Process of cracking in reinforced concrete beams (simulation and experiment) (original) (raw)
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Process of cracking in reinforced concrete beams (simulation and experiment).PDF
The paper presents the results of experimental and theoretical investigations of the mechanisms of crack formation in reinforced concrete beams subjected to quasi-static bending. The boundary-value problem has been formulated in the framework of brittle fracture mechanics and solved using the finite-element method. Numerical simulation of the vibrations of an uncracked beam and a beam with cracks of different size serves to determine the pattern of changes in the spectrum of eigenfrequencies observed during crack evolution. A series of sequential quasi-static 4-point bend tests leading to the formation of cracks in a reinforced concrete beam were performed. At each loading step, the beam was subjected to an impulse load to induce vibrations. Two stages of cracking were detected. During the first stage the nonconservative process of deformation begins to develope, but has not visible signs. The second stage is an active cracking, which is marked by a sharp change in eingenfrequencies. The boundary of a transition from one stage to another is well registered. The vibration behavior was examined for the ordinary concrete beams and the beams strengthened with a carbon-fiber polymer. The obtained results show that the vibrodiagnostic approach is an effective tool for monitoring crack formation and assessing the quality of measures aimed at strengthening concrete structures.
Investigation of the effect of cracks on the vibration processes in reinforced concrete structures
The validity of the mathematical model describing the propagation of vibrations in the reinforced concrete structures (RC structures) was verified by comparing the experimental and numerical data. The proposed model allowed us to perform numerical experiments aimed at comparing vibrorecords obtained for the structure without defects and the structure with typical fracture caused by crack formation. Based on the results of comparison, an informative diagnostic parameter was proposed. This parameter makes it possible to control the nucleation and growth of cracks in a RC structure.
Mechanics of Solids, 2015
The contemporary construction industry is based on the use of reinforced concrete structures, but emergency situations resulting in fracture can arise in their exploitation. In a majority of cases, reinforced concrete fracture is realized as the process of crack formation and development. As a rule, the appearance of the first cracks does not lead to the complete loss of the carrying capacity but is a fracture precursor. One method for ensuring the safe operation of building structures is based on crack initiation monitoring. A vibration method for the monitoring of reinforced concrete structures is justified in this paper. An example of a reinforced concrete beam is used to consider all stages related to the analysis of the behavior of natural frequencies in the development of a crack-shaped defect and the use of the obtained numerical results for the vibration test method. The efficiency of the method is illustrated by the results of modeling of the physical part of the method related to the analysis of the natural frequency evolution as a response to the impact action in the crack development process.
Mechanics of Solids, 2015
Construction of numerical models which reliably describe the processes of crack formation and development in reinforced concrete permit estimating the bearing capacity and structural strength of any structural element without using expensive full-scale experiments. In the present paper, an example of four-point bending of a rectangular beam is used to consider a finite-element model of concrete fracture. The results obtained by quasistatic calculations and by solving the problem with inertia forces taken into account are compared. The kinetic energy contribution to the total mechanical energy of the system at the crack origination moment, which is greater than 30%, is estimated to justify the expediency of taking the inertia forces into account. The crack distribution characters obtained numerically and observed experimentally are compared. It is shown that the leading role in the evolution of the crack formation process is played by the mechanism of fracture of bonds between the reinforcing elements and the concrete.
Time-Dependent Behavior of Cracked Concrete Beams Under Sustained Loading
2013
Under sustained loading, the propagation of cracks in concrete is assumed to be related to the elastic deformation, material parameters and time. Based on the fictitious crack model (FCM), a finite element method is proposed to explain the behavior of cracks in time using current constitutive relations to approximate the time-dependent crack strain. Experiments have been performed on small concrete specimens to determine the cracking strain and to validate the finite element model. For flexural cracks, a creep coefficient model is adopted for bulk creep and a cracking strain rate based on test results is employed. For shear cracks fracture mode II is considered as well. The development of concrete strength in time is taken into account. The model is applied to predict the behavior of a cracked concrete beam subjected to sustained loading. Finally a comparison is made between the results of different approaches.
