Update April 2011

Material tests

Below are the results of the first material tests.

Tension

The material appears to be very strong, but not amongst the strongest of its kind. The average tension tension strength is about 135 N/mm2, but the looking at the deformation the material behaves to a different standard. When a straight line is considered in the tension graphs, it shows the E-modulus. The average there is only about 1750 N/mm2, which seems very low compared to the tensile strength.



Bending

Below are the results of the bending test. These test show enormous deflections in the material, but also a great resilience. When loaded with a bending moment bamboo should break at the top when the maximum compression is reached there. Instead it failed on shear. Failure only appears after a relative big force has been applied.

These results are still to be evaluated.



Digital modeling

Although the digital models haven´t changed much, the way the results are shown are different. Also the diameters of the elements has changed, as it seems likely that the material can be get in bigger diameters then initially thought.

Below are some results of a model. Although the results are promising, the strength of the design seems to fail still. The images show the directions of the forces, so new diameters of bundles of bamboo can be designed to take these forces better. So even though the design still fails structurally under a high wind load, the results give a better insight into the design and may lead to a design that won't fail.



Sponsor for prototype

Because the material tests and digital models are still two different approaches to the research, plans are made to make a prototype scale 1:5 to test half of the pavilion and compare the results with the digital model. To accomplish this a lot of bamboo is needed. Thanks to BAMBOE BOUW NEDERLAND this can be accomplished. They will provide the bamboo for the prototype.

Read more about bamboebouwnederland at http://www.bamboebouwnederland.nl/

Photo's of 1:50 model

Finished pavilion model

Below are some pictures of the model that I made to check on the theory that the diagonals could be tensile elements. From the model, although it's not super accurate, I can tell that the combination of "stiff" joints and the tensile elements could work very well. Next I will have to check if the resulting deformations are not too large.


Front view


Side view


Inside view

Below are some pictures of the building process


First part - work in progress


Second part - Work in progress


Impression of the model

Final results

After the first model more models were made and calculated. After a few fails the following model was baked:


Elevations and plans of model 2

The model was imported into DIANA and given material and physical properties. The differences between the models is the diameter used for the main parts.
Model 2.2
The diameters are 0.1 meter for the edges and the middle arc and 0.05 for the other straights. The crosses in each diamond are strips of 0.02 x 0.05 meters.
Model 2.3
The diameters have increased to 0.16 and 0.08 meters.
Model 2.4
Same diameters as Model 2.3 with the addition that the crosses now also have a diameter of 0.08.
For details I recommend the report.
Below are the results:


Model 2.2


Model 2.3


Model 2.4


Conclusion

The bamboo pavilion design concentrates the forces in the middle, because the hypar is cut and mirrored. The pavilion also bends asymmetrical under the load, because the pavilion has a wide and a narrow side. At the wide side a higher force concentrates at the arc then at the narrow side. The result is a higher stress.
The pavilion was tested at the largest configuration. Even with the largest possible diameters the compression stress is to high (> 100 N/mm2). The tension stresses are within the limits, with the set Cross as strip or as pipe; pipe has a higher section area and can therefore take more force.
The load on the pavilion should be limited to a maximum of 700 N/m2. Higher loads are not likely.
The stresses in the crosses in each diamond are both tension and compression. Because of the design concentrations can happen where there is two compressive forces or two tensional forces.
Not all the goals of this research have been reached. In this configuration of parameters the pavilion cannot be build with bamboo. The compressive stresses are too high. The pavilion cannot be build with only tensile elements in each diamond. Concentration of compressive forces can occur. The size of the pavilion has not been determined yet. The size of the load has been determined and should not exceed 700N/m2.

First Results

First results
Following are the first results of the first 4 weeks of SA.
The results consist of three parts:
1. Grasshopper and Rhino model
2. DIANA input
3. DIANA output
4. Conclusions

Grasshopper
The first step in the research is a parametric model made using Grasshopper. The model describes a hyperbolic paraboloid (hypar); a double curved surface build up from straight parts. The hyper is cut and mirrored, so the result is a pavilion standing on 3 points and resembling a butterfly.




DIANA input
To make mechanical calculations a few steps must be taken to create a DIANA model.
1. The parameters are set at a certain value
2. The models are exported from Grasshopper (Baked) to Rhino
3. In Rhino all the lines are cut into small pieces
4. The model is exported as a IGIS
5. DIANA imports the IGIS

The next step is preparing the DIANA model
1. All the lines are put into sets
2. Each set gets physical and material properties
3. Each set gets a mesh division and type

Output #1 (bake #1)
Arm 1: 20 meters
This arm is mirrored, so the length of the pavilion is 40 m
Arm 2: 20 meters
This arm is angled
sin (angle 1) * arm 2 è sin 45 x 20 = 14.1 m

Angle 1: 45˚ (wing tip angle)
Angle 2: 0 ˚ (mirror angle)

Height 1: 6 m
Height 2: 6 m
This height is cut at 30%, so 1.83 m

Division: 8

DIANA input
First input is the IGIS, based on the dimensions of #1 bake of Grasshopper
Second input is the material: Bamboo
Young's modulus: E = 15000 N/mm2 è 15E9 N/m2
Poisson's ratio: 0.32
Weight: 600 kg/m3
Dimensions
Straight frame: Tube
ø = 0.1 m
t = 0.02 m
Diagonals: Strip
a = 0.02 m
b = 0.07 m


Mesh
Type: CL18B (BE3)
Division: 2
Loads
Gravity: factor 1
(dead weight)

DIANA output
The output from DIANA can be seen in three categories:
1. Shape
2. Local tensions
3. Local force

Shape
The maximum deflection of the wingtips is about 0.01 meters.


