Brazilian Potential of Eucalyptus benthamii Maiden & Cambage for Cross-Laminated Timber Panels: Structural Analysis and Comparison with Pinus spp. and European Standards

Abstract

This study investigates the potential of Eucalyptus benthamii wood from planted forests in southern Brazil for the production of cross-laminated timber (CLT) panels. The performance of E. benthamii CLT panels is compared to that of Pinus spp. panels and European commercial panels (KLH^®), using the finite element method applied to a two-story building model. Class 2 of the Brazilian standard ABNT NBR 7190-2 was adopted as the reference for the physical and mechanical properties of Pinus spp., while the European commercial specifications from KLH^® were used to represent European reference panels. The results indicate that E. benthamii wood exhibits superior mechanical properties, enabling reductions of 12.5% to 27.3% in panel thickness and a 20.7% decrease in wood volume when compared to Pinus spp., without compromising structural safety. Relative to the KLH^® and ETA 06/0138 standards, E. benthamii wood demonstrates higher stiffness (modulus of elasticity of 15,325 MPa vs. 12,000 MPa) and greater flexural strength (109.11 MPa vs. 24 MPa), allowing for the use of thinner panels. Stress and displacement analyses confirm that E. benthamii CLT slabs can withstand critical loads (wind and vertical) within normative limits, with maximum displacements of 18.5 mm. The reduction in material volume (22.8 m³ versus 28.7 m³ for Pinus spp.) suggests potential benefits in terms of environmental impact and logistical efficiency. It can be concluded that E. benthamii represents a sustainable and efficient alternative for CLT panels, combining high structural performance with resource optimization and contributing to the decarbonization of the construction industry.

1. Introduction

The construction sector is one of the largest contributors to global carbon dioxide (CO₂) emissions, accounting for approximately 37% of energy-related emissions and 34% of final energy demand [1]. In this context, replacing traditional materials such as concrete and steel with wood has gained prominence as an effective strategy for reducing environmental impact. In addition to being a renewable resource, wood stores CO₂ in its structure, effectively turning buildings into carbon sinks and contributing to climate stabilization [2].

Cross-laminated timber (CLT) panels have emerged as a promising solution. First developed in Austria in the 1990s to make use of surplus wood [3], CLT panels consist of layers of orthogonally arranged lamellas, which provide the material with two-dimensional rigidity and enable its use as walls, floors, and slabs [4]. Recent studies show that CLT constructions can reduce CO₂ emissions by up to 45% and energy consumption by 49% compared to concrete walls [5]. In addition to its environmental advantages, CLT stands out for its excellent strength-to-weight ratio [6], making it suitable for use in multi-story buildings.

CLT panels provide wood with more homogeneous properties and greater dimensional stability, due to the strict quality control involved in their manufacturing process. However, as wood is a natural material, its physical and mechanical properties are influenced by factors such as species, growing conditions, and anisotropy [7].

For this reason, research has been conducted to evaluate the performance of different wood species in the production of CLT panels, aiming to expand the range of raw material sources and optimize material use. Typically, wood from planted forests is employed, which helps reduce the reliance on native timber in Brazil. In this way, it is possible to preserve native forests, such as the Amazon, by using wood from planted Eucalyptus and Pinus species.

Several studies have validated numerical methodologies, such as the finite element method (FEM), for analyzing CLT panels. For example, research by Navaratnam et al. [8] investigated the bending and shear behavior of Australian Pinus radiata CLT panels, reporting maximum differences of 20% between experimental and numerical results, and concluding that FEM can be an effective tool for predicting structural performance. Another study by Hematabadi et al. [9] evaluated the bending and shear properties of CLT panels made from Populus alba sourced from planted forests. In this case, FEM successfully predicted bending and shear stress values in relation to mechanical bending tests, yielding favorable results that support the feasibility of using CLT panels for structural applications.

Li et al. [10] investigated the out-of-plane bending and shear performance of CLT and cross-laminated bamboo timber (CLBT) panels, achieving finite element (FE) simulations with results comparable to both experimental and theoretical outcomes. Their findings support the potential application of CLBT panels in flooring systems.

Sciomenta et al. [11] analyzed the performance of CLT panels used as shear walls in multi-story buildings with multiple openings. The authors validated experimental data through FEM models that accounted for crack propagation around the openings, resulting in numerical simulations capable of predicting both the elastic behavior of the walls and their inelastic response following crack development in the CLT panels.

More recently, Teixeira et al. [12] manufactured CLT panels using Eucalyptus benthamii Maiden & Cambage from Brazilian planted forests, validating mechanical properties via FEM with an average difference of 21.61% compared to bending test results. However, there are still gaps regarding the application of these findings in real buildings, particularly concerning the optimization of panel thickness and comparisons with well-established species.

In Brazil, the potential for producing CLT panels is significant, with approximately 10.2 million hectares of planted forests—76% of which are Eucalyptus and 19% Pinus [13]. In the southern region of the country, where the climate is colder, Eucalyptus benthamii was introduced in 1988 by the Brazilian Agricultural Research Corporation (Embrapa) due to its resistance to low temperatures and frost [14,15]. Despite its potential, this species remains underexplored in comprehensive structural models, particularly in comparison with traditional species such as Pinus spp. and international CLT panel standards.

Building upon this background, this article addresses this gap by applying the validated properties of E. benthamii CLT panels [12] to a two-story model building. Using the FEM, panel thicknesses are optimized, and the structural performance and material efficiency (in terms of volume and weight) of E. benthamii CLT panels are compared with those of Pinus spp. CLT panels (Class 2, ABNT NBR 7190-2 [16]) and European commercial CLT panels (KLH Massivholz GmbH^®, ETA 06/0138 [17]). The results demonstrate that E. benthamii performs competitively when compared to traditional species and European standards, offering a sustainable alternative for the Brazilian timber construction industry, with potential for cost reduction and decreased environmental impact.

