Uses of Bamboo for Sustainable Construction—A Structural and Durability Perspective—A Review

Abstract

Bamboo is a natural biodegradable material used as a strength-bearing material that operates for system works, formwork supporting stands, structural members in low-rise houses, props, framing, bridges, laminated flooring, facades, walls, roofs, and trusses. Over recent years, there has been an increased demand for bamboo, considering sustainable construction practices. Exploring bamboo’s physical and mechanical behaviour is essential to develop innovative construction methods and design guidelines. Therefore, this paper aims to review the studies on bamboo culms’ material properties and physical behaviour, considering the load-bearing capacity and structural adequacy. This study summarises the physical and mechanical properties of a wide array of bamboo species grown worldwide. Mechanical properties such as compressive, tensile, flexural, shear, and bucking strengths are explored, highlighting the key findings in previous experimental works. Results have indicated a significant variability in bamboo’s material and mechanical properties considering the growth conditions, location along a culm, geometric imperfections and environmental conditions. In addition to material and mechanical properties, structural bamboo connections, engineered bamboo products, and preservative treatment of bamboo are also investigated. The construction industry can utilise the summary of the findings of this study to develop design guidelines for sustainable bamboo construction. Overall, this paper presents an overview of structural capability and drawbacks for future research and development using bamboo in modern construction.

1. Introduction

Bamboo is a renewable resource and a fast-growing species that can be harvested in 3–6 years [1]. Further, bamboo enables similar mechanical properties to those of structural timber [1]. It can be used as an environmentally friendly and cost-effective sustainable construction material. Bamboo is typically a strength-bearing material for system works, formwork supporting stands, structural members in low-rise houses, props, framing, bridges, laminated flooring, facades, walls, roofs, and trusses. Using bamboo as a construction material has a wide array of advantages. The benefits include a convenient size and form for straightforward handling, a high strength-to-weight ratio, diaphragms at nodes to forestall native buckling, and strengthened nodal zones for focused load transfer [2]. Furthermore, robust and laborious tissues square concentrated close to the outer surface, and flexibility enables high wind and earthquake resistance [3]. Moreover, a low level of skills is needed for the erection of bamboo structures. Despite these benefits, the typical connections (i.e., mortise–tenon and lashing joints) increase the construction cost and time and create structural vulnerability [4]. The culms are typically drilled and curved into curved shapes to provide these connections, which makes the material vulnerable to longitudinal cracks [5]. The culms’ transverse capacity can generally be increased by a mortar injection. A study by Correal [6] showed that a mortar injection increases bamboo culms’ bending strength and stiffness by up to 40% and 60%, respectively. However, it is essential to note that while a mortar injection can increase the strength of bamboo, it also adds weight to the structure, which can be a disadvantage in some applications. Furthermore, bamboo linkages are incapable of transmitting moments. This limitation reduces the flexibility of the construction methods, particularly when it is necessary to be used as frames and panels with door and window openings [4]. Furthermore, Nurmadina et al. [7] stated that bamboo’s structural grading was appropriate for capacity grading rather than strength grading. Strength parameters are properties of the material, whereas capacity is a property of the member. Since the bamboo culm shape is not uniform in bamboo construction, the strength approach may not be feasible. The additional predictor variables, such as eccentricity or ovality, wall density, culm density, and moisture content in capacity grading, significantly increase the coefficient of determination for estimating MOE (modulus of elasticity) and MOR (modulus of rupture). It was demonstrated that in bamboo culm capacity grading, diameter, linear mass, and combinations were good quality indicators.

Recently, construction industries have sought sustainable alternative construction materials to reduce environmental impacts. Using bamboo in construction can reduce environmental impacts as well as global greenhouse gas emissions [8,9]. However, the absence of design guidelines for mechanical qualities and structural soundlessness poses a significant barrier to advancing structural bamboo as a contemporary construction material [10]. Attempts to investigate the use of bamboo and its components in construction and design made using them effectively be ascertained by studying relevant previous studies.

This study aims to explore the material and mechanical properties of different bamboo species to understand the physical behaviour of bamboo in sustainable construction practices. This paper is organised as follows. Section 1 provides a brief background and introduction to bamboo as a construction material. Section 2 and Section 3 summarise the studies about bamboo’s material and mechanical properties. Engineered bamboo products are explored in Section 4, focusing specifically on cross-laminated bamboo. Bamboo connections and preservative treatments are investigated in Section 5 and Section 6, respectively. Finally, conclusions and future research directions are described in Section 7. Overall, this paper provides a comprehensive summary of the previous studies about bamboo, focussing on the aforementioned areas to improve the current understanding and design practices in bamboo construction.

2. Materials and Methods

Bamboo is a natural composite material in most tropical nations that grows abundantly. It comprises of cellulose fibres, which constitutes most living things in nature, embedded into a lignin matrix. The cellulose fibres are straight. The longitudinal orientation of the bamboo has the highest tensile strength, flexural strength, and stiffness, similar to structural timber, where higher strength is observed in the direction parallel to the grain. The density of bamboo fibres is not uniform and is more prominent on the outer periphery, which improves the material’s flexural properties [11]. Various factors influence bam-boo structural performance, including species and harvesting age, exposure time after harvesting, growth conditions, specific gravity, and exposure period. In addition, strength parameters vary depending on the position along the culm, node disposition, moisture content, diameter, thickness, curvature, modulus of elasticity, loading duration, seasoning, and other flaws [12]. Bahtiar et al. [13] developed a culm diameter versus thickness scatterplot of Indonesia’s Hitam, Andong, and Tali bamboo species. A weak positive correlation was found between diameter and thickness for each species, with linear regression yielding a coefficient of determination (R²) of 0.14–0.22.

Further, Trujillo and López [14] reviewed the material property variations considering different species. The material and mechanical properties of bamboo used for construction vary depending on environmental factors. Thus, experimental tests should be conducted to assess the material and mechanical properties. Further, Nugroho et al. [15] highlighted that 5–20 cm diameter bamboo can be used for structural purposes. Whilst the large diameter species can be used to make heavy constructions, the other sized species are appropriate for medium-sized structures.

2.1. Density

ISO/TR. 22157-1 [16] specifies the methods to calculate the density of bamboo using physical and mechanical tests. To evaluate the density, oven-dry mass and green (just harvested) volume are used since both are independent of the weather conditions. When the density of a test sample is to be measured at a specific moisture content, mass is taken as the oven-dry mass, and only the volume is measured at the sample’s relevant moisture content. Bamboo moisture content should be standardised to 12% to adjust the determination of linear mass and density values [15]. The volume of the vascular bundles’ fraction influences bamboo density. Because of the low fibre density, the lower regions of bamboo have the most insufficient specific gravity [17].

