Effectiveness of Elastomeric Bearings in Reducing Pounding Effects between Reinforced Concrete Buildings under Seismic Condition

Insufficient separation distance between adjacent buildings may lead to their pounding during strong earthquakes causing damage or local failure. Accordingly, most of the design codes specify a minimum separation or gap distance between adjacent buildings to prevent their seismic pounding. Main objectives of this research are studying the seismic pounding between adjacent reinforced concrete (RC) buildings under various ground motions and studying the effect of gap distance on seismic pounding. The studied buildings are modeled as three-dimensional frames to idealize the adjacent buildings. This study considers adjacent frame buildings having the same number of floors as well as frames having a different number of floors. Nonlinear finite element time history analysis is performed using ETABS commercial software. Three different real earthquake records with different characteristics are scaled and used to simulate ground motion. Nonlinear gap element is used to model pounding between buildings at their interface points. The results of the study indicate that, the maximum pounding force was investigated for each of the studied cases. Pounding does not occur between buildings having equal height. Increasing separation distance between buildings reduces the pounding force between them. Separation distance, which is estimated by the Egyptian code, is conservative.

Earthquakes with high magnitudes and strong ground motion have a more pronounced impact on structures that are positioned in close proximity to one another, as opposed to those that are more widely spaced. This proximity can lead to structural pounding, resulting in significant damage or even localized failure. The extent of pounding is influenced by both the insufficient separation distance between adjacent structures and the intensity of ground motion. Building codes worldwide stipulate a minimum separation distance to mitigate these effects. This study aims to evaluate the seismic pounding forces between adjacent reinforced concrete structures under varying ground motions, and to assess the influence of separation distance and structural irregularity on pounding behavior. Additionally, the effect of the structural mass on pounding force has also been discussed. Adjacent structures with differing floor levels were considered, and non-linear time history analyses were conducted using finite element-based software. Four real earthquake records with diverse characteristics and magnitudes were used to simulate ground motion effects. The results demonstrate that both Peak Ground Acceleration (PGA) and separation distance significantly affect the magnitude of pounding forces. Specifically, higher PGA values lead to substantial variations in pounding forces across different floors, while increased separation distance reduces the impact of pounding forces between adjacent structures. Moreover, structural irregularity and structural mass also contributes to differentiating the pounding forces.

Utilizing tuned mass damper for reduction of seismic pounding between two adjacent buildings with different dynamic characteristics

Seismic pounding and out-of-phase vibrations are critical issues for adjacent reinforced concrete structures. This research introduces an innovative shear link coupling system to synchronize inter-structural vibrations and mitigate pounding. The shear link coupling system connects adjacent buildings through replaceable, energy-dissipative shear links with tailored stiffness and ductility, allowing controlled deformation and energy absorption. The efficacy of this Novel Coupling System (NCS) is compared against a conventional Individual Building Retrofit (IBR) for two adjacent four-story reinforced concrete buildings with a 2.5 cm gap. The IBR uses steel chevron braces with aluminum links, while the NCS connects the buildings with steel rigid beams and aluminum links to enforce response synchronization. Advanced finite element modeling and nonlinear time-history analysis are used to evaluate interstory drift ratio, acceleration, and pounding potential. The analysis reveals that while the IBR reduces impacts, it cannot prevent hazardous collisions. In contrast, the NCS completely eliminates pounding by enforcing synchronization. The NCS dissipates nearly 65% of input energy through its links, compared to 45% for the IBR. Fragility analysis demonstrates that the NCS increases the median collapse capacity of the structures by over 300% relative to their as-is condition. The results show a significant reduction in seismic demand and pounding forces. The shear link coupling system’s enhanced resilience and reparability make it a viable solution for dense urban areas. This confirms that a design philosophy based on enforced synchronization is fundamentally more effective for mitigating seismic pounding than conventional independent-building strengthening.

