Papers by Author: Robert Jankowski

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Authors: Robert Jankowski
Abstract: The reports after earthquakes indicate that earthquake-induced pounding between insufficiently separated structures, or their parts, may cause substantial damage or even lead to structural collapse. One of the most spectacular example of pounding-involved destruction resulted from interactions between the Olive View Hospital main building and one of its independently standing stairway towers during the San Fernando earthquake of 1971. The aim of the present paper is to assess the range and intensity of damage caused by collisions between these reinforced concrete structures based on the results of a detailed 3D non-linear FEM analysis of poundinginvolved response. In the study, reinforced concrete has been modelled as layered material with rebar elements embedded into concrete. The non-linear material behaviour, including stiffness degradation of concrete due to damage under cyclic loading, has been incorporated in the numerical model. The results of the study show that pounding may lead to the significant increase of the range and intensity of damage at the base of the stairway tower, as a lighter structure, as well as may cause substantial damage at the points of contact. On the other hand, the intensity of damage induced in the heavier main building has been found to be nearly unaffected by structural interactions.
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Authors: Sayed Mahmoud, Ayman Abd-Elhameed, Robert Jankowski
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.
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Authors: Robert Jankowski
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.
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Authors: Robert Jankowski
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.
309
Authors: Daniel Burkacki, Robert Jankowski
Abstract: Diagnosis of damage in civil engineering structures has recently become an important issue in the safety assessment procedure. Among a number of different approaches, a method of measuring the changes in natural frequencies is one of the most effective indicators of global damage. It has been successfully applied to relatively small structures, however, the tests on large structures are very difficult and the practical application of the method still requires further investigations. The aim of the present paper is to show the results of the shaking table experimental study concerning the diagnosis of damage in a model of cylindrical steel tank with self-supported roof which is filled with liquid. During the tests, the base of the structure was excited under the harmonic loading with variable frequency. The tests were repeated for different stages of damage, which was introduced in the model by easing the bolts of structural supports as well as by cutting the welds between the shell and roof as well as between roof elements. The results of the study show a characteristic decrease in the natural frequencies for the case of structural supports with reduced stiffness (global type of damage). On the other hand, cutting the welds (local type of damage) has lead to the considerable increase in the power spectral density values for higher vibration modes.
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Authors: Daniel Burkacki, Michał Wójcik, Robert Jankowski
Abstract: The safety of civil engineering structures is one of the most important issues of building industry. That is why the assessment of the damage-involved structural response has recently become of major concern to engineers. Among a number of different approaches to diagnosis of damage, the method of measuring the changes in natural frequencies is considered to be one of the most effective indicators of global damage. From the practical point of view, the method has been successfully applied to relatively small structures, while in-situ tests on large structures, such as bridges, tanks or dams, are very difficult. The aim of the present paper is to show the results of the numerical analysis concerning the diagnosis of damage in a cylindrical steel tank with self-supported roof which is filled with liquid. The tests have been conducted for various stages of damage, introduced in the numerical model by reducing the stiffness of tank-soil system as well as by cutting the connection between the shell and roof of the tank as well as between roof elements. The results of the numerical analysis have shown the characteristic decrease in the natural frequencies for the case of tank-soil system with reduced stiffness, which is the global type of damage. On the other hand, cutting the welds, which can be considered as the local type of damage, has not lead to the differences in the natural frequency values, although differences in local deformations of shell in the vicinity of cuts have been observed in vibration modes.
374
Authors: Natalia Lasowicz, Arkadiusz Kwiecień, Robert Jankowski
Abstract: In this paper, the results of two experiments, focused on testing the effectiveness of a method of enhancing the seismic (dynamic) resistance of masonry columns with the use of flexible polymer adhesive, are shown. The first experiment was devoted to investigate the damping properties of a polymer working between two stiff layers, whereas the aim of the second one was to verify if the identified damping properties of the polymer can improve the dynamic behaviour of short masonry columns (prisms) strengthened by confinement made of GFRP grid bonded by the polymer adhesive. The results of the first stage of experimental investigation indicate that bonding two stiff elements with the analyzed polymer adhesive leads to the significant increase in overall damping properties. The results of the second experiment show that the GFRP grid confinement with flexible polymer adhesive is more effective than stiff epoxy and mineral adhesives.
478
Authors: Tomasz Falborski, Robert Jankowski, Arkadiusz Kwiecień
Abstract: A new method of repairing damaged structures by injecting the cracks with specially designed polymer mass (flexible two-component grout based on polyurethane resin) has been recently proposed. The technique is mainly dedicated to damaged masonries, especially historical structures where minimum intervention is permitted. The cracks are filled with the special injection, forming the flexible joints bonding the disrupted structural elements. The aim of the present paper is to show the results of the experimental study focused on properties of the polymer mass used for the injections. First, the material has been subjected to static compression tests. Then, the polymer mass has been examined dynamically under harmonic excitations with different frequencies and strain levels. The results of the study indicate that the tested polymer mass shows highly non-linear behaviour with relatively low resistance under small displacements and stiffening effect for higher strain levels. Moreover, it is substantially dependent on the strain rate having higher initial deformation modulus for higher strain rate values. Finally, the observed hysteretic behaviour of the material confirms its potential to dissipate the energy during vibrations preventing from further structural damage in the case of dynamic loading.
347
Authors: Robert Jankowski, Ayman Seleemah, Saher El-Khoriby, Hytham Elwardany
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.
249
Authors: Robert Jankowski
Abstract: Past earthquakes indicate that pounding between inadequately separated structures may cause considerable damage or even lead to collapse of colliding structures. Intensive study has been recently carried out on mitigation of pounding hazards. The assessment of damage due to structural pounding, or its prediction under a particular ground motion, requires the knowledge of the maximum impact force value expected during the time of earthquake. The aim of the present paper is to consider the concept of impact force response spectrum for two closely-spaced structures, which shows the plot of the peak value of pounding force as a function of the natural structural vibration period. The spectrum can be used as a practical tool to assess the magnitude of the expected pounding-induced damage and, if necessary, to apply some damage reduction techniques. In the analysis, both interacting structures have been modelled by single-degree-of-freedom systems and pounding has been simulated by the non-linear viscoelastic model, which accounts for the energy dissipation during impact. The examples of response spectra show that the appropriate selection of the separation gap between structures as well as the dynamic structural parameters, such as the natural vibration period, mass and damping, might have a significant influence on the intensity of damage due to earthquake-induced pounding.
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