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Student Projects
Name:Megan Knoch
University: University of Minnesota-Twin Cities
Faculty Advisor: Peter McMurry
Email: knoch017@umn.edu
Project Description:
Bamboo Scaffolding has been used for more than 5000 years in Southeast Asia. As well as being an economical and environmentally friendly method of construction some people also believe that bamboo has good feng shui properties and can be a trusted bringer of good luck and calming energy. So, can this versatile material, with its positive energy, be utilized as scaffolding in the US? In general, the use of bamboo has its advantages over other types of scaffolding, in terms of low material cost, simple erection, and adaptability. Strain and loading difference could make this material suitable for certain US building conditions. Using a strain gage, the strain in both the vertical and horizontal directions can be determined and compared with empirically determined steel values, therefore determining if bamboo scaffolding is suitable for US conditions.
Products: DAQ-6008
The Challenge:
How do the structural characteristics of bamboo scaffolding compare with steel?
The Solution:
Bamboo deflects more then 3 times as much as steel, while deflection can be unnerving when experiencing it, it is not a critical factor until failure occurs. Bamboo breaks at about a fifth of the force required to break steel. Although this experiment tests the loading of one piece of bamboo, it can be combined in a structural unit to have the same capabilities as steel. A cost benefit analysis is beyond the scope of my project, but it would be a worth while pursuit. Depending on the application and types of forces acting on the scaffolding, bamboo can be used in the place of metal scaffolding.
Benefits from LABVIEW:
LabView assisted me in the calculation of the strain, standard deviation of the measurements, and also allowed me to look at the dynamic response of the vertically loaded bamboo, to determine the impulse force required to break it. Without LabView the procedure would be complicated by the need to calculate the average strain for each load and standard deviation. Also, the dynamic response could not be observed without LabView.
**For additional images see PowerPoint
Bamboo Scaffolding
Building and construction consume more than 3 billion tons of raw materials each year. Using green building materials and products promote conservation of the world’s resources. Bamboo is a fast growing and renewable natural resource. It is extensively used in construction in Southeast Asia. In Hong Kong, it is estimated that the erection of bamboo scaffolding is about 6 times faster and dismantling of bamboo scaffolds about 12 times faster, than metal scaffoldings. In general, the use of bamboo has its advantages over other types of scaffolding, in terms of low material cost, simple erection, and adaptability. Strain and loading difference could make this material suitable for certain US building conditions. Dried bamboo is used 2 ways for scaffolding, as a support, and as strengthening bars. Since, bamboo is a fibrous material the strength of the bamboo must be tested both vertically and horizontally. Using a strain gage the strain in both the vertical and horizontal directions can be determined and compared with empirically determined steel values.
A bamboo stick was loaded both vertically and horizontally with known weights, 0lb to 290lbs. The inner and outer diameters were be measured because the thickness of the bamboo is a factor in how the strain and stress will change. Two strain gages were attached in the center of the bamboo, on opposite sides, to amplify the resistance, which will give more accurate readings. This is assuming the strain is equal and opposite on both sides. The strain was collected at 75 samples at 5 kHz. The stress was calculated for the horizontally loaded bamboo and compared with a horizontally loaded steel tube with same cross sectional area. Also, the strain was compared for the horizontally and vertically loaded bamboo to empirically determined strain in steel. In addition, the horizontally loaded bamboo had an impulse force applied until it broke and therefore the corresponding force to the strain was calculated. The graphs for force versus strain and stress versus strain are shown below.
The strain increases linearly as force and stress are increased, which is expected. The horizontally loaded bamboo has the highest strain and the vertically loaded one has the lowest. This is because the bamboo fibers make the bamboo stronger when loaded vertically versus when loaded horizontally. Using the modulus of elasticity and the empirically determined strains, the stress of the steel can be found. The stress in the steel increases more rapidly than the bamboo.
Not enough weights were available to break the bamboo, thus, an impulse force was used to break the bamboo. The relationship will only be linear up to a point and will flatten off near the fracture; therefore the linear line cannot be used to determine the force needed to break the bamboo. Based on acceleration and mass of the person providing the impulse, the force required to break a horizontally loaded bamboo is estimated to be 8500lb.
| Force to Break Bamboo (est.) | Force to Break Steel[1] |
Force (lb) | 8500 | 50,000 |
Strain (micro-strain) | 360,000 | 1,300,000 |
The force required to break bamboo is about 17% that of the force required to break the steel and the strain is 28% of the strain at the breaking point of steel. The vertically loaded bamboo would require a much higher force to break, since the strain for the given forces is much lower than the horizontally loaded steel; this is because the fibers make the material stronger. Depending on the application and types of forces acting on the scaffolding, bamboo can be used in the place of metal scaffolding.
[1] Tensile Strength Testing. Stainless Steel Tube and Pipe. < http://www.stainless-steel-tube.org/Tensile-Strength-Testing.htm>
