Research Article - (2021) Volume 11, Issue 6
Received: 04-Jun-2021
Published:
01-Jul-2021
, DOI: 10.37421/2165-784X.2021.11.399
Citation: Sumit Guha. “Residual Life Assessment of EOT Crane.” Civil Environ Eng 11 (2021): 399.
Copyright: © 2021 Guha S. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Loads and working conditions of the cross-section of 36 m span crane beam can be analyzed by finite element method. Firstly, analysis of the stress and deformation is completed under the dangerous condition of crane beam based on the ANSYS software; secondly, found out the stress concentration and fatigue crack sensitive area of the bearing; finally, captured the position of fatigue crack. All these methods can provide strong basis for implementing effective monitoring to the state of the crane beam stress. Thus, ensure safe operation of equipment and improve equipment utilization rate in work
Fatigue cracks • Crane beam • Stress concentration • Finite element analysis
In recent years, the steel structure is widely used in industry and civil construction. Steel structure of crane beam is one of them which are used in industrial workshop electric hoist of wall or bridge supporting beam, wall cranes and other type of cranes. In industrial workshop, cross section of the crane beam is needed to be changed at joints as well as the production technology and economy requirements [1]. So, designers can use a variety of ways that can be summarized up as: cross-section of the end trapezoidal, cross-section of the end Angle variable and cross-section of the end arc variable. Trapezoid transition of variable cross-section bearing is widely applied in engineering practice because of its relatively high anti-fatigue performance. The stress of steel crane beam structure is complex; the repeated actions of vertical wheel crane pressure often does not meet the design stress, so fatigue crack happened at the parts [2]. Now, more and more crane beam fatigue cracks of heavy duty welded steel have been discovered, especially more serious on large tonnage of heavy duty steel crane beam. Because the early cracks that is tiny and more hidden, often ignored by people. Dozens of crane beams cracking in the original rough rolling mill of a steel plant in recent years, feeding oblique beam fatigue cracking in iron. All of these caused by fatigue crack or damage, are directly or indirectly affect the safety in production [3,4]. So the unit should census earnestly to deal with this kind of heavy duty welded steel crane beams, who find the problem and deal with as soon as possible to ensure the safe use of this important component. So in this paper, the variable cross section of the crane beam should be simulated to find out the static characteristics and fatigue performance by application of finite element analysis software ANSYS, which can determine the trapezoidal variable crosssection stress concentration, produce the detection of cracks and establish an effective monitoring system [5,6]. It can avoid unnecessary loss. The cracks often appear in the section of trapezoidal variable crane beam in actual engineering such as Figure 1.
Figure 1. Actual crack of crane girder.
Overall layout of crane beam
Crane beam is mainly composed of main girder and end beam, main beam and side beam is rigid connection, on both ends of the beam is equipped with wheel, in order to support bridge running on crane beam. Crane beam is generally designed as simply supported beam, whose characteristic is force, simple structure and convenient construction. The different column spacing in the workshop leads to the different heights of the adjacent crane beams [7]. And to make the same column rail surface elevation at the same height, the crane beam is trapezoidal mutation type bearing, the beam end using the trapezoidal cross section. Steel structure design specification is in accordance with the crane use status and level of work, divided the work level as 4 working system such as light, medium, weight and heavy duty. Crane design specification and the crane load code divided crane work level into grade A1~A8. The crane beam span of this study is 36 meters, work level for the A7, namely the structure of heavy duty.
Finite element analysis
Finite element method is a method of structural analysis; its basic idea is to disperse solving continuous area to unit assembly which is composed of a finite number of units connected together in a certain way to analyze. The current finite element software analysis function covers almost all engineering field; the use of the program is also very convenient. Currently, finite element analysis software which is widely used and very popular in engineering field contain: ANSYS, Abacus etc. Finite element equation principle: By the known Element Stiffness Matrix and Equivalent Node Load Array Assembled into the whole Stiffness Matrix of the whole structure and load array, assisted by a total stiffness matrix [K], total load vector {F} and integral nodal displacement vector {F} balance equations.
The overall nodes displacement vector is obtained after introducing displacement boundary conditions. The finite element discrete equation is an algebraic system of equations, the symmetric stiffness matrix after introducing boundary conditions is a definite sparse equation, algebraic equations of such a can be solved by using a variety of methods.
