Modeling the dynamic stiffness of cracked reinforced concrete beams under low-amplitude vibration loads

• A dynamic stiffness model of cracked reinforced concrete beams is presented.
• The influence of bending cracks and interfacial microcracks on stiffness is analyzed.
• The effects of two kinds of cracks should be considered under static loading.
• Steel–concrete bond damages do not influence significantly the dynamic stiffness.

In this paper, a model, initially developed to calculate the stiffness of cracked reinforced concrete beams under static loading, is used to assess the dynamic stiffness. The model allows calculating the average inertia of cracked beams by taking into account the effect of bending cracks (primary cracks) and steel–concrete bond damage (i.e. interfacial microcracks). Free and forced vibration experiments are used to assess the performance of the model. The respective influence of bending cracks and steel–concrete bond damage on both static and dynamic responses is analyzed. The comparison between experimental and simulated deflections confirms that the effects of both bending cracks and steel–concrete bond loss should be taken into account to assess reinforced concrete stiffness under service static loading. On the contrary, comparison of experimental and calculated dynamic responses reveals that localized steel–concrete bond damages do not influence significantly the dynamic stiffness and the fundamental frequency.