چكيده فارسي :
بررسي و مطالعه پراكندگي خسارات زلزله‌هاي مختلف بيانگر اهميت تاثير ساختگاه بر مشخصات و خصوصيات لرزش زمين در سطح است. از سوي ديگر، اثر محلي ساختگاه نقش مهمي در طراحي و مقاوم سازي سازه ها در برابر زلزله دارد. طبيعت اثر محلي ساختگاه را مي توان با بهره‌گيري از روش هاي مختلف مانند تحليل ساده نظريه پاسخ زمين، اندازه‌گيري جنبش واقعي سطحي و زيرسطحي در همان ساختگاه و اندازه‌گيري جنبش سطحي در ساختگاه هايي با شرايط متفاوت نسبت به ساختگاه مورد نظر تشريح كرد. در اين مقاله عوامل تاثيرگذار بر حركت زمين و پاسخ ساختگاه تحت تاثير زلزله طبس و بم به روش عددي و با بهره‌گيري از نرم‌افزار تفاضل محدود flac در ساختگاه هاي نوع 2 و نوع 3 در شهر تهران بررسي و ارزيابي مي شود. براي بررسي تاثير پارامترهاي توده خاك بر پاسخ زمين، مطالعه پارامتريك انجام شده است. در اين روش شتاب بيشينه سطح زمين و ضريب تشديد مقايسه مي شوند. اين دو كميت تاثير مهمي بر جرم سازه و نيروي زلزله وارد بر سازه دارند. نتايج اين تحقيق نشان مي دهد شتاب بيشينه سطح زمين با شتاب سنگ بستر متفاوت است و به‌طور درخور توجهي تابع مشخصات ساختگاه و لايه زمين‌شناسي است. مطابق نتايج، افزايش سرعت و عمق سنگ بستر (براي هر دو نوع خاك)، تاثير چشمگيري بر شتاب سطح زمين و ضريب تشديد لايه هاي سطحي خاك دارد.
چكيده لاتين :
The study of variations of damage intensity for different earthquakes indicates the importance of the site effects
on earthquake induced damage and ground motion parameters such as peak ground acceleration and induced
amplification. In the occurrence of an earthquake, local site conditions such as soil characteristics, dimension of
topographic irregularities, seismic bedrock depth, etc. as well as characteristics of incident wave have important e
ects on seismic ground responseLocal site effects play an important role in earthquake-resistant designs and
should be assessed carefully. By assessment of induced damages to structures and major infrastructures, seismic
geotechnical researchers have concluded that the site conditions significantly influence on the failure distribution
in urban and rural areas. Consequently, to determine the characteristics of seismic motions of the ground, it is
essential to study the effective geotechnical factors. Consideration of the effects of the site response in the design
of civil structures systems is of important to mitigate the damages to a certain extent on structures and the
environment. Hence, it is relatively crucial to reliably attain the dynamic soil parameters of an earthquake-prone
city/state. The nature of local site effects can be explained by using different methods such as simple theoretical
analysis of ground response, measuring of surface and subsurface actual motion at the same site, and measuring
the movements of the ground in sites with different conditions in comparison with the proposed site. In this
paper, the effective factors on ground motion and site response in the soil classes II and III for Tehran city under
the influence of Tabas and Bam earthquake were reviewed with numerical method and by using the finite
difference software (FLAC 2D). Some of the effective parameters of the site dynamic characteristics on the
seismic response of the ground surface have been studied and the response of peak ground acceleration and the
resonance function has been compared.
The results of this study show that at both sites, the horizontal maximum acceleration of the ground
surface increases with respect to the bedrock shear velocity, reflecting the influence of the site on
ground movement. At both sites, with increasing soil internal friction angle, the maximum acceleration
at ground level increases and the acceleration response decreases. Also, as the shear wave velocity
increases, the horizontal maximum acceleration at ground level for both structures decreases.
Increasing the shear wave velocity in the surface layer, assuming the thickness of the layer is constant,
results in a decrease in the natural frequency, which is far from the normal frequency range of
conventional structures in Tehran. This indicates a decrease in the earthquake's dynamic force on
surface structures. The natural frequency of five to seven story buildings in Tehran is about 0.5 to 0.7
Hz. As the surface layer thickness and bedrock depth increase, the horizontal maximum acceleration of
the ground surface also decreases, meaning that the structural response can also be reduced.
