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Calculation and analysis of boom tip deflection of tower crane

Abstract: Based on the structural deformation analysis of a certain tower crane, this paper studies the contribution of the deformation of tower body, upper and lower supports, jib, etc. to the boom tip deflection, and puts forward measures to reduce the boom tip deflection as a guide

key words: deflection, contribution

excessive deflection of the boom tip during the operation of the tower crane will affect the working performance of the traction trolley. Therefore, in the design of the tower crane, the stiffness of each part of the tower crane must be reasonably controlled to make the deflection of the boom tip within a certain range; However, since the deflection of the boom tip is the comprehensive result of the deformation of the whole tower crane, and the structural shape and connection form of each part of the tower crane are very complex, and the load is also very complex, it is impossible to conduct manual analysis and calculation. This project uses I-DEAS software as the research platform, and based on the static structure analysis of a test tower crane that has been erected by the company, establishes the finite element model of the whole tower crane, calculates the boom tip deflection of the tower crane, and studies the contribution of the upper and lower support deformation, tower body deformation and boom deformation to the boom tip deflection. Aripack1 has been providing customized flexible and hard packaging materials for various companies and industries in North America, The correctness of the finite element calculation results is verified by experiments. On this basis, the main factors affecting the boom tip deflection are analyzed, and the measures to control the boom tip deflection are put forward

2 establish the finite element model of the tower crane

2.1 composition of the physical model

in order to facilitate the establishment of the finite element model of the test tower crane, the physical model shall not be greater than 0.1 times the diameter of the reinforcement, which is simplified as mainly composed of: jib, tower top, balance arm, jib pull rod, balance arm pull rod, slewing tower body, upper and lower supports, and tower body (including 8 tower body sections). There are three types of tower body sections of this type of tower crane, The design codes are a, B and C respectively, and the type A is the strengthened tower body section chord, and the specification is □ 135 × one hundred and thirty-five × 12. 16mm reinforcing plate is added inside, and the specification of B-type tower body section chord is □ 135 × one hundred and thirty-five × 12. The specification of C-type tower body section chord is □ 135 × one thousand three hundred and fifty-five × 10. The tower body section of the tower crane is composed of two models: B and C. The layout form from bottom to top is 4 (b) 3 (c) 1 (b); Since the deformation of other mechanisms contributes little to the deflection of the boom tip, it is not considered

2.2 lattice division of the model

due to the large number of components of the tower crane, the structure of each part is also quite different. In order to facilitate the division of the finite element model lattice and the modification of the model, the assembly finite element method is used to establish the finite element model of the tower crane

most of the tower crane structures are rod structures, and rod elements and beam elements can be selected. The web member element is also more suitable for the habit of manual calculation. Therefore, the beam member hybrid element model is adopted for the tower crane, that is, the main chord beam element and the web member member element. For example, the beam rod hybrid element model is adopted for the jib, tower top, slewing tower body and tower body section. The balance arm tie rod and the jib tie rod are represented by a rod element, and the deformation of the balance arm has little effect on the deflection of the jib tip, so it is simplified as a rigid rod element

the upper and lower supports are typical thin plate structures, so the upper and lower supports are divided into shell elements. The finite element elements of each component are connected, the upper support and the lower support are connected by rigid elements, and the different types of elements are connected by rigid elements; Release the end points of the beam elements of the boom root and the balance boom root; And adjust the normal direction of the shell element; Finally, carry out unit quality inspection. Generate the finite element lattice of the whole tower crane, as shown in Figure 1

2.3 boundary conditions

the definition of boundary conditions in this project is based on finite element, which includes constraint set and load set

(1) the constraint set

fixes the lower ends of the four main chords of the lowest tower section

(2) load set

this project is to study the deflection of the boom tip of the tower crane under the static action of the lifting weight. Therefore, the deformation position of the tower crane under the two load sets of no lifting weight and lifting weight must be calculated, and then the deformation amount of the tower crane under the action of lifting weight can be obtained from the two deformation positions of the tower crane. Under these two load sets, the tower crane does not consider the influence of wind load, dynamic load coefficient and various inertia forces. Here, the load only considers the role of self weight and lifting weight. For the jib, tower top, balance arm, jib pull rod, balance arm pull rod, and then within a period of time, the rod, slewing tower body, upper and lower supports, as well as the self weight of the tower body are loaded on each unit with gravity acceleration; The weight of other mechanisms is simplified as a concentrated load acting on the corresponding position of the physical model to generate the finite element model of the tower crane, as shown in Figure 1

no lifting weight (load Set1): refers to that the trolley on the tower crane is placed at the boom tip, and the lifting weight is zero

load set2: refers to the lifting weight of the trolley on the tower crane at the boom tip of 1.3t, and other loads are the same as those not lifted

the reference coordinate system is defined as: the X axis is right along the direction of the boom and coincides with the upper surface of the lower chord of the boom, the Z axis is vertically upward along the tower body, and the coordinate origin is located on the center line of the tower body

3 calculation and test result analysis

calculate the above tower crane finite element model, and get the vertical deflection of the boom tip of the whole tower crane and the contribution of each part of the tower crane to the vertical deflection of the boom tip (Table 2). The tower crane is tested under the same conditions. The results of the deflection of the boom tip and the deflection contribution of each part of the tower crane measured by theodolite are shown in Table 2. The relative error between the calculation and test results is within 9%, which is basically consistent, proving that the above finite element model and its calculation method are correct. The calculation and test results of the great development period of composite Aeronautical Materials Show (Table 2): when the tower crane is hoisted by the trolley at the boom tip, the vertical deflection of the boom tip reaches 783~800mm, which is mainly contributed by the tower crane and the tower body, of which the contribution of the tower crane is more than 350mm, accounting for more than 40%. The calculation further shows that: the contribution of the tower top is 177mm, the weight is 22.6%, and the contribution of the boom and the boom tie rod is 174mm, The weight accounts for 22.2%; The contribution of the tower body is 318~346mm, and the weight is more than 40%; However, the contribution of the slewing tower body and the upper and lower supports to the vertical deflection of the boom tip is relatively small, only 48 and 66mm respectively, and the weight only accounts for 6.2% and 8.4% respectively. Even if the sum of the contributions of these three parts is only 104~112mm, the weight only accounts for about 14%, which is far less than the contribution and weight of the tower crane and the tower body

after the above calculation and analysis, we can draw the following conclusions:

(1) the method of using the above finite element method to calculate and analyze the vertical deflection of the boom tip of the tower crane and the deflection contribution of each part is correct and feasible

(2) when the trolley of the test tower crane lifts weight at the boom tip, the vertical deflection of the boom tip reaches 783mm, the contribution of the tower body is 318mm, and the weight accounts for 40.6%, which is the main factor affecting the vertical deflection of the boom tip; The second is the tower top, the jib and the jib tie rod, with contributions of 177 and 174 mm respectively, with weights accounting for 22.6% and 22.2% respectively; The least affected are the upper and lower supports and the rotating tower body, with contributions of 66 and 48mm respectively, and the weights only account for 8.4% and 6.2% respectively; And the boom tip deflection h has the following approximate linear relationship with the number of tower body sections:

h=465 26.2na 38nb 43nc

where Na, Nb, NC are the number of tower body sections of the corresponding model, Na NB NC ≤ 16

the main measure to reduce the vertical deflection of the boom tip is to strengthen the stiffness of the tower body. In addition, strengthening the stiffness of the tower top can also effectively reduce the vertical deflection of the boom tip

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