• Earthquakes and Structures
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• v.20 no.3
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• pp.295-307
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• 2021

The gap provided between adjacent structures in the metropolitan cities is mostly narrow due to architectural and financial issues. Consequently, structural pounding occurs between adjacent structures during earthquakes. It causes damages, ranging from minor local to more severe ones, especially in the case of seismically isolated buildings, due to their higher displacements. However, due to the increased flexibility of isolated buildings, the problem could become more detrimental to such structures. The effect of the seismic pounding of moat walls on the response of buildings isolated by Triple Friction Pendulum Bearing (TFPB) is investigated in this paper. To this propose, two symmetric three-dimensional models, including single-story and five-story buildings, are modeled in Opensees. Nonlinear Time History Analyses (NTHA) are performed for seismic evaluation. Also, five different sizes with four different sets of friction coefficients are considered for base isolators to cover a whole range of base isolation systems with various geometry configurations and fundamental period. The results are investigated in terms of base shear, buildings' drift, and roof acceleration. Results indicated a profound effect of poundings against moat walls. In situations of potential pounding, in some cases, the influence of impact on seismic responses of multistory buildings was more remarkable.

• Coupled systems mechanics
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• v.3 no.2
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• pp.213-232
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• 2014

Pounding is a major cause of bridge damage during earthquakes. In an extreme situation, it can even contribute to the unseating of bridge girders. Long-span bridges will inevitably experience spatially varying ground motions. Soil-structure interaction (SSI) may play a significant role in the structural response of these structures. The objective of this research is to experimentally investigate the effect of spatially varying ground motions on the response of a three-segment bridge considering SSI and pounding. To incorporate SSI, the model was placed on sand contained in sandboxes. The sandboxes were fabricated using soft rubber in order to minimise the rigid wall effect. The spatially varying ground motion inputs were simulated based on the New Zealand design spectra for soft soil, shallow soil and strong rock conditions, using an empirical coherency loss function. The results show that with pounding, SSI can amplify the pier bending moments and the relative opening displacements.

• Earthquakes and Structures
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• v.7 no.3
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• pp.385-400
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• 2014

Pounding damage to bridges and buildings is observed in most major earthquakes. The damage mainly occurs in reinforced concrete slabs, e.g. building floors and bridge decks. This study presents the results from pounding of reinforced concrete slabs. A parametric investigation was conducted involving the mass of the pendulums, the relative velocities of impact and the geometry of the contact surface. The effect of these parameters on the coefficient of restitution and peak impact acceleration is shown. In contrast to predictions from numerical force models, it was observed that peak acceleration is independent of mass. The coefficient of restitution is affected by the impact velocity, total participating mass and the mass ratio of striker and struck block.

• Earthquakes and Structures
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• v.18 no.2
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• pp.171-184
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• 2020

The potential of using the roof water tanks as a mitigation measure to minimize the required separation gap and induced pounding forces due to collisions is investigated. The investigation is carried out using nonlinear dynamic analysis for two adjacent 3-story buildings with different dynamic characteristics under two real earthquake motions. For such analysis, nonlinear viscoelastic model is used to simulate forces due to impact. The sloshing force due to water movement is modelled in terms of width of the water tank and the instantaneous wave heights at the end wall. The effect of roof water tanks on the story's responses, separation gap, and magnitude and number of induced pounding forces are investigated. The influence of structural stiffness and storey mass are investigated as well. It is found that pounding causes instantaneous acceleration pulses in the colliding buildings, but the existence of roof water tanks eliminates such acceleration pulses. At the same time the water tanks effectively reduce the number of collisions as well as the magnitude of the induced impact forces. Moreover, buildings without constructed water tanks require wider separation gap to prevent pounding as compared to those with water tanks attached to top floor under seismic excitations.

• Structural Engineering and Mechanics
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• v.10 no.6
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• pp.621-633
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• 2000

Dynamic responses of a bridge system with several simple spans under longitudinal seismic excitations are examined. The bridge system is modeled as the multiple oscillators and each oscillator consists of four degrees-of-freedom system to implement the poundings between the adjacent oscillators and the friction at movable supports. Pounding effects are considered by introducing the impact elements and a bi-linear model is adopted for the friction force. From the parametric studies, the pounding is found to induce complicated seismic responses and to restrain significantly the relative displacements between the adjacent units. The smaller gap size also restricts more strictly the relative displacement. It is found that the relative displacements between the abutment and adjacent pier unit became much larger than the responses between the inner pier units. Consequently, the unseating failure could take a place between the abutment and nearby pier units. It is also found that the relative displacements of an abutment unit to the adjacent pier unit are governed by the pounding at the opposite side abutment.

