very good agreement with the simulated ones, demonstrate that the prototype bearings exhibit the desired variable hysteretic property. The test results also show that the VFRB system with the proposed mechanical property is able to effectively suppress the excessive isolator displacement induced by a near-fault earthquake, while retaining a reasonably good isolation efficiency for the superstructure.

Pounding force response spectrum for near-field and far-field earthquakes

Inadequate separation distance between neighboring buildings with out-of-phase response would increase the probability of pounding during an earthquake and may cause severe damages to the structures. A rational estimation of the maximum impact force would help us to control the extent of damages in different structures. As a practical tool, the pounding force response spectrum, which shows the value of maximum impact force as a function of the structural vibration periods, is considered in this paper. It is well-known that strong ground motion in the near-field area has different characteristics from far-field ones. In this paper, pounding force response spectra for elastic structures subjected to near-field and far-field ground motions are presented. Both of the adjacent buildings were modeled simply as Single-Degree-Of-Freedom (SDOF) systems and pounding effect has been simulated by applying the nonlinear viscoelastic model. In the analysis, the effect of different parameters, such as mass, damping ratio has been studied. The effects of gap distance on maximum pounding force due to near- and far-field earthquake ground motions were investigated comprehensively. As a result, the characteristics of earthquake ground motions along with the properties of structures should be considered in gap distance controlling between adjacent buildings.

Utilization of object-oriented programming, design patterns and java for simulating earthquake-induced poundings of base-isolated buildings

Base-isolated buildings experience large horizontal relative displacements during strong earthquakes due to the excessive fl exibility that is purposely incorporated, through seismic bearings, at their bases. When the available clearance around a base-isolated building is limited, there is a possibility of the building pounding against the surrounding moat wall or adjacent structures. Considering the nonlinearities involved in this structural impact problem, it is evident that the effects of potential pounding on the overall seismic response of base-isolated buildings during earthquake excitations should be investigated numerically through appropriate simulations. Object-oriented programming (OOP), design patterns (DPs), and the Java programming language have been utilized in order to design and implement a fl exible and extendable software application that can be effectively used to perform the necessary numerical simulations and parametric studies of base-isolated buildings that may experience structural poundings during earthquake excitations. The aim of this paper is twofold: (i) to explain the signifi cant advantages of utilizing OOP, DPs, and Java in structural analysis software and (ii) to use the developed software to study earthquake-induced poundings of base-isolated buildings.

A Numerical Study on Impact Damage Assessment and Dynamic Behaviour of Concrete Bridges by Pounding Effect

The South Hyogo prefecture earthquake indicated that various kind of damage was incurred under severe ground motion. Some of the reported damage cases are caused by pounding between bridge girders and between a superstructure and an abutment. To establish the reasonable and safe seismic design for bridges, it is necessary to evaluate the damage level of bridge abutment under impact of bridge girder and to clarify dynamic behaviour of whole bridge under pounding. So the main objective of this study is to evaluate the damage level of an abutment by pounding. To achieve this, impact response analyses of pounding effect were conducted by using 3-dimensional FEM. Furthermore, to clarify dynamic behavior of whole bridge under pounding, frame analyses were conducted.

Effects of Pounding and Skewness on Seismic Responses of Typical Multispan Highway Bridges Using the Fragility Function Method

This paper uses the fragility function method to study the effects of pounding and skewness on the seismic behaviors of typical multispan RC highway bridges. Three-dimensional numerical models are built for typical three-span bridges in California that include nonlinear pier columns, distributed gap elements simulating pounding at both expansion joints and end abutments, and soil-structure interaction effects. The spatial differences of seismic excitations at various supports caused by varied soil profile properties and wave propagation effects, etc., are also included. As indicated by the nonlinear time history analyses using a large set of three-component earthquake ground motion records, fragility functions are derived and compared for bridges with various structural details, including the location of gaps, deck skew angle, and gap size. Although pounding causes significant local damage, the fragility functions show relatively moderate change in damage probability of the entire bridge. When pounding does not happen, skewed bridges outperform straight ones because of their coupled responses. For straight bridges, the pounding has a limited effect on bridge level damage and can be negligible. However, pounding results in increased damages of skewed bridges which aggravate with large skew angles. Using fragility functions, this paper clarifies the interactive roles of skewness and pounding for seismic damage probability of multispan highway bridges. These findings can provide valuable guidance for future bridge design.

A nonlinear impact model for simulating the use of rubber shock absorbers for mitigating the effects of structural pounding during earthquakes

SUMMARYDuring strong earthquakes, structural poundings may occur between adjacent buildings because of the limited separation distance and the deformations of their stories. A potential mitigation measure for this problem is the incorporation of layers of soft material, such as rubber, which can act as collision bumpers, in order to prevent the sudden impact pulses. In an effort to investigate the effectiveness of such an impact mitigation measure, relevant numerical simulations and parametric studies can be performed. However, none of the known impact models, which are available in the literature, is able to represent the usage of rubber bumpers with sufficient accuracy. The current study presents a simple but efficient methodology that can be used to simulate the incorporation of rubber layers between neighboring structures with relatively narrow seismic gaps. Such methodology will enable us to numerically investigate the effectiveness of using rubber bumpers to mitigate potential earthquake‐induced pounding. In particular, a new nonlinear inelastic force‐based impact model, able to appropriately describe the behavior of rubber under impact loading, taking also into account the limited thickness of the bumper, is introduced. Finally, a numerical example of simulating earthquake‐induced pounding between two multistory buildings with the consideration of rubber bumpers at impact locations is presented. 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.

Structural performance of a base‐isolated reinforced concrete building subjected to seismic pounding

SUMMARYThe effects of seismic pounding on the structural performance of a base‐isolated reinforced concrete (RC) building are investigated, with a view to evaluate the influence of adjacent structures and separation between structures on the pounding response. In particular, seismic pounding of a typical four‐story base‐isolated RC building with retaining walls at the base and with a four‐story fixed‐base RC building is studied. Three‐dimensional finite element analyses are carried out considering material and geometric nonlinearities. The structural performance of the base‐isolated building is evaluated considering various earthquake excitations. It is found that the performance of the base‐isolated building is substantially influenced by the pounding. The investigated base‐isolated building shows good resistance against shear failure and the predominant mode of failure due to pounding is flexural. Copyright © 2012 John Wiley & Sons, Ltd.

The 3D Seismic Pounding Effect of High-Pier Bridge Based on OpenSees

In this paper, a real high-piers bridge was taken as the example, the 3D nonlinear finite element model of this high-pier bridge is built based on OpenSees, then to do the analysis of seismic collision effects of the high-pier bridge under uniform excitation and multi-excitation considering the effect of traveling wave. And analyzing the reaction rule under different ground motions, and focusing on the differences of the effects of seismic pounding between uniform excitation and multi-excitation considering the effect of traveling wave. the seismic responses of high-pier bridge are closely related with its inherent dynamic characteristics and the spectral characteristics of ground motion and closer to the natural cycle of the bridge the main periods of ground motion is,greater the bridge collision response; traveling wave effect amplifies seismic pounding response, while the end of piers are adversely affected, exacerbating the damage. Although whether or not the traveling wave effect is harmful to the bearing, the traveling wave effect has obvious influences to bearing. Therefore, in the analysis of bridge seismic collision response it is necessary to consider traveling wave effect.