Non-linear behaviour of reinforced concrete beams under low-amplitude cyclic and vibration loads

Recently, there has been increased interest in using non-linear vibration techniques to detect damage in reinforced concrete beams. To understand better the non-linear behaviour of damaged concrete beams during low-amplitude vibration, modelling is necessary. This could be achieved with knowledge of the moment–relative rotation relationship of a section of beam within the damaged region. An experimental method of studying the static moment–rotation relationship over a short subsection of the beam is presented here. Tests are conducted at the mid-span of a beam, damaged by overload. Initially the stiffness of the damaged section decreases rapidly with increased damage but above 27% of failure load the change with increased damage is very small. Several possible non-linear crack mechanisms are then discussed, two of which may be assessed using the experimental data.