structure interaction
در نشریات گروه عمران-
The undeniable impact of soil-structure interaction on the behavior of structures, coupled with the increased importance of explosive loads in current global security and social conditions, has led to the modeling and sensitivity analysis of the distance effect and explosive load on concrete structures, taking into account the effects of soil-structure interaction. Three types of structures with 3, 7, and 15 floors were modeled for this investigation, and the results were evaluated. The software tools ETABS and ABAQUS were utilized, with ETABS for structural element design and ABAQUS for examining the effects of soil-structure interaction. The input energy and induced displacements in the structures have a meaningful relationship with the explosion force. In all three structures (3, 7, and 15 floors), the energy and displacements created vary proportionally with the explosion distance or the reduction in explosive material weight. The plasticity rate reflects a substantial reduction in damage with an increasing explosion distance from the structure. Additionally, according to the research results, an increase in the number of floors undoubtedly leads to more noticeable displacements. Therefore, these displacements and energy absorption in the 15-floor structure exceed those in other structures. The failure zone in the 3-floor structure is mostly in the last floor, in the 7-floor structures in the middle floors, and in the 15-floor structures in the initial floors. Displacement in the 3-floor structure is at the upper levels, in the middle of the 7-floor structure, and at the lower levels of the 15-floor structure.
Keywords: Nonlinear Dynamic Analysis, Soil, Structure Interaction, Explosive Load, Sensitivity Analysis, Distance Effect -
در احداث ساختارهای زیرزمینی شهری، عبور تونل ها از زیر سازه های سطحی امری اجتناب ناپذیر است. پیش بینی و کنترل تغییر شکل های حاصل از حفاری، به ویژه نشست سطحی زمین، همواره باید پیش از حفاری مورد توجه قرار گیرد. به این منظور در مقاله به بررسی اثر حفر تونل بر نشست ساختمان های مجاور تونل با نگرش ویژه بر ارتفاع و عرض سازه پرداخته شده است. تونل مترو اصفهان به صورت موردی در نظر گرفته شده است و از نرم افزار FLAC2D جهت مدل سازی در استفاده شده است. در این مقاله محدوده ایستگاه میدان آزادی تا ایستگاه شیخ کلینی و اطلاعات ساختمان های منطقه در نظر گرفته شده و به بررسی اثر عرض و ارتفاع سازه های اطراف تونل بر میزان نشست سطح زمین در اثر حفر تونل پرداخته شده است. با توجه به تراکم زیاد سازه ها در این منطقه و برنامه توسعه شهری احتمال تخریب بسیاری از سازه ها و احداث سازه های جدید در این منطقه وجود دارد. جهت تعیین مشخصات ژیوتکنیکی محدوده مورد مطالعه در سه منطقه مطالعات ژیوتکنیکی صورت گرفته است و جهت صحت سنجی نتایج با استفاده از ابزاردقیق نشست سازه مجاور در مدت زمان 90 روز بررسی شده است. با توجه به تحلیل های انجام گرفته، در ساختمان با عرض 10 متر و تعداد طبقات 4 (ارتفاع 12 متر) محدوده ی مجاز ساخت سازه در حدود 65/1 متر و با افزایش تعداد طبقات به 8 و 12 طبقه این فاصله به حدود 5/4 و 9 متر رسیده است و نسبت به ساختمان 4 طبقه به ترتیب 72/2 و 45/5 برابر افزایش یافته است. با افزایش تعداد طبقات به 12، محدوده مجاز ساخت سازه برای عرض 20 و 30 متر به ترتیب نسبت به ساختمان با عرض 10 متر به ترتیب 5/1 و 7/2 برابر افزایش یافته است. لازم به ذکر است، نتایج به دست آمده برای مناطق مشابه با منطقه مورد نظر از نظر ویژگی های ساختگاه و مشخصات تونل می تواند مورد استفاده قرار گیرد.
کلید واژگان: تونل، ارتفاع سازه، عرض سازه، نشست مجاز، ابزاردقیقIn the construction of urban underground infrastructures, the passage of tunnels below the surface structures is inevitable. Prediction and control of deformations resulting from excavating, especially the ground's surface subsidence, should always be considered before drilling. For this purpose, the present study deals with the numerical analysis of the interaction between the tunnel and its adjacent buildings. In this paper, the Isfahan Metro Tunnel in the range of Azadi Square to Sheikh Koleini Station is considered and FLAC2D software is used for modeling. The characteristics of the buildings in the limited area have been considered and the effect of the width and height of the structures around the tunnel on the rate of ground subsidence caused by the tunnel excavation has been investigated. In order to validate the results, data of the subsidence instrumentation were utilized. Finally, based on the performed analysis, it was concluded that the permissible range of constructing structures around the tunnel area depends on the geometry of the structure and as the size of the structure increases, reliable limits for the construction of structures around the tunnel drilling area are reduced. As a practical result, a diagram was provided to determine the permissible range of construction around the twin tunnel based on different values of the width and height of the structure.
