Modeling the stress-strain behavior of Bamboo under cyclic uniaxial loading

This paper presents a series of cyclic uniaxial compressive loading tests carried out on cylindrical samples of bamboo, in order to develop unloading and reloading stress-strain models. Two bamboo species from Congo Basin, the Bambusa vulgaris and Oxytenantera abyssinica were used for these experiments.

It is found from the test results that the unloading and reloading do not essentially change the shape of the envelope curves of the stress-strain relations and that to predict models for an unloading and a reloading path, the plastic strain, the unloading strain, the strain at yield, the unloading stress, the initial tangent modulus and the tangent modulus at zero stress (after specimen is completely unloaded) are the controlling parameters. These controlling parameters  were  analyzed  based  on  the  data  obtained from test results to propose empirical relations for the unloading and reloading curves. Two empirical relations, one an exponential type relation and the other a power type relation are proposed to idealize the unloading path while the reloading curve is idealized as a combination of a parabolic curve and a straight line. The proposed unloading and reloading stress-strain models were compared to the tests results and the comparison showed that the predicted unloading and reloading stress-strain relations provide a good agreement with the test data. The empirical relations proposed are adapted from those for plain concrete under similar loading