فهرست مطالب

Structural Engineering and Geotechnics - Volume:2 Issue: 2, 2013
  • Volume:2 Issue: 2, 2013
  • تاریخ انتشار: 1392/02/18
  • تعداد عناوین: 7
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  • Majdedin Mir Hosseini, R. Bahrami, M. Asadolahipajouh Pages 1-10
    The number of constructed dams has been largely increased due to high demands of water supplies, and earth dams are the most common types since they are more compatible to the environment. Nevertheless, the stability of these important structures during earthquakes has to be carefully evaluated and guaranteed. In the past, earth dams usually designed with pure clay core, but in recent decades they are widely designed and constructed with mixed clay core due to their better performance against vibrations particularly earthquake loadings. This paper evaluates the displacement performance of the Karkheh Large Embankment Dam with mixed- clay core, recently constructed in south-western part of Iran, under earthquake motions and compares the dynamic analyses’ results with those of pure-clay core. In this work, the Karkheh Dam with both mixed and pure clay core is numerically modeled using the FLAC 4.0software. After calibrating the model and completing the static and dynamic analyses under different excitations, belonged to some heavy past earthquakes, the results in terms of the maximum settlements, horizontal displacements of upstream and downstream shells are estimated, compared and discussed. Based on the obtained results, it is noted that the dynamic performance of earth dams with mixed-clay core is more desirable than that of pure-clay core. It is also observed that the seismic settlements of the dam with pure-clay core averagely show an increase of 20 percents compared with that having the mixed-clay core.
    Keywords: Karkheh earth dam, Mixed clay core, Dynamic analyses, Numerical modeling, Earthquake, Deformation
  • Seiyed Ali Haj Seiyed Taghia, A.S. Moghadam Pages 11-17
    This paper examines differences in performances of a range of torsionally stiff and flexible single story buildings designed with the provisions of Iranian Standard 2800. Seismic nonlinear dynamic time history behavior of eight building models subjected to seven horizontal bi-directional design spectra compatible ground motions are investigated. These models cover a wide range of very torsionally stiff to very flexible buildings. Response parameters are element ductility demand and building story drift ratio. These criteria are appropriate indices for structural and nonstructural damages, respectively. This investigation shows that the linear static analysis of building code such as Iranian Standard 2800 is not generally adequate for structures with very low torsional stiffness.
    Keywords: Torsion, Torsionally stiff, torsionally flexible, Standard 2800, Non, linear dynamic analysis, Story drift ratio, Performance level
  • Armin A.Nobakhtnamin Pages 19-28
    This study aimed to investigate the effects of stiffeners on buckling of thin cylindrical shells under uniform axial compression. To this end, more than 300 finite element models of stiffened cylindrical shells were prepared. The variables considered are shell thickness, number, dimension and the location of the vertical and horizontal stiffeners as well as circular symmetrical imperfections. Results show that the stiffeners can increase buckling of the stiffened cylindrical shells under axial compression. It is also shown that buckling of the cylindrical shells is susceptible to some circular imperfection patterns. In this context, buckling graph of the models are compared with each other; obviously, the stiffened shells with more stiffeners have upper buckling graph in force - displacement curves.
    Keywords: Cylindrical shell, Thin, walled, Stiffener, Buckling, Axial compression
  • M.H. Jahangir Pages 29-38
    To evaluate the earth seismic response due to earthquake effects, ground response analyses are used to predict ground surface motions for development of design response spectra, to compute dynamic stresses and strains for evaluation of liquefaction hazards, and to determine the earthquake induced forces that can lead to instability of earth and earth-retaining structures. Most of the analytical solutions presented are affected by the defect that the stress-strain relationship must be of rather simple form (linear elastic, with perhaps linear hysteretic damping), and that the soil properties must be homogeneous. Real soils are often composed of several layers of variable properties, and often they exhibit non linear properties. Therefore, a numerical solution may be considered, because this can more easily be generalized to non-linear and non-homogeneous properties. In this paper, a simple numerical solution method is presented, again with damping property. The considerations will be restricted to one-dimensional wave propagation in a linear elastic layer which the equation of motion will be resolved with weighted residual method and the advantages of using this method will be ultimately discussed. Of course, the most important benefit of this element free approach is having a suitable approximated function for wave displacement in height of a soil layer.
