Pounding Cases Research Articles

A risk-targeted decision model for the verification of the seismic performance of RC structures against structural pounding

In this study, a novel risk-targeted decision model is introduced to verify the seismic performance of RC structures against structural pounding and then to define the minimum demand for separation gap distance (dg) between adjacent structures at a target probability Pt. The derivations are based on a linear approximation of the seismic hazard function and well-established probabilistic seismic demand models (PSDMs). New performance objectives (POs) dedicated to structural pounding risk are proposed based on engineering demand parameter (EDP) hazard curves and on the separation gap distances (dg: available or acceptable) between adjacent structures. The theoretical background in the context of the risk-targeted decision model is presented, and then the adjustment to the structural pounding risk is introduced. The minimum separation gap distance (dg,minPt) at a target Pt is defined considering a) the demand hazard curve for the maximum displacement (without pounding) at the top contact floor level of the structure (δmax), and b) the acceptable structural pounding PO of an EDP. The proposed risk-targeted decision model is then demonstrated by means of a structural pounding case study of a RC structure. Local and global EDPs at different performance levels are considered and several POs at different dg are compounded. The verification of the seismic performance of the RC structure at a target probability Pt is carried out either with or without considering the structural pounding risk. Numerical examples of the verification and the definition of the dg,minPt at different pounding risk levels (Pt) of the examined RC structure are also presented and discussed. Based on these results, a distinct PO of an EDP was identified. This PO is characterized as a critical level of structural pounding risk at the capacity level of the EDP and is associated with an explicit-critical separation gap distance between the adjacent structures. In a future research study, this PO could be the basis for providing a design solution against structural pounding risk when the estimated minimum separation gap distance at a target Pt between the adjacent structures cannot be implemented. The provided solution through the proposed decision model also indicates that the maximum demand for separation gap distance between the adjacent structures can safely be shifted to smaller values, notwithstanding that pounding risk is increased.

Experimental and numerical studies of seismic induced story-to-story and inter-story pounding

Pounding between adjacent buildings was repeatedly observed during many major earthquakes. Previous studies on building pounding are mainly based on the analytical and numerical investigations. A few experimental studies were reported, but these studies mainly focused on the story-to-story pounding, which is not necessarily the case in engineering practices. When the story heights of two adjacent buildings are different, inter-story pounding occurs. Moreover, most buildings have irregular shapes, which may result in the eccentric poundings. Few experimental studies have been performed to understand the combined inter-story and eccentric poundings between adjacent buildings yet. This paper presents the experimental studies on the seismic pounding between adjacent multi-story buildings. Shaking table tests on three 1/3 scaled 2-story and 3-story buildings were performed to understand their behaviors when they were subjected to the earthquake ground motions. The story-to-story pounding, inter-story pounding, and eccentric pounding are experimentally investigated and the results are presented and analyzed in this paper. Then a detail 3D FE model is developed and validated by experiment data. The effect of mass eccentricity on inter-story pounding is analyzed by the numerical model. The experimental and numerical results show that, pounding can induce much higher frequency contents to the structural responses compared to the case without pounding, and the pounding forces in the story-to-story pounding case are larger than those in the inter-story pounding case; mass eccentricity has obvious influence on the base share force and displacement response of the building.

Shaking table experimental study on pounding between adjacent structures founded on different soil types

The aim of this study is to extensively investigate the effect of the soil type on the response of colliding structures based on shaking table experimental tests. Two single-storey models of steel buildings with different dynamic parameters were considered in this study. Three pounding scenarios were taken into account by applying different seismic gaps (0.5 cm, 1 cm and 1.5 cm as well as the no pounding case). First, the effect of pounding on the response of these two structures was analysed. Then, the effect of the seismic gap on the response of colliding structures was studied. Finally, the effect of soil type on the response of structures exposed to interactions was investigated. Five soil types were considered in the study, which are the five soil types defined in the ASCE 7-10 code (hard rock, rock, very dense soil and soft rock, stiff soil and soft clay soil). The results of the investigation show that pounding significantly increases the level of accelerations of structures during the whole time of vibrations as well as the peak acceleration itself. Pounding is more significant for the flexible structure than for the stiff one. Also, the seismic gap has a significant effect on the acceleration response of colliding structures. Not necessarily larger gap leads to lower responses unless it is large enough to eliminate collisions at all. Moreover, the results of the study show that the soil type has a significant effect on the response of colliding structures. The soil type effect is more significant when pounding takes place. The maximum and minimum peak acceleration differs for various soil types, pounding scenarios, seismic gaps and earthquakes.