Table 1. The specific gravity of bamboo species.

Reference	Species	Average Specific Gravity
Chung and Yu [1]	Bambusa pervariabili	0.708
	Phyllostachya pubescens	0.794
Kamthai and Puthson [18]	Dendrocalamus asper	0.725
Moroz et al. [19]	Arundinaria amabilis	1.100
Nagarnaik et al. [20]	Dendrocalmus strictus	0.799
Fabiani [21]	Phyllostachys edulis	0.765
	Phyllostachys viridiglaucescens	0.805
Unnikrishnan and Shastry [22]	Not mentioned	0.731
Trujillo et al. [23]	Guadua angustifolia	0.669
Parasuram and Baskaran [24]	Bambusa vulgaris	0.700
Bahtiar et al. [25]	Guadua angustifolia	0.564
Correal [6]	Dendrocalamus strictus	0.64
	Guadua angustifolia	0.68
	Phyllostachys edulis	0.79
Nugroho et al. [15]	Bambusa vulgaris	0.698
	Gigantochloa pseudoarundinaceae	0.576
	Dendrocalamus asper	0.640
	Gigantochloa atroviolacea	0.626
	Gigantochloa apus	0.642
Iswanto et al. [26]	Gigantochloa pruriens	0.593

summarises the specific gravity of bamboo reported in the literature.

2.2. Moisture Content

In structural timber, strength properties greatly rely on moisture content [27,28]. In codes of practice, strength modification factors are defined to account for different service classes, depending on the moisture content [29]. Generally, the strength and stiffness of wood increase with the reduction of moisture content below the fibre saturation point [30]. Moisture content must be considered when using bamboo as a construction material, as it impacts its long-term performance. Green (just harvested) bamboo is less intense than dry bamboo, much like wood [31]. The fibre saturation point varies between culms and species, but is usually between 20% and 30% [32]. Moisture content can affect dimensional stability, bending strength, and the load duration (creep) effect [6]. According to Bahtiar et al. [13], the samples obtained from the top sections of the bamboo culm were drier than those acquired from the bottom parts. This was because the thickness in the samples collected from the upper parts of the bamboo culm were thinner than in the samples obtained from the bottom portions. Thinner walls dried faster than thicker walls. Bamboo has better mechanical properties in dry conditions because the bamboo culms have homogeneously reached equilibrium status in moisture content. Thus, there is no significant variation in moisture content between species.

3. Mechanical Properties

Due to the hollow nature of the culms, the mechanical properties can be studied parallel and perpendicular to the fibre orientations. Testing specifications for determining mechanical properties can be found in ISO 22157-1:2004 (Bamboo—Determination of physical and mechanical properties—Part 1: Requirements) [16]. The testing sample must accurately reflect the final structure’s substance variation. This diversity should cover factors like place of origin, age, and location on the culm. Samples must be collected from each culm’s bottom, middle, and top [33]. An overview of the current standard test procedures, their application, and their usefulness in a field situation can be found in Harries et al. [34].

3.1. Compressive Strength

According to ISO 22157-1:2004 [16], the ultimate compressive strength of bamboo specimens from culms is measured parallel to the axis. Different researchers have explored the compressive strength of bamboo for various species from different countries. When investigating the results of compression tests, it is paramount to consider the moisture content, since the ultimate compressive strength significantly affects the specimen’s moisture content [30]. Due to the hygroscopic nature of bamboo, the Indicating Property (IP) should be adjusted to a standardised moisture content (12% Mc). If densities are chosen as the IPs, the moisture content effect on compressive strength and capacity should also be measured to improve estimation reliability. Density and linear mass were determined to be the best indicating properties for structural grading of bamboo subjected to an axial compressive load due to their higher correlation values [25]. If the cross-sectional area is assumed to be a hollow cylinder, density is reliable for estimating compressive strength. Structural grading can be done based on strength grading or capacity grading. Bahtiar et al. [25] concluded that capacity grading is more reliable than strength grading due to higher coefficient of determination values (R²).

Chandrakeerthy [12] performed compression tests for untreated Bambusa vulgaris specimens, the most widely used bamboo species for temporary structures in Sri Lanka. Different diameters (d) of bamboo were selected to represent small (63 mm < d < 72 mm), average (72 mm < d < 88 mm), and large sizes (d > 88 mm). For each dimension, 3 test specimens of 300 mm length having a centrally placed node were cut from each culm top, middle, and bottom. A total of 108 samples were tested, and a mean compressive strength of 29.33 MPa resulted in a moisture content of 30%. Chung and Yu [1] explored the mechanical characteristics of two bamboo species, Bambusa pervariabilis and Phyllostachys pubescent. These bamboo species are commonly found in Southeast Asia, especially in Hong Kong and China. The compression test specimens’ height was preserved at least twice the exterior diameter of the bamboo culm. Specimens were categorised into three groups according to the moisture content (MC), such as MC < 5%, 5% < MC < 20%, and MC > 20%. As expected, the compressive strength decreased as the moisture content increased. For the Bambusa pervariabilis species, the average compressive strengths were recorded as 103, 69, and 48 MPa for the 3 moisture contents. Similarly, for the Phyllostachys pubescens species, the average compressive strengths were recorded as 134, 75, and 57 MPa for the 3 moisture contents.

Sakaray et al. [35] conducted a similar work to determine the compressive strength of hollow culms to be used as reinforcing material in concrete. The test used three different kinds of specimens: specimens with a central node, specimens with an end node, and specimens without any nodes. Bamboo specimens were subjected to a progressively increased load until failure, and the load was applied parallel to the axis. The ultimate load was used to calculate compressive strength. Samples with a central node provided a higher compressive strength than the other two specimens. The average compressive strength of all specimen types was 108.2 MPa. Nevertheless, the moisture content of the samples needed to be clearly stated in this study.

Fabiani [21] explored the compressive strength of two Italian bamboo species, namely Phyllostachys edulis and Phyllostachys viridiglaucescens. Twelve specimens of each species were used, cut straight from the culm at a height equal to the exterior diameter. There were specimens with and without nodes. Each instance was positioned between two steel plates that applied pressure to both extremities. A hemispherical bearing on the upper plate distributed the load uniformly over the specimen’s ends. Maximum and minimum compressive strengths for Phyllostachys edulis and Phyllostachys viridiglaucescens species were recorded as 59, 51.1, 66.2, and 46.4 MPa, respectively. The average compressive strength and the average moisture content of the two species were 55.7 MPa, 56.8 MPa, and 43.7%, 24.9%, respectively. Bhonde et al. [20] investigated the mechanical properties of Dendrocalamus strictus, the predominant bamboo species discovered in India, covering about 53% of the total bamboo area in India; 50 mm long bamboo specimens were subjected to a compression test, and the measured moisture content of the specimens was around 7%. The average compressive strength of the 6 models examined was 78.03 MPa.

