Journal of Seismology and Earthquake Engineering
Volume:21 Issue: 3, Summer 2019

In this study, the waiting time, spatial distance, and migrating trend pattern ofsuccessive large earthquakes in Iran have been investigated. In order to carry outthis work, the earthquake data of Iran with M >= 4.5 (1976-2018) have beenobtained from the USGS catalog. Then, the statistical distribution of the Intereventtime, migrating distance, and directional trend of migration of successiveevents were studied using different lower magnitude thresholds. The statistical andprobability distributions of inter-event times of earthquakes were assessed andmodelled by different distribution models. Furthermore, the directional analysisof migrating trends, as well as the spatial distances of successive events withdifferent lower magnitude, was carried out. It is observed that the inter-event timedistribution of earthquakes can be quite well fitted by the Gamma distributionmodel. The results obtained also indicate a decreasing trend in spatial distancedistribution and a meaningful correlation between the directional pattern of themigrating trends of successive events and the dominant trends of the active faults ofthe region. The results of this study can be considered as an effective step to betterunderstanding the temporal-spatial pattern of seismicity in Iran and also as anattempt to achieve earthquake prediction in this country, in a regional scale.

Cylindrical tanks are fundamental structures used for the storage of liquids.Sloshing caused by earthquakes in tanks without enough freeboard leads to aliquid impact on the roof of tanks. This study aims to explore the base shearvariation due to insufficient freeboard using experimental and numerical methods.The experimental tests are performed using a cylindrical liquid tank excited byvarious harmonic loads. The impact of some parameters such as the water height totank radius ratio and freeboard on base shear force are investigated by conducting90 tests. Impulsive and convective masses for simplified mass-spring are modifiedin numerical models so that experimental and numerical base shear resultsare consistent. Finally, a simple analytical solution to estimate the reduction ofconvective mass due to insufficient freeboard is suggested and validated usingexperimental results.

This paper presents an assessment on a friction-slip connection for moment frameswith continuous beams based on the current detail. It also proposes a new configurationfor rigid connections in moment frames with continuous beams, whichcan be developed as a friction-slip connection. In conventional moment frames,beams are placed between two adjacent columns and connected to the columnflanges faces. However, in moment frames with continuous beams, two beams arecontinuously passed next to the column. In the existing practice for connections inthese frames, two vertical connection plates placed on column flanges, and thebeams are connecting to these plates via their wings. In the mentioned detail, it wasassumed that the load transfers with in-plane action between connection platesand column; therefore, the design force is pure shear, and based on the designprocedure, it should have been able to be developed for a friction-slip connection.However, the results showed that the out-of-plane action of RPLs could be significant;although this action provides extra capacity in moment connections, itis not desirable in friction connections due to changes in the developed forcesin pretension bolts. Based on this action, a locking occurs, which changes theperformance of the connection considerably. As an alternative to this detail, a newconfiguration is proposed in this paper, which can also be used as a friction-slip connection and provides a friction connection in moment frames with continuousbeams. In new detail, by eliminating the effect of connection plate thickness, thefriction joint works as expected. Thus, instead of the plastic behavior of structuralelements, these friction joints can be used as an energy-dissipating system.

Vertical mass isolation is one of the new techniques in the seismic design ofstructures that consists of two stiff and soft substructures connected by viscous dampers.Adding to the flexibility and energy dissipation potential of the system is the mainfeature of some new approaches in the seismic design of structures. Extra flexibilityhelps to reduce earthquake-induced forces and accelerations in the building andprovides higher energy dissipation potential for the system (by creating largerelative deformations in the structure). Mass subsystem possesses low lateralstiffness but carries the major part of the mass system. Stiffness subsystem, however,controls the deformation of the mass subsystem and attributes with much higherstiffness. In this paper, the aim is to find the limitation of the stability of asoft structure and to obtain the maximum period available for a soft structure.According to the studies, the most important obstruction in increasing the periodof the soft structure, assuming control of its deformation by connecting to thestiff substructure, is to maintain the stability of the structure. In this paper, first, arelationship has been presented to calculate the period of the structure in terms ofthe stability factor that estimates the period of structure with good agreement byanalytical results. This paper deals with presenting a procedure for designing theMass Isolation System (MIS) with consideration of stability constraints. To this end,the paper presents mathematical solutions to calculate the period of the structurefollowed by proposing a design procedure of the soft substructure.

In this paper, we investigate the long-range correlations and trends betweenconsecutive earthquakes by means of the scaling parameter so-called locally Hurstparameter, H(t), and examine its variations in time, to find a specific pattern thatexists between Earthquakes. The long-range correlations are usaully detectedby calculating a constant Hurst parameter. However, the multi-fractal structure ofearthquakes caused that more than one scaling exponent is needed to accountfor the scaling properties of such processes. Thus, in this paper, we consider thetime-dependent Hurst exponent to realize scale variations in trend and correlationsbetween consecutive seismic activities, for all times. We apply the Hilbert-Huangtransform to estimate H(t) for the time series extracted from seismic activitiesoccurred in California during 12 years, from 2/24/2007 to 9/29/2017. The superiorityof the method is discovering some specific hidden patterns that exist betweenconsecutive earthquakes, by studying the trend and variations of H(t). EstimationgH(t) only as a measure of dependency, may lead to misleading results, but using thismethod, the trend and variations of the parameter is studying to discover hiddendependencies between consecutive earthquakes. Recognizing such dependencypatterns can help us in prediction of future main shocks.

Historical heritage structures are especially vulnerable to earthquakes becausethey were designed only for gravity loads without any consideration of lateralloads. For this reason, the preservation and maintenance of these structures are ofgreat cultural, economic, and social importance. The present study investigates theseismic vulnerability of a historical structure called Kashan Bazaar, located inKashan (central Iran), dating back to the 17th century. The detailed 3D geometricalmodel of this structure was drawn using SolidWorks software. Finite elementnumerical method was used to evaluate the response of Bazaar structure usingmacro-modeling approach. Static, modal, and nonlinear static (pushover) analyseswere carried out using two cases, with soil-structure interaction (SSI) and withoutSSI (fixed-base). According to the results, considering the SSI has a significantinfluence on the mode shapes, vibration frequencies, and the structural responses.The structure of Bazaar can withstand gravity loads as well as DBE demandsin fixed-base model. However, the results of the SSI analyses show the structureweakness against lateral loads.