Journal of Seismology and Earthquake Engineering
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Journal of Seismology and Earthquake Engineeringendaily1Sun, 01 Dec 2019 00:00:00 +0330Sun, 01 Dec 2019 00:00:00 +0330Some Contribution to Rational Design of Piled Raft Foundation for Oil Storage Tanks on Non-Liquefiable Ground: Application of Dynamic Centrifuge Modeling
http://www.jsee.ir/article_243313.html
Some level of settlement is allowed in the design of oil tanks if uneven settlement iscontrolled within allowable values. Considering the critical condition of Piled RaftFoundation (PRF), that is, secure contact of raft base to the ground surface, PRF isconsidered as one of the rational foundations for the oil tanks. However, PRF has acomplicated interaction with soil under horizontal seismic loading. Regarding thiscomplexity, the main concern in use of PRF for oil tanks is proper design ofthis foundation system. In this study, a series of centrifuge tests were performed toinvestigate the mechanical behavior of oil tanks supported by PRF on non-liquefiablesand. Using the observed results, such as accelerations of the tank and groundand displacements of the foundation, some practical hints for reasonable design ofpiled raft foundation for oil tanks on non-liquefiable sand are discussed. Accordingto the results of this study, the main concern in the rational design of the foundationis piles' design and their punching effect on the raft, in case of PRF of oil tank onnon-liquefiable sand.Buckling Response and Elastic Stiffness of Butterfly Dampers
http://www.jsee.ir/article_243312.html
Butterfly dampers dissipate energy through the flexural, shear, or axial response ofthe strips when the device is subjected to inelastic cyclic deformation. The bucklingresponse, elastic stiffness, and cyclic performance of non-uniform steel butterflydampers have been studied in this paper. Validated material and geometric nonlinearfinite element models in the ABAQUS has been used to perform a comprehensiveparametric study on a wide range of geometrical parameters to evaluate theresponse of non-compact butterfly dampers. The results showed that although thelow-cycle-fatigue response of butterfly dampers can be improved by altering the sideedge shapes, the buckling capacity and elastic stiffness of non-uniform strips woulddecrease in comparison with uniform ones. Hence several analytical equations wereprovided to quantitative prediction of the buckling capacity and elastic stiffness ofbutterfly dampers.Modification of Park-Ang Damage Index to Accommodate Effect of Aftershocks on RC Structures
http://www.jsee.ir/article_243311.html
Seismic design codes do not consider the effects of aftershocks on structures.Moreover, most damage estimation methods disregard the effects of consecutiveearthquakes. Recent earthquakes have demonstrated that the aftershocks can causemajor damage to mainshock-damaged structures. After a strong seismic event, itshould be determined if a mainshock-damaged building is safe for reoccupation inthe event of aftershocks. This study examined the effects of both the main shock andaftershocks on the damage index of reinforced concrete (RC) structures. Recordsfrom 19 mainshocks that occurred in the Japan seismic region with momentmagnitudes of greater than 4 were examined. More than 100 acceleration timeseries from these events (mainshock + aftershock events) were applied to evaluatethe damage index. Seismic damage analysis was performed on a series of RCcolumns and RC frames. The natural period of these structures varied from 0.1 to 2.5s. The damage index introduced by Park and Ang was employed to estimate thestructural damage. Acceleration time series were applied to the structures in twosteps. First, only mainshocks were applied to the structures and the damage indexwas obtained. Next, both the mainshock and aftershocks were applied to thestructures and structures damaged by a mainshock were analyzed under periodicaftershock events. The results showed that the increase in structural period and thePGA of the aftershocks amplified the damage index under the effects of theaftershocks. A modification to Park-Ang damage index is proposed using a dimensionlessterm to accommodate the effect of aftershocks.Initial Solution for Designing a Soft Substructure in a Mass Isolation System with Consideration of Stability Constraints
http://www.jsee.ir/article_243310.html
