Pounding Response Research Articles

Multi-Sided Pounding Response of Bridge Structures with Non-Linear Bearings to Spatially Varying Ground Excitation

Considerable research of pounding effect on adjacent structures has been conducted in the past. However, most of them neglected the effect of multi-sided poundings. In bridges multiple adjacent bridge structures are common. Consequently, restraint due to additional neighbouring bridge structures cannot be avoided. This study addresses the effect of multi-sided pounding on structural responses due to spatially varying ground movements. Additional effect of non-linear bearing supports of the girders is also considered. The ground motions were simulated stochastically according to the Newmark-Hall spectrum. The result shows that in order to estimate the pounding and bearing forces as well as unseating potential of the girders realistically a consideration of non-uniform ground motions, end-restraint effect and non-linear girder bearings is necessary.

A Hertz contact model with non-linear damping for pounding simulation

This paper investigates the cogency of various impact models in capturing the seismic pounding response of adjacent structures. The analytical models considered include the contact force-based linear spring, Kelvin and Hertz models, and the restitution-based stereomechanical approach. In addition, a contact model based on the Hertz law and using a non-linear hysteresis damper (Hertzdamp model) is also introduced for pounding simulation. Simple analytical approaches are presented to determine the impact stiffness parameters of the various contact models. Parameter studies are performed using two degree-of-freedom linear oscillators to determine the effects of impact modelling strategy, system period ratio, peak ground acceleration (PGA) and energy loss during impact on the system responses. A suite of 27 ground motion records from 13 different earthquakes is used in the analysis. The results indicate that the system displacements from the stereomechanical, Kelvin and Hertzdamp models are similar for a given coefficient of restitution, despite using different impact methodologies. Pounding increases the responses of the stiffer system, especially for highly out-of-phase systems. Energy loss during impact is more significant at higher levels of PGA. Based on the findings, the Hertz model provides adequate results at low PGA levels, and the Hertzdamp model is recommended at moderate and high PGA levels. Copyright © 2006 John Wiley & Sons, Ltd.

Effect of Frame-Restoring Force Characteristics on the Pounding Response of Multiple-Frame Bridges

This study examines the effect of column hysteretic behavior on the impact response of adjacent frames in multiple-frame bridges. A simplified planar analytical bridge model is developed including inelastic frame action, nonlinear hinge behavior, and abutment effects. Pounding is simulated using a stereomechanical approach. The frame hysteretic models considered include the elasto-plastic and bilinear (traditional), Q-Hyst (stiffness-degrading), and pivot hysteresis (strength-degrading) models. Analytical studies conducted on adjacent bridge frames reveal that the traditional models underestimate the stiff frame displacement amplification due to pounding, and overestimate the flexible frame displacement amplification, when compared with other hysteretic models. A stiffness-degrading model is recommended to accurately estimate the pounding response of bridge frames subjected to far-field ground motion. The use of a strength-degrading model increases the stiff frame displacement amplification by 125% when compared to the stiffness-degrading model for highly out-of-phase frames, and is recommended in the presence of near-field ground motions.

Study of SSI and non-uniform ground motion effect on pounding between bridge girders

Abstracts This paper addresses the effect of spatial variations of ground motion with different wave propagation apparent velocities in soft and medium soil, and the influence of soil–structure interaction (SSI) on the pounding response of two adjacent bridge frames. Spatial ground motion time histories are simulated according to the Japanese design spectra and an empirical coherency loss function. In order to obtain a more reliable conclusion, three sets of spatial ground motions are independently simulated for each considered case. The ensemble mean girder responses obtained from the three independent time history analyses are used for the evaluation of the gap size required to avoid pounding between the bridge girders. The pounding behaviour of girders is analysed by using a combined finite element and boundary element method. The study reveals that both the ground motion spatial variation and SSI should be considered in the analysis of pounding responses of bridge girders.

