Pounding Force Research Articles

Transient responses of girder bridges with vertical poundings under near‐fault vertical earthquake

SummaryPrevious studies on pounding responses of bridge structures mainly focus on the horizontal pounding between adjacent structures. However, the vertical pounding responses of bridge are rarely studied. The aim of this paper is develop a theoretical approach to investigate the transient behavior of continuous bridge under near‐fault vertical ground motions. The transient behavior of bridge manifests as the earthquake‐induced response wave and pounding‐induced response wave travel throughout bridge. Based on a new continuous model of beam–spring–rod, the theoretical solution of bridge responses involving multiple vertical poundings is derived by the expansion of transient wave functions in a series of eigenfunctions. A new theoretical solving approach of the multiple vertical pounding forces is presented based on the transient internal force on the contact surface of the girder and bearing. The numerical results show that the present method can reasonably capture the propagations of the earthquake‐induced response wave and pounding‐induced response wave. The calculations of pounding force by the present method are convergence of the time‐step size and truncation number of wave modes. As the effect of transient wave is taken into account, the numerical results show several transient phenomena involving the vertical pounding, the high pounding force, the multiple‐pounding phenomenon, the vertical separation of girder from the bearing, the dependence of poundings on earthquake period and the narrow period window of poundings. Copyright © 2015 John Wiley & Sons, Ltd.

SEISMIC POUNDING BETWEEN ADJACENT RC BUILDINGS WITH AND WITHOUT BASE ISOLATION SYSTEM

Among the possible structural damages during an earthquake, the seismic induced pounding also has been one of the commonly observed phenomena. This is because the separation gap between many adjacent buildings is inadequate to accommodate the relative motions, so buildings vibrate out of phase and collides. Despite the fact that the seismic pounding between nearby structures is considered in the codal procurements, the act of development is still an issue in numerous metropolitan zones where the structures are built with no adequate partition separation which brings about their pounding. In this study E-Tabs nonlinear software is used for simulation of adjacent multi-storeyed RC frame buildings of G+14 and G+9 storey, the provisions that may reduce the effects of pounding like the separation distance, addition of shear walls, lateral bracings and variation in storey height of the buildings have been considered for analysis. And the responses like storey-displacement and pounding force by considering both fixed base and base-isolated conditions are arrived.

Dimensional analysis of earthquake-induced pounding between adjacent inelastic MDOF buildings

In this study the seismic pounding response of adjacent multi-degree-of-freedom (MDOF) buildings with bilinear inter-story resistance characteristics is investigated through dimensional analysis. The application of dimensional analysis leads to a condensed presentation of the response, and the remarkable self-similarity property for bilinear MDOF buildings with inelastic collision is uncovered. It is shown that when the response is expressed in the appropriate dimensionless form, response spectra for any intensity of the excitation collapse to a single master curve. The reduced Π set explicitly describes the interaction between the colliding structures. The effect of pounding on the MDOF building’s response is illustrated using three well-divided spectral regions (amplified, de-amplified and unaffected regions). Parametric studies are conducted to investigate the effects of the story stiffness of structures, the story stiffness ratio and mass ratio of adjacent buildings, the structural inelastic characteristics and the gap size values. Results show that (i) the influence of system stiffness ratio to the lighter and more flexible building is more significant in the first spectral region, where the maximum response of the building is amplified because of pounding; and (ii) the velocity and pounding force of the heavier and stiffer building is unexpectedly sensitive to the mass ratio of adjacent buildings.

