Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Analysis of the bond-slip performance of steel bars and steel fiber recycled concrete based on the constitutive relationship model
Get PDFIn order to promote the application of steel fiber recycled concrete in projects such as roads and bridges, 25 groups of steel fiber recycled concrete with different mix proportions were designed, taking the replacement rate of recycled aggregate and the volume fraction of steel fibers as experimental parameters, and 77 steel bars and steel fiber recycled concrete bonded specimens were made and pasted with strain gauges for the pull-out test. The research results showed that the greater the replacement rate of recycled aggregates was, the lower the bond strength between steel bars and steel fiber recycled concrete was; in the range of 0~1.2%, the higher the mixing amount of steel fibers was, the greater the bond strength of the specimen was; in the range of 0~1.6%, the higher the mixing amount of steel fibers was, the greater the slip value of the specimen under the peak load was; the addition of steel fibers improved the failure behavior of the recycled concrete pull-out specimens; the test specimens mainly had pull-out failure when the mixing amount of steel fibers was 1.2% and 1.6%. Finally, this study modified the bond-slip constitutive relationship model of steel and steel fiber recycled concrete, analyzed the influence of the replacement rate of recycled aggregate and the mix proportion of steel fibers on its bonding performance, and compared the results with the test results. The results demonstrate that the test curve is in good agreement with the fitted curve, which can provide theoretical support for engineering applications. 
RC beams damaged by cracking and strengthened with NSM CFRP/GFRP rods
Get PDFThe near surface mounted (NSM) method of inserting fiber reinforced polymer (FRP) elements (rods or lamina) into notches has been shown to be a good way for restoring reinforced concrete (RC) elements. The knowledge about the use of Glass-FRP rod following the NSM to reinforce RC beams is limited. This paper deals with the analysis of static and dynamic behaviour of RC beams with and without strengthening. The response of RC beams was assessed at different concrete’s damage level by non-destructive vibration tests. First, a couple of beams have been analysed: one RC beam subjected to bending and under vibration tests; another one beam, damaged by bending and strengthened with NSM Carbon-FRP rods tested again under vibration. Further, one RC beam damage was analysed under bending and vibration tests without strengthening; successively, the beam model with NSM GFRP rod has been tested following the same loading path. Below experimental results are shown and commented; in particular, changes in frequency values are related to the evolution of damage level affected RC beams with NSM CFRP and GFRP rods
Enhancement of circular RC columns using steel mesh as internal or external confinement under the influence of axial compression loading
Get PDFReinforced concrete (RC) columns cannot get supreme confinement by using the customary steel stirrups reinforcement because of the requirements for the spacing distances between the stirrups in addition to concrete continuance trouble. For this, Steel Mesh (SM) externally wrapped around the outer perimeter of the column as contributory confinement are being widely used due to its features. Limited tests focused on using SM for the internal confinement around the reinforcing cage of RC columns. Moreover, no experimental comparison was presented between RC columns internally and externally confined using SM. This paper investigates experimentally the behavior of circular RC columns confined internally or externally by SM. Six short RC columns have been subjected to axial loading until failure. The main studied parameters were SM schemes, number of SM wraps, SM position (internally or externally), and the steel stirrups existence. Results demonstrated that SM could decrease the crack opening, diminish the concrete spalling, increase the maximum failure load, and enhance the ductility, energy absorption, and column stiffness. Furthermore, the partially internal confinement using two wraps of SM around the steel ties presented the maximum capacity with reasonable ductility. In general, internally confined columns showed better behavior than the externally confined one
Influence of themo-mechanical treatments and microstructural state on the fatigue behaviour of a weald seam: case of API X60 steel
Get PDFThe aim of this work is the study of the fatigue behaviour of API X60 steel and the influence of thermal and mechanical treatments. The evaluation of the integrity and safety of welded structures dictates the approach taken in this research. The microstructural observations on the different zones of the weld seam indicates that the variation of heterogeneous structure is a progressive destruction of the strips of lamination which cause a new phase leading to a drop in the mechanical properties requiring treatment after welding. The fatigue cracking rate diverges beyond the threshold of DK, but no deviation of the crack from its propagation axis was noticed, which confirms the correct choice of filler metal over that of the base metal with an overmatching M = 1.1, and the treatments applied to the structure. This fatigue cracking rate transversal to the welding direction initially presents an aspect similar to that of BM but registers a delay as soon as the crack tip enters the second zone (HAZ) then it progresses rapidly. This evolution is characterized by a disturbance due to the repeated change of microstructure
The critical influence of some “tiny” geometrical details on the stress field in a Brazilian Disc with a central notch of finite width and length
Get PDFThe role of some geometrical characteristics of the notches machined in circular discs, in order to determine the mode-I fracture toughness of brittle materials, is discussed. The study is implemented both analytically and numerically. For the analytic study advantage is taken of a recently introduced solution for the stress- and displacement-fields developed in a finite disc with a central notch of finite width and length and rounded corners. The variation of the stresses along strategic loci and the deformation of the perimeter of the notch obtained analytically are used for the calibration/validation of a flexible numerical model, which is then used for a parametric investigation of the role of geometrical features of the notched disc (thickness of the disc, length and width of the notch, radius of the rounded corners of the notch). It is concluded that the role of the width of the notch is of critical importance. Both the analytic and the numerical studies indicate definitely that ignoring the accurate geometric shape of the notch leads to erroneous results concerning the actual stress field around the crown of the notch. Therefore, it is possible that misleading values of the fracture toughness of the material of the disc may be obtained
