This article shines a light on four commonly employed structural systems in bamboo construction:
The support system of a post and beam structure is composed of three key elements: vertical posts, horizontal beams, and cross-bracing. The latter helps to triangulate the structure, enhancing its stability against lateral loads such as winds and seismic forces. Usually, round bamboo poles serve as the backbone of these structural systems. The result is a structure that is not only sturdy but also visually appealing.
The process often requires skilled craftsmanship to carve and assemble various types of joints, including fish mouth joints and angle joints. A simple bolted joint, for instance, can be used in this structural system to alleviate some of the manual labor. When used alongside mortar for grouting, this type of joint has proven to be incredibly strong.
Nowadays, we even see the use of 3D-printed inserts that mimic the function of fish mouths. These inserts can be placed into cleanly cut bamboo, offering an innovative, modern solution. This blend of time-honored techniques and modern solutions is what makes bamboo architecture so exciting and dynamic.
A hyperbolic paraboloid, or a ‘hypar’ for short, is a structural system that’s as intriguing as its name suggests. Recognizable by its signature ‘saddle’ shape, it presents a marriage of concave and convex surfaces. The result is a structure where two straight lines intersect at every point, creating a captivating visual effect.
The curvature of the surface lends these shells extraordinary stiffness, allowing them to bear considerable loads over vast spans. These qualities make them especially suited for roof structures.
The building process typically commences by first laying poles in one direction and then in the other. These are temporarily secured using rubber bands. Then two opposing vertices of the structure are hoisted using ropes and tripods, while the alternate vertices are simultaneously pressed together. This action induces the characteristic curvature of the hypar, with individual poles adjusting to match the desired shape. The process culminates in the permanent securing of the hypar members, typically through the use of bolted joints or bamboo pins.
The shape of a Reciprocal Tower is reminiscent of a hyperboloid. A key difference lies in the geometric construction of the reciprocal tower, which involves rotating a hyperbola around a defined axis.
Embarking on the construction of a hyperbolic tower, it is beneficial to first create a model. This preliminary step allows you to visualize the final product, enabling you to determine the appropriate diameters for the base circle, as well as the middle and top sections of the tower. Alternatively, computerized design tools can be employed to facilitate the planning process.
The reciprocal tower’s unique characteristic lies in the marriage of reciprocal structure principles with the efficient hyperboloid shape, making it an optimal choice for larger constructions. To further increase the tower’s strength, reinforcement rings can be added throughout the structure.
The construction starts by arranging a specific number of bamboo poles vertically on the ground in a circular pattern. Following this, a central ring, smaller than the base circle, is fixed at the chosen height above ground. Once the central ring is secured, the exciting part begins – twisting the poles. Each pole is uniformly twisted in one direction and temporarily attached to the central ring to maintain its position. Then, a second set of poles is introduced. The base of these poles aligns with the first set, but they’re twisted in the opposite direction, following the same angle as the first set. These poles are also temporarily fastened to the central ring. At the level of the top ring, all pole ends must meet as well. Once all poles are in position and the desired shape of the tower is achieved, the poles are permanently secured at the points where they intersect. This step ensures the tower’s stability and strength.
Spatial Gridshells are fashioned from a lattice of bamboo splits. These splits, either intertwined organically or arranged in precise shapes, create captivating, often dome-like structures. Gridshells excel in crafting large, open spaces, without the need for additional interior supports.
The construction of these structures commences with establishing the main frames, arches, or rings that provide the foundational support and overall shape for the grid-shell. Typically, these elements are composed of split bundles, secured together using bamboo pins, and occasionally fortified with glue. Once these primary structural components are set, the gridshell begins to take shape with the addition of bamboo splits, progressively filling the gaps and generally culminating in a curved structure.
The construction process can be playful and organic, as bamboo splits are easy to handle and can be shaped into various forms. Organic woven patterns can be determined on-site through trial and error, guided by reference splits. Alternatively, structures can also be built by adhering to predetermined measurements, thus creating beautiful geometric patterns. In either case, green bamboo splits, which have been recently treated, work best and are more flexible, as dry splits tend to be too rigid and often crack. Upon adding a sufficient number of members, the grid shell becomes sturdy enough to be climbed on, and in some cases even endure heavy winds and earthquakes.
Bamboo’s inherent characteristics of aesthetic and structural versatility make it an ideal material for grid shell structures. With prudent planning, a sound understanding of the material, and a dash of creativity, constructing with bamboo presents opportunities to create sustainable, resilient, and visually arresting structures.
This article was originally published here by Bamboo U, a bamboo architecture and design enterprise that focuses on sharing sustainable ways of building. Bamboo courses are available on their campus in Bali, Indonesia.