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Seismology and Earthquake Engineering - Volume:17 Issue: 4, Winter 2015

Journal of Seismology and Earthquake Engineering
Volume:17 Issue: 4, Winter 2015

  • تاریخ انتشار: 1395/02/12
  • تعداد عناوین: 6
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  • P. Sunitha, C.V.R. Murty, Rupen Goswami Pages 223-231
    Methods are proposed to develop idealized moment-curvature response curves of slender rectangular RC wall sections with uniformly distributed longitudinal reinforcement, using limit states, namely, cracking of concrete in tension, tensile yielding of reinforcement layers, and compression failure of concrete. It is recommended that tensile yielding of an inner layer of reinforcement is considered to develop idealized moment-curvature response curve of RC wall sections in the absence of compressive axial load, as against tensile yielding of extreme layer of reinforcement in the presence of compressive axial loads. Distance of the critical inner layer of reinforcement from highly compressed edge depends on percentage of longitudinal reinforcement in the section; the distance varies from 0.5D to 0.98D with an increase in percentage of longitudinal reinforcement, where D is the length of the wall, but does not depend on plan aspect ratio. Furthermore, axial-flexure interaction envelope can also be developed from the idealized moment-curvature response curves.
    Keywords: Flexural rigidity, Curvature ductility, Compression failure, Limit state design, RC walls
  • Jalal Kasebzadeh, Ali Noorzad, Ahmad Reza Mahboubi Pages 233-248
    Liquefaction analysis is one of the most challenging issues in seismic geotechnical engineering. The unknown factors and pertinent uncertainties involved in the evaluation of liquefaction potential make the problem to be complicated. Liquefaction evaluation include deterministic and probabilistic methods. Deterministic methods are simple but they are not capable to consider the uncertainties. With regard to heterogeneous nature of the soil and probabilistic nature of earthquake loading, it seems that deterministic method is not sufficient for evaluation of liquefaction. Reliability methods are able to capture the uncertainties depending on variability of soil parameters and also to determine the factor of safety proportional to the acceptable risk. In recent years, reliability analysis of liquefaction has been done using approximated method. In the present research, reliability analysis of liquefaction triggering has been discussed using Monte Carlo simulation that is an accurate method. For this purpose, the parameters earthquake magnitude (Mw ), maximum horizontal acceleration (amax /g), total stress (sv ), effective stress (sv ), fines content percent (FC), and SPT blow count (NSPT) are selected as stochastic parameters and the probability of liquefaction has been estimated. Application of the proposed method to the 233 well-documented case studies verify that deterministic method is not accurate enough to predict the liquefaction and reliability analysis should be used instead. Besides, the sensitivity tests indicate that the SPT blow count is the most influential parameter in liquefaction evaluation and large number of iterations is not required in Monte Carlo Simulation and the results converge after a specific number of iterations.
    Keywords: Liquefaction, Monte Carlo simulation, Geotechnical uncertainty, Reliability analysis, Probability of liquefaction
  • Laya Abbasi, Mohsen Ghafory, Ashtiany Pages 249-263
    Floor response modification factor (R) under near-field strong ground motions (SGMs) with directivity pulses are proposed in this paper. The R factor is defined as the floor response spectrum (FRS) for linear elastic primary structures normalized by the FRS for an inelastic primary structure. The terms ‘elastic’ and ‘inelastic’ refer to the behavior of the supporting structure while only elastic nonstructural components (NSCs) are used in this study.
    Considering the lack of comprehensive study on the behavior of NSCs under near-field SGMs with directivity pulses, this study evaluates the dependence of the proposed response modification factor (R) under bunches of near-field records with wide ranges of directivity pulse periods. A statistical analysis of the peak response of NSCs supported on inelastic regular moment-resisting frame structures exposed to near-field pulse-like SGMs is presented. Peak component demands were quantified based on the FRS method with considering dynamic interaction effects. In This paper the main factors affecting the FRS caused by inelasticity in the primary structures represented by parameter R has been evaluated. The results show that FRS values at the initial modal periods of the supporting structure are reduced due to the inelastic action in the primary structures. Comparing the results with the same earthquake events without directivity pulses shows that the reduction factor in near-field pulse-like SGMs is considerably larger than R factor in far-field SGMs.
