Design and Characteristics of a Hybrid Wood-Soil System Made from Casuarina glauca Wood

Abstract

Wood has been used in construction has for several millennia; however, global warming has created situations in which the wood needs to be utilized in a more eco-friendly, sustainable, and cost-effective manner. Using wood from trees farmed on wastewater is an ideal option that has been found to be sound for this use. Casuarina glauca wood has been farmed on wastewater for years, making it eco-friendly and cost effective, in addition to being of relatively high strength when compared to soft woods. Hence, within this research, Casuarina glauca wood is used within a hybrid wood-soil system. A scaled model of the structure was constructed and tested structurally until failure in two horizontal planes: the lateral and transverse. The points of weakness in the connections were identified in order to adjust the design, which mainly involved the nails connecting the studs to the upper and lower beams. The adjusted model was constructed including additional X-braces and tested structurally, and was proven to have sufficient strength compared to the wind loads according to the Egyptian Code of Loading. The design was compared to its reinforced concrete alternative to assess its cost-effectiveness and eco-friendliness in terms of the cost per unit area and the carbon emissions per unit area. The system proved to be more cost-effective and eco-friendly when compared to its reinforced concrete counterpart.

1. Introduction

Climate change has been an escalating problem within recent years. One of the primary causes of this phenomenon is the use of non-biodegradable materials that produce significant carbon emissions during the manufacturing process. With the increase in construction all over the world, the idea and concept of seeking construction materials that are sustainable as well as green began at the start of the 1990s. With that in mind, the construction industry alone is responsible for more than one third of the carbon emissions produced in the world [1]. That is why it is crucial to regularly innovate more green and sustainable construction alternatives to better decrease that amount.

Building construction is one of the major sources of greenhouse gas emissions in addition to the buildings being one of the largest energy consumers globally, as buildings produce approximately 33% of greenhouse gases and consume 40% of energy worldwide [2]. On the other hand, construction activities directly produce 12.6% of building carbon emissions worldwide [3]. However, the choice of building materials and the various aspects within a building’s design significantly affect the carbon emissions along a building’s life cycle [3]. Hence, using more eco-friendly materials in construction is a necessity in order to protect the environment.

Meanwhile, due to the increased costs of housing, over one billion people live in slums around the world [4], including 22 million in Egypt [5]. According to the UN, more than 2 billion people will not have proper shelter by 2030, and 60% of the world’s population already does not live in proper housing [6]. The costs of construction in developing nations such as Egypt, especially the material costs, have been significantly increasing over the last three decades. The main source of this increase is the increase in costs of cement, steel, and masonry [7]. This has negatively affected the lives of more than 55 million Egyptians living in rural areas, especially since the most common structural system used in Egypt is concrete [8]. Hence, one of the potential methods of reducing the costs of construction materials is the usage of low-cost raw materials such as waste materials. Besides waste, underutilized local wood types could be a source of material for construction.

A prominent local wood species is Casuarina glauca. A previous study has covered the mechanical properties of different species of Casuarina [9]. Within that study, the glauca specie of Casuarina proved to be stronger than several types of oaks. The study was further extended to investigate the different properties of that wood within different percentages of moisture content ranging from 20% to 60%, which was still found to be stronger than several types of timber having the same moisture content [10]. The researchers used the findings of these two studies to design and manufacture a k-truss made from Casuarina glauca wood which was tested until failure and proven to carry a load higher than the design load [11]. Meanwhile, the high strength of that type of wood encouraged researchers to further study its mechanical properties, its grading categorization, and the usage of coatings to protect it [12]. Furthermore, this group has studied using this type of wood to design a 12-m span truss and has experimentally proven that the truss pieces made of Casuarina glauca could carry even more weight than the design loads [13]. Meanwhile, another group continued with the theme of these studies and manufactured blockboards from that type of wood, and these blockboards were of sufficient strength to be used for structural purposes [14]. Another aspect studied about this wood was the fact that it could be efficiently dehumidified by burying it in quicklime, and this process saves energy and costs and further reduces the carbon emitted through the process of drying wood; however, these savings were not quantified prior to now [15].

On the other hand, the usage of earth in construction has been increasingly progressing within the past years. In some of these alternatives, the earth could be rammed or compressed [16]. Furthermore, the mortars used within this construction process could include various materials including loam, sand, palm fibers, and lime [17]. One of the technologies being increasingly used involving both earth and wood is hybrid wood-soil systems (HWS). The usage of wood as a structural element within an earth structure dates back to the Middle Ages [18]. Although the energy conservation properties of earth shelters are proven [19], the studies on the structural characteristics of earth structures in general and HWS specifically are scarce.