Keywords: Soil, structure interaction, Tunnel, Isfahan -
در این تحقیق، رفتار لرزه ای مخازن بیضویروزمینی چهارقلو مورد مطالعه قرار گرفته است. اساسا مخزن سازه ای است که برای ذخیره انواع مایع به کار می رود و در انواع زمینی و هوایی و نیز بتنی و فولادی کاربرد گسترده ای در تصفیه خانه ها و پالایشگاه ها و کارخانه ها دارد. با توجه به اعمال نیروهای دینامیکی و هیدرودینامیکی عظیم به یک مخزن بزرگ در هنگام زلزله و اهمیت زیاد تداوم عملکرد کامل سازه مذکور در شرایط بحرانی، مطالعه رفتار لرزه ای آن از اهمیت بالایی برخوردار است. در میان تحلیلهای گوناگون، تحلیل لرزه ای مخزن دارای اهمیت قابل ملاحظه ای است زیرا با بررسی نتایج حاصل از آن می توان شناخت مفیدی را از کیفیت رفتار مخزن در هنگام وقوع یک زلزله واقعی به دست آورد. در این تحقیق مخازن بیضوی روزمینی یک قلو و چهارقلو در حالتهای مختلف کشیدگی و لاغری مخزن تحت زلزله های کیپو طبس و منجیل به طور همزمان در جهات طولی و عرضی تحت تحلیل دینامیکی قرار گرفته اند و پارامترهای فشار ماکزیمم صلب و ارتفاع ماکزیمم موج حالتهای متناظر با هم مقایسه شده اند. با بررسی نمودارهای حاصله مشخص شد که درصد کاهش پارامترهای فشار ماکزیمم صلب و ارتفاع ماکزیمم موج به واسطه تقسیم مخزن در مخازن لاغرتر بیشتر است. همچنین مشخص گردید که درصد کاهش پارامترهای فشار ماکزیمم صلب و ارتفاع ماکزیمم موج به واسطه تقسیم مخزن در مخازن کشیده تر کمتر می باشد.کلید واژگان: تحلیل لرزه ای، مخزن بیضوی، تقسیم مخزن، کاهش تموج، اندرکنش آب و سازهThe seismicbehavior of the on ground quadroplete elliptical tanks has been investigated in the current study. Basically, the tank is a structure used to store different types of fluid, and it is also widely used in refineries, sewage treatment plants and factories in the form of on ground and elevated tanks made from concrete and steel. Regarding the application of the huge dynamic and hydrodynamic loads on a tank at the time of earthquake and the great importance of the structure’s complete function continuity in the critical situations, it is highly important to study its seismic behavior. Among the different analyses, the seismic analysis of the tank is highly important because by investigating the results obtained from this analysis, a useful recognition of the quality of the tank’s behavior at the time of a real earthquake can be obtained. The monoplete and quadroplete on ground elliptical tanks have been dinamicallyanalyzedunder Cape and Tabas and Manjil earthquakes simoultaneously in the longitudinal and transverse directions in various conditions of prolateness and slenderness of the tankand the maximum impulsive pressure and the maximum wave height parameters of corresponding cases have been compared with eachother in the current research. By study of the concluded diagrams, it was revealed that the reductionpercent of the maximum impulsive pressure and the maximum wave height parameters due to partitioning of the tank is higher in the more slender tanks. It also was revealed that the reductionpercent of the maximum impulsive pressure and the maximum wave height parameters due to partitioning of the tank is lower in the more prolate tanks.Keywords: seismic analysis, Elliptical tank, Tank partitioning, Sloshing mitigation, Fluid, structure interaction
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Ground cylindrical steel fluid storage tanks are widely used in different industries. Regarding the significance of these structures, it is important to establish their proper performance in earthquakes by evaluating their seismic performance. The present study examines the seismic behavior of an unanchored fluid storage system via ABAQUS after validation using an experimental model. Next, the uplift of the bottom sheet is studied using the accelerogram records of the 1940 El Centro and 1994 Northridge earthquakes. The overturning moment time history of the fluid storage system and the maximum overturning moments were obtained to identify their behavior. The results indicated that not bracing storage tanks leads to the uplift phenomenon. Finally, the maximum axial stress of the storage tank shell was compared with the values recommended in the construction codes to control the buckling.
Keywords: Ground Reservoir Tanks Seismic BehaviorWater, Structure Interaction -
یکی از مسایل مهم و اساسی که امروزه با توجه به اهمیت آن همواره مهندسین عمران به آن میپردازند، بررسی عملکرد و رفتار سازه ها تحت شرایط مختلف است. عالوه بر این در بسیاری از موارد، ساختمانها بطور جداگانه و بدون در نظر گرفتن اثر دیگر المانها ازجمله پی و خاک زیر سازه ها مورد تحلیل و طراحی قرار میگیرند که این امر در بسیاری از موارد ایجاد خطرات جبران ناپذیری مینماید؛ از اینرو بررسی و ارزیابی اثر اندرکنش خاک-سازه بر عملکرد و طراحی ساختمانها به منظور مدیریت هزینه و زمان پروژه های عمرانی ضرورت پیدا میکند. در این تحقیق، عملکرد سازه های فولادی با مهاربند همگرا 5، 10 و 15 طبقه با در نظر گرفتن اندرکنش خاک سازه در سه حالت خاک مختلف با استفاه از تحلیل دینامیکی غیرخطی تاریخچه زمانی تحت 3 زلزله نزدیک به گسل انجام شده است. نتایج نشان می دهد که لحاظ نمودن اندرکنش خاک و سازه باعث افزایش دقت پاسخ های سازه ای می شود.کلید واژگان: سازه فولادی، مهاربند همگرا، اندرکنش خاک و سازه، زلزله نزدیک به گسلOne of the most important and fundamental issues that civil engineers always deal with today due to its importance is the study of the performance and behavior of structures under different conditions. In addition, in many cases, buildings are analyzed and designed separately and without considering the effect of other elements, including the foundation and soil of the infrastructure, which in many cases creates irreparable risks; Therefore, it is necessary to study and evaluate the effect of soil-structure interaction on the performance and design of buildings in order to manage the cost and time of construction projects. In this study, the performance of steel structures with concentric brace of 5, 10 and 15 floors by considering the interaction of soil structure in three different soil modes using nonlinear dynamic analysis of time history under 3 near-fault earthquakes has been done. The results show that considering the interaction of soil and structure increases the accuracy of structural responses.Keywords: steel structure, Concentric brace, Soil, Structure Interaction, Near-fault earthquake
