The analytical prediction of residual flexural strength of corroded beams has been revisited in the context of relatively larger size beams reinforced with larger diameter tension bars to exclude the size-effect of beams in the proposed modelling and to improve further the accuracy of the analytical method. Most of the past research, including that conducted by the authors, has used smaller size beam specimens to generate test data for modelling. A new experimental programme was undertaken using 48 beams of width 200 mm and depth varying from 215 to 315 mm, reinforced with tension bars of 16 and 18 mm in diameter. The beams were subjected to a varying degree of corrosion damage using accelerated corrosion and then they were tested in a four-point bending test to determine their residual flexure capacity. When the two-step analytical procedure, proposed by the authors in an earlier work to determine the residual flexural strength of corroded beams, was applied to the test beams used in this new experimental work, it was found that the theoretical predictions were consistently lower than the actual flexural strength of the beams. The search for a more compliant prediction method has been accomplished by proposing a new correction factor that replaces the previous one by correctly taking into account the size-effect of the tension bars. In order to show the accuracy of the proposed method, the test data published by other researchers have been compared with the values predicted by the proposed method. The comparisons clearly show that the proposed method yields values which are in good agreement with the test data from this and other experiments, lending confidence to the proposed method to serve as a reliable analytical tool to predict the flexural capacity of a corroded concrete beam.
Initiation of corrosion of steel in reinforced concrete (RC) structures subjected to chloride exposures mainly depends on coefficient of chloride diffusion, , of concrete. Therefore, is one of the key parameters needed for prediction of initiation of reinforcement corrosion. Fick's second law of diffusion has been used for long time to derive the models for chloride diffusion in concrete. However, such models do not include the effects of various significant factors such as chloride binding by the cement, multidirectional ingress of chloride, and variation of with time due to change in the microstructure of concrete during early period of cement hydration. In this paper, a review is presented on the development of chloride diffusion models by incorporating the effects of the key factors into basic Fick's second law of diffusion. Determination of corrosion initiation time using chloride diffusion models is also explained. The information presented in this paper would be useful for accurate prediction of corrosion initiation time of RC structures subjected to chloride exposure, considering the effects of chloride binding, effect of time and space on , and interaction effect of multidirectional chloride ingress.
This computational investigation focused on numerical modeling of the shear behavior of ultra-high-performance concrete (UHPC) beams reinforced longitudinally with high-strength rebars and ordinary-strength steel (stirrups). Nonlinear three-dimensional finite element model, using the concrete damaged plasticity model and material properties obtained from uniaxial compressive and tensile laboratory tests, was conducted to simulate UHPC concrete beams within a commercial finite element software package ABAQUS 6.13. This investigation included the effects of various parameters; shear span-to-effective depth ratio (a/d), volume fraction of steel fibers, V f , longitudinal reinforcement ratio, ρ, and stirrups spacing, s, on shear behavior of UHPC beams. Numerical results compared with previously obtained experimental results in terms of shear force-midspan deflection and cracking-propagation behaviors. The results showed that finite element analysis predicted the shear behavior of UHPC beams in good agreement with the experimental data and predicted the response of the beam with variation in various parameters with a good accuracy. K E Y W O R D S ABAQUS, concrete damaged plasticity (CDP) model, high-strength rebars, numerical modeling, shear behavior, ultra-high-performance concrete (UHPC) beams 1 | INTRODUCTION New construction methods and technologies are growing to extend the lifespan of existing and new structures. As part of the new technologies, new developments in concrete are gradually changing the design and construction worlds. 1Invented about two decades ago, ultra-high-performance concrete (UHPC) is characterized by steel fibers, cement, silica fume, fine sand, superplasticizer, and very low watercement ratio. 2 This new-generation concrete material possesses high tensile and compressive strengths, high ductility, low permeability, and good durability because of its dense microstructure. The use of UHPC allows designers to select lighter sections and longer spans for structural members. 3,4 The inclusion of steel fibers in UHPC improves its mechanical properties, reduces its brittleness, and alters the crackpropagation behaviors. 5 The shear behavior of concrete is one of the very important, but complex, topics in concrete structures, which has been investigated by many researchers. The brittle shear behavior of concrete in structural elements makes experimental investigations difficult to conduct, time consuming, expensive, and need more human resources to accomplish, as compared to finite element model (FEM). 6 Although many aspects of structural behavior of reinforced UHPC beams have been studied experimentally (e.g., in References 7 and 8), a limited number of numerical studies have been reported in the literature on the shear behavior of UHPC beams. Schramm and Fischer 9
This paper presents a study on the shear behavior of reinforced concrete (RC) beams strengthened by jacketing the surfaces of the beams using ultra-high performance fiber reinforced concrete (UHPC). The surfaces of the RC beams were prepared by sandblasting and UHPC was cast in situ over the surfaces of RC beams. The beams were strengthened using two different strengthening configurations; (i) two longitudinal sides strengthening (ii) three sides strengthening. The bond between normal concrete and UHPC was examined by conducting splitting tensile strength and slant shear strength tests on composite cylindrical specimens cast using normal concrete and UHPC. The control and strengthened beam specimens were tested using four-point loading arrangement maintaining different shear span-to-depth ratios. The results of tested beams showed the beneficial effects of strengthening the RC beams using UHPC, as evident from enhancement of the shear capacity and shifting of the failure mode from brittle to ductile with more stiff behavior. In addition, a non-linear finite element model (FEM) was developed to examine the sufficiency of the experimental results used to study the shear behavior of control and strengthened beams. The failure loads and the crack patterns determined experimentally matched well with those predicted using the proposed model with a reasonably good degree of accuracy.
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