Ingenium 2016
height. Though not taken into account in this study, it is interesting to recall that Young’s modulus and the uniformity of sectional stiffness of the cross-section will increase along the height of the culm, theoretically helping to offset the reduction in section geometry that occurs with height along the culm.
Figure 6. Applied axial load versus displacement results for Moso, culm C4
With this in mind, there exists a noticeable effect on the column buckling behavior of single-culm columns. In Figure 6, it can be seen that the upper third point (0.66L) of the culm experiences greater lateral deflections, after the critical buckling load is reached, than the lower third point (0.33L). Additionally, it can be seen in Figure 5 that the greatest lateral deflection appears to occur slightly above mid height of the culm. Thus if the column were to be reinforced to reduce deflection, it should occur here, rather than the more conventional location of mid
Using the Southwell method [4], the critical buckling load was found as the slope of δ versus δ/P curve plotted for the prebuckled column in which P is the applied load and δ is the lateral displacement at the mid height of the culm obtained from the DWT data. The intercept of this slope with the δ axis provides an estimate of the initial imperfection of the column along its length. It was found that the Southwell method captured the apparent buckling load very well but did not capture the initial imperfection. The latter is believed to arise because the Southwell approximation is based on a homogenous prismatic column having an initial shape that may defined by a sine function; this is not the case for the bamboo culms tested. Predicted values for the buckling capacity were calculated based on Eq. 1 and Eq. 2, using the aforementioned data for Young’s modulus. It was found that there appears to exist no distinct trend in the relationship of the predicted versus experimental values for buckling capacity of the thick and thin-walled species when they were observed either separately or together. As a result, it can be concluded that the geometric variability of
Table 1. Buckling capacities for Moso and TreGai columns a Denotes predicted values
Undergraduate Research at the Swanson School of Engineering
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