Analysis of floor-to-column pounding of buildings founded on different soil types

The aim of this study is to investigate the effect of the soil type on buildings experiencing floor-to-column pounding during earthquakes. Five buildings with 4-storeys, 6-storeys, and 7-storeys were considered. Three types of the 4-storey building with different total heights were taken into account which leads to floor-to-column pounding at 1/3, 1/2 and 2/3 of the height of the impacted column. Two pounding scenarios were considered, i.e. pounding between the 4-storey and 6-storey buildings (three cases when collisions occur at 1/3, 1/2 and 2/3 of the height of the impacted column) and pounding between the 4-storey and 7-storey buildings (three cases when collisions occur at 1/3, 1/2 and 2/3 of the height of the impacted column). In the first part of this study, the shear demands of the columns at the contact area were studied and compared with the no pounding case to investigate the effect of the floor-to-column pounding. Then, the shear demands of the columns at the contact area were studied for buildings founded on different soil types to investigate the effect of the soil type on the structural response. The results of this study illustrate that the shear demands of the impacted column significantly increase due to collisions and it exceeds the shear strength in all cases. Moreover, impacted column experiences higher shear demands for buildings founded on the soft clay soil, then for buildings founded on the stiff soil, then for buildings founded on very dense soil and soft rock, and finally for buildings founded on the rock and hard rock.

Analysis of pounding between adjacent buildings founded on different soil types

Earthquake-induced pounding was experienced in many previous earthquakes and it was found to be a critical issue. This study investigates the effect of pounding between buildings founded on the same and different soil types. Three 3-D buildings with 4, 6 and 8 storeys were considered in this study. Three pounding scenarios were taken into account, i.e. pounding between 4-storey and 6-storey buildings, between 4-storey and 8-storey buildings and between 6-storey and 8-storey buildings. To consider the soil type, the effects of different site parameters on the response of buildings exposed to earthquakes was firstly investigated so that the values that lead to significant effects and larger responses could be taken into account in further study related to structural interactions. In the next stage of the investigation, the effects of pounding between buildings founded on a specified soil type were analysed and compared with the no pounding case. The results of this part of this study show that pounding significantly increases the peak accelerations in all situations. Indeed, the peak displacements experience both amplification and de-amplification. Moreover, the shear forces were found to be increased for all storeys in all the cases with few exceptions concerning the top storeys. Finally, pounding between 4-storey and 8-storey buildings as well as between 6-storey and 8-storey buildings was considered under different soil types defined in the ASCE 7–10 code (hard rock, rock, very dense soil and soft rock, stiff soil and soft clay soil). The results of this stage of this study show that the highest displacements and shear forces can be expected for buildings founded on the soft clay soil, then for buildings founded on the stiff soil, then for buildings founded on very dense soil and soft rock, and finally for buildings founded on the rock and hard rock.

Incremental dynamic analysis and fragility assessment of buildings founded on different soil types experiencing structural pounding during earthquakes

The effect of the soil type on buildings experiencing pounding during earthquakes is investigated in this study using the incremental dynamic analysis and fragility assessment methods. Three 3-D structures with different number of storeys (4, 6 and 8) were considered in this study. Three pounding scenarios between these three buildings were taken into account, i.e. pounding between 4-storey and 6-storey buildings, between 4-storey and 8-storey buildings and between 6-storey and 8-storey buildings. First, the effect of the site parameters was investigated so as to take into consideration the values that lead to higher responses. Then, the effects of earthquake-induced pounding between buildings founded on a specified soil type for these three pounding scenarios were analysed and compared with no pounding case. Finally, pounding for these three scenarios was studied under different soil types defined in the ASCE 7–10 code (hard rock, rock, very dense soil and soft rock, stiff soil and soft clay soil). The results of this study indicate that the effect of pounding follows two general trends which are destructive and beneficial. Also, the vibrating buildings were found to be more vulnerable to damage due to pounding when they are founded on the soft clay soil, then when they are founded on the stiff soil, then when they are founded on very dense soil and soft rock, and finally when they are founded on the rock and hard rock.

