Papers by Keyword: Structural Pounding

Abstract: During earthquakes, structures can collide with each other due to provision of very small or no gap between them. This collision can cause massive amount of damage and it can be a very critical issue for structures which get subjected to mainshock-aftershock sequence of significant magnitude. In the usual design practice of building structures, neither pounding nor aftershocks are considered. Therefore, in the current study, a detailed investigation of structures which can be commonly found in Karachi is performed when they are subjected to pounding under mainshock-aftershock sequences. To this end, a FEM model was developed and processed through nonlinear time-history analysis under natural and artificial mainshock-aftershock sequences. It was found that pounding under aftershocks can increase story shears up to 2.18 times and story drifts up to 1.46 times that in the absence of pounding. Results of this study also showed that during pounding under aftershock, structure is still subjected to similar amount of force as in mainshock, however it is already in a damaged state due to mainshock.

Abstract: During earthquakes, structures move laterally and since usually a proper gap distance between structures is not provided so the structures can collide with each other. Building codes which are commonly used, do not offer any provisions for designing the structures for additional forces due to pounding and so structures are susceptible to damage subjected to pounding during strong seismic events. Therefore, in the current study, effect of pounding on a structure is studied considering different parameters including number of stories, total weight, story stiffness and floor alignment with adjacent structure. Furthermore, to investigate the effect of each parameter in isolation and avoid the effect of speed difference of colliding structures, a similar gap in fundamental periods has been used. It was found that pounding significantly effects the upper stories as compared to lower stories. It was also found that if the floors are aligned, total weight of the adjacent structure is the most critical parameter which severely effects on a structure’s upper stories. It was also observed that if the floors are not aligned, a significant increase in story shear occurs.

Abstract: During severe earthquakes, pounding between adjacent superstructure segments of highway elevated bridges was often observed. It is usually caused by the seismic wave propagation effect and may lead to significant damage. The aim of the present paper is to show the results of the numerical analysis focused on damage-involved pounding between neighbouring decks of an elevated bridge under seismic excitation. The analysis was carried out using a lumped mass structural model with every deck element discretized as a SDOF system. Pounding was simulated by the use of impact elements which become active when contact is detected. The linear viscoelastic model of collision was applied allowing for dissipation of energy due to damage at the contact points of colliding deck elements. The results show that pounding may substantially modify the behaviour of the analysed elevated bridge. It may increase the structural response or play a positive role, and the response depends on pattern of collisions between deck elements. The results also indicate that a number of impacts for a small in-between gap size is large, whereas the value of peak pounding force is low. On the other hand, the pounding force time history for large gap values shows only a few collisions, but the value of peak pounding force is substantially large, what may intensify structural damage.

Abstract: Earthquakes are the most unpredictable damaging loads which can affect civil engineering structures. Due to insufficient separation distance between adjacent structures with different dynamic properties, structural collisions may occur during ground motions. Although the research on structural pounding has recently been much advanced, the studies have mainly been conducted for concrete structures. The aim of this paper is to show the results of experimental investigation, focused on dynamic behaviour of closely-separated three models of steel structures which have been subjected to damaging earthquake excitations. The study was performed using three models of steel towers with different dynamic parameters and various distances between the structures. The acceleration time histories of the Kobe and the Northridge earthquakes were applied as the seismic excitation. The unidirectional shaking table, located at the Gdansk University of Technology (Poland), was used in the experimental study. The results have confirmed that collisions may lead to the increase in the structural response, although they may also play a positive role, depending on the size of the separation gap between the structures.

Abstract: Structural interactions between adjacent, insufficiently separated buildings have been repeatedly observed during damaging ground motions. This phenomenon, known as the structural pounding, may result in substantial damage or even total collapse of structures. The aim of the present paper is to show the results of the nonlinear numerical analysis focused on pounding between inelastic three-storey buildings under seismic excitations. The discrete lumped-mass numerical models of two building have been used in the analysis. The results of the study indicate that the response of the lighter and more flexible inelastic building can be substantially influenced by structural interactions, and collisions may even lead to the permanent deformation of the structure. On the other hand, the behaviour of the heavier and stiffer building does not really change considerably during the earthquake. The results of the study also indicate that incorporation of the inelastic behaviour of colliding buildings with different dynamic characteristics is very important for the purposes of accurate numerical modelling of pounding-involved structural response under damaging seismic excitations.

