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Recently, base isolation techniques are applied as a resisting system to protect the structures from seismic and dynamic loadings. Due to their importance, in this paper, an optimum arrangement of lead rubber bearing (LRB) and friction pendulum system (FPS) is investigated in irregular buildings and its performance is compared with a regular case. For this purpose, 3 types of irregularities have been adopted. Accordingly, 3, 7 and 10 story buildings have been performed and 12 possible combination have been applied for the isolators in each model. Afterwards, the numerical models have been analyzed using nonlinear time-history analysis and direct integration method and applying 7 earthquake records along the longitudinal and transverse directions of the building. The obtained results of the numerical study show that the application of FPS and LRB isolators in outer and inner columns respectively, led to a better performance compared to the other arrangements by reduction of the inter-story drifts as well as base shear and enhancement of the energy dissipation which is due to the characteristics of FPS isolators in balancing the applied forces with the building’s mass and prevention of torsion occurrence in irregular structures. Unlike the irregular buildings, application of FPS and LRB isolators in inner and outer columns, result in a better performance by reducing the story drifts in regular structures.

One of the simplified methods, which is progressing and completing every day, is a nonlinear static analysis that can directly evaluate the performance of a structure in any limit state and provide information about the nonlinear behavior of the structure, and it also does not have the complexity of nonlinear dynamic analysis. In this study, the structural responses of nonlinear static procedure (NSP) based on standard 2800 were compared with ASCE 41-13 code and displacement -based adaptive pushover (DAP) method in three models of reinforced concrete structures including the 3, 7 and 10 story with medium ductility. In order to study the accuracy of nonlinear static analysis and seismic behavior of structures, nonlinear time history analysis (NTHA) which is the most accurate method in seismic assessment of structures was conducted.The results show that in 3 and 10 story the NSP according to standard 2800 with forces distribution obtained from the spectral dynamical analysis is more accurate than other NSPs in evaluating of story drifts ratio and maximum displacement along the height of buildings. In 7 story, displacement -based adaptive pushover (DAP) method can be estimated story drift ratio more precisely. In 3 and 10 story, the NSP based on 2800 with forces distribution obtained from the spectral dynamical analysis, can estimate the mean story drifts with a lower percentage error. According to the results, in each three model the uniform distribution of nonlinear static procedure (NSP) based on standard 2800 estimates the story drifts with less accuracy and high error. As a suggestion, nonlinear static analysis based on uniform distribution can be eliminated from the standard 2800.

Nonlinear time history analysis is recognized as the most appropriate tool for assessing the real behaviour of structures during seismic excitations. Validity rate of obtained results from this analysis significantly depends to the modeling, details and defined parameters. One of the main aspects of dynamic modeling is the consideration of natural viscous damping as well as value of damping ratio (ξ), which during last years evaluating the effects of these factors on nonlinear responses of moment-resisting steel frames has been limited, and Rayleigh damping model with ξ of 5% was used by researchers. Therefore, in this study attempt has been made to examine the impacts of value and modeling approach of natural damping on nonlinear responses of moment-resisting steel frames. For this purpose, a full scale 4 story steel structure which tested on shake table in 2007 has been considered as reference and modeled by OpenSees software. Natural damping has been defined with three methods; Rayleigh damping, mass-proportional damping and stiffness-proportional damping, for five different values of damping ratio (ξ=0.01, 0.02, 0.03, 0.04, 0.05). After conducting the nonlinear time history analyses, difference of obtained structural responses compared to the experimental responses has been investigated, and then errors of them have been extracted. Results indicate that reduce of damping ratio leads to the notable decrease of responses, specially, for story shear and overturning moment. The use of 5% damping ratio for nonlinear dynamic analysis of low rise moment-resisting frames is not appropriate and in most of cases leads to the underestimate and unreal results. Besides, it should be noted that the mass-proportional and Rayleigh damping models have higher accuracy in comparison with stiffness-proportional damping model, and these models show lower error.

Replacing of conventional concrete by High Performance Fiber Reinforced Cementitious Composite (HPFRCC) could improve tensile strength, bending strength, shear strength and other capability of behaviour such as ductility, energy absorption and toughness. Strain hardening behaviour in (HPFRCC) could result in restrict of crack and prevent from crack widening. Also, because of the high strain capacity of (HPFRCC), using this material in the beam-column connection is more attention paid by researchers. After verification of numerical models for frame using OPENSEES software and comparison with experimental results, two 2D frames with 3 and 6 stories has been created to study. These frames have been designed based on ACI 318. Each frame is considered in 4 formats containing conventional concrete in all elements (RC), containing of (HPFRCC) in beam-column connection (RCH1), containing of (HPFRCC) in beam-column connection and first story column base (RCH2) and containing of (HPFRCC) in all elements. Results from nonlinear static analysis (pushover analysis) show increase of lateral strength, ductility and ultimate displacement of frames containing (HPFRCC) with respect to (RC) frames. Also, using of (HPFRCC) in frames has been decreased maximum story drift ratio, maximum roof displacement and has been increased maximum base shear and story shear in nonlinear time history analysis.