So far, none of the researchers have structurally designed a HWS structural system and tested it and assessed its cost-effectiveness and eco-friendliness. Performing such a comprehensive study is the core objective of the current study. Within this study, a single-storey building was designed and structurally tested by loading it in the two perpendicular horizontal directions until it failed. After that, the structural design was adjusted by strengthening the connections, and the structure was re-tested. The cost of the structure was calculated together with the cost per unit area, which was compared to its reinforced concrete (RC) control system. The produced carbon emissions per unit area was also calculated and compared to that of a reinforced concrete control system.

2. Materials and Methods

2.1. Initial Structural Design

The structure under study is a model for a school classroom to be constructed in various locations in Egypt that is co-funded by the government of Egypt and an NGO. Consequently, the building construction costs had to be reduced through using HWS instead of reinforced concrete, as this class is a single-storey building with a non-accessible roof with no entrance to the roof to make it accessible, which results in a low live load of 80 kg/m² according to [20]. Hence, the structural system of wooden members was plotted as initially designed, as shown in Figure 1.

2.1.1. Design Criteria

The most important concept when structurally designing an HWS structure is the fact that the wooden members are the sole contributor to the resisting loads structurally, while the role of the soil mixture is only acting as an infill for thermal insulation and acoustic isolation purposes. The design criteria for the wooden floors were mainly two. The first is the strength criterion, which involved the designing of the beams to withstand bending moments and shear forces, while for the trusses the truss members were designed to withstand axial forces, whether tensile or compressive. The second design criterion is the serviceability criteria, which involved limiting the deflections so as not to exceed the value of the span/360. Meanwhile, and as they were under compression in the principal load combination, the main design criterion for the wooden studs was designing them for buckling and checking the sections for tension when subjected to cases of wind load uplift. The design of all members was done according to the Canadian Standards O86-14 Engineering design in wood [20].

2.1.2. Design Assumptions

Preliminary design assumptions included that the single-storey structure would have a non-accessible roof. It was also assumed that this structure is to be built in the north coast of Egypt, which has the highest wind speed. The concrete used in the design of the control case to which the HWS is compared is of a compressive strength of 30 MPa, while the reinforcing steel is of a yield strength of 360 MPa based on the most locally available materials and practices in Egypt.

For wooden members, the Casuarina glauca material properties have been acquired from tests performed by [9], as summarized in

Table 1. Material properties according to [9].

Property	Value
Density	630 kg/m3
Bending strength	62.1 MPa
Shear strength	12.3 MPa
Tensile strength	162.9 MPa
Compressive strength	32.2 MPa
Modulus of elasticity	8418 MPa
Moisture content	18%

. As all these strengths were average values, and as the coefficients of variance (COV) reported within the same study were all ranging between 9% and 10% [9], these average values were all reduced by 20% to conservatively get the design strengths used when designing the different wooden components. All wooden beams were safely designed to be 150 mm deep and 50 mm wide, while all wooden studs were safely designed to be of a 70 mm × 70 mm cross-section.

Loads were calculated according to the Egyptian Code of Practice for Calculating Loads and Forces on Buildings ECP 201-2012 [21]. Both live and wind loads were considered, along with the structure’s own weight, in the analysis with the different design load combinations. Accordingly, for the non-accessible roof, the live load was 0.8 kN/m². Meanwhile, assuming that the structure is in the suburbs of a coastal area of Egypt with a height less than 10 m and a wind velocity of 42 m/s and the terrain factor k is 1. Using the code exposure factors, terrain factors, and pressure coefficients, the design wind pressure was 1.2 kPa with a suction of 0.88 kPa on the roof, a suction of 0.57 kPa on the leeward side, and a pressure of 0.88 kPa on the windward side.

2.2. Structural Testing and Adjusted Design

Since the nails used in the Egyptian market are non-standardized, the connections were not designed based on well-known strengths within the initial structural design phase. Consequently, the structure under study had to be tested for lateral loading in two horizontal directions (lateral and transverse) to guarantee its structural soundness and perform any required adjustments in the design. Due to the fact that the strengths and the COV acquired from the research by [10] have been previously used in the designs by [11] and [13], in which the structural failures happened in the connections and not in the Glauca members, a similar behavior is expected to happen while testing the structure at hand. Hence, the finalized design is expected to include adjustments in the connections to increase the structural soundness of the structure.

