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Kendinden yerleşen betonda bindirmeli eklerin aderansı.
No full textSelf-compacting concrete is an innovative construction material; its priority to normal vibrated concrete is that there is not any vibration requirement. Bond strength of reinforcement is one of the key factors that ensures the usefulness of any reinforced concrete structure. In this study, 6 full-scale concrete beams spliced at the mid-span were tested under two-point symmetrical loading. Test variables were bottom cover, side cover, free spacing between longitudinal reinforcement, lap-splice length and presence of transverse reinforcements within the lap-splice region. Specimen SC_22_44_88_800 had cover dimensions close to the code limits and had 36db lap splice length. This specimen showed flexural failure. Specimen SC_44_44_44_710 had 32db lap splice and cover dimensions greater than code minimums. This specimen showed yielding primarily. With the increasing loading, however, bond failure occurred with side splitting. ACI 408 descriptive equation for normal vibrated concrete predicted bar stresses of the unconfined specimens produced with self-compacting concrete acceptably well. The predicted values were lower than the measured values to be on the safe side. The error varied between 3.4% and 6.5%. All predictions of the ACI408 descriptive equation was higher than the measured bar stresses of the confined specimens produced with SCC. All the calculated values were unsafe. The error varied between 10.6% and 34.5%. Specimen SC_44_22_22_530_T4 with 24db lap splice length had side cover and spacing between bars 63.3% and 56.7% less than the ACI 318 limits. The calculated bar stress was 21.6% higher than the measured value. The main reason of the deviation was inadequate cover dimensions. In specimen SC_44_22_22_530_T6, number transverse reinforcement was increased to 6 stirrups to overcome the small cover and spacing problem. However, increased number of stirrups inside a small side and face cover caused weak plane and measured bar stress decreased.M.S. - Master of Scienc
Betonda ısı ve rötreden kaynaklı çatlamaların hesaplamalı modellenmesi
No full textThis work is concerned with the computational modeling of thermal and shrinkage-induced cracking in concrete. Thermal and hygral gradients develop within concrete structures of varying sizes and aspect ratios due to the intrinsic physicochemical phenomena accompanied by adverse environmental effects. These spatio-temporal gradients invariably result in uneven volumetric deformations that can cause stress concentrations when the concrete is sufficiently rigid. Then, when the gained tensile strength is lower than the principal stresses generated by the non-uniform volume changes, cracks will occur and make concrete structures prone to deleterious environmental effects that can cause consequent destructive durability problems. Therefore, predictive computational models are crucial to conduct crack risk analyses not only during the design stage but also during and after the construction of important concrete structures. For this purpose, we develop multi-field computational models to simulate thermal and shrinkage-induced cracking separately. For the former, we developed a novel chemo-thermo-mechanical model coupled with a quasi-brittle phase-field model where the hydration, thermal, mechanical, and fracture problems are solved in a coupled manner. For the drying shrinkage-induced cracking, we develop a new coupled chemo-hygro-mechanical model within the framework of poro-viscoelasticity to describe the basic and drying creep of concrete in short- and long-terms. The latter model is further supplemented by a cohesive phase-field model to simulate shrinkage-induced cracking. The capabilities of the proposed models are assessed through the benchmark problems and experimental results reported in the literature.----Ph.D. - Doctoral Progra
Computational Modeling of Durability Phenomena in Concrete
No full textIn this contribution, coupled constitutive models furnished by robust computational framework are developed to address the durability problems that arise due to the uneven chemical heating through hydration in mass concrete [4] and the non-uniform shrinkage by means of the reduction in relative humidity [5]. In the case of mass concrete structures such as dams, the coupling between the hydration reaction, temperature evolution, and deformation at early ages may lead to cracking. In many hydraulic and building structures, located in a region with high temperature variations between day and night, the humidity diffusion leading to a highly heterogeneous shrinkage strain distribution is observed. The parameters governing shrinkage can be classified in three groups: (i) environmental parameters (relative humidity, temperature, rate of moisture loss, duration of moisture loss), (ii) geometry of the concrete element (surface area to volume ratio, thickness), (iii) cementitious paste parameters (water- cementitious material ratio, amount and composition of the cementitious material, degree of hydration). Hence, the proposed approaches account for the chemo-thermo-mechanical coupling to investigate the cross effects between the evolution of temperature due to hydration and stresses through the deformation in mass concrete for the former problem. While the latter class of problems are tackled by the coupled hygro-thermo-mechanical models incorporating shrinkage-induced stress concentrations either in hardening or hardened concrete within the framework of Reactive Porous Media [1] based on the coupled problem of Darcy-Biot-type fluid transport. These coupled models are further supplemented by the Phase Field models [2], [3] to predict the crack initiation and propagation under the considered coupled effects
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Computational Modeling of Shrinkage-Induced Cracking in Concrete
No full textThis contribution is concerned with the computational modeling of durability problems related to drying shrinkage. The associated formulations are conducted by developing a coupled constitutive modeling approach, which is furnished by the robust computational tools within the framework of poroviscoelasticity. In contrast to the existing studies, we employ a physically motivated technique where the pore pressure is obtained as a function of the water content that is determined using sorption‐desorption equations for a given value of the local relative humidity. Therefore, the proposed model accounts for the hygro‐chemo‐mechanical cross coupling effects between the shrinkage‐induced strain development due to the pressure evolution through humidity variations and the stress concentrations in hardening and hardened viscoelastic concrete. The comparison of the numerical examples with experiments
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