Awalluddin et al. [36] monitored the strength improvement and moisture content of four bamboo species commonly found in Malaysia. The study period was five months. Studies species were Bambusa vulgaris, Dendrocalamus asper, Gigantochloa scortechinii, and Schizostachyum grande. The moisture content dropped with time, and the average moisture content at the end of five months was less than that of the initial moisture content. The compressive strength was measured at each culm’s top, middle, and bottom. The top of all bamboo species was identified to have the maximum compressive strength, which was succeeded by the middle and bottom. The average compressive strength at the top was 68.05, 76.52, 30.42, and 69.02 MPa for Dendrocalamus asper, Bambusa vulgaris, Schizostachyum grande, and Gigantochloa scortechinii, respectively. The average moisture content of the tested specimens from the 4 species varied from 15.3% to 23.4%. Samples collected close to the base of the culm were slightly older and weaker than those gathered further away from the bottom. Large vascular bundles in bamboo were determined to be the cause for this property’s distinction. A second compression test was undertaken five months later. The findings followed a similar pattern, demonstrating that the compressive strength of the culm is greater at the top than at the middle and bottom. After five months, the average compressive strength at the top was found to be 73.65, 78.74, 40.03, and 68.62 MPa for Dendrocalamus asper, Bambusa vulgaris, Schizostachyum grande, and Gigantochloa scortechinii, respectively. A summary of the compressive strengths of bamboo found from different studies is illustrated in

Table 2. Summary of the material and mechanical properties found in the literature.

Study & Country	Species	Type of Preservation	Moisture Content %	Compressive Strength (MPa)	Tensile Strength (MPa)	Flexural Strength (MPa)	Youngs Modulus (GPa)
Chandrakeerthy [12] (Sri Lanka)	Bambusa vulgaris	Seasoning	30	29.33	89.91	53.88	18.57
Chung and Yu [1] (China)	Bambusa pervariabili	Air drying	5–20	69	-	82	9.3
	Phyllostachya pubescens		5–30	75	-	88	9.4
Mahzuz et al. [37] (Bangladesh)	Bambusa balcooa	-	-	-	92.84	-	6.26
Sabbir et al. [38] (Bangladesh)	-	Untreated	-	-	117.1	-	51.4
Sakaray et al. [35] (India)	Bambusa vulgaris	Seasoning and applying a waterproof coating	-	108.2	121.0	-	15.00
Parasuram and Baskaran [24] (Sri Lanka)	Bambusa vulgaris	Air seasoning and applying wood preservatives	13.3	-	90.0	-	9.92
Fabiani [21] (Italy)	Phyllostachys edulis	-	43.7	55.70	126.7	97.3	13.21
	Phyllostachys viridiglaucescens		24.9	56.8	159.0	-	-
Bhonde et al. [20] (India)	Dendrocalmus strictus	Untreated	6.92	78.03	95.78	-	-
Awalluddin et al. [36] (Malayasia)	Dendrocalamus asper	Boric acid treatment	15.9–18.4	73.65	232.8	-	20.00
	Bambusa vulgaris		14.0–19.2	78.74	231.67	-	-
	Gigantochloa scortechinii		15.6–18.1	68.62	187.67	-	-
	Schizos tachyum grande		16.9–19.6	40.03	149.20	-	-
Nugroho et al. [39] (Indonesia)	Gigantochloa apus	Air drying	16.9	-	-	67.3	17.95
Nugroho et al. [15] (Indonesia)	Bambusa vulgaris	Conditioning using a fan in an indoor environment	15.3	-	-	40.05	-
	Gigantochloa pseudoarundinaceae		16.7	-	-	63.98	10.46
	Dendrocalamus asper		14.4	-	-	99.74	18.00
	Gigantochloa atroviolacea		15.9	-	-	91.87	-
	Gigantochloa apus		16.9	-	-	76.9	15.68

.

3.2. Tensile Strength

Similar to compression tests, guidelines for performing tension tests are provided in ISO 22157-1:2004 [16]. This section summarises the previous studies investigating the tensile strength of bamboo. Mahzuz et al. [37] explored the tensile strength of a commonly found bamboo species in Bangladesh—Bambusa balcooa. Fault-free bamboo specimens were selected for the test after performing a visual inspection. After chopping, the bamboo was left in the open for two months to dry. Thirty samples were tested, and the average tensile strength was identified as 92.84 MPa. Further, the mean modulus of elasticity was found as 6.26 GPa. Sabbir et al. [38] investigated the tensile properties of bamboo to be used as concrete reinforcement. Three specimens of untreated bamboo were tested initially, and five models with wire spiral to improve the grips at the ends were also tested. Samples were inspected to avoid imperfections that may affect the results. The average tensile strength was identified to be 117.1 MPa. However, the moisture content of the specimens was not indicated in this study.

Sakaray et al. [35] presented the tensile strengths of the Bambusa vulgaris and Dendrocalamus species by testing specimens ranging from 4.55 to 5.8 m. Failure mode in the tests was identified as node failure due to the brittle nature of nodes. Some of the illustrations showed a splitting failure mode. The average tensile strength was found as 121 MPa. A similar study was conducted by Bhonde et al. [20] to investigate the tensile strength of bamboo. Specimens of 70 cm in length were prepared to have 10 cm grips on each side. Sand and high-strength epoxy glue Araldite were used to fill the curved areas of the bamboo split at the end. The assessed 10 specimens’ average tensile strength was 95.78 MPa. Fabiani [21] tested dog-bone shaped specimens to evaluate the tensile strength of 2 bamboo species found in Italy. The model measured 500 mm long, whereas the reduced portions measured at 140 mm. The height was 30 mm and the radius was 80 mm. The specimen’s thickness was identical to the bamboo culm’s wall thickness. In the shortened section, there was a node on each instance. The average tensile strength was 126.7 and 159 MPa for the Phyllostachys edulis and Phyllostachys viridiglaucescens species.

Parusaram and Baskaran [24] investigated the feasibility of bamboo being used as supplementary reinforcement for concrete slabs. Three samples were chosen at random. The test samples’ failure was caused by breaking fibres when force was applied parallel to the bamboo fibres. The average moisture content of the 3 specimens was 13.3%, and the mean tensile strength was 90 MPa. A summary of the tensile strength of bamboo found in the literature is illustrated in Table 2. Furthermore, Molari and García [40] studied the transverse mechanical characteristics of five bamboo species through digital image correlation technology. Experimental results are shown in

Table 3. Radial variation of the transverse mechanical properties of bamboo [40].

