Luis Eustáquio Moreira

Limits States Analysis for Bamboo Pin Connections

In this paper the result of an investigation using finite element model (FEM) of a simple bamboo pin joint as commonly used in many types of structures especially in plane and space structures is presented. The nonlinear pressure distributions at the contact area of a steel pin in a bamboo circular hole were analyzed considering the anisotropy and heterogeneity of the functionally graded material. In turn the obtained results of the analysis are compared with those based on simplified constitutive models assuming isotropic and homogeneous representations for bamboo. The experimental results are compared with the results obtained from both methods. The assumption of the bamboo as an orthotropic material presented more reliable design method of bamboo structures Although the different maximum forces applied in each case, local stress are relatively high on both cases, showing that this type of connection depends on local reinforcements to be a safe connection. Finally the suggestion that bamboo joints at the hole can be improved by reducing the stress concentration factors, through applying reinforcing elements such as natural fiber straps composites close to the hole.

Buckling of Masts of Bamboos Bundles

Bamboos generally have elasticity module in compression of about 9 GPa, which is a relatively low value compared to timber and concrete, 20 GPa, and steel, 200 GPa. However, the compressive strength is high - 40 to 80 MPa – that, combined with axissimetria of the cross section, makes the bamboos structural elements with high strength and flexibility. Considering the low apparent specific weight of the material 8 kN/m3, photosynthetic production and workability, bamboos have no competitor in the market so that loads can be absorbed independently by any of the above materials. But the industrial structural elements may be produced with dimensions and geometries provided in accordance with the load to be transported. This is not the case of bamboo. Thus, the capacity of the bamboo in compression becomes limited by its natural flexural rigidity, EI. Thus, different structural systems with pipe threads to make large columns or masts were investigated, [1,2], all with bamboo Phyllostachys pubescens species. In this paper, a kind of mast composed of a central bamboo 6 m in length and six smaller segments axi-symmetrically distributed around this central bamboo will be presented. This proposed design is organizationally a set of bars shackled by steel bands along the length of the beam. Flexion-compression tests with bamboo species Phyllostachys pubescens, combined with numerical modeling through the MEF were made. The loading capacity was tripled and the lateral deviations are negligible when compared with the axial bamboo tested alone. This mast, while consuming a relatively high number of bamboo units, has the advantages of ease and constructive possibility of structural use of smaller diameter bamboo. All the design and results of experimental and numerical analyzes will be discussed in this paper.

Bamboo Mast for Lightweight Arquitecture

Bamboo is a pipe produced by solar energy. It is a plant of the graminae family which grows up all over tropical and part of subtropical regions of the world in more than 1250 species. High biomass production, high mechanical resistance, low specific weight and easy workability has done of bamboo a promise to future generations in relationship to sustainable construction systems. Bamboos of the Phyllostachys pubescens species are one of the most resistant and straight axis bamboos, used in China as material construction and other applications, as paper and fabrics. They are the most commercial bamboos of China and its forests covers 5,6 millions of hectare in that country. This exotic species is met on small plantations in Rio de Janeiro and São Paulo states of Brazil. Many characteristics turns bamboo a smart structural element: high resistance/weight ratio; natural nodes spaced along the culm which avoids local buckling and graded distribution of the fibers from inner to outer side of the thickness wall. So, the application of bamboos as tensile structures supports is a coherent choice since these modern tents characterize a lightweight architecture. Some structural bamboos can attain even more than 15 meters long with 10 cm mean diameter. To increase the load capacity of this slender bar and make feasible bamboo use as masts for tensile structures, an hybrid mast using bamboo as axis and 4 steel cables along of was designed and tested in the Structural System Laboratory LASE, and Structures Experimental Analysis Laboratory LAEES, respectively. In this paper it will be presented the results of the mechanical tests for 2 different masts with 6 meters long. Both masts have the same design but important differences which will be discussed in the paper.

Design and Mechanical Tests of Bamboo Masts

Bamboos are smart natural tubes and a resistant material. Many species can be selected with 10 cm basal diameter, 12 m high and approximately straight longitudinal axis. A slender element like that has a relatively low load capacity under compression force. This limitation can be by passed through a composition of bamboo and cables. Through coherent design, this composition may produce an aesthetical and light mast with high axial compression resistance. This hybrid structure opens a big application for bamboo tubes, as for example, masts for the modern tents, known as tensile structures in the low weight architecture. Different compositions which use a large number of bamboos can be derived from this one. So, the mast mechanical performance investigation opens the way for another more complex systems understanding. In this paper, the design of a bamboo mast with 6 meters long is developed. A previous numerical investigation through SAP 2000 v14 structural analysis software was used for mast design and project. Cables and accessories; length and connections of the bracings and others constructive details are investigated until the conquest of a well fitted mast. A non destructive compression mechanical test of the mast rotation free at ends was done. Loads, tension in cables and lateral displacements were gauged in real time. Test results and numerical analysis show that masts can support compression forces many times bigger than bamboo itself.