Journal of Seismology and Earthquake Engineering
Volume:18 Issue: 3, Autumn 2016

Although bearing capacity of footings on top of slopes under monotonic loadings have been investigated widely so far, safety and bearing capacity of these structures against repeated dynamic loads have not been considered well enough. In this paper, lower bound dynamic shakedown theorem in its numerical form has been employed to firstly obtain bearing capacity of strip footings on top of slopes, and secondly to determine safety factor of slopes by strength reduction method subjected to repeated dynamic loads. Following a try and error procedure, factor of safety against cyclic loads were determined based on the strength reduction concept. Results indicate that bearing capacity of footings is affected by dynamic properties of both slope and the loads so that minimum bearing capacity obtained when resonant occurs. Furthermore, results show that the safety factor of slopes is extremely affected by dynamic properties of both slope and dynamic load as well. The minimum factor of safety was found to arise at resonance. Besides, findings suggest that unlike Pseudo-Static method that does not differentiate between embankments (with wide crest) and slopes, here factor of safety of slope and embankment are not the same due to their difference in dominant natural period.

The use of passive control systems is widely considered as a reliable approach for controlling earthquake vibrations in steel structures. First, under frequently occurring low to moderate earthquakes, the structure should have sufficient strength and stiffness to control deflection and prevent any structural damage. Second, under rare and severe earthquakes, the structure must have sufficient ductility to prevent collapse. For this case, significant damage of the structure and non-structural elements is acceptable. In this paper, the performance and the lateral stiffness of a new eccentric and knee bracing system named Eccentrically Knee Brace (EKB) is investigated. The stiffness of eccentrically knee braced frames (EKBs) is difficult to calculate by hand because they are indeterminate and have significant shear, flexural and axial deformations in different members. EKB stiffness is important for design, because it is used to compute story drifts and the knee and link rotations, which have prescribed limits. This note presents an equation for the stiffness of an EKB story in terms of the design story shear, frame geometry, and beam depth. The equation is independent of specific member sizes, making it useful for determining appropriate geometry in design. The equation is developed numerically and verified with experimental data from code compliant. One application of the equations is the estimate of the beam depth required to ensure a link or knee will satisfy inelastic rotation limits.

Due to the correlation of natural vibration modes of skewed bridges, and the multi-directional nature of the earthquake ground motions; piers of skewed bridges would be subjected to combined axial, flexural and torsional loadings. The characteristic of combined loading of the piers depends upon several parameters including the strong ground motion characteristics and the structural system type. In this research seismic performance of a group of torsion sensitive skewed bridges with three different pier-deck connections is studied. Skew angles vary from 0° to 60°. Seismic performance of the bridges is investigated conducting bidirectional nonlinear time history analysis in OpenSees. Considering the effect of different pier-deck connection types, combined loading demand on the skewed piers is compared with those on the straight piers. On the basis of results, for both pinned and fixed piers, ductility demand increases with the skew angle. Opposed to pinned piers, fixed piers are subjected to combined torsional-flexural loadings, and the torsional demand increases with an increase in the skew angle. The value of torsional demand on fixed piers is limited to one half of cracking torque of the section (Tcr/2). Concerning to the collapse prevention criteria, 30 degree skew angle is found to be a threshold skew angle. For bridges with skew angles greater than 30 degree, applying monolithic pier-deck connections is more sensible.

Pipe-Soil interaction is one of the fundamental challenges to analyzing and designing of buried pipelines. Even though the accuracy of ASCE relations for calculating pipe-soil interaction is proper in certain cases, several researches have demonstrated the inaccuracy of these relations for cases such as fault movement. This research evaluates the interaction between sandy soil and polyethylene pipe subjected to strike-slip faulting on the basis of a non-linear finite element numerical model. Once the results of the numerical model were verified using the previously conducted experiments, several numerical analyses were carried out for pipes with different diameters, thicknesses and burial depths. The results suggest that the pipe thickness and the fault-pipe angle considerably affect pipe-soil interaction, which is not allowed for in ASCE relations. Finally, according to the obtained results, the ASCE relation for the transverse-horizontal interaction between sandy soil and polyethylene pipe subjected to strike-slip faulting was modified.

The study aims to describe the potential seismic tectonic structures and the seismic hazard mapping. The pre-seismic assessing is initiated for two regions belonging to Algerian Maghrebides chain, Constantine area in the East and Relizane area in the West. It is based on the inventory of mainly tectonic structures reported in the bibliography as being active within a radius of 50 kilometers of the both regions. For this purpose, a map of the principal neotectonic structures is established on basis of morphotectonic and structural interpretations of the zones which reveal indices of active tectonics. Then, seismotectonic analysis is carried out by correlation between tectonic structures and historical seismicity. A preliminary seismotectonic zonation is established. The seismic zonation map enlightens seismic source zones and seismic lines; the identified faults and suspected active faults affecting the both areas aremodeled as source lines. And the areasmarked by diffuse seismicity, are modeled as sources zones; therefore, three seismotectonic provinces have been defined. This preliminary seismotectonic zonation will direct the field work and also the management of data in GIS for quick response to any improvement in the assessment.

Buildings with high degree of importance such as hospitals, police stations, fire stations and other vital facilities play a crucial role in crisis and risk management of cities. Therefore, special attention should be paid to design and construction of these buildings in order to maintain their performance during and after the earthquake. Important buildings in Iran is designed according to the Iranian code of practice for seismic resistant design of buildings (ISC). So far, four editions of the code have been published. In this study, improvement of seismic safety of important buildings in the first three editions of ISC are examined and the results are compared with an acceptable level of safety. In this study, a 3-story steel moment resisting frame is selected and designed based on different editions of ISC for high seismic zones. The seismic fragility functions of frames are estimated in all soil classifications of the code. The probability of failure of frames are estimated for Tehran and Tabriz, two major cities located in high seismic zones. Results shows a good improvement in safety of different frames in recent editions of ISC, especially from the first to the second editions due to mandatory of ductile design and increase of the design forces. However, the functionality and safety of buildings do not satisfy the minimum requirements of the code. In addition, the results indicated that the probability of failure of frames located in softer soil types is higher than others. This show that within any code edition, a constant limit of safety was not provided in different soil types. Therefore, an improvement in the spectral acceleration of different soil type is required.