Construction with Bamboo
Diplom-Ingenieur Christoph Tönges
design projects    
  glued bamboo  
NEW >>> www.bambus-conbam.de <<< NEW

glued bamboo

In timber construction, gluelam beams are produced by glueing together individual timber planks. These beams provide higher strength values than conventional ones because the used timber is sorted out so that possible weak parts got eliminated.
The characteristic strength values of Guadua are higher than that of timber, so the idea to produce gluelam beams of Guadua suggests itself. High-quality boards and beams could be produced, for which there exist diverse uses all over the world.

Production of gluelam in Germany
 (148) Production of gluelam in Germany
Production of glued bamboo in China

The production of corresponding products represents a big chance for the countries, that are 'blessed with the wealth of bamboo'. But equally it is a chance for the nature since bamboo binds more CO2 than most trees and, moreover, produces more biomass than timber due to its fast growth.
The project FUNBAMBU in Costa Rica made the construction of about 1000 bamboo houses annually possible. The building material came from bamboo plantations of 60 hectares. To build the same number of houses an area of 500 hectares of tropical rain forest would have to be felled! (>Efficiency).

 (149) Production of glued bamboo in China

Laminated bamboo has similar qualities like laminated timber, however, it is much more elastic (>earthquake-proof). For example, in China it was used for construction of airplanes in the World War II - in contrast to steel bamboo is not only powerful but also lightweight.
The advantages of bamboo and glued bamboo, respectively, that are presented above, were reason enough for us to execute an experimental production in order to learn more about the manufacturing possibilities and the subsequent products.
Jörg Stamm went to China in November 2001 to learn about the local processing technologies and partially took them over.

Products of laminated bamboo in China
 (150) Products of laminated bamboo in China
Guadua slats Manufacturing process

To be able to glue Guadua, rectangular slats must be extracted from the canes at first. There are different ways for this:
For the production of parquet in China, sections of 1,50 m in length of still green bamboos are divided into four-sided splits with a star-shaped cutter and then additionally planed.

 (151) Guadua slats

If the bamboo cane is divided using a special circular saw with two parallel saw blades the slats only have to be planed on two sides. Depending on the diameter, five to eight slats can be extracted from one Guadua culm. The distance of the two saw blades corresponds to the requested slat width.

The remaining parts of the diaphragms are removed and afterwards the slats have to be dried. Dry rooms or solar dryers can be used to accelerate the desiccation process.

Special circular saw
 (152) Special circular saw
Solar dryers

We produced a very simple solar dryer to dry the green slats:
We dagged a canal on an inclined terrain and then covered it with a foil. The warm air ascends through this canal directly under a stack of Guadua slats. The stack is protected with sheet metal from direct sun radiation and is covered with foil. Additionally a bamboo tube serves as a chimney.

 (153) Solar dryers

In our experiments we cut away the interior and exterior curve of the half-done slats with two other parallel circular saws, too. The possible slat height and so the distance of the circular saw blades is determined by the particular wall thickness of the different bamboo culms.
The slats which still showed interior or exterior curve were planed, so that they could be glued positively.

Special circular saw
 (154) Special circular saw
Product spectrum

The Guadua slats were glued this way: To manufacture the beams we glued the individual slats together on the broad side. The interior side of the slats with their coarser fiber structure were glued to the interior side of the following slat and vice versa, to raise the bending stiffness of the beam.
In arched beams the interior sides of the slats are glued to the exterior sides of the next slat. The interior sides lie at the inner side of the arch, because the slats can be bent better in that direction. Since arches are put under normal/longitudinal stress, a high bending stiffness is not necessary.

 (155) Product spectrum

Two beams can be combined (next to or on top of the other). Also constructively advantageous I-beams can be produced, laminated bamboo boards consist of crosswise glued slats.

Board and I-beam Laminated bamboo board
 (156) Board and I-beam  (157) Laminated bamboo board
Testing glued bamboo Tests

In order to learn more about the mechanical-technical material properties of the produced Guadua beam, we made several tests with beams of different forms and lengths at the Universidad Nacional de Colombia in Manizales. Influencing forces as well as the resultant deformations were recorded and analyzed afterwards.

 (158) Testing glued bamboo

The observation of the way the tests failed revealed interesting realizations about the product properties. The laminated bamboo beams were supported at both ends and the load was put on at two points.
As expected the beams took the load in a very favorable way, the elastic deflection was quite high in comparison to timber.

Elastic deflection
 (159) Elastic deflection
Failure of a beam of 3 meters in length

Specimens of approximately 1,50 and 3 meters in length were tested. The failure behavior of these two lengths differed much, because the longer beams were produced of 1,50 meters long, offset glued slats.
Therefore these specimens failed in the extremely stressed zone at the bottom of the beam at the butt joints between the slats. Joggle joints would minimize this weakness.

 (160) Failure of a beam of 3 meters in length

The approximately 1,50 meters long specimens were glued of one slat per layer. At failure these tests behaved similar to bamboo canes. In fact, the high shear stresses led to longitudinal cracks. The failure always took place at the interior side of the culm wall, because it is weaker than the exterior side. The beams do not collapse completely, so a remaining load-carrying capacity is still available in case of shear failure.

Shear failure of a 1,50-meter-specimen
 (161) Shear failure of a 1,50-meter-specimen
Shear failure of the I-beam

The I-beam behaved very well. Because of its favorable cross-section form, the deflection under load was relatively low until failure. This specimen was 1,50 meters long and had no joints in the slats, therefore it failed due to shear stress in the lower area.

 (162) Shear failure of the I-beam

The experimental production of glued bamboo and the subsequent tests showed that Guadua serves very well as source material for high-quality products with good material properties. However, the development of marketable products with uniform quality standards is still required. Both the possibilities and the demand for these products do exist. For now, it is necessary to study the latest findings and to carry on working on this chance.

 (163) Tests
Observing a test

Jörg Stamm wrote a study about this topic by order of the 'Deutsche Gesellschaft für Technische Zusammenarbeit' (GTZ) at their partner university in Pereira (UTP). He illustrated the results of the above presented experimental production, the exploitation of Guadua culms, the production techniques, as well as costs and economic efficiency of corresponding production installations. The abstract of the study can be download here:

Download Study, PDF-File, Spanish,
8 Pages, 508 kB

 (164) Observing a test

  glued bamboo  
NEW >>> www.bambus-conbam.de <<< NEW
Author and Copyright: CONBAM
Translation: Victor Löffler --- 06.08.2002 --- last update: 23.07.2005