The use of steel bolted connections in multi-culm bamboo members reveals significant potential for sustainable construction applications. However, the low elastic stiffness of these members necessitates a thorough investigation of their behaviour to fully realize this potential in a design setting. Previous studies introduced an analytical method to characterize the elastic stiffness of bolted multi-culm bamboo axial members. The method effectively integrates the contributions of bamboo culms, steel bolts, washers, and gusset plates in determining the overall stiffness of the member. Despite these advancements, important geometric parameters of bamboo culms, such as their taper and straightness along their length, remain unaddressed. Therefore, this study addresses these gaps by examining a rational range of taper and straightness in bamboo culms and investigates the influence of these parameters on the elastic stiffness of bolted multi-culm bamboo members. The findings contribute to the design of bamboo structures, highlighting the effect of the unique geometric properties of bamboo culm on their stiffness parameter.