It is important to be able to accurately assess seismic risk so that vulnerabilities can be prioritized for retrofit, emergency response procedures can be properly informed, and insurance rates can be sustainably priced to manage risk. To assess the risk of a building (or class of buildings) collapsing in a seismic event, procedures exist for creating one or more mathematical models of the structure of interest and performing nonlinear time history analysis with a large suite of input ground motions to calculate the building's seismic fragility and collapse risk. In this dissertation, three aspects of these procedures for assessing seismic collapse risk are investigated for the purpose of improving their accuracy. It is common to use spectral acceleration with a damping ratio of 5% as a ground motion intensity measure (IM) for assessing collapse fragility. In this dissertation, the use of 70%-damped spectral acceleration as an IM is investigated, with a focus on evaluating its sufficiency and efficiency. Incremental dynamic analysis (IDA) is performed for 22 steel moment frame (SMF) models with 50 biaxial ground motion records to formally evaluate the performance of 70%-damped spectral acceleration as an IM for highly nonlinear response and collapse. It is found that 70%-damped spectral acceleration is much more efficient than 5%-damped spectral acceleration and much more sufficient with respect to epsilon for all considered levels of highly nonlinear response. Its efficiency and sufficiency compares also compares well with more advanced IMs such as average spectral acceleration. When selecting input ground motions for nonlinear time history analysis, most engineers select ground motion records from the NGA-West2 database, which are processed with high-pass filters to remove long-period noise. In this dissertation, the extent to which these filters remove actual ground motion that is relevant to nonlinear time history analysis is evaluated. 52 near-source ground motion records from large-magnitude events are considered. Some records are processed by applying high-pass filters and others are processed by record-specific tilt corrections. Raw and NGA-West2 records are also considered. IDA is performed for 9-, 20-, and 55-story steel moment frame models with these processed records to assess the effects of ground motion processing on the calculated collapse capacity. It is found that if the cutoff period (Tc) is at least 40 seconds, then applying a high-pass filter does not have more than a negligible effect on collapse capacity for any of the considered records or building models. For shorter Tc (e.g. 10 or 15 seconds), it is found that the filters sometimes have a large effect on calculated collapse capacity, in some cases by over 50%, even if Tc is much larger than the building’s fundamental period. Of the considered ground motions, simply using the raw, uncorrected records usually yields more accurate results than using ground motions that have been processed with Tc less than or equal to 20 seconds. For an existing building with unknown design plans, one might perform a collapse risk assessment using an archetype model for which the specific member sizes are assumed based on the relevant design code and building site. In this dissertation, the sensitivity of seismic collapse risk estimates to design criteria and procedures are evaluated for six 9-story and four 20-story post-Northridge SMFs. These SMFs are designed for downtown Los Angeles using different design procedures according to ASCE 7-05 and ASCE 7-10. Seismic risk analysis is performed using the results of IDA with 44 ground motion records and the results are compared to those of pre-Northridge models. It is found that the collapse risk of 9-story SMFs designed according to performance-based design vary by 3x, owing to differences in GMPEs used to generate site-specific response spectra. There is generally less variation in the collapse risk estimates of 20-story post-Northridge SMFs when compared to 9-story post-Northridge SMFs because wind drift limits control the design of many members of the 20-story SMFs. Differences in collapse risk between pre- and post-Northridge SMFs are found to be at least 4x and 8x for the 9- and 20-story models, respectively. Furthermore, in response to four strong ground motion records from large-magnitude events, some of the 9-story and all of the 20-story pre-Northridge SMFs experience collapse and most of the post-Northridge SMFs experience significant damage (MIDR > 0.03).

The estimation of pounding effects between adjacent buildings in dense urban areas during strong ground motions is highly significant for practitioners. In this paper, the pounding-induced effects and the associated seismic damage states are evaluated for two colliding 6-story reinforced concrete (RC) frame structures. The nonlinear-induced behavior and the associated damage state are described using the force analogy method (FAM) coupled with a numerically efficient state-space formulation of the equations of motion. The pounding forces are computed using the nonlinear viscoelastic impact element. The force analogy method coupled with the state-space formulation conducts to an explicit integration scheme. Finally, the nonlinear time-history analyses and the damage evaluation are performed using three seismic accelerations recorded in the same site during the 1977, 1986 and 1990 earthquakes that took place in Romania.

Nowadays, architectural requirements affect structural design investigations. On the other hand, the pounding effect is one of the crucial effects between two adjacent high-rise buildings under seismic load. Because shear walls experience higher stresses at their ends, end shear walls alleviate these stresses and enhance the effect of shear walls in high-rise buildings. This study aimed to evaluate the impact of end shear walls on the seismic pounding between two adjacent 20-story reinforced concrete buildings subjected to seven far-field seismic records by nonlinear time history analysis. Also, the distance between the two buildings is considered zero. The inclusion of end shear walls was found to significantly reduce seismic pounding effects. Specifically, notable reductions were observed in average pounding displacements and rotational accelerations in the horizontal (X) direction. Average pounding drifts in the X-direction decreased by up to 26%, while average pounding accelerations in the X-direction were reduced by up to 9%. Similarly, pounding accelerations in the vertical (Z) direction and vertical pounding rotations were also substantially reduced. These findings highlight the effectiveness of end shear walls in mitigating seismic pounding and improving the overall seismic performance of adjacent reinforced concrete high-rise buildings subjected to far-fault ground motions.