Fragility Curves and Probabilistic Seismic Demand Models on the Seismic Assessment of RC Frames Subjected to Structural Pounding

This study aims to evaluate five different methodologies reported in the literature for developing fragility curves to assess the seismic performance of RC structures subjected to structural pounding. In this context, displacement-based and curvature-based fragility curves are developed. The use of probabilistic seismic demand models (PSDMs) on the fragility assessment of the pounding risk is further estimated. Linear and bilinear PSDMs are developed, while the validity of the assumptions commonly used to produce a PSDM is examined. Finally, the influence of the PSDMs’ assumptions on the derivation of fragilities for the structural pounding effect is identified. The examined pounding cases involve the interaction between adjacent RC structures that have equal story heights (floor-to-floor interaction). Results indicate that the fragility assessment of the RC structure that suffers the pounding effect is not affected by the examined methodologies when the performance level that controls the seismic behavior is exceeded at low levels of IM. Thus, the more vulnerable the structure is due to the pounding effect, the more likely that disparities among the fragility curves of the examined methods are eliminated. The use of a linear PSDM fails to properly describe the local inelastic demands of the structural RC member that suffers the impact effect. The PSDM’s assumptions are not always satisfied for the examined engineering demand parameters of this study, and thus may induce errors when fragility curves are developed. Nevertheless, errors induced due to the power law model and the homoscedasticity assumptions of the PSDM can be reduced by using the bilinear regression model.

Comparison of Interstorey Drift in General RC Buildings in Pounding and No Pounding Case

Inter-storey drift is an important parameter of structural behavior in seismic analysis of buildings. Pounding effect in building simply means collision between adjacent buildings due to earthquake load caused by out of phase vibration of adjacent buildings. There is variation in inter-storey drift of adjacent buildings during pounding case and no pounding case.
 The main objective of this research was to compare the inter-storey drift of general adjacent RC buildings in pounding and no pounding case. For this study two adjacent RC buildings having same number of stories have been considered. For pounding case analysis there is no gap in between adjacent buildings and for no pounding case analysis there is sufficient distance between adjacent buildings.
 The model consists of adjacent buildings having 4 and 4 stories but unequal storey height. Both the buildings have same material & sectional properties. Fast non-linear time history analysis was performed by using El-centro earthquake data as ground motion. Adjacent buildings having different overall height were modelled in SAP 2000 v 15 using gap element for pounding case. Finally, analysis was done and inter-storey drift was compared. It was found that in higher building inter-storey drift is greater in no pounding case than in pounding case but in adjacent lower height building the result was reversed. Additionally, it was found that in general residential RC buildings maximum inter-storey drift occurs in 2nd floor.

Study and Analysis of Pounding Effect between Adjacent RC Buildings

Pounding occurs when the adjacent buildings start vibration out of phase during the seismic activity which causes the collision between the adjacent structures. Due to higher cost of land in cities people have tendency to attach the buildings at property line. Earthquakes can cause pounding when adjacent buildings have little gap or no gap providing separation. Due to pounding effect structural and non – structural damage may occur in the adjacent buildings.
 The main objective of this research is to assess the seismic response of common residential RC buildings that has been constructed with no gap with the adjacent structures and to find the minimum gap requirement for the commonly constructed buildings of Nepal.
 For this study two different cases with varying separation distance between adjacent buildings have been considered. First case is the adjacent buildings having equal storey height but different number of stories. It includes models having 4 and 2 stories and 4 and 3 stories. Second case is the adjacent buildings having unequal storey height but same number of stories. It includes models having 3 and 3 stories and 4 and 4 stories. In both cases adjacent buildings have same material & sectional properties. Non-linear dynamic analysis is performed using El-centro earthquake data as ground motion. Gap element has been used to simulate the pounding force between buildings. Adjacent buildings having different overall height are modelled in SAP 2000 v 15 using gap element for pounding study. The seismic responses in terms of joint displacement, joint acceleration, pounding force are presented. Joint displacement and joint acceleration comparison for both pounding and no pounding cases are presented.
 Gap calculation from NBC and IS code, ABS and SRSS method was compared with gap required to avoid pounding force between adjacent structures and appropriate gap was recommended.

