Strength

Nature has had the advantage of millions of years of product development to perfect tall, slim structures which stand up to strong winds and earthquakes. The Organic Builder can take advantage of natural materials, such as wood and bamboo, which have a very high strength to weight ratios. This strength was highlighted by a recent earthquake in Colombia which flattened almost all buildings except those built with bamboo. One of the buildings left unscathed was an 18 metre tall bamboo building designed by local bamboo building guru, Simon Velez. Simon Velez's are so impressive that he was asked to design a large bamboo pavilion for the World EXPO in Hanover, Germany. This pavilion was sponsored by the ZERI Foundation (Zero Emissions Research and Initiatives). It is well worth visiting their site at www.zeri.org

Bamboo has higher tensile strength than steel when compared on a strength to weight basis. Wood in general compares well with steel, and has much higher strength to weight ratio when used as a column, or as a panel. Wood's advantages become even more impressive when strength to embodied energy ratios are compared. The following 2 tables give comparative figures.

Strength to weight ratios - the higher the better

Material Strength to weight ratio Strength column to weight Strength panel to weight
Steel 25,000 190 7.5
Aluminium 25,000 310 15.0
Brick 7,000 150 9.0
Concrete 6,000 160 10.0
Wood-Spruce 25,000 750 48.0

The next table gives structural efficiency of materials in terms of energy cost based on mild steel being 1.

Strength to Embodied Energy Ratios - the lower the better



Material Energy needed to ensure given stiffness of structure Energy needed for panel of given compressive strength
Steel 1 1
Aluminium 4 2
Brick 0.4 0.1
Concrete 0.3 0.05
Wood (Spruce) 0.02 0.002

Source - "Structures or Why Things Don't Fall Down" - J E Gordon

With appropriate design, it is easy for the Organic Builder to create buildings which are well above local building code strength standards. It is a matter of using enough of the organic building materials which have an abundant local supply. Strong buildings can be made of bamboo, wood, straw, earth, etc, either separately, or in appropriate combinations, along with small quantities of non renewable materials.