BULLETIN OF EARTHQUAKE SCIENCE AND ENGINEERING
Year:2020 | Volume:17 | Issue:3|Papers Count:6

Seismic isolation is an earthquake resistant design method based on reducing seismic demand instead of increasing structural capacity. With regard to the multiplicity of studies conducted to investigate the seismic behaviour of isolators under the effect of earthquakes, in this study, role of the base isolator in improving the behaviour of steel structures under the influence of earthquakes with different angles was investigated along with considering the effect of structural height and plan shape. In the present study, steel structures with and without Lead Rubber Bearing (LRB) base isolator are modelled in 3D with 8 and 12 stories and square and rectangular plans. The seismic performance of these buildings has been reviewed and compared according to 4 pairs of near-fault earthquake records (8 records) with angles (0° , 30° , 60° and 90° ) based on FEMA P695 instruction under the nonlinear dynamic time history analyses in SAP2000 software. The results showed that steel structures at angles of 60 and 90º had larger and more critical seismic responses. Based on results, the effect of seismic isolator on reducing the seismic responses of buildings at angles of 0 and 30º was low, while at the angles of 60 and 90º was more significant. The use of separators had a great impact on improving the performance and seismic responses of structures. The results also presented that in most records, the height of the structure was more effective than the plan shape regarding the seismic responses of the isolated structures.

Elastic analysis of structures creates basic shearing forces and stresses that are significantly larger than the actual responses of the structures. By entering the inelastic domain, the structure can absorb and resist a large amount of earthquake energy. On the other hand, nonlinear analysis of structures requires timeconsuming and voluminous computational operations, so in most of the codes, a simple and appropriate method called equivalent static method is presented to achieve a reasonable answer to the nonlinear behavior of the structure (without performing a nonlinear analysis). Therefore, due to the importance of ductility in the absorption of seismic energy, the computational forces caused by the earthquake are reduced by introducing the coefficient of structural behavior, R. In this paper, an extensive database consisting of 12, 960 eccentrically braced frame (EBF) structures with varying story numbers of 3, 6, 9, 12, 15 and 20, three types of column stiffness and three degrees of bracing slenderness was designed and analyzed under 20 near-faults pulse-like earthquakes. To generate the estimated relation R, 6769 data were interpreted using particle swarm algorithm. The results of a correlation of 0. 86 in the test data presented the accuracy of the proposed relation.

After the Northridge earthquake, it was determined that the beam-to-column connections in the moment frames were weak and needed to be revised. In recent years, the use of bolted connections have expanded and replaced almost welded connections. The US Code of Conduct (AISC358-16) introduced a new connection called the Simpson Connection, which is a semi-rigid connection with the idea of damage control. Progressive connection is a new and smart type of screw connection that includes a weakened plate, end plate, corner as well as a buckle plate. The main purpose of this study is to investigate the linear and nonlinear behavior of Simpson connectivity using ABAQUS software. The baseline sample was selected from the model outlined in US Code (AISC358-16). To gain a better understanding of the new Simpson junction model, 14 numerical specimens were modeled and the strengths and weaknesses of the models including ductility, stiffness, strength, and energy absorption of the models were compared. In this connection, the geometry of weakened plate and its performance is important. In so doing, variables such as mid-length, mid-width, initial length, as well as stiffeners were evaluated in the initial length of the weakened plate. The model with a thickness of 30 mm thicker than the other models with respect to the mentioned characteristics, showed acceptable results including anchor tolerance of 1010 kN. m and energy absorption of 55. 53 kN/mm which showed that its use is suitable for areas with high seismicity.

