Variation of bending capacity along the lamina length of a grass, Imperata cylindrica var. major (Gramineae)

Abstract

The aim of this paper is to investigate variation of the bending moment capacity along the lamina of a grass (Imperata cylindrica (L.) Raeusch. var. major (Nees) C. E.Hubb. ex C. E. Hubb. and Vaughan). It is postulated that the bending strength of the grass section is obtained predominantly from the midrib and that the grass lamina contributes little to the overall bending behaviour. By observing transverse sections of the midrib, it can be estimated that the thickness of the outer sclerenchyma zone is approx. 10% of the midrib diameter and that the pith parenchyma makes up most of the rest of the midrib. This observation is taken to be valid for the entire length of the lamina. A simple structural model of an elliptical tube is proposed for the midrib. Bending tests on the grass lamina have shown that the bending moment capacity is very low in the distal third, but increases linearly in the middle third and is generally constant in the proximal third. Using the structural model for the midrib, the results indicate that the maximum bending stress of the midrib remains fairly constant over the length of the grass.