Prefabricated Timber Roof Trusses

""La tesi si inserisce nell'ambito di ricerca della storia delle tecniche costruttive e analizza l'evoluzione tecnologica e tipologica delle coperture lignee in Italia nel periodo che va dall'inizio del XIX alla metà del XX secolo.
Dopo una parte di inquadramento delle condizioni tecnologiche, del contesto socio-economico e produttivo generale e delle teorie e pratiche costruttive delle coperture lignee italiane della fine del XVIII secolo, la ricerca ne analizza i progressivi mutamenti cercando di individuare alcune "fasi omogenee" e di rintracciare i nessi tra i processi evolutivi del contesto e quelli che interessano le coperture lignee.
Particolare attenzione è attribuita allo sviluppo delle tipologie costruttive delle capriate e alla diffusione di altri tipi di strutture lignee di copertura (cavalletti centinati, archi, portali a due o tre cerniere, ecc.), rapportati ai vari aspetti del contesto tecnico-culturale e produttivo: livello e tipo di formazione culturale e tecnica dell'ingegnere e dell'architetto; sviluppo e diffusione delle teorie della meccanica delle strutture e della resistenza dei materiali; cambiamenti nei modi di produzione e lavorazione dei materiali edilizi; variazione dei prezzi della manodopera e dei materiali; invenzione di nuovi sistemi di connessione dei legnami.""

► A kind of Elastic Composite, Reinforced Lightweight Concrete (ECRL.C) with the mentioned specifics is a type of "Resilient Composite Systems (RCS)" in which, contrary to the basic geometrical assumption of the flexure theory in Solid Mechanics, "the strain changes in the beam height during bending" is typically "Nonlinear". (The RCS could be counted as "The Methodically Reinforced Nonlinear Porous Materials", also having the high specific modulus of resilience in flexure.)

♦ Through employing this integrated structure, with significantly high strain capability and modulus of resilience in bending, we can achieve the high bearing capacities in beams with the secure fracture pattern, in less weight.

♦ Due to the system particulars and its behavior in bending, the usual calculation of the necessary equilibrium steel amount to attain the low-steel bending sections with the secure fracture pattern in the beams and its related limitations do not become propounded. Thereby, the strategic deadlock of the high possibility of the brittle fracture pattern in the bending elements made of the usual reinforced lightweight concretes, especially about the low-thickness bending elements as slabs, is unlocked.

♦ This simple, applied technology and the related components and systems can have several applications in the road and building industries. (It can also be used in making the resilient pieces and constructions "with appropriate behavior and high resistance against severe blasts and shocks.)

♦ Regarding the "strategic importance of Lightweight and Integrated Construction in the practical increase of the resistance and safety against earthquake" and considering the appropriate behavior of this "resilient", durable structure against the dynamic loads, shakes, impacts, blasts, and shocks and the possibility of making some lightweight and insulating, non-brittle, reinforced sandwich panels and pieces, this resilient system and its components can especially be useful in the "seismic areas".

♦ This system can also be employed in constructing the vibration and impact absorber bearing pieces & slabs, which can be used in the "Railroad & Subway Structures" too.

