Cengiz Dundar

Effect of loading types and reinforcement ratio on an effective moment of inertia and deflection of a reinforced concrete beam

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.

Intrapulpal Heat Generation during Provisionalization: Effect of Desensitizer and Matrix Type

PURPOSE This study investigated the effect of different matrices and application of a desensitizer on pulpal temperature rise during direct provisionalization. MATERIALS AND METHODS The apical third of a second premolar was resected and pulpal tissue was removed. Silicone heat-conducting medium was injected, and a J-type thermocouple was inserted into the pulp chamber and sealed. The tooth was embedded in acrylic resin with its cervical line 1 mm higher than the base. Addition and condensation silicone impression materials were mixed and placed inside plastic molds. Impressions were taken before tooth preparation. The tooth was then prepared with a 1.5-mm shoulder finish line. The experimental model was kept in a 36 degrees C water bath. Four provisional materials were applied in sequence onto the prepared tooth using matrices. Each provisional resin was used in combination with each matrix (n = 12). Then a dentin desensitizer was coated on the prepared tooth and provisionalizations were made in the same manner. The thermocouple was connected to the data-logger. During setting of the resins, pulp temperatures were recorded and transferred to the computer. Measurements were conducted for each test group by calculating the temperature rise as the difference between the start and highest temperature reading. RESULTS The type of the silicone matrix used and the use of desensitizer did not affect the intrapulpal heat generation during direct provisionalization. CONCLUSION Application of a desensitizer and different type of matrix seems to be noneffective on intrapulpal heat rise, although the type of provisional material used may be effective.

Three-Dimensional Analysis of Tall Reinforced Concrete Buildings with Nonlinear Cracking Effects#

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.

Prediction of deflection of reinforced concrete shear walls

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 ACI 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.

Theoretical and experimental investigation of a vertical wall response to wave impact

The laboratory and field experiments so far have shown that when a wave breaks directly on a vertical faced coastal structure, the resulting impact pressures may become very severe in magnitude and short in duration. Some experimental evidence in the literature suggests that the structural response to the extremely high magnitude impact forces is only limited. This study is mainly concerned with the comparison of the theoretical and experimental results of a vertical wall response under the wave impact loading. In the dynamic analysis of the wall the classical elastic plate theory is used and the numerical results for the dynamic values of the transverse displacement are obtained by employing the method of finite elements. In the theoretical analyses the experimental pressure histories are used and the theoretical wall deflection histories are compared with the experimental results. The computational and experimental deflection histories exhibit similar patterns. The theoretical maximum wall deflections are mostly found to be slightly smaller than the experimental values.

Investigation of the behavior of carbon fiber reinforced polymer confined standard cylinder concrete specimens under axial load

Lif takviyeli polimer kompozitlerin betonarme yapılarda güçlendirme amaçlı olarak kullanımı son yıllarda oldukça yaygınlaşmıştır. Özellikle yüksek dayanımlı beton kullanılarak üretilen yapı elemanlarının yük etkisi altında sünek davranmasını sağlamak için, dışarıdan lifli polimer malzemeler kullanılarak sarılması alternatif bir güçlendirme yöntemi olarak öne çıkmaktadır. Yüksek çekme dayanımına sahip olan bu malzemeler, kolay uygulanabilmeleri ve hafif olmaları sebebiyle sıklıkla tercih edilmektedir. Bu çalışmada dayanımı 53.13-74.87 MPa arasında değişen silindir şeklindeki beton numuneler (tek veya çift kat) çift yönlü karbon lifli kumaş (CFRP) kullanılarak sarılmıştır. Söz konusu numunelerin eksenel basınç altında test edilmesiyle CFRP sargısının betonun basınç dayanımına ve sünekliğine olan etkileri araştırılmıştır. Ayrıca test edilen numunelere ait elde edilen gerilmedeformasyon ilişkileri literatürde mevcut olan CFRP ile güçlendirilmiş silindir numunelere ait modellerin sonuçları ile kıyaslanmıştır. Sonuç olarak CFRP sargılı numunelerin basınç dayanımlarında ve şekil değiştirme kapasitelerinde önemli artışlar elde edilmiştir. Özellikle çift kat CFRP sargılı durumda elde edilen gerilme-deformasyon değerlerinin, modellerden elde edilen değerler ile oldukça uyumlu olduğu gözlenmiştir. The use of fiber reinforced polymer composites for strengthening in concrete structures has become quite prevalent in recent years. Especially, to provide ductile behavior from the structural elements that produced by using the high strength concrete under the load effects, the externally wrapping of these elements with using the fiber reinforced polymer materials comes into prominence as an alternative method for strengthening. These materials with high tensile strength can often be preferred due to their lightweight and easy to apply. In this study, cylinder-shaped concrete specimens with compressive strengths range between 53.13~74.87 MPa, are wrapped one or two layer with using bi-directional carbon fiber reinforced fabric (CFRP). These wrapped specimens were tested under the axial comprehensive loads and the effects of the CFRP wrapping on concrete strength and ductility was investigated. In addition, stress-strain relations obtained from the tested specimens were compared with the results of existing models for strengthened cylindrical specimen with CFRP in literature. As a result, a significant increase was obtained in the compressive strength and deformation capacity of CFRP wrapped specimens. Especially, it was observed that the stress-strain values obtained from the two layers CFRP wrapped specimens show good agreement with the values obtained from the models.