2.2.1. Testing in the Lateral Direction

A scaled model of the structure was manufactured with a scale factor of 1:3. The scaled structure was tested in the lateral direction in the manner shown in Figure 2. The load was applied using an actuator with a load cell having a capacity of 70 metric tons and a precision of 1%. The deflections were measured using three linear variable differential transformers (LVDTs) with a 0.1 mm precision. Two of the LVDTs were placed in the direction of loading, while the third was placed in the perpendicular direction to measure the perpendicular deflection resulting from any possible twisting effect, as shown in Figure 2.

After the test was completed, the points of weakness were determined and the connection design was adjusted accordingly. The new scaled model was manufactured and retested using the same set-up to confirm that the structure carries a load exceeding its design load in the lateral direction without any possibility of failure in the connections.

2.2.2. Testing in the Transverse Direction

The 1:3 scaled model of the adjusted structure was manufactured and tested in the transverse direction in the manner shown in Figure 3. The load was applied using an actuator with a load cell having a capacity of 70 metric tons and a precision of 1%. The deflections were measured using three linear variable differential transformers (LVDTs) with a 0.1 mm precision. Two of the LVDTs were placed in the direction of loading, while the third was placed in the perpendicular direction to measure the perpendicular deflection resulting from any possible twisting effect, as shown in Figure 3.

After the test was done, the points of weakness were determined and the suggested adjustments in the connections were tested experimentally to verify its effectiveness. The stiffest connection was determined, and the design was adjusted accordingly. The new scaled model was manufactured and retested using the same set-up to confirm that the structure carries a load exceeding its design load in the transverse direction without any possibility of failure in the connections.

2.3. Carbon Emissions Comparison

After the design is finalized, the quantity of wood and soil to be used in the construction process are calculated and then multiplied by the carbon emissions per unit volume to produce the total carbon emissions of the structure. As the building is designed to be constructed mainly from Casuarina glauca wood together with a soil mixture acting as an infill, the carbon emissions for the building were calculated based on the assumption that as the soil mixture is made mainly of soil and water without even mechanical mixing, the soil mixture is assumed to have no carbon emissions while the timber is assumed to emit 0.35 kg of CO₂/kg of timber, which is equivalent to 0.55 ton of CO₂/m³ according to [22]. Furthermore, the steel connections are taken into account when calculating the carbon emissions, as steel with average recycled content emits 1 kg of CO₂/kg of steel [22]. It is worthy of note that these figures assume that the wood drying process would be undertaken using the most commonly used kiln-drying technology; however, these figures are expected to decrease significantly when using the new drying technique of the burial of wooden planks in quicklime, as specified by [15] due to this new technology producing zero carbon emissions. After calculating the total carbon emissions of the HWS structure, this figure was divided by the area of the building to produce the carbon emissions per unit area.

To properly assess the carbon emissions of the structure, it had to be compared to its reinforced concrete alternative. Hence, a reinforced concrete structure including a slab, beams and columns was designed covering the same area. The quantity of reinforced concrete was calculated and multiplied by the carbon emissions per unit volume of reinforced concrete with a strength of 25 MPa, and was found to be 0.09 kg of CO₂/kg of concrete and a 100 kg/m³ is 0.03 kg of CO₂/kg reinforcement [22]. Meanwhile, as the masonry used are light-weight concrete bricks plastered with cement-based plaster, it is assumed to have the same carbon emissions per unit volume of light-weight concrete, which was 0.27 of CO₂/kg of reinforced concrete ton of CO₂/m³ according to [22]. After calculating the total carbon emissions of the reinforced concrete structure, this figure was divided by the area of the building to produce the carbon emissions per unit area. It is worthy of note that the carbon emissions per unit weight and the carbon emissions per unit volume reported by [22] have been calculated based on a life cycle analysis for several constructed buildings, so these figures already take such an effect into account.

2.4. Cost Comparison

As the building is designed to be constructed mainly from Casuarina glauca wood together with a soil mixture, the unit cost of wood was calculated to be 8000 LE/m³ (320 USD/m³), while the cost of the soil mixture was calculated to be 50 LE/m³ (2 USD/m³). These figures assume that the wood drying process would be conducted using the most commonly used kiln-drying technology; however, these figures are expected to decline significantly when using the new drying technique involving the burial of wooden planks in quicklime, as specified by [15], due to this new technology consuming no energy and therefore saving costs. After calculating the total cost of the HWS structure, this figure was divided by the area of the building to produce the cost per unit area.