2. Materials and Methods

2.1. Architectural Design of the Building

The building under analysis was a two-story residential structure with a total area of approximately 80 m². It was modeled to evaluate the behavior of CLT panels as structural elements for walls and slabs. The original project had been developed by Dlubal^® (Tiefenbach, Germany) and was adapted by the authors to comply with the dimensional guidelines of the European standard ETA 06/0138 [17], which governed CLT panels manufactured by KLH Massivholz GmbH^® (Teufenbach-Katsch, Austria), one of the leading European manufacturers in the sector.

The building comprised 14 wall panels (oriented along the X and Y axes), 4 floor slab panels on the upper floor, and 4 roof slab panels, totaling 22 CLT panels. To simulate real design conditions, some panels included openings for doors, windows, and stairs, allowing the structural behavior to be evaluated under different scenarios and geometries (Figure 1). All panels were numerically labeled to facilitate the analysis and interpretation of results (Figure 1a).

2.2. Characteristics and Physical–Mechanical Properties of the Panels

To investigate the physical–mechanical properties, two wood species from Brazilian planted forests were selected: Eucalyptus benthamii and Pinus spp. Additionally, specifications of commercial CLT panels from the European company KLH Massivholz GmbH^® were included, resulting in three treatments.

For E. benthamii, the properties of 23-year-old wood, validated by Teixeira et al. [12], were adopted in the numerical models, developed using the FEM in RFEM^® software, version 5.26, and experimentally, by comparing displacements in the middle of the span in mechanical bending tests.

For CLT panels made from Pinus spp., the strength Class 2 property values from ABNT NBR 7190-2 [16], representative of wood from Brazilian planted forests, were used. Since the Brazilian standard does not provide all the parameters required for structural modeling of Pinus CLT panels, the methodology proposed by Teixeira et al. [12] was employed to estimate the remaining properties, based on empirical relationships and complementary current technical regulations.

The shear moduli were determined using the relationships established by Bodig and Jayne [18], based on the modulus of elasticity in bending. The Poisson’s ratio (ν_xy) adopted was the average value of 0.37 for both conifers and hardwoods, as also proposed by Bodig and Jayne [18].

The tensile strength perpendicular to the fibers (f_t90) was considered to be 0.40 MPa for conifers, as defined by ABNT NBR 7190-1 [19]. The compressive strength perpendicular to the fibers (f_c90) and the tensile strength parallel to the fibers (f_t0) were estimated using ABNT NBR 7190-3 [20]. The rolling shear strength (f_R,m) was adopted as 1.10 MPa, in accordance with the European standard EN 16351 [21] for panels without lateral gluing of the lamellas.

For in-plane shear strength (f_xy), specific approaches were adopted for each material. The f_xy values for KLH^® panels were obtained directly from the technical specification ETA 06/0138 [17], using linear interpolation for layer thicknesses of 20, 30, and 40 mm. For E. benthamii and Pinus spp., the f_xy values were calculated proportionally to the ratio between their shear strengths (f_v) and that of KLH^®, according to the methodology detailed in Appendix A.

For KLH^® panels, the specifications of ETA 06/0138 [17] were followed, which provided all the parameters required for modeling CLT panels marketed by the company. According to KLH^®, these panels were typically manufactured using spruce, pine, fir, and stone pine. These parameters are already available in the library of the RF-Laminate^® add-on module of the RFEM^® software. All the properties used in the modeling for the three treatments are presented in

Table 1. Physical and mechanical properties adopted for the CLT panel modeling.

Property	Un.	CLT Panel
		E. benthamii a	Pinus spp. b	KLH® b
ρ	kg/m3	610.00	400.00	560.84
Ex	MPa	15,325.24	8,000.00	12,000.00
fb	MPa	109.11	27.00	24.00
fv	MPa	13.07	3.50	2.70
fc0	MPa	43.51	18.00	24.00
fc90	MPa	10.88	4.50	2.70
ft0	MPa	56.51	23.38	16.50
ft90	MPa	0.60	0.40	0.12
fR,m	MPa	1.10	1.10	1.20
Gxz	MPa	1028.98	537.14	690.00
Gyz	MPa	109.47	57.14	50.00
Gxy	MPa	1094.66	571.43	500.00
fxy (20 mm)	MPa	39.69	10.63	8.20
fxy (30 mm)	MPa	30.01	8.04	6.20
fxy (40 mm)	MPa	21.01	6.63	4.34

^a Average experimental and estimated values, validated through finite element modeling, as detailed in [12]. ^b Properties derived from technical standards, including average modulus E_x and characteristic strengths. Legend: ρ = density or specific weight; E_x = modulus of elasticity obtained in the bending test; f_b = bending strength or modulus of rupture in the static bending test; f_v = shear strength; f_c0 = compressive strength parallel to the fibers; f_c90 = compressive strength perpendicular to the fibers; f_t0 = tensile strength parallel to the fibers; f_c90 = tensile strength perpendicular to the fibers; f_R,m = rolling shear strength; G = shear modulus in the indicated plane; f_xy = in-plane shear strength. Source: Adapted from Teixeira et al. [12], ABNT NBR 7190-2 [16] and ETA 06/0138 [17].

.

2.3. Structural Modeling of the Building

The CLT panel building was modeled using the FEM in the RFEM^® software, version 5.26, employing the RF-Laminate^® add-on module, which enables the design of lamellar surfaces. RF-Laminate^® applies advanced numerical methods to solve equilibrium and compatibility equations, considering the stress and strain distribution in each layer of the CLT panel and adopting second-order analysis to incorporate non-linear effects. The non-linear system was solved through algebraic equations using the Picard method. The entire methodology and the equations implemented in RF-Laminate^® were described by Dlubal [22]. Stresses were evaluated relative to the characteristic strengths of the materials, while displacements were compared against the serviceability limits established by ABNT NBR 7190-1 [19].

The FE mesh consisted of square elements, tested in various sizes to assess result accuracy. After refinement studies, a 10 cm × 10 cm element size was adopted, as this configuration provided an optimal balance between computational accuracy and processing time in RFEM^®.

