IJE TRANSACTIONS C: Aspects Vol. 30, No. 9 (September 2017) 1309-1318   

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

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, construction of steel cylindrical tanks in one of the refinery site is monitored using a field survey and created imperfections are identified and introduced. 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 analysis of the test specimens are performed by ANSYS software. Finally experimental results, finite element and analytical relations are compared. The obtained results show that the imperfections have a direct impact on the structural behavior of shells during the buckling under uniform external pressure load. Also, some imperfections caused by welding increase the buckling resistance of cylindrical shells.


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


چکیده    در اجرای سازه هاي پوسته ای جدار نازک، به علت وسعت زياد پوسته، امکان ساخت يکپارچه وجود نداشته و از تعدادی قطعات پانلي دارای انحنا که به يکديگر جوش داده شده اند ساخته مي شوند به همين دليل يک سری نقص های هندسي يا به عبارت بهتر ناکاملي های هندسي بروز مي کند. عمده اين ناکاملي ها در اثر فرآيند جوشکاري، حمل و نقل، رولينگ نامناسب و مشکلات نصب و اجرا بوجود مي آيند. در اين تحقيق، اجرای مخازن استوانه اي فولادي در يکي از سايت های پالايشگاهي، به صورت ميداني تحت نظارت قرار گرفته و ناکاملي های ايجاد شده شناسایی و معرفي مي شوند. با برداشت آماري و اندازه گيري اين ناکاملي ها، گروه بندي آنها انجام گرفته و با بررسی منشا و عوامل موثر در پيدايش آنها، ناکاملي های رايج مشخص مي گردد. در ادامه تاثير ناکاملي ها بر رفتار کمانشی بصورت آزمايشگاهي تحت اثر فشار خارجي يکنواخت بر روی نمونه های آزمايشگاهي با مقياس مشخص مورد ارزيابي قرار مي گيرد. همچنين آناليز المان محدود غيرخطي اين نمونه هاي آزمايشگاهي توسط نرم افزار المان محدود ANSYS انجام شده و نتايج آزمايشگاهي، المان محدود و روابط تحليلي مقايسه مي شوند. نتايج به دست آمده نشان مي دهند که ناکاملي ها تاثير مستقيمي بر رفتار سازه اي پوسته ها هنگام کمانش تحت بار فشار خارجي یکنواخت دارند. همچنین بعضی از ناکاملی های ناشی از جوشکاری باعث افزایش مقاومت کمانشی پوسته های استوانه ای می شوند.


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