Modares Civil Engineering journal
مهندسی عمران مدرس
MCEJ
Engineering & Technology
http://mcej.modares.ac.ir
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2476-6763
10.22034
fa
jalali
1397
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2018
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بررسی عرض موثر شاهتیرهای مرکب فولادی-بتنی
Investigation on the effective width of steel-concrete composite girders
یکی از عوامل مهم که در تعیین ظرفیت باربری تیرهای مرکب نقش مهمی ایفا میکند، عرض مؤثر آنها است. علیرغم مطالعات فراوانی که درباره عرض مؤثر تیرچههای مرکب صورت گرفتهاست، هنوز شاهتیرهای موجود در سیستم سقفهای مرکب -بنا به دلایلی و در جهت اطمینان- غالبا" به صورت غیرمرکب و بدون لحاظ کردن اثر دال بتنی طراحی میشوند که این امر میتواند منجر به غیراقتصادی شدن طرح گردد. با توجه به اینکه تا کنون عرض مؤثر این قبیل شاهتیرها بررسی نشده است، در این مقاله عرض مؤثر شاهتیرهای مرکب در قابهای ساختمانی ساده ابتدا با فرض رفتار الاستیک- خطی از طریق روش اجزای محدود مورد ارزیابی قرار میگیرد. برای این منظور، تعدادی شاهتیر مرکب با نسبتهای S/L مختلف به صورت دو سر مفصل با توجه به تقارن و یا عدم تقارن پانلهای مجاور و همچنین با در نظر گرفتن اثر تیرچههای فرعی مرکب تحلیل شده و تغییرات مقادیر عرض مؤثر آنها در طول دهانه محاسبه گردید. در ادامه جهت بررسی اثر ترک خوردگی و خرابی دال بتنی در میزان عرض مؤثر این نوع از شاهتیرها، تعدادی از نمونهها به روش غیرخطی نیز تحلیل شده و عرض مؤثر آنها مجددا" محاسبه گردید. مقایسه مقادیر عرض مؤثر بدست آمده از تحلیل عددی با مقادیر پیشنهادی مبحث دهم از مقررات ملی ساختمان ایران نشان میدهد که این قبیل شاهتیرهای مرکب -حتی با وجود اثرات تیرچههای مرکب متعامد و عملکرد دوجهته دال بتنی- قادر به تامین عرض مؤثر مقررات ملی ساختمان بوده و میتوان آنها را بصورت مرکب تحلیل و طراحی نمود.
Steel-concrete composite beams have been widely used in building and bridge construction since about a century ago. Construction with composite system provides some advantages including: reduction in the weight of steel (saving of 20 to 30%), increasing floor stiffness and increasing span length.In order to analyze such composite beams using the ordinary beam theory, the concept of effective width is used instead of their actual width. Effective width is one of the most influencing factors which plays an important role in determining the ultimate load bearing capacity of steel-concrete composite beams. There are a number of influencing parameters which affect the value of composite beams’ effective width including the ratio between the half width of the slab and the beam length (S/L), the number and rigidity of the shear connectors, the steel section yield strength and the concerte slab strength. There are numerous studies in the literature which have been conducted on the effective width of composite I-beams. However, the steel-concrete composite girders are generally analyzed and designed in current practice (on the safe side) as non-composite steel girders without taking into account the effect of concrete slab, yet. This procedure may lead to an uneconomic design. Although such girders have been widely used in the construction of residential steel building frames, however, their effective with has not been investigated, yet. This paper develops a three dimensional finite-element model using ABAQUS for the elastic and inelastic nonlinear static analysis of steel-concret copmposite girders and uses it to investigate the real effective width of concret slab in these kinds of girders under two types of loadings (a concentrated point load and a uniform distributed load) on their moment gradient factor in different behavioral zones. The concrete slab and steel section were modeled using the three-dimensional eight-node solid element (C3D8). However, the reinforcements were modeled using the Truss one-dimensional elements. To simulate the shear connectors implicitly, the concrete slab and steel girder were joined together with the Tie command available in ABAQUS. To achieve this end, some simply-supported with differet ratios of S/L, and symmetric/unsymmetric adjacent concrete panels were designed first taking into account the effects of secondary perpendicular composite I-beams. Then, considering the actual distribution curve of axial elastic compressive stress within the concrete slab in each model and estimating the area under the curves, their effective width was calculated in different locations along the girders lengths. Furthermore, in order to investigate the effects of concrete slab cracking and damage on the effective width of such composite girders, some of the above mentioned girders were analyzed nonlinearly and their effective widths were recalculated. Comparison of the calculated effective width values with the corresponding values proposed in the Iranian National Building Codes (INBC- Part 10) showed that such composite girders are capable of providing the effective width given in INBC. This indicates that despite the effects of perpendicular composite I-beams as well as bi-directional action of concret slab, the investigated steel-concrete composite girders can be analyzed and designed as common composite beams.
شاهتیر مرکب,مدل اجزاء محدود,عرض موثر,تیرچه مرکب,رفتار غیرخطی,
Composite beam,Steel girder,Finite element method,Nonlinear analysis,Concrete slab,
183
192
http://mcej.modares.ac.ir/browse.php?a_code=A-16-39633-137&slc_lang=fa&sid=16
Amin
Mohebkhah
امین
محب خواه
1003194753284600188189
1003194753284600188189
Yes
Dean of Civil and Architectural Eng. Faculty
سرپرست دانشکده مهندسی عمران و معماری
Hamed
Ivakpour
حامد
ایوک پور
1003194753284600188190
1003194753284600188190
No
دانش آموخته
علیرضا
جهان پور
1003194753284600188191
1003194753284600188191
No
استادیار گروه عمران