The structure was simulated with hinged supports at the base of the first-floor walls, where horizontal displacements were restrained to represent foundation constraints. The analysis followed Mindlin’s Theory to account for transverse shear deformations and rotational inertia. Full coupling between panel layers was assumed, without lateral gluing between lamellas, in accordance with standard industrial practice for CLT panels. The stiffness matrix was calibrated using torsional stiffness reduction factors (K33 = 0.489) and layer stiffness reduction factors (K88 = 0.585), as prescribed by Eurocode 5 [23] for CLT panels without lateral bonding. Linear elastic springs with a service stiffness (k_ser) of 2.400 kN/m² (i.e., stiffness per unit area) were introduced at panel joints to simulate CLT connections (Figure 2b). Given the density variability of southern Brazilian wood, where juvenile and mature wood may coexist within the same log depending on tree age [24], the connection service stiffness was calculated in accordance with ABNT NBR 7190-1 [19] and Eurocode 5 [23], using a conservative equivalent density of 360 kg/m³ for 8 mm diameter screws. This standardized value was applied across all three material treatments to ensure structural safety and enable direct comparisons. The springs were placed exclusively along two orthogonal directions: vertically, to transfer axial loads between overlapping wall panels (across stories) and to simulate bearing support between slab and wall panels; and horizontally, to resist in-plane shear between adjacent wall panels on the same floor.

To optimize the thicknesses of the CLT panels, the layer pattern established by the European manufacturer KLH^®, in accordance with standard ETA 06/0138 [17], was adopted. The optimization process was conducted iteratively in the RFEM^® software, following these steps: the panel thicknesses were initially defined based on the KLH^® configurations; structural analyses were then performed to verify compliance with the ultimate limit state (ULS) and serviceability limit state (SLS) criteria; and a progressive thickness reduction was implemented. For each treatment (Eucalyptus benthamii, Pinus spp., and KLH^®), the thicknesses of the layers were sequentially reduced, with new analyses performed at each stage until the maximum stresses did not exceed the characteristic strength of the material (ULS), the maximum deflections remained within the L/300 limit (SLS), where L is the free span of the panel, and the total thickness was minimized without compromising safety and structural performance.

This procedure was repeated for each panel group (X-Walls, Y-Walls, Floor Slabs, and Roof Slabs), ensuring that the final thicknesses met the minimum structural design requirements.

2.4. Definition and Application of Permanent, Variable, and Wind Loads

The loads applied in the modeling followed the Brazilian standard ABNT NBR 8681 [25], which classifies load cases and combinations. In addition to the self-weight of the structure, which was automatically considered by the RFEM^® software, permanent and variable vertical loads were applied to the CLT slabs, both on the upper floor and on the roof. The load values were determined in accordance with ABNT NBR 6120 [26], which establishes the actions to be considered in the structural design of buildings.

Table 2. Permanent and variable loads applied in the building modeling.

Permanent Load
CLT Set	Material	Load (kN/m2)	Total Load (kN/m2)
Upper floor slab	Floor covering for residential and commercial buildings (5 cm)	1.00	1.08
	Waterproofing with simple asphalt blanket (0.3 cm)	0.08
Roof slab	Roof waterproofing with asphalt blanket and mechanical protection, without finishing (10 cm)	1.80	2.50
	Roof with general ceramic tiles (excluding Germanic and colonial types), with a wooden structure and slope ≤ 40%	0.70
Variable Load
CLT Set	Site	Load (kN/m2)	Total Load (kN/m2)
Upper floor slab	Bedrooms, living room, pantry, kitchen, and toilets in residential buildings	1.50	1.50
Roof slab	Roofs with maintenance-only access	1.00	1.00

Source: Adapted from ABNT NBR 6120 [26].

presents the permanent and variable loads applied to the building slabs, including cladding, roof tiles, and occupancy loads.

The wind loads were calculated for the walls along the X and Y axes, following the parameters established by ABNT NBR 6123 [27]. The analysis considered a residential building located on flat terrain in an urban area, characterized by high turbulence winds, defined as winds where the building height is less than twice the average height of neighboring buildings.

The basic wind speed (V₀) was defined as 45 m/s, based on the isopleth map from NBR 6123 [27] for the state of Santa Catarina, Brazil. The characteristic wind speed (V_k) was calculated considering the following factors:

• Topographic factor (S₁): 1.00 (flat terrain);
• Roughness factor (S₂): 0.74 for the first floor (z = 3.00 m) and 0.81 for the upper floor (z = 6.00 m), where z represents the floor height, determined using the following expression:

  $$S_2=b\ast F_r{\ast \left({\displaystyle \raisebox{1ex}{$z$}\!\left/ \!\raisebox{-1ex}{$10$}\right.}\right)}^p$$

  (1)
• where b = 0.86, F_r = 1.00, and p = 0.12 (Category IV, Class A);
• Statistical factor (S₃): 1.00 (residential building, Group 2).

Consequently, the characteristic wind speeds (V_k) and dynamic wind pressures (q) were calculated using the following expressions, respectively:

$$V_k=V_0\ast S_1{\ast S}_2\ast S_3$$

(2)

$$q=0.613\ast {V_k}^2$$

(3)

Finally, the drag force (F_a) was determined according to

$$F_a=C_a\ast q$$

(4)

where C_a represents the drag coefficient, obtained from NBR 6123 [27] for parallelepiped buildings subjected to high turbulence winds. For the X direction (l₁ = 4.00 m, l₂ = 10.00 m, h = 6.00 m, where l₁ and l₂ correspond to the building dimensions in the Y and X directions, respectively, and h is the total building height), C_a is 0.85. For the Y direction (l₁ = 10.00 m, l₂ = 4.00 m, h = 6.00 m), C_a is 1.05.

Table 3. Wind loads applied in the building modeling.