Evaluation on Impact Interaction between Abutment and Steel Girder Subjected to Nonuniform Seismic Excitation

This paper aims to evaluate the impact interaction between the abutment and the girder subjected to nonuniform seismic excitation. An impact model based on tests is presented by taking material properties of the backfill of the abutment into consideration. The conditional simulation is performed to investigate the spatial variation of earthquake ground motions. A two-span continuous steel box girder bridge is taken as the example to analyze and assess the pounding interaction between the abutment and the girder. The detailed nonlinear finite element (FE) model is established and the steel girder and the reinforced concrete piers are modeled by nonlinear fiber elements. The pounding element of the abutment is simulated by using a trilinear compression gap element. The elastic-perfectly plastic element is used to model the nonlinear rubber bearings. The comparisons of the pounding forces, the shear forces of the nonlinear bearings, the moments of reinforced concrete piers, and the axial pounding stresses of the steel girder are studied. The made observations indicate that the nonuniform excitation for multisupport bridge is imperative in the analysis and evaluation of the pounding effects of the bridges.

Pounding between adjacent buildings of varying height coupled through soil

Pounding between adjacent buildings is a significant challenge in metropolitan areas because buildings of different heights collide during earthquake excitations due to varying dynamic properties and narrow separation gaps. The seismic responses of adjacent buildings of varying height, coupled through soil subjected to earthquake-induced pounding, are evaluated in this paper. The lumped mass model is used to simulate the buildings and soil, while the linear visco-elastic contact force model is used to simulate pounding forces. The results indicate while the taller building is almost unaffected when the shorter building is very short, it suffers more from pounding with increasing height of the shorter building. The shorter building suffers more from the pounding with decreasing height and when its height differs substantially from that of the taller building. The minimum required separation gap to prevent pounding is increased with increasing height of the shorter building until the buildings become almost in-phase. Considering the soil effect; pounding forces are reduced, displacements and story shears are increased after pounding, and also, minimum separation gap required to prevent pounding is increased.

Discussion on ‘relaxation method for pounding action between adjacent buildings at expansion joint’ by H. Takabatake, M. Yasui, Y. Nakagawa and A. Kishida

SUMMARYThe paper under discussion presents a detailed study on the reduction of pounding force on buildings due to expansion joints being filled with rubber. From shake table experiments and numerical simulations, the authors of the paper concluded that the rubber can reduce the maximum pounding force and hence the pounding damage to buildings. However, the writers of this short communication observed some significant issues in the experimental results as well as the numerical simulations. These observations are presented and raise questions about the validity of the results and the subsequent conclusions. Copyright © 2014 John Wiley & Sons, Ltd.

Effectiveness of using rubber bumper and restrainer on mitigating pounding and unseating damage of bridge structures subjected to spatially varying ground motions

Pounding and unseating damages to bridge decks have been observed in almost all the previous major earthquakes. Recent studies have highlighted that adjusting the fundamental periods of adjacent structural elements close to each other, the only method suggested by the codes to mitigate pounding and unseating damage, is not sufficient to prevent such damages owing to the relative displacement induced by spatially varying ground motions. As pounding and unseating damage could lead to significant loss of economy and life owing to inability to quickly access the damaged area immediately after an earthquake, it is important to protect lifeline bridge structures. Past earthquakes have revealed that the commonly used steel cable restrainers have limited effectiveness. Additionally, only limited research has focused on mitigating pounding forces on the bridge joints that lead to localized damages and disruptions of the serviceability of the bridge after strong shakings. This study presents an extensive investigation on the effectiveness of combining rubber bumpers as a shock absorbing device along with Shape Memory Alloy (SMA) or steel cable restrainers to mitigate pounding and unseating damages on multiple-span bridges subjected to spatially varying ground motions. The responses of bridge structures with different restraining devices acting alone and in combination with rubber bumpers subjected spatially varying ground motions are compared and discussed. The result indicates that the SMA restrainers combined with rubber bumpers could lead to better performance in terms of reduction of joint opening and mitigation of large pounding forces.

Limitations in Simulation of Building Pounding in Earthquakes

Several methods have been proposed for the analysis of building pounding. In previous studies some of these models have been considered in isolation, while others have been studied as a specific configuration of buildings. Although the pounding force predicted by each model varies significantly, results from the evaluation of these models have been inconclusive. This leads to uncertainties in the practical applications of pounding force models. This study addresses the limitations in numerical and experimental simulations of building pounding. The Sears impact model is suggested to overcome some of these limitations. It is concluded that contact stiffness and coefficient of restitution are the main reason for the diverse numerical results, while differences observed in the experiments could be due to sampling rate and instrumental constraints.

