آناليز دقيق توالي ساخت و مقايسه‌ي آن با آناليز متداول و روش تقريبي ضرايب اصلاح

Investigation of the exact sequential construction analysis in comparison with the Conventional analysis and the approximate CFM method

در تحليل‌هاي متداول سازه‌‌‌يي، كل طبقات سازه با فرض عدم اعمال بار تا اتمام مراحل ساخت به طور هم‌زمان و يك‌باره تحت بارگذاري قرار مي‌گيرند، در حالي كه بارهاي مرده ناشي از وزن سازه و كف‌سازي همگام با پيشرفت مراحل ساخت به تدريج به اعضا ساخته‌شده در مراحل قبلي اعمال مي‌شوند. طبقات پايين سازه تحت بارهاي ثقلي مذكور، تغييرشكل‌ مي‌يابند و طبقات فوقاني، برروي سازه‌‌ي تغيير‌شكل يافته‌ي زيرين قرار مي‌گيرند. تغييرشكل‌هاي نهايي سازه، از جمع كليه‌ي تغييرشكل‌هاي رخداده در هر مرحله تا تكميل نهايي سازه حاصل مي‌شود. در اين نوشتار، آناليز دقيق توالي ساخت و محاسبه‌ي دستي آن به جهت آگاهي از نحوه‌ي عملكرد نرم‌افزار ETABS مورد بررسي قرار گرفته و ميزان اختلاف نتايج با آناليز متداول و روش‌هاي شبيه‌ساز رفتار واقعي سازه منطبق با مراحل عملي ساخت مانند روش ضرايب اصلاح، در قالب مطالعه‌ي موردي سازه‌ي فلزي 21 طبقه مقايسه شده است. عدم لحاظ توالي ساخت در سازه‌ي مورد بررسي، موجب طرح غيراقتصادي تيرها و بادبندها شده است.

Nowadays, in common structure analyses, dead and live loads of all floors are applied instantaneously. In fact, it is assumed that the structure does not bear any load before the end of construction. This assumption could be valid for lateral loads or the dead loads of subsequently installed components, but it is unsuitable for the dead loads of the structural members and floor because these types of loads are gradually applied to the previously constructed members during the progress of construction, which depends on technology and construction planning. According to the sequence of construction, structural members are added to stages as the building construction proceeds; therefore, their dead load is carried by the part of the structure completed during their installation stage. Hence, it is clear that the distribution of displacements and stresses in the constructed part of the structure at any stage does not depend on the sizes, properties, or the presence of members composing the remainder of the structure. In this procedure the deformations of the lower stories are already taken place under the self weight of their floors even before the upper floors are built. Hereupon, in each stage of construction, the newly- built members are installed on the previously deformed members of the structure, and the final deformation of structure is the cumulative outcome of deformations in construction of each story until the completion of the final stage of construction. Ignoring the effect of sequence of construction may lead to seriously incorrect analysis results, particularly at the upper floors of the building. In this paper, the exact method of sequential construction analysis has been investigated, and also the manual method of calculating the elastic sequential analysis has been studied in order to have the sufficient knowledge of how the software works. To comprehend the necessity of sequential construction analysis, the outcomes are eventually compared with the conventional analysis and simulation methods of the real behavior of the structure, compatible with the real construction schedule such as CFM method. A 21-story steel structure has been chosen as a case study to achieve the aforementioned purpose of this paper.