• Earthquakes and Structures
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• v.16 no.4
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• pp.437-453
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• 2019

This study investigates a new optimal placement method for viscous dampers between structures in order to prevent pounding of adjacent structures with different dynamic characteristics under earthquake effects. A relative displacement spectrum is developed in two single degree of freedom system to reveal the critical period ratios for the most risky scenario of collision using El Centro earthquake record (NS). Three different types of viscous damper design, which are classical, stair and X-diagonal model, are considered to prevent pounding on two adjacent building models. The objective function is minimized under the upper and lower limits of the damping coefficient of the damper and a target modal damping ratio. A new algorithm including time history analyses and numerical optimization methods is proposed to find the optimal dampers placement. The proposed design method is tested on two 12-storey adjacent building models. The effects of the type of damper placement on structural models, the critical period ratios of adjacent structures, the permissible relative displacement limit, the mode behavior and the upper limit of damper are investigated in detail. The results of the analyzes show that the proposed method can be used as an effective means of finding the optimum amount and location of the dampers and eliminating the risk of pounding.

• Earthquakes and Structures
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• v.7 no.4
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• pp.415-448
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• 2014

A method is presented in this paper to analyze the dynamic response behavior of suspended building structures. The effect of semi-rigid connections that link suspended floors with their supporting structure on structural performance is investigated. The connections, like the restrains in non-structural suspended components, are designed as semi-rigid to avoid pounding and as energy dissipation components to reduce structural response. Parametric study is conducted to assess the dynamic characteristics of suspended building structures with varying connection stiffness and suspended mass ratios. Modal analysis is applied to identify the two distinct sets of vibration modes, pendulum and bearing, of a suspended building structure. The cumulative modal mass is discussed to ensure the accuracy in applying the method of response spectrum analysis by SRSS or CQC modal combination. Case studies indicate that a suspended building having semi-rigid connections and proper suspended mass ratios can avoid local pounding failure and reduce seismic response.

• Earthquakes and Structures
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• v.12 no.1
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• pp.35-45
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• 2017

The current paper investigates the effect of the seismic pounding of neighboring buildings on the response of structures isolated by Triple Friction Pendulum Bearing (TFPB). To this end, a symmetric three-dimensional single story building is modeled for analysis with two specified levels of top deck and base deck, to capture the seismic response of the base isolators and building's roof. Linear elastic springs with different level of gaps are employed to calculate the impact between the buildings. Nonlinear Dynamic Time History Analyses (NDTHA) are conducted for seismic evaluation. Also, five different sizes with four different sets of friction coefficients are assumed for base isolators to cover a whole range of base isolation systems with various geometry configurations and fundamental period. The results are investigated in terms of base shear, buildings' drift and top deck acceleration of the superstructure. The results also indicate the profound effect of the stiffness of the adjacent buildings on the value of the impact they impose to the superstructure. Also, in situations of potential pounding, the increment of the fundamental period of the TFPB base isolator could intensify the impact force up to nearly five-fold.

• Journal of Korean Association for Spatial Structures
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• v.14 no.3
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• pp.75-84
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• 2014

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.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.5
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• pp.301-310
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• 2016

There are differences in seismic behavior between non-skewed bridges and skewed bridges due to in-plane rotations caused by pounding between the skewed deck and its abutments during strong earthquake. Many advances have been made in developing design codes and guidelines for dynamic analyses of non-skewed bridges. However, there remain significant uncertainties with regard to the structural response of skewed bridges caused by unusual seismic response characteristics. The purpose of this study is performing non-linear time history analysis of the bridges using abutment-soil interaction model considering pounding between the skewed deck and its abutments, and analyzing global seismic behavior characteristics of the skewed bridges to assess the possibility of unseating. Refined bridge model with abutment back fill, shear key and elastomeric bearing was developed using non-linear spring element. In order to evaluate the amplification of longitudinal and transverse displacement response, non-linear time history analysis was performed for single span bridges. Far-fault and near-fault ground motions were used as input ground motions. According to each parameter, seismic behavior of skewed bridges was evaluated.