Strength of Composite Bamboo and Reinforced Concrete Beams

Strength of Composite Bamboo and Reinforced Concrete Beams
Siwar Moukatash1, a, Oubay Hassan 2, b
1
College of Engineering, Swansea University, Singleton Park, Swansea, United Kingdom,
SA2 8PP
2
College of Engineering, Swansea University, Singleton Park, Swansea, United Kingdom,
SA2 8PP
a
[email protected], [email protected]
Keywords: Composite, Reinforced Concrete, Bamboo, Sustainability
Abstract. Concrete is the most used man-made material in the world, with approximately three tons
used per annum per individual. Twice as much concrete is consumed around the world than the
entirety of all other construction materials, including wood, steel, plastic, and aluminum [1].
However, the material is used so widely that world cement production now contributes 5 percent of
annual global CO2 production [2]. Thus, the idea of reducing the amount of concrete in structures
becomes attractive. By constructing a hollow section in the reinforced concrete elements, a smaller
quantity of concrete would be utilized. Hollow concrete sections are commonly used but their
construction tends to complicate the setting up stage and increase the cost. In this paper, the strength
of hollow reinforced concrete beams produced by the insertion of a bamboo tube during
construction is investigated. Treatment of the bamboo is considered to ensure that cracks in the
concrete do not occur during curing. Experimental modeling and numerical simulation is carried out
on three sets of composite beams, designed to fail in shear, bending, and a combination of shear and
bending. Each set contains one beam with bamboo insert and one without the bamboo to be used as
a reference beam. The results of both experiments and numerical simulation show that, in addition
to the reduction in weight and the volume of concrete used, the strength of the beams increased
noticeably.
Introduction
A composite material can be defined as a combination of a matrix and a reinforcement, which
when combined gives properties superior to the properties of the individual components [3].
Composite action is developed when the two load carrying structural members are integrally
connected and deflect as one [4]. In the case of a composite, the reinforcement is the fibers and is
used to fortify the matrix in terms of strength and stiffness. The reinforcement fibers can be cut,
aligned, and placed in various ways to enhance the properties of the resulting composite [3]. A
notable natural composite member that has yielded favorable results in previous studies is bamboo
for use as reinforcement in concrete.
Bamboo is a sustainable and sturdy building material, widely used in Asian, Pacific Islander, and
Central and Southern American cultures [5]. Bamboo holds a number of benefits over other
construction materials – it is affordable, it grows extremely quickly, and is renowned for a strength
that is comparable to steel [6]. Hence, the use of bamboo tubes to construct the hollow section in the
reinforced concrete elements was proposed. There are many different ways of combining reinforced
concrete and bamboo together to make the best use of the two materials, but the scope of this study
was limited to reinforced concrete-bamboo beams.
Two key factors that were considered before finalizing the concept proposed above were the
location of the hollow section in the reinforced concrete beam and how to create the hollow section.
The importance of these two factors stems from the impact they would have on the strength and
ease of buildability of the reinforced concrete-bamboo beam. Since the top of a reinforced concrete
beam is under compression and the bottom is under tension, and steel has a tensile strength far
greater than that of concrete, the concrete in the lower part of a reinforced concrete beam becomes
relatively ineffective. Therefore, the hollow section was placed underneath the neutral axis of the
reinforced concrete beam.
In this paper, the strength of a hollow reinforced concrete beam produced by the insertion of a
bamboo tube during construction will be investigated. Treatment of the bamboo has to be
considered to ensure that cracks in the concrete do not occur during curing. Numerical simulation
will also be carried out to identify the best simulation method for the constructed beams in order to
obtain the experimental results.
Experimental Modeling
Method. The aim of the experiment was to test how reinforced concrete and bamboo work together,
and to investigate the impact of adding a bamboo tube on the structural properties of a reinforced
concrete beam. The idea was to test the beams in the different types of failure: shear, bending, and a
combination of shear and bending.
Three sets of reinforced concrete beams were designed to ensure bending failure, shear failure,
and a combined shear and bending failures. The reinforcement and the value of the predicted failure
load for each beam were obtained using the limit state method (LSM). The limit state method is a
theoretical design method used for the design of reinforced concrete structures/elements. In the limit
state method, a structure is designed for safety against collapse (i.e., for ultimate strength to resist
ultimate load), and checked for its serviceability at working loads. To ensure the above objectives,
the design should be based on characteristic values for material strengths and applied loads, which
take into account the variations in the material strengths and in the loads to be supported. Normally,
the design values are obtained from the characteristic values through the use of partial safety factors
[12]. However, for the purpose of this experiment, to ensure the exact collapse load was obtained,
partial safety factors were not used.