Species	Tensile Strains		Effective Modulus (MPa)	Young’s Modulus (MPa)		Tensile Strength (MPa)
	Inner	Outer		Inner	Outer	Inner	Outer
Phyllostachys edulis	0.014–0.035	0.008–0.0019	1209–2983	30% Lower than the outer	1976–4694	39.9	14.5
Phyllostachys bambusoides				796–1694		17.6	30.5
Phyllostachys iridescens						16.9	23.2
Phyllostachys violascens						24.1	22.6
Guadua angustifolia			931–1148			17.6	30.5

. This research demonstrated variations in the transverse behaviour of bamboo based on both the species and the location along the culm wall.

3.3. Flexural Strength

The ultimate load, span, and section modulus of a bamboo specimen subjected to a bending test can be used to compute its maximum flexural strength. ISO 22157-1:2004 [16] specifies a four-point bending test to determine the flexural strength of bamboo, as illustrated in Figure 1. Similar to determining the compressive and tensile strength, researchers have investigated the flexural strength of different bamboo species worldwide. In addition to determining flexural strength, bending test results (load-displacement curves) can be utilised in determining the modulus of elasticity. A summary of the flexural strengths and modulus of elasticity is illustrated in Table 2, considering the conducted review. Like structural timber, flexural strength is calculated parallel to fibre along the longitudinal axis.

Chandrakeerthy [12] performed tests to explore the flexural strength of untreated Bambusa vulgaris specimens. This study presented a formula to evaluate the design’s flexural strength using the bending test results. This formula is shown below where the design flexural strength, $f$, is calculated as;

$$f=\frac{\left(F_m-K.S.\right)}{F}$$

(1)

where $F$ is a reduction factor similar to the convenience factor of safety that accounts for minor errors in moisture content, loading duration, sectional properties, design assumptions, analysis, and construction tolerances. $K$ is a statistical constant for a 5% exclusion. $F_m$ is the mean ultimate flexural strength. $S$ is the standard deviation of maximum flexural strength. The test specimens’ external diameter and thickness ranged from 54.5 to 95.0 mm and 5.0 to 23.0 mm, respectively. The specimen lengths were approximately 2.2 m, and each specimen was tested with ends supported and the specimen subjected to a mid-span load. The resulting design flexural strength was 16.7 MPa by using $F_m$ as 53.88 MPa, $K$ as 1.645, $S$ as 9.61, and $F$ as 2.25.

Li [41] determined that bamboo’s bending strength and stiffness were influenced by age, height, and specific gravity. Lopez [42] proposed that bamboo nodes be placed away from the immediate location of an applied flexural force wherever possible to maximise strength capabilities. Studies discovered that eliminating the nodes reduced bending stiffness by 6.2% [43]. Additionally, the results were affected by the point at which the specimen was cut from the culm. The outer layers’ specific gravity and bending properties were much higher than the inner layers. Along the culm height, specific gravity fluctuated. The upper parts’ specific gravity was constantly more elevated than the bottom. The outer layer was more crucial than the inner layer in supporting bamboo. The modulus of rupture (MOR) and modulus of elasticity (MOE) were measured by removing varying percentages of the test specimen’s cross-sectional area from the outer and inner surfaces. Extracting sound wood from the outer shell had a higher MOR reduction than a deduction from the inner surface. Therefore, leaving the outer surface material on bamboo strips is advised if using them industrially to create high-strength bamboo composites. MOR and MOE were evaluated for different age groups of bamboo. Tests were carried out from specimens aged one, three, and five years. With age, both MOR and MOE showed a significant increase [42,43].

Further, tests were conducted to investigate the effect of specific gravity on the strength characteristics. MOR and MOE have a positive trend with specific gravity [43]; it means bamboo specimens with higher density result in better bending strength. Using statistical analysis, Sá Ribeiro et al. [44] aimed to determine the bending strength properties of bamboo culms through non-destructive evaluation (NDE). This research analysed the correlations between bamboo’s mechanical and physical properties. Linear regression analyses were conducted to determine which NDE factors could efficiently predict the modulus of rupture (MOR) and modulus of elasticity (MOE). This study found the coefficients of determination (R²) 83% between MOR and MOE, 66% between MOR and 𝜌 (apparent density), 70% between MOR and E_d (dynamic modulus of elasticity), 66% between MOE and E_d, 62% between MOE and 𝜌, and 77% between E_d and 𝜌. The corresponding relationships are illustrated in Figure 2, along with the regression equations.

The bending test of the Phyllostachys edulis bamboo, the classification of the P. edulis bamboo, and the analysis of the P. edulis bamboo for strength design was investigated by Liu et al. [45]. MOE was utilised as an index to evaluate mechanical qualities in the P. edulis bamboo performance evaluation system. MOE was classified into three grades based on their analysis (Grade I, II, and III). Bending strength was ordered from small to large, and strength values were divided based on the number of different fitting data points. The Weibull distribution has the least appropriate degree, while the average and lognormal distributions have comparable fitting effects. Four load combinations (variable load to permanent load ratio) were investigated in the dependability analysis. The strength design value of bamboo was computed using the coefficient of resistance derived by the initial investigation. The design bending strengths of the P. edulis bamboo were determined as 27.40 MPa, 27.69 MPa, and 28.47 MPa for the aforementioned grades I, II, and III, respectively. In the calculation of design bending strength, uncertainty coefficients and conversion coefficients were introduced to account for the potential variability in geometry and material properties.

3.4. Buckling

Bamboo members subjected to compression can be subjected to buckling depending on the slenderness of the member. Slenderness relies on the geometry of the member and the end conditions. Chandrakeerthy [12] investigated the buckling stresses and slenderness ratio of the Bambusa vulgaris species. Three specimens with lengths of 1.5 m, 0.9 m, and 0.6 m were loaded axially, and the central outward deformation was recorded. The specimen’s vertical deformation was also measured between its two ends. The guidelines in the BS 5268—Structural use of timber [46] was taken into consideration in this study. Experimental values of ultimate buckling stress were determined for 108 specimens. In exposed bamboo structures, slenderness ratios were thought to encompass the entire practical range of slenderness ratios. Slenderness ratios for 1.5 m specimens ranged from 44.16 to 85.30, 0.9 m specimens from 26.28 to 44.28, and 0.6 m specimens from 17.52 to 28.44. The range of the overall variation was 17.52 to 85.3. By analysing the obtained results, modification factors for compressive strength for varying slenderness ratios were proposed to account for the buckling failure.