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The behavior of storage tanks'' analysis in seismic areas is of major importance because of the strategic nature of these works. The steel cylindrical tanks are the most susceptible to damage due to dynamic buckling during earthquakes. In this study, three criteria are used to estimate the critical peak ground acceleration caused the tank instability. The liquid inside the tank was modeled using specific Ansys''s finite elements and fluid-structure interaction. The calculation includes modal and time history analysis, including material and geometric non-linearity. The result values are compared with standard code previsions as well as the results of previous numerical research, and show the need to improve code provisions.Keywords: Dynamic buckling, tanks, earthquakes, finite element, fluid, structure interaction, instability criteria
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Seismic response of a prestressed concrete wind turbine towerThis paper compares the seismic load of a 5MW wind turbine supported by a 100-m-high prestressed concrete tower calculated via time history analysis and response spectrum analysis using elastic acceleration spectrum provided by the China Aseismic Code for Buildings. With 5% damping ratio, the fixed-based Multi-degree of freedom model and Finite element model considering soil structure interaction are used for response spectrum analysis and time history analysis, respectively. The results indicated that the seismic load calculated by response spectrum analysis is significantly larger than the results associated with the time history analysis method. It implies that the seismic load determined from common building code procedures along with other loads for wind turbine foundation design is too conservative. Within this paper, the effects of damping ratio, horizontal acceleration amplitude, spring stiffness and damping coefficient of foundation on the seismic load of the prestressed concrete wind turbine tower are discussed. It is shown that the seismic load with mode damping ratio for the prestressed concrete wind turbine tower is not significant when compared with traditional tubular steel designs. The maximum moment demand at the base of the tower may be controlled by earthquake loading as the seismic fortification intensity lever is more than seven. The foundation spring stiffness has a immensely impact on the base bending moment and the natural frequency. Finally, seismic load should be considered in more detail when designing wind turbines that are supported by concrete towers, particularly for turbines over 100-m tall and located in seismically active zones.Keywords: Wind turbine, Prestressed concrete tower, Seismic response, Damping ratio, Soil, structure interaction
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به منظور کاهش هزینه و زمان تحلیل های لرزه ای و نیز به دلیل عدم شناخت صحیح مشخصات سازه ها و نیروهای وارد بر آن ها، معمولا در مدلسازی، از فرضیات ساده کننده ای استفاده می شود که می تواند موجب حصول پاسخ های غیر واقعی گردد. از جمله فرضیات ساده کننده در مدلسازی پل ها می توان به عدم لحاظ پدیده ی ضربه و اندرکنش خاک- سازه اشاره کرد. لذا، در این تحقیق، با مدلسازی سه پل سه دهانه، با دوره های تناوب مختلف، اثر پدیده ی ضربه که در محل درز انقطاع بین دو بخش از عرشه و یا عرشه و پایه های کناری (کوله) رخ می دهد بر پاسخ های لرزه ای پل ها تحت شتابنگاشت های حوزه دور و نزدیک بررسی شده است. همچنین، اثر مشخصات دینامیک پل و اندرکنش خاک- سازه بر پدیده ی ضربه با محاسبه پارامترهای بیشینه نیروی ضربه و تعداد برخورد مورد مطالعه قرار گرفته است. نتایج نشان می دهد که مدلسازی اثر ضربه، به علت محدود کردن حرکات عرشه ، موجب کاهش بیشینه جابجایی آن می گردد. به طوری که رفتار پایه ها در برخی تحلیل های انجام شده با این فرض در محدوده رفتار الاستیک قرار می گیرد. مقادیر کاهش جابجایی در پل های مختلف، حداقل برابر 31% و حداکثر برابر 48% می باشد. از سوی دیگر، ملاحظه ی اثر اندرکنش خاک- سازه، حداکثر موجب افزایش 40 و 45 درصدی به ترتیب در مقادیر بیشینه جابجایی و بیشینه نیروی ضربه در پل های مورد مطالعه (نسبت به حالت بستر صلب) می گردد. همچنین، بررسی پاسخ ها از منظر نوع زلزله نشان می دهد که زلزله های حوزه نزدیک موجب ایجاد پاسخ های لرزه ای بزرگتری نسبت به زلزله های حوزه دور در پل ها می گردند.کلید واژگان: پل، ضربه، اندرکنش خاک، سازه، زلزله های حوزه دور و نزدیکIn order to reduce the cost and time of seismic analyses, as well due to lack of deep understanding of structural characteristics and the acting forces, usually, simplified assumptions are applied in structural modeling that could lead to unrealistic responses. Some of these simplified assumptions in bridge modeling are ignoring the pounding phenomenon and soil-structure interaction. Therefore, in the present study, by modeling three 3-span bridges, with different periods of frequency, the pounding effect, which happens in the gap between two parts of the deck and/or the deck and the abutments, on seismic responses of bridges under the near and far field accelerograms, was investigated. Also, the effect of dynamic properties of bridge and soil-structure interaction on pounding phenomenon was studied by calculating the parameters of maximum pounding force and number of impacts. Results showed that considering the pounding effect reduces the maximum displacement due to limiting the movements of the deck such that some of the piers remain within the elastic phase. Minimum and maximum reduced-displacements in different bridges were 31% and 48%, respectively. On the other hand, modeling the soil-structure interaction effect increased the values of maximum displacement (40%) and maximum pounding force (45%), as compared to that of fixed-base model. Also, the analysis of results in terms of the type of earthquake indicated that the near field earthquakes lead to greater responses in the bridges than the far field earthquakes.Keywords: Bridge, Pounding, Soil, structure interaction, Near, field, far, field earthquakes