The new techniques in seismic design of structures are usually attributed to highdamping ratios. Mass isolation of structures is one of the new techniques in seismicdesign of structures that focuses on the mass of the structure as the main target forseismic isolation and reducing earthquake effects on buildings. Mass IsolationSystem (MIS) consists of two stiff and soft substructures connected by a viscousdamper. The mass subsystem comprises the main mass of the structure, which isattached to a frame with a low stiffness by a separation mechanism at the height ofthe structure including viscous dampers to a stiffness subsystem consisting of amoment or braced frame system with great stiffness. In this paper, the aim is topresent a simple preliminary design method based on the normalized pushovercurve. The most important problems for increasing the period of the soft structureare deformation and structural stability. This paper presents a preliminary designsolution for a soft substructure of the Mass Isolation System (MIS) with considerationof stability constraints. To this end, the paper presents mathematicalrelationships to calculate the period of the structure followed by proposing a simplesolution for the design of the soft substructure.Parallelization of 3D Pseudo-Bending Algorithm for Seismic Ray Tracing
http://www.jsee.ir/article_243309.html
Bending ray tracing is a technique for finding the shortest travel path from a fixed source to a fixed receiver. Ray tracing is a time-consuming computing technique in applications such as tomography, which involves a large number of source-receiver pairs. In this regard, parallel programming makes it possible to reduce the running time of a serial program significantly by breaking it into a discrete series and solve it by different processing units simultaneously. Along with the rapid development of parallel computing technologies in both hardware architecture and system software, parallel computing is growing rapidly in a broad range of scientific computing applications. In this paper, the parallelization of pseudo-bending ray tracing algorithm is presented using both task and data parallelization strategies. In the task parallelization, the bending calculation of each path section is distributed to different processors, while in the data parallelization, due to the independent calculation for each pair of source-receiver, the data parts are distributed to different processors. The performance results of the parallelizations of the pseudo-bending algorithm for ray tracing in a 3D velocity model are shown using OpenMP, which is an application programming interface for shared memory multiprocessing programming. The advantage of OpenMP programming model is its simplicity to parallelize an existing serial code. This is especially useful now that multi-core CPUs are common. The results show the effectiveness and efficiency of the approach. A significant speedup in the ray tracing implementation is achieved. This reduction in computation time allows more rays to be traced, which directly affects the accuracy of tomography results. Sufficient ray coverage is needed to obtain tomography images with perfect resolution.Interaction of Underground Tunnel and Existing Shallow Foundations Affected by Normal Faults
http://www.jsee.ir/article_243314.html
In major earthquakes, permanent ground deformations due to the fault movementscause serious damage to the foundations and structures. Although many ofstructural seismic design codes have recommended avoiding the construction ofstructures in the adjacent to active faults, it is not always a viable option. Forexample, the lifeline facilities such as gas tunnels, water supply tunnels andtransportation tunnels, due to their extensive length, cannot often avoid crossingactive faults. Therefore, it is necessary to evaluate the interaction mechanismbetween structures and fault rupture for effective design to reduce the hazardsassociated with surface faulting. This study investigates the interactions ofunderground tunnel and existing shallow foundation affected by normal faultusing the finite element method. The results show that the existence of a tunnelchanges the fault rupture path and in some cases can increase the foundationrotation. It causes the occurrence of severe level of damage to the structure andincreases fear about its instability.Preliminary Estimation of Ground Motion of September 24, 2013, Pakistan Earthquake Using Modified Semi-empirical Approach
http://www.jsee.ir/article_243385.html
Hazard plays a vital role in assessing the risk of any area. For hazard estimation, it is essential to obtain ground motion records from various seismic stations. However, it is not always easy to get ground motion data. The present study is an attempt to generate ground motions of recent September 24, 2013, Pakistan earthquake using modified semi-empirical approach. It is based on ?2 model. The first part of the method considers a time series having the basic spectral shape of acceleration. The deterministic model of rupture source has been used in the second part of the method to simulate the envelope of accelerogram. For the study, a MATLAB code is written to generate synthetic accelerograms at stations Awaran, Panjgur, Tagas, Korak, and Gajar. The results are compared with peak ground acceleration (PGA) of seismic zonation map of Pakistan and the United States of Geological Survey (USGS). The PGA values obtained from modified semi-empirical method gives satisfactorily good with the PGA values of USGS. But, slightly significant variation is observed between synthetic accelerogram PGA values and Pakistan PGA values at stations all stations.