Study of the Behavior of Beam due to the Variation in Strength of Concrete and Steel Bars

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RCC structures are primarily based with beams and columns. In general, the compressive strength of concrete and the yield strength of steel are specified in the design process. Compressive strength of concrete depends on a number of factors and generally shows some degree of variation from the desired strength. On the other hand, reinforcing bars with higher yield strength than that recommended in the Bangladesh National Building Code is available in the market and being used in construction. So, in practical cases, after casting the compressive strength as well as the tensile strength are not generally achieved as desired. Therefore, increase in yield strength of steel and decrease in compressive strength of concrete may have adverse effects on the flexural behavior of beams. This study includes the behavior of reinforced concrete beam due to this variation in strengths. This study shows that how certain beam behaves due to the variation of strength. Besides, reduction in ductility is also observed due to strength variation in the properties of the major constituent materials. A complete theoretical analysis along with some experimental investigation is presented in this paper.

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The paper analyzes the structural behavior of concrete beams reinforced with hybrid fiber-reinforced polymer (FRP)-steel reinforcements. The analysis refers to concrete beams reinforced with FRP rebars placed near the outer surface of the tensile zone, with low cover thickness values, and steel rebars placed at the inner level of the tensile zone, with high cover thickness values, able to protect the steel from the corrosion. Such reinforcement allows one to optimize the structural behavior of beams and guarantees a good level of ductility and rigidity. Results of an experimental and theoretical investigation are presented and discussed. Significant features of the structural behavior regarding deflection, curvature, ductility, crack width, and spacing are pointed out. Ultimate and serviceability conditions are examined, highlighting the influence of mechanical and geometrical parameters affecting the behavior of hybrid reinforced-concrete beams.
This paper describes an investigation to obtain fundamental information on the mechanical behaviour of high strength concrete (HSC) mixes and the flexural behaviour of high strength reinforced concrete (HSRC) beams. In the first part of the paper the design of HSC mixes using local aggregates is described. HSC mixes of strength from 80 to 12OMPa at 28 days (100mm × 100mm cubes) were produced at low w/c ratios, with the use of pozzolanic additives (silica fume) and superplasticiser. The principal aim at the mix optimisation stage was focused on the role of w/c ratio, concrete ingredients, and their relative contents in producing HSC. Furthermore, compressive strength, splitting tensile strength, elastic modulus, Poisson 's ratio, and stress-strain behaviour, were obtained for moist cured cubes and for cylinders. Based on the experimental data, and other reported data, an expression was developed for predicting the strength of HSC mixes based on their ingredients. A new relationship between the compressive strength and splitting tensile strength is also proposed. The second part of this paper is concerned with the flexural behaviour of HSRC beams. Three concrete mixes were selected from the first stage and employed in this part of the investigation. Flexural tests were carried out on singly reinforced beams. The variables were concrete strengths, and tensile steel ratios (1.03%-4.04%). Test results are presented in terms of loaddeflection behaviour, ductility indices, and cracking propagation. An empirical design method has been established in the context of HSC beams subjected to pure flexure. Moreover, the BS 8110 design recommendation is critically examined at ultimate strength capacity for HSRC beams having concrete strengths far beyond the present Code limits.
A total of 18 concrete beams were tested to study the influence of adding steel fibers (SF) to concrete mix on the ductility of concrete beams reinforced with fiber reinforced plastics bars (FRP beams). The main variables in the study were the type and volume fraction of the steel fiber. The study also investigated the accuracy of an available model, developed originally to predict the flexural strength of concrete beams reinforced with SF and steel bars (SF-steel beams), after modification in estimating the flexural capacity of the fibrous FRP beams (SF-FRP beams). The results indicate that the ductility of FRP beams is less than 50% of that of the respective steel beams. The results also reveal that the ductility of SF-FRP beams is directly related to the fiber content. In addition, the test results show that inclusion of 1% of hooked SF can improve the ductility of FRP beams to be the same as that of the steel beams. Furthermore, comparison between the predicted and measured flexural capacity of SF-FRP beams shows that the modified model can predict the measured results within a reasonable accuracy.
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