1. Introduction and research needTraditionally, bamboo has been limited for the use of building low-rise
structures located in tropical countries. In recent years, there has been a
massive increase in the use of bamboo products and the design of bamboo-
based, load-bearing systems..
Few studies have studied the structural fire performance of bamboo,
which is essential if fire safety considerations must be accounted for (e.g.
complex architectures, or mid-, high-rise construction).
The reduced mechanical properties and reduced cross-section methods both
form the basis of understanding the behaviour of bamboo under fire
conditions.
This work is focused on the reduction of the compressive strength of
bamboo at elevated temperature.
2. Test methodologies
Heating of test samples
The samples were tested at temperatures ranging between ambient
temperature (around 23○C) to 250○C.
Thermal penetration tests showed the temperatures changes inside the
samples at different temperatures. The tests were used for defining the
steady state conditions and the temperature inside the sample during the
test.
Figure 1. Thermal penetration test on round bamboo (left) and
variation of temperatures and thermal gradients in the sample (right)
Mechanical tests at elevated temperature
The compression test was developed in a novel set-up. the samples were
mechanically tested within the environmental chamber. and after specific
periods of time, the mechanical test was developed at the same time than
the sample was being heated up.
A set of thermocouples measured the temperature on the sample’s surface
with strain gauges and a load cell also being used to measure strain,
displacements and load.
Figure 2. Compression test set up at elevated temperatures
3. Analysis of compressive strength and failure modes
The compression strengths of the samples were obtained at different
temperatures calculated due to the correlation between surface and interior
temperatures. The strain was taken from the measurements of displacement
delivered by the machine crosshead. Afterwards, new measurements were
incorporated using strain gauges that can accurately be used at
temperatures up to 120○C.
Round bamboo has a substantial drop in the compression strength below
ambient temperature. Between 120○C and 160○C, there is a slight increase
in the strength. Beyond 160○C, the mechanical properties of the samples
decreased significantly.
Figure 3. Tested samples at ambient temperature (left), 120○C
(middle), and 250○C (right)
Figure 4. Stress – strain curves at elevated temperature on round
bamboo
Figure 5. Compressive strength reduction at elevated temperature on
round bamboo
4. Discussion & concluding remarks
Bamboo normally presents an elephant foot buckling failure, which induces
a splitting of the sample due to the low shear strength and poor
perpendicular tension strength of the material. However, a different failure
mode can be seen in samples tested at a higher temperature. e.g. buckling
at half – height or crushing.
At elevated temperatures, the material loses its plastics behaviour, losing
the capacity of resist higher deformations. At lower temperatures, bamboo
keeps resisting load in an inelastic zone.
5. Future work
The same experiments will be used for the testing of laminated bamboo.
Other load conditions will be tested during the development of the PhD
project. Dynamical Mechanical Analysis Tests (DMTA) will be performed
to understand the elasticity modulus variation. Mechanical tests in larger
elements will be conducted at temperatures and heat fluxes below and
above the ignition point.
Bamboo compressive strength at elevated temperaturesMateo Gutierrez, Joshua Madden, and Dr Cristian Maluk
School of Civil Engineering at The University of Queensland
Round Bamboo Sample
Thermocouples on the sample’s surface
Environmental Chamber case
Strain gauges on bamboo’s surface
Mobile machine crosshead for applying compression load
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