At present, common finite element software incorporates a fixed crack model in numerical simulations by default. Application of a rotating crack model, which is more practical, requires secondary analysis by the finite element software, and there are few systematic studies in this aspect.
Vertical cracks were first observed at midspan when the loading force approached 40% , where is the peak load. These vertical cracks at midspan further propagated and widened with the increase of the applied load. When the loading force reached 85% , diagonal shear cracks simultaneously appeared on the side of the concrete and peeling of the steel plate appeared near the loading area on the top. The pattern of the cracks is shown in Figure 5, where the number denotes the load at the time of crack development at the respective location.
As is evident from the damage to SCS-2 and SCS-3 when , the mode of failure appears to be typical shear-compression failure. The failure process was rapid. The failure load and the load at the time of development of diagonal cracks were similar. The development of cracks in the diagonal section was more sudden, and the brittleness was more obvious in the specimen with smaller shear stud spacing. Due to the increased shear span ratio of specimens SCS-1 () and SCS-4, the concrete failure appeared to be bending one, and the concrete failure of SCS-4 was the result of the failure of the normal section of the bending member, which was sparsely reinforced. Therefore, the mode of failure of the steel plate-concrete composite slab was related not only to the shear stud spacing but also to the shear span ratio of the composite slab.
The load-displacement relations of the three composite slabs and the plain concrete slab are shown in Figure 6, where the x-coordinate denotes the midspan deflection and the y-coordinate denotes the load of the specimen. As shown in Figure 6, the loading process of the steel plate-concrete composite slabs could be separated into three stages:(a)Elastic stage: the stage lasted from the start of loading until the elastic shear capacity stage. All parts of the specimen were in the elastic state, and the relationship between the shear stress and midspan deflection was essentially linear for all specimens.(b)Elastoplastic stage: when cracks appeared on the concrete, the stiffness of the specimen decreased and deflection development was accelerated. The load-displacement curve of the composite slab was nonlinear. Vertical cracks appeared on the concrete at the midspan and the cracks widened as the load increased.(c)Descending stage: as the load was continually increased, once a certain load-carrying capacity of the steel plate-concrete composite slab was reached, diagonal cracks appeared in the concrete. At this point, the load-carrying capacity was at its maximum and shear failure occurred at the side of the concrete. Due to the increase in shear span ratio and decrease in shear stud spacing, the descending branch of the curve was smooth. The three composite slabs demonstrated outstanding ductility compared to SCS-4.
Here, two models were used to simulate the concrete cracking: (a) the rotation crack model using the developed UMAT subprogram of the concrete rotation crack model (denoted as RCM) and (b) a fixed crack model (denoted as FCM), which is presented in the next section.
According to the fixed crack model, the direction of the cracks that appeared after the first was identical to that of the first. In other words, the shear stress at the crack surface increased until shear locking occurred. In practice, crack direction angles vary as the load increases, and the shear stress at the crack surface remains steady or even decreases. However, the fixed crack model cannot simulate the shear softening problem of concrete in practical situations and it overestimates the analytical result of shear capacity. The rotation crack model can demonstrate the variation in angle direction, as presented in the next section. The stiffness matrix can vary at any time under different crack directions, and the shear stress at the crack surface can be better simulated.
The UMAT in ABAQUS was used to define the subroutine of the MCFT for describing the rotation crack model for the concrete. When the state variant and strain increment were input by the main program, the UMAT solved the stress increment according to the strain variant, solved and returned the Jacobian matrix to develop the global stiffness matrix, and then temporarily stored the state variant for the next increment. The key was to solve the Jacobian matrix.
Because the coordinates and positive direction were different before and after the appearance of cracks in the concrete, the Jacobian matrix was also different. When , where is the principal tensile strain, refers to the cracking strain, the uniaxial tensile stress of concrete is equal to the value before cracking, and the shear modulus of concrete is represented by , as recommended by Zhu et al. . The derived stiffness matrix is shown in equation (8); when , the uniaxial tensile stress is equal to the value after cracking, and the other parameters are not varied. According to the transformation of coordinates, the transformation matrix is obtained in equation (9) and the stiffness matrix after the appearance of cracks is shown in equation (10). In these formulas, is the average tensile stress, is the average compressive stress, is the principal compressive strain, θ is the directional angle of principal strain, is the average shear stress in the 1-2 coordinate, and is the average shear strain in the 1-2 coordinate
In accordance with the MCFT, the cracked concrete was treated as a new type of material. The reinforcement and cracks were smeared within the material so that no crack existed. The MCFT model used in this study required modification in order to cancel crack detection. The constitutional relationship of the MCFT was used as the compressive constitutional relationship of the concrete; the tensile constitutional relationship is represented by equations (11) and (12) in accordance with the modification of coefficient due to the cancellation of crack detection.
The tensile stress-strain relationship of concrete is written aswhere is the elastic modulus of concrete, is the principal tensile stress, is the cracking stress, is the principal tensile strain, and is the cracking strain.
The results of simulation and the experimental data are listed in Table 3, in which is the experimental shear capacity, is the shear capacity calculated by the RCM, and is the shear capacity calculated by the FCM. As shown in Table 3, in comparison to the results obtained by the FCM, the shear capacity acquired by the RCM better matches that in the experimental results, validating the selection of the element and material properties of the shear model of the steel plate-concrete composite slab. The analytical shear capacity results were larger than the experimental results when the default concrete fixed crack model in ABAQUS was directly applied. The errors were equal to 8.7%, 9.5% 15.3%, and 40.2% for each specimen, with SCS-4 having the largest error. This was due to the use of the default fixed crack model in ABAQUS.
Figure 9 shows the load-displacement diagram during the numerical calculation and experimental process. It also demonstrated that the analytical results obtained by the RCM fitted the experimental curve better than the results obtained by the FCM, suggesting that the rotation crack model secondarily developed from ABAQUS was more suitable for the analysis of the steel plate-concrete composite slab shear capacity.
Abstract-In India railways transportation service is the cheap and the majority convenient mode of passenger transport and also for long distance and suburban traffic. The main cause of the accidents happened in railways are railway track crossing and unrevealed crack in railway tracks. Therefore, there is a need to have new technology which will be robust, efficient and stable for both crack detection in railway track as well as object detection. This project discusses a Railway track crack detection using sensors and is a dynamic approach which combines the use of GPS tracking system to send alert messages and the geographical coordinate of location. Arduino Microcontrollers used to control and coordinate the activities of this device.
disadvantage, here sensors are used, which will detect the crack accurately. The existing system is slow, tedious and time consuming. This system has GSM and GPS module which will give the real time location or coordinates in the form of Short Message Service (SMS) to the nearest railway station.
These types of incidents motivate us to think over the above mentioned issue and take necessary steps to protect those lives. Through our proposed system, we need to establish more modern and secure railway system. Besides this, there is no such type of technology or system in our country which can stop the collision between two trains coming from the opposite direction of each other on the same track. We actually think over this matter and motivated to do so. Moreover natural disaster can throw any object on the rail track which cannot be removed very quickly in the remote area. We thought if our system can detect those object or barrier and inform to the control room then they can take necessary steps 3 to avoid accident. Figure1 depicts the crack on track. The Rail transport is growing at a rapid pace in India. It is one of the major mode of transport but still our facilities are not that accurate, safer as compared to international standards. A survey on the internet states that about 60% of all the railway accidents is due to derailments, recent measurements shows that about 90% are due to cracks on the rails. Hence, it is not safer for Human Life. This needs to be at the utmost attention. These goes unnoticed and the properly maintenance of tracks is not done. 2b1af7f3a8