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Space with a font size 28 EXPERIMENTAL STUDY OF SELF-COMPACTING REINFORCED CONTINUOUS DEEP BEAMS Space with a font size 24 Space with a font size 12 Space with a font size 24

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Abstract

Test results of twelve reinforced self-compacted concrete two-span deep beams casted by using self-compacting concrete are reported. The main variables studied were shear span-to-overall depth ratio (a/h), concrete strength (fʹc) and the amount of vertical shear reinforcement ratio (ρ v). All specimens had the same dimensions and main flexural reinforcement. Tests pointed out that all beams failed in shear with diagonal splitting mode. It was found that shear span to overall depth ratio (a/h) effects the load carrying capacity of beams such that a decrease of 50 % in that ratio from 1 to 0.5, the cracking load (P cr) and ultimate load (P ult) increase by average ratios of 29% and 25% respectively. The concrete compressive strength (fʹc) are also had a noticeable influence on the continuous deep beams behavior such that increasing (fʹc) to almost twice from (33.81 to 67.8) MPa led to an increase in the cracking load (P cr) and ultimate load (P ult) by average ratios of 12.75% and 16.5% respectively. When (ρ v) is increased by 80% from (0.25% to 0.45%) a better increase shear capacity of both NSCC & HSCC deep beam having (a/h) ratio of 1.0 (enhancement reached to18.56% and 23.1% respectively) as compared to the reference beams without shear reinforcement (ρ v =0).S

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SCC can be classified as High-Performance Concrete. As the name suggests, it does not require to be vibrated to achieve full compaction. This offers many benefits and advantages over conventional concrete. This study aims to evaluate the properties of SCC produced by locally available materials and the influence of types, dosages, and fineness of the mineral admixtures and the ternary blend of powders on these properties in fresh and hardened phases. Also, aims to evaluate the influences of steel fibers on the same properties. To achieve these aims, 20 different mixes of SCC are mixed, tested and evaluated. The results indicate that acceptable SCC mixtures can be created. The influences of the mineral admixtures on the fresh properties of SCCs are not same and vary according to the type, particle-distribution system, fineness, dosage and the number of these admixtures. As the fineness, dosages or the numbers of the mineral admixtures increase, the flowability decrease and the viscosity increase. In the same way the irregular particle-distribution system affects. There are very little negative effects on the workability when the steel fibers are added with fiber factor of 32. These effects will be more negative when the fiber factor increases. The type of the mineral admixtures according to its pozzolanic activity has significant effects on the strengths of the studied SCC mixes especially at the 28 and 90 days ages. The excess fineness negatively affects the early age strengths, but it improves the later age strengths. Irregular particle-distribution system and the more dosage of the mineral admixtures negatively affect the strengths of the mixes. The modulus of elasticity of the mixes is slightly lower than that of conventional concretes. The addition of the steel fibers enhances the strength of the matrix by means of post-cracking ductility. The influence of steel fibers on the flexural and tensile strength is greater than compressive. Non-destructive tests confirm an inference that there is less heterogeneity of the SCCs.
Article
The strut-and-tie method can be used for the design of Disturbed regions (D-regions) of structures where the basic assumption of flexure theory, namely plane sections remaining plane before and after bending, does not hold true. Such regions occur near statical discontinuities arising from concentrated forces or reactions and near geometric discontinuities, such as abrupt changes in cross section etc. The strut-and-tie method of design is based on the assumption that the D-regions in concrete structures can be analysed and designed using hypothetical pin-jointed trusses consisting of struts and ties inter- connected at nodes. Continuous deep beams occur as transfer girders in multi-storey frames, as pile caps and as foundation wall structures etc. The usual design practice for continuous deep beams has been to employ empirical equations, which are invariably based on simple span deep beam tests. Given the unique behavioural pattern of continuous deep beams, this practice is unrealiable. Since continuous deep beams contain significant extents of D-regions and they exhibit a marked truss or tied arch action, the strut-and-tie method offers a rational basis for the analysis and design of such beams. The mechanics and behavior of continuous deep beams are briefly discussed from which a strut-and-tie model for such a beam is developed. A complete example on the analysis and design of a continuous deep beam using the strut-and-tie method is presented. The design has been carried out using the recommendations of the ACI Code 318-02.
Article
Synopsis thirteen simply supported reinforced concrete deep beams with span/depth ratios of 1,2 and 3 are loaded to failure. The percentage of main reinforcement varies from 0·22 to 1·16 and three modes of failure are reported, namely flexure, diagonal splitting and local crushing. Detailed experimental evidence including some strain measurements is presented to enable the development of the failure mechanism to be monitored. The failure loads are compared with values predicted by CIRIA Guide 2, which is shown to be safe provided that failure is by diagonal splitting (the commonest case in practice). It is argued that a need exists for design recommendations for deep beams with larger span/depth ratios than those covered by the Guide.
Article
An upper-bound analysis of reinforced-concrete continuous deep beams is presented. The concrete is assumed as a rigid-perfectly plastic material obeying the modified Coulomb failure criteria with zero tension cutoff. Two collapse modes are considered, each idealized as an assemblage of rigid blocks moving in plane, separated by yield zones. These zones are idealized as lines, the limiting case of narrow zones of failing material undergoing very high strains. Calibration of the computed failure loads against the experimental failure loads for 20 test beams produces the value of the effectiveness factor for concrete in compression for this type of structure. The effectiveness factor may be allowed to vary with the concrete strength and the amount of web reinforcement, but this provides little improvement over the adoption of a uniform value. The effect of the horizontal and vertical web reinforcement on the load capacity is mainly influenced by the shear span to depth ratio. The deeper the beam, the less effective the vertical web reinforcement, and the more effective the horizontal web reinforcement.
Behavior and Analysis of Reinforced Concrete Continuous Deep Beams
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