The use of pseudo-dynamic method in the evaluation of damping characteristics in reinforced concrete beams having variable bending stiffness

The objective of this work is to determine experimentally the damping properties of concrete reinforced beams under mechanical vibrations. This is a very important property in earthquake engineering once damping provides structure energy dissipation during moderate or strong earthquake motions. The experimental campaign used the pseudo-dynamic (PsD) method to analyse the beam dynamic behaviour. Essentially the PsD test method is a hybrid computer-driven testing procedure where a numerical algorithm and experimental step are used and combined on-line in order to solve a dynamic problem. The implementation of the method is not expensive and has the leading advantage of offering the operator a total control of any intermediate structure state during the test still keeping the realism of a real dynamic testing. In this analysis the dynamic model was assumed as single degree-of-freedom system (SDOF). For the calculation of the structural damping factor, the structure stiffness was determined prior the set-up of the time integration algorithm; thereafter a pseudo-dynamic process dealing with a free and a forced vibration scheme, where this last was achieved with an external harmonic load, led to the definition of the structure response where the dissipative effect of the damping properties of reinforced concrete beams was evidenced.