Seismic pounding is defined as the collision of structures during earthquakes when these structures have different dynamic characteristics. It is an instance of rapid strong pulsation like hammering and repeated heavy blows. This pounding of closely spacedbuildings can be seen largely in some densely populated urban areas. Some modern codes have included seismic separation gap requirement clauses for adjacent structures but since large parts of metropolitan cities in seismically active regions of India were built before such requirements were introduced, the seismic separation gap requirements have not been fulfilled. Pounding can be catastrophic and even more dangerous than the effect of earthquakes on a single building. Thus, the action of pounding of buildings needs to be mitigated to avoid loss of life and property during earthquakes. The problem of pounding is particularly common in many cities in India, located in seismically active zones, where due to various socio-economic factors and land usage requirements, buildings are often constructed crowded together. This paper is focused on the study of the seismic pounding between two RC buildings with different dynamic characteristics. A systematic study of response of seismic pounding between adjacent buildings and seismic hazard mitigation practices like effect of different separation distances and effect of providing dampers are investigated, using the ETABS software. A 12-storey and a 16-storey building have been considered for the study of pounding. Time history analysis is carried out for seven real earthquake ground motions on the models with varying separation gaps. The results were obtained in the form of pounding force and point displacements. It is revealed that the pounding effect varies inverselywith the separation distance. With increasing separation distance pounding effect is reduced greatly and so the damage to the neighbouring buildings is also minimized. Also, the pounding forces are seen to be decreasing considerably between the adjacent buildings due to the provision of dampers at suitable locations, as compared to the case of adjacent buildings without dampers. The study even confirms that the pounding effect can be mitigated considerably by installing dampers between adjacent structures.Dampers modelled in this study prove to be effective in reducing the displacement and driftin the range of15%-20%

Because of the irregular geometries, earthquake-induced adjacent curved bridge pounding may lead to more complex local damage or even collapse. The relevant research is mainly concentrated on the numerical analysis which lack experimental verification and discussion by changing of structural parameters. In this paper, a scaled three-dimensional numerical model of a curved bridge is established based on 3D contact friction theory for investigating the uneven distribution of pounding forces at the expansion joint of the bridge. Shaking table tests were carried out at first on a curved bridge to validate the numerical model. A series of parametric studies were then conducted to examine the impacts of the radius of curvature and longitudinal slope of the superstructure of the curved bridge on its seismic pounding response. The results show that the maximum pounding force first increases and then decreases as the radius of curvature increases, but that it decreases monotonically with the growth of the longitudinal slope. These results suggest that controlling the radius of curvature and the longitudinal slope of the superstructure of the bridge can reduce the localized high stress that is induced by seismic pounding. Also, the unevenly distributed pounding forces can significantly increase the relative radial displacement of the bridge’s deck corners, although the relative tangential displacement may decrease. It is thus necessary to adopt effective anti-pounding measures to prevent the superstructure of the bridge from being unseated.

Seismic pounding between closely spaced building structures is one among the main causes of severe building damages observed in seismically proven regions. Due to the earthquake-induced vibrations, the buildings which are adjacent to each other with dissimilar dynamic characteristics will move out of phase resulting in the collision as there would be no energy dissipation system to accommodate the relative motions. Seismic pounding can be prevented by passive structural control of energy dissipation systems, i.e., dampers. The current study aims to mitigate the seismic pounding observed in the adjacent buildings connected with fluid viscous dampers (FVDs). G+14 and G+9 multistoried adjacent buildings are modeled and analyzed using ETABS 2017. Two stories are connected with one viscous damper. Adjacent buildings with similar height (G+14 storied) and varying height (G+14 & G+9 storied) connected with FVDs subjected to El Centro earthquake are studied. Nonlinear time history analysis is carried out. Considering displacement and seismic gap as the main parameters, adjacent buildings with similar and different height connected with and without FVDs are compared.KeywordsSeismic poundingSeismic gapAdjacent buildingsFluid viscous dampers (FVDs)Time history analysis (THA)

