PSI - Issue 75

Jeroen Van Wittenberghe et al. / Procedia Structural Integrity 75 (2025) 111–119 Jeroen VAN WITTENBERGHE and Vitor ADRIANO / Structural Integrity Procedia (2025)

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4. Dynamic crane behaviour 4.1. Dynamic coefficient for hoisting

When a load is being lifted, the crane is subject to dynamic effects of transferring the load off the ground onto the crane. Also, when a lifted load is further being lifted up or down, similar effects occur. Such dynamic effects are considered during the crane design [4-5] by multiplying the gravitational force due to the mass of the hoist load with a †›ƒ‹ factor ϕ . Typically, this factor is used as a constant, while in practice the dynamic effects will depend on how the crane is operated and the dynamic properties of the crane. Basically, the crane will act as a combined mass spring system where the mass is affected by the lifted load and the spring stiffness is a function of the free hoisting cable length and position of the trolley. When the hoisting mechanism accelerates or decelerates, the load and therefore the crane bridge structure will undergo dynamic effects (oscillation of the load in the direction of the speed vector). These effects can be measured through the optical strain gauges of the SHM system. In Figure 8 the setup for the Crane-OCAS that has been used to measure the dynamic coefficient in controlled conditions.

Figure 8: Setup for measuring the dynamic hoisting coefficient.

The crane is equipped with optical strain gauges positioned at nine locations along the crane girder, as illustrated in the figure. To accurately capture peak effects, one wheel of the trolley was aligned with a strain sensor. The procedure involved lifting a load, then halting to allow oscillations to diminish. Subsequently, the load was lifted further and stopped again. After reaching the maximum height, the hoist lowered the load in intermittent steps. Measurements were conducted at varying speeds, different trolley positions, and different payloads. For each measurement, the dynamic factor ϕ and oscillation frequency were calculated from the strain gauge data. 4.2. Influence of hoisting speed and trolley position The tests are carried using the high and low lifting speeds of the crane that correspond to 4 m/min and 1 m/min respectively. Results are shown for lifting a weight of 2.88 ton (measured using a calibrated lifting scale) with the trolley positioned at the location of strain sensors 2, 3 and 4. The measured values of the dynamic factor are provided in Figure 9. Each value is the average of at least 3 measurements. Overall, it can be observed that the dynamic factor is higher for measurements at high speed than at low lifting speed. This can be explained by the lower kinetic energy at lower speeds and is also in line with the guidance on the dynamic factor in [6]. No significant differences have been found between the dynamic factors for hoisting up and down. When comparing the results obtained at different trolley positions and at different hoisting heigths, one can observe that the dynamic increases for a higher hoisting height and when the payload is closer to the side of the crane. This can be explained by the changed stiffness of the complete structure. When the free length (between the trolley and the crane hook) of the hoisting cable decreases, the vertical stiffness will increase. Hence sudden dynamic actions will have a larger effect. The same holds true for the bending stiffness that increases when the trolley is moving closer to the end of the crane. These observations correspond well to the observed trends described in [7].