The design considered the availability of molds; hence, assumptions were made as follows, the
beams were 1000 mm long, with a cross sectional area of 120 × 150 mm2. The concrete strength
was taken to be 30 MPa, and the concrete cover was 10 mm. The links had 6 mm diameter, and
yield strength of 250 MPa. The longitudinal steel yield strength was 500 MPa.
The method can be summarized as follows:
•Three beams were designed then assembled and used as a control for testing against another set of
equivalent composite reinforced concrete-bamboo beams to evaluate the performance of the
composite beams.
•The steel cages were built by tying the stirrups and the longitudinal bars using wires.
•Two days before testing, the bamboo was soaked in water to allow it to expand. This was done for
two reasons. Firstly, to prevent pre-test cracking in the concrete, caused by the expansion of dry
bamboo when submerged in the water from the concrete mix. The other reason was so the water
being absorbed into the bamboo will not influence the properties of the concrete.
•The bamboo tube was then attached at a distance of 50 mm from the lower end of the cage, as
shown below in Figures 1a and b, to increase the strength of the element.
Figures 1a and b. Bamboo tube attached to steel cage.
The final step before casting was designing the concrete mix. 6 mm maximum size gravel, and
zone 2 sand were used for the concrete mix. 6 mm maximum size gravel was used, instead of the
usual 20 mm maximum size gravel, so the aggregates in the concrete mix would be small enough to
fit evenly between the bamboo tube and the steel cage. However, the mix was then adjusted to
account for the percentage of water that was already present in the aggregates, based on the results
of the aggregates-water content test conducted the day before casting.
Due to limitation in the size of the mixer, a total of three concrete mixes were required. Each mix
made two beams, a composite beam and its control, and three cubes. The same mix was used for
each composite beam and its reference beam to ensure that any change in structural properties
would not be due to disparities in the concrete structural properties. The cubes were used to obtain
the real strength of the mix. The specimens were then left to harden for a day, before removing
them from the mold and wrapping them in polythene. The beams and cubes were then watered on a
daily basis and allowed to cure for 28 days before testing.
The cubes were tested first to obtain the concrete strength of the beams. Next, the beams were
inserted into the flexural test machine. Two rollers spanning 950 mm supported the beams. A
LVDT, Linear Variable Differential Transformer, was used to measure the deflection of the beams
at the center. Finally, two point loads were applied symmetrically, each 100 mm away from the
center of the beam. Since the machine used for testing the beams only controlled the speed of the
displacement, not the load, care was taken to ensure a slow rate whilst loading, in addition to
pausing at intervals to allow time for stresses to propagate (i.e., for the dynamic affect to disappear).
Results. As can be seen in Table I, the results obtained from the cube test show that the average
concrete strengths obtained from the three mixes range between 32-33 MPa. This slight discrepancy
between the values obtained and the 30 MPa strength expected, indicates that the desired strength
was reached. However, the predicted failure load was recalculated using the actual strength to
ensure accurate results.
Table I. Cube Test Results
Cube
Force Applied (kN)
Average Force Applied (kN)
Average Cube Strength (MPa)
Shear 1
710
717
32
Shear 2
695
Shear 3
745
Bending 1
735
740
33
Bending 2
750
Bending 3
750
Combination 1
750
Combination 2
735
Combination 3
750
740
33
Figure 2 shows the cracks obtained after loading the composite designed to fail in shear. In
reinforced concrete beams, shear cracks form diagonally with an inclination towards the axis of the
beam [13]. The Eurocode adopts a traditional, empirical approach to determine the shear behavior of
reinforced concrete beams without shear reinforcement. This assumes that the shear resistance is
derived from a shear capacity (stress) acting uniformly over the effective area of the section. The
shear capacity is strongly dependent upon the shear-span to depth ratio (𝑎! 𝑑), as 𝑎! 𝑑 increases,
the shear capacity decreases. The shear-span (𝑎! ) is the distance between the loading point and the
supporting point. For 𝑎! 𝑑 > 3, which is the case for this experiment, it is expected that, the shear
crack forms in a stable fashion, and the shear capacity is almost constant, i.e., independent of the
value of 𝑎! 𝑑 [14]. Since both the composite beam and the reference beam presented a crack pattern
similar to the one described above, it is clear the beams failed in the mechanism required.
Figure 3 presents the ‘Load vs. Displacement’ graph of the set of beams designed to fail in shear.