Yu et al. [47] established and effectively calibrated a design strategy against column buckling of structural bamboo based on improved slenderness against test data of both Kao Jue (Bambusa pervariabilis) and Mao Jue (Phyllostachys pubescens) species. This work included extensive and systematic experimental testing on the column buckling behaviour of bamboo culms. The proposed design approach was demonstrated to be structurally adequate following contemporary structural design philosophy. It could be successfully implemented to design against structural bamboo column buckling in scaffolds and other bamboo structures. Yu et al. [48] expanded their study to examine the axial buckling behaviour of four comprehensive double layered bamboo scaffolds (DLBS) with various member configurations and lateral restraint systems bamboo pillars. Experimental results indicated that by considering the deformation and strength, the structural effectiveness of DLBS was satisfactory. Axial buckling of the bamboo columns only happened instead of any overall collapse of the bamboo scaffolds. While measuring the bamboo columns’ axial buckling resistances under axial buckling, various types of failure in DLBS components were recognised and reported.

Nie et al. [49] summarised that both the slenderness and diameter-thickness ratios notably impact the failure modes and ultimate bearing capacity of columns. The failure modes of columns are significantly influenced by two factors: slenderness ratio and diameter-thickness ratio. Columns with similar diameter-thickness ratio displayed a negative correlation between ultimate bearing capacity and slenderness ratio, with up to 44.39% reduction rate. However, when the diameter-thickness percentage increased by 18.75%, the maximum bearing capacity rose by 82.65%, given the same slenderness ratio. The eccentricity, taper, and bow are flaws that may contribute to the buckling behaviour of a bamboo column [50]. These flaws complicate buckling analysis and are thus frequently overlooked in practical applications. Bahtiar et al. [50] performed an Experimental Investigation of Guadua angustifolia Column buckling resistance. The load-carrying capacity of long columns was significantly impacted by buckling, making it necessary to include the buckling reduction factor (ψ- the ratio between the ultimate buckling load and the ultimate compressive load) in the design and structural analysis of bamboo culms. According to this study, buckling behaviour could be successfully fitted with Rankine-Gordon and Ylinen’s formulas over the entire slenderness ratio range, as illustrated in Figure 3. Because of its superior statistical performance, Ylinen’s formulas were recommended for designing compressed columns. The essential slenderness ratio was 30.5, and the critical buckling reduction factor was 0.75, according to the curve fitting of Ylinen’s formula. Long columns with slenderness ratios more significant than the critical value is well fit by the Euler buckling reduction factor curve, whereas intermediate columns use the Johnson parabola formula. Furthermore, based on the results of the conducted study, it was found that Guadua bamboo columns should not be longer than 67 times their diameter, considering the effects of buckling.

3.5. Shear Strength

As evaluated from the face of the support, the depth of the element can be used to compute the critical point for shear. Apart from cantilever beams, where the maximum shear stress should be determined at the face of the support, this depth for beams with a single culm should be the same as the culm outside diameter. The depth for built-up beams made of two or more bamboo culms is the same as the element’s real depth [6].

The optimum shear stress must be less than the maximum permissible shear-parallel-to-grain strength after appropriately adjusting for a non-uniform stress distribution along the cross-section [6]. The ISO 22157-1:2004 [16] could be used for estimating the shear strength of bamboo specimens following the standard testing procedure.

Sakaray et al. [35] conducted shear tests for Moso bamboo samples of 50 mm in length. In this test, three specimens were used: one with a central node, one with an end node, and one without any nodes. The testing process used for bamboo is the same as for steel. The test is known as a double shear test because the shear shackle employed has a double shear action. Shear restraints were placed in a universal testing machine (UTM) with a 400 KN capacity, and a load was gradually added until the specimen failed. The maximum load upon failure was noted. Center node samples yielded higher shear strength values. An average shear strength of 29.12 MPa resulted from the tested bamboo specimens. A similar study was carried out by Bhonde et al. [20] by performing single and double shear tests on several circular bamboo samples with a 10 mm diameter. Bamboo is weak along its longitudinal fibres, and the ultimate shear is along the grains. A shear test parallel to the fibres determines the ultimate shear strength. Shear strength was determined to be 85.3 MPa for a single shear and 99.71 MPa for a double shear. A study by Iswanto et al. [26] indicated that the shear strength ranged from 7.39 to 7.79 MPa for the Gigantochloa pruriens bamboo species. Parallel to the fibres was the direction of the tests. The upper part of the bamboo culm resulted in the greatest value, whereas the bottom part resulted in the lowest. Low lignin content at the bottom was identified as a cause of the low shear strength.

4. Cross-Laminated Bamboo

In the timber industry, readily available solid-sawn wood is limited in size and quality. Therefore, engineered wood products have been developed to address this issue using wood adhesives [51]. Typical engineered wood products include glue-laminated timber, laminated veneer lumber (LVL), oriented strand board (OSB) and parallel strand lumber (PSL). In bamboo construction, cross-laminated bamboo is getting popular due to its relative advantages compared with raw bamboo columns [52]. Researchers have investigated different aspects of cross-laminated bamboo, such as compressive behaviour, bending behaviour, shear behaviour, bonding, and thermal performance [53,54].

Li et al. [55] investigated the compressive performance of laminated bamboo. The experimental programme consisted of testing 24 laminated bamboo specimens in compression. Three groups of specimens were produced from different growth portions of bamboo culm, such as the upper third, middle third, and lower third. It was observed that the mean compressive strength of samples from higher growth heights was higher. In contrast, the largest modulus of elasticity resulted in bamboo laminates from the middle growth section. However, the variation of elastic modulus with growth height was smaller. The mean compressive strength and the standard deviation for the tested 24 specimens were 60.9 MPa and 5.2 MPa, respectively. The mean elastic modulus was reported as 9391 MPa with a standard deviation of 719 MPa. Li et al. [56] explored the off-axis compressive behaviour of cross-laminated bamboo and timber (CLBT) wall elements. Two hundred twenty-four specimens were tested, which were constructed from hem-fir lumber and bamboo mat-curtain panels. Dominant failure modes observed in the experiments were delamination between layers and slender failure zones parallel or perpendicular to the off-axis angles. Mechanical properties of the off-axis tests were predicted with the use of compressive failure criteria and available prediction models for off-axis apparent compressive modulus. Results indicated that the off-axis compressive performance of CLBT specimens varied smoothly with the increase of off-axis angle compared with glue-laminated timber specimens. Li et al. [57] extended their study to investigate the in-plane compressive performance of CLBT wall panels. The compressive angle of the specimens was varied from 0 to 90 degrees. The compressive stress, apparent compressive modulus and the apparent Poisson’s ratio were calculated from the test results. For the testing, two types of CLBT specimens were prepared where the position of bamboo and timber layers were varied. Bamboo panels were either placed as outer layers or the inner layer. Depending on the position of layers and the compression angle, mechanical properties showed a significant variation.