This paper summarizes the results of current research, sponsored by the SAC Steel Project, on the reliability of nonlinear static methods for predicting the seismic performance of steel moment frame buildings. As part of previous SAC studies, three steel moment frame buildings (3, 9, and 20-story), located in Los Angeles, were designed using Pre-Northridge earthquake connection details. Two DRAIN-2D models (M1 and M2) were created for each building. Model M1 is a centerline-to-centerline model, while model M2 explicitly accounts for the strength and stiffness of the panel zone and represents the more accurate model. Nonlinear dynamic time history analyses were performed for each building model using a total of 60 earthquake ground motions with seismic hazard levels having a 2%, 10%, and 50% probability of exceedance in 50 years. In the current study, nonlinear static “pushover” analyses of the buildings were performed with the same models and ground motions used in the nonlinear time history analyses. The Coefficient Method, Capacity Spectrum Method, Equivalent System Method were used to calculate building performance response quantities. The maximum roof displacement and maximum interstory drift response for models M1 and M2 were compared with the model M2 results from the nonlinear dynamic time history analyses.

Seismic response of structures involved soil-structure-interaction (SSI) that need to consider both inertial and kinematic interaction. Many underground SSI has been developed such as modelling the structures and soils as continuum with seismic load simplified as pseudo-static or static equivalent. More recent and more realistic SSI model consider non-linear time-history analysis in the form of 2-D site-specific response analysis (SSRA), in which both inertial and kinematic interaction in combination with non-linear soil model, as well as time-history ground-motions are simulated. This paper presents simplified pseudo-static soil-structure interaction finite-element (FE) response of underground box-station structure under prescribed maximum strain displacement as resulted from 1-D site-specific response analysis under various ground-motions characteristics of subduction and shallow crustal earthquakes. More complex model of SSI system of basement is also presented. This basement SSI model incorporates non-linear time-history analysis with dynamic soil properties considered through 2-D SSRA simulating seismic wave propagation from reference base-rock to ground surface. Various base-rock seismic ground-motions are simulated from results of de-aggregation analysis from probabilistic seismic hazard analysis considering both subduction and shallow crustal earthquakes scaled at various ground-motion periods. The analysis adopts dynamic soil model with non-linear modulus and damping using FLAC computer program.

Seismic pounding between closely spaced buildings during earthquakes becomes increasingly severe when structures exhibit asymmetrical configurations or misaligned centers of mass and stiffness. Multi-directional seismic forces amplify stresses in such unbalanced buildings, highlighting the necessity to consider both structural movement and irregular geometries or eccentric loadings when determining adequate separation distances. This study investigates the seismic response of two adjacent buildings with off-center floor layouts subjected to various collision scenarios, focusing specifically on asymmetric impacts. The analysis emphasizes seismic forces acting laterally in the x-direction, evaluating configurations with different bidirectional eccentricity combinations (ex, ey). Four eccentricity cases were considered: (+ ex, + ey), (− ex, + ey), (− ex, − ey), and (+ ex, − ey). Nonlinear time history analyses were performed on structural models across three distinct collision scenarios. Nonlinear dynamic analyses and three-dimensional finite element modeling using ETABS software were employed to simulate the interaction between neighboring structures with asymmetric configurations under earthquake loading. Structural response demands including lateral displacements, torsional rotations, and accelerations were compared across cases. Results indicate that the bidirectional eccentricity parameters of adjacent buildings significantly influence seismic response demands. Specifically, asymmetric collisions between buildings with bidirectional eccentricities under x-direction seismic excitation markedly affect their seismic behavior, emphasizing the need to account for such eccentricities in design and evaluation.

The traditional restraint systems limit the deformation of curved bridge under temperature load, which results in radial and tangential secondary internal forces in the bridge. This paper proposes a pin-bearing restraint system (PBRS) for curved bridge, which can relax the rotational deformation of curved bridge under temperature load. Its configuration and working mechanism are illustrated. The finite element model of a curved bridge with PBRS is established using ANSYS software, and nonlinear time history analysis is conducted. The pounding force and pounding number between pin and slot under ground motion are analyzed. The pin stiffness, the gap and the ratio of upper structure mass to lower structure mass are selected for parametric study. The results show that the pounding force and pounding number present dramatic changes with pin stiffness. As the pin stiffness increases, the pounding force presents a logarithmic linear tendency, and the pounding number shows a reduce tendency. Gap has little influence on pounding force and pounding number. The radial pounding force and pounding number increase with the increase of mass ratio.

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.