Seismic Collapse Probability Considering Pounding and Financial Loss Estimation of Base-Isolated Reinforced Concrete Buildings

In this paper, the seismic collapse probability of base-isolated reinforced concrete buildings considering pounding with a moat wall and financial loss estimation is studied. For this purpose, three-dimensional finite element models of a code-compliant 10-story base-isolated shear wall-frame (BI-SWF) building and a 10-story base-isolated moment resisting frame (BI-MRF) building are used. Results indicate that the BI-MRF building has a greater probability of collapse compared to that of the BI-SWF building, the probability of collapse in 50 years for the BI-MRF building is 1.3 times greater than that of the BI-SWF building for both no pounding and pounding cases. The probability of collapse increases when pounding is considered, which results in a smaller value of the collapse margin ratio compared to no pounding case for both the buildings. The financial losses resulting from damage to the BI-MRF and BI-SWF buildings under design earthquake (DE) and risk-targeted maximum considered earthquake (MCER) levels are calculated for the no pounding case, since there was no pounding under DE-level and very few instances of pounding under MCER-level. Calculation of financial losses due to damage to structural and nonstructural components, service equipment and downtime shows that the BI-SWF building results in larger repair costs and downtime cost compared to the BI-MRF building.

Torsional behavior of multistory RC frame structures due to asymmetric seismic interaction

Collisions between structures due to seismic oscillations have been reported many times in literature as a common case of damage. Further it is quite usual seismically induced oscillations of a structure in a city center block of buildings to be partly restrained in lateral displacements and therefore torsional behavior to be introduced in the structure. Two different types of structural interaction may be defined: (a) Diaphragm-to-diaphragm collisions (Type A). (b) The floor levels of the two structures are different. Consequently during the seismic oscillations the diaphragms of the first one impact the columns of the other (Τype B or interstory pounding). In this work the cases of an 8-story reinforced concrete building that suffers pounding with an adjacent structure that has 1, 2, 3, 4, 5, 6, 7 or 8 stories are studied. Pounding occurs only in one (Case 1) or in two (Case 2) columns of the structures and since the other columns are free to move without restrictions a torsional behavior is introduced (asymmetric pounding). Moreover in Type B interaction these columns of the 8-story frame structure undergo impacts at a height equal to 2/3 of their deformable length from the diaphragms of the other structure. The influence of an initial distance between the two interacting structures on the torsion effect is investigated too. Nonlinear seismic step-by-step analyses are performed. More than two hundred pounding cases with torsional effect each one for three natural seismic excitations are studied. Results in terms of shear and ductility demands of the columns are presented and commented. Both types A and B yielded high torsional structural rotation. In interaction Type B it can be deduced from the cases under examination that the column that is endured the impact from the top floor of the other structure develops high shear demands that exceed the available capacity many times during the step-by-step seismic analysis. Moreover high ductility demands have been observed for this column. Finally it is concluded that for buildings that may undergo asymmetric pounding not taking it into account may lead under certain conditions to non-secure design or even critical situations.