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In this paper six tank models, three cylindrical and three rectangular with the same liquid capacity but with different slimness: tall, medium and shallow are numerically simulated using FEM in order to investigate their seismic behavior under three seismic components of four distinct ground motions with different frequency parameters. The results showed the important effect of vertical component of earthquakes on the response of rectangular tanks especially when its frequency content in the same range as that of the tank, while the cylindrical tanks were less affected by the vertical component and of the frequency content of the records.Keywords: Rectangular, cylindrical tanks, fluid, structure interaction, vertical component, frequency content
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پل ها به عنوان یکی از سازه های بسیار حساس و همچنین به عنوان یکی از زیرساختارها در آبادانی و شاهرگ حیاتی هر کشور در امور مربوط به حمل و نقل شناخته می شوند. تخریب بسیاری از پل ها بعد از زلزله های 1971 (سان فرناندو)، 1994 (نورتریج)، 1995 (هانشین) ژاپن و 1999 (چی- چی) تایوان نشان داد که هنوز هم در مورد طراحی لرزه ای پل ها مسائل ناشناخته زیادی وجود دارد. در این پژوهش، یک پل روگذر موجود در شهر ارومیه مورد تحلیل دینامیک غیرخطی توسط نرم افزار SAP2000 قرار گرفته است و پاسخ دینامیک آن با دو نوع سیستم جداسازی لرزه ای نئوپرن لاستیکی و جداساز LRB و همچنین در نظر گرفتن اندرکنش خاک و سازه، که شامل اندرکنش خاک و شمع و اندرکنش خاک و دیوار کوله می شود، بررسی شده است. از نکات قابل اهمیت در این پروژه، مدل کردن توده خاکریز پشت کوله پل می باشد که بسته به نوع جداسازی پل می تواند پاسخ آن را تحت تاثیر قرار دهد. جهت انجام تحلیل دینامیک تاریخچه زمانی در این پژوهش از رکورد زلزله های حوزه نزدیک و حوزه دور برای مقایسه پاسخ این پل تحت اثر این زلزله ها استفاده شده است. نتایج تحلیل نشان می دهد که جداسازهای LRB باعث افزایش جابجایی نسبی روسازه و کاهش جابجایی نسبی زیرسازه نسبت به جداساز الاستومری شده و تاثیر اندرکنش خاک و کوله را کم می کنند. از طرف دیگر، جداسازی پل سبب کاهش نیروها و توزیع بهتر نیروی برشی بین کوله و پایه های میانی می گردد. همچنین، خاکریز پشت دیوار کوله سبب اتلاف بخشی از انرژی زلزله شده، که میزان کاهش نیروی برشی زلزله در مدل های جداسازی نشده بیشتر از مدل های جداسازی شده می باشد. از طرفی، از مقایسه زمان تناوب ها، در صورت عدم وجود فاصله مناسب بین روسازه و زیرسازه در محل درز انبساط، نتیجه می شود که این میزان در مدل E، 52/0 و در مدل E-S حدود 36/0 است. در صورت وجود فاصله مناسب بین روسازه و زیرسازه در محل درز انبساط، این مقادیر به ترتیب به 89/0 و 87/0 افزایش می یابند.کلید واژگان: پل، تحلیل دینامیک، اندرکنش خاک و سازه، زمین لرزه حوزه نزدیکBridges are very important and vital structures in any country and have main roles in transportation. Collapse of bridges due to earthquakes in San Fernando (1971), Northridge (1994), Hanshin (1995) and Chi-Chi (1999) showed that there are still many unknown and unsolved problems in seismic design of bridges. In this research, an existing overpass bridge in Urmia was analyzed by nonlinear dynamics, using SAP2000 software, and its dynamic response has been investigated with different kinds of seismic isolation systems (elastic neoprene and LBR isolators), considering the effects of soil structure interaction. One of the important tasks in this project is modeling the abutment backfill of the bridge which can affect its response depending on the type of bridge isolation. To perform a time-history dynamic analysis, this research uses near-field and far-field earthquakes records to compare the bridge response affected by these earthquakes. Results of the analysis showed that LRB isolators would increase deck displacement and decrease pier and abutment displacement, as compared to elastomeric isolators, and also decreases the soil-abutment interaction. On the other hand, bridge isolation causes a decrease in forces and better distribution of shear force between abutment and piers. Also, the abutment backfill would dissipate some parts of the earthquake energy. The decrease of the earthquake shear force in non-isolated models is more than the isolated ones. On the other hand, by comparing the periods of absence of proper distance between superstructure and infrastructure in the expansion joint position, it follows that this parameter is 0.52 in model E and about 0.36 in E-S. If there is sufficient distance between superstructure and infrastructure in the expansion joint position, these values increase to 0.89 and 0.87, respectively.Keywords: Bridge, Dynamic analysis, Soil, structure interaction, Near field earthquake
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حرکات لرزه ای ثبت شده در مناطق نزدیک گسل که جهت گسیختگی گسل به سمت آنها می باشد با حرکات مشاهده شده در مناطق دور از گسل بسیار متفاوت هستند. در این تحقیق برای مقایسه اثر زلزله های حوزه نزدیک و زلزله های حوزه دور بر روی یک سیستم خاک، گروه شمع و سازه از مدل سازی به روش اجزاء محدود استفاده شده، و امکان رفتار غیرخطی برای سازه در مدل سازی لحاظ شده است. جهت مدل سازی خاک دانه ای(ماسه) از مدل هایپوپلاستیک Von Wolffersdorff با در نظر گرفتن مفهوم کرنش بین دانه ای استفاده شده است. 5 رکورد زلزله حوزه نزدیک و 5 رکورد زلزله حوزه دور، که روی سنگ سخت ثبت شده اند، به مدل اعمال شده اند. نتایج نشان می دهند که با عبور امواج زلزله از خاک، زمان تناوب اصلی لایه خاک در اثر تغییرشکل های غیرخطی افزایش می یابد. همچنین در زلزله های حوزه نزدیک به دلیل حرکات پالس-شکل زمین، یک پالس تغییرمکان در شمع ایجاد می شود. درصورتی که در زلزله های حوزه دور به دلیل توزیع یکنواخت تر انرژی در طول مدت زلزله، ماهیت پاسخ تغییرمکان شمع متفاوت است. در زلزله های حوزه نزدیک به ازای یک PGA ثابت مقادیر تغییرمکان نسبی شمع با مقادیرPGVو همچنین PGD رکوردها دارای همبستگی مثبت می باشند، ولی در هنگام اعمال زلزله های حوزه دور این همبستگی دیده نمی شود.