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Load of cranes (II): Dynamic load is generated when the moving state of a crane changes. The effect of dynamic load increases the static load value of the gravitational load acting on the crane due to Earth’s gravity (including its own weight and the load being lifted). When designing crane parts, components, and assemblies, conducting safety inspections, selecting safety protection devices, and analyzing crane accidents, it is necessary to consider the direction of action of dynamic loads. 1. Vertical load: For ease of calculation, the dynamic load effect in the vertical direction is usually represented by different dynamic coefficients φi. The dynamic loads resulting from various operating conditions are calculated by multiplying the dynamic coefficients by the corresponding static loads. The dynamic coefficient is generally obtained from the ranges specified in crane design codes or relevant manuals, and is selected based on the actual operating conditions. The commonly used dynamic coefficients and the applicable operating conditions are as follows: (1) Lifting impact coefficient φ1 – When the lifted load suddenly leaves the ground during lifting or braking, the crane’s own weight exerts an impact force in the direction opposite to its acceleration. φ1 is the self-weight impact coefficient taking this operating condition into account; when calculating the load, it is multiplied only by the crane’s self-weight load. (2) The dynamic load factor φ2 for lifting loads: When the lifting mechanism is in operation and the lifted mass suddenly rises off the ground or descends under braking, the gravitational load of the lifted item will experience a dynamic increase. φ2 is the increase factor for the lifting load under such operating conditions; it should be multiplied by the lifting load when performing load calculations. The value of φ2 is related to the lifting speed, system stiffness, and the manner of operation; generally, the higher the lifting speed, the greater the system stiffness, and the more forceful the operation, the larger the value of φ2. (3) Sudden unloading impact coefficient φ3: When grab cranes and electromagnetic chuck cranes are unloading, or in the event of an accident where the hook or wire rope breaks and the load falls, it can lead to a sudden partial or total unloading of the lifted mass, which exertes a dynamic unloading effect on the structure. φ3 is the unloading impact coefficient taken into account under this operating condition. When performing stability calculations for metal structures and cranes against overturning, the effect of this dynamic load reduction should be taken into account. (4) Running impact coefficient φ4: When the crane or the lifting trolley passes over uneven roads or track joints, vertical running impact loads are generated; φ4 is the running impact coefficient that takes this effect into account. The running impact coefficient is related to the operating speed of the crane or trolley, as well as the condition of the tracks or roads. 2. Horizontal load: The horizontal load includes the inertial loads generated by the crane’s own mass and the lifted load as a result of changes in driving or braking forces in the running, slewing, and luffing mechanisms. This load relates only to the inertial forces determined by rigid-body dynamics, without taking into account elastic vibration effects. Horizontal loads also include horizontal lateral loads generated when a track crane deviates while moving along the tracks, as well as impact loads resulting from moving beyond the designated range. Due to the different mechanisms by which various horizontal loads occur, the calculation methods also vary. (1) Inertial force due to horizontal motion: The inertial force that occurs when the moving mechanism changes speed is calculated as 1.5 times the product of the mass responsible for generating the horizontal motion inertial force and the acceleration; this 1.5 factor takes into account the dynamic effects exerted by the driving force on the crane’s metal structure. The calculated value of the inertial force during operation should be taken as not exceeding the adhesion force between the driving wheels and the rails. (2) Horizontal forces resulting from rotation and luffing motions: When the rotation and luffing mechanisms of a jib crane move, horizontal forces are generated by the lifted load. Due to various factors such as the inertial forces arising from braking during luffing and rotation, the centrifugal force during rotation, as well as the operator’s method of operation, additional horizontal forces are generated. It is generally calculated based on the horizontal force resulting from the deflection angle of the wire rope holding the suspended object relative to the vertical line. (3) Horizontal lateral force when the crane operates at an angle: When a bridge-type crane operates at an angle during its horizontal movement, a horizontal lateral force is generated, which acts vertically on the wheel rims or horizontally on the guide wheels. The factors that cause a crane to operate at an inclined angle are very complex, making it difficult to conduct quantitative analysis theoretically; instead, empirical formulas derived from experiments and statistical methods are typically used for approximate calculations. (4) Impact load: This occurs when a crane or its trolley exceeds the limits of its travel and collides with the end stops on the track, or when there are multiple cranes on the same track span, resulting in collisions between those cranes. The impact load is calculated based on the principle of energy, using the assumed impact kinetic energy and the kinetic energy completely absorbed by the buffer.