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EFFECTIVE STIFFNESS MODEL FOR REINFORCED CONCRETE SLABS

By Maria Anna Polakl

ABSTRACT: A simple procedure for calculating deflections of reinforced concrete two-way slabs is presented

in this paper. The material model for reinforced concrete based on the effective stiffness approach has been

implemented in a finite-element program incorporating Mindlin-plate-bending elements. Uncracked concrete is

treated as an isotropic linear elastic material, and after cracking, the concrete is considered to be an orthotropic

material. The reduced stiffness coefficients after cracking are calculated from the effective moments of inertia

in the x- and y-directions. These effective moments of inertia are determined using the formula proposed by

Branson (1963). The influence of both bending and torsional moments is included in the formulation. The

proposed model has been verified by comparisons with results from tests on slabs with various loading and

boundary conditions. A study has also been undertaken to check the sensitivity of the proposed formulation

when applied to the analysis of slabs with different reinforcement ratios, boundary conditions, and reinforcement

orientations.

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  • مطالب مشابه

    • توسط masoodbehnia
      1- باربری یکطرفه دال:
      فلسفه استفاده از تیرچه‌ها تشکیل المان‌های T شکلی است که بار سقف را به صورت یک‌طرفه به تیرهای دوطرف منتقل می‌کنند. آنچنان که می‌دانید شکل T به واسطه حذف قسمت کششی بتن و جایگذاری آرماتور در تیرچه ها می‌باشد که باعث کاهش وزن سقف خواهد شد.
       
       

       
      اما در سیستم کانتراس، با استفاده از قالب‌های کامپوزیتی ماندگار در بتن، قسمتی از بتن غیرباربر میانی دال را حذف و تیرچه هایی I شکل با باربری دوطرفه ایجاد می‌نماییم. بنابراین با شکل‌گیری غشای بتنی مستحکم در قسمت فوقانی و تحتانی دال به همراه شکل‌گیری شبکه‌ی تیرچه‌های داخلی در دو امتداد، می‌توان باربری بسیار مناسبی را برای دال متصور شد.
       
      صلبیت بالای سقف کانتراس در هنگام زلزله موجب توزیع متناسب نیروها درون دیافراگم می‌گردد و در حین ساخت نیز افزایش دهانه و حذف ستون‌های میانی را ایجاد خواهد کرد.
       


       
       
      کلمات کلیدی:
      کانتراس - تیرچه و بلوک - سقف - دال مجوف - دال دو طرفه - سقف بتنی - کوبیاکس - یوبوت - یوبوت اصلاح شده -
       
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    • توسط admin
      Innovative Structural Slab Practices – Voided Slabs
      Session sponsored by ACI/ASCE 421
      Mike Mota Ph.D., P.E., F.ASCE
      CRSI - Atlantic Region Manager
      Session Moderator
      April 14, 2013
      Minneapolis, MN
       
       
      ACI 421 Session on Innovative Slab Design 2013 for cobiax, uboot and bubble deck slabs
      راهنمایی برای سقف های یوبوت و کوبیاکس و بابل دک
       
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    • توسط admin
       
      Comparison of plasticity and stiffness of steel shear walls with composite steel plate shear wall

      Leila Shahryari; Mahdi Esfandiari

      The steel shear wall and composite steel plate shear wall is introduced in recent three decade and is considered and is spread rapidly. Composite steel plate shear wall which is made of a layer of thin steel sheet with coating of reinforced concrete in one or both sides of steel palate is considered a third generation of resistance shear walls against lateral loads that in addition to increasing the strength, ductility and energy absorption, it is very economical and affordable and it is used in constructing high buildings, retrofitting buildings and tanks. In this paper we have tried to examine the seismic behavior of steel and composite shear walls. For this purpose several models of steel shear and composite walls from one to five stories were constructed and analyzed by Abaqus software. The result show that composite steel plate shear walls has more ability to absorb energy, spread produced stress to different parts of the steel plate and ductile than steel shear walls. The curve hysteresis loop of composite steel palate shear walls is more stable and sustainable than steel shear wall. With increasing the number of stories, the initial strength and stiffness is decreased due to increase in lateral shift but the amount of absorbing energy and ductility is increased. The force tolerance in composite steel plate shear wall models is increased in comparison with steel shear walls


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    • توسط admin
      Seismic Structural Failure Potentialities of Newly Constructed Buildings in Iran.

      Mohajerani P.

      J. Civil Eng. Urban., 5(5): 200-209, 2015; pii:S225204301500032-5

      Abstract

      As Iran is located at high seismic risk region and future ground motions are predicated by seismologist, thus, A Case study was conducted to investigate the major seismic structural failure potentialities due to design and constructional flaws in two province of Iran, Tehran and Esfahan, the former with high seismic risk and the latter with an intermediate risk. More than forty buildings were inspected to find the four major failure potentialities in these two provinces. Two imperfections were found in steel structures and two in reinforced concrete buildings. Design and constructional imperfections in protected zone in steel structures and latticed column details are two main points threaten newly constructed steel structures. In reinforced concrete structures, stairway constructional flaws and wrong pipe passing constructional details are the two main defects covered in this study for this type of structures. This paper also presents solutions for each failure potentiality and recommends some constructional and design hints to increase the safety of structure and make them ready for future seismic excitations.

      Key words: Structural failure potentiality, Constructional imperfection, Earthquake, Risk mitigation, Steel structure, Reinforced concrete structures, Iran

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    • توسط admin
      An evaluation of impressionableness structural systems under the condition of foundation and bed resistance
      Original Article, A7
      Zare HR, Dehghani M.
      Journal. Civil Eng. Urban. 2(1): 49-52. 2011.
      ABSTRACT: The analysis of the structures under the influence of the earthquake load is usually done independent of the conditions and the soil variable under them. In other words, the bed of the structure location is supposed to be rigid. In these conditions seismic excitation in the bed of the structure is conducted in the form of a displacement with acceleration with time (or equivalent force). What happens in reality is that the structure is situated on the soil environment as a flexible bed, and from the view point of dimension as semi-infinite and earthquake vibrations from its source reach the foundation of the structure by passing from this environment which results in soil-structure interaction. The flexibility of the structure foundation and the emission of system energy by the waves in the infinite environment of soil (radiation depreciation) are two important results of soil-structure interaction phenomenon. One of the methods of considering the above-mentioned phenomenon in the analysis of the structure-supposing the elastic linear behavior of the soil environment-is by using SSI equivalents by which we have analyzed frame structures and shear wall frame structures under the earthquake load by considering SSI. By extraction of base shear amounts and displacement of the head of the structures under the influence of different earthquakes quantitative and different results have been obtained in a way that mentioned amounts strong dependence on the stiffness of the structure, stiffness of the soil, the kind of the earthquake ,etc. For this reason, the amount of the base shear and displacement in shear wall frame structures is more different from frame structure system in a way that these variations have twofold decrease or increase in a shear wall frame structure comparison with a frame structure system. This matter and the subsequent results reveal the necessity of paying attention to SSI in analysis and design of important structures from the view point of safety factor economic issues.
      Keywords: Soil–structure interaction, frame structure, shear wall, stiffness
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