کلید واژگان: زلزله حوزه نزدیک، زلزله حوزه دور، اندرکنش خاک، شمع، سازه، هایپوپلاستیسیته، روش اجزاء محدودGround motions recorded in near-fault sites, where the rupture propagates toward the site, are significantly different from those observed in far-fault regions. In this research, finite element modeling is used to compare the effects of near- and far-fault ground motions on a system consisting of soil, pile group and structure, considering the possibility of non-linear behavior for the structure. The Von Wolffersdorff hypoplastic model with intergranular strain concept is applied for modeling of granular soil (sand). Five fault-normal near-fault ground motion records and five far-fault ground motion records, recorded on rock, are applied to the model. The results show that when seismic waves pass through the soil layer, the fundamental period of the soil layer lengthens, due to non-linear deformations. Also, in near-fault pulse-like ground motions a displacement pulse is generated in the pile response. Whereas, in the far-fault ground motions, due to the more uniform distribution of energy during the record, such pulse-like displacements are not observed in the pile response. Based on the obtained results, for a constant PGA, there are positive correlations between the values of maximum pile displacement, and PGD and PGV values of near-fault ground motion records. But such correlations are not observed in the case of far-fault ground motions.Keywords: Near, fault ground motions, Far, fault ground motions, Soil, pile, structure interaction, Hypoplasticity, Finite element method
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Assessment of near-field and far-field strong ground motion effects on soil-structure SDOF systemThe distinctive characteristics of near-field earthquake records can lead to different structural responses from those experienced in far-field ones. Furthermore, soil-structure interaction (SSI) can have a crucial influence on the seismic response of structures founded on soft soils however, in most of the time has been neglected nonchalantly. This paper addresses the effects of near-field versus far-field earthquakes on the seismic response of single degree of freedom (SDOF) system with considering SSI. A total 71 records were selected in which near-field ground motions have been classified into two categories: first, records with a strong velocity pulse, (i.e. forward-directivity) second, records with a residual ground displacement (i.e. fling-step). Findings from the study reveal that pulse-type near-field records generally produce greater seismic responses than far-field motions especially at high structure-to-soil stiffness ratios. Moreover, the importance of considering SSI effects in design of structures is investigated through an example. Finally, parametric study between Peak Ground Velocity to Peak Ground Acceleration ratio (PGV/PGA) of pulse-like ground motions and maximum relative displacement indicate that with increase in structure-to-soil stiffness ratios, earthquakes with higher PGV/PGA ratio produce greater responses.Keywords: Soil, structure interaction, SDOF system, Near, field earthquake, Far, field earthquake, PGV, PGA
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Accounting for soil nonlinearity in three-dimensional seismic structure-soilstructure-interaction analyses of adjacent tall buildings structuresThe interactive effects of adjacent buildings on their seismic performance are not frequently considered in seismic design. The adjacent buildings, however, are interrelated through the soil during seismic ground motions. The seismic energy is redistributed in the neighboring buildings through multiple structure-soil-structure interactions (SSSI). For example, in an area congested with many nearby tall and/or heavy buildings, accounting for the proximity effects of the adjacent buildings is very important. To solve the problem of SSSI successfully, researchers indicate two main research areas where need the most attention: 1) accounting for soil nonlinearity in an efficient way, and 2) spatial analysis of full 3D soil-structure models. In the present study, three-dimensional finite element models of tall buildings on different flexible foundation soils are used to evaluate the extent of cross interaction of adjacent buildings. Soil nonlinearity under cyclic loading is accounted for by Equivalent Linear Method (ELM) as to conduct large parametric studies in the field of seismic soil-structure interaction, the application of ELM is preferred over other alternatives (such as application of complicated constitutive soil models) due to the efficiency and reliability of its results. 15 and 30 story steel structures with pile foundations on two sandy and clayey sites are designed according to modern codes and then subjected to several actual earthquake records scaled to represent the seismicity of the building sites. Results show the cross interaction of adjacent buildings on flexible soils, depending on their proximity, increases dynamic displacements of buildings and reduces their base shears.Keywords: Equivalent linear method (ELM), Structure, soil, structure interaction, Adjacent tall buildings structures, Frequency content, High amplitude records, Low amplitude records
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The degradation of concrete due to various hygro-chemo-mechanical actions is inevitable for the structures particularly built to store water. Therefore, it is essential to determine the material properties of dam like structures due to ageing in order to predict the behavior of such structures after certain age. The degraded material properties are calculated by introducing isotropic degradation index. The predicted material properties are used to study the behavior of aged dam-reservoir coupled system. Both the dam and infinite reservoir are modeled by finite elements. Displacement and pressure are considered as nodal variable for dam and reservoir respectively. The effect dynamic interaction between dam and reservoir are calculated in a coupled manner. The parametric study reveals that the responses of damreservoir system are unexpectedly large at an age when system frequency matches with the exciting frequency. The outcomes of the present study indicate the importance of the consideration ageing effect of concrete exposed to water for the safe design of dam throughout its life time.Keywords: Hygro, chemo, mechanical, pine flat dam, dam, reservoir system, isotropic degradation index, fluid, structure interaction, finite element method.
