Journal of Seismology and Earthquake Engineering
Volume:15 Issue: 1, Spring 2013

In this paper, the well-established probabilistic seismic hazard - Poisson occurrence model - technique is applied to estimate the seismic severity of Syrian region. Syrian seismic catalog, which extends from 19 AD to 2012, as well as seismotectonic features of the region have been utilized. The seismic hazard assessment carried out using eight seismic active zones based on tectonic settings and spatial distribution of the seismic activity. We assessed the modified Gutenberg-Richter Model parameters and the maximum credible earthquake magnitude for each seismic zone. Suitable numeric attenuation models have been used for the considered seismic zones. An increment of 0.1 x 0.1 degree is used. The seismic hazard maps are developed for return periods (50, 100, 175, 475 and 975 years) and for the seven structural periods. Integrating PGA to PSA hazard maps have done based on site-effect factors of PSA/PGA. Seismic hazard curves are obtained for all major cities. Relatively high levels of PGA as well as PSA are found in regions: Lebanese part of DSFS, Al-Ghab region of Syria, along the border of Turkey and Bitilis zone. Remarkable seismicity has noticed in the eastern part of Syria.

Reinforced concrete (RC) structural walls are effective for resisting lateral loads induced by earthquakes on building structures. They provide substantial strength and stiffness as well as deformation capacity needed to meet the demands of strong ground motions. In some cases because of architectural limitations and/or form-work difficulties, the shear walls are constructed with an eccentricity with respect to the frame axis. The provision of shear wall’s eccentricity may be needed for strengthening of existing building as well. However, most of the reinforced concrete code of practices such as ACI-318-05 and Iranian concrete code (ABA) have no recommendation(s) and/or limitations concerning this eccentricity. In this paper the effect of Shear Wall''s eccentricity on the seismic performance of RC dual system is studied. For this purpose, three two-dimensional (2D) frames with 6, 9 and 12 stories were selected from three-dimensional (3D) buildings, which were analysed and designed according to the third edition of Iranian standard 2800 and ACI-318-02 concrete code of practice. The nonlinear time history and nonlinear static analyses carried out for three different amounts of eccentricities. ABAQUS finite element program is utilized for nonlinear static and time history analysis. To calibrate numerical modelling, experimental results were compared with numerical model results which show good agreement, making sure that the computer numerical simulation of this study is satisfactory. The result indicate that by increasing the eccentricity, the torsional moment of boundary elements and the on-plane bending moment of shear wall significantly increase. Also shear wall''s eccentricity cause of on-plane shear in shear wall.

Underground structures, which are located in seismic zones, should undergo staticloads induced by the ground and dynamic earthquake-induced forces. Cross sectionof the underground structures is usually less than the wavelength of input ground motion. Therefore, semi-static or semi-dynamic methods can be used in cross sectional analysis of these types of structures. In this paper, based on the beam on dynamic visco-elastic foundation theory, a new analytical method was developed to determine the shear deformations of the buried box structures. The proposed method is able to consider the characteristics, such as frequency of the ground motion and the damping ratio, in calculating the seismic displacements, which is less considered in the past analytical methods that was introduced by other researchers. The results of the proposed method indicate that the seismic deformation of underground structures is considerably dependent to damping ratio and frequency of ground motion as well as mechanical and geometrical properties of the surrounding medium and structure. In addition, in some frequencies, the results of the new method indicate good general agreement with the methods developed by other researchers. Nonetheless, according to the effect of the frequency, in some frequencies, remarkable differences are observed.

In order to reduce the seismic risk in urban fabrics effectively, it is necessary to make a comprehensive assessment of vulnerability and seismic hazards in different parts of the urban area. This could provide essential information for city managers and decision makers for better understanding of risk mitigation priorities. Since in most cities of Iran, the required data are usually unavailable or inadequate, estimation of absolute risk is not possible. In this paper, a simple and comprehensive methodology is introduced to estimate the relative seismic risk among urban zones instead of absolute risk. For this purpose, parameters with significant contribution to seismicrisk are selected and classified into physical, human life and socio-economic categories. The seismic risk associated to indicators of each category is estimated according to the vulnerability and relevant hazard factors. It can conceptually reduce uncertainties in combination of earthquake hazard and vulnerability through definition of separate hazard factors. The effect of response capacity and recovery capability are also considered in estimation of total risk; however, relevant methodology and parameters of this item are now under study. Finally, the model is applied to estimate the seismic risk of Tehran at district level, and results are compared to other works. Considering the impacts of all presented indicators, results of the proposed model show that district 15 has the highest rank of seismic risk in Tehran Metropolitan area.

Endurance Time Analysis (ETA) method is a time-history based dynamic pushover procedure in which structures are evaluated using predesigned intensifying acceleration functions from linear elastic range to collapse point. In this paper, ETA is compared with well-established incremental dynamic analysis (IDA) for high-rise steel moment frames. Different scalar intensity measures (IMs) are used to figure out the most efficient one, which reduces the dispersion of the results in both methods. It was observed that ETA could estimate the general trend of IDA curves while it needs a few numbers of analyses. In addition, based on the results, the peak ground velocity and the spectral acceleration are the best IMs for comparing the results of IDA and ETA methods in steel moment frames.

There are a large number of old arch bridges in Iran that have been serving as railway bridges for more than seventy years. Field load testing of an old railway bridge in km-24 of Tehran-Qom railway has revealed important characteristics of the bridge and has proven that there is still a large capacity under service load. It is known that most of these bridges are not designed for earthquake and their seismic vulnerability is uncertain. This fact necessitates the investigation of earthquake resistance of these kinds of bridges. In this paper, an attempt has been made to assess seismic performance of the bridge. The bridge is a plain concrete arch structure with five six-meter spans, which has built 70 years ago. The results of dynamic load test have used to calibrate a finite element model of the bridge in which a plain strain analysis has been carried out. Vertical displacement of the arch is used as the calibration criterion. To investigate the seismic performance of the bridge, a nonlinear static analysis (pushover analysis) method is applied. Choosing several points as a control ones, the choice of control points in the pushover analysis of masonry arch bridges and its influences on seismic evaluation is investigated. The capacity curve of structure and damage levels is drawn and the creation of hinges due to the lateral loading are studied. Finally, the capacity curves and the nonlinear demand spectrum are drawn and the performance of the structure is determined. The results show that these kinds of structures are still strong under seismic exciting.