Concept and development of a steel–bamboo SI (skeleton–infill) system: experimental and theoretical analysis
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A steel–bamboo SI (skeleton–infill) system with steel frame as the skeleton and bamboo box as the filler is proposed, which realizes the requirements of building assembly and sustainable development. As a first step in studying the seismic behavior of the steel–bamboo SI (skeleton–infill) system, a simplified plane steel frame–bamboo infilled wall structure is tested under low-cycle reversed loading in this paper. The deformation mode, failure mode, hysteretic behavior and energy dissipation performance of the system are discussed. The test showed that the steel frame and the bamboo infilled wall were well connected and could work together. Then, the formulas for calculating the lateral stiffness of the system and the axial stiffness of the equivalent diagonal brace which replaced the infilled wall are obtained by theoretical analysis. The error between theoretical calculation and test results was about 1.3%, which proved the correctness of the proposed formula.
KeywordsSteel–bamboo skeleton–infill system Hysteretic behavior Lateral stiffness Equivalent diagonal brace
Stichting Architecten Research
China skeleton infill
In recent years, the bamboo has replaced wood as a new type of material and suddenly becomes very popular. After being processed, modern engineering materials  such as bamboo veneer, laminated bamboo  and bamboo scrimber  which are able to be applied in housing can be produced. The bamboo house has good seismic performance and can resist the magnitude 7 earthquake in India and the magnitude 7.8 earthquake in Hyogo of Japan . After the major earthquake in Wenchuan (China) on May 12, 2008, the bamboo anti-seismic living rooms were designed and constructed by one of the authors . In addition, the engineering bamboo can be used in bridge construction. Hunan University has built the world’s first 10-m-long bamboo bridge in Lei yang City, Hunan Province (China). It was officially opened to traffic in December 2007 and is still in use today . However, due to the small elastic modulus of bamboo, the stiffness of bamboo structure is insufficient, and the performance of bamboo in different directions is quite different ; hence, it is necessary to consider the need for combining bamboo with other materials. The effect of the FRP (fiber-reinforced polymer), reinforcement, concrete and thin-walled steel on the bamboo structure was studied by many scholars. A novel FRP–bamboo–concrete composite beam was proposed by Wei et al. . The test result showed that the load-carrying capacity and stiffness of this structure were greatly improved when compared with ordinary bamboo beam. Later, Wei et al.  investigated FRP sheet-reinforced bamboo beams and found the mechanical properties were good. The strength and stiffness of reinforcement–bamboo scrimber beam have also been greatly improved .
At present, steel frames and concrete boxes are used in most SI systems, but the concrete is a non-renewable resource and using concrete can produce lots of pollutions . The concrete has a large weight which makes it difficult to be lifted and transported, and it is easily damaged. Therefore, the bamboo has entered authors’ sight with its own advantages: lightweight, good mechanical properties and environmental friendliness [19, 20]. Moreover, both the bamboo structure and steel structure have the characteristics of easy assembly construction. Combining bamboo box and steel frame into steel–bamboo SI system can better highlight the building industrialization characteristics of SI system.
In this paper, a new SI structural system consisting of steel–frame skeleton and bamboo-box infills is proposed to satisfy requirements of the structural strength and stiffness in the multi-story buildings. In this new steel–bamboo SI system, the steel frame provides major structural strength and stiffness, and bamboo box is used to integrate building functions and bear part of the load. The bamboo box is made of indoor decoration, kitchen equipment, toilet equipment and partition wall that can be assembled with steel frame on site, which meets the requirements of building industrialization and sustainable development. Effective joint connection between bamboo box and steel frame is adopted. Compared with concrete box, the connection of the bamboo box is easier, and there is no wet work on site. Multiple seismic defense lines can also be formed through the connections which can increase the energy dissipation capacity of the structure, so that the structure can better resist influence from earthquakes. Different building requirements can be met by adjusting the size of the steel frame and filling bamboo box, and the internal device of bamboo box can be produced according to different needs. Figure 1b shows the draft of the proposed steel–bamboo SI system.