A generic structural pounding model using numerically exact displacement proportional damping

Pounding damage in bridges and buildings range from minor aesthetic effects up to major structural damage inducing building collapse or bridge girder’s unseating. This study proposes the Hunt–Crossley model, a generic model that can have either a linear or nonlinear force–deformation relationship, for the analysis of building pounding. This model has been extensively employed in Mechanical Engineering. There are several approximate solutions for the damping of the model and one of them has been introduced as the ‘Hertzdamp’ model for structural pounding analysis. The exact solution of damping constant for this model has been presented here. The performance of the linear and nonlinear Hunt–Crossley models in simulating impact force between concrete bodies is compared against other existing pounding models, namely: linear viscoelastic, nonlinear viscoelastic and modified linear viscoelastic models. The nonlinear Hunt–Crossley model best predicted the contact force while the linear Hunt–Crossley model had twice the normalized error of the Hertzdamp model, which was still only half as much as the error in other three models. Finally, a numerical simulation of pounding of bridge segments at an expansion joint is conducted with all models. It was observed that the pounding force predictions from Hunt–Crossley models are similar to that obtained in impact experiments while other models produced very different force developments. The Hunt–Crossley models do not have the discontinuities i.e. negative force, instantaneously high initial force or discontinuous transition between deformation and restitution phases of impact which are present in the other models.

Damage assessment of adjacent buildings under earthquake loads

This paper deals with damage assessment of adjacent colliding buildings under strong ground motion. In previous studies, the structure input-response pair is used to examine pounding effects on adjacent buildings under seismic loads. In this paper, pounding of adjacent buildings is assessed using input energy, dissipated energy and damage indices. Damage indices (DI) are computed by comparing the structure’s responses demanded by earthquakes and the associated structural capacities. Damage indices provide quantitative estimates of structural damage level, and thus, a decision on necessary repair can be taken. Adjacent buildings with fixed-base and isolated-base are considered. The nonlinear viscoelastic model is used for capturing the induced pounding forces. Influences of the separation distance between buildings, buildings properties, such as, base-condition (fixed or isolated), and yield strength on damage of adjacent buildings are investigated. The set of input ground motions includes short-, moderate- and long-duration accelerograms measured at near-fault and far-fault regions with different soil types. Earthquake records with different characteristics are considered to study damage of adjacent buildings under seismic loads. Numerical illustrations on damage of fixed-base and isolated-base adjacent buildings with elastic–plastic force–deformation relation are provided.

Mitigation measures for earthquake induced pounding effects on seismic performance of adjacent buildings

Post-earthquake damages investigation in past and recent earthquakes has illustrated that the building structures are vulnerable to severe damage and/or collapse during moderate to strong ground motion. Among the possible structural damages, seismic induced pounding has been commonly observed in several earthquakes. A parametric study on buildings pounding response as well as proper seismic hazard mitigation practice for adjacent buildings is carried out. Three categories of recorded earthquake excitation are used for input excitations. The effect of impact is studied using linear and nonlinear contact force model for different separation distances and compared with nominal model without pounding consideration. The severity of the impact depends on the dynamic characteristics of the adjacent buildings in combination with the earthquake characteristics. Pounding produces acceleration and shear forces/stresses at various story levels that are greater than those obtained from the no pounding case, while the peak drift depends on the input excitation characteristics. Also, increasing gap width is likely to be effective when the separation is sufficiently wide to eliminate contact. Furthermore, it is effective to provide a shock absorber device system for the mitigation of impact effects between adjacent buildings with relatively narrow seismic gaps, where the sudden changes of stiffness during poundings can be smoothed. This prevents, to some extent, the acceleration peaks due to impact. The pounding forces exerted on the adjacent buildings can be satisfactorily reduced.

