Structural Performance of Arched Space Trusses Using Date Palm Midribs for Light and Cost-Effective Construction in Egypt
Abstract
:1. Introduction
- (1)
- The fibers of the midribs are arranged longitudinally in fibro-vascular bundles [2,18]. Accordingly, the mechanical properties vary according to the direction of those bundles [8]. Those bundles are the solo structural unit in the cross-section, where no cross linking is found between the bundles as the midribs belong to the monocotyledons class [2]. As a result, date palm midribs can be considered as an orthotropic material. In engineering elastic models, orthotropic materials are materials where the properties vary according to three planes in the material: longitudinal, tangential and radial [19]. In date palm midribs, the lack of growth rings leads to the unification of the tangential and radial planes [8]. The orthotropic mechanical properties of date palm midribs, the Baladi species, are shown in Table 2.
- (2)
- The area and the density of the fibro-vascular bundles vary along the radial line from the highest at the peripheral cover to the lowest at the core area [2]. Accordingly, the cross-section of a date palm midrib can be classified into peripheral cover, transition area and core area.
- (3)
- At the 1.25 mm thick peripheral cover, the density reaches 1.14 gm/cm3. At the transition area and down to the core area, the density decreases to 0.885 gm/cm3 and 0.823 gm/cm3, respectively [18]. As a result, the tensile strength is the highest at the peripheral cover, at 248 N/mm2, and decreases to 78 N/mm2 and 69 N/mm2 in the transition area and the core zone, respectively [3,18]. This means that sustaining the peripheral cover of the midribs is crucial for the overall strength. Those values, while compared to the corresponding values of the European red pine wood, 78 N/mm2 and beech wood, 97 N/mm2, show promising competitiveness that encourages previous and current researches to introduce date palm midribs as source for wood substitute [2,3,18].
- (1)
- (2)
- Choosing the forms of those building elements carefully to adapt to the high flexibility of date palm midribs and to reduce the impact of the deflection on the overall behavior [20].
- (1)
- Wide-span coverage: The 3D distribution and the maximum utilization of each element offer high rigidity and stiffness under heavy distributed and concentrated loads. This qualifies the structural system to be used in structures that require high flexibility and wide spans without the necessity of intermediate columns or complicated joinery [24]. Such system can be used for light wide-span multi-purpose halls, traditional open markets, sheds and garages. Those functions are allowed to be built from natural materials, under specific design guidelines, by the Egyptian Code of the Design fundamentals and execution requirements for structures fire protection.
- (2)
- Mass-production: The stability of a trussed system under loads depends on the self-stabilizing nature of the triangle, the main element of a truss, where the fixed lengths of the sides of the triangle keep its form steady [21]. This means that the predetermined fixed lengths of the repetitive members inside a truss make it simple to depend on prefabrication, which simplifies the process of mass production [8].
- (3)
- Flexibility: The basic truss action can be sustained even with the simplification of using continuous members through the joints. Those members, usually the chords, can reduce the truss deflections slightly but will not restrain the free deformation of the truss if the continuous members are flexible enough. This flexibility is required so that when the vertical loads on the truss lead to tension on the bottom chord, for instance, the chord and the unrestrained supports can take the deformation safely [23]. This characteristic is highly required when dealing with a material of high deformations such as date palm midribs [7].
- (4)
- Joinery simplicity: By shaping the chords of the truss to be parabolic arch, the internal forces in the arched chords would be exclusively compression [23]. This compression of the bundles would be exerted on the triangulation members inserted with friction into the chords. This friction-based joinery can be assumed to be hinged joints with no moment resistance, as no adhesives are used to resist moment.
- (5)
- Cost-efficiency: using date palm midribs in their natural form without excessive processing, depending on friction joinery without customized connections, and employing simple building sequence with moderate manpower [8] contribute to decreasing the overall cost of the system relatively while compared to conventional structures made of steel and concrete or imported timber.
2. Material and Methods
2.1. Shape and Preparation of Date Palm Midribs
2.2. Design of the Test Specimens
2.3. Building Procedures of the Specimens
2.3.1. Building the Arched Chords
2.3.2. Installing Bracings and Additional Members
2.4. Test Setup and Instrumentation
3. Results and Discussion
3.1. Experimental Program Results
3.1.1. Performance of the First Specimen
3.1.2. Performance of the Second Specimen
3.1.3. Performance of the Third (Long Term) Specimen
3.1.4. Failure Analysis
3.1.5. General Behavior
3.2. Analytical Program Results
3.2.1. Development of the Finite Element Method (FEM) Model
3.2.2. Validation of the Model
3.3. Analysis of 12 m Span Tri-Arched Space Truss and Discussion
4. Conclusions
Author Contributions
Funding
Conflicts of Interest
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Annual Quantities | Palm Midribs | Palm Leaflets | Spadix Stems | Coir | Petiole | Total (Kg/palm) |
---|---|---|---|---|---|---|
Dried Kg (per 1 mature female palm) | 15 | 14.6 | 9 | 1.56 | 14 | 54.2 |
Test | Property Description | Value (N/mm2) |
---|---|---|
Tension | Longitudinal Modulus of Elasticity | 3790 |
Effective Yield Stress | 99 | |
Effective Tensile Stress | 117 | |
Compression | Longitudinal Modulus of Elasticity | 825 |
Tangential Modulus of Elasticity | 105 | |
Radial Modulus of Elasticity | ||
Effective Yield Stress | 45 | |
Effective Compressive Stress | 50 | |
Bending | Longitudinal Modulus of Elasticity | 10,287 |
Longitudinal-Radial Shear Modulus | 109 | |
Longitudinal-Tangential Shear Modulus | ||
Effective Yield Stress | 120 | |
Effective Bending Stress | 135 | |
Calculated | Radial-Tangential Shear Modulus | 39.05 |
Longitudinal-Radial Poisson’s Ratio | 0.372 | |
Longitudinal-Tangential Poisson’s Ratio | 0.467 | |
Radial-Tangential Poisson’s Ratio | 0.435 | |
Mass per Unit Volume | 0.95 m/cm3 |
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A. Darwish, E.; Mansour, Y.; Elmously, H.; Abdelrahman, A.; Moustafa, A. Structural Performance of Arched Space Trusses Using Date Palm Midribs for Light and Cost-Effective Construction in Egypt. Buildings 2020, 10, 106. https://doi.org/10.3390/buildings10060106
A. Darwish E, Mansour Y, Elmously H, Abdelrahman A, Moustafa A. Structural Performance of Arched Space Trusses Using Date Palm Midribs for Light and Cost-Effective Construction in Egypt. Buildings. 2020; 10(6):106. https://doi.org/10.3390/buildings10060106
Chicago/Turabian StyleA. Darwish, Eman, Yasser Mansour, Hamed Elmously, Amr Abdelrahman, and Ayman Moustafa. 2020. "Structural Performance of Arched Space Trusses Using Date Palm Midribs for Light and Cost-Effective Construction in Egypt" Buildings 10, no. 6: 106. https://doi.org/10.3390/buildings10060106
APA StyleA. Darwish, E., Mansour, Y., Elmously, H., Abdelrahman, A., & Moustafa, A. (2020). Structural Performance of Arched Space Trusses Using Date Palm Midribs for Light and Cost-Effective Construction in Egypt. Buildings, 10(6), 106. https://doi.org/10.3390/buildings10060106