پديد آورندگان :
رحمن شكرگزار، حامد دانشگاه محقق اردبيلي - دانشكده ي فني و مهندسي , زارع آقبلاغ، مريم دانشگاه محقق اردبيلي , خدايي اردبيلي، احمد علي دانشگاه صنعتي خواجه نصيرالدين طوسي
كليدواژه :
اندركنش خاك – فونداسيون - سازه , نوع خاك و فونداسيون , قاب خمشي فولادي ويژه كوتاه مرتبه , ضريب اطمينان
چكيده فارسي :
در اين پژوهش، تاثير تغيير نوع خاك، فونداسيون و ضريب اطمينان طراحي بر پاسخ لرزه اي ساختمان فولادي ارزيابي شده است. بدين منظور ساختمان پنج طبقه از نوع قاب خمشي ويژه واقع بر دو نوع خاك متفاوت (ii و iv) درنظر گرفته شده است. دو نوع فونداسيون سطحي براي اين ساختمان با ضرايب اطمينان 2، 3 و 4 در ظرفيت باربري طراحي گرديده اند. به منظور ارزيابي عملكرد مدلهاي اجزا محدود، با لحاظ اندركنش خاك فونداسيون سازه توسط نرم افزار اپنسيس ساخته شده است. اين مدل ها تحت تحليلهاي استاتيكي و ديناميكي غيرخطي توسط هفت ركورد زلزله قرار گرفته و پاسخهاي آنها با يكديگر مقايسه گرديده است. نتايج بدست آمده حاكي از آن است كه در قابهاي خمشي واقع بر خاك نوع iv، سازه با فونداسيون منفرد، ظرفيت و برش پايه كمتري نسبت به سازه با فونداسيون نواري و مدل داراي تكيه گاه صلب دارد و ماكزيمم تغييرمكان نسبي بين طبقات در مدلهاي با فونداسيون نواري بيشتر از مدلهاي با فونداسيون منفرد و مدل داراي تكيه گاه صلب ميباشد. بررسي اثر تغيير ضريب اطمينان طراحي فونداسيونها نشان ميدهد كه ظرفيت سازه اي، ماكزيمم برش پايه و ماكزيمم تغييرمكان نسبي طبقات در سازه با فونداسيون منفرد، با افزايش ضريب اطمينان، افزايش مييابد، اما اين كميت در سازه با فونداسيون نواري تاثير چنداني ندارد. در قابهاي خمشي واقع بر خاك نوع ii، ضريب اطمينان طراحي و نوع فونداسيون تاثير چنداني بر ظرفيت سازه و پاسخ ديناميكي ندارد.
چكيده لاتين :
Shallow foundation is one of the most common types of foundations used in mid–rise buildings in high seismic zones. The effects of soil-foundation-structure interactions are generally not significant in the structure with rigid bases, while the nonlinear behavior of soil and soil-structure interaction phenomenon cause various changes in the seismic response of structures with flexible bases. When a structure supported on shallow foundations is subjected to inertial loading due to earthquake ground motion, the foundation may undergo sliding, settling and rocking movements. If the capacity of the foundation is mobilized, the soil-foundation interface will dissipate significant amounts of vibrational energy, resulting in a reduction in structural force demand. This energy dissipation and force demand reduction may enhance the overall performance of the structure, if the settlement or bearing failure potential is considered. In this paper, the effect of soil and shallow foundation types, and variation of safety factor are studied to assess the seismic response of steel buildings. For this purpose, five stories special steel moment frames with two different soil types (II and IV) have been considered. The footing and strip shallow foundations have been designed for these buildings with safety factors of 2, 3 and 4. The finite element models are developed using OpenSees software. The structural members such as beams and columns are modeled by nonlinear beam–column elements and fiber sections. The soil–foundation interface is modeled using Beam-on-Nonlinear-Winkler foundation. In this procedure, an array of vertical q–z springs is used to capture vertical and rotational resistance of the foundation, while two springs, namely p–x and t–x, are placed horizontally to capture the passive and sliding resistance of the foundation, respectively. The constitutive relations for the q–z, p–x, and t–x springs are represented by nonlinear backbone curves that have been constructed from the pile-calibrated backbone curves developed by Boulanger. The independent p-x and t-x springs are connected to identical end nodes with zero distance between them. The seismic performance of these special steel moment frames with various foundation and soil type are evaluated using nonlinear static pushover and nonlinear dynamic time history analyses through seven far–fault ground motions. The numerical results for each case of soil-foundation-structure systems and rigid base conditions are then presented and compared in terms of maximum base shear and maximum inter–story drifts. These results are shown that in the soil type IV, the steel moment frames with the footing foundations have lower structural capacity and maximum base shears than structures with the the strip foundations or rigid bases, but the maximum inter-story drifts in the strip foundation bases are higher than others. It is also observed that by enhancing the safety factor, the structural capacity, the maximum base shear and the maximum inter-story drifts in the models with the footing foundations are increased, but changing in the safety factors do not influence in the structural response of models with the strip foundation. On the other hand, the safety factor and foundation types have not any effect on the structural capacity and the seismic responses of the structures that located on the soil type II.
