Sharif Digital Repository

In this study, a nonlinear absorber that works with a negative stiffness is introduced to control vibration and its effect on reducing earthquake damage is investigated. Negative stiffness increases structural softness and damping. Also, due to its inherent nonlinear nature, negative stiffness can cause internal resonance and transfer vibration energy from a directly excited vibrating mode to a higher frequency mode. Using these features can be effective in reducing vibration. First, to investigate the dynamic behavior in conditions without internal resonance and with 1:3 internal resonance, the proposed absorber is added to a nonlinear main system and when the system is under external... 

In this article, a new method for the seismic resistant design is introduced. At first some formulation necessary for the introduction of the proposed method is carried out. This new procedure directly deals with ductility and takes into account the amount of ultimate displacement and required strength interactively. This design procedure is verified by extensive numerical examples using some actual earthquake records. The procedure is shown to be completely safe and to reduce the amount of inherent conservatism. Moreover, it has been tried to introduce some applicable correction factors. Copyright © (2006) by Earthquake Engineering Research Institute  

In this paper, a simple finite element model for seismic analysis of retaining walls is introduced. The model incorporates nonlinearity in the behavior of near wall soil, wall flexibility and elastic free field soil response. This model can be employed in nonlinear modeling of retaining walls and bridge abutments. The advantages of this model are simplicity and flexibility in addition to acceptable precision. Using this finite element model, an analytical study is conducted on several soil-wall systems using nonlinear time-history analysis by applying real earthquake records. Based on the results of these analyses, new seismic soil pressure distributions are proposed for different soil and... 

Most seismic design codes accept heavy damages to buildings in case of large earthquakes, provided that they are prevented against collapse. However, this leads to unacceptable consequences, such as very large volume of the required reconstruction works, in large populated cities. One way to get rid of these adverse consequences is using the idea of combining rocking/seesaw motion of the building's structure and energy dissipation at base level to create buildings easily repairable even after a large earthquake. In the present study, this idea has been employed for designing steel buildings with seesaw motion capability by using a central massive column at ground floor, with elastic behavior... 

In this paper, a technique for the study of nonlinear performance of structures in different levels of earthquakes is developed. In this method, the Incremental Dynamic Analysis (IDA) curves are not achieved from nonlinear dynamic analysis of multi-degree-of-freedom (MDF) structure. However, the procedure of constructing these curves is based on modelling of the entire structure with several single-degrees-of-freedom (SDF) structures and evaluating them through the modal pushover analysis method. An innovative idea for approximating pushover curves that is based on error distribution is introduced in this investigation. Furthermore, the total input energy applied towards the SDF oscillator,... 

In this study, the performance of a proposed friction damper with two slip loads in controlling the seismic response of steel moment resisting buildings structures under moderate and intense earthquake excitations is investigated. The proposed friction damper initially operates with a smaller slip load and could shift to the higher slip load after a certain amount of slippage when subjected to intense ground motions. In this regard, the hysteresis behavior of the proposed double slip loads (DSL) friction damper is modeled and after necessary verifications is imported to the material library of OpenSees software to be used for parametric study. To evaluate the performance of the proposed DSL... 

Shape Memory Alloys (SMA) are among the new passive control devices that have gained a large attention due to its inherent features, i.e., recovering the induced residual strains upon unloading (superelastic effect) or by heating (shape memory effect). In this work, the seismic behavior of a set of steel structural models with different number of stories and eccentricities equipped with a type of fixed SMA connections is investigated. Considering an existing SMA connection model in austenite phase, the related moment-rotation behavior is verified through numerical simulation. Then, extensive nonlinear dynamic analyses are performed using a number of 3, 6, 9, and 12 story structural models... 

In order to estimate the seismic demands at the performance level, the inelastic behavior of concrete structures should be considered. Incremental dynamic analysis (IDA) based on a nonlinear response time history analysis (NL-RHA) is considered to be the most accurate method in seismic demand calculations. However, modal incremental dynamic analysis (MIDA), based on the equivalent single-degree-of-freedom (SDF) oscillator, is also often used in studying structural engineering performances. As the MIDA method has usually not been applied to reinforced concrete (RC) structures, in this study an attempt is made to investigate the performances of RC frames and to compare the results obtained... 

Accelerograms recorded near active faults have some important characteristics that make them different from those recorded in far-fault regions. High-frequency components in acceleration records and long-period velocity pulses are among notable specifications of such ground motions. In this paper, a moving average filtering with appropriate cut-off frequency has been used to decompose the near-fault ground motions into two components having different frequency contents: first, Pulse-Type Record (PTR) that possesses long-period pulses; second, the relatively high-frequency BackGround Record (BGR), which does not include large velocity pulses. Comparing the results with those extracted through...