Wavelet-based multiresolution analysis coupled with deep learning to efficiently monitor cracks in concrete
Get PDFThis paper proposes an efficient methodology to monitor the formation of cracks in concrete after non-destructive ultrasonic testing of a structure. The objective is to be able to automatically detect the initiation of cracks early enough, i.e. well before they are visible on the concrete surface, in order to implement adequate maintenance actions on civil engineering structures. The key element of this original approach is the wavelet-based multiresolution analysis of the ultrasonic signal received from a sample or a specimen of the studied material subjected to several types of solicitation. This analysis is finally coupled to an automatic identification scheme of the types of cracks based on artificial neural networks (ANNs), and in particular deep learning by convolutional neural networks (CNNs); a technology today at the cutting edge of machine learning, in particular for all applications of pattern recognition. Wavelet-based multiresolution analysis does not add any value in detecting fractures in concrete visible by optical inspection. However, the results of its implementation coupled with different CNN architectures show cracks in concrete can be identified at an early stage with a very high accuracy, i.e. around 99.8%, and a loss function of less than 0.1, regardless of the implemented learning architecture
Preliminary results on the effects of orthopedic implant stiffness fixed to the cut end of the femur on the stress at the stump-prosthetic interface
Get PDFA lot of trans-femoral amputation patients experience skin breakdown due to the pressures and shear stresses in the stump-prosthesis interface. In this study, a finite element model was employed to investigate the stresses at the stump interface in the case of an orthopedic implant fixed to the cut end of the femur. By changing the stiffness of this implant, we aim to see how the stiffness of this implant affects the stresses in the interface between the amputated limb and the prosthesis. To find out the effects of implant stiffness, five values for the elastic modulus, ranging from 0.1 to 0.5 Mpa, with an interval of 0.1 Mpa were employed in the implant structure of the FE model.
Obtained results show that the implant played important role in reducing the stresses at the stump-prosthesis interface where the contact pressure did not exceed 53 Kpa and 17.3 Kpa for shear stress in the stiffer case of an implant, while the contact pressure in the case of femur without implant exceeded 79Kpa and 42 Kpa for shear stress. We also noted that the intensity of the contact pressure and the shear stress is proportional to the stiffness of the implant, as the greater the implant stiffness, the higher the peak of these stresses
Optimization of Ultimate Tensile Strength with DOE Approach for Application FSW Process in the Aluminum alloys AA6061-T651 & AA7075 -T651
Get PDFAs it is imperative to control the materials development processes well, in parallel, it will be necessary to constantly adapt very efficient assembly methods. Friction stir welding makes it much easier for us to fusion the aluminum alloys like AA6061-T651 and AA7075 -T651. But we noted the difficulty of containing its many parameters such as the welding speed, the rotation speed and the type of pin used during the operation to optimize mechanical properties and in particular to obtain high rupture strength with the tensile test. This why in this paper we treat carefully this process in order to define it drastically, by using the design of experiment method which is an original approach that resides in the possibility of interpretation of experimental results with a minimal effort on the experimental level whichever generates the minimization of the necessary number of experiments and allows a saving in time and in financial cost
Numerical Assessment of Reinforced Concrete Beams Strengthened with CFRP Sheets under Impact Loading
Get PDFThis paper investigates numerically the behavior of Reinforced Concrete (RC) beams, strengthened using Carbon Fiber Reinforced Polymers (CFRP) sheets, subjected to impact loading. Three-dimensional finite element analysis was performed and its results were verified against experimental ones available in the literature showing good agreement. Then, a comprehensive parametric study was performed to investigate the effect of studied parameters on the strengthened RC beams. The main studied parameters were type and size of reinforcing bars, geometric characteristics of externally bonded CFRP sheets (width, length, and thickness), impact velocity, and the position of the impactor with respect to the beam. Results showed that the use of externally bonded CFRP sheets enhanced the beam capacity and failure mode, and reduced the mid-span deflection. Moreover, a reduction in the mid-span deflection was observed due to the use of CFRP bars as internal reinforcement. On the other hand, the deflection was increased due to the increase of the impact velocity, and the change of the impact load position
Lumped damage mechanics as a diagnosis tool of reinforced concrete structures in service: case studies of a former bridge arch and a balcony slab
Get PDFReinforced concrete structures may need repair in order to ensure the designed durability. Such necessity vary in cause and effect, but the structural diagnosis serves as the basis for adopting intervention measures. The assessment of the structural condition usually is made in loco, but sometimes numerical analyses are required as a low cost and effective preliminary diagnosis. In general, numerical analyses use hundreds or thousands of finite elements and nonlinear theories that are not often used in engineering practice. As an alternative, lumped damage mechanics (LDM) uses key concepts of classic fracture and damage mechanics in plastic hinges throughout well-known quantities such as ultimate moment and cracking moment. Such theory describes the concrete cracking by a damage variable, which can be used as a diagnosis criterion. Therefore, this paper presents LDM as a diagnosis tool to analyse actual structures. The case studies presented in this paper are a former bridge arch tested in China and a balcony that collapsed in Brazil. The results show that LDM numerical response of those structures are quite close to laboratory observations (former bridge arch) and in loco measurements (balcony)