Seismic pounding effects on adjacent buildings in series with different alignment configurations

Numerous urban seismic vulnerability studies have recognized pounding as one of the main risks due to the restricted separation distance between neighboring structures. The pounding effects on the adjacent buildings could extend from slight non-structural to serious structural damage that could even head to a total collapse of buildings. Therefore, an assessment of the seismic pounding hazard to the adjacent buildings is superficial in future building code calibrations. Thus, this study targets are to draw useful recommendations and set up guidelines for potential pounding damage evaluation for code calibration through a numerical simulation approach for the evaluation of the pounding risks on adjacent buildings. A numerical simulation is formulated to estimate the seismic pounding effects on the seismic response demands of adjacent buildings for different design parameters that include: number of stories, separation distances; alignment configurations, and then compared with nominal model without pounding. Based on the obtained results, it has been concluded that the severity of the pounding effects depends on the dynamic characteristics of the adjacent buildings and the input excitation characteristics, and whether the building is exposed to one or two-sided impacts. Seismic pounding among adjacent buildings produces greater acceleration and shear force response demands at different story levels compared to the no pounding case response demands.

Minimum required separation gap for adjacent RC frames with potential inter-story seismic pounding

The aim of this study is to correlate the seismic performance of a real RC frame structure at different seismic demand levels with the separation gap that would be inadequate against pounding with an adjacent shorter and stiffer structure. In this direction 882 nonlinear step by step seismic analyses have been performed. The first part of this study includes the evaluation of the inter-story (floor to column) pounding problem at nine seismic demand levels, using for each level 14 seismic excitations that have been properly scaled. The examined cases are inter-story pounding cases between an 8-story RC frame and a 3-story RC frame - wall structure or a 3-story rigid barrier (very stiff structure) while the adjacent structures are considered to be in contact from the beginning. The seismic performances of the structures without the pounding effect have also been evaluated. The results of the assessment indicate that: (a) at all the examined levels of the seismic demand, the local performance of the external column of the tall building that suffers the impact from the upper floor slab of the adjacent shorter structure is the most important issue in the inter-story pounding phenomenon, (b) this column is always in a critical condition due to shear action and in the case of pounding with the 3-story rigid barrier this column appears to be critical due to high ductility demands as well, (c) the level of the seismic demand that is used to assess the pounding problem on the local performances of the critical column that suffers the hit, altered the developing requirements for flexural and shear capacity of the column. Thereafter, the minimum required gap distance against pounding between the adjacent structures has been estimated taking into account two different criteria: (a) avoidance of the shear failure in the critical column that suffers the hit and (b) complete avoidance of the contact between the adjacent structures. The separation gap is evaluated at all the seismic demand levels for both pounding cases. In comparison to the Eurocode 8 provisions the results of this study indicate less conservative separation gap distances between the adjacent structures at different levels of seismic demand.

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.

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.

Influence of exterior joint effect on the inter-story pounding interaction of structures

The seismic induced interaction between multistory structures with unequal story heights (inter-story pounding) is studied taking into account the local response of the exterior beam-column joints. Although several parameters that influence the structural pounding have been studied sofar, the role of the joints local inelastic behaviour has not been yet investigated in the literature as key parameter for the pounding problem. Moreover, the influence of the infill panels as an additional parameter for the local damage effect of the joints on the inter-story pounding phenomenon is examined. Thirty six interaction cases between a multistory frame structure and an adjacent shorter and stiffer structure are studied for two different seismic excitations. The results are focused: (a) on the local response of the critical external column of the multistory structure that suffers the hit from the slab of the adjacent shorter structure, and (b) on the local response of the exterior beam-column joints of the multistory structure. Results of this investigation demonstrate that the possible local inelastic response of the exterior joints may be in some cases beneficial for the seismic behaviour of the critical column that suffers the impact. However, in all the examined cases the developing demands for deformation of the exterior joints are substantially increased and severe damages can be observed due to the pounding effect. The presence of the masonry infill panels has also been proved as an important parameter for the response of the exterior beam-column joints and thus for the safety of the building. Nevertheless, in all the examined inter-story pounding cases the presence of the infills was not enough for the total amelioration of the excessive demands for shear and ductility of the column that suffers the impact.

