جستجوی مقالات مرتبط با کلیدواژه "نقص" در نشریات گروه "عمران"

The most important point in performing the Pile Integrity Test (PIT) is the correct interpretation of the results. This insitu tests is very useful in the estimation of the pile length embedded in the soil or the control of the cross section of bored piled where the quility of the pile construction is in doubt. Two common defects of the bored piles are buldging and necking of the pile cross section which correspond to the over-size and narrowing of the pile diameter alonng the pile length. Thses two anolamies in the pile geometry inflence the pile functionality and an approperiate reaction is required. Correct identifications of the length and dpeth of an anomaly are among the factors that are influenced by the anomaly location and the interaction of the waves passing through the pile. In this research, an attempt is made to interpret the results of PIT by examining the dimensions and location of anomalies in different parts of the pile as well as the effect of the presence of soil on the obtained results. PIT is simulated by the numerical finite difference method and the results have been investigated. The pile head is loaded by a semi-sinusoidal impact which is defined as a compressive pressure over a circular region at the cross section centroid during a short period of time. The verification of the simulations is established by the compariosn of the results with those one-dimentional wave theory which is based on the arrival time of the impact wave to the reciever situated on the pile head. In addition, by changing the position of the wave vreciving in the numenrical mode, it was shown that the best place to install the accelerometer as the recivier would be at the distance of 0.6R from the pile center where R is the pile radius. This finding is consistent with the results of previous studies which confirms the validiy of the simulations. According to the results, the existance of the soil around the pile causes to deform the figure of the waves and it required to modify the records before a correct interpretation. The soil atound the pile plays a role of damper of the waves passing through the pile and it causes that the magnitude of the peaks observed in the records diminish and the interpretaion may not be so easy as that in a free pile. For the pile embeded in the soil, the closer the anomaly location is to the pile head, the less the damping effect of the soil is and thus, the wave forms are more similar to the free pile. Based on the findings of this study, to interprete correctly the PIT results, it is recommended to use the first peak of the recorded velocity if there is a necking defect, while the use of the second peak is recommneded for a buldging defect to estimate the anomaly depth based on the free pile diagrams.It is also seen that as the defect length increases to about twice the diameter of the pile, the peak value of the velocity changes (in most cases, it increases) and remains almost constant at larger lengths.

In recent years, engineers have faced many structural problems, such as buckling, corrosion and excessive loading in damaged steel structures. The labor force's mistakes during welding and the destruction of the weld are among the many problems in steel structures. Therefore, strengthening and repairing the welding place in steel structures is inevitable. In this article, the influence of polymers reinforced with carbon fibers for strengthening steel studded double columns with defects caused by welding has been investigated. For this purpose, seven steel columns were modelled in Abaqus finite element software. A CONTROL column was modelled as the first sample with no defects and welded all over. The rest of the defective samples were reinforced using CFRP fibers. On the other hand, strengthening using CFRP fibres to improve the location of the defect was investigated in detail for three samples. Reinforcement of these sections using CFRP fibers is not only an effective method to increase the maximum axial force in these columns, but it has also helped to improve resistance and delay local buckling in them. According to the results, it was observed that among all the samples, the maximum bearing capacity is related to the 2UW3 model, and it has increased by 29.9% and 21.7% in the laboratory sample and numerical modelling, respectively, compared to the 2UW3C1 sample. In addition, 2UW3C1 and 2UW1C1 samples have the highest hardness among laboratory and numerical modelling samples, respectively.

In this paper, the performance of box steel columns with corrosion is investigated. Thus the steel columns are made with different defect locations (6 modes) and are subjected to temperatures of 20 °C and 700 °C. Then, two retrofitted methods (CFRP composites and steel plates) are used in the defect area in order to improve the performance of columns. Afterwards, bearing capacity of all column specimens (38 specimens) has been obtained. The results indicate a decrease in the bearing capacity of the columns and weakness in their performance due to the two factors of defect and heat so that the greatest decrease in the column compression strength is about 32% and 35% due to defect and high temperature, respectively. Also, the comparison of retrofitting methods indicates that the use of composite is more effective in improving the performance of steel columns. Finally, For further investigation, 5 specimens are modeled in ABAQUS finite element software and the results are compared with similar experimental results.

Recently, application of concrete filled steel tubes (CFST) columns has been widely trended due to their several advantages. Some of the CFST columns may been damaged due to different problems and need to be strengthened. One of the methods which can be applied to improve the efficiency of the damaged columns is the strengthening using fiber reinforced polymers (FRP). The present research investigates the effects of strengthening deficient CFST columns trough numerical and experimental studies. The numerical simulation has been adopted using ABAQUS software in 3D simulation method, and the experimental test has been done using steady pressure test machine. The defects created horizontally and vertically at the center of the columns. The specimens include one control and four deficient specimens which two of them were strengthened using four carbon fiber reinforced polymers (CFRP) layers. The results show that the horizontal deficiencies in CFST columns resulted the most reduction in load bearing capacity in comparison with Control (-46%). Strengthening using four CFRP layers (two-transverse and two-longitudinal) resulted in improving load bearing capacity appropriately (approximately %27 increment in comparison by the deficient column). The application of CFRP improved confinement strength and controled the local failures.

Failure and buckling in shell structures, including silos, can be created for various reasons such as distortion, defects created during construction, defects created during operation, or environmental factors, etc. Silos can be subjected to a variety of lateral and axial loads, but since they are in fact affected by the combination of these loads, silos behave under the influence of composite loads. The silos in this research are hot-rolled and located on the ground. The variables of this research are type and scope of defect. Silos are also evaluated in semi-filled and semi-solid state. The model silos were analyzed in ANSYS software. The radial radial neural network RBF was used to predict the buckling capacity of the cylindrical shells. The results of this study indicate that artificial neural networks are a good tool for predicting buckling capacity of silos with defects.