Geometric and material effects on bamboo buckling behaviour

Bamboo is a functionally graded, sustainable construction material that has evolved to resist its primary loading in nature. This study focuses on the effects of geometric and material property variation along the culm length on the capacity of an axially loaded member. Conservatively, compression capacity may be calculated using the smallest section of the member; however, this results in an inefficient use of the culm and may limit the use of long compression members. A more realistic estimate of capacity is obtained by considering the effects of culm taper on buckling capacity. In this work, culm taper was experimentally investigated for three representative bamboo species. The effects of culm section gradient on geometric properties were examined followed by an assessment of geometric variation along the culm height. Following this, a series of buckling analyses of tapered culms was conducted to illustrate the significant effects of taper on culm compression capacity. This analysis was supplemented with comparisons with experimental culm buckling data. Beyond compressive capacity, the paper discusses the implications of culm taper in terms of flexural behaviour, the design of gridshells (involving pre-bent axial load-carrying members), visual grading of bamboo and, ultimately, classification of the many species of bamboo presently used in construction worldwide.