پاسخ سه بعدي سازه ها تحت شش مولفه اي زلزله هاي نزديك و دوراز گسل

Considering the Effect of Six Component of Near-Fault Earthquake Ground Motions on the Three Dimensional Systems

از زماني كه مشخص شد مولفه هاي دوراني جنبش قوي زمين بر پاسخ لرزه اي سازه ها اثرگذار است ، توجه جدي محققين به اين مولفه ها جلب شد. در اين مطالعه يك روش توسعه يافته براي محاسبه تاريخچه زماني مولفه هاي پيچشي و دوراني حركت زمين، وابسته به سه مولفه انتقالي، ارايه مي شود. در اين مطالعه سه مولفه دوراني از مشتق مولفه هاي انتقالي و ميزان سرعت موج برشي ساختگاه به دست مي آيد. براي ايجاد مولفه هاي دوراني زمين لرزه هفت ركورد انتقالي دور و هفت ركورد نزديك گسل انتخاب شده است. طيف پاسخ مولفه هاي دوراني نزديك و دور از گسل از ركوردهاي دوراني ايجاد شده به دست آمده است. سپس طيف هاي پاسخ دوراني نزديك و دور از گسل مقايسه وارزيابي شده است. همچنين آثار ركوردهاي دوراني زمين لرزه بر پاسخ سازه تحت هر شش مولفه ركورد زلزله هاي نزديك و دور از گسل، بر سيستم ايده آل شده اعمال و ارزيابي شد

The rotational components of seismic strong-motion are attracting attention since it is becoming evident that it may contribute considerably to the overall response of structures to earthquake motions. Also, it is clear that the effects of near-fault ground motions with large velocity pulses, large amplitude, long period, and pulse type of excitation can create critical working conditions. In the near-field of an earthquake the effects of the rotational components of ground motion may not be negligible specially for important structures. In this paper, an improved method for calculating the time histories of torsional and rocking components of ground motion corresponding to a set of three recorded orthogonal translational components is presented. The current processing of earthquake records provide information only about the three translational (two horizontal and one vertical) components of the ground motion, primarily because these are the only components that can be directly instrumentally measured. However, the translational components during a seismic event are always accompanied by rotational components because of the traveling wave effects. Several studies have shown the importance of rotational components in the seismic analysis and design of structures. The seismic design codes also prescribe "accidental eccentricity" in the design force calculations to account for the unknown torsional inputs and unintended eccentricity in the design of a building. One of the reasons why this input is not explicitly taken into account in the seismic design codes is the lack of reliable information on torsional ground spectra. In this study the three rotational components of earthquakes records is generated artificial by three translational components. The torsional motions in terms of time derivative of translational components and shear wave velocity of site are derived. Seven translational earthquake records of far fault and seven translational earthquake records from near-fault have been selected. The rotational components of far fault and near fault are generated the response spectral for translational as well as rotational components are presented and compare to each other in other to verify the characteristic of the near fault response spectral compare to the far fault response spectral. Furthermore, the effect of rotational motion on structural response is investigated. Therefore the six components of earthquakes records of far fault and near fault applied to the idealized system model and the response of the system are determine.