Axial elongation in ductile reinforced concrete walls

Axial elongation has been observed during tests of reinforced concrete (RC) members subjected to either monotonic or cyclic loading. The implications of elongating plastic hinges in beams on the seismic performance of RC frame buildings, and in particular the floor systems, has been extensively studied. However, few investigations have addressed axial elongation of RC walls. To expand on the existing knowledge of axial elongation in RC members, the measured axial elongations of 13 previously tested RC walls were investigated. These tests included a wide range of vertical reinforcement ratios, vertical reinforcement layouts, and axial loads. The procedures to estimate wall elongation that were proposed in the Public Comment Draft Amendment No. 3 of the New Zealand Concrete Structures Standard (NZS 3101:2006) were also evaluated and compared against the measured elongations from the tests. The experimental results showed that elongation magnitudes in the analysed walls were between 0.4-0.8% of the wall length at 1.5% lateral drift, and that the elongation equations proposed for NZS 3101:2006 provided an acceptable estimation of the expected elongation in RC walls. Additionally, numerical models were developed using distributed-plasticity fibre-based elements in OpenSees and membrane elements in VecTor2 to verify the ability of these commonly used modelling techniques to capture wall elongation. The numerical simulations were able to represent the global and local behaviour with good accuracy and both models were able to capture the peak elongations. However, the more sophisticated concrete material models in OpenSees allowed the fibre element models to more accurately represent the experimental wall elongations, especially when considering residual elongations.