To properly assess the carbon emissions of the structure, it had to be compared to its reinforced concrete alternative. Hence, a reinforced concrete structure including a slab, beams and columns was designed to cover the same area. The quantity of reinforced concrete was calculated and multiplied by the cost per unit volume of reinforced concrete, which was 3920 LE/m³ (156.8 USD/m³) according to [22]. After calculating the total cost of the reinforced concrete structure, this figure was divided by the area of the building to produce the cost per unit area.

3. Results

3.1. Structural Testing Results

3.1.1. Results of Lateral Direction Load Tests

The scaled structure was tested in the lateral direction in the manner shown in Figure 2. The deflections from the two LVDTs placed in the direction of loading were plotted versus the load, as shown in Figure 4. The achieved ultimate lateral load of 0.28 kN is significantly low compared to the loads resulting from a lateral wind load that the structure could be subjected to. Furthermore, the lateral drift in the structure is significantly high, exceeding 1/6 of the height of the structure, significantly exceeding the limits for the serviceability design criteria of height/360 specified by the Canadian Standards O86-14 Engineering design in wood [20], which is an important reason for stiffening the structural system in this direction. Meanwhile, noteworthy issue is that the differences between the deflections measured by the two LVDTs were small, pointing out that the effect of twisting due to asymmetricity is minor.

The failure of the initially tested scaled model is shown in Figure 5. When examining the failure in the structure it could be noticed that the bracing members and the studs were disconnected from each other due to failures in the nails connecting these members to each other. The failure in the connections before the members is expected due to [11] and [13] experiencing the same behavior when testing their trusses manufactured from the same type of Casuarina glauca wood. However, what is different in this case is the fact that the loads carried are significantly less than the design loads, driving the researchers to make significant changes in the connections designed.

Consequently, the bracing members were adjusted to be X-braces and the connection design was changed by adding wooden members connecting the studs and the bracing members through steel nails, as shown in Figure 6. This design was chosen due to its simplicity and cost-saving, as the additional wood used was from left-overs of the wood sawing processes.

The adjusted version of the scaled structure was manufactured and tested in the lateral direction in the same manner of testing as the previous sample. The deflections from the two LVDTs placed in the direction of loading were plotted versus the load, as shown in Figure 7. The achieved ultimate lateral load of 53 kN is significantly large, as it reflects a pressure of 17 kPa on the surface of the building, which is much higher than any lateral wind load that the structure could be subject to according to the Egyptian Code of Practice for Calculating Loads and Forces on Buildings ECP 201-2012 [21], as the maximum wind pressure according to this code would never exceed 1 kPa. Furthermore, the lateral drift in the structure is significantly lower than the previous sample, showing a significant increase in the lateral stiffness of the structure after adjusting its design. The new drift corresponding to the design load was less than the value of the height/360 specified by the Canadian Standards O86-14 Engineering design in wood [20], showing no further reason for stiffening the structural system in this direction. Meanwhile, another issue worth noting is that the differences between the deflections measured by the two LVDTs were larger than the previous sample, which could be because of geometric non-linearity causing more significant deflections on one side of the structure than the on other.

The failure of the adjusted tested scaled model is shown in Figure 8. When examining the failure in the structure, it could be noticed that the upper and lower beams and the studs were disconnected from each other due to failures in the nails connecting these members to each other. Again, the failure happened in the connections rather than the members; however, it could be seen that the upper beam had experienced significant deformations, as shown in Figure 8. However, this failure was only experienced at a level of loading more than ten times the design load, confirming that this second version of the design satisfies the design criteria in the lateral direction.

3.1.2. Results of Transverse Direction Load Tests

The second version of the scaled structure was manufactured and tested in the transverse direction in the manner shown in Figure 3. The achieved ultimate transverse load was 0.5 kN, which is negligible compared to the loads resulting from a transverse wind load that the structure could be subject to with failures happening in the connections. Consequently, the connection design had to be significantly changed, resorting to steel connections. To guarantee the strength of the connections, five different configurations were prepared and tested until failure. The five tested connection details are shown in Figure 9. The first is the control sample including only nails connecting the two wooden members without any steel angles. The samples numbered as 2a and 2b include two nails per side; however, the location of the nails are what differentiate 2a from 2b. Meanwhile, the samples numbered as 3 and 4 include three and four nails per side, respectively.

