فهرست مطالب

Seismology and Earthquake Engineering - Volume:16 Issue: 3, 2015
  • Volume:16 Issue: 3, 2015
  • تاریخ انتشار: 1394/08/19
  • تعداد عناوین: 6
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  • Seyed Reza Mehrnia, Roya Khaleghi Pages 147-156
    This research is based on revealing hidden seismic lineaments by interpreting airborne gravimetric and magnetic gradients along with structural patterns [4] in north of Qazvin. IIEES Earthquake catalogue (M> 2 since 1962) has been plotted and analyzed for integrative geophysical purposes. Our research showed that hidden lineaments not only coincide with structural pattern, but spatially control the seismic behaviors in North Qazvin Fault (NQF) branches. The surveyed area is achieved by 56432 points with isometric grids. Besides, geological evidences have been used for facies changing and fault map verification according to seismic events. The facie's change is an innovative process for evaluating gravity lineaments related to NQF hidden lineaments. Such a pattern provides the spatial association of NQF seismic patterns with the revealed seismogenic lineaments of which evidences can be proved by airborne geophysical dataset. As a result, at least two hidden lineaments can be distinguished in north and eastern part of NQF according to geophysical evidences. Therefore, the east and north east of Qazvin have more seismic potentials than other regions because of an observed and meaningful variation of gravimetric facies next to NQF.
    Keywords: Airborne geophysics, Gravity facies, Hidden lineaments, North Qazvin fault
  • Alireza Mortezaei, Keyvan Abdollahi Pages 157-167
    The increase of effective period of structures results fromthe increase of foundation movement due to changes of soil stiffness. In high-rise buildings, due to the seismic motions, the bending moment in sub-structure will cause foundation rotation. The increase of rotation in the sites with different shear wave velocity will cause different behaviors. The increase of the site stiffness leads to the decrease of settlement and generation of uplift condition in the foundation. This circumstance will ultimately lead to the increase of structural movements and seismic response. Applying the circular micropile group as foundation will reduce and control the rotations of foundation. In this paper, by means of FLAC3D software and by parametric study of the inclination angles, distance ratio, and slenderness changes in circular micropiles group, a new equation is developed. Developed expression is used for showing how to affect the decrease of foundation rotations in sites with high shear wave velocity and to decrease structural seismic responses by presenting necessary diagrams.
    Keywords: Rocking stiffness, Effective period, Subgrade reaction modulus, Rotational angle of micropile foundation, Uplift
  • Ali Akhtarpour, Ali Khodaii Pages 169-184
    Seismic response of the asphaltic concrete used as an impermeable core of a rockfill dam was investigated. In the first part of the study, geotechnical parameters of the asphaltic concrete were obtained from a series of monotonic and cyclic triaxial tests. In the second part, 2D and 3D Nonlinear numerical analyses were performed for the highest dam with asphalt concrete core in Iran (Shur River Dam) under seismic forces. Different stages of construction and reservoir filing were analysed using the hyperbolic model with finite difference method. Both 2D and 3D analysis confirms that the earthquake shock can lead to developing some cracks and increasing permeability of asphalt in the upper part of the core; moreover, maximum vertical deformations occur near the crest and at the lower part of the upstream slope. The pattern of the core deformation in 2D analysis includes settlements of the shells behind the asphaltic core and the core remains upright, but 3D analysis shows that the core can settle with the neighbouring shells. Furthermore, 2D analysis shows more settlements in the shells and less crest accelerations in comparison with 3D analysis. Shear strains in the asphaltic core have different trends in the two types of analyses.
    Keywords: Dynamic behaviour, Nonlinear dynamic analysis, Asphaltic concrete core dam, Newark pproach, Equivalent linear analysis
  • Javad Yadegari, Omid Bahar, Mohammad Khanmohammadi Pages 185-197
    To assess collapse risk of the older reinforced concrete buildings in Iran, six 1/2-scale concrete columns were tested under Quasi-static cyclic loading, simulating earthquake actions along with constant axial forces. Based on the test results, cracking patterns, hysteretic response, shear strength and drift ratio at axial failure of each specimen are presented. Two different failure modes of columns are recognized. The first mode is S-shaped failure pattern, and the second mode is related to a mushroom failure mode. The latter was developed by crushing of the concrete and lacking of longitudinal reinforcing bars. The mushroom failure mode is expected where the axial force is reasonably large. Experimental results of test specimen are compared with ASCE/SEI 41-06 analytical models. It is found that shear strength of columns is estimated reasonably well by ASCE/SEI 41-06 flexure and shear models. However, the predicted ultimate displacement is too conservative and ASCE/SEI 41-06 does not properly predicted failuremechanismof columns.
    Keywords: Concrete column, Cyclic load test, Seismic loading, Axial failure
  • Majid Mohammadi, Aran Naserpour Pages 199-207
    An extensive investigation is conducted on experimental data to improve modification factors of masonry infills. For this, available experimental data are classified based on the frame and infill materials. Then a sensitivity analysis is carried out for the effective parameters on the m-factor, including relative stiffness of infill to the frame, the material of infill or frame, aspect ratio, etc. To calculate m-factors of specimens, both the backbone and the envelope curves of the hysteresis curves, proposed in ASCE41-06 and ASCE41-13, respectively, are applied. The obtained results confirmASCE41-13 for giving more conservative m-factor values. Sensitivity analysis shows that infill m-factors highly depend on the infill and frame materials, rather than the infill aspect ratio and relative stiffness of the frame to the infill. Finally, some values are proposed for m-factors of infill panels, made of clay brick or clay tile, surrounded by steel or concrete frames.
    Keywords: Modification factor, Seismic rehabilitation, Infill panel, Masonry
  • Elham Rezaei, Ali Massumi Pages 209-217
    In this paper, the seismic performance of a multi-story reinforced concrete frame building has been studied. A typical reinforced concrete moment-resisting frame building was designed according to the current Iranian seismic code (IS 2800-14). Seven earthquake records were selected and scaled based on IS 2800-14 requirements. In order to assess the seismic vulnerability of the case study structure, nonlinear static (push-over) analysis and nonlinear dynamic time-history analysis have been conducted. The performance has been evaluated based on both the member and global level criteria. Comparison between push-over and nonlinear analyses results shows a relatively good consistency. The numerical results additionally show that the case-study building frames designed by IS 2800-14 satisfy the intended code requirements and meet the inter-story drift and maximum plastic rotation demands suggested byGuide 360 (Instruction for Seismic Rehabilitation of Existing Buildings).
    Keywords: Reinforced concrete frame, Seismic performance, Push, over analysis, Time, history analysis