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Month: March 2018
BEARABLE MAXIMUM SEISMIC ACTION FOR EXISTING CONCRETE DAMS BY ITALIAN STANDARD
The recently updated Italian standard adds, to the conventional safety assessment, the evaluation of the bearable maximum seismic action for existing concrete dams. This prescription actually represents a trend of current International guidelines that are gradually replacing the previous, deterministic safe/fail rationale and are accounting for nonlinear behavior. Depending on dam typology, a preliminary evaluation of the maximum bearable seismic action can be interpreted as the research of a capacity function for a given failure mechanism. In this work, the bearable maximum seismic action is investigated through numerical, three-dimensional, finite element simulations via a multipurpose code for two existing concrete dams placed in a region of low-to-moderate seismicity. In the first case, an arch-gravity dam, the overcoming of the limit stress conditions in wide parts of the bulk, the stiffness degradation in the global nonlinear response, and the displacement discontinuity in structural joints are used for the evaluation. In the second case, for a buttress-gravity dam, the sliding in the construction and foundation is instead considered.
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SEISMIC MICROZONATION MAP OF PENANG ISLAND
The Peninsula of Malaysia is situated at a distance of 350 km from the seismic zone of Sumatra fault. However, some ground motions are caused by the Sumatra Earthquake. According to the announcements by the Malaysian Metrological Department, the earthquake occurred near Sumatra on 2nd November 2002 with the magnitude of 7.4 had caused tremors in various parts of the Malaysian Peninsula including Penang Island. Penang Island is the most populous island city which is situated in the state of Penang with a rising population of 0.7 million people. Hence, the need for seismic hazard mitigation is evident. In this research, seismic microzonation maps presenting amplification and surface acceleration are plotted to produce a comprehensive microzonation model, to indicate the high risk earthquake areas for land use management. 24 boreholes were located and drilled for data collection. The collected data from boreholes and the bedrock motion obtained were calculated by NERA (Nonlinear Earthquake site Response Analysis), which had generated the surface acceleration and amplification needed for mapping. The results of this paper show the high seismic risk areas on eastern part of the Island that can be used in the planning of urban city infrastructure, which can recognize, control and prevent geological hazards.
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THE WHOLE LIFE SEISMIC OPTIMAL DESIGN OF THE STEEL FRAME STRUCTURE BASED ON DAMAGE RELIABILITY UNDER ACIDIC ATMOSPHERE
In order to realize the seismic optimum of steel frame structure, the influence of coupling effect of earthquake and corrosion is considered on the reliability. This paper presents an internal-and-external optimized design flow iterative process; the outer layer is used to optimize the model while the inner layer for analyzing the reliability. The optimization model is on the basis of “investment-benefit”, and its objective function is established by the linear weighted method. In addition, the reliability analysis is simulated by Monte Carlo method and the overall damage is calculated by the time-varying seismic damage model, which is used to evaluate the reliability and calculate the failure probability under different performance states. Finally, by the Visual studio 2010 software the optimization program is realized. As the increasing of the iterated times the total cost of structure decreases and converges to the optimal cost. The optimization is effective and feasible
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EVALUATION OF THE SEISMIC DEMAND OF AN EXISTING TALL BUILDING
We show the results of response spectrum analyses performed on a 1980’s steel structure with a seismic-resistant system made of RC walls. The aim is to quantify the impact of different choices, usually left to the engineering judgment, on the evaluation of the seismic demand for structures like that of the case study. The analyses show that seismic demand can increase of 170% passing from stiff to soft ground, revealing how site effects can be far more important than other issues related to concrete cracking and foundation stiffness. Therefore, a study of local seismic site response is crucial for tall buildings.
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A STUDY ON FORM AND SEISMIC VULNERABILITY OF THE DOME OF SAN FRANCESCO DI PAOLA IN NAPLES.
The aim of this research is the structural study of the hemispherical dome of San Francesco di Paola in Naples and, in particular, the evaluation of its degree of seismic safety not considering the role of the supporting structures. The methods we adopt are based on the determination of a class of purely compressive stress regimes, which are balanced with the load. Within the unilateral model for masonry (Heyman’s model), the mere existence of such a class is a proof that the structure is safe; members of this class can be used to assess the geometric degree of safety of the structure and to estimate bounds on the thrust forces exerted by the structure on its boundary. The analysis has been performed, by using both the graphical method and the membrane approach. The methodological innovation consists in the use of both the analytical and the traditional methods of graphical calculation of masonry structures, considering both vertical and horizontal loads. As a result of our analysis, we conclude that the sole dome can sustain a horizontal load of 0,577 g.
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ON THE SIMULATION OF THE SEISMIC ENERGY TRANSMISSION MECHANISMS
In recent years, considerable attention has been paid to research and development methods able to assess the seismic energy propagation on the territory. The seismic energy propagation is strongly related to the complexity of the source and it is affected by the attenuation and the scattering effects along the path. Thus, the effect of the earthquake is the result of a complex interaction between the signal emitted by the source and the propagation effects. The purpose of this work is to develop a methodology able to reproduce the propagation law of seismic energy, hypothesizing the “transmission” mechanisms that preside over the distribution of seismic effects on the territory, by means of a structural optimization process with a predetermined energy distribution. Briefly, the approach, based on a deterministic physical model, determines an objective correction of the detected distributions of seismic intensity on the soil, forcing the compatibility of the observed data with the physical-mechanical model. It is based on two hypotheses: (1) the earthquake at the epicentre is simulated by means of a system of distortions split into three parameters; (2) the intensity is considered coincident to the density of elastic energy. The optimal distribution of the beams stiffness is achieved, by reducing the difference between the values of intensity distribution computed on the mesh and those observed during four regional events historically reported concerning the Campania region (Italy).
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A BEAM ELEMENT ALLOWING MULTIPLE SLOPE DISCONTINUITIES FOR RC STRUCTURES: AN APPLICATION
A beam/column element allowing the formation of multiple plastic hinges in columns or beams of a reinforced concrete (RC) framed structure is used in this work to show, through an application, its advantages with respect to conventional lumped plasticity models. Slope discontinuities can be located at any position of an Euler-Bernoulli beam span and not at the two extremes only. The model is in fact written in the framework of a modified lumped plasticity theory, and respectful of a thermodynamic approach. Flow rules and state equations are derived invoking the Theorem of maximum dissipation and using a Bresler’s type activation domain. The beam element has already been implemented in a research-oriented code to run nonlinear analyses on RC frames. The discretized loading process is separated, at each step, in two phases: a predictor and a corrector phase. Numerical examples highlight how the new finite element permits to run nonlinear analyses avoiding a mesh refinement.
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