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This paper shows the simplified equation to predict the ultimate moment capacity and corresponding rod stress in reinforced concrete beam with external post-tensioning rods. Because the stress of external post-tensioning rod depends on the beam deflection, the previous analytical model for post-tensioned beams requires a tedious iteration process. Also, the stress equations in ACI code or other researchers' models are suitable only for internal tendons in concrete beams. In this study, given the lack of analytical approaches to predict the nominal stress of the external unbonded rod, a simple and robust equation has been proposed for externally post-tensioned concrete beams. It is concluded that the proposed equation predicted the stress of external steel rods in post-tensioned concrete beams reasonably well.
This experimental investigation was conducted to observe the shear strengthening behavior of pre-damaged reinforced concrete (RC) beams strengthened with externally post-tensioning steel rods. A total of six simply supported beams -two control beams and four post-tensioned beams using external steel rods - were tested to failure in shear. The external steel rods of 18 mm or 28 mm diameter were respectively employed as post-tensioning material. The four post-tensioned beams have a V-shaped profile with a deviator (or saddle pin) located at mid-span, and the post-tensioning system increased the low load-carrying capacity and overcame a little bit of deflection caused by damage. Concretely, the load-carrying capacity and flexural stiffness were respectively increased by about 25~57% and 263~387% due to the post-tensioning when compared with the unstrengthened control beams.
Concrete is the well-used material in many architectural and civil structures. The behavior of concrete does exhibit a different characteristic in compression and tension, and it also shows an inelastic-nonlinear behavior. In addition, the concrete properties vary slightly depending on the environmental factor and manufacturer. These properties of concrete make the modeling or simulation of concrete material difficult. In reinforced concrete, particularly, there is a difficulty in bond-slip relationship between concrete and steel. However, in this paper, reserving remainder of these limits the finite element analysis for reinforced concrete beams through ABAQUS simulation has been carried out with some assumptions. Assumptions include the perfect bond of steel and concrete as well as the concrete damaged plasticity (CDP) in concrete property. There is a reasonable agreement between the experimental and numerical results, although the analytical strength and external rod deformation are slightly overestimated. The average and standard deviation between two results are 1.05 and 0.05, respectively. And the models and the computations lead to the evolution of fracture in bending beam.
The objective of this study is to develop equations or the method that can predict the strengthening effect on shear capacity of RC beams with high tension bars. The shear capacity of these beams is defined as summation of shear force by concrete, stirrup and high tension bars. To estimate the shear force by concrete and stirrup, Zsutty equation is used. As like other paper, the Zsutty shear equation produces satisfactory predictions as compared to ACI code equation. And the strengthening effect on shear capacity is achieved through the geometrical method. The basic concept of this method is that externally unbonded high tension bars are converted to a vertical component which affects the shear capacity. This geometrical equation contains three parameters such as the area, inclined angle and specified yield strength of high tension bars. Especially, the high tension bars of experimental specimens in this paper didn`t reach the yield point. Therefore it is necessary to estimate the stress of high tension bars at nominal flexural strength for more exact predicting results. There are two ways to estimate this stress; the flexural design code equations of prestressed concrete in ACI 318-05 and the relation equations between load and deflection. In flexural design code, experimental result of theoretical result is about 0.56~0.62. On the other hand, the relation equations betweem load and deflection show that experimental result of theoretical result is about 0.96~1.01 agreement. This paper presents equations to estimate the stress in high tension bars at nominal flexural strength. From the comparison of experimental and predicted shear capacity, an exact agreement is achieved in proposed method.
This paper described the shear strengthening effect by deviator location in pre-damaged reinforced concrete (RC) beams strengthened with externally post-tensioning steel rods. Three reinforced concrete beams as control beam and eight post-tensioned beams using external steel rods were tested to fail in shear. The externally post-tensioning material was a steel rod of 22 mm diameter, and it had a 655 MPa yield strength and an 805 MPa tensile strength. Specimens depend on multiple variables, such as the number of deviators, location of deviator, and load pattern. The pre-damaged loads up to about 2/3 of ultimate shear capacities were applied to specimens using displacement control and the diagonal shear crack just occurred at these loading levels. And then, the post-tensioning up to when a strain of steel rod reaches about 2000 με was continuously applied to beam. A displacement control was changed to a load control during post-tensioning. The post-tensioning resulted in increase of load-carrying capacity and restoration of existing deflection. Also, it prevented the existing diagonal cracks from excessively growing. Two deviators effectively improved the load capacity when compared with in case of test which one deviator at mid-span installed. When deviators were located near region which the diagonal crack occurred on, the strengthening impact by post-tensioning was greater.
This paper presents the shear strengthening effect of externally post-tensioning (EPT) method using high-strength steel rod in pre-cracked reinforced concrete (RC) beams. Three- and four-point bending tests were performed on a total of 8 specimens by adjusting the strengthening depths in the deviator position of EPT. The effective strengthening depths were 435, 535, and 610 mm. The pre-loading up to about 2/3 of ultimate load capacity measured in unstrengthened RC beam were applied in the beam to be post-tensioned. The EPT method was then applied to the pre-damaged RC beams and re-loading was added until the end of the test. EPT restored deflections of 3 mm or more, which account for about 40% of deflection when the pre-loading was applied. The shear strengthening increases more than 3 times and 36~107% in terms of the stiffness and load-carrying capacity compared to unstrengthening RC beams. The increased load-carrying capacities of the post-tensioned beam with strengthening depths of 435 and 535 mm are almost the same as 36~61%, and those of 610 mm are 84~107%, which shows the greatest shear strengthening effect.
An experimental work was undertaken to observe and assess the behavior of damaged reinforced concrete (RC) beams with external post-tensioning steel rods. Six simply supported beams - two control beams and four comparable beams post-tensioned using externally steel rods - were tested in three-point bending. The main parameters are the diameter of external post-tensioning rods (ø22 mm and ø28 mm) and the ratio of tension steel reinforcement (p =0.0106 and 0.0166). For the post-tensioned beams, V-shaped profiles were used with a deviator located at the bottom of mid-span, and the post-tensioning force was applied to beams in order to overcome the low load-carrying capacity and existing deflection. The post-tensioning force acting on the steel rods was applied by tightening nuts of anchorage and its value was monitored by attached strain gauges. The initial strain of about 2000µε was chosen for post-tensioning force because it is about the maximum strain that two adult men can apply without struggle. Test results indicate that the externally post-tensioning increased the load-carrying capacity by about 40~101% and the flexural stiffness by about 27~43% compared to control beams. On the other hand, the larger steel reinforcements and external rods of the section disturbed the yielding of external rod at ultimate strength.
Recently the study of heavy structure systems using a high strength tension member or cable has been increased abroad. The representative example is the suspension structure system. The tension member in the suspension structure systems used in long span structure resists load. A tum-buckle is a device adjusting the tensile force between tension members, but it is not easy- to measure the design tensile force by a conventional tum-buckle. So the measurable turn-buckle has been developed to improve the difficulty of measurement. The straight tensile elements of conventional turn-buckle were pre-deformed to a diamond shape, and, then, the lateral displacement of the curved elements was measured to convert it to load when tensile force was applied to the measurable tum-buckle. This study proposes analytical models of tum-buckles for the 100kN and 300kN capacities not being proposed in the previous study, and improves the shape of the previous tum-buckle for the 200kN capacity. The finite element analysis were conducted using eight-node reduced integration elements in ABAQUS/CAE. And the result of finite element analysis was compared with the result of theoretical analysis. The results of theoretical analysis agreed well with that of ABAQUS analysis. Therefore, the theoretical modeling could be used for the draft design of turn-buckle.