Wind Load
CLT Set	Vk (m/s)	q (kN/m2)	Load Direction	Fa (kN/m2)
Ground floor walls	33.q30	0.68	X	0.58
			Y	0.71
Upper floor walls	36.45	0.82	X	0.70
			Y	0.86

Legend: V_k = characteristic wind speed; q = dynamic wind pressure; F_a = drag force.

presents the calculated wind load values (drag forces) applied in the structural modeling, and Figure 3 illustrates the distribution of these loads on the building walls.

The load combinations were defined in accordance with ABNT NBR 8681 [25], considering normal situations with unfavorable effects. The RF-Laminate^® module automatically selected the critical combination for each group of CLT panels, ensuring that the most demanding loading scenario was analyzed. The combinations adopted were as follows:

$${CC}_1=(1.25\ast CP)+(1.50\ast CV)+(0.84\ast F_{ax})$$

(5)

$${CC}_2=(1.25\ast CP)+(1.50\ast CV)+(0.84\ast F_{ay})$$

(6)

$${CC}_3=(1.25\ast CP)+(1.20\ast CV)+(1.40\ast F_{ax})$$

(7)

$${CC}_4=(1.25\ast CP)+(1.20\ast CV)+(1.40\ast F_{ay})$$

(8)

where CC refers to the load combination, CP corresponds to the permanent load (self-weight and cladding), CV represents the variable load (occupancy and use), F_ax is the wind drag force in the X direction, and F_ay is the wind drag force in the Y direction.

The CC₁ and CC₂ combinations considered wind as a secondary variable action (γ = 0.84), applicable when wind was not the dominant effect. In contrast, CC₃ and CC₄ treated wind as the primary variable action (γ = 1.40), ensuring safety in regions subject to intense winds. This distinction followed the normative criteria established by ABNT NBR 8681 [25], which requires higher load factors for critical actions to address uncertainties associated with dominant loading scenarios.

3. Results

3.1. Optimization of CLT Panel Thicknesses

Table 4. Optimized thicknesses of the building’s CLT panels.

CLT Set	Panel Layer	CLT Panel Thickness (mm)
		E. benthamii	Pinus spp.	KLH®
X-axis Walls	1	20	30	30
	2	30	30	20
	3	20	30	30
	Total	70	90	80
Y-axis Walls	1	20	20	20
	2	20	20	20
	3	20	20	20
	Total	60	60	60
Floor Slabs	1	30	40	40
	2	20	30	20
	3	40	40	40
	4	20	30	20
	5	30	40	40
	Total	140	180	160
Roof Slabs	1	40	30	40
	2	20	40	40
	3	40	30	30
	4	20	20	40
	5	40	30	40
	6	-	40	-
	7	-	30	-
	Total	160	220	190

presents the minimum panel thicknesses obtained through FEM analysis for each structural group (X/Y walls, floor slabs, and roof slabs), comparing the performance of E. benthamii CLT panels with commercial references (KLH^®) and Pinus spp.

All treatments achieved the minimum wall panel thickness of 60 mm (three 20 mm layers) for Y-axis walls. For X-axis wall panels, E. benthamii required 12.5% less total thickness (70 mm) compared to KLH^® (80 mm) and 22.2% less than Pinus spp. (90 mm), reflecting its superior capacity to resist combined bending and shear loads.

For floor slabs, E. benthamii CLT showed a thickness reduction of 12.5% (140 mm compared to 160 mm for KLH^®) and 22.2% (compared to 180 mm for Pinus spp.). For roof slabs, the difference was even more pronounced: 160 mm for E. benthamii, compared to 190 mm for KLH^® and 220 mm for Pinus spp., corresponding to reductions of 15.8% and 27.3%, respectively. The performance hierarchy shown in Figure 4 followed the trend: E. benthamii < KLH^® < Pinus spp., except for the Y-axis walls.

This relationship between thickness and structural efficiency was explained by the superior mechanical properties of E. benthamii, such as its higher modulus of elasticity (E_x = 15,325.24 MPa) and flexural strength (f_b = 109.11 MPa), as validated by Teixeira et al. [12]. These properties enabled Eucalyptus to deliver equivalent or superior performance with less material, providing a competitive advantage over consolidated species and international standards.

3.2. Maximum Stresses in CLT Panels

The maximum stresses calculated by RFEM^® and the corresponding stress-to-strength ratios for CLT panels made from E. benthamii, Pinus spp., and KLH^® are detailed in

Table A2. Maximum stresses in Eucalyptus benthamii CLT buildings.

