بررسی رفتار لرزه ای قاب های فولادی صلب پس از آتش سوزی

نوع مقاله : Articles

نویسندگان

دانشگاه بین المللی امام خمینی (ره)

چکیده

ساختمان­های زیادی به دلایل مختلف آتش­سوزی را تجربه می­کنند. مشاهدات نشان می­دهد بسیاری از آنها که همچنان پایدار مانده­اند با اصلاح ظاهر سازه به کاربری خود ادامه می­دهند. با وجود احتمال وقوع زلزله­، لازم است بررسی شود که آیا سازه در شرایط جدید همان مقاومتی که در طراحی برای آن در نظر گرفته ­شده را دارا می‌باشد یا خیر. در این مطالعه، سه قاب خمشی فولادی 4، 7 و 10 طبقه پس از طراحی، تحت دو سناریوی حریق متقارن قرار گرفته­اند. قاب­ها ابتدا مطابق بخش گرم شدن منحنی حریق پارامتری یکی از سناریوها حرارت دیده و با­ تعیین یک معیار خرابی برای قاب فولادی، حداکثر زمان و در ­نتیجه درجه حرارت متناظر برای حصول فاز سرد شدن به‌دست‌آمده است. پس از فرآیند آتش­سوزی-سرد شدن، رفتار لرزه­ای قاب­ها با استفاده از روش تحلیل­ استاتیکی ­غیرخطی بررسی شده است. نتایج نشان می­دهد سازه­های حرارت­دیده، هنگامی­که تحت بارگذاری لرزه­ای قرار می­گیرند، در برش پایه­ی مشخص، تغییر مکان بیشتری نسبت به سازه­هایی دارند که پیش از زلزله، هیچ­گونه تجربه­ای از آتش­سوزی­ ندارند. همچنین تفاوت عمده‌ی سازه­های با و بدون تجربه‌ی آتش­سوزی، در جابه­جایی نسبی چند طبقه‌ی فوقانیِ موقعیت آتش­سوزی است که از مقدار جابه­جایی نسبی مجاز طبقه تجاوز می­کند. ازاین‌رو به طور لزوم باید سناریوهای محتمل و بحرانی حریق در ارزیابی­ها منظور گردد.

کلیدواژه‌ها


عنوان مقاله [English]

Seismic Behavior Investigation of Rigid Steel Frames after Fire

نویسندگان [English]

  • Hamed Hajikarimian
  • Farzaneh Hamedi
  • Ramezan Ali Izadifard
Department of Civil Engineering, Faculty of Science and Technology, Imam Khomeini International University, Iran
چکیده [English]

There is a large number of situations which expose structures to the fire. Most of the studies have focused on the safety of structures after fire, or the effect of fire that would take place after earthquakes. Observations show that there have been structures that experienced fire and still remained stable, and only by modifying the appearance, have continued to serviceability without structural retrofitting. Due to the risk of earthquakes, it is necessary to determine whether the seismic resistance of the structure to tackle against lateral load is enough or not. In this study, therefore, the seismic behaviour of three steel moment frames after fire were assessed and compared with a building which have not experienced fire. For this purpose, these models with different stories have been selected and designed. The structural models have been designed according to the Iranian seismic code 2800 (4th edition). For performing the nonlinear static analysis, ABAQUS software was implemented. Because most of the existing steel structures are not insulated against the fire with fire-retardant cover, it is assumed that the investigated frames do not equipped with any fire-resistant substances such as fire-fighting foams or fire-retardant gels. For these frames, two symmetrical fire scenarios were considered: 1) each corner spans in the ground floor were exposed to fire; 2) the middle spans in the ground floor were exposed to fire. The process of fire consists of two stages. The first stage illustrates the heating process causing by ignition, and the second stage illustrates the effects of cooling process in fire extinguishing duration. In structural analysis, according to the Eurocode, the parametric curve has been used to apply the first stage, and a linear curve has been used for cooling stage. Having been heated frames according to parametric time-temperature curve of the fire, in order to obtain the maximum time and the corresponding temperature, a failure criteria was determined. By determining these parameters and the fire compartment’s properties, the second stage of the fire behaviour (the cooling curve) was obtained. The seismic behavior of frames, by imposing the complete curve (fire-cooling) to the structure, through a nonlinear static analysis were examined. In the process of the analysis, the maximum relative displacement specified by the Iranian seismic code 2800 has been applied to each story, then the response of the structure has been evaluated. The illustrated results of this research show that in a similar base shear, the nodal displacements of the structure exposing to fire and cooling are more than that of a structure which have never experienced fire. In addition, in the structures that were exposed to fire, the limited drift was not satisfied above the story where the fire was applied. Besides, the maximum drift in the first scenario in which the fire was happened in the corner spans, was significantly higher than that of the one in the second scenario (fire in the middle spans).

کلیدواژه‌ها [English]

  • Earthquake after Fire
  • Nonlinear Static Analysis
  • Fire Scenario
  • Parametric Time-Temperature Curve
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