Research On Prediction Methods Of Girder Deflection For Large Tonnage Bridge/gantry Crane

Lifting appliance is an important basic equipment in national industrial enterprises, is widely used, the number of machinery using in the country was about 2.1 million units, more people pay more attention to their security problem.The inspection system about crane is implemented compulsorily in China. When inspecting cranes for safety reasons, the deflection value of the crane girder under the rated load was one of the important safety indicators to assess the state of metal structures.The recorded deflection must not exceed the critical value specified in the relevant national or international regulations/standards. For heavy-duty cranes, the rated load required for acceptance tests could be enormous, for instance, reaching thousands of tons. To obtain, transport and apply such a large dead weight is expensive and difficult. In some cases the rated load test could not be performed because it was restricted by the location and the environment. If the crane load test is not carried out, the subsequent use of crane is illegal, but also will bring huge hidden trouble to the safe production. A large number of such cases exist, in practical application, when the test weight: is insufficient, it is an urgent problem to be solved that the safety and reliability of crane structure is judged by testing. Therefore, it is very necessary to study on prediction methods of girder deflection for large tonnage bridge-gantry crane, is also very meaningful.Traditional prediction method of crane girder deflection is linear, the calculation accuracy needs to be improved. In this paper, a in-depth study was launched to prediction methods of girder deflection for large tonnage bridge-gantry crane. The methods based on the concept of generalized stiffness, combining methods such as the classical elasticity theory, energy method, support vector machine theory and experimental study. These methods considered the effects of service years, level of fatigue, times of heavy loads, manufacturing and installation processes on girder deflection. These methods predict the deflection and tests using lower rated loading tests which can be carried out economically and with better practicability. It provides more theoretical significance and practical value to the large tonnage bridge-gantry crane inspection and girder deflection prediction.The main contents are as follows.1. Through researching the relationship between the bending moments of legs and on the girder mid-span deflection, using the virtual work principle and establishing the Lagrange function, it is concluded that as follows. The larger the stiffness ratio, the smaller horizontal binding force. The smaller the stiffness ratio, the smaller the girder deflection. When some factors (such as temperature) influence is very small, the support legs at two sides are designed into the same size, the structure stiffness is best, minimum material consumption. That is to say, when the inertia moment of the legs at two sides is equal, the structure stiffness for the gantry-frame is the best. The range of stiffness ratio in 0.5-1.5 is more reasonable, not more than 2.2, it should not be less than 0.3.2. Under the inertia moment of the left is not equal to the right, the deflection polynomial was derived in three-small-loads method, using the classical mechanics theory and energy method with the help of the concept of generalized stiffness. The deflection polynomial coefficients are calibrated by the small load test data, and the deflection prediction function is obtained. Three-small-loads method can accurately predict the large tonnage bridge/gantry crane girder deflection, and can be realized by computer program, simple, strong operability. Under used only small fixed weight load in the field, three-positions small load test method is used to prediction deflection. When the fixed load is applied to the position of l/2,l/3 and 2l/3 of girder. The girder deflection value can be obtained under small load at the position of l/2,l/3 and 2l/3,and the actual inertia moment of girder and two side legs can be obtained. In this way, the deflection of the large tonnage bridge/gantry crane are predicted through the data of the three-positions method in the small load test.3. Researched the gantry-frame structure deformation through the experiment, the deflection and the load is not a linear relationship. At the beginning of loading, the stiffness of gantry-frame structure was large, and then it decreased, increased, decreased, and increased successively. Load-deflection curve presented a turning point when the load reached a certain value, and the structure stabilized. The structure stiffness increased along with the increasing of load which caused deformation of gantry-frame structure. Therefore, when the load was applied to the mid-span, the deformation of the gantry-frame structure would resist to external load and do work. That is the gantry-frame structure deformation resulted in the structure stiffness increase (for the load position). After the gantry-frame structure was loaded at the mid-span point, it not only produced vertical deflection but also generated the horizontal displacement. The relationship between the deflection and the horizontal displacement is nonlinear also.4. The mathematical model is established for universal large-span and heavy-duty gantry cranes. The analytical solution for the mid-span deflection of gantry-frame structure girder is derived and obtained based on the variation principle by considering the coupling effect of the bending moments of girder and legs and the axial force and the secondary bending moments. The calculation precision for the nonlinear analytical solution of the girder deflection, improves about 12% comparing to pre-existing equations.5. The application of SVM in crane deflection prediction is researched. The deflection prediction method based on SVM combined with the field knowledge and support vector regression. Based on the revealed main parameters affecting deflection, the input sample factors for SVM were determined. The actual test data and experimental data of the crane deflection include the effects of service years, level of fatigue, times of heavy loads, manufacturing and installation processes on girder deflection. The SVM model was trained through the experimental and measured data, and the SVM model parameters was optimized. Finally, the SVM prediction model was obtained. Namely a SVM function was obtained, realizing the deflection prediction.Traditional deflection prediction methods for large tonnage bridge/gantry crane have many limitations. The research results in this dissertation can not only greatly reduce the cost of loading test, but also reduce the detection cost and work of the quality inspection departments, and shorten the inspection cycle. It can achieve efficient, energy-saving. It is important significance and utility value, and extensive application prospects.