Journal of Seismology and Earthquake Engineering
Year:2006 | Volume:8 | Issue:2|Papers Count:8

This paper uses geomorphic features to constrain active structural deformation at the Natanz region, central Iran. Offset stream beds indicate rightlateral strike slip motion at a rate of about 2.5 mm/yr along the NW-SE trending Qom-Zefreh fault zone. Deep incision of the Moghar river which crosses the Charkheh and Zardkuh anticlines also indicates uplift at depth on thrust faults dipping SSW beneath the anticlines. The fact that the active Qom-Zefreh strike-slip fault runs parallel to the active fold and thrust zone suggests that oblique motion of Arabia with respect to Eurasia is partitioned in this part of central Iran. We conclude that the active blind faults which leave clear signatures in geomorphology should be seriously considered as a seismic source while assessing seismic hazard in the region.

Although the seismic behavior of a hill could be considerably affected by its geometrical shape, no comprehensive research has been reported in the literature, clarifying the weight of this parameter. This paper compares numerically the seismic behavior of two-dimensional semi-sinusoidal, semi-elliptical and trapezoidal shaped hills subjected to vertically propagating incident P- and SV- waves, using the well known 2D transient boundary element method. It is shown that although altering the shape would not change some general observations common to all hills, but could affect the amplification patterns along the hill significantly, depending on its shape ratio as well as the length of the incident wave. Some approximate formula and tables are proposed for estimating the characteristic site period and the average amplification potential of an arbitrary shaped homogeneous single hill, which could be applied in site effect microzonation studies of topographic areas.

Abstract: Soil mixtures such as clayey sands, silty sands, and clayey silts are more commonly found in the nature that pure clays, silts, and sands. Most previous studies on liquefaction have been focused on clean sands and sands with little fines, for it was believed that fines and sands containing fines are not prone to liquefaction. However, after a number of earthquakes where soils with high plastic fines liquefied, the subject drew the attention of a number of researchers. One of the interesting cases of liquefaction occurred on June 22, 2002 during Changureh, Iran earthquake. Surface soil in this area is mostly clay; however, clear traces of sand boiling, softening of soil, and consequent deformations were observed. The preliminary tests showed that the soil has a < No. 200 fraction of 44% with a liquid limit and a plasticity index of 38 and 18, respectively. As these types of soils are commonly found on the western-north and west of Iran, it seems necessary to investigate the problem in the country. This paper investigates the effect of plastic fines and their plasticity on the cyclic resistance of sands.

Composite clay is a mixture of clay, as the main body and aggregates, which are floating within the clayey matrix. Undrained behavior of composite clays in its natural or compacted state e.g., core material of embankment dams has a great importance for the geotechnical engineers. An extensive test program was conducted on kaolin-gravel mixtures to investigate the effects of aggregate on the cyclic deformational properties, including shear modulus and damping ratio. Test results reveal that shear modulus for various mixtures, depends on aggregate content, shear strain amplitude, number of loading cycles and initial confining stress. Meanwhile damping ratio mainly depends on aggregate content and shear strain amplitude and is less affected by the number of loading cycles.

In this paper, results of Standard Penetration Test (SPT) and shear wave velocity (Vs) measurements have been compared for liquefaction potential evaluation in south of Tehran in Iran. Liquefaction potential by SPT was evaluated based on the simplified procedure of Seed and Idriss [1-2] and specifications for highway bridges [3] for sandy soils and silty soils respectively. On the other hand, the liquefaction potential assessed using the Vs measurements based on the method proposed by National Institute of Standards and Technology (NIST) in 1998 [4]. In this study, 118 borehole data were studied considering the soil type and ground water level. Vs data was obtained based on 9 downhole and 75 seismic refraction tests performed by the International Institute of Earthquake Engineering and Seismology (IIEES) [5]. The safety factor at different depths and liquefaction Potential Index at different boreholes was compared. Generally, results of the two methods are in agreement, especially if the soil is considered to be cemented.

Displacement based seismic design usually requires nonlinear dynamic or static analyses to assess the performance level of the structure under seismic action. To trace the exact performance point of a structure these analyses should sometimes be repeated several times. Analysis iterations mainly depend on the initial design and performance of the structure. In this paper an intelligent system has been presented for estimation of plastic hinge distribution and lateral ductility distribution of steel structures based on direct displacement based design procedure. The method has been applied to the steel braced frames with concentric and eccentric bracing systems in low, medium and high rise buildings. Finally the intelligent system has been verified using nonlinear dynamic analysis.

Recent studies have shown that the configuration of centers of mass, strength and stiffness can affect behavior of an asymmetric building. With change in configuration of centers, damage parameters such as interstory drift and ductility demand parameters may decrease. These parameters are good indicators of structural and non structural damages during earthquake excitations. But decrease of one damage parameter in specific centers configuration necessarily will not cause decrease of another parameter. The importance of damage parameters relative to each other in a building can be function of earthquake intensity, strength and deformation capacity of building. In this paper behavior of asymmetric buildings with different configuration of centers in different excitation levels are studied. For this purpose 3D building models are subjected to both one directional and two directional earthquake excitations and the ductility and interstory drift responses of models are compared. The results have shown that for different damage parameters, the proper configuration of centers is different, so to improve performance of a building, proper configuration of centers corresponding to the critical damage parameter must be used.

The state of hydrostatic pressure inside of elastomeric isolators is the key point in providing the high ratio of vertical to horizontal stiffness in such devices. In this study the state of hydrostatic pressure is provided by steel rings instead of steel shims used in classical elastomeric isolators. In the theoretical part of the work, a formula for calculating vertical stiffness of the bearing was presented. Later this formula was verified through experimental studies. In the experimental phase of the study some prototype bearings were made and their performances were compared with classical isolators using test results. The numerical part of the work was based on studying the possible application of such bearings in floor isolation of buildings. The results of the numerical studies have shown the potential of these devices in reducing force and displacement responses of the building subjected to a series of earthquakes.