CLT Set	Panel	σb,0 (MPa)	σb,0/Strength	σt/c,0 (MPa)	σt/c,0/Strength	σb,0+t/c,0 (MPa)	σb,0+t/c,0/Strength	Ɣy′z′ (MPa)	Ɣy′z′/Strength	Ɣx′z′ (MPa)	Ɣx′z′/Strength	Ɣx′y′ (MPa)	Ɣx′y′/Strength
Y-axis Walls	1	−1.410	0.01	−3.601	0.08	−4.398	0.09	0.250	0.23	0.426	0.03	−0.995	0.03
	2	−0.727	0.01	2.542	0.04	2.653	0.05	−0.213	0.19	0.213	0.02	0.557	0.01
	3	2.439	0.02	−3.800	0.09	−4.885	0.10	0.221	0.20	−0.714	0.05	−1.414	0.04
	4	−0.889	0.01	−1.989	0.05	−2.035	0.05	−0.241	0.22	0.241	0.02	0.619	0.02
	12	−1.309	0.01	−2.705	0.06	−3.025	0.05	−0.082	0.07	0.143	0.01	−1.041	0.03
	13	−1.008	0.01	−2.113	0.05	−2.249	0.05	−0.117	0.11	−0.251	0.02	−0.736	0.02
	14	−3.014	0.03	−4.475	0.10	−5.783	0.11	0.180	0.16	−0.868	0.07	−1.742	0.04
	15	−1.036	0.01	−2.714	0.06	−3.750	0.07	−0.136	0.12	0.245	0.02	1.198	0.03
X-axis Walls	5	0.672	0.01	−8.624	0.20	−8.717	0.20	−0.097	0.09	0.097	0.01	−1.727	0.04
	6	−0.392	0.00	8.405	0.15	8.458	0.15	0.072	0.07	−0.072	0.01	1.365	0.03
	7	−1.269	0.01	9.233	0.16	9.349	0.16	0.107	0.10	0.187	0.01	1.603	0.04
	16	−2.028	0.02	2.783	0.05	4.781	0.07	−0.089	0.08	0.375	0.03	−1.000	0.03
	17	−1.608	0.01	3.506	0.06	4.249	0.07	0.070	0.06	0.278	0.02	0.537	0.01
	18	−2.125	0.02	3.867	0.07	−5.868	0.11	−0.089	0.08	−0.351	0.03	0.955	0.02
Slabs	8	−0.786	0.01	2.177	0.04	2.766	0.04	0.131	0.12	−0.147	0.01	−0.476	0.02
	9	−0.788	0.01	2.191	0.04	2.782	0.04	−0.132	0.12	0.148	0.01	−0.356	0.01
	10	−1.324	0.01	3.758	0.07	4.751	0.08	−0.253	0.23	0.284	0.02	−0.718	0.02
	11	−1.518	0.01	4.284	0.08	5.423	0.09	0.376	0.34	0.415	0.03	−1.242	0.04
	19	−0.682	0.01	−2.053	0.05	−2.735	0.05	−0.160	0.15	0.173	0.01	−0.382	0.02
	20	−0.683	0.01	2.057	0.04	2.740	0.04	0.188	0.17	−0.204	0.02	0.359	0.02
	21	−1.354	0.01	4.090	0.07	5.444	0.08	−0.344	0.31	0.373	0.03	−0.934	0.05
	22	−1.354	0.01	4.066	0.07	5.420	0.08	−0.344	0.31	0.373	0.03	0.927	0.05

Legend: σ_b,0 = Maximum local bending stress parallel to the grain; σ_t/c,0 = Maximum tensile/compressive stress parallel to the grain; σ_b,0+t/c,0 = Maximum global bending stress parallel to the grain; Ɣ = Maximum in-plane shear stress in the corresponding plane.

,

Table A3. Maximum stresses in Pinus spp. CLT buildings.

CLT Set	Panel	σb,0 (MPa)	σb,0/Strength	σt/c,0 (MPa)	σt/c,0/Strength	σb,0+t/c,0 (MPa)	σb,0+t/c,0/Strength	Ɣy′z′ (MPa)	Ɣy′z′/Strength	Ɣx′z′ (MPa)	Ɣx′z′/Strength	Ɣx′y′ (MPa)	Ɣx′y′/Strength
Y-axis Walls	1	−1.351	0.05	−2.222	0.12	−1.679	0.14	0.246	0.22	0.360	0.10	−0.655	0.08
	2	−0.804	0.03	2.178	0.09	1.876	0.10	−0.221	0.20	−0.253	0.07	0.409	0.05
	3	−2.065	0.08	−2.277	0.13	−1.544	0.15	0.222	0.20	−0.580	0.17	−0.896	0.11
	4	−0.949	0.04	−1.800	0.10	−1.819	0.10	−0.240	0.22	0.265	0.08	−0.548	0.07
	12	1.051	0.04	−1.751	0.10	−0.312	0.11	0.078	0.07	0.135	0.04	−0.812	0.10
	13	0.857	0.03	1.901	0.08	−1.358	0.08	−0.120	0.11	−0.200	0.06	−0.633	0.08
	14	−2.541	0.09	−2.780	0.15	−1.879	0.19	0.131	0.12	−0.711	0.20	−1.130	0.14
	15	−0.907	0.03	−1.582	0.09	−0.836	0.12	−0.118	0.11	−0.254	0.07	0.897	0.11
X-axis Walls	5	−0.668	0.02	−7.630	0.42	−7.550	0.43	−0.079	0.07	0.079	0.02	−1.480	0.14
	6	0.318	0.01	7.387	0.32	7.338	0.32	0.059	0.05	−0.059	0.02	1.327	0.12
	7	1.267	0.05	−6.779	0.38	−5.668	0.42	0.093	0.08	0.191	0.05	1.463	0.14
	16	−1.648	0.06	−2.156	0.12	−0.081	0.16	−0.072	0.07	0.307	0.09	−0.810	0.08
	17	0.826	0.03	3.565	0.15	3.116	0.17	0.056	0.05	0.142	0.04	0.452	0.04
	18	1.695	0.06	3.726	0.16	−1.132	0.22	−0.068	0.06	−0.285	0.08	0.742	0.07
Slabs	8	0.363	0.01	−1.257	0.07	−1.620	0.08	0.098	0.09	−0.105	0.03	−0.328	0.06
	9	−0.364	0.01	−1.254	0.07	−1.618	0.08	0.099	0.09	−0.106	0.03	−0.232	0.04
	10	−0.621	0.02	−2.089	0.12	−2.710	0.14	−0.184	0.17	0.197	0.06	−0.440	0.08
	11	0.735	0.03	−2.487	0.14	−3.222	0.17	0.279	0.25	0.279	0.08	−0.717	0.13
	19	−0.252	0.01	−1.601	0.09	−1.853	0.10	−0.148	0.13	0.148	0.04	0.175	0.03
	20	0.260	0.01	−1.662	0.09	−1.922	0.10	−0.148	0.13	0.148	0.04	0.190	0.03
	21	0.456	0.02	−2.865	0.16	−3.320	0.18	−0.269	0.24	0.269	0.08	−0.416	0.07
	22	−0.456	0.02	−2.884	0.16	−3.340	0.18	−0.269	0.24	0.269	0.08	−0.433	0.08

Legend: σ_b,0 = Maximum local bending stress parallel to the grain; σ_t/c,0 = Maximum tensile/compressive stress parallel to the grain; σ_b,0+t/c,0 = Maximum global bending stress parallel to the grain; Ɣ = Maximum in-plane shear stress in the corresponding plane.

