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.