Implications of seismic pounding on the longitudinal response of multi-span bridges—an analytical perspective

Seismic pounding between adjacent frames in multiple-frame bridges and girder ends in multi-span simply supported bridges has been commonly observed in several recent earthquakes. The consequences of pounding include damage to piers, abutments, shear keys, bearings and restrainers, and possible collapse of deck spans. This paper investigates pounding in bridges from an analytical perspective. A simplified nonlinear model of a multiple-frame bridge is developed including the effects of inelastic frame action and nonlinear hinge behavior, to study the seismic response to longitudinal ground motion. Pounding is implemented using the contact force-based Kelvin model, as well as the momentum-based stereomechanical approach. Parameter studies are conducted to determine the effects of frame period ratio, column hysteretic behavior, energy dissipation during impact and near source ground motions on the pounding response of the bridge. The results indicate that pounding is most critical for highly out-of-phase frames and is not significant for frame period ratios greater than 0.7. Impact models without energy dissipation overestimate the displacement and acceleration amplifications due to impact, especially for elastic behavior of the frames. Representation of stiffness degradation in bridge columns is essential in capturing the accurate response of pounding frames subjected to far field ground motion. Finally, it is shown that strength degradation and pounding can result in significant damage to the stiffer frames of the bridge when subjected to large acceleration pulses from near field ground motion record.

Effect of simultaneous spatial near-source ground excitation and soil on the pounding response of bridge girders

Effect of simultaneous spatial near-source ground excitation and soil on the pounding response of bridge girders

Effect of Pounding and Restrainers on Seismic Response of Multiple-Frame Bridges

Pounding between adjacent frames in a multiple-frame bridge produces undesirable forces resulting in large displacements, local damage, and possible failure of column bents. In this study, analytical models are used to examine the factors affecting the global response of a multiple-frame bridge due to pounding of adjacent frames. Parameter studies of one-sided and two-sided pounding are conducted to determine the effects of frame stiffness ratio, ground motion characteristics, frame yielding, and restrainers on the pounding response of bridge frames. It is determined that the most important parameters are the frame period ratio and the characteristic period of the ground motion. The amplification in the frame response due to one-sided pounding is most severe for cases with highly out-of-phase frames, in particular for short period structures. Two-sided pounding amplifies the stiff frame response, and reduces the flexible frame response. The addition of restrainers has a minor effect on the one-sided pounding response of highly out-of-phase frames. Current recommendations by Caltrans for limitations in frame period ratios to reduce the effects of pounding are evaluated through an example case.

Influence of soil-structure interaction on pounding response of adjacent buildings due to near-source earthquakes

A numerical approach to analyse pounding responses of adjacent buildings on subsoil to earthquakes is presented. The nonlinear calculation of the soil-structure system is performed subsequently in the Laplace and the time domain. The adjacent buildings and the subsoil are described by finite elements and boundary elements, respectively. In the numerical investigation the effect of Kobe, Northridge and Chi-Chi near-source earthquakes is considered. The result reveals that both the subsoil and long-period pulses in the ground motions can increase the pounding potential of buildings. In addition, poundings can amplify the induced floor vibrations. In contrast, soil-structure interaction has reduction effect on the induced vibrations. In order to estimate the distance required to prevent pounding the influence of the soil-structure interaction is significant.

Seismic pounding of a case of adjacent multiple-storey buildings of differing total heights considering soil flexibility effects

Collisions between adjacent structures due to insufficient separation gaps have been witnessed in almost every major earthquake since the 1960's. Although many analytical, numerical and experimental studies have been conducted into the pounding phenomenon, the number of those which take into account the effects of the underlying soil mass on the dynamic response of the colliding structures are almost negligible. The present study incorporates the effects of soil flexibility on the inelastic dynamic response of a particular case of adjacent 12- and 6-storey reinforced concrete moment-resisting frames. The time- history response of this system (linear soil behaviour and nonlinear structural response) subjected to actual earthquake records is evaluated by means of the structural analysis software RUAUMOKO developed at the University of Canterbury. A simple mass-spring-dashpot model is used to represent the frequency independent dynamic soil properties. Impacts at storey levels only are considered.
 This study highlights serious inconsistencies in the assumptions of previous pounding studies, which neglect the effects of soil flexibility. Also, the pounding response of the adjacent structures is found to be highly sensitive to the characteristics and direction of the seismic excitation.