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In this paper, an optimization methodology proposed for the achievement of optimal (minimum) structural weight for flexible-base shear buildings under earthquake excitation. The underlying soil is considered as a homogeneous half-space which is replaced by a simplified 3-DOF system, based on the concept of Cone Models. Through intensive nonlinear dynamic analyses of buildings with consideration of soil-structure interaction (SSI) effect subjected to a group of artificial earthquakes, and using uniform distribution of inter-story ductility demand over the height of structures, an optimization procedure for seismic design of inelastic shear-buildings incorporating SSI effects is developed to achieve minimum structural weight. It is shown that the seismic performance of such a structure is superior to those designed by code-compliant seismic load pattern such that the optimized structures experience significantly less structural weight as compared with those designed based on ASCE/SEI 7-10 load pattern.Keywords: Soil, structure interaction, optimal design, inelastic behaviour, seismic code, optimal structural weight
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در این نوشتار روشی برای طراحی مستقیم براساس تغییرمکان با لحاظ کردن اثر اندرکنش خاک و سازه ارائه شده است. روش پیشنهادی شامل 2 مرحله است: در مرحله ی اول با فرض صلب بودن تکیه گاه سازه ی برش پایه با استفاده از طیف تغییرمکان، تغییرشکل های موردنظر برای طراحی در سطح عملکرد مربوط، و سیستم یک درجه آزاد معادل محاسبه شده است. در مرحله ی دوم، تغییرمکان های نسبی اضافی ناشی از دوران پی به تغییرمکان های محاسبه شده در مرحله ی اول اضافه شده و برش پایه ی طراحی اصلاح شده با احتساب اندرکنش سازه و خاک به دست آمده است. در این روش تغییرمکان های طراحی براساس نیازهای طرح و سطوح عملکرد مورد انتظار از سازه قابل انتخاب اند و کنترل خسارت به صورت مستقیم انجام می شود. برای ایجاد درک بهتر، مراحل کامل روش با ارائه ی مثال هایی تشریح و نتایج طراحی با روش آیین نامه یی مرسوم مقایسه شده است.
کلید واژگان: طراحی براساس تغییرمکان، سطح عملکرد، اندرکنش سازه و خاک، طیف تغییرمکان، شکل پذیریDisplacement-based design is a procedure for attaining an acceptable level of damage during earthquakes, which provides a new tool for performance-based design. In this paper, a method of direct displacement-based design considering the effects of soil-structure interaction is proposed. The suggested method is in two stages. First, the base of the structure is assumed to be rigid. In a sequence of different steps, the base shear is calculated for the assumed fixed-base condition. In these steps, first, the yield displacement of the system is estimated using empirical relations. Then, the basis displacement, which is the maximum displacement of an equivalent single degree of freedom system that will be subsequently used for calculation of the lateral displacement profile, is determined. The ductility factor is calculated using the yield and basis displacements and an equivalent damping ratio is computed next. The effective mass of the system is determined using the displacements profile. Using a design displacement spectrum, the effective period and then the effective lateral stiffness are calculated. The fixed-base base shear comes as the effective lateral stiffness multiplied by the basis displacement. In the second stage, the base shear is modified due to the flexibility of the base. For this purpose, the additional displacement due to rotation at the base is calculated and added as a modification to the basis displacement. This modified deformation is used in a similar way as above to compute the modified base shear. In this method, the design displacements can be selected based on the design needs and expected performance levels, and seismic damage control is directly applicable. For clarity of presentation, the steps of the method are explained through an illustrative example, and the results are compared with those of a conventional design code. It is shown that the proposed displacement-based design method can result in heavier or lighter structural members compared with the code-based sections based on the structural dynamic properties.
Keywords: Displacement Based Design, Performance Level, Soil, Structure Interaction, Displacement Spectrum -
پی های شمعی اغلب به صورت گروه شمع برای سکوهای دریایی، پل ها و ساختمان های بلند استفاده می شوند. هدف این پژوهش، بررسی اثر سختی کلاهک گروه شمع در رفتار شمع ها تحت اثر بار دینامیکی با استفاده از روش تفاضل محدود سه بعدی در خاک های ماسه یی است. تحقیقات نشان می دهد که سختی کلاهک گروه شمع، شرایط اتصال شمع به کلاهک و اندرکنش سازه شمع خاک تاثیر قابل ملاحظه یی در رفتار گروه شمع در برابر بارهای جانبی دارد. در این نوشتار، برای اتصال شمع ها به یکدیگر از المان تیر استفاده شده است. مطالعه ی سختی کلاهک شمع نشان می دهد با افزایش یا کاهش سختی کلاهک شمع، بیشینه ی جابه جایی، بیشینه ی نیروی برشی و بیشینه ی لنگر خمشی در شمع ها الزاما کاهش یا افزایش نمی یابد، بلکه با توجه به جرم مجموعه، برای هر گروه شمع محدوده یی از سختی کلاهک وجود دارد، که در آن بیشترین جابه جایی، نیروی برشی و ممان در شمع ها ایجاد می شود.
کلید واژگان: سختی کلاهک گروه شمع، تحلیل دینامیکی، اندرکنش سازه، شمع، خاک، تحلیل تفاضل محدود سه بعدیPiles are often placed closely in a group to serve as the foundation of specific structure, such as offshore platforms, bridge structures and tall buildings. Pile groups should be capable of withstanding significant lateral loads induced by seismic excitations, winds, waves, and current loads. The main objective of this research is to investigate the effect of the stiffness of the pile cap on the behavior of piles embedded in sand under dynamic loads, by means of the 3D finite difference method. Previous research shows that pile cap stiffness, connection type of pile-cap and soil-pile-structure interaction play important roles in the behavior of laterally loaded pile groups. Beam elements are used in this study to connect each of the piles, and these connections are rigid. Further, due to he nfluence f he uperstructure on the behavior of pile foundations, this effect is modeled in the analyses. To account for the soil stiffness acting on the pile shaft, normal and shear springs are accommodated in the interface of the soil and pile elements. To evaluate the data for the parameters of the interface elements, a 2D finite difference analysis has been performed to calculate the required parameters of the interface elements at various depths. To model sand and structural members, Mohr-Coulomb and elastic models are employed, respectively. For dynamic analyses, attention has been paid to quiet boundaries, free fields, and wave propagation in the soil medium. Four different arrangements have been considered for pile cap. Results of analyses show that a increase or decrease in cap stiffness does not necessarily change extreme induced forces (i.e., maximum shear force, bending moment and lateral displacement) along the piles in the group. However, for a given mass of the system, there is a range of stiffness for the pile group that has maximum effect on induced internal forces and lateral displacements. For a flexible pile cap, the induced bending moments and shear forces along the individual piles depend on the location of the piles in the group.