A modified Kelvin impact model for pounding simulation of base-isolated building with adjacent structures

Base isolation can effectively reduce the seismic forces on a superstructure, particularly in low- to medium-rise buildings. However, under strong near-fault ground motions, pounding may occur at the isolation level between the base-isolated building (BIB) and its surrounding retaining walls. To effectively investigate the behavior of the BIB pounding with adjacent structures, after assessing some commonly used impact models, a modified Kelvin impact model is proposed in this paper. Relevant parameters in the modified Kelvin model are theoretically derived and numerically verified through a simple pounding case. At the same time, inelasticity of the isolated superstructure is introduced in order to accurately evaluate the potential damage to the superstructure caused by the pounding of the BIB with adjacent structures. The reliability of the modified Kelvin impact model is validated through numerical comparisons with other impact models. However, the difference between the numerical results from the various impact analytical models is not significant. Many numerical simulations of BIBs are conducted to investigate the influence of various design parameters and conditions on the peak inter-story drifts and floor accelerations during pounding. It is shown that pounding can substantially increase floor accelerations, especially at the ground floor where impacts occur. Higher modes of vibration are excited during poundings, increasing the inter-story drifts instead of keeping a nearly rigid-body motion of the superstructure. Furthermore, higher ductility demands can be imposed on lower floors of the superstructure. Moreover, impact stiffness seems to play a significant role in the acceleration response at the isolation level and the inter-story drifts of lower floors of the superstructure. Finally, the numerical results show that excessive flexibility of the isolation system used to minimize the floor accelerations may cause the BIB to be more susceptible to pounding under a limited seismic gap.

Seismic Pounding between Adjacent Building Structures

Investigations of past and recent earthquake damage have 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. 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. Pounding produces acceleration and shear 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 practically to eliminate contact.

Inter-story pounding between multistory reinforced concrete structures

The influence of the inter-story structural pounding on the seismic behaviour of adjacent multistory reinforced concrete structures with unequal total heights and different story heights is investigated. Although inter-story pounding is a common case in practice, it has not been studied before in the literature as far as the authors are aware. Fifty two pounding cases, each one for two different seismic excitations, are examined. From the results it can be deduced that: (i) The most important issue in the inter-story pounding is the local effect on the external column of the tall building that suffers the impact from the upper floor slab of the adjacent shorter structure. (ii) The ductility demands for this column are increased comparing with the ones without the pounding effect. In the cases that the two buildings are in contact these demands appear to be critical since they are higher than the available ductility values. In the cases that there is a small distance between the interacting buildings the ductility demands of this column are also higher than the ones of the same column without the pounding effect but they appear to be lower than the available ductility values. (iii) It has to be stressed that in all the examined cases the developed shear forces of this column exceeded the shear strength. Thus, it can be concluded that in inter-story pounding cases the column that suffers the impact is always in a critical condition due to shear action and, furthermore, in the cases that the two structures are in contact from the beginning this column appears to be critical due to high ductility demands as well. The consequences of the impact can be very severe for the integrity of the column and may be a primary cause for the initiation of the collapse of the structure. This means that special measures have to be taken in the design process first for the critically increased shear demands and secondly for the high ductility demands.

Earthquake-induced interaction between adjacent reinforced concrete structures with non-equal heights

The influence of the structural pounding on the ductility requirements and the seismic behaviour of reinforced concrete structures designed to EC2 and EC8 with non-equal heights is investigated. Special purpose elements of distributed plasticity are employed for the study of the columns. Two distinct types of the problem are identified: Type A, where collisions may occur only between storey masses; and Type B, where the slabs of the first structure hit the columns of the other (72 Type A and 36 Type B pounding cases are examined). Type A cases yielded critical ductility requirements for the columns in the pounding area mainly for the cases where the structures were in contact from the beginning of the excitation. In both pounding types the ductility requirements of the columns of the taller building are substantially increased for the floors above the highest contact storey level probably due to a whiplash behaviour. The most important issue in the pounding type B is the local response of the column of the tall structure that suffers the hit of the upper floor slab of the adjacent shorter structure. In all the examined cases this column was in a critical condition due to shear action and in the cases where the structures were in contact from the beginning of the excitation, this column was also critical due to high ductility demands. It can be summarized that in situations of potential pounding, neglecting its possible effects leads to non-conservative building design or evaluation that may become critical in some cases. Copyright © 2004 John Wiley & Sons, Ltd.