    Keywords: Ground response, Wave propagation, Numerical solution, Weighted residual method, Element free approach
  • Elnaz Peyghaleh, M.R. Zolfaghari, P. Vaziric Pages 39-50
    This paper presents a study on determining the degree of effectiveness of earthquake risk mitigation measures and how to prioritize such efforts in developing countries. In this paper a model is proposed for optimizing funds allocation towards risk reduction measures (building retrofitting) and reconstruction process after potential earthquakes in a regional level. The proposed model seeks optimized strategy towards risk reduction based on minimizing or maximizing various criteria such as retrofitting costs, economic damages including business interruption losses, number of human casualties and other seismic hazard consequences. The main objective of this model is to find optimum strategy for maximizing the benefits of available economic resources for retrofitting and reconstructions. Regional seismic hazard and building stocks and their vulnerability functions are used to model probabilistic seismic risk for a given region. The proposed model is adjusted for developing countries exposed to high seismic sources like Iran. In order to present the application of the proposed method, the approach is applied for a pilot area in Tehran. Results illustrate the variation of mitigation in particular, structural retrofitting expenditures and reconstruction expenditures by structural type for buildings in this region. In addition, recommended expenditures by year for the case study are obtained according to the results.
    Keywords: Optimization, Vulnerability, Reconstruction, Earthquake Risk Mitigation
  • M. Askari, Hasan Aghbarati Pages 51-65
    Near-fault ground motions have caused very much damage in the vicinity of seismic sources during recent earthquakes. It is well known that under specific circumstances, intensive ground shakings near fault ruptures may be characterized by short-duration impulsive motions. This pulse-type motion is generally particular to the forward direction, where the fault rupture propagates towards the site at a velocity close to shear wave velocity. Ground motions affected by directivity focusing at near-field stations contain distinct pulses in acceleration, velocity and displacement histories. These ground motions can generate much higher base shears, inter-story drifts and roof displacements as compared to far-fault ground motions. Since structures under the effect of destructive earthquakes enter an inelastic phase, so the study of inelastic behavior of structures under the effect of such earthquakes seems to be important. This study examined maximum acceleration, velocity, displacement of the roof mass center, inter-story drifts and base shears of building in inelastic state at moment steel frame buildings designed on the basis of buildings design code against earthquake (2800 Standard, the third edition) under the near-fault records and the comparison of these parameters with the simulated ones. The results indicate that the maximum demand of drift of stories, acceleration, velocity, displacement of roof mass center and inelastic base shear and the way of hinge formation in non-linear state under the near-fault records is the same as simulated records in short buildings. Moreover, the more the height of structure becomes, the more different the behavior of structure becomes and the response is affected by more faults or errors.
    Keywords: Near, fault ground motion, Near, fault simulated records, Non, liner the histories analysis
  • F. Barati, A. Esfandiari Pages 67-73
    In this paper, seismic behavior of the existing buildings equipped by friction dampers is studied. Seismic performance of6-story, 9-story and 12-story steel buildings with damper and without damper were studied. The finite element modeling technique (SAP2000 Software) is used for analysis. Time History analyzing was done to achieve this purpose. For nonlinear dynamic analysis, the responses of the structures to three earthquake records (Tabas, Naghan, and artificial waveform) were obtained. A series of analyses were made to determine the optimum slip load of the friction dampers to achieve minimum response. Also, in order to evaluate the performance of the friction dampers in asymmetric structures, an asymmetric structure was utilized. The obtained results show significant improvement of seismic behavior and efficiency of the friction damper for seismic retrofitting to these buildings.
    Keywords: Friction damper, Slip load, Nonlinear dynamic analysis, Seismic retrofitting, existing building