, and

Table A4. Maximum stresses in KLH^® CLT buildings.

CLT Set	Panel	σb,0 (MPa)	σb,0/Strength	σt/c,0 (MPa)	σt/c,0/Strength	σb,0+t/c,0 (MPa)	σb,0+t/c,0/Strength	Ɣy′z′ (MPa)	Ɣy′z′/Strength	Ɣx′z′ (MPa)	Ɣx′z′/Strength	Ɣx′y′ (MPa)	Ɣx′y′/Strength
Y-axis Walls	1	−3.162	0.13	3.153	0.19	−3.579	0.15	0.262	0.22	0.526	0.19	−0.719	0.12
	2	−1.242	0.05	3.139	0.19	3.617	0.21	−0.234	0.20	−0.264	0.10	0.399	0.06
	3	−4.492	0.19	−2.650	0.11	−4.738	0.20	0.238	0.20	−0.849	0.31	−0.996	0.16
	4	−1.515	0.06	−2.786	0.12	−2.794	0.12	−0.252	0.21	0.271	0.10	0.439	0.07
	12	−1.756	0.07	2.135	0.13	−3.65	0.15	0.088	0.07	0.179	0.07	−0.709	0.11
	13	−1.480	0.06	2.521	0.15	2.605	0.16	−0.106	0.09	−0.221	0.08	−0.612	0.10
	14	−5.542	0.23	−3.223	0.13	−6.328	0.26	0.179	0.15	−1.043	0.39	−1.247	0.20
	15	−2.539	0.11	−1.712	0.07	2.700	0.12	−0.125	0.10	−0.155	0.06	0.864	0.14
X-axis Walls	5	−0.643	0.03	−8.308	0.35	−8.414	0.35	−0.073	0.06	−0.074	0.03	−1.201	0.15
	6	−0.398	0.02	8.066	0.49	8.117	0.49	0.059	0.05	0.060	0.02	1.008	0.12
	7	−1.199	0.05	8.836	0.54	8.838	0.54	0.083	0.07	0.136	0.05	1.157	0.14
	16	−2.408	0.10	2.725	0.17	4.987	0.26	−0.062	0.05	0.414	0.15	−0.675	0.08
	17	−1.604	0.07	3.348	0.20	3.706	0.22	0.041	0.03	0.251	0.09	0.416	0.05
	18	−2.198	0.09	−3.806	0.16	−6.004	0.25	−0.050	0.04	−0.372	0.14	0.742	0.09
Slabs	8	−0.513	0.02	1.552	0.09	2.065	0.12	0.102	0.08	−0.110	0.04	−0.336	0.07
	9	−0.515	0.02	1.566	0.09	2.081	0.12	0.102	0.08	−0.110	0.04	−0.187	0.04
	10	−0.949	0.04	2.956	0.18	3.905	0.22	−0.193	0.16	0.209	0.08	−0.358	0.08
	11	1.104	0.05	3.425	0.21	4.529	0.25	−0.276	0.23	0.299	0.11	−0.711	0.15
	19	−0.462	0.02	−1.736	0.07	−2.197	0.09	−0.129	0.11	0.134	0.05	−0.173	0.04
	20	−0.462	0.02	1.741	0.11	2.203	0.12	−0.129	0.11	0.134	0.05	−0.194	0.04
	21	0.935	0.04	3.538	0.21	4.473	0.25	−0.233	0.19	0.242	0.09	−0.439	0.10
	22	−0.935	0.04	3.512	0.21	4.447	0.25	−0.233	0.19	0.242	0.09	0.448	0.10

Legend: σ_b,0 = Maximum local bending stress parallel to the grain; σ_t/c,0 = Maximum tensile/compressive stress parallel to the grain; σ_b,0+t/c,0 = Maximum global bending stress parallel to the grain; Ɣ = Maximum in-plane shear stress in the corresponding plane.

, respectively, and available in Appendix B. These ratios made it possible to identify which panels approached the ULS, thereby indicating the structural efficiency of each treatment.

For the wall panels, local bending stresses (σ_b,0) were most critical in panels nº 14, located at the edges of the openings, with values of 3.01 MPa for E. benthamii, 5.54 MPa for KLH^®, and 2.54 MPa for Pinus spp. These results indicated that E. benthamii exhibited intermediate stress levels, while KLH^® showed the highest values, possibly due to its lower bending resistance compared to Eucalyptus.

Total bending stress (σ_b,0+t/c,0) was more significant in panel nº 7 (for E. benthamii and KLH^®) and panel nº 5 (for Pinus spp.), both located at the ends of the first floor. The maximum values were 9.35 MPa for E. benthamii, 8.84 MPa for KLH^®, and 7.55 MPa for Pinus spp. This trend likely reflected the influence of vertical loads from the upper floor and the lower thicknesses of these panels.

Another important stress to consider in CLT wall design is the in-plane shear stress (Ɣ_x′y′), which was most critical in panels nº 5 and nº 14. Panel nº 5, located on the first floor, was primarily affected by vertical loading, while panel nº 14, on the upper floor, was more influenced by wind loads and the presence of a large opening.

Vertical shear stresses (Ɣ_x′z′) were also analyzed, with panel nº 14 standing out as the most stressed. Located on the upper floor, this panel experienced the highest stresses due to the combined effects of wind loads and a large window opening. The recorded values were 0.87 MPa for E. benthamii, 1.04 MPa for KLH^®, and 0.71 MPa for Pinus spp.

For the slab panels, vertical shear stresses (Ɣ_y′z′ and Ɣ_x′z′) were more pronounced in panel nº 11, which spanned 600 cm and included an opening for a staircase. The maximum global bending stress (σ_b,0+t/c,0) appeared in panels 21 and 22 of the roof, also due to the 600 cm clear span.

