Over the years, through projects such as the Green School and homes at the Green Village, bamboo has become an increasingly popular material in Bali, Indonesia. While design firms in Bali such as IBUKU have most often worked with bamboo in its round-pole form, advancements and testing in recent years are looking to increase the use of bamboo split beams in the realm of construction.
Bamboo split beams are structural members that have been made from bamboo that has been split lengthwise and layered. They are extremely versatile because they can be prefabricated to match specific aesthetic and engineering requirements. For example, designers can specify exact curves for the craftsmen to match in the prefabrication process. Similarly, the engineers can indicate the required dimensions of a structural member, based on that particular component's load-bearing capacity for the space being designed.
Because of the options that split beams provide with regard to their form, design appeal, and structural capabilities, they can provide more flexibility than typical round-pole construction. This has sparked experimentation and testing carried out by IBUKU's sister companies, Bamboo Pure and Bamboo U, on Dendrocalamus Asper bamboo split beams. Through this research, 3 key design features are manipulated to produce variations in the structural members and compare how split beams compare against round poles with regard to factors such as geometry, strength, and even material waste.
3 Design Features of Bamboo Split Beams
Bamboo split beams can vary based on 3 key features: the method of fastening the splits together, the amount of bamboo skin (epidermis) that the splits retain, and the number of beam modules. By manipulating these three features, one can drastically change the visual appearance and structural capabilities of a particular split beam.
Fastening
Fastening refers to how the components of the split beam are held together, typically using bamboo pins, glues, or both in combination.
Bamboo pins, also called pegs, are inserted roughly perpendicular to stacked splits to secure them. These are commonly used when the splits retain some bamboo skin, as the silica-rich epidermis makes gluing difficult due to its slippery texture. Wires may also be used alongside pins to prevent the splits from sliding.
Adhesives such as epoxy resin, PVA, and modified latex, are another method of fastening. These require partial removal of the bamboo skin to achieve a secure bond. Fully-planed splits can be glued to create laminated forms of the material. These split beams look and perform similarly to other forms of engineered lumber.
Some split beams rely solely on pins or adhesives, while others may combine both techniques for added strength and stability.
Bamboo Skin
Depending on the design, bamboo split beams may retain some of the plant's epidermis, giving them a rustic look compared to fully-planed split beams.
Unlike its effect on bamboo poles, the skin does not add strength to split beams. In fact, fully-planed, laminated beams held with epoxy are much stronger. A more "solid" beam can bear heavier loads because it acts as a single unit rather than separate parts.
Testing at the Bamboo Pure Factory showed that beams that are slightly planed, glued, and pinned bear three times the load of full-skin beams held together with pins. Meanwhile, fully-laminated beams (held together with glue only) are nearly twice as strong as slightly-planed beams.
Modules
Split beams are modular, with each module consisting of vertically stacked splits that form a single beam. Joining two of these beams side by side creates a double beam, while three create a triple beam, and so on. Beams with multiple modules are optimal for larger loads.
The depth of a module depends on the engineering requirements of that member, with each added split nearly doubling the beam's strength. For example, two splits stacked on top of each other provide almost double the strength of one single split, while three splits nearly triple it.
Modules can be added to handle project-specific loads, such as wind or seismic forces. Unlike round-pole construction, which is limited by the dimensions of the poles being used, split beams can be extended in length or depth by adding more splits, which leads to a more efficient construction process.
The Pros and Cons of Using Bamboo Split Beams
When comparing bamboo split beams to traditional round-pole construction, split beams generally outperform round poles in terms of design flexibility, preparation, waste reduction, and compliance with legislative requirements.
Split beams can be prefabricated, ensuring that both aesthetic and structural needs are met during the manufacturing process. They can be created to precise geometries without compromising strength. In fact, bamboo split beams possess more inherent strength per square centimeter than other forms of laminated timber and can be engineered to handle specific loads. In contrast, while round poles maintain their rustic aesthetic, they require careful selection, transport, and on-site testing to ensure viability for each structural member.
Although split beams have a slightly higher environmental footprint due to their processing, they reduce material waste. Round-pole construction requires only the highest-quality, visually appealing, and straight poles, resulting in significant waste. However, split beams can use all forms of bamboo, including scraps from discarded poles, hence minimizing waste.
Due to their similarities to other forms of engineered lumber, bamboo split beams are also more likely to be accepted in countries with stricter building codes than in Indonesia. Currently, bamboo round-pole construction is limited to certain countries due to code requirements and niche carpentry skillsets. While round pole construction tends to have lower material costs, it does require more niche skills for joinery. Conversely, split beams tend to have higher costs due to their processing requirements, but are easier to work with for those familiar with traditional timber construction.
While bamboo round-pole construction is traditional and widely used in Bali, the advantages that split beams offer cannot be overlooked. Their efficiency in prefabrication and practicality make them ideal for modern design. Thanks to their flexibility, split beams are increasingly being adopted in architectural practices, including projects underway by IBUKU Studio and Bamboo Pure Construction.
While bamboo round-pole construction remains traditional and widely used in Bali, the advantages of split beams are becoming increasingly clear. Thanks to their flexibility, split beams are being adopted in architectural practices, including projects underway by IBUKU studio and Bamboo Pure Construction.