In this study, in order to provide a new analytical relationship for evaluating the bearing capacity of a two layered cohesive-frictional soil mass, 12 sets loading tests of physical model for three types of upper layers with different thicknesses and compactions. In continuation, a series of parametric studies were performed to evaluate the accuracy of the proposed relationship using PLAXIS 2D finite element software. In order to study the results of numerical modeling and control of the accuracy of the modeling, results of these analyzes were compared with the experimental results of corresponding physical models by considering the effect of different parameters)relative thickness, compaction ratio and different shear strength parameters of soil layers) on the failure mechanism and the ultimate bearing capacity of the soil. Considering the appropriate fit of the load-displacement curves, the failure pattern and the average difference of the bearing capacity about 3. 3% between the physical and numerical models, show that finite element models have good accuracy in predicting the actual behavior of laboratory samples and the results of numerical simulations can be trusted. After the verifying of the numerical analysis results, the values of the bearing capacity obtained from both numerical and analytical methods for 88 different modes of the strip foundation with dimensions B = 1 and 2 meter and soil mass with different layering, depth and shear strength parameters were compared and a difference of about 7 and 12. 5% were observed for foundations with dimensions of 1 and 2 meters, respectively. The results showed that there is a relatively good agreement between all three experimental, numerical and analytical methods in the evaluation of the ultimate bearing capacity and the analytical relationship can predict the process of limit pressure changes in terms of the relative thickness of the layers and the evaluation of the ultimate bearing capacity for various states of the strip footing resting on two layeres ground with relatively good accuracy.

Iran is located in a region that has critical conditions in terms of seismicity, so structures designed in the country must be resistant to lateral loads. Reinforced concrete shear walls are the most common systems resistant to the lateral loads of wind and earthquake in the structures. One of the types of shear walls is the shear wall with openings, which are created for mechanical and architectural reasons. The presence of these openings in the shear wall causes changes in the ultimate resistance, changes in the behavior of the force distribution, and changes in the failure mechanism. Due to the fact that some shear walls are designed using old regulations that these regulations do not provide the ductility of the shear wall, so due to the incompatibility of the seismic design of these regulations with the new regulations, it is necessary to repair and strengthen these walls. Due to the fact that the effect of the wall with opening and reinforced with special flexural frame at a relatively high height was not studied in previous studies, so in this study, by studying the behavior of this type of frame, the coefficient of behavior of this type of system was evaluated. In this study, the concrete shear wall was added as a reinforcement to the flexural frame of the special reinforced concrete in two heights of 8 and 12 storeys, which were pre-designed, then circular, rhombic and rectangular openings were created in the walls and compared with each other. The results of the analyses present that the strength and behavior coefficient of the structure decrease with the opening of the wall, which is different for openings with different shapes. At the same level analysis, circular-shaped openings and among all openings, openings with half the original dimensions exhibited the best performance, indicating that the smaller the dimensions of the openings, the higher the structural strength.

This research are considered and analyzed threedimensional high rise building three frames of 28-story reinforcedconcrete in each direction X, Y structural structure of a tube in tube, In the zone of high relative risk(A=0. 3g), With fixed number and bays the length, different heights and types of soil(I, III), Once without affecting soil-structure interaction Once again, the effects of soil-structure interaction are considered and analyzed. The purpose of the present study is to determine the maximum lateral displacement frames floors of gravity loads(dead, live)and earthquake loads. In order to analyze the structure of the structurethe soil-structureintraction impact of the substructure is assumed to be used for the modeling of the sub-surface soil from the cone model, the structure of the structure and the determination of the dynamic hardening coefficient and damping coefficient soil of the discrete model based on the cone model in the homogeneous space stream. In order to analyze earth quake loads in the studied models, a dynamic analysis of the nonlinear time history of the modal method under seven accelerations accelerations. The geometric modeling of the all frames with shear walls in the SAP 2000-V17 software package was performed. The results show that with increasing elevation of floors(model 1 to 3), the maximum lateral displacment floors on type I soil in the direction of X increase in the direction Y is significant increase, in model, in the model 2 to 1by changing the type of soil type, the maximum lateral displacment floors with out and with Soil-Structure intraction in the each two direction is dramatic increase.