Usually during moderate and strong earthquakes, if the space between the adjacent structures is not enough, structural pounding will occur which is due to the out-of-phase vibration of the structures regarding the differences in dynamic properties of the structures. Different factors contribute in the state of structural pounding, and researchers have already studied several factors including the space between two structures, the type of pounding, force transmission means, reducing the pounding damage and etc. Record is one of the factors which can affect the structural pounding, and one of the most crucial parameters of record is strong ground motion duration which its analysis is very important in the quality of structural response.In this study, effect of strong ground motion duration on the adjacent structural pounding is investigated. To do so, steel moment resisting frames in 5, 8 and 12 floors are designed which are paired together in three forms of 5-8, 5-12, and 8-12 models for nonlinear time history analysis. In this analysis, 15 records that include three intervals for strong ground motion duration are being implemented (0 to 10 seconds, 10 to 30 seconds, 30 seconds and more). Besides, in order to obtain the pounding force between structures, linear elastic elements are used in floor levels.Results show that in structures in which the space equal to 1% of their heights are not considered, with increasing the strong ground motion duration, maximum structural pounding will also increase with a smooth gradient, and for the structures with space equal to 0.5% of their heights, this increase rate is more compared to the structures with no space.

In the seismically active countries such as Iran, there are many structures that have been designed and constructed in recent years that do not conform to the terms and provisions of the design codes. On 26 December 2003 at 1:57 GMT, the historical city of Bam, located in the south-eastern region of Kerman province in Iran, was shaken by a relatively strong and destructive earthquake. This earthquake clearly demonstrated that combination of relatively rigid load-bearing external brick walls and flexible internal steel columns, existing similarly in most other regions of the country, is quite hazardous. Also the use of steel beams and columns in buildings without observing proper seismic provisions showed no improvement over non-engineering designed buildings. In this research, two steel frame buildings which had been damaged in the bam earthquake were studied. The first building has bracing system in both directions and in the second building the bracing system only exist in one direction fallowed by infilled panel with saddlebag type connection(semi-rigid Khorjini connection) in opposite direction. In both buildings all the standard of criteria 2800 and Seismic provisions are considered. Nonlinear static analysis (Pushovers) and nonlinear time-history analysis are implemented on both structures. After determining the vulnerability of structures, using steel plates and viscous damper, the results show that retrofitted buildings with fluid viscous damper dissipate higher energy in comparison with the buildings retrofitted by the steel plate. Strengthening the existing buildings were investigated and compared with each others through three different methods: 1. replacing relatively strong bracing system with the relatively weaker bracing 2. Strengthening the columns by adding cover steel plates to the columns of building and 3. Global Strengthening bracing and columns system of buildings.

In the design of high-rise buildings, three parameters such as resistance, hardness and stability are very important and when the height of building rises, effect of toughness and stability in optimum design will be dominate more than of the effects of these two factors against the lateral loads from wind and earthquake. The best ways to satisfy these two factors is the use of innovative forms and models of structures, so that, while maintaining stiffness, reducing deformation and drift caused by lateral loads, increase the stability of the structure. Outrigger and belt truss system are one of the innovative systems in high-rise structures that use it substantially reduces the consumption of structural steel and construction costs are high.In this research, two 2D frame with 5 spans and 30 and 50 stories according to the Iranian codes were designed in two cases of: the moment frames and frames with outrigger and belt with. Then maximum displacements of nodes and maximum inter stories drifts calculated for every earthquake records with use of SAP2000 software and time history analysis and has defined three different threshold IO, LS, and CP and acceleration of each record based on the severity of the earthquake. Then curves were plotted for each case; the results indicate that the outrigger and belt truss system would reduce the maximum inter story drift about 12 to 28 percent.

In recent years some studies have been done on the moment rredistribution in buildings and new methods offered for calculating of redistribution. Observations demonstrated that the combination of moment and shear force is important in analysis of reinforced concrete structures. But little research is done about the effect of redistribution by using moding in software. In order to study the effect of moment redistribution on the stability of RC moment resisting frame structures, four buildings with 4, 7, 10 and 13 story have been considered. In these models, the nonlinear behavior of elements (beam and column) is considered by the use of interaction PMM hinges. The average plastic rotation was calculated by performing pushover analysis and storing stiffness matrix for 5 points and then the buckling coefficients were obtained by conducting buckling analysis. By the use of modal analysis natural frequency was calculated and it was attempted to be related the average plastic rotation with the buckling coefficients and the natural frequency. It could be concluded that increase in the plastic rotation reduce the buckling coefficients to about 96% which this amount of reduction is related to the average plastic rotation. Moreover, the buildings experience instability state when the average plastic rotation reached to 0.006 radian.

Having very simplicity, nonlinear static procedures (NSPs) are the most popular tools for estimation of structural capacity. These approaches construct a graphic display of the overall structural response via a pushover curve. The overall response of the system provides a direct simulation of the building as single degree of freedom (SDOF) system that simplifies the design and evaluation of the structure. In this research, the first step in any nonlinear static analysis or in other words perform a pushover analysis has been studied. Applied lateral load to the structural model not only affects the overall responses of the structure through structural capacity curve, but also directly affects the local responses of the structure. In order to evaluate these lateral loads, steel buckling restrained braced frame structures are examined by advanced modal pushovers. Next, the results of these pushover analyses will be compared with nonlinear time history analysis as the most accurate method. Finally, the most efficient method in this particular structure is introduced. The analysis conducted in these structures shows that the lateral load pattern based on story shears offers a good prediction of the maximum response of the concentrically buckling restrained braced frame buildings.