Pull-in capacity of unfilled T-connections using Bambusa blumeana bamboo

Abstract

Bolted bamboo connections are ubiquitous in contemporary bamboo structures, yet their performance remains under-researched—particularly in configurations without cement mortar infill. This study investigates the structural behaviour of a T-shaped fish-mount joint, commonly used to connect two angled bamboo members. The joint consists of two culms connected using through-culm threaded rods—one straight and one with a hooked end. A critical loading scenario arises when the threaded rod is pulled through the bamboo, causing the washer to bear against the outer culm wall. To simulate this, the study replicates the failure mechanism by pushing the rod inward, effectively assessing the rod pull-in capacity. In this context, the study tests one hundred connection specimens made of Bambusa blumeana bamboo poles and threaded rods of 8 mm and 12 mm in diameter, with corresponding nuts and washers. From the experimental results, it then develops three predictive models for estimating maximum capacity: (1) a dimensional analysis model, (2) a regression-based model, and (3) a bending-perpendicular-to-fibre model. Among these, the dimensional analysis model based on bamboo density, culm diameter, and wall thickness demonstrates the best performance, offering a simple, unit-consistent formulation with a strong fit ( $R^{\mathit{2}}=0.82$ ). Accordingly, the dimensional analysis model is further developed into a practical design formula aligned with the structural bamboo design code ISO 22156:2021, enabling engineers to apply it directly in the design of bolted bamboo connections.