Local tensions
The maximum tensions can be divided into positive and negative, also tension and compressive.
Maximum tensile stress: 0.552 N/mm2
Maximum compressive stress: -0.626 N/mm2


Local normal force
The maximum local force is almost -2,000,000 N. The number doesn’t really give extra information, but the shading shows a better division of the forces.


Conclusions
One of the first conclusions is:
Bamboo is strong.
The pavilion has a lot of potential, because the stresses stay well below the maximum allowed levels.

Next conclusion to be made is that the model isn’t perfect yet. It needs lot of improvement. The following things will be altered:
1. The size of the pavilion
2. The dimensions of the bamboo
3. The loads on the pavilion
Grasshopper and Rhino will be used for 1
DIANA will be used for 2 and 3

Boundary Conditions

Boundary conditions
The Bamboo Hypar Pavilion needs boundary conditions, so the research isn’t endless. For the research to have useable results, at least two boundary conditions must be made:

Maximum size on site
The site for the pavilion is a resort in Pejaten, Bali (Indonesia). The building will have the function of reception building, an eye catcher. It will house a bar and will be in the restaurant section of the resort.
The location shown is in the middle of the resort. The boundary conditions are given by the surrounding buildings and site elevations. Trees are not taken into account.



Bamboo material properties
The material bamboo has several properties that are needed for the mechanical analysis. The properties can be found in scientific papers and in the program CES EduPack. This program shows the following properties:
Young’s modulus E = 15000 - 20000 N/mm2
Poisson’s ratio 0.32 - 0.46
Tensile strength σ = 160 - 320 N/mm2
Compressive strength σ = 60 - 100 N/mm2

For the diameters CES has no additional information. On bamboo.com and from the book IL31 BAMBUS – BAMBOO various information can be found on the sizes. These range between very small (several centimeters) to quite large (up to 20 cm in diameter).
To stay within a certain range diameters will be used up to 10 cm.

For the first research in DIANA (as described in the Research for StandUpArchitecture) first the lowesr values will be used. In later models these values will vary.

Assumptions
For the research a number of assumptions has been made. Because these assumptions may prove false in future research, I will list them here to be rectified or confirmed later.
• All the joints are hinges
• The foundation is rigid and does not deform
• The connection between the foundation and the pavilion is clamped
• The material has no flaws

Stand up Architecture - Bamboo

Introduction
Stand up Architecture (SA) gives the student the opportunity to investigate a subject of their liking. It also provides the opportunity to do preliminary research for the Graduation Project of Building Technology (MSc4).
The tools students can use are the usual tools, like AUTOCAD, MAYA and SKETCH-UP. But the students can also use parametric models and are even encouraged to use these. The programs available for that are Rhinoceros 4.0, with the Grasshopper plug-in, MAYA, with the MEL scripting plug-in and Generative Components.

Bamboo
Even before starting SA I was always interested in the use of wood in construction. Searches for interesting wood related subjects in the past always brought me to results that seemed unfit for further investigation. Then a project by Florian Heinzelmann got thrown into my lap and ideas for a Graduation Project were born.
At Pejaten on Bali, Indonesia, a resort builder asked Florian to design an entrance pavilion made out of bamboo. The resulting design is a bamboo Hypar construction with an ingenious shading system. But the design didn’t ensure that the structure could actually be build. The research needed to calculate the forces flowing in the structure was beyond the reach of the designer.
The project, unfinished, was presented by Andrew Bogart to the coming students of SA. As this project would need a lot of research, I thought it would take enough time to fill my graduation year. It also involved researching a wood construction, although bamboo can be seen as a different category. I decided to take up the challenge.

Design by Florian Heinzelmann.

The Hypar roof
The design for the bamboo pavilion is a Hypar. The Hypar is a Hyperbolic Paraboloid and is doubly ruled. This means that the surface consists of straight sections in two directions. Such a geometry could be made from straight, long bamboo sticks, following the scheme shown below and layering them on top of each other.


The designed construction will need to be researched in various ways. The main research parts are:
· Strength constraints of bamboo
· Boundary conditions of the pavilion
· Connections
· Elements to take in plane forces (shear/tension/compression)
· Shading elements
Although these might not be the only parts to be researched, they will most likely take up most of the research. Also, parts can be combined.
One of the first ideas is to combine the shading elements and the elements that take the in plane forces. Bamboo strips could be used, but so far no conclusions can be made.

Research for Stand up Architecture
For SA I will start researching the design. For this a number of steps will be taken.

1. Wire model
Parametrically modeled in Rhinoceros using Grasshopper to change the height, length and width of the model. The subdivision of the plane, the angle of the mirror plane and the angle of the triangles will be fixed.

2. Creating an IGIS
From the Grasshopper model wire models will be “baked” with a fixed height, length and width. These will be prepared to be exported as IGIS, so they can be imported into DIANA.

3. DIANA analysis
Using DIANA, the IGIS will be given material and physical properties. The resulting models will be analyzed in strength. The output file will show the forces flowing in the model. This way the strains and stresses can be analyzed to see if the bamboo is strong enough to create the design.


4. Making a physical model
Using the information from the DIANA analysis a physical model can be made. This physical model can then be used to support the theory.

5. Comparing lighting
The physical model, if successful, can provide a view into the shading. The physical shading elements, applied to the model, can then be compared to a digital model, based on the Rhino models.


The steps above should ensure a full circle of research from parametric to constructive to physical and then back to parametric.

StandUpArchitecture Take 2

From August 30th I started StandUpArchitecture for the second time. The last time I had some problems finishing the subject, because other matters required my attention more.

Now those matters are out of the way. This means the subject will not be interrupted again and will also be used for the Master Graduation for Building Technology.

In the next few weeks I will post all the progress on the StandUpArchitecture and on my graduation project, which are related. Research from StandUpArchitecture will be used to make a proposal for graduation.