A quick recap on characteristics of bamboo. Bamboo is a type of hollow grass native to many areas of the world. It is sometimes thought of as the poor man's building material because of its widespread cultivation and use in tropical climates where much of the world's poor live. Many of these cultures find use for bamboo as building material.
Advantages
Bamboo is considered to be sustainable and renewable alternative to hardwoods, foremost because it regenerates at exceptionally fast rates. Some bamboo species have been known to grown more than several feet per day. A bamboo forest may be harvest every 6 years while hardwood require decades between harvests.
Disadvantages
Bamboo does not contain cross fibers and is consequently, not designed to bear weight width-wise, with the exception of the points at the nodes. Bamboo is prone to splitting, especially when standard construction fasteners, such as bolts, screws and nails are inserted. Special fastening techniques are required when joining pieces of bamboo.
Based on the previous post, having the research question;
How can a combination of Kaccha and Pukka styles can be used to increase bambo's characteristic thus improve its durability and feasibility of the building?
To simplify the research question, the research will be regarding the type of material used, having a natural material and a common construction structural material to increase the bamboo's durability; functioning as a structural material or building construction material to sustain live load and dead load of the building.
New Research Question:
How can a composite of natural and structural material increase the durability of Vernacular Architecture in the modern industrialize constructions?
Modern connections have been proposed by Huybers, Shoei Yoh and Renzo Piano. These connections solve the issues of complex geometries by joining the members in various ways. These connections require puncture of the bamboo walls sine all fibers in a bamboo culm run parallel once a bolt is placed through it and the connection loaded in tension, the bolt acts like a wedge and splits the bamboo. Also the puncture allows moisture to enter the culm and accelerate decay.
More recent systems have been engineered to make joinery stronger and less labor intensive. The joint of preference has developed by Simon Velez where he uses a bolted connection with an understanding the bolt alone concentrate much on the wall of the bamboo. Therefore, the point where every bolt penetrates each bamboo culm, the void between the solid internal nodes is filled with solidifying mortar. Members of a truss come together at angles and tension forces are anticipated, a steel strap is placed to bridge the pieces. It is important to design with redundant system that is capable of both compression and tension.
What is compression? What is tension?
Bamboo + Cement
The curing process of the cement will affect the structure of the bamboo due to lack of hydration. It absorbs moisture from the bamboo fiber, causing the bamboo to crack.
Using bamboo as structural material project by utilizing bolted with or without concrete mortar infill provide strength rigidly. This experiment does not require for shape deformation of bamboo; thus this frame truss system is certainly prevent bamboo from bending and buckling in the middle of the culm.
Larger holes were drilled into the bamboo to insert the mortar into the joint segments. The mortar was mixed with the optimal quantity of water; the bamboo pieces where then duck taped together ti maintain their positions as they were filled with mortar and left to sure for a week. Once mortar is cured, the tape can be removed.
Bamboo can be cut into different shapes to make 4 kinds of joints: corner, T, point and extension joint. Though holes were drilled into bamboo segment to insert re-bars. This re-bars will absorb most of the stress moments and allow the bamboo structure to sustain high stress impacts as occur during earthquakes.
Bamboo tends to shrink with time making the string joinery slack and insecure. Therefore the joinery system replies on bolts and mortar-fillings maintaining their shape over time.
Bolted Bamboo with Infilled Mortar + Reinforcement Steel Bar
Bamboo filled with mortar are reinforced by an additional the rebar is embedded in mortar, the load is transferred evenly across the member's cross section and can transfer high acial loads to the bamboo.
The bamboo is cut at the end axially crosswise to generate a cone by tightening a steel clamp. The cone is filled up with mortar so that the cone is able to transfer its force to the outer high tensile fibers. The mortar cylinder transferred the forces to the screws.
Since bamboo is very strong when loaded axially, the new connection developed to resist only axial tension and compression forces and not increase resistance to bending. This is consistent with the loading of the truss in which the truss members experience axial loads and any bending is small and accidental. The new connection involves embedding a common steel reinforcing bar into mortar filled bamboo culm and fillet welding several of these members to a steel gusset plate. The innder surface of the bamboo is roughened to provide a bond between the mortar and the bamboo while avoiding puncturing the member. A common steel clamp is also placed at the end of the member to provide confinement of the bamboo and prevent splitting of the bamboo. Because the rebar is embedded in mortar, the load is transferred evenly across the member's cross section and can transfer high acial loads to the bamboo. Finally, the incorporation of the steel gusset plate makes the bamboo easy to connect in any configuration desired.
To construct this connection, steps required as follows:
1. cut the bamboo culm allowing the first node
2. punch out the first internal node to provide hollow section in the bamboo
3. removal of the node can be done easily with a hammer and a piece of rebar
4. provide positive connection between the mortar and the bamboo
5. inner surface of the bamboo will be roughened by constructing gouges
6. splace at 6mm are made for the first 3-5 diameters of the bamboo using a drill
7. compress sand, water and cement to form mortar and placed in the hollow ends of bamboo
8. rebar is embedded into the mortar and the side of the bamboo is tapped repeatedly to vibrate mortar to eliminate voids
9. steel clamp is then placed at the end of the bamboo and allowed to cure for 28 days
10. member can be welded to the gusset plate and the truss is erected
Experiment: To study the strength of specific bamboo joints and structural behaviors
While bamboo has been used for centuries, the traditional methods of lashing bamboo together are not appropriate for the design of long span trusses. These lashed connections also do not fully utilize the its strength; it solely rely on friction, transferring load between members is limited thus require more members to do the same job. Therefore joints in bamboo always has been difficult because it is hollow, has nodes and resists only a little shear stress. Many traditional joints suffer from weakness or deformation. Many joints cannot take advantage of the strength of the culm itself and a special problem is to design a joint for tensile forces.
The New Connection (to be continue)
Pecha-Kucha on Durability of Bamboo (slides will change automatically after 20 seconds)
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