Dong et al. [58] investigated the bending properties of CLBT composites. Two types of CLBT specimens were used for the experiments, where bamboo scrimber was used as a transverse layer or as both the transverse layer and outermost longitudinal layer. Dynamic tests and three-point bending tests were carried out to determine the bending properties. Test results indicated that one group of CLTB specimens had 23.7% and 60.5% higher apparent bending modulus and peak load than the corresponding spruce–pine–fir specimens. Flexural strengthening of cross-laminated bamboo slabs was studied by Lv et al. [59] by incorporating carbon fibre reinforced polymer (CFRP) grids. One-way and two-way slabs with and without CFRP strengthening were subjected to four-point bending. It was found that the load-carrying capacity of the composite slabs increased with the number and thickness of layers as well as the application of CFRP grids. Further, a theoretical method for the calculation of the load-carrying capacity of cross-laminated bamboo slabs was proposed, and the accuracy was evaluated. Xiao et al. [60] experimentally investigated the behaviour of cross-laminated bamboo and timber beams. Both flatwise and sidewise setups to were used to conduct three-point bending tests. Test results showed an elasto-brittle behaviour of CLBT beams having an adequate load-carrying capacity. The relative slip assumption model and plane assumption model were used as prediction models in calculating the bending stiffness and capacity.

The bonding shear strength of cross-laminated bamboo is crucial for the overall structural performance. Xing et al. [61] explored the bonding shear capacity of different cross-laminated bamboo configurations. Three parameters were studied—namely, grain direction, adhesive type and clamping pressure. Five types of adhesives, three clamping pressures and specimens glued together with grain in the same direction and cross-laminated configuration were used for the experiments. Based on the test results, the most suitable adhesive for glue laminated bamboo was selected as melamine-urea-formaldehyde. Among the different configurations, end grain specimens showed the highest bond shear strength. Li et al. [62] conducted a similar study to explore the shear behaviour of cross-laminated bamboo panels. Shear strength and the shear modulus were evaluated by conducting two plate planar shear tests and short-span bending tests. It was concluded from the results that engineered bamboo panels’ shear properties fulfilled the standards and specifications for cross-laminated timber strength. From all these conducted studies on the mechanical properties of cross-laminated bamboo, it can be concluded that cross-laminated bamboo has a huge potential to be used in the industry as a sustainable construction material.

5. Connections

Connections are a key element in bamboo structures which ensure a smooth load transfer. Due to the hollow and thin-walled nature of bamboo culms, the joints in raw bamboo structures have always been a primary difficulty that hinders the potential use of bamboo for construction purposes [5]. Although researchers have investigated numerous joint types based on the properties of raw bamboo and conducted several experimental investigations, the current jointing techniques are only partially suitable. Hong et al. [5] reviewed connections for original bamboo structures. Bamboo connection joints could be categorised as traditional and modern connection joints. Mortise–tenon joints and lashing joints are the most used traditional joints [5]. The mortise–tenon junction is formed by the continuous transverse penetration of bamboo beams through many columns, which has the advantages of low material consumption and high integrity. The mortise–tenon junction, which can be viewed as a type of inheritance and reproduction of the mortise–tenon connection in timber construction, is placed where the beam and the column intersect [5]. Lashing joints are where bamboo is tightly woven at links, as illustrated in Figure 4. Lashing, which has the advantages of superior adjustability and low cost, is the most popular connection strategy in older residential buildings. However, lashing construction could be more efficient and efficient, and human operation significantly impacts the performance of joints. Further, the durability of these connections is in question.

Higher expectations apply to the usage of raw bamboo in contemporary construction. Adopting an acceptable form of structural stress and a more exact form of joint construction is essential to effectively utilise raw bamboo’s material attributes. Using metal connectors to link natural bamboo can successfully address issues with low durability, elements at the joints that are probably easier to slip off, and other issues, as opposed to the two traditional joints stated above. Bolted joints, steel member and steel plate joints, and filler-reinforced joints are the modern bamboo connections widely used in contemporary bamboo constructions [5].

Many experimental studies have been carried out to investigate the moment capacity of different bamboo connection types [64,65]. Camacho and Páez [64] reported the results of six different bamboo Guadua moment connections, most based on fish-mouth incisions and mortar injection. The moment strength and stiffness ranges were 0.36–1.49 kNm and 16.7–284.5 kNm/rad, respectively. Four typical bamboo connectors were tested for tension, shear, and moment by Davies [65]. The top models, one with a gusset plate and the other with mortar injection, each obtained the highest moments of 0.6 kNm and 0.45 kNm. Moreira and Ghavami [66] reported testing a link made of six bamboo culms and bolted bamboo. The evaluated moment strength and stiffness were 2.5 kNm and 24.2 kNm/rad. The use of wooden clamps in the connection system has also been investigated, and it has been observed that a connection capacity increase of up to 40% (in comparison with a connection system without clamps) can be achieved by employing wooden clamps [67]. Finite element analysis of a simple bamboo pin joint, typically found in plane or space structures, was carried out by Moreira and Ghavami [68]. The nonlinear local pressure distributions at the contact area of the circular bamboo hole were investigated. It was observed that a bamboo diaphragm beneath the pinhole reduces the possibility of splitting failure. Given the high local stress concentrations, this study recommended employing local reinforcements to make a bamboo connection safer. Besides the conventional bamboo connections and infilled joints to enhance the connection capacity, steel clamps and steel plates have been employed in developing innovative connections [69,70].

Nie et al. [69] tested Moso bamboo connections with steel clamp plates on the exterior subjected to static tension force on the bolts. In this study, the effect of bolt diameters and end distances was considered, as well as the connections’ failure modes and bearing capacities. The connection has three failure modes: bolt shear failure, bolt hole bearing failure, and punching shear failure. The bearing controls the main failure modes of bamboo connections with steel clamp plates on the exterior. It was advised to set the safety factor at 3.0 to guarantee a secure storage of bearing capacity. The calculated values were also close to the experimental findings, and the average measured results are 0.96 times that. The strength of bamboo connections increases with larger bolt diameters, but this effect diminishes when the bolt diameter becomes excessively large. There is no linear relationship between the bamboo connection end distance and bearing capacity. The gap between the parts it connects influences the strength of a bolt in shear failure. Small gaps result in ductile bearing failure, whereas large gaps and small bolt diameters can result in bending and shear failures. Excessive gaps should be avoided to avoid this. Punching shear damage to bamboo is more likely when the end distance of the bolt hole is short, which can be avoided by keeping an end distance-to-bolt diameter ratio of at least 8. Masdar et al. [71] proposed that the crucial space from the end of the bamboo culms without nodes to the bolt is 4–5 times the bamboo diameter.