Figure 5 illustrates the distribution of local bending stresses (σ_b,0) and in-plane shear stresses (Ɣ_x′y′) in the X-axis façade walls of the E. benthamii building, as well as the vertical shear stress distribution (Ɣ_y′z′) in the floor slab containing the stairwell opening.

These results highlighted that larger spans and openings were key factors contributing to increased stresses in slab panels. Despite the slightly higher stress levels observed in E. benthamii, its stress-to-strength ratios remained below 0.34, confirming structural safety even with reduced panel thicknesses.

3.3. Maximum Displacements of CLT Panels

The maximum displacements of the CLT panels, as presented in

Table 5. Maximum displacements of the building’s CLT panels.

CLT Set	Panel	E. benthamii		Pinus spp.		KLH®
		uz (mm)	Ratio uz/Limit	uz (mm)	Ratio uz/Limit	uz (mm)	Ratio uz/Limit
X-axis Walls	1	−6.60	0.33	−6.6	0.33	−8.10	0.41
	2	0.60	0.03	1.00	0.05	1.00	0.05
	3	−11.50	0.57	−11.60	0.58	−15.10	0.76
	4	0.60	0.03	1.10	0.05	1.10	0.05
	12	−3.60	0.18	−3.80	0.19	−3.60	0.18
	13	−2.90	0.15	−2.70	0.14	−2.60	0.13
	14	−14.00	0.70	−14.50	0.73	−18.70	0.94
	15	−3.30	0.17	−3.10	0.16	−2.80	0.14
Y-axis Walls	5	0.20	0.01	0.30	0.01	0.30	0.01
	6	−0.20	0.01	−0.20	0.01	−0.30	0.01
	7	−3.50	0.17	−6.90	0.35	−4.70	0.24
	16	−1.40	0.07	−1.50	0.07	−1.30	0.07
	17	3.40	0.17	3.30	0.17	3.40	0.17
	18	−5.50	0.28	−7.20	0.36	−6.10	0.31
Floor Slabs	8	4.90	0.25	4.80	0.24	4.50	0.22
	9	4.90	0.25	4.80	0.24	4.50	0.22
	10	17.10	0.85	16.40	0.82	16.60	0.83
	11	17.10	0.85	16.40	0.82	16.60	0.83
Roof Slabs	19	4.50	0.23	4.90	0.25	4.80	0.24
	20	4.50	0.23	4.90	0.25	4.80	0.24
	21	18.50	0.93	17.60	0.88	18.20	0.91
	22	18.50	0.93	17.60	0.88	18.20	0.91

Legend: u_z = maximum displacement; Limit = 20 mm, corresponding to L/300, where L is the largest panel span (600 cm).

, demonstrated that the serviceability limit state (vertical deflection ≤ 20 mm) governed the optimization of panel thicknesses.

The most critical slab panels were nº 10 and 11 (floor slabs) and nº 21 and 22 (roof slabs). For E. benthamii, the maximum displacements reached 17.10 mm (floor slabs) and 18.50 mm (roof slabs). In comparison, Pinus spp. presented displacements of 16.40 mm (floor) and 17.60 mm (roof), while KLH^® recorded 16.60 mm (floor) and 18.20 mm (roof). These values resulted from the 600 cm clear spans, which increased deformation under vertical loads. The roof slabs exhibited slightly greater deflections than the floor slabs due to the higher magnitude of vertical loads applied to the roof.

For the CLT X-wall panels, Panel nº 14, with a length of 600 cm and subjected to wind loads, showed displacements of 14.00 mm (E. benthamii), 14.50 mm (Pinus spp.) and 18.70 mm (KLH^®). The greater deflection observed in KLH^® was attributed to its lower stiffness compared to E. benthamii.

Among the Y-walls, Panel nº 18, located on the upper floor and subjected to wind loads, presented the highest displacements: 5.50 mm for E. benthamii, 6.10 mm for KLH^®, and 7.20 mm for Pinus spp. Since the Y-walls for all three treatments had the same total thickness (60 mm), the lower deflection observed in E. benthamii directly reflected its higher modulus of elasticity (E_x = 15,325.24 MPa).

The surface graphs in Figure 6 illustrate the maximum displacement distribution for the CLT panels in the E. benthamii building.

These results highlighted the influence of mechanical properties on dimensional stability. E. benthamii, with its higher density (610 kg/m³) and superior strength, enabled the use of thinner panels with lower displacements compared to the other materials. Although its slabs presented higher displacement ratios (due to their reduced thickness), all structures remained within the safety limits, confirming the technical feasibility of Eucalyptus for CLT applications.

3.4. Volume and Weight of CLT Panels

The volume and weight of the CLT panels were calculated to compare the amount of wood required for each prototype. Figure 7 presents the corresponding graphs.

The E. benthamii building required 22.80 m³ of CLT, representing a reduction of 11.5% compared to KLH^® (25.77 m³) and 20.7% compared to Pinus spp. (28.74 m³). These material savings were directly associated with the reduced thickness of the Eucalyptus panels, as shown in Table 4.

The Pinus spp. prototype was the lightest, with 12.35 tons of CLT, followed by E. benthamii (13.64 tons) and KLH^® (14.17 tons). The higher density of E. benthamii resulted in an intermediate weight but with significantly lower volume, which may reduce logistical costs and environmental impacts.

This relationship between weight and volume reflected the physical properties of the woods used. E. benthamii, with its greater density and strength, enables thinner panels with less volume while maintaining dimensional stability within safety limits.

4. Discussion

This study demonstrated, for the first time, that Eucalyptus benthamii from planted forests in southern Brazil served as a structurally efficient material for the manufacture of CLT panels, competing directly with consolidated species (such as Pinus spp.) and international standards (such as KLH^®). The results showed that E. benthamii not only met structural safety requirements but also exceeded expectations in terms of material efficiency, sustainability, and economic viability, positioning itself as a strategic alternative for the Brazilian timber construction industry.