    Keywords: Floor response spectra, Modification factor, Nonstructural component, Primary structure, Near-field earthquake, Directivity pulse
  • Afshin Kalantari, Morteza Amooie Pages 265-280
    In high seismic regions, such as Persian Gulf zone in Iran, corrosion of reinforcement and concrete deterioration can affect the seismic capacity of the structures and increase the vulnerability to the future seismic events. Although corrosion of reinforcement has the potential to affect all types of reinforced concrete structures, the highway bridges are vulnerable to more damage because of deicing salts, water splash or even seawater during their life cycle. The long-term corrosion process of a deteriorated typical RC highway bridge in Iran is analyzed as a function of time by using nonlinear static and dynamic analyses for seven earthquake ground motion records at three levels of intensity (0.3g, 0.5g and 0.75g). Three combined effects of corrosion (the loss of the cross sectional area of the reinforcement bars, decrease of the capacity of corroded reinforcing bars, and stiffness degradation of concrete cover resulting from reinforcement corrosion) were used in the time-dependent nonlinear analyses for six different time steps (i.e., non-corroded (t: 0), 10, 20, 30, 40, and 50 years) after corrosion initiation time. The results show that removing the concrete cover on bottom of columns has a greater impact on the structural capacity of the RC bridge than decreasing the rebar mechanical parameters.
    Keywords: Corrosion, RC highway bridge, Persian Gulf zone, Time-dependent nonlinear analyses, Seismic response
  • Seyed Mehdi Zahrai, Amir Parsa Pages 281-292
    Among the passive dampers, using Vertical Link Beam (VLB) is one of the most effective and simplest methods, while not embedded in the floor they can be easily replaced after earthquakes. These dampers dissipate a major part of the input energy resulting in a minimized damage of the main structural components of system. This paper presents a numerical study on the impact of flange width of VLB on cyclic performance of chevron braced steel frames. Despite most previous research projects in which wide-flange I sections were considered for the VLB and the length of VLB was studied, here, the objective is to investigate the possibility of using narrower flange. Verification has been made on the basis of the experimental results from the IPE160 model. By changing the flange width, the cyclic behavior has been investigated. The results show that while the vertical link beam has sufficient lateral support, in spite of the flange width reduction, stable hysteretic cycles still form accompanied with considerable energy dissipation. Based on the hysteretic curves, using modification of the narrower flange section, the shear force at last cycle increased about 20.74% and 16.17% in IPE160 VLBs with a half and quarter flange width respectively, and the proportion of VLB in plastic energy dissipation increased from 78.9% to 90.4% in half flange VLB and from 74.2% to 90.9% in quarter flange VLB only by this simple modification, showing an increase in ductility of the system.
    Keywords: Vertical link beam, Chevron bracing, Eccentrically braced frame, Flange width, Passive control
  • Hamzeh Shakib, Mehdi Nodeh, Farshad Homaei Pages 293-304
    In this paper, the fragility curves have been developed for assessing vertically irregular midrise steel building with Buckling Resistant Braced (BRB) system. The effect of different vertical irregularities of mass, stiffness and the concurrent variation of stiffness and strength was investigated in the seismic response of a ten-story steel building. The fragility curves of both the regular and irregular structures were developed through the incremental dynamic analysis and the effects of vertical irregularities were evaluated in the seismic performance of the structure. Fragility curves show that among all the vertical irregularities, variation in the mass has little effect on the probability exceedance of demand from capacity. Meanwhile, the concurrent variation of stiffness and strength shows a significant increase in the probability exceedance of demand from capacity, especially through the nonlinear phase of structural behavior, through the collapse prevention to the global instability limit states.
    Keywords: Fragility curve, Buckling resistance brace, Vertical irregularity, Incremental dynamic analysis