IJE TRANSACTIONS C: Aspects Vol. 30, No. 9 (August 2017) 1385-1394    Article in Press

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M. Rastgar and H. Showkati
( Received: February 24, 2017 – Accepted: July 07, 2017 )

Abstract    Abstract. Construction and assembling process of shell structures has caused main problems. In these structures, there is no possibility for the integrated construction due to their large shell extent and they are built using a number of welded curved panel parts; hence, some geometrical imperfections emerge. Most of these imperfections are caused by the process of welding, transportation, inappropriate rolling, as well as installation and implementation problems. In this research, the imperfections made in steel cylindrical tanks being constructed in one of the refinery site are introduced and evaluated using a field study. Relying on the statistical inference, they are classified and then, by studying the effective factors and origin in their generation, the common imperfections are identified. The impact of common imperfections on the buckling behavior is experimentally evaluated under uniform external pressure. Then, nonlinear numerical analysis of the test specimens are performed. Finally experimental results, finite element and analytical relations are compared. The results show that the imperfections have a direct impact on the structural behavior of shells during the buckling and external compressive load.


Keywords    field study, buckling behavior, external pressure, cylindrical tank, geometric imperfection.


چکیده    چکيده در اجرای سازه هاي پوسته ای جدار نازک، بعلت وسعت زياد پوسته، امکان ساخت يکپارچه آن وجود نداشته و از تعدادی قطعات پانلي دارای انحنا که به يکديگر جوش داده شده اند ساخته ميشوند به همين دليل يک سری نقص های هندسي يا به عبارت بهتر ناکامليهای هندسي بروز ميکند. عمده اين ناکامليها در اثر فرآيند جوشکاري، حمل و نقل، رولينگ نامناسب و مشکلات نصب و اجرا بوجود مي آيند. در اين تحقيق ناکامليهای ايجاد شده در مخازن استوانه اي فولادي در حال احداث يکي از سايت های پالايشگاهي، بصورت ميداني مورد بررسي و ارزيابي قرار گرفته و معرفي مي شوند با برداشت آماري و اندازه گيري اين ناکامليها، گروه بندي آنها انجام گرفته و با بررسی منشا و عوامل موثر در پيدايش آنها، ناکاملي های رايج مشخص ميگردد. در ادامه تاثير ناکامليهای رايج بر رفتار کمانشی بصورت آزمايشگاهي تحت اثر فشار خارجي يکنواخت بر روی نمونه های آزمايشگاهي با مقياس مشخص مورد ارزيابي قرار ميگيرد. همچنين آناليز المان محدود مقدار ويژه و غيرخطي اين نمونه هاي آزمايشگاهي توسط نرم افزار المان محدود انجام شده و نتايج آزمايشگاهي، المان محدود و روابط تحليلي مقايسه ميشوند. نتايج نشان مي دهند که ناکامليها تاثير مستقيمي در رفتار سازه اي پوسته ها به هنگام کمانش و بار فشاری خارجي دارند.

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