Whilst the reference beam peaked at a load in the [45-50 kN] interval, the reinforced concretebamboo beam peaked in the [60-65 kN] interval. This peak, in addition to the drop in the load
bearing capacity of the beam that ensues, signifies the load at which the concrete in each of the
beams cracked. Once the concrete cracked, the curves then exhibited a linear depreciation. This
occurred because the spacing between the shear links was greater than smax; hence, while the steel
continued to carry the load, the cracks were also expanding (i.e., there was no shear transfer). Lastly,
it can be seen from the graph that the reinforced concrete-bamboo beam sustained this depreciation
longer than the reference beam, probably due to the hollow bamboo tube playing a part in carrying
the load with the rebar. To sum up, the results illustrate that the composite beam’s performance was
far superior to that of the reference beam, as the reinforced concrete-bamboo beam managed to
withstand a larger load and a greater displacement.
Figure 4, in turn, exhibits the cracks obtained after loading the reinforced concrete-bamboo beam
designed to fail in bending. In reinforced concrete beams, flexural cracks start at the tension side and
extend up to the neutral axis. In general, the cracks are uniformly spaced along the most stressed part
of the beam, i.e. near the mid-span in sagging [15]. As the composite beam and the reference beam
presented crack patterns similar to the one described above, it is clear they failed in the expected
mechanism.
Figure 5 presents the ‘Load vs. Displacement’ graph of the set of beams designed to fail in
bending. Both the reinforced concrete-bamboo beam and the reference beam peaked at
approximately the same load. In this case, the spacing between the shear links was smaller than smax;
hence, the peak signifies the load at which the steel had started yielding (the concrete had not
cracked yet). The graph then shows the reference beam sustain a slight linear appreciation (steel
continued yielding), before failing and recovering its elastic deformation. However, while the
reference beam experienced a very small increase in the load carried before failing, the reinforced
concrete-bamboo beam displayed a steeper slope, suggesting that the bamboo was also playing a
part. The curve corresponding to the reinforced concrete-bamboo beam then peaked again before the
steel continued to yield until failure. This second peak was the point at which the bamboo cracked.
The bamboo most likely cracked because it was confined, despite being able to carry the load. As
with the case of shear failure, the composite beam failing only in bending again managed to
withstand a larger load than its reference beam. However, both the reinforced concrete-bamboo beam
and the reference beam sustained a somewhat equivalent displacement.
The composite and its reference beam, that were designed to fail in a combined shear and
bending failures, exhibited crack patterns associated with shear failure near the supports, and
flexural failure at the center.
Figure 6 presents the ‘Load vs. Displacement’ graph for the two beams. As expected, the graph’s
outline is a compilation of the two previous cases. As demonstrated by the beams that failed due to
shear, whilst the reference beam peaks at a load in the [70-75 kN] interval, the reinforced concretebamboo beam peaks in the [85-90 kN] interval. This peak, in addition to the drop in the load
bearing capacity of the beam that ensues, signifies the load at which the concrete in each of the
beams cracked. Once the concrete cracked, the curves then exhibited a linear depreciation. The
curves then pick up again (shear links kicked in) before they maintain a smaller angle of
depreciation, until finally failing. It is most likely that the bamboo, in the reinforced concretebamboo beam, played a part alongside the shear links, explaining the stark difference in load
bearing capacity between the two beams at the second peak.
Table II summarizes the results of the beams tested. The significant increase in the load bearing
capacity, and maximum displacement of the composite beams relative to their reference beams
prove the experiment successful. The increase in the load bearing capacity achieved verifies the
notion that the creation of a hollow section in a reinforced concrete beam, by using a bamboo tube,
produces a substantial increase in the strength of the reinforced concrete beam. Inserting a bamboo
tube into a reinforced concrete beam also improves its carbon footprint by reducing the amount of
concrete utilized due to the hollow section. The improvement in the load bearing capacity takes
place because the bamboo tube has a tensile strength similar to that of mild steel; hence, by
replacing part of the concrete, which has a negligible tensile strength, under the neutral axis by the
bamboo tube, the beam was able to carry a far larger load. Furthermore, it is worth noting that the
improvement in structural properties achieved suggests that composite reinforced concrete-bamboo
elements may, in future, be used for improving the strength at an early stage in construction.