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.

Park-Angov indeks oštećenja sudara susjednih čeličnih okvirnih konstrukcija

The pounding of two adjacent 3-bay and 5-bay 5-storey frames is studied in this paper. These frames are analysed under eight different ground motions in two leftto-right and right-to-left directions for 17 separations between them. Park- Ang damage indices of adjacent frames are studied. The results show that the use of elastic impact elements is generally conservative. The direction of ground motion influences the level of damage of colliding structures. The separation equalling to 1% of storey height can eliminate or strongly decrease pounding force.

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.

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.

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.

Earthquake-induced pounding between equal height multi-storey buildings considering soil-structure interaction

The present paper investigates the coupled effect of the supporting soil flexibility and pounding between neighbouring, insufficiently separated equal height buildings under earthquake excitation. Two adjacent three-storey structures, modelled as inelastic lumped mass systems with different structural characteristics, have been considered in the study. The models have been excited using a suit of ground motions with different peak ground accelerations and recorded at different soil types. A nonlinear viscoelastic pounding force model has been employed in order to effectively capture impact forces during collisions. Spring-dashpot elements have been incorporated to simulate the horizontal and rotational movements of the supporting soil. The results of the numerical simulations, in the form of the structural nonlinear responses as well as the time-histories of energy dissipated during pounding-involved vibrations, are presented in the paper. In addition, the variation in storeys peak responses and peak dissipated energies for different gap sizes are also shown and comparisons are made with the results obtained for colliding buildings with fixed-base supports. Observations regarding the incorporation of the soil-structure interaction and its effect on the responses obtained are discussed. The results of the study indicate that the soil-structure interaction significantly influences the pounding-involved responses of equal height buildings during earthquakes, especially the response of the lighter and more flexible structure. It has been found that the soil flexibility decreases storey peak displacements, peak impact forces and peak energies dissipated during vibrations, whereas it usually leads to the increases in the peak accelerations at each storey level.

Seismic Control of Power Transmission Tower Using Pounding TMD

Lattice transmission towers are vital components of transmission line systems, which play an important role in the operation of electrical power systems. This paper proposes a new type of tuned mass damper (TMD), the pounding tuned mass damper (PTMD), to upgrade the seismic resistant performance of a transmission tower. In the PTMD, a limiting collar with viscoelastic material laced on the inner rim is installed to restrict the stroke of the TMD and to dissipate energy through collision. The pounding force is modeled based on the Hertz contact law, whereas the pounding stiffness β is estimated in a small-scale test. A multimass model of a 55-m tower is established to verify the effectiveness of the PTMD numerically. Harmonic excitation and time-history analysis demonstrate the PTMD’s superiority over the traditional TMD. Finally, a parametric study is performed for the optimal design.

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

Structural Pounding Detection by Using Wavelet Scalogram

Structural pounding can cause considerable damage and even lead to collapse of structures. Most research focuses on modeling, parameter investigation, and mitigation approaches. With the development of structural health monitoring, the on-line detection of pounding becomes possible. The detection of pounding can provide useful information of potential damage of structures. This paper proposed using wavelet scalograms of dynamic response to detect pounding and examined the feasibility of this method. Numerical investigations were performed on a pounding system that consisted of a damped single-degree-of-freedom (SDOF) structure and a rigid barrier. Hertz contact model was used to simulate pounding behavior. The responses and pounding forces of the system under harmonic and earthquake excitations were numerically solved. The wavelet scalograms of acceleration responses were used to identify poundings. It was found that the scalograms can indicate the occurrence of pounding and occurrence time very well. The severity of the poundings was also approximately estimated. Experimental studies were carried out, in which shake table tests were conducted on a bridge model that underwent pounding between its different components during ground motion excitation. The wavelet scalograms of the bridge responses indicated pounding occurrence quite well. Hence the conclusions from the numerical studies were verified experimentally.