The results of the tests are shown in

Table 2. Results of connection testing.

Connection ID	Steel Member	Number of Nails	Ultimate Load Carried (N)
Control	None	1 screw in middle of the member	350
2a	50 mm × 50 mm angle	2 staggered	1230
2b	50 mm × 50 mm angle	2 lined	1230
3	50 mm × 50 mm angle	3	1350
4	50 mm × 50 mm angle	4	1380

. The results show that the strongest connection configuration was the one with four nails per side. However, as shown in Figure 5, the wooden Glauca members did not fail for any of the connections; the failure was either in the screws or in the steel angle members. That means that the capacity of the structure could increase if the connections are stiffened further. Hence, the connection was stiffened using two parallel triangular stiffeners, as shown in Figure 10, with connection dimensions of 50 mm × 50 mm × 50 mm.

Furthermore, and to act as a second line of defense, the gusset plates of 150 mm wide and 200 mm high shown in Figure 11 were used to connect some of the members in addition to the stiffened steel connection shown in Figure 10.

The adjusted version of the scaled structure was manufactured and tested in the transverse direction in the same manner of testing as the previous sample. The deflections from the two LVDTs placed in the direction of loading were plotted versus the load, as shown in Figure 12. The achieved ultimate lateral load of 47 kN is significantly large compared to the loads resulting from a transverse wind load that the structure could be subject to, as it reflects a pressure of 29.5 kPa on the surface of the building. This is much higher than any transverse wind load that the structure could be subject to according to the Egyptian Code of Practice for Calculating Loads and Forces on Buildings ECP 201-2012 [21], as the maximum wind pressure according to this code would never exceed 1 kPa. Furthermore, the transverse drift in the structure is significantly lower than the previous sample, showing a significant increase in the transverse stiffness of the structure after adjusting its connection design. The new drift corresponding to the design load was less than the value of the height/360 specified by the Canadian Standards O86-14 Engineering design in wood [20], showing no further reason for stiffening the structural system in this direction. Meanwhile, another issue worthy of mention is that the differences between the deflections measured by the two LVDTs were large, which could be because of geometric non-linearity causing more significant deflections on one side of the structure rather than on the other.

The failure of the adjusted tested scaled model is shown in Figure 13. When examining the failure, it could be noticed that the upper beam had experienced significant deformations, while some of the connections connecting the lower beam to the studs had failed. However, this failure was only experienced at a level of loading more than ten times the design loads, confirming that this third version of the design satisfied the design criteria in the transverse direction.

A comparison of the equivalent wind pressures withstood by the four tested structures and the wind design load is shown in Figure 14. This comparison shows that the strengthened structure could withstand a pressure significantly larger than the 1 kPa wind pressure that corresponds to a 42 m/s wind speed, which is the highest wind speed in Egypt.

3.2. Carbon Emissions Comparison

The carbon emissions for the building were calculated based on the assumption that as the soil mixture is made mainly of soil and water without even mechanical mixing, the soil mixture is assumed to have no carbon emissions. The amount of wood used in each HWS structure was 3.5 m³. Meanwhile, the weight of steel connections used to connect the members was about 139 kg. Each of these two figures was multiplied by the material carbon emissions per unit weight or volume and summed to get the total carbon emissions. After calculating the total carbon emissions of the HWS structure, this figure was divided by the area of the building to produce the carbon emissions per unit area.

For the control reinforced concrete structure, the calculated carbon emissions were calculated as the quantities of RC were calculated and multiplied by the carbon emissions per unit volume of reinforced concrete, which equaled 0.12 kg of CO₂/kg of reinforced concrete, which is equal to 0.3 ton of CO₂/m³ of reinforced concrete. Meanwhile, as the masonry used were light-weight concrete bricks plastered with cement-based plaster, it was assumed to have the same carbon emissions per unit volume of light-weight concrete, which was 0.27 ton of CO₂/m³ according to [22]. After calculating the total carbon emissions of the reinforced concrete structure, this figure was divided by the area of the building to produce the carbon emissions per unit area.

The total amounts of CO₂ emissions of each system and the total amounts of CO₂ emissions per unit area were both calculated and compared, and the findings are summarized in

Table 3. The CO₂ emissions for the two studied systems.