Numerical Simulation
Method. Simulation has become an essential constituent of composite element design
development in the current engineering environment. Engineers can use multiphysics to better
foretell how composite elements will respond to every possible environment in an attempt to design
cheaper, faster, and better performing structural elements [16]. The computer modeling will serve as
a second method to investigate the impact of adding a bamboo tube on the structural properties of a
reinforced concrete beam. The numerical simulation will be limited to that of the tested composite
reinforced concrete-bamboo beam that failed only in shear. For the beam to fail in shear, the shear
links were spaced apart at a distance greater than smax, thus rendering the shear links immaterial to
the structural properties of the beam. This important design property meant that this beam could be
credibly modeled without any shear links.
The software was first used to determine the strength of a concrete beam without steel rebar, then
a reinforced concrete beam was analyzed, and finally a beam with steel rebar and bamboo was
investigated.
There are numerous finite element structural softwares such as ANSYS, ANSYS Workbench,
Abaqus FEA, SolidWorks, etc., each with its own set of advantages and disadvantages. The
engineering simulation software Ansys Workbench was used to construct the composite reinforced
concrete model because of its user friendly interface, flexibility, robustness, and unique capability in
multiphysics.
ANSYS Workbench is a general purpose software, used to simulate interactions of numerous
disciplines for engineers, making it possible to simulate tests that verify and improve the product
tested in virtual environment. ANSYS Workbench can also execute advanced engineering analyses
safely, rapidly, and practically, by its assortment of time based loading features, contact algorithms,
and nonlinear material models [17]. Due to the aptness of the software to diverse engineering
disciplines, and to improve its computing speed, the software package is split into many categories,
including static structural analysis, model analysis (vibration analysis), thermal analysis, etc., each
with a set of finite elements, specifications, and instructions of their own. Static structural was used
to model the composite reinforced concrete-bamboo beam. In this interface, one can apply forces,
pressures, torques, etc., on the models and see how the stresses develop. Ansys Workbench, like
other similar software, consists of five main divisions: geometry building, model discretization,
simulation setup (materials, boundary conditions, loading, and solution controls), solution process,
and result analysis.
A composite reinforced concrete-bamboo beam comprises of various elements for which the type
of element, material properties, and real constants, should be defined. The principal elements of the
reinforced concrete-bamboo beam are steel rebar, bearing plates, concrete beam, and bamboo tube.
All engineering simulation begins with construction of the geometry that represents the design. This
could be the air volume for a fluid or electromagnetic study or a solid component for a structural
analysis [18]. ANSYS Workbench can import CAD data and is also able to build a geometry with its
DesignModeler software [17].
For modeling of the concrete beam in ANSYS Workbench, a rectangle was drawn and then
extruded to create a rectangular prism. Four bearing plates were then constructed. Bearing plates are
steel plates with 25×120 𝑚𝑚! cross-section and a thickness of 5 mm. The plates were used to ensure
the beam does not fail due to localized stresses at the loading points or supports. To create the first
bearing plate, a rectangle was drawn, and then extruded to create a rectangular prism. The bearing
plate was then replicated at the other three locations using the Pattern function. Pattern allows the
user to replicate a chosen body, and move it to other locations in the geometry, all while maintaining
the original body in its original position. Lastly, three holes equivalent in size to the rebar and the
bamboo tube were created to prepare for the addition of the steel reinforcement and the bamboo tube.
For simplification purposes, it was decided that the bamboo tube would be modeled as a third rebar.
This assumption is justified since bamboo has the same tensile strength as mild steel; hence, by
calculating the area of the outer crust of the bamboo, a third rebar of the attained area may serve as a
substitute to the bamboo tube. Three circles were then drawn at the same location as the holes and
extruded to create the three rebar. This step marks the end of the geometry building section. All the
details are shown in Figure 7.
The next step was model discretization. A finite element model consists of a system of points,
termed nodes, which form the shape of the structure. Linked to these nodes are the elements which
form the finite element mesh and encompass the material and structural properties of the model,
specifying how it will respond to certain conditions [19]. Mesh classification is based on the
connectivity of the mesh: structured or unstructured. A structured mesh is identified by regular
connectivity that can be expressed as a two or three dimensional array. This limits the element
choices to quadrilaterals in 2D or hexahedra in 3D [20]. An unstructured grid typically comprises of
tetrahedral shapes and is identified by irregular connectivity, implying that it can usually be used for
peculiar or unusual shapes. This flexibility is particularly beneficial for complex geometry, where a
structured mesh may be challenging to generate around or in the shape [21]. A hybrid mesh is a mesh
that comprises of structured portions and unstructured portions [20]. Hybrid meshes, consisting of
mixed element types, permit combining the ease of tetrahedral meshing on complex geometries, with
the advantages of traditional hexahedral cells in regions of less geometric intricacy [22]. A hybrid
mesh was used for the analysis. The density of the finite element mesh was determined after
conducting convergence tests. Figures 8a and b display the mesh produced.