Paraskeva et al. [72] investigated the use of steel connections for bamboo footbridges. The bridges were made from prefabricated bamboo, and low-cost steel connections could be assembled quickly on-site. The study focused on designing, constructing, and testing simple truss bamboo bridges. Full-scale testing showed that safe and reliable connections are critical for the success of these bridges, with splitting perpendicular to the bamboo fibres and bolt sliding along the bamboo stems being the two main failure modes. Existing formulas for estimating the load-carrying capacity of steel-to-timber bolt connections could not predict bamboo splitting failure. However, dowel-bearing tests accurately predicted the tensile opening stresses in bamboo. Hose clamps provided efficient radial confinement, preventing splitting and increasing the load-carrying capacity of the bamboo members.

Three types of connections (Types A, B, and C) between multi-full-culm bamboo and steel under monotonic axial loading was tested by Paraskeva et al. [70] to understand their mechanical behaviour. Type A specimens comprise a pair of bamboo culms secured together using bolts placed on both sides of a steel plate, creating a double-shear connection. Type B connections are distinct from Type A connections in that they involve the installation of three stainless steel hose clamps on both sides of the bolts at each culm, and Type C connections are the same as Type B, but they were filled by infill mortar. Figure 5 illustrates some common failure modes of connection Types A, B and C. Figure 5a shows the tensile failure of Type A connection. In Figure 5b, it can be observed that the bolts are being pulled through the culm wall in a Type B connection. Other failure modes of Type B connections can be differential movement between culms, culm end crushing, and embedment damage. Failure by pushout of infill material in a Type C connection is illustrated in Figure 5c.

The load-carrying capacities of Type B connections were greater than that of Type A connections. Type C connections further increased the load-carrying capacity due to the presence of infill material. It was recommended to avoid plain bolted bamboo connections due to poor mechanical performance caused by the brittle splitting of bamboo stalks. Moran and García [4] studied the mechanical analysis of three innovative moment-transmitting bamboo beam column connectors. Five clamps were made for each of the three suggested beam–column connections illustrated in Figure 6. Five clamps and three connections were made for the SC (Simple-Clamp) connection using a steel angle that is 3.2 mm (1/800) thick and 25.4 mm (100) wide. A diagonal brace is one of the connectors, while the other two attach the beam’s inner clamp and the column’s top clamps. Welded nuts were included in three clamps to attach pieces in different planes, as illustrated in Figure 6a. The TS (Through-Screw) connection uses three clamps with a centre hole and through screws in place of welded nuts, as shown in Figure 6b. The 5 clamps, 3 of which were semi-rings with lateral holes, 2 brief platen connectors, and an angle saving as a diagonal, all measuring 25.4 mm broad and 3.2 mm thick, made up the DW (Drywall) connection, as illustrated in Figure 6c.

The mechanical behaviour of these connections was characterised using static monotonic and cyclic testing. Compared to conventional bolted and mortar injected connections, the average stiffness and moment strength of the connections proposed in this study were at least 29% and 250% greater, respectively. Steel clamps made it easier to assemble joints and provided enough confinement to prevent early splitting failures. As a result, they offer a practical solution for creating bamboo linkages. Bending strength increased as the joint moved away from the central load along the bamboo’s longitudinal direction [73].

An experimental study of bamboo–concrete and wood–concrete connections was conducted by Wang et al. [74] to investigate their similarities and differences in mechanical properties. Bamboo–concrete connections were found to have a 19% higher shear stiffness than wood–concrete connections. As the concrete strength increased, shear stiffness also increased, with little change in deflection. Bamboo–concrete specimens had up to 31% greater ultimate capacity than wood–concrete specimens. The maximum shear capacity increased as dowel diameter and concrete strength increased. The variation in strength and modulus of elasticity between the two materials contributed to differences in the mechanical properties of their composite connections. In addition to the joint functionality, the raw bamboo reduced the hollow and thin-walled features of the application [52]. Although considerable study on the advancement of basic materials has been done, it cannot resolve the issue entirely. Engineered bamboo’s appearance, however, offers a practical solution to these issues. Laminated bamboo lumber and glue beams are commonly engineered bamboo used in building structures [5].

6. Preservation

All lignocellulosic biomass, including bamboo, is subjected to biodegradation, which reduces its durability. The post-harvest preservation of bamboo culms is crucial for extending the service life. It is challenging to prevent splitting in exposed structures due to drying shrinkage with time, so full benefits of preservatives and remedies may not be found structurally for bamboo [12]. It was revealed that green bamboo possessed only 60% of the tensile and between 30% and 35% of the compressive strength compared to seasoned bamboo [19]. Therefore, seasoning and preservative treatment are essential to maximising the mechanical properties of bamboo while preserving its durability.

6.1. Oil-Heated Treatment

Researchers with different types of oils, like flax or sunflower oils, explore the oil-heated remedy. These treatment techniques are expected to enhance bamboo’s durability while preserving or enhancing its mechanical properties and sturdiness. Initially, bamboo specimens should be treated to reduce their moisture sensitivity and improve their durability. Then, samples can be treated with flax, sunflower, and without oil at specific conditions (different temperatures). Various cooling methods and different durations can also be added for variations. Uniaxial compression tests, water immersion tests, three-point bending tests, and humidity tests can be carried out to evaluate the effectiveness of the treatment. According to Bui et al. [75], the best findings were observed on specimens tested by heating at 1800 °C for 1 hour or 2 hours without oil, and then cooling in 200 °C sunflower oil.

6.2. Borax Solution

The mineral deposit known as borax, a significant boron compound, is created by the repetitive evaporation of seasonal lakes. It typically comes from a white powder of pliable, colourless crystals that dissolve quickly in water. It has numerous industrial uses and functions as an insecticide, fire retardant, and antifungal agent. As boric acid and borax oxide, borax is available as granulated or powder.

The preservation of bamboo is accomplished by employing a pH-neutral 5% borax solution. Borax oxide and boric acid, both in powder form, are combined in equal proportions to create a pH-neutral solution by dissolving them in warm water [76]. One to two months are needed for the borax solution to work. Considering the mix proportions, 25 kg of boric acid and 25 kg of borax oxide are required to make 1000 litres of borax solution. It can preserve over a hundred or more bamboo culms, depending on their size. The pH of the 5% borax solution is neutral, making it safe to use on the skin. Nevertheless, long-term contact should be avoided.

Bamboo can be submerged into the solution or poured into bamboo culms for the borax treatment to function. The diaphragms of the nodes (without the bottom node) must be punctured [76]. It helps to fill the solution interior of the culm to work on the entire structure. The borax solution progressively penetrates the inner and exterior tissues of the culm through the mechanism of osmosis. However, this osmotic diffusion process is only effective while the culm’s cell walls are still alive and functioning. Although dry bamboo will absorb water, boron molecules will not be able to penetrate the dried-out cell tissues and will instead remain on the surface. Therefore, attempting to cure dry culms is pointless. Borax treatment can be effective only when the bamboo is green. Freshly cut bamboo absorbs boron more quickly than poles in service for a month or two. The empirical formula for diffusion calls for employing a pH-neutral 5% borax solution for at least a week at average tropical temperatures of 20 to 30 °C [76].

