Yazar "Dundar, Cengiz" seçeneğine göre listele

Listeleniyor 1 - 9 / 9
  • Küçük Resim Yok
    Öğe
    2 years of monitoring results from passive solar energy storage in test cabins with phase change materials
    (Pergamon-Elsevier Science Ltd, 2020) Cellat, Kemal; Beyhan, Beyza; Konuklu, Yeliz; Dundar, Cengiz; Karahan, Okan; Gungor, Caner; Paksoy, Halime
    Buildings are one of the major consumers of global energy with a significant share reaching to 40%. Phase change materials (PCMs) are used in building materials and structures for energy saving in buildings. PCM absorbs heat from solar energy during daytime and releases that heat when temperatures cool down at night. The benefits of using PCMs in building materials are to reduce peak load and energy demand for heating and cooling and attain smaller temperature fluctuations. The aim of this study is to demonstrate passive utilization of solar energy storage in buildings with a new microencapsulated bio-based PCM (mPCM). The demonstration involves several development steps, which start in the laboratory for development of mPCM suitable for concrete and go to the building application with an innovative panel design under real climate conditions in the field. Monitoring of the test buildings with and without mPCM showed that developed microencapsulated PCM-concrete composite panels helped to maintain thermal comfort in buildings with a change in indoor air temperature with respect to reference building reaching 2 degrees C, which corresponds to up to 13% energy savings.
  • Küçük Resim Yok
    Öğe
    Deflection of concrete structures reinforced with FRP bars
    (ELSEVIER SCI LTD, 2013) Kara, Ilker Fatih; Ashour, Ashraf F.; Dundar, Cengiz
    This paper presents an analytical procedure based on the stiffness matrix method for deflection prediction of concrete structures reinforced with fiber reinforced polymer (FRP) bars. The variation of flexural stiffness of cracked FRP reinforced concrete members has been evaluated using various available models for the effective moment of inertia. A reduced shear stiffness model was also employed to account for the variation of shear stiffness in cracked regions. Comparisons between results obtained from the proposed analytical procedure and experiments of simply and continuously supported FRP reinforced concrete beams show good agreement. Bottom FRP reinforcement at midspan section has a significant effect on the reduction of FRP reinforced concrete beam deflections. The shear deformation effect was found to be more influential in continuous FRP reinforced concrete beams than simply supported beams. The proposed analytical procedure forms the basis for the analysis of concrete frames reinforced with FRP concrete members. (C) 2012 Elsevier Ltd. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Effect of loading types and reinforcement ratio on an effective moment of inertia and deflection of a reinforced concrete beam
    (ELSEVIER SCI LTD, 2009) Kara, Ilker Fatih; Dundar, Cengiz
    In the design of reinforced concrete structures, a designer must satisfy not only the strength requirements but also the serviceability requirements, and therefore the control of the deformation becomes more important. To ensure serviceability criterion, it is necessary to accurately predict the cracking and deflection of reinforced concrete structures under service loads. For accurate determination of the member deflections, cracked members in the reinforced concrete structures need to be identified and their effective flexural and shear rigidities determined. The effect of concrete cracking on the stiffness of a flexural member is largely dependent on both the magnitude and shape of the moment diagram, which is related to the type of applied loading. In the present study, the effects of the loading types and the reinforcement ratio on the flexural stiffness of beams has been investigated by using the computer program developed for the analysis of reinforced concrete frames with members in cracked state. In the program, the variation of the flexural stiffness of a cracked member has been obtained by using ACI, CEB and probability-based effective stiffness model. Shear deformation effect is also taken into account in the analysis and the variation of shear stiffness in the cracked regions of members has been considered by employing reduced shear stiffness model available in the literature. Comparisons of the different models for the effective moment of inertia have been made with the reinforced concrete test beams. The effect of shear deformation on the total deflection of reinforced concrete beams has also been investigated, and the contribution of shear deformation to the total deflection of beam have been theoretically obtained in the case of various loading case by using the developed computer program. The applicability of the proposed analytical procedure to the beams under different loading conditions has been tested by a comparison of the analytical and experimental results, and the analytical results have been found in good agreement with the test results. (C) 2009 Elsevier Ltd. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Prediction of deflection of high strength steel fiber reinforced concrete beams and columns
    (TECHNO-PRESS, 2012) Kara, Ilker Fatih; Dundar, Cengiz
    This paper presents an analytical procedure for the analysis of high strength steel fiber reinforced concrete members considering the cracking effect in the serviceability loading range. Modifications to a previously proposed formula for the effective moment of inertia are presented. Shear deformation effect is also taken into account in the analysis, and the variation of shear stiffness in the cracked regions of members has been considered by reduced shear stiffness model. The effect of steel fibers on the behavior of reinforced concrete members have been investigated by the developed computer program based on the aforementioned procedure. The inclusion of steel fibers into high strength concrete beams and columns enhances the effective moment of inertia and consequently reduces the deflection reinforced concrete members. The contribution of the shear deformation to the total vertical deflection of the beams is found to be lower for beams with fibers than that of beams with no fibers. Verification of the proposed procedure has been confirmed from series of reinforced concrete beam and column tests available in the literature. The analytical procedure can provide an accurate and efficient prediction of deflections of high strength steel fiber reinforced concrete members due to cracking under service loads. This procedure also forms the basis for the three dimensional analysis of frames with steel fiber reinforced concrete members.
