Month: December 2019

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Tuned mass dampers (TMDs) and tuned liquid dampers (TLDs) are the most well-known passive control systems used to decrease structural responses against earthquake excitations. In the present study, the performance of equipped low-rise and mid-rise buildings with these kinds of dampers was evaluated, and the effects of near-field and far-field earthquakes were compared. To this end, the dynamic analyses have been accomplished in both controlled and uncontrolled states using seven ground motion records of near-field and far-field. Furthermore, both TMD and TLD at these buildings have been modeled with five various mass, stiffness, and damping percentages. The results demonstrate that TMD has better performance as compared to TLD, and descending structural responses in a low-rise building in near-field ground motion are more than far-field earthquakes. However, the responses of a mid-rise building in far-field are less than the near-field records.

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The assessment of damage in structures that have suffered one or more earthquakes is of paramount importance to better understand the post-earthquake effective behaviour, and eventually to define the more appropriate design strategies for retrofitting and repairing.
The paper, which is focused on moment-resisting (MR) steel frames, deals with post-earthquake assessment after one or more seismic events. A procedure combining non-linear time-history finite element analysis with the low-cyclic fatigue theory have been applied to appraise the damage level of each frame component and then the residual load carrying capacity have been evaluated via the incremental static analysis of the damaged frames. It is worth underlining that, on the basis of the discussed numerical results, the damage measurement and the residual load carrying capacity, which are often neglected in routine design, appear very useful to increase the knowledge on the effective safety level of the frame after one or more earthquake.

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The definition of a seismic action for the structural analysis of existing buildings generally consists in the selection of a response spectrum. The Italian design code offers a basic procedure to define a reference spectrum that includes amplification effects from site conditions. However, when considering architectural heritage buildings, a more accurate determination of the local spectrum could be of interest, given the need to effectively protect these assets. A local seismic response analysis has been performed in three study sites using geological and geophysical tests for the reconstruction of the seismo-stratigraphy, individuation of the expected seismic inputs on bedrock, numerical analyses and individuation of the expected elastic acceleration response spectra. Test results have been applied in the structural analysis of the heritage buildings at the sites, showing significant effects on the assessment of their seismic safety.

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According to the researches, the performance of masonry buildings in severe earthquakes is very weak and on the other hand, there is no comprehensive research regarding a suitable strategy for strengthening of these buildings. The use of shot-Crete concrete cover on the masonry walls building is one of the solutions, but due to the fact that this solution is a precious price method, a modern and low cost method is needed. In this paper, for the numerical simulation of a masonry wall, ABAQUS software with EXPLICIT method is selected and in order to achieve a new improvement method, first, reinforcement models of masonry wall made by hollow clay blocks using nonlinear incremental loads has been investigated and then the best adapted model is chosen. The results of study (before and after improvement) of application of two Bam and Manjil seismic accelerometer data on a school model and simulation of them by finite element method shows the effectiveness of new method for improving the performance with featuring lower cost.

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This paper deals with a critical analysis of the current seismic design criteria provided by Eurocode 8 for Moment Resisting Frames. This approach is based on the capacity design principle, in which the design is governed by the strength and stability of the structural elements and by hierarchy of strength, this in order to allows development of high dissipative collapse mechanism. The drawbacks of this approach is that the maximum required inter-storey drifts, at service limit states, are not directly satisfied. This leads to an enlargement of geometrical dimensions of the elements, producing significant over-strength and nullifying the use of high behaviour factors.
In this paper, an alternative design criterion is proposed. According to this the design is governed by maximum inter-storey drift at service limit state, whereas the satisfaction of capacity design rules is contextually verified. This means to design the structure with seismic actions corresponding to service earthquakes (i.e. unitary q-factor). Linear and non-linear static analyses on 3, 6 and 9-storey steel frames were performed to compare the design methodologies in terms of push-over curves (i.e. over-strength), inter-storey-drifts and collapse mechanisms. Furthermore, the effect of panel zone on the global seismic response of frames was taken into account in the performed analyses. It has been properly modelled using one of the most diffused literature model, the so called Krawinkler’s ‘frame model’, accounting both its elastic and plastic behaviour.

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To study the seismic behavior of corroded steel frame beam-column joints in acid atmosphere, the hysteretic behavior of 6 steel frame beam-column joints with different degrees of corrosion were investigated experimentally, which have been damaged by the different acid salt spray corrosion cycles under low cyclic reversed loading. The test results show that as the corrosion degree increases, the mechanical and seismic properties of the specimen such as strength, stiffness, ductility and hysteretic energy are deteriorating. In addition, the restoring force model of the rusted steel frame beam-column joints was studied. Based on the test results, the formula of the characteristic points of the skeleton curve of steel frame beam-column joints with corrosion was obtained, which considered the steel corrosion rate. The cyclic degradation index based on hysteretic energy loss was introduced, and the hysteresis rule applied to steel frame joint specimens after corrosion cycles were proposed, and then restoring force model of corroded steel frame beam-column joint was established, which considered the strength and stiffness degradation. And then, the applicability of the model was verified. The results show that the proposed hysteretic model can desirably reflect the hysteretic behavior of corroded steel frame beam-column joints. This study may provide theoretic basis for elastoplastic analysis of existing steel structures in acid atmospheric environment.

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In this comprehensive study, the effect of the interaction between tunnel lining and the surrounding medium on the monolithic tunnel lining (MTL) under earthquake loading is investigated using different methods including five analytical methods, quasi-static approach, and numerical simulation (time history) under full-slip and no-slip conditions considering. The results showed that the stress induced by seismic loads in tunnel lining in no-slip condition is approximately three times higher than that in the full-slip condition. The results also presented that numerical and quasi-static methods have a meaningful agreement with analytical methods under both conditions. In the next step, dynamic analysis of segmental tunnel lining (STL) was performed using Discrete Element Method (DEM), and the results was compared with the monolithic lining.. The resultsindicated that maximum stress in the MTL is more than STL, while the maximum strain in MTL is less than that in STL. This is occurred because joints in segmental lining reduce the lining stiffness. In other words, the rigidity increase in the supporting system is associated with a flexibility decrease in the lining with respect to rock medium.

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