Abstract




 
   

IJE TRANSACTIONS B: Applications Vol. 30, No. 11 (November 2017) 1664-1672   

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  STIFFNESS-BASED APPROACH FOR PRELIMINARY DESIGN OF FRAMED TUBE STRUCTURES
 
R. Rahgozar, A. Alavi and P. Torkzadeh
 
( Received: April 09, 2017 – Accepted in Revised Form: September 08, 2017 )
 
 

Abstract    A parametric formulation for preliminary design of tubed-system tall buildings is presented in which some optimality criteria and practical constraints are considered. Here, a minimum compliance optimization formulation, developed by other researchers, is applied to a framed-tube structure. The tube behavior is modeled as a cantilevered box beam. Independent variable in this problem is thickness of the box, and a formulation for its optimal value is proposed. The challenge in this research was treatment of the lower bound constraint on thickness in an analytical manner. To deal with this constraint, a critical height parameter is introduced, and the design domain is divided into two zones of constant thickness and constant curvature. This definition allows for computation of optimal thickness distribution along the structure through an analytic dimensionless equation. Most of the previously published papers in the field of tall structures are suitable for abstract analyses but not for design. In addition, most of them are computer-based. Considering these limitations, the current research presents a hand-calculation method for preliminary design, suitable for sensitivity analyses and parametric studies. As the presented formulations are dimensionless, they are applicable in any dimensional system. Different static loading patterns are considered; including the concentrated, uniform, triangular and quadratic forms. A numerical example is presented to demonstrate the ease of the proposed method in application, and the analysis results are presented by charts to validate the efficiency of it.

 

Keywords    Structural Optimization, Tall Building, Tube System, Stiffness Distribution, Preliminary Design

 

چکیده    یک فرمولبندی پارامتریک جهت طراحی سیستمهای لوله‌ای در سازه‌های بلند، با در نظر گرفتن بعضی‌ معیارهای بهینه‌سازی و قیود کاربردی، ارائه شده است. مساله مینیمم‌سازی نرمی، که قبلاً توسط بعضی‌ محققین ارائه شده است، بر یک سیستم لوله‌ای اعمال می‌شود. رفتار سازه به صورت یک کنسول با مقطع قوطی مدل خواهد شد. متغییر مستقل در این فرمولبندی ضخامت قوطی معادل انتخاب شده است و مقدار بهینه آن‌ ارائه خواهد شد. چالش پیش‌رو در این تحقیق حل مساله مقید به قید حداقل ضخامت، با یک رویکرد تحلیلی، بوده است. در برخورد با این قید، پارامتری به نام ارتفاع بحرانی معرفی شده است که محدوده طراحی را به دو ناحیه‌‌ ضخامت یکنواخت و انحنا یکنواخت تقسیم می‌کند. استفاده از این پارامترها امکان محاسبه ضخامت بهینه در ارتفاع سازه را در قالب یک فرمولبندی تحلیلی و بی‌بعد فراهم خواهد کرد. بیشتر مقالات گذشته در زمینه سازه‌های بلند برای تحلیل مناسب هستند نه طراحی. به علاوه بیشتر آنها مبنای کامپیوتری دارند. با در نظر گرفتن این محدودیت‌ها در این تحقیق یک روش دستی جهت طراحی اولیه ارایه می‌گردد که تحلیل حساسیت و مطالعه پارامتریک را نیز میسر می‌کند. از آنجا که فرمول‌های ارایه شده بی‌بعد هستند، استفاده از آنها در هر سیستم ابعادی امکان‌پذیر است. الگوهای بارگذاری استاتیکی مختلفی‌ شامل بارگذاری متمرکز، یکنواخت، مثلثی و درجه دو مدنظر قرار گرفته‌اند. جهت نشان دادن سادگی‌ روش پیشنهاد شده، یک مثال عددی ارائه شده است و برای صحت سنجی روش، نتایج تحلیل توسط چند نمودار ارائه خواهد شد.

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