  • Küçük Resim Yok
    Öğe
    Prediction of deflection of reinforced concrete shear walls
    (ELSEVIER SCI LTD, 2009) Kara, Ilker Fatih; Dundar, Cengiz
    Reinforced concrete shear walls are used in tall buildings for efficiently resisting lateral loads. Due to the low tensile strength of concrete, reinforced concrete shear walls tend to behave in a nonlinear manner with a significant reduction in stiffness, even under service loads. To accurately assess the lateral deflection of shear walls, the prediction of flexural and shear stiffness of these members after cracking becomes important. In the present study, an iterative analytical procedure which considers the cracking in the reinforced concrete shear walls has been presented. The effect of concrete cracking on the stiffness and deflection of shear walls have also been investigated by the developed computer program based on the iterative procedure. In the program, the variation of the flexural stiffness of a cracked member has been evaluated by ACl and probability-based effective stiffness model. In the analysis, shear deformation which can be large and significant after development of cracks is also taken into account and the variation of shear stiffness in the cracked regions of members has been considered by using effective shear stiffness model available in the literature. Verification of the proposed procedure has been confirmed from series of reinforced concrete shear wall tests available in the literature. Comparison between the analytical and experimental results shows that the proposed analytical procedure can provide an accurate and efficient prediction of both the deflection and flexural stiffness reduction of shear walls with different height to width ratio and vertical load. The results of the analytical procedure also indicate that the percentage of shear deflection in the total deflection increases with decreasing height to width ratio of the shear wall. (C) 2009 Elsevier Ltd. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Robust microencapsulated phase change materials in concrete mixes for sustainable buildings
    (WILEY-BLACKWELL, 2017) Beyhan, Beyza; Cellat, Kemal; Konuklu, Yeliz; Gungor, Caner; Karahan, Okan; Dundar, Cengiz; Paksoy, Halime
    For passive building applications, phase change materials (PCMs) are microencapsulated to avoid leakage of PCM from concrete structure. The primary challenge of using microencapsulated PCM (MPCM) is its weak shell structure. New MPCMs with different shell compositions to prevent breakage during mixing in fresh concrete are needed. In this study, free radical polymerization method to microencapsulate capric acid-myristic acid mixture as PCM with two different methyl methacrylate co-polymers is proposed to produce robust MPCMs for building applications. Two new microcapsules (MPCM-1 and MPCM-2) having latent heats of 91.9 and 97.3 J/g were synthesized. SEM analyses showed the size of microcapsules being in the range of 400-850 nm for MPCM-1 and 250-475 nm for MPCM-2. Analyses also reveal that the shells of MPCMs were not harmed, as they were added into concrete mixes. The microsphere's geometry was preserved, and distribution was homogeneous. The MPCMs were also studied under thermal tests of 1000 heating/cooling cycles. No significant changes in thermal properties were observed after thermal cycling tests. Copyright (C) 2016 John Wiley & Sons, Ltd.