Keywords: Pile Cap Stiffness, Dynamic Analysis, Soil, Pile, Structure Interaction, 3D Finite Difference Analysis -
نشریه مهندسی عمران و محیط زیست دانشگاه تبریز، سال چهل و چهارم شماره 3 (پیاپی 76، پاییز 1393)، صص 98 -110هدف از این تحقیق، بررسی پاسخ دینامیکی سدهای بتنی وزنی با در نظر گرفتن اثر همزمان مولفه های همبسته انتقالی و دورانی شتاب زمین در طی زلزله در حالت دو بعدی و با احتساب اندرکنش سیستم سد- پی- مخزن می باشد. برای این منظور، مولفه های دورانی حرکت زمین با استفاده از مولفه های انتقالی و نیز روابط کلاسیک تئوری الاستیسیته و تئوری انتشار امواج و با در نظر گرفتن سرعت امواج وابسته به فرکانس تولید و به روش مناسب به مدل اجزاء محدود سیستم اعمال و پاسخ دینامیکی آن به روش نیومارک و استفاده از تغییر مکان به عنوان متغیر مجهول در گره های شبکه اجزاء محدود کل سیستم که به روش لاگرانژی-لاگرانژی معروف می باشد، به دست می آید. بر اساس فرمول بندی مطرح شده حساسیت پاسخ سد با تغییر مدول الاستیسیته پی، تراز آب مخزن و نیز ضریب جذب کف مخزن تحت شتاب نگاشت های مختلف با احتساب اثر مولفه دورانی زلزله مورد بررسی قرار گرفته است. نتایج نشان می دهند که بسته به محتوای فرکانسی و طیف توان مولفه دورانی زلزله، تاثیر آن بر پاسخ سد می تواند کم یا زیاد باشد. در هر حال در مواردی که تاثیر مولفه دورانی بر پاسخ سد قابل توجه باشد، با افزایش سختی پی سد و افزایش ضریب جذب کف، اثر مولفه دورانی کاهش می یابد. علاوه بر این با افزایش تراز آب مخزن، اثر مولفه دورانی زلزله بر پاسخ تاج سد افزایش می یابد ضمن این که تغییرات کیفی قابل توجهی نیز در تاریخچه زمانی پاسخ مشاهده می شود.
کلید واژگان: مولفه های همبسته انتقالی و دورانی زمین، سیستم سد، پی، مخزن، اندرکنش سازه و سیالJournal of Civil and Environmental Engineering University of Tabriz, Volume:44 Issue: 3, 2015, PP 98 -110IntroductionThe kinematics of any point in a medium is ideally expressed in terms of three translational and three rotational components. Observations of earthquake events have shown that many structural failures and damage are associated to rotational components of ground motions. Newmark [1] was perhaps the first to establish a relationship between the torsional and translational components of a ground motion based on constant velocity of wave propagation assumption. Lee and Liang [2] have used wave propagation and classical elasticity theories based on constant wave velocity to develop the algorithms for generating rotational motion from the corresponding available translational motions and Hong-Nan Li et al. [3] proposed an improved approach based on frequency dependent wave velocity to generate the rotational components. Kalani Sarokolayi et al. [4] have used this method and they have verified their results using recorded rotational components. Recently the effect of rotational component on dynamic analysis of dam- reservoir system without foundation effect is considered by authors in their previous research [5]; but the effects of rotational components have not been considered in dynamic analysis of dam-reservoir-foundation systems in previous researches. The fluid- structure interaction is also an important subject to dynamic analysis of dams. The Lagrangian approach which were proposed by Hamdi [6] and completed by Wilson and Khalvati [7], have been used by many researchers such as [7-9]. In addition the reservoir bottom absorption effects in earthquake response of concrete gravity dams have been also investigated by some researchers such as Fenves and Chopra [10].MethodologyThe main purpose of this research is the evaluation of dynamic response of concrete gravity dams considering three correlated translational and rotational components of ground motion and dam-reservoir-foundation interaction using finite element method. For this purpose, the rotational component of ground motion is obtained using translational components and relation of classical elasticity between rotation and wave propagation theories considering frequency dependent wave velocity. Then, these rotational and translational components are applied in finite element model and the dynamic response of system are calculated using Newmark method and Lagrangian- Lagrangian approach based on displacement unknown in both solid and fluid domains. In addition, with the change of elasticity modulus of foundation, earthquake acceleration, water elevation and absorption coefficient of reservoir bottom, the sensitivity of response with respect to these parameters are evaluated.Results And DiscussionThe horizontal displacement of dam crest for dam-reservoir (D-R) and dam-reservoir-foundation (D-R-F) systems subjected to two translational components, 2C, and two translational added by their correlated rotationalcomponents, 3C, are obtained and the ratio of response due to 3C and 2C which is named as Normalized response, are presented in Table 1. The effects of absorption coefficients on Normalized response of system are also shown in Table 2 and the effects of water elevation on dam crest response subjected to 3C are shown in Fig. 2.ConclusionsResults showed that the effects of rotational components of ground motion on the dynamic response of concrete gravity dams can be low or high depending on their frequency range and power spectrum. In cases which the rotational effect is high, the dam response to rotational component of earthquake will be decreased with the increase of the foundation elasticity modulus and reservoir bottom absorption coefficients. In addition with the increase of water elevation, the rotational effect will increase and the response time history also will change.Keywords: Correlated translational, rotational components, Dam, reservoir, foundation system, Fluid, structure interaction -
مشاهدات حاصل از زلزله های پیشین، موید اعمال خسارت به سازه های زیرزمینی واقع در خاک های با پتانسیل روان گرایی است؛ با وجود این، در پژوهش های پیشین توجه کم تری به مکانیزم ها و عوامل موثر در خسارت ها صورت گرفته است. در این پژوهش، پاسخ های لرزه یی سازه ی زیرزمینی سطحی واقع در خاک ماسه یی مستعد روان گرایی با استفاده از نرم افزار المان محدود 3C O M ارزیابی می شود. نتایج پژوهش نشان می دهد که توزیع غیریکنواخت اضافه ی فشار آب حفره یی در زیر سازه و تغییرشکل جانبی سازه به دلیل تغییرمکان جانبی خاک روان گرای پیرامون، از عوامل موثر و لازم در تغییر حجم خاک روان گرای فشرده شده به زیر سازه به عنوان مکانیزم متداول بلندشدگی سازه است. در شرایط زهکشی شده، تغییرشکل جانبی سازه تاثیر چشمگیری در میزان نشست آن داشته که با نیروی اینرسی سازه تحت تحریک لرزه یی مرتبط است. افزایش وزن سازه، تاثیرات مثبت یا منفی و افزایش تراکم تاثیر مثبت دربهبود رفتار لرزه یی سازه در شرایط مختلف خاک ماسه یی سست دارند.