ANSYS is one kind of engineering analysis software, mainly in the mechanical & structural analysis by external load of reaction, such as displacement, temperature stress [6]. The state of mechanical structural analysis system can be evaluated according to the reaction by external loads. General geometry of mechanical structural system is very complex; the load is considerable, so theory analysis often cannot be conducted. In order to answer the analysis, the structure should first simplified by using the numerical simulation analysis method. Finite element software ANSYS has strong treatment before solving and post-processing function. It has reliable calculation and high efficiency, and it also is a powerful tool in structural analysis. It is widely used in engineering, which can reduce the design cost and shorten the design time.
The calculation of crane girder structure was introduced by using the finite element analysis software ANSYS. The local stress state of the crosssection is investigated and the stress concentration position of variable crosssection is found, which can provide a theoretical basis for the establishment of monitoring system.
Loading analysis
The calculation load of the crane beam is shown in Figure 2, including: vertical loads generated by the crane, transverse horizontal loads and longitudinal horizontal loads. The longitudinal horizontal load is along the direction of crane rail, which is supported by column crane beam. So it can be ignored when calculating.
Figure 2. Loading on the crane beam.
Transverse horizontal load is mainly composed of crane beam on the flange of the directly to the brake structure, relative to the vertical load, its effect on crane beam is smaller, for which the influence of the flange and its nearby area is much smaller than top flange and bearing variable cross-section is generally close to the flange. Therefore, in order to simplify the calculation, only the vertical load on the web need considering [8,9].
Considering a variety of adverse conditions, the most dangerous situation of crane beam is when the bending moment is maximum. Then the crane is not located in the center of the crane beam, but located in the position shown in Figure 3. The material setting of the crane beam is shown as Table 1.
Figure 3. Worst situation of crane loading.
| Material | Elastic Modulus (MPa) | Poisson Ratio | Density (t/mm3) |
|---|---|---|---|
| Q235 | 2.1 × 105 | 0.3 | 7.85 × 10-9 |
Steel crane beam is composed of web plate, flange plate, stiffener and many other small plates. It is very complicated if all parts are considering, and parts or less important small ribs can make the ANSYS calculation inaccurate even not able to be calculated. So it is necessary to make model simplified, the reasonableness of finite element model of the crane girder structure directly affects the accuracy of the finite element results. Therefore, in this paper, the finite element model of the crane girder is drawn by the three-dimensional mapping software of PROE, then change into IGES format an import into ANSYS [5,6]. The selected units of PROE is mm/N/s, coordinate origin is fixed at the center of the bottom flange.
Load case of the crane girder
Meshing: The entire structure meshed by solid element (Solid 45). The meshed map of crane girder is shown in Figure 4.
Figure 4. Meshing of crane girder.
Constraint: Because the size of crane girder is large, the structure is complex. So it is simplified to simply supported beams (Figure 5). One side is fixed hinged bearing and the other is horizontal movable hinged bearing.
Figure 5. Simplified as simply supported beam.
Loading: In static analysis, the weight of crane girder is not considered, only hanging wheel pressure is considered. So the calculated stress is the stress amplitude. There are four small wheels on each side, whose maximum wheel pressure is 272 KN. The wheel pressure distribution is shown in Figure 6. The concentrated load of each wheel is evenly distributed to the corresponding nodes nearby, direction is vertically downward.
Figure 6. The wheel pressure distribution.
By static analysis of crane beam with trapezoidal variable cross section, the stress levels and performance indicators of the dangerous parts of crane beam are obtained. The welded crane girder destruction is mainly fatigue failure, and stress concentration is the main reason of fatigue failure. The results show that stress concentration phenomenon appears on ladder variable cross section. Under repeated loads, fatigue crack appears easily. So the realtime monitoring of trapezoidal variable cross section is conducted to prevent fatigue failure. At the same time, the crane beam should be checked regularly in use process, which can contribute to find obvious deformation and steel plate cracking of the crane beam. These problems should be timely reported, and then take the necessary measures to avoid certain losses and damage.
In order to ensure the safe use of the crane girder with trapezoidal variable cross section, the real-time monitoring system is established by using advanced sensor technology, which can monitor the crane beam timely and effectively. Especially the trapezoidal variable cross section and the middle of the bottom flange are focal monitoring areas. Therefore, the flange and web connection strength should be strengthened in the process of design and manufacturing under, especially the welding quality of these parts, which can improve the fatigue life of crane beam, reduce the accident rate and promote safety production.
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