  • Küçük Resim Yok
    Öğe
    Thermal enhancement of concrete by adding bio-based fatty acids as phase change materials
    (ELSEVIER SCIENCE SA, 2015) Cellat, Kemal; Beyhan, Beyza; Gungor, Caner; Konuklu, Yeliz; Karahan, Okan; Dundar, Cengiz; Paksoy, Halime
    An effective way to enhance the thermal storage capacity of buildings is to incorporate phase change materials (PCM) into building materials. Fatty acids are derivatives of materials readily found in nature and labeled as bio-based. In this study, we tested binary mixtures of capric acid (CA), myristic acid (MA), lauric acid (LA), and palmitic acid (PA) as candidate materials for building applications. The melting points of such fatty acid mixtures may further be adjusted, to agree with human comfort zone temperatures by regulating their compositions. We developed two binary mixtures of CA-LA and CA-MA as candidate PCMs for building applications. Thermal storage capacities were measured to be 109.0-155.4 J/g with a differential scanning calorimeter. Thermal cycle tests showed that both PCMs are thermally and chemically stable. Durabilities of PCM mixtures determined by the thermal gravimetric analysis indicated that degradation started at 120 degrees C. The compressive strengths of 1 wt.% PCM added to concrete mixtures were reduced by 12%, yet stayed within the desired limits for C35/45 concretes. However, when PCM contents were increased to 2 wt.%, compression strengths were reduced further, to be within the limits of C30/37 concretes. Both PCMs were suitable for self-compacting concrete mixtures used in buildings. (C) 2015 Elsevier B.V. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Three dimensional analysis of reinforced concrete frames considering the cracking effect and geometric nonlinearity
    (TECHNO-PRESS, 2009) Kara, Ilker Fatih; Dundar, Cengiz
    In the design of tall reinforced concrete (R/C) buildings, the serviceability stiffness criteria in terms of maximum lateral displacement and inter-story drift must be satisfied to prevent large second-order P-delta effects. To accurately assess the lateral deflection and stiffness of tall R/C structures, cracked members in these structures need to be identified and their effective member flexural stiffness determined. In addition, the implementation of the geometric nonlinearity in the analysis can be significant for an accurate prediction of lateral deflection of the structure, particularly in the case of tall R/C building under lateral loading. It can therefore be important to consider the cracking effect together with the geometric nonlinearity in the analysis in order to obtain more accurate results. In the present study, a computer program based on the iterative procedure has been developed for the three dimensional analysis of reinforced concrete frames with cracked beam and column elements. Probability-based effective stiffness model is used for the effective flexural stiffness of a cracked member. In the analysis, the geometric nonlinearity due to the interaction of axial force and bending moment and the displacements of joints are also taken into account. The analytical procedure has been demonstrated through the application of R/C frame examples in which its accuracy and efficiency in comparison with experimental and other analytical results are verified. The effectiveness of the analytical procedure is also illustrated through a practical four story R/C frame example. The iterative procedure provides equally good and consistent prediction of lateral deflection and effective flexural member stiffness. The proposed analytical procedure is efficient from the viewpoints of computational effort and convergence rate.
  • Küçük Resim Yok
    Öğe
    Three-Dimensional Analysis of Tall Reinforced Concrete Buildings with Nonlinear Cracking Effects#
    (TAYLOR & FRANCIS INC, 2010) Kara, Ilker Fatih; Dundar, Cengiz
    In this study, a computer program based on the iterative analytical procedure has been developed for the three-dimensional analysis of reinforced concrete frames with beam, column and shear-wall elements in cracked state. ACI and probability-based effective stiffness models are used for the effective moment of inertia of the cracked members. In the analysis, shear deformation effects are also taken into account, and the variation of the shear rigidity due to cracking is considered by employing the reduced shear stiffness models available in the literature. The computer program is based on an iterative procedure which is subsequently verified experimentally through a reinforced concrete wall-frame test. The effectiveness of the analytical procedure is also illustrated through a practical three-dimensional reinforced concrete shear wall frame example. The iterative analytical procedure can provide an accurate and efficient prediction of deflections of reinforced concrete structures due to cracking under service loads. The main advantage of the proposed procedure is that the variations in the flexural stiffness of each member in the reinforced concrete structures can be observed explicitly.