EXPERIMENTAL ANALYSIS OF A BEAM-COLUMN SUBJECTED TO NONCON- SERVATIVE FORCES

Resumo

The structure known as Beck’s Column consists of a beam-column, subject to a tangential fol-
lower force applied at its free end. Beck presented in 1952 the critical load, which induces the vibration

of the structure (flutter). This paper uses a simple and general numerical model that allows the solu-
tion of the problem of columns with different properties and different boundary conditions associated to

follower forces. In this work, emphasis was given to the experimental simulation of the phenomenon,
in a qualitative way. A metal ruler was adopted to represent a slender fixed-free beam-column and, to
simulate the following force, a brushless motor was attached to the free end. A thrust force is generated

when air is moved by the propeller and the motor follows the rotation of the free end, changing the direc-
tion of the thrust force. Tests were performed with different setups in order to observe the effect caused

in the presence of gravitational force (motor weight) in concomitance with the tensile and compression

follower effect. The results were remarkably different, showing that the follower force can induce stabi-
lization, flutter and divergence. As the analysis was qualitative, videos and photos were made to record

the results. The values of critical loads and frequencies were within the range expected by numerical
analysis. Attempts to instrument the tests with accelerometers and LVDTs (Linear Variable Differential
Transformer) were made and a discussion is presented on the differences and influence of these devices
on the structure behavior.