Internal Damping Rates of Construction Cranes

Abstract

The conveyance of payloads by construction cranes generates pendulations of the payload. This research provides a critical design parameter for the development of a device that aids in reduction of these pendulations. Previous research developed a tuned mass damping system, that effectively attenuated the energy of a pendulating payload. In order to be effective the internal damping rate of the tuned mass damper must be at least twice that of the system to be damped. Prototypes of a tuned mass damping system have achieved damping rates between 6 and 12 %, making cranes with damping rates below 3% attractive. This research indicates that the internal damping rate of construction cranes is on the order of one percent, suggesting that a tuned mass damping system could be retrofitted to today's construction cranes.

This thesis is an investigation of the internal damping rates of construction cranes. Three hydraulic and two lattice boom cranes were tested. The motion of pendulating payloads was modeled after a simple pendulum. The internal damping rate was calculated using logarithmic decrement technique. Light to medium duty cranes were tested with loads similar to those used in duty cycle operations. Damping tests were performed both perpendicular and parallel to the mast of the crane. Values were calculated from data extracted from videos of a payload oscillating over a measurement scale.

A FMC Link Belt 25-ton hydraulic crane was tested at 6.4 % of capacity and displayed damping rates between 0.25 and 0.6 %. A 50-ton FMC Link Belt was tested at 10 % of capacity and had damping rates of 0.18 % for both tests. The third hydraulic crane was a 60-ton P&H T-600XL. The test parallel to the mast was performed at 6 % of capacity having a damping rate of 0.22 %. The test-performed perpendicular to the mast was at 3.5 % of capacity with a damping rate of 0.65 %.

Two lattice boom cranes with capacities of 70 and 100 tons were tested. The 70-ton LIMA 778c's damping rates were 0.06 and 1.3 percent. This test was performed at 15 % of capacity. The 100-ton Link Belt LS318 was tested at 6.8 % of capacity and had damping rates between 0.07 and 0.08 percent.