Buckling of Bamboo Masts with Interposed Spacers

摘要

A hollow bamboo in its raw state, from the geometrical point of view and language engineering can be defined as an element of tubular bar, not prismatic, approximately circular cross sections, stiff by intermittent internal disks positioned along the bar. The decrease in the diameter and wall thickness usually happens from the bottom up, the basal part may contain some exceptions, with sections of the base with diameters smaller than the second, then to diminish steadily to the top. This architecture has a genetic component that resulted from constant interactions of bamboo with the actions of wind, which stimulated increased local resistance of the most requested points mechanically, not only by concentrated lignification in cellulosic tissues, such as the geometric localized variations. From the viewpoint of composite materials science, bamboo can be defined as a composition of two different materials, a first fiber and vessels oriented and aligned along the internodal stem sections, which connect to another material with fibers and vessels tangled - anastonose - intermittent stiffeners composing the above cited nodes. In both materials vessels and fibers are surrounded by a parenchymathous matrix of hollow cells that store sugars. The mechanical point of view, bamboo, due to the configuration, the rigidity and strength components and a tubular geometry is a flexible structural element with high mechanical resistance. This flexibility makes the long elements have low load capacity in flexion compression, if the goal is the application of bamboo in construction structures. This issue can be circumvented by systemic compositions, called masts, [1,2] which can be applied in a single long bamboo element resistant to relatively high compressive loads. In the present investigation, four parallel bamboos 5.5 meters long, the species Phyllostachys pubescens are discontinuously connected by bamboo segments interposed fixed by steel pins, achieving this composition with a load limit of 48 kN in controlled experiments. These experiments were also used and motivated to find the numerical modeling by the MEF, whose results were widely discussed.