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ملاحظاتی در باره اثر شیب بار بر ضرائب ظرفیت باربری لرزه‌ای پی نواری | ||
| نشریه مهندسی عمران و نقشه برداری | ||
| مقاله 12، دوره 45، شماره 4 - شماره پیاپی 708182، مهر 1390، صفحه 495-504 اصل مقاله (993.38 K) | ||
| نویسندگان | ||
| محسن کمالیان1؛ کامبیز بهنیا2؛ محمدرضا لطفی زاده3؛ ابوالفضل رستگار4 | ||
| 1Associate Professor, International Institute of Earthquake Engineering and Seismology. | ||
| 2Associate Professor, School of Civil Engineering, College of Engineering, University of Tehran, I.R. Iran. | ||
| 3Graduate Student, International Institute of Earthquake Engineering and Seismology. | ||
| 4Ph.D Student, Science and Research Branch, Islamic Azad University. | ||
| چکیده | ||
| محققین پیشین ضرائب ظرفیت باربری لرزه‌ای پی نواری را عمدتا با این فرض متعارف برآورد کردند که نه تنها نیروی حجمی و نیز سربار وارده بر سطح آزاد مجاور پی، بلکه حتی فشار تماس زیر پی، با راستای قائم زاویه‌ای یکنواخت و متناسب با ضریب افقی شتاب زلزله می‌سازند. براستی اگر در قاب‌های خمشی دارای چند دهانه، از بادبند، تکیه‌گاه غلطکی یا برخی عوامل دیگر در مکانیسم باربری افقی سازه استفاده شود و لذا شیب بارهای لرزه‌ای وارده بر کف پی‌ها متفاوت باشد، ظرفیت باربری لرزه‌ای پی‌ها چگونه تغییر خواهد یافت؟ مقاله‌ی حاضر بر آن است تا به این سؤال پاسخ دهد. برای این منظور ضرائب ظرفیت باربری لرزه‌ای پی نواری با بکارگیری روش خطوط مشخصه برآورد و اثر شیب بار کف پی مورد توجه قرار گرفته است. نشان داده شده است که هر قدر شیب بار کف پی کمتر باشد، ظرفیت باربری قائم پی فزون‌تر خواهد شد. همچنین این یافته‌ی محققین پیشین مورد تأکید قرار گرفته است که اثر زلزله بر هر یک از نیروی حجمی خاک و سربار، همانند اثر آن بر شیب بار کف پی، بیش از آن است که نادیده گرفته شود. | ||
| کلیدواژه‌ها | ||
| پی نواری؛ خطوط مشخصه؛ زلزله؛ شیب بار.؛ ظرفیت باربری لرزه‌ای | ||
| عنوان مقاله [English] | ||
| Considerations about Load Inclination Effect on Seismic Bearing Capacity Factors of Strip Foundations | ||
| نویسندگان [English] | ||
| M. Kamalian1؛ C. Behnia2؛ M.R. Lotfizadeh3؛ A. Rastegar4 | ||
| چکیده [English] | ||
| Assessment of seismic bearing capacity of strip foundations has been the concern of only few researchers in the field of geotechnical earthquake engineering during the last decades. The previous works have mostly assumed that in the presence of a horizontal earthquake acceleration (kh.g) besides the body force due to gravity, the ratio of the shear stresses to the normal stresses along the ground surface is equal to kh and the load inclination beneath the footing with respect to vertical equals to tan-1(kh). But this assumption does not seem to be always correct. For example in the case of multi span frames where only some spans may be braced and the support conditions at the end of the columns may not be uniform, the load inclination beneath some footings may not be equal to tan-1(kh). This paper presents the seismic bearing capacity factors N?, Nq and Nc of a rigid strip foundation resting on a horizontal ground surface, when the load inclination beneath the footing is not equal to tan-1(kh). All calculations are executed by the well known stress characteristic method, commonly referred to as the slip-line method. It is assumed that the soil behaves rigid perfectly plastic and obeys the well known Mohr-Coulomb failure criteria under plane strain conditions. It is assumed that the state of the stress everywhere in the neighborhood of the foundation is at failure. It is also assumed that everywhere along the surface of the foundation, the ratio of the shear to the normal stress is equal to the horizontal earthquake acceleration coefficient (kh). The N? parameter was calculated based on the both-sides failure mechanism, whereas the Nq and Nc parameters were calculates based on the single-side failure mechanism. The Nc parameter for cohesive media was calculated using the rule of equivalent states. Some graphs and tables are presented that could be used in order to assess the seismic bearing capacity factors of rigid strip foundations obtained by the stress characteristic method for various load inclinations. It is shown that the seismic bearing capacity factors, just like the static bearing capacity factors, increase considerably with reduction in the load inclination and vice versa. Further, this important outcome of some previous research works has been confirmed once again that the earthquake's effect on each of the body force as well as the overburden is as important as the earthquake's effect on the load inclination which should not be neglected. It is also shown that because of the non-symmetric nature of the seismic loading, the disposal of the characteristic lines as well as the pressure distribution below the foundation is non-symmetric. In other words, the foundation would be subjected to a moment in addition to the vertical and horizontal reactions, as a result of the non-symmetric soil pressure distribution during earthquakes. | ||
| کلیدواژه‌ها [English] | ||
| Load Inclination., Seismic Bearing Capacity, Stress Characteristic Method, Strip Foundation | ||
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