The first step in the simulation setup was to choose Bonded for the Contact Region Type between
the concrete and the steel rebar, the concrete and the bamboo, and the concrete and the bearing
plates. When two separate surfaces touch each other such that they become mutually tangent, they
are said to be in contact [23]. Bonded means that both surfaces are not allowed to separate or slide,
i.e., surfaces will be together irrespective of – gap, penetration, loading, and behavior of other parts/
contacts.
The concrete was modeled using SOLID65. SOLID65 is applied for the three-dimensional
modeling of solids with or without rebar. The solid is able to crack in tension and get crushed in
compression. The element is characterized by eight nodes, each with three degrees of freedom,
translations in the nodal x, y, and z directions. The most vital aspect of this element is the treatment
of nonlinear material properties. The concrete is capable of cracking (in three orthogonal directions),
crushing, plastic deformation, and creep [24]. Conventional shear transfer coefficients range from
0.0-1.0. Typically, the range for an open crack is from 0.15-0.3, and for closed crack is from 0.7-1.00
[25]. Subsequently, 0.2 and 0.8 were chosen as shear transfer coefficients as recommended in
Ansys Workbench settings. The Young’s modulus, Poisson’s ratio, tensile strength, and compressive
strength were taken as 20000 MPa, 0.18, 2.6 MPa and 30 MPa, respectively.
The rebar and bamboo tube were modeled using Structural Steel and Stainless Steel from Ansys
Library, respectively. However, modifications to both of the materials properties were carried out in
the Ansys Library to ensure they were project specific. The density, Young’s modulus, Poisson’s
ratio, tensile yield strength, compressive yield strength, tensile ultimate strength, and compressive
ultimate
strength
assigned
for
the
steel
reinforcement
were
as
follows:
!
!!
!
!
!
7850 𝑘𝑔 𝑚 , 2×10 𝑃𝑎, 0.3,5×10 𝑃𝑎, 5×10 𝑃𝑎, 5.1×10 𝑃𝑎, 𝑎𝑛𝑑 0 𝑃𝑎, respectively. Moreover,
the density, Young’s modulus, Poisson’s ratio, tensile yield strength, compressive yield strength,
tensile ultimate strength, and compressive ultimate strength assigned for the rebar representing the
bamboo tube were as follows: 7850 𝑘𝑔 𝑚! , 1.9×10!" 𝑃𝑎, 0.3,2.5×10! 𝑃𝑎, 2.5×10! 𝑃𝑎, 2.6×
10! 𝑃𝑎, 𝑎𝑛𝑑 0 𝑃𝑎, respectively.
The supports were modeled in such a way that a hinged roller simply supported beam was
created. A Remote Point was created for each of the bearing plates so it could be used to set the
supports. Remote Point is a point in the center of a body that controls the entire body selected. The
first support was constraint in X Component, Y Component, Z Component, Rotation Y, and Rotation
Z. This setup allows the beam to rotate at the support. The second support was constraint in X
Component, Y Component, Rotation Y, and Rotation Z. This ensured the outcome was an
indeterminate structure.
Each force was applied as a pressure, equal in magnitude to the value of the point load, distributed
across the entire cross section of the bearing plate. The loads were applied in 50 steps in order to
view the results obtained at each sub step. This is vital when attempting to locate the collapse load
as it allows the user to monitor the variation in stresses and deformation at each sub step, both
numerically and graphically.
As the materials behave nonlinearly, a nonlinear elastic analysis was performed for the simulation
of the tested beam. Analysis was carried out based on the total deformation of the beam, and the
stresses in each element individually. Failure of the beam takes place when deformation increases
nonlinearly with a very small load increment. The load incremental trace provided by the analysis
was used to confirm the failure load.
Figure 7. Geometry of model.
Figures 8a and b. Hybrid Mesh.
Results. To ascertain the success of the simulation of the model, the beam had to be analyzed at
three key stages. First, as a concrete beam without steels, then as a reinforced concrete beam and
finally, as a beam with rebar and bamboo.
The concrete beam model was investigated by evaluating the failure load achieved against the
predicted failure load. The predicted failure load was calculated using the laws of equilibrium to be
3120 N. The actual failure load obtained was 3200 N. The minor eccentricity present between the
predicted and actual results is most likely due to the bearing plates used in the simulation, a factor
that was not taken into consideration when calculating the predicted failure load. Due to the minute
deviation between the predicted and actual failure load values, the model was judged successful.
