فهرست مطالب

  • Volume:13 Issue: 3, 2012
  • تاریخ انتشار: 1391/06/01
  • تعداد عناوین: 6
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  • Reza Mehrnia Page 139
    In this research, a nonlinear analysis of geophysical databases has been performed with spectrum-area applications for revealing seismogenic decomposed lineaments in northern regions of Tehran. According to geophysical concepts, a fabricated pattern that is generated by multiplicative processes usually represented to powerlaw relationships under different statements. Therefore, a multifractal solution is proposed by this research for obtaining iterative peculiarities of seismogenicresources as an imagery location of triggering movements before destructive earthquakes. Several casual studies on North Tehran Faulted regions have performed since 1965, but it is theoretically updated in current research by considering a coherent concept to geospatial evidences. In practice, available databases including vectors and instrumental acquisitions have been processed by GIS facilities due to applying a multicriteria decision-making algorithm into gridded values. The results showed that nonlinear analysis of decomposed lineaments around North Tehran Fault can provide a new seismogenic pattern for updating Hazard Analysis Programs based on reducing in structural complexities.
    Keywords: Coherency, Lineaments, Multifractal, Nonlinear, Seismogenic, Tehran
  • Ali Lashkari Page 149
    It has been revealed that both elastic and plastic components of the granular soils behavior are affected by the stress induced anisotropy as a result of the history of previous shear loadings. While the influence of fabric anisotropy on the plastic elements of the elasto-plastic constitutive models has been extensively studied in the literature, the anisotropic elastic response is usually neglected mainly because of avoiding complication. Herein, a simple anisotropic elasticity theory is proposed. To this aim, the fourth order elasticity tensor is related to a second order fabric-dilatancy tensor describing magnitude and direction of induced anisotropy. Proper constitutive equations for calibration of the proposed elasticity theory using data of triaxial and simple shear tests are presented. Then, the introduced elasticity theory is implemented within an advanced sand constitutive model. The model predictions are compared with the experimental data of independent research teams. It is shown that the modification of the basic platform by the proposed anisotropic elasticity theory leads to improvement of liquefaction predictions.
    Keywords: Granular soils, Liquefaction, Elasticity, Anisotropy, Fabric tensor, Dilatancy
  • Kiran K. Shetty, Krishnamoorthy Page 167
    Dynamic response of a multi-storey symmetrical and asymmetrical space frame structures having six degrees of freedom (three translations along x, y, z-axes and three rotations about these axes) at each node, with multiple tuned mass dampers (MTMD) on its top is obtained. Each tuned mass damper (TMD) is modeled using atwo-noded element having two translational degrees of freedom at each node. MTMD with uniformly distributed frequencies is considered for this purpose. The effectiveness of MTMD in suppressing the structural response is determined by comparing the response of corresponding structure without MTMD. It is found that the MTMD can be used effectively to suppress the acceleration, base shear, bending moment, translational and rotational responses of the symmetrical and asymmetrical structures. The effect of important parameters on the effectiveness of the MTMD is also studied. The parameters include the fundamental characteristics of the MTMD such as damping, mass ratio, total number of MTMD, tuning frequency ratio, frequency spacing of the dampers and structural damping. It is shown that these parameters have considerable influence on the effectiveness of the MTMD in reducing the dynamic response of the structure.
    Keywords: Vibration control, MTMD, Base, excitation, Six degrees of freedom at each node, Symmetrical, asymmetrical space frame structures
  • Alireza Mortezaei, Hamid Reza Ronagh Page 179
    During past decades, many control algorithms with some advantages/weaknesses have been proposed. However, the most famous and historic algorithm which has found widespread applications in different fields of science, is the family of optimal control method (OCM). Today, this family includes many different approaches using various performance indices in continuous or discrete domain of consideration. The main stem of OCM is rooted in a simple definition, say performance index (PI), which should be minimized with respect to the main independent variables of the system. Although, different proposed algorithms are employed various performance indices besides simple or stable weighting matrices, their performances are noticeably similar. Extensive analysis shows that the main aspect, which results in reasonable similar performances in spite of their assumption for determining control force, arise from solving the Riccati matrix equation (RME) during their procedure or their stability criteria. This idea is examined by introducing a new simple but unusual assumption, named the simplified LQR (SLQR), via considering seismic behavior of an eight-story shear type building structure.
    Keywords: Optimal control method, Riccati matrix equation, Simplified LQR, SLQR, AMD
  • Rahman Mirzaei, Omid Bahar Page 195
    During past decades, many control algorithms with some advantages/weaknesses have been proposed. However, the most famous and historic algorithm which has found widespread applications in different fields of science, is the family of optimal control method (OCM). Today, this family includes many different approaches using various performance indices in continuous or discrete domain of consideration. The main stem of OCM is rooted in a simple definition, say performance index (PI), which should be minimized with respect to the main independent variables of the system. Although, different proposed algorithms are employed various performance indices besides simple or stable weighting matrices, their performances are noticeably similar. Extensive analysis shows that the main aspect, which results in reasonable similar performances in spite of their assumption for determining control force, arise from solving the Riccati matrix equation (RME) during their procedure or their stability criteria. This idea is examined by introducing a new simple but unusual assumption, named the simplified LQR (SLQR), via considering seismic behavior of an eight-story shear type building structure.
    Keywords: Optimal control method, Riccati matrix equation, Simplified LQR, SLQR, AMD
  • Roberto Villaverde Page 209
    Base isolation is a technology that is widely accepted by the profession as an effective means to protect structures and non-structural components against earthquake damage. This is demonstrated by the large number of buildings and bridges that have been built or retrofitted using this technology. It is contended, however, that, at present, the existing isolation systems have limitations and that these limitations have prevented a widespread use of the technology in ordinary structures and in developing and emerging countries. It is the purpose of this paper to make a brief review of the predominant isolation systems, pinpoint their major disadvantages, and describe some of the solutions that have been proposed to overcome these disadvantages. The systems considered are (a) laminated elastomeric bearings, (b) friction pendulum bearings, and (c) sliding bearings. Special attention is given to the description of two recently proposed sliding systems that incorporate unusual features: (a) hydrostatic bearings, and (b) hydromagnetic bearings. The review reveals that many researchers are still active in the base isolation field and that many interesting improvements have been proposed over the last few years.