Abstract

One of the major factors contributing in structure collapse is the emergence and development of damage (visible or concealed) in structural components during lapse of time. This paper investigates through lab research, the effects of damage on dynamic characteristics of the reinforced concrete beams as one of the most common elements used in civil engineering structures such as bridges, etc., by retrieval of a number of parameters like natural frequency, damping, bending stiffness, and max vibration amplitude against increasing of damage. The damage has been defined by loading a static load and creating flexural crack for a simple support reinforced concrete beam. The static load on the center of the beam span has been increased in 5 steps from the elastic range to the elasto-plastic range. Following each step of the static loading and creating damage in the form of crack development, the beam vibrated by a vibrating motor and the said dynamic characteristics were measured. Since the damping ratio is highly dependent on the linear or non-linear behavior of the element, and also the stiffness is related to the damping, dynamic experimentation through creating week dynamic forces has been performed, meanwhile maintaining the linear behavior of the element. The results show that the beam damping around the cracked section is not mere a viscous damping, but rather a combination of viscous and frictional damping, and the frictional damping role increases by development of the crack or damage. This paper in replace of using static experiment methodology, introduces two methods of plotting the force-displacement curve and determining the concrete beam stiffness through performing dynamic experiments. One of the proposed methods is less dependent to the damping ratio. The accuracy and precision of these two methods is proved by the experiments performed. Dynamic assessment of the structure has been effected via investigating the dynamic parameters retrieved for the concrete beam under examination. Also to authenticate the dynamic experiment results and exploring the beam behavior under static loads, the finite-element analytical method has been used.