Flexural properties as a basis for bamboo strength grading

Abstract

Current design and construction codes and standards for bamboo do not contain strength grading procedures beyond cursory visual inspections. This deficiency arguably limits the safe and economic use of the material. This paper presents findings from an international research project which seeks to develop a strength grading system for bamboo culms. Over 200 four-point bending tests were carried out on Guadua angustifolia Kunth culms for which numerous mechanical and physical properties were measured. Correlations between flexural strength, static modulus of elasticity, dynamic modulus of elasticity from stress waves and density provided mediocre results, with R2 ranging from 0·27 to 0·47. However, properties such as flexural stiffness, flexural capacity and mass per unit length, which are less dependent on geometric properties, provided much stronger correlations, with R2 ranging from 0·86 to 0·92. The quality of these correlations indicates that these could be used as indicating properties for flexural capacity in a simple yet reliable strength grading procedure for bamboo. The findings of this paper invite a reconsideration of the extant stress-based approach for bamboo design, and instead a move to a capacity-based approach, as is often used with engineered timber products.