6.3. Water Soaking

Comparing this preservation method to other conventional ones, soaking bamboo culms in water resulted in a considerable reduction in the nutrients present. Singha and Borah [77] investigated the starch content of several treated and untreated (control) bamboo samples after water soaking. The control samples had the greatest average starch concentration (3.64%) compared to the treated samples. In bamboo samples that had been treated for 3 months, the lowest average starch concentration was (0.50%). As the soaking time increases, the moderate starch content decreases. Consequently, the treated and untreated samples differ significantly from one another. Additionally, the length of soaking is favourably correlated with the reduction in bamboo’s carbohydrate content. The fewer carbohydrates that are present, the longer the soaking time. After three months of soaking, the specie’s sugar content is reduced by 50–60%. A durability test revealed that treated bamboo culms deteriorated far more slowly than untreated ones [57]. Additionally, during durability testing, bamboo samples that had been treated for a month showed a minor percentage biomass loss. This means that the soaking bamboo culm in water for a month is adequate to increase its serviceability. This technique can also reduce the use of environmentally and human-harmful chemical preservatives.

7. Discussion

Bamboo is a natural material, and its growth characteristics and natural imperfections affect its material properties. Further, the strength parameters vary depending on the harvesting age, exposure time after harvesting, position along the culm, moisture content, node disposition, seasoning and other flaws. Additionally, it is important to note that the density of bamboo fibres is not uniform and is more prominent on the outer periphery, improving the materials’ mechanical properties [11]. There is a significant variation in the average specific gravity of different bamboo species, ranging from 0.564–1.1. The moisture content of bamboo is crucial when used as a construction material, and the fibre saturation point varies between culms and species, but is usually between 20% and 30% [32]. Moisture content varies along a bamboo culm, and samples obtained from the top sections of the bamboo culm are drier than those acquired from the bottom parts [13]. Therefore, when determining the mechanical properties, the test samples should be collected from each culm’s bottom, middle, and top [33]. Types of preservation such as seasoning, air drying and boric acid treatment also alter the moisture content of bamboo and, subsequently, its mechanical properties.

Further, due to the hollow nature of the culms, the longitudinal fibre orientation of the bamboo has the highest tensile strength, flexural strength, and stiffness, similar to structural timber. The presence of nodes in bamboo culms enhances the buckling resistance, and the slenderness ratio and the diameter–thickness ratio influenced the buckling failure. Bamboo culms with similar diameter–thickness ratios negatively correlated with the ultimate bearing capacity and slenderness ratio [49]. The engineered bamboo products can reduce these material properties and strength variations. Cross-laminated bamboo has a huge potential to be used in the industry as a sustainable construction material as it reduces natural material variability and environmental impacts.

The connections play a major role in the load transfer of bamboo structures; thus, the load resistance of the connection should be checked before it applies the modern construction. The load resistance of conventional mortise–tenon and lashing joints is lesser than the modern connection. Bolted joints, steel member and steel plate joints, and filler-reinforced joints are the modern bamboo connections widely used in contemporary bamboo constructions [5]. In addition, mortar injection at bamboo connections enhanced the moment capacity while increasing the stiffness [64]. The mechanical behaviour of these advanced connections was characterised using static monotonic and cyclic testing. Test results indicated an increased resistance of the connections compared to conventional connections [73].

Although bamboo construction is identified as a sustainable method of construction with a huge potential for commercial uptake, the lack of design standards has hindered the application of bamboo in modern construction [78]. Different countries have developed their standards and specifications to utilise bamboo as a building and structural element. The Bureau of Indian Standards has developed a series of Indian standards, and other countries such as China, USA, and African countries also have developed country-specific design standards. A few bamboo design standards were developed by the International Organization for Standardization (ISO). ISO 22156-2021 Bamboo structures- Bamboo culms- Structural design [79], ISO 22157-1, ISO 22157-2 Bamboo—Determination of Physical and Mechanical Properties [16] and ISO 19624 Bamboo structures—Grading of Bamboo Culms—Basic Principles and Procedures [80] are the leading international design standards for bamboo. ISO standards permit an allowable load-bearing capacity design and an allowable stress design approach for the design of bamboo structures. However, there must be more design standards for modern bamboo connections, types of preservative treatment, bamboo composites, and engineered bamboo products. The skill shortage and limited understanding of bamboo construction practices further limit the application of bamboo construction. Therefore, developing the required design standards to promote bamboo construction and improve the quality for commercial industry applications is essential.

8. Conclusions

When using bamboo as a construction material, it is essential to carefully study its physical, mechanical, and chemical properties and their behaviour. Further, the durability aspects of bamboo are paramount as a biodegradable material, and advancements in preservative techniques should be explored. Therefore, this paper summarised the previous studies on the material property characterisation (moisture content and density variation) and the mechanical property (tensile, compressive, flexural, shear and buckling strength) investigation of bamboo species commonly found in different countries. When using bamboo as a construction material, it is crucial to confirm the connections’ stability and long-term performance by testing, designing calculations, and adhering to appropriate design guidelines. The review highlighted that advanced high-performance types of bamboo connections could replace the conventional mortise–tenon joints and lashing joints. Steel plates, clamps and bolted connections are a few examples of advanced connection types that can transfer the moment. Furthermore, different preservative techniques were explored, highlighting each technique’s advantages and disadvantages. It was observed that an oil-heated treatment, a borax treatment, and water soaking are the common types of preservative treatments, considering their practical applicability and effectiveness.

From the summary of the mechanical properties of bamboo, it can be noticed that there is significant variability in the strength parameters relying on the bamboo species and its moisture content. Further, the age of the plant, growth conditions, and location along the bamboo culm affect the mechanical properties. Considering this variability, it can be recommended to perform mechanical testing and determine the mechanical properties of a particular bamboo plant considering its source and all the factors mentioned above before employing it as a construction material. Considering the durability aspect, borax preservation was found to be a feasible and effective option for bamboo among the other treatment techniques such as heat treatment, oil treatment, and water soaking. However, more work must be reported on the borax treatment for bamboo and the quantification of its effects on durability. Therefore, future research can be directed towards enhancing the durability aspects of bamboo using preservative techniques. In addition, engineered bamboo products, such as cross-laminated bamboo, are getting popular due to their enhanced mechanical properties. Future studies can be focused on engineered bamboo products to explore their potential and identify their drawbacks.