Item	HWS	RC
Skeleton	1.93 tons	3.99 tons
Steel Connections	0.139 tons	0 tons
Wall & Plaster	0 tons	3.44 tons
Total CO2 (tons)	2.07 tons	7.43 tons
Total CO2 per unit area (t/m2)	0.043 t/m2	0.15 t/m2

. The results show that the carbon emissions of the HWS are less than its RC counterpart by 72%, indicating a significantly large amount of carbon emissions savings.

3.3. Cost Comparison

Based on the unit costs mentioned in Section 2.4 and the quantities of the materials used, the total costs of each system and the total costs per unit area were both calculated and compared, the findings of which are summarized in

Table 4. The costs of the two studied systems.

Item	HWS	RC
Skeleton	80,000	120,000
Wall	35,000	92,000
Plaster	16,500	26,000
Total Cost (EGP)	131,500	238,000
Total Cost (USD)	4870.37	8814.82
Total Cost per unit area (USD/m2)	100.74	182.33

. The results show that the costs of the HWS are less than its’ RC counterpart by 45%, indicating a significant cost savings, although the cost of the HWS includes the additional costs of the added steel connectors within the cost of the skeleton.

4. Discussion

With regard to the structural capacity of the tested specimen, when examining the failure in the different scaled structures tested, it was noticed that the members were disconnected from each other due to failures in the connections between these members. The failures in the connections between the members was expected, as a similar behavior was observed by [11] and [13] for their structures made of Glauca wood trusses, although they were of different designs and dimensions. Consequently, significant changes had to be performed in the connection designs. These changes lead to significant increases in the lateral stiffness and the transverse stiffness leading to significantly lower drifts in the horizontal plane and significantly higher capacities in the lateral and transverse directions, reducing the drifts corresponding to the design loads to be less than the height/360 specified by the Canadian codes and standards. Meanwhile, when examining the capacities in these two directions, it could be noticed that when loaded in the transverse direction, the strengthened structure carried a significantly higher load than when loaded in the longitudinal direction. This could be attributed to the fact that when loaded in the longitudinal direction, only the bracing members on the two sides resist such loads; however, when loaded in the transverse direction, the beams spanning the structure contribute to resisting the loads together with the bracing in that direction. This is also the reason for the deflections at failure in the two directions being different, as the stiffnesses in the two directions are different.

Meanwhile, according to the CO₂ emission calculations, the HWS system has been proven to save 72% of the CO₂ emissions compared to its RC counterpart. Furthermore, according to the cost calculations, the HWS system has been proven to save 45% of the costs of its RC alternative. Meanwhile, it is evident that the cost of the skeleton made of wooden members with steel connections is about 61% of the cost of the HWS structure, which means that reducing the costs of wood through mass-producing it could further reduce the costs. It is even worth noting that these savings are expected to increase when using the new drying technique of burying wooden planks in quicklime (as specified by [15]) due to this new technology consuming no energy, and thus possibly reducing costs while producing zero carbon emissions. However, this technique of wood drying has not been fully studied yet, so it is recommended that a detailed study similar to the one at hand using such an alternative be performed, while monitoring the costs and accurately calculating the carbon emissions.

5. Conclusions and Recommendations

Based on the results reached, the following conclusions can be drawn:

• Casuarina glauca wood proved that it is a good material for simple construction in a hybrid wood-soil system;
• Due to the high strength of the Casuarina glauca wood, the strength of the connections was the governing factor in the structural performance of the HWS structure;
• When designing HWS systems using a hardwood such as Casuarina glauca, it is important to design the connections to be of sufficient stiffness, especially when it comes to the design for loads acting within the horizontal plane, such as wind loads;
• In general, HWS structures are proven to be of sufficient structural strength in the horizontal plane according to Canadian and Egyptian building codes;
• The HWS system has been proven to be of high capacity in both horizontal directions after strengthening the connections when comparing it to the wind loads specified in the Egyptian code of loading;
• The HWS system is proven to be eco-friendly compared to its RC control structure;
• The HWS system is proven to be cost-effective compared to its RC control structure.
• It is recommended that a detailed study similar to the one at hand be performed using wood dried using quicklime, while monitoring the costs and accurately calculating the carbon emissions;
• It is recommended that the study at hand be repeated on a full-scale structure in the field to take the scaling effect into account and to accurately monitor the actual full-scale costs and carbon emissions associated with a full-scale prototype.