Mechanical properties of steel, bamboo and screw
Elastic modulus (MPa)
Yield strength (MPa)
Elastic modulus (MPa)
Shear modulus (MPa)
Ultimate bending strength (kN)
Initial stiffness (kN/mm)
2.1 × 105
Steel frame (S)
Bamboo infilled wall (I)
Dimension l × b × t (mm)
Horizontal bamboo keel
1250 × 100 × 32
Middle-vertical bamboo keel
1500 × 40 × 32
End-vertical bamboo keel
1500 × 100 × 32
1500 × 1250 × 8
Experimental device and loading method
Results and discussions
Then, when loaded to 28 mm, the third crack expanded upward about 30 cm from the bottom bolt hole, while the first batch of screws broke. When loaded to 32 mm, three cracks mentioned above continued to develop and the second batch of screws broke. The loading path was broken so that lateral bearing capacity and lateral stiffness of the steel–bamboo SI system were reduced. When loaded to 36 mm, the first and second cracks expanded from top to bottom. At the same time, the fourth crack appeared due to the out-of-plane buckling failure of the cover panel, and the crack developed from the middle position to the top and the bottom. At this time, the entire bamboo infilled wall had been severely damaged and the test was over. No diagonal cracks were observed during the whole test because the cementation seam exists in the bamboo infilled wall. So, in this test, only the vertical cracks were found at the cementation seam of bamboo panel and the bolt holes.
Mechanical properties of the steel–bamboo SI system
Yield load Vy (kN)
Initial stiffness K (kN/mm)
Ductility coefficient D
Steel–bamboo SI system
Energy dissipation capacity
Theoretical analysis of steel–bamboo SI system
In the steel–bamboo SI system, the stability of the steel frame is enhanced because the bamboo infilled wall acts as diagonal bracing. Because the low cyclic loading is used in this test, the infilled wall is needed in order to play a supporting role in both push and pull directions, so the equivalent cross bracing is more reasonable. Based on the above principle, the lateral stiffness formula of the structure is summarized through theoretical analysis, and the axial stiffness and ultimate bearing capacity of the diagonal bracings are derived.
Lateral stiffness formula
The horizontal internal force components of horizontal keel will be uniformly distributed along the keel, and the vertical internal force components of vertical keel will be uniformly distributed along the keel.
The influence of vertical internal force component of the horizontal keel and horizontal internal force component of the vertical keel on bamboo infilled wall’s shear deformation is ignored;
The shear stress of the bamboo infilled wall is uniformly distributed in the effective force range;
The initial stiffness and bearing capacity of the screws are equal in all directions;
The vertical deformation of screws of horizontal bamboo keels is neglected, and the lateral deformation of screws of vertical bamboo keels is neglected.
Equivalent diagonal bracing formula
The formulas mentioned above are mainly aimed at structural design, and no specific study has been made on the overall yield of the system. Therefore, only the equivalence of the system in the linear elastic stage is emphasized.
Comparison of theory and experiment
In order to verify the correctness of the simplified formula, the elastic lateral stiffness obtained by theoretical calculation is compared with the elastic stiffness obtained by the experiment. The material properties of bamboo scrimber and screws are referred from Table 1.
Comparing the test results with the theoretical calculation results, the theoretical calculation value is greater than the test value, and the relative error between the two is about 1.3%. The main reasons for this result are: In the actual test, the internal forces of screws and infilled walls are not uniform; the stress concentration phenomenon occurred in the screw joint; the actual bamboo infilled walls are anisotropic materials; and the mechanical properties of the transverse and longitudinal walls are quite different. However, these factors have little effect on the lateral displacement of bamboo infilled wall, and the test value is in good agreement with the theoretical calculation value. Based on the above considerations, the lateral stiffness formula proposed in this paper can be basically used to calculate the lateral stiffness of infilled walls.
The main failure modes of steel–bamboo SI system under low-cycle reversed loading are the failure of screws and cover panels, and the bolts are not damaged.
The strength degradation of the steel–bamboo SI system is slow, and it still maintains good bearing capacity in this test. The peak load in the positive direction is 159.37 kN and in the negative direction is − 194.99 kN. The initial stiffness is 19.96 kN/m. The energy dissipation capacity of the steel–bamboo SI system is good, and the energy dissipation capacity shows a rising trend.
The formula for calculating the lateral stiffness of the steel–bamboo SI system is summarized. The error between the test results and the theoretical results is about 1.3%. It is proved that the formula can be used for calculating the lateral stiffness basically.
The authors would like to extend their sincere gratitude for the financial support from the Integrated Key Precast Components and New Wood-bamboo Composite Structure Foundation of China (2017YFC0703502) and for the test work provided by the Jiangsu Transportation Institute Structural Laboratory.
QL designed the test plan, led the whole test and analyzed the test data. YD deduced the theoretical formula and is also the main author of the manuscript. YL revised the manuscript and is the main corresponding author. All authors read and approved the final manuscript.
The whole test study is supported by the Integrated Key Precast Components and New Wood-bamboo Composite Structure (2017YFC0703502).
The authors declare that they have no competing interests.
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