کلید واژگان: سازه ی زیرزمینی، خاک ماسه یی سست، روان گرایی، رفتار لرزه یی، اندرکنش خاک و سازه، تحریک لرزه ییNowadays, population growth and civil facility development requirements have caused increases in the construction of underground structures in urban residential zones. Previous earthquake observations show that severe damage may occur to underground structures such as pipelines, manholes and even large underground structures, including ubway tunnels. However, the seismic performance of subway tunnels buried in loose sandy soil with liquefaction potential needs further investigation, in order to recognize common contributed mechanisms to the seismic responses of nderground structures from performance based seismic schemes. In this paper, the seismic responses of a subway tunnel buried in loose soil with liquefaction potential are numerically studied with a three-dimension finite element program called COM3. According to numerical studies, the subway tunnel shows upward movement in the liquefied soil with simultaneous occurrence of two conditions. These include non-uniform excess pore pressure distribution under the subway tunnel and lateral deformation of the structure due to lateral displacement of the surrounding soil. These are necessary and sufficient parameters that affect the amount of liquefied soil moved to the bottom of the structure, as a common mechanism in the uplift response of a shallowly buried subway. Although the subway tunnel is symmetrically simulated, the amount of liquefied soil moved from each bottom side of the structure is not identical because of seismic excitation characteristics. The lateral deformation of the subway tunnel causes the downward movement of the structure in the un-saturated soil condition, due to its inertial force under seismic excitation. Increasing the unit weight of a subway tunnel has a contrary effect on the seismic response of structures in loose soil conditions, and it is rational to consider the influence of both soil conditions on the seismic behavior of subway tunnels in the design stage. The reinforcement ratio variation of a subway tunnel has no significant effect on the seismic behavior of the subway tunnel under a saturated condition, but the reduction of reinforcement ratio may increase lateral deformation and settlement of the structure in an un-saturated condition. The loose soil relative density growth improves the seismic responses of subway tunnels under both soil conditions, and the traditional remedial method, including densification, is numerically verified as a useful procedure.
Keywords: Underground Structure, Loose Sandy Soil, Liquefaction, Seismic Response, Soil, Structure Interaction, Seismic Excitation -
در این نوشتار، اثرات انعطاف پذیری پی در نحوه ی اعمال ضریب اصلاح تقاضای عضو در دستورالعمل بهسازی لرزه یی ساختمان های موجود بررسی شده است. بدین منظور از روش ساده و کارآمد و در عین حال با دقت مناسب تیر مستقر بر خاک غیرخطی وینکلر استفاده شده است. در این راستا، قاب های 3، 6، 10 و 15 طبقه ی بتنی مستقر بر خاک های نرم، متوسط، و سخت طراحی و نتایج تحلیل های غیرخطی تاریخچه ی زمانی هر یک در حالت های پایه ی صلب و انعطاف پذیر با نیروهای پیشنهادی روش استاتیکی خطی دستورالعمل مقایسه شده است. نتایج نشانگر آن است که ترکیبات بارگذاری دستورالعمل برای اجزاء کنترل شونده توسط تغییرشکل با بارهای ثقلی قابل توجه (برای نمونه ی تیرها) می تواند به برآورد غیرواقع گرایانه ی تقاضای لرزه یی منجر شود. در انتها، یک ترکیب بارگذاری جدید، به منظور رفع این نقیصه، پیشنهاد شده است.
کلید واژگان: اندرکنش خاک، پی، سازه، مدل سازی، وینکلر، انعطاف پذیری، حرکت زمینSoil-Foundation-Structure Interaction (SFSI) in a structural modelling procedure can change seismic structural response. However, SFSI effects are mostly ignored in the analysis procedure of structures, due to a general engineering belief regarding its conservative effects. This conservativeness is not always the case, although the period and the damping of the structure changes by considering the SFSI effects and, consequently, seismic demand decreases. Consideration of SFSI effects still contains some level of difficulty due to the needed in dvance modelling procedures, but this issue can be solved by employing advanced finite element modelling programs, e.g; OpenSees software. The aim of the current paper is to evaluate the influence of SFSI effects on the component demand modifier factor, based on Iranian instructions for the seismic rehabilitation of existing buildings. For this purpose, the beam on the nonlinear Winkler foundation approach is used, which is a simple and efficient method. First, a collection of 3, 6, 10 and 15 storey concrete moment-resisting frames, founded on soft, medium and hard soil, are designed and analysed for the case of fixed-base and flexible-base assumptions. Eight ground motion records were chosen in order to estimate the median response of frames for a pre-defined seismic scenario. A comparison has been made between the results of the nonlinear response history analysis of each frame under flexible-base and fixed-base conditions, with the response based on the equivalent linear static approach. The results show that the equivalent linear static approach load combinations for the elements with significant gravity loads that are controlled by deformation actions (e.g. beams) can lead to non-conservative prediction of the seismic demand. Finally, a new load combination has been proposed in order to limit the influence of the demand modifier factor only on the seismic loads. This new proposed load combination can be used to improve the equivalent linear static approach in the instructions for seismic rehabilitation of existing buildings.
Keywords: Soil, Foundation, Structure Interaction, Modelling, Winkler, Flexibility, Ground Motion
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