BULLETIN OF EARTHQUAKE SCIENCE AND ENGINEERING
Year:2016 | Volume:12 | Issue:4|Papers Count:8

The present study investigates the seismic performance of reinforced concrete moment frame system retrofitted with different steel bracing systems. Two types of structural combinations including concentric steel bracing system and steel mega bracing system were used in two types of structures with different numbers of stories. These two structures which are designed by 5 and 10 story reinforced concrete moment frame system have poor lateral stiffness. They were considered to compensate for the limitations of drift regulations in areas with high seismic risk and life safety performance level. Then, these frames are improved by concentric steel bracing system and mega bracing system. In this study, the nonlinear static (pushover) analysis was used to evaluate the performance of the structure under the influence of ground motions. Also chord rotation, story drift and base shear were used to compare the response of the improved structure. It was shown that the steel mega bracing system and the concentric steel bracing system are respectively the best types of steel bracing systems for upgrading and retrofitting the structures in terms of drift control regulations, the amount of base shear, the number of plastic hinges, the number of collapse elements and the economic issues.

Unexpected brittle failure in steel rigid frame connections by concentrated tensions on the welded area and connection vulnerability in high ductility demands as occurred during the Northridge (1994) and Kobe (1995) has challenged ductility properties and ability to absorb seismic energy in this type of structural system. So in design of this type of structural system, creating ductility and ability to withstand cyclic large deformations is important. On this basis, in present study two new beam-to-column moment connections with reduced beam section by double or reverse arc-shaped fuse are studied in capacity design approach. The arc-shaped fuse, by removing flange and a part of web and replacing double or reverse arc-shaped in the section bending of the beam, resulted in a ductile fuse away from beam-to-column connections components, which prevents connection vulnerability in high ductility demands. The purpose has been numerically studied by four numerical models under cyclic load using ABAQUS 6.10 finite element software. Obtained numerical results were compared with those of other studies. The numerical results show that arc-shaped fuse creates ductile fuses faraway from beam-to-column connection components and can satisfy acceptance conditions of special moment resistance connection based on AISC and FEMA. The arc-shaped fuse can increase drift story capacity up to 8% without any significant strength loss through increasing the out-of-plane stiffness of the beam longitudinal axis against lateral-torsional buckling. According to elastic flexural strength and stiffness of beam criteria, the reverse arc-shaped fuseisabetter choice than double arc-shaped fuse.

In recent years, we have witnessed a considerable increase in the study of thin flat sheet and various issues related to it. However, comprehensive studies on the formulation of curved plates are rare. Due to the growing use of curved panels in various fields, in this study, the effects of torsional stiffness, bending stiffness and axial stiffness of the peripheral members on shear buckling and post buckling behavior of curved steel panels were investigated. To do this, ABAQUS software and Riks method were used. The findings revealed that flexural stiffness and axial stiffness do not increase buckling resistance of panels while the torsional stiffness on elastic buckling resistance of panels was found to be effective. The nonlinear behavior of panels is the function of stiffness ratio of peripheral members to stiffness of panels. Stiffness of peripheral members on capacity after buckling and development of principal stresses of panels were not affected.

Different methods may be used for strengthening weak concrete connections. Because of the unique characteristics of FRP composites, they are widely used for strengthening concrete moment resisting frames. These retrofitting techniques are widely considered in research and practical applications. The retrofitting cost is an important factor in the selection of the most suitable retrofitting techniques. In the application of FRP laminates, the cost of retrofitting is mainly the function of FRP volume and the surface preparation. In this research, using ABAQUS general purpose finite element software, the effect of different FRP configuration in X-shape connection strengthening scheme were considered and the results were compared with full FRP coverage of connection. In this strengthening scheme, the effect of parameters such as strip width and thickness was examined. The results showed that in strengthening with x-shape strips, the connection could develop the capacity of connection strengthened by full FRP coverage, while it needs about 16 percent less FRP laminates, which meaningfully could reduce the price of connection strengthening.

The target of seismic improvement of a building is to strengthen the structural and non-structural members in order to reduce the earthquake damage.Dampers dissipate the structure’s energy. By using these types of equipment, the damage to the structure is dramatically reduced. In this article steel frames with three, six and ten stories with and without dampers are modeled in SAP software. They are evaluated by using seismic retrofitting guidelines and nonlinear static method. The results show that adding a viscous damper reduces seismic effect and damage performance level. In addition, using dampers in high-rise structures is more effective than shorter ones in reducing the effects of an earthquake.

Plate girders structure is a major industry which is mainly used in the systems covered by these beams. Reducing deflection and decreasing the maximum bending moment can be considered as a development in methodology. By the use of cross beams or braced beams, element perpendicular to the girders is provided. In this paper, the effect of stiffness and distance elements development are studied. Differential equation of degree four governing the behavior of the partial structures which is a quadratic relationship is determined by solving the following mathematical transformations, and the fundamental equations are derived. The resulting equations are solved by a practical problem and the answer to the problem. The modeling results are compared with the SAP2000 program. The findings show highly accurate implementation and compliance. It is also revealed that stiffness changing elements within the cross can include different amounts of stress, bending moment and improved cover system.

Since the application of composite shear wall is increasing rapidly throughout the world, it is necessary to study its behavior. General interest of engineers in using this unique system due to its application and behavior indicates the need for better understanding of this system.In this paper, by modeling composite shear walls and using Abaqus software and its verification, the results have been used for modeling composite shear wall with emphasis on the impact of number and diameter of bolts under cyclic loading. Solid and shell cements are used for modeling concrete and steel elements respectively. The results of the numerical study shows that 3´3 and 3´2.5 configuration with diameter of 22.2 millimeters of bolts are the best sizes.

There is a growing need for dynamic time history analysis and the absence of proper records in different areas has necessitated the production of artificiall accelerograms compatible with the whole plan. This study presents a new approach based on wavelet packet transform and artificial intelligence techniques to produce artificial earthquake accelerograms compatible with the whole plan. This approach takes into account the magnitude and the distance from the fault. The study of neural networks and fuzzy wavelet packet analysis has been used to achieve the desired goal. To do so, first earthquake accelerograms have been collected according to specific site conditions, earthquake magnitude and distance from origin. Then all records have been gatehered for training with fuzzy neural network. Attenuation spectra have been developed on the basis of information in the area using nonlinear regression. Then using fuzzy neural networks, the relationship between earthquake records and the devloped spectra from each record is calculated. In this satge, using wavelet packet analysis, mapping acceleration are analyzed and converted in to accelerograms (wavelet coefficients).