The limit state method was used to establish the accuracy of the results of the reinforced concrete
beam model. Once the model was complete, convergence tests were conducted. It is vital to carry out
convergence tests on a model to confirm that a fine enough element discretization has been used
[26]. The convergence tests were carried out by gradually refining the mesh size and comparing the
resulting deformations. Figure 9 displays the results of the convergence tests. As the results of the 40
mm and 30 mm element size mesh were similar, this signified that the 40 mm element size mesh was
good enough for the model’s particular geometry, loading, and constraints. Therefore, 40 mm
element size mesh was used for the model. Table III displays the results obtained after loading the
reinforced concrete beam to failure. Despite the increase in load applied being minimal, the analysis
results showed a significant increase in deformation in the time step shown below, indicating failure.
The drop in the value of the maximum stresses in both steel and concrete is a further indicator of
failure. Lastly, it was observed that the failure load from the analysis, which lies somewhere in the
interval [37.2-38.4 kN], was comparable to both the collapse load obtained using hand calculations,
32 kN, and the experimentally obtained failure load, 47.57 kN.
The limit state method was used once again to establish the accuracy of the results of the
composite reinforced concrete-bamboo beam model. Table IV displays the results obtained after
loading the composite beam to failure. Despite the increase in load applied being minimal, the
analysis results showed a significant increase in deformation in the time step shown below; hence,
indicating failure. The drop in the value of the maximum stresses in both steel and bamboo is a
further indicator of failure. Lastly, the stress results indicated that the bamboo rebar yielded far
slower than the steel rebar, most likely because bamboo has a smaller Young’s Modulus than steel,
i.e., bamboo requires a far larger load than steel to produce the same increase in stresses.
Figure 10 displays the ‘Load vs. Displacement’ graph, of the results obtained both experimentally
and by simulation, for the composite beam and its reference beam failing only in shear. As expected,
the beams from the simulation initially slope at a steeper angle than the beams from the experiment,
despite having the same Young’s modulus values. This disagreement is due to the simplifications
assumed by setting the Contact Region Type between the concrete and bamboo as Bonded. Unlike
steel, which is bonded to the concrete, the bamboo tube is only confined by the concrete.
Nonetheless, the results obtained are still reliable as the behavior of the curves obtained bear stark
similarities. For instance, the curves of both reference beams, obtained using experimental and
simulation results, demonstrate a peak (concrete cracked), followed by a somewhat linear increase in
displacement (steel yielding), before failure. Furthermore, the curves of both composite beams,
obtained using experimental and simulation results, exhibit a second peak after the concrete cracks
initially (most likely due to the bamboo playing a part in carrying the load with the steel rebar).
Hence, as exhibited by the graphs from the experiment, the simulation results also indicate that the
composite beam sustained a larger load and displacement than the reference beam before failure.
Lastly, an appraisal of the composite beam and the reference beam failure loads obtained using
numerical simulation, suggests an approximate 25 % increase in the load bearing capacity of the
reinforced concrete beam due to the addition of the bamboo, relatively similar to the 31 % figure
obtained experimentally.
Figure 9. Convergence tests results.
Figure 10. Load vs. Displacement graph for beams failing in shear.
Conclusion
Summarized below are the results of the study:
• The results of both experiments and numerical simulation show that, in addition to the reduction
in the weight of the beam and the volume of concrete used, creating a hollow section in a reinforced
concrete beam by inserting a bamboo tube during construction increased the strength of the beams
noticeably.
• The experimental results showed a 31 %, 16 %, and 18 % increase in strength between the
reference beam and the composite beam failing in shear, bending, and a combination of shear and
bending, respectively.
• A 25 % increase in strength between the reference beam and the composite beam failing only in
shear was attained using numerical simulation.
• It is deduced through comparing Load vs. Displacement graphs, which show reference beams in
the different modes of failure with the corresponding composite beams, that the addition of the
hollow bamboo tube causes a considerable decrease in deflection of the beams.
• Since a close agreement exists between Load vs. Displacement graphs of test and modeled
beams failing only in shear, the model constructed can be used for future research and is valid for
modeling of composite reinforced concrete-bamboo beams failing only in shear.
• This improvement in structural properties achieved suggests that composite reinforced concretebamboo elements may, in future, be used for improving the strength at an early stage in
construction.
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