Damage assessment in reinforced concrete beams using eigenfrequencies and mode shape derivatives
Engineering Structures, 2002
The use of changes in dynamic system characteristics to detect damage has received considerable attention during the last years. This paper presents experimental results obtained within the framework of the development of a health monitoring system for civil engineering structures, based on the changes of dynamic characteristics. As a part of this research, reinforced concrete beams of 6 meters length are subjected to progressing cracking introduced in different steps. The damaged sections are located in symmetrical or asymmetrical positions according to the beam tested. The damage assessment consists in relating the changes observed in the dynamic characteristics and the level of the crack damage introduced in the beams.
Integrated fracture-based model for the analysis of cracked reinforced concrete beams
2015
Due to the rapid advances in the development of techniques for monitoring and retrofitting concrete, there is a need to revisit and generalize classical theories in order to better assess the strength of existing reinforced concrete structures and to encompass strengthening systems. An improved understanding of concrete cracking taking into consideration local phenomena such as tensile and compressive concrete softening as well as the bond between the reinforcement and the concrete is required. In this paper, a fracture-based model is developed to describe the cracking process in reinforced concrete by integrating different local phenomena to more precisely describe the flexural behaviour of reinforced concrete beams. The model results show a good correlation with experimental data obtained by testing small scale concrete beams subjected to three-point bending. The beams exhibited mode I fracture propagation and during testing crack measurements were undertaken using a non-destructi...
International Journal of GEOMATE, 2019
This paper presents the use of Frequency Response Functions (FRFs) to determine damage index and crack damage in reinforced concrete (RC) beam structures using vibration signals. Three methods consisting of Static Residual Strength Index (SRSI), Intermediate Load Damage Index (ILDI), and Modified Flexure Damage Index (MFDI) were adopted in this research. Impact tests on simply supported RC beams were conducted to measure vibration signals on the beams by recording the curvature mode shapes during the experimental testing. The ICATS software was carried out to capture the Frequency Response Functions (FRFs) data at each load step. Cracks occurred on the beam due to the applied load, reducing its natural frequency, indicating an initial stage of the damage having occurred. The midspan vertical deflection of the beam results in its mode shape changes and curvatures increased. The mode shape curvature square difference was used to determine the extent of damage and location of damage indicating the beam residual strength. A numerical algorithm of the finite difference method was performed using the FRFs data to calculate the different FRFs for undamaged and damaged beam conditions based on the mode shape curvature square (MSCS) method. The damage index and crack detection based on the numerical computation were determined by subtracting the MSCS between undamaged to damaged beams. The resulting accuracy of the damage index used to define the level of damage and damage location was absolutely achieved by comparing the numerical and observed experimental results.
International Journal of Safety and Security Engineering
It has been well understanding that the occurrence of various crack patterns in the building during its construction life (from first time of construction up to finishing) then subjected to super imposed load or during the service life. Cracks developed due to exceeding of stresses more than the allowable strength, wherever happened on building component. This research works used the finite element method as a powerful tool to simulate the behavior of full constructed building with both concrete system and brick bearing wall. Where the adopted numerical procedure allows to the users to predict the response of building elements due to conventional state of loading. one of the most important response features was the cracking phenomenon, where the numerical model shown that its capability to predict the cracking sequence from the first time of initiating. The prediction of full response and behavior of each element and their connection, shown that the precise of factor of safety used ...
2010
Non-prismatic beams are widely used in many engineering structures such as bridge girder and long-span structure. Damages in a reinforced concrete beam are categorized as light/small, medium, and wide cracks. Every typical crack-damage requires a special treatment to strengthen its structure. A reinforced concrete beam experiencingcrack damages reducesits stiffness and strength. This paper presents an investigation of non-prismatic reinforced concrete beams considering curvature mode shape changes to locate damage. Laboratory vibration tests were undertaken in an attempt to measure crack damage taking into account a modified flexure damage index (MFDI) expressed in terms of frequencies.Based on experimental studies and finite element modeling show that this approach is practicallyused for detecting crack damage in reinforced concrete beams, which exhibit high non-linearity behavior.