Pounding Response of Adjacent Buildings Subjected to Spatial Earthquake Ground Excitations

Pounding damage is a serious seismic hazard in highly populated areas during major earthquakes. This paper evaluates the effect of earthquake ground motion spatial variations on pounding responses of adjacent structures. Adjacent structures are modeled as two single-degree-of-freedom (SDOF) oscillators with multiple supports. Pounding effects are simulated by spring-dashpot pounding elements. Linear elastic and nonlinear inelastic responses are considered in the analysis. Spatial ground motion input is stochastically simulated. The simulated spatial ground motion time histories are compatible with Newmark and Hall design spectrum individually and with an empirical coherency function between each other. The Newmark method with constant acceleration assumption is employed in step-by-step integration to calculate structural response. Numerical results are presented and discussed in terms of various structural and ground motion parameters.

Three-Dimensional Simulation of Structural Pounding during Earthquakes

A three-dimensional model is developed for the simulation of the pounding response of two or more adjacent buildings during earthquakes. The contact-impact problem is treated by the Lagrange multiplier method. The structures are modeled as multiple-degree-of-freedom systems with finite elements and with the possibility of contact between slabs or slabs and columns. Contact points are not known a priori, and are located through a searching procedure among the candidate contact surfaces. The dynamic equilibrium equations of contact follow an iterative formulation at each time step to account for the current contact conditions. With this three-dimensional idealization, the effect of various in-plan configurations of adjacent buildings as well as the induced deformations due to torsion during pounding are investigated for two real earthquake motions.

Analytical prediction of experimental building pounding

AbstractValuable insights on the problem of seismic pounding have been obtained recently from analytical studies. So far, the proposed analytical models have not been validated experimentally. This paper presents the results of shake table tests of pounding between adjacent three‐ and eight‐storey single‐bay steel framed model structures. The pounding response of the frames was measured for various earthquake intensities and initial separations. The experimental results were compared to the predictions resulting from two existing pounding analysis programs. The solution strategy of the first program, SLAM‐2, is based on a modal superposition technique. The second program, PC‐ANSR, is a non‐linear time‐step analysis code in which an elastic gap element has been included. Modelling the pounding effect by elastic gap elements in the two programs produced accurate displacement and impact force results. Amplitudes of short acceleration pulses were not well predicted, however, for practical time‐step increments. Relative rotations between adjacent floors induced grinding contacts which cannot be captured by uni‐axial gap elements.

Seismic Analysis of Base-Isolated San Bernardino County Building

The authors investigate the seismic behavior of an existing base isolated building and interpret its recorded response to the 1990 Upland California earthquake. They formulate a linear-elastic model that accurately represents the building during the earthquake and infer its response behaviors. Additional analyses using severe earthquake excitations demonstrate the building behavior in major events and hypothetical seismic gap pounding situations. Key findings include the following: • The Upland earthquake resulted in relatively low intensity shaking at the site, and the building did not exhibit a classic soft story effect in the isolation system. • A linear-elastic model can accurately idealize the building during this event. • Under major earthquake excitation, base isolation can lead to peak story drifts, shears, overturning moments, and accelerations that are much smaller than those of nonisolated buildings. • Pounding at seismic gaps can produce large story drifts, shears and accelerations. These peak pounding responses can be greater than those from nonisolated buildings (i.e., having no pounding).

A lagrange multiplier solution method for pounding of buildings during earthquakes

AbstractAn effective solution method for studying the pounding response of two or more adjacent buildings during earthquakes is presented. The method is based on the Lagrange multiplier approach by which the geometric compatibility conditions due to contact are enforced. The energy and momentum balance criteria for the contacting bodies are satisfied according to the laws of impact with proper post‐impact conditions, which can also take into account local energy absorption phenomena during impact. A solution scheme is proposed which can be incorporated easily into existing computer programs for static and dynamic analysis of structures. The applicability of the algorithm is illustrated in a number of selected sample problems and the correlation of numerical results to analytical solutions, whenever possible, is very satisfactory.