Abstract: Mutual pounding between structures during earthquakes may cause serious structural damage. The aim of this paper is to show the results of a shaking table experimental study focused on pounding between structures in series under several earthquake excitations. The experiments were performed using three tower models with different configurations and different gap distances between them. In the first stage of the study, one rigid tower was installed between two flexible structures, while later on, the flexible tower was located between two rigid structures. The results of the study show that pounding observed during damaging earthquakes might affect the behaviour of structures significantly. It was observed that the rigid towers are more influenced by pounding than the flexible structures. Moreover, the optimal gap size was found to be either the distance which prevents pounding (and therefore prevents from damage) or the zero gap.

Abstract: Pounding between insufficiently separated buildings, which may result in considerable damage or may even lead to the total collapse of colliding structures, has been repeatedly observed during earthquakes. Earthquake-induced collisions of buildings has been intensively studied applying various structural models. It was assumed in the analyses, however, that the seismic excitation is identical for all structural supports; whereas, in the reality, the ground motion differs from place to place due to spatial seismic effects connected with propagation of the seismic wave. The aim of the present paper is to conduct a detailed non-linear damage-involved analysis of pounding between two structures under non-uniform earthquake loading. A case of pounding between the Olive View Hospital main building and one of its stairway towers, observed during the San Fernando earthquake of 1971, has been considered in the study. In the numerical FEM analysis, non-linear material properties have been simulated using stiffness degradation (due to damage under cyclic loading) model of concrete and elastoplastic damage model of reinforcing steel. A method of conditional stochastic modelling has been used to generate the input ground motion records. The results of the study indicate that the incorporation of the non-uniform ground motion excitation may lead to substantial change of pounding-involved response of the structures. The difference between the uniform and non-uniform responses has been found to be relatively large considering the fact that the variation in the simulated input ground motion records was rather small. This shows the importance of incorporation in the damage-involved numerical analysis the effects connected with propagation of the seismic wave.

Abstract: This paper investigates the coupled effect of the supporting soil flexibility and pounding between neighbouring, insufficiently separated 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 the time history of the Kobe earthquake of 1995. A nonlinear viscoelastic pounding force model has been employed in order to effectively capture the impact forces during collisions. A discrete element model has been incorporated to simulate the horizontal and rotational movements of the supporting soil. Numerical simulations have been performed using developed software based on the Matlab code. The variation in storeys peak displacements, peak accelerations and peak impact forces for various gap sizes is presented in the paper and comparisons are made with the results obtained for colliding buildings with fixed-base supports. The results of the study indicate that the incorporation of the soil-structure interaction decreases both storey peak displacements and peak impact forces during collisions, whereas increase the peak accelerations at each floor level.

Abstract: In order to compare the initial and improved Hertz-damp model, the dynamic equations of collision system were established based on Hertz-damp model and mode superposition method. Hertz-damp model can account for the influence of the nonlinear contact stiffness as well as the energy loss during structural pounding. The results analysis show that the initial model have the same simulation results with the improved model initial model when the restitution coefficient or the contact stiffness large enough. For typical concrete structural pounding, the initial model is available.

Abstract: Damage-involved structural pounding during earthquakes has been recently intensively studied using different impact force models. The results of the previous studies indicate that the linear viscoelastic model is relatively simple yet accurate in modelling pounding-involved behaviour of structures during earthquakes. The only shortcoming of the model is a negative value of the pounding force occurring just before separation, which does not have any physical explanation. The aim of the present paper is to verify the effectiveness of the modified linear viscoelastic model, in which damping term (related to modelling of damage effects) is activated only during the approach period of collision therefore overcoming this disadvantage. The accuracy of the model is checked in a number of comparative analyses, including the comparison with the results of impact experiments and shaking table experiments on pounding between two steel towers. The results of the study indicate that the use of the modified linear viscoelastic model leads to very similar pounding-involved responses as in the case of the linear viscoelastic model.