The observed superiority of E. benthamii was fundamentally attributed to its hardwood nature and high basic density (610 kg/m³). Hardwoods like Eucalyptus tended to exhibit greater anatomical variability, featuring shorter fibers, vessel elements, and parenchyma, resulting in a more complex internal structure compared to conifers like Pinus, which consisted predominantly of long, uniformly arranged tracheids. This anatomical configuration directly correlated with higher density, modulus of elasticity, and bending strength [28,29]. As a result, the high density of E. benthamii was a key factor in its excellent mechanical properties (Ex = 15325.24 MPa; f_b = 109.11 MPa), experimentally validated by Teixeira et al. [12], which enabled the significant thickness reductions observed.

FEM simulation played a crucial role in exploring the relationship between thickness, material properties, and structural performance. The optimization process revealed that E. benthamii requires 12.5% to 27.3% less material than Pinus spp. and KLH^® in slabs and walls without compromising structural safety. This reduction was directly linked to the superior mechanical properties of Eucalyptus, derived from its density and anatomical features. As widely recognized [30,31,32], density served as a key parameter for the structural performance of wood, acting as a predictor for stiffness and strength. This relationship explained the significant volumetric reduction (22.80 m³ vs. 28.74 m³ for Pinus spp.), with positive impacts on logistical costs and global competitiveness of CLT.

Beyond structural efficiency, the results of this study underscored the economic potential of using E. benthamii in CLT production. Its strong adaptability to colder climates and high productivity position this species as a strategic resource for sustainable construction in southern Brazil. Unlike other tropical eucalyptus, E. benthamii thrives in frost-prone regions, enabling the establishment of productive plantations in areas where few other fast-growing species are viable.

According to the Brazilian tree industry [13], the average productivity of Eucalyptus plantations in Brazil, considering all cultivated species, is approximately 33.7 m³/ha/year. However, specific studies on E. benthamii in southern Brazil have reported productivity rates ranging from 35 to over 50 m³/ha/year, depending on site conditions, silvicultural practices, and genetic material [33,34,35,36]. This high yield potential may reduce land-use pressure and improve cost-efficiency throughout the production chain.

Moreover, the regional cultivation of E. benthamii supports the development of a local CLT industry, minimizing the need to transport materials from distant regions or rely on imported products. This proximity can significantly lower logistical costs and carbon emissions. Additionally, fostering local supply chains has the potential to stimulate economic development in rural areas, support job creation, and promote technological advancement within the national engineered wood sector. Another relevant aspect is the considerable variability in the properties of Pinus spp. grown in different regions [37,38,39,40,41,42,43,44,45,46,47]. This study addressed this issue by directly comparing panels made from Brazilian Pinus spp. with commercial panels manufactured by KLH^® in Europe. For example, European Pinus sylvestris, widely used in CLT production in Austria and Germany, exhibits higher mechanical properties than Pinus taeda grown in Brazil, due to climatic, soil, and silvicultural differences [37,38,39,40,45,46,47]. This distinction underscores the importance of local experimental characterization to support the appropriate use of species cultivated in Brazil for CLT production.

In terms of structural performance, the maximum stresses and displacements confirmed the robustness of E. benthamii under critical loads, such as wind and vertical loads. Although the maximum stress values for E. benthamii were slightly higher than those for KLH^® and Pinus spp., the stress-to-strength ratios remained consistently below 1.0, ensuring adequate safety margins. The maximum displacements of Eucalyptus slabs and walls remained within serviceability limits (deflection ≤ 20 mm), with values comparable to or lower than those of the other materials. This balance between material efficiency and dimensional stability reinforces the technical feasibility of E. benthamii for applications in multi-story buildings.

The adoption of E. benthamii in CLT systems offers significant contributions to the decarbonization of the construction sector. The reduction of 5.94 m³ and 1.29 tons of wood per building (compared to Pinus spp.) represents not only a savings in natural resources but also a reduction in the carbon footprint associated with the transportation and processing of timber. Moreover, the cultivation of Eucalyptus in planted forests, which already covers 76% of reforested areas in Brazil, strengthens the principles of the circular economy, promoting the use of renewable raw materials with low environmental impact.

This study pioneered the application of validated E. benthamii CLT properties [12] in a two-story model building, demonstrating its technical feasibility and structural efficiency within a complete construction system. However, certain limitations should be considered. For example, the study focused on a single Eucalyptus species and a specific building configuration. Future research could explore the application of E. benthamii in larger-scale buildings, different climatic zones, and hybrid systems combining other species, such as bamboo (CLBT), which has also been investigated as a sustainable alternative [10]. Additionally, further studies are necessary to evaluate the performance of E. benthamii CLT under dynamic loading conditions, such as seismic events.

The scarcity of similar studies underscores the originality and relevance of this research for advancing knowledge in the field of wood engineering. Diversifying raw materials in the CLT industry by incorporating cultivated species like E. benthamii can significantly reduce pressure on native forests, contributing to Amazon conservation. The competitiveness of E. benthamii relative to KLH^®, a consolidated European standard, demonstrates Brazil’s potential to become a global player in CLT production, positioning this species as a viable alternative for timber construction projects in both domestic and international markets.

5. Conclusions

This study demonstrates that Eucalyptus benthamii represents a promising technical alternative for the production of CLT panels. With mechanical properties superior to those of Pinus spp. and the European standard KLH^®, the species enables a reduction of up to 20.7% in the volume of wood required while maintaining structural safety and performance under critical loads. Additionally, its high productivity and adaptability to colder climates position E. benthamii as a strategic resource for fostering a local CLT industry in southern Brazil, with potential benefits for economic development and environmental sustainability. These findings highlight the potential of E. benthamii to drive the advancement of timber construction in Brazil and to increase competitiveness in the international market, with lower resource consumption and reduced environmental impact. Future research should explore its application in larger buildings, different climatic zones, and under dynamic loading conditions.