♦ Here, the "Resilient Composite Systems (RCS)" and particularly, the ECRLC as a type of the RCS have been concisely presented. [By the way, an instance of the said new structure and its components and the results of some performed experiments (as bending loading and compressive loading of the slabs made of this structure, similar to ASTM E 72 Standard) have been shown in the related pictures & figures.]
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/ ● Key Words: Strength of materials (solid mechanics), Civil (construction), Materials, Earthquake (resistance and safety), Resilient concrete (flexible concrete, bendable concrete, elastic concrete), Composite concrete, Lightweight concrete, Reinforced concrete, Fibered concrete, Lightweight and integrated construction, Rail (railroad, railway), Subway, Road, Bridge, Resilience, Energy absorption, Fracture pattern, Non-linear, Strain changes, Beam, Ductility, Toughness, Insulating (insulation), Thin, Slab, Roof, Ceiling, Wall (partition), Building, Tower, Plan of mixture, Insulating reinforced lightweight pieces, 3d, Sandwich panel, Dry mix, Plaster, Foam, Expanded polystyrene (EPS), Polypropylene, Pozzolan, Porous matrix (Pored matrix), Mesh (lattice), Cement, RCS, ECRLC
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/ ► Contents:
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* ABSTRACT
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* I. INTRODUCTION
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* II. WHAT ARE THE RESILIENT COMPOSITE SYSTEMS
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- A. General Review
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- B. Components
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. - 1) Mesh or Lattice
. - 2) Fibers or Strands
. - 3) "Matrix" With the Suitable Hollow "Pores (Voids)" and/or "Lightweight Aggregates" in its Context
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- C. More Explanations About the RCS
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- D. Why Are These Systems Called "Composite"?
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- E. The General Structural Particulars and Functional Criteria as the Necessary Specifications of the Compound Materials Generally Called "Resilient Composite Systems"
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. - 1) General Structural Criteria
. - 2) Functional Criteria (Required Specifications)
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* III. "ELASTIC COMPOSITE REINFORCED LIGHTWEIGHT CONCRETE (ECRLC)" AS A TYPE OF THE RESILIENT COMPOSITE SYSTEMS (RCS)
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- An Instance of the Lightweight Concrete That Could be Used in Making the ECRLC
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* IV. REVIEW OF SOME EXPERIMENTS, AND MORE DESCRIPTION ABOUT ECRLC
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* V. SUPPLEMENTARY ELEMENTS
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* VI. APPLICATIONS
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* VII. FINAL REVIEW
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* ACKNOWLEDGEMENTS
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* REFERENCES 
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/ ● General Review:
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• A kind of "Elastic Composite, Reinforced Lightweight Concrete" with the said specifics is a type of the "Resilient Composite Systems (R.C.S.)" in which, contrary to the basic geometrical assumption of flexure theory in the Solid Mechanics, the strain changes in the beam height during bending is typically "Non-linear".
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• Indeed, the RCS, as the Elastic Composite, Reinforced Lightweight Concrete (ECRLC), do not behave as most of the solid materials in bending.
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• In the "Resilient Composite Systems", distributed pores and/or appropriate lightweight aggregates or beads, accompanied by the reticular structure of the strengthened conjoined matrix, bring about the expedient internal shape changes during bending and continuing the elasticity in bending with the said nonlinearly pattern. This means better distribution of the stresses and strains and better utilizing the potential capacities of the employed reinforcements in bending and tension; whereas, in the usual lightweight concretes for instance, distributed hollow pores (such as the gas bulbs in the cellular concretes) or lightweight aggregates (such as Plastic, Rubber or polystyrene beads or any other kind of lightweight aggregates such as Perlite and Vermiculite) decrease the modulus of resilience in bending and could increase "the possibility of beam fracture of brittle and primary compressive type" in bending (compared to the concrete with higher density) according to the case.
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• In this way, by using the mentioned method to make the said particular composite systems, we could considerably increase the modulus of resilience and bearing capacity in bending "together with" significant decrease of the weight and also the possibility of beam fracture of primary compressive type. Through making these particular integrated functioning systems, for the first time, the said (paradoxical) properties have been concomitantly fulfilled in "one functioning unit" altogether.
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• Respect to the special pattern of the strain changes during bending in the particular Resilient Composite System termed ECRLC, this system as an integrated functioning unit with the reticular arrangement and texture has more strain capability (particularly within the elastic limit), energy absorption and load bearing capacities in bending compared to the usual reinforced concrete beams.
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• Thereby, through employing this applied structure, solving some of the main problems in lightweight concretes application, especially the deadlock of brittle and insecure being of fracture pattern in many of the usual reinforced lightweight concrete structures, is provided; reaching to the high bearing capacities in bending elements (even with low dimensions & weights) is to hand, and getting access to a simple and practical opportunity for "qualitative development of possibilities of using lightweight concretes" (especially with oven-dry densities of < 1350-1400kg/m3 and compressive strengths of <14-17mpa, and even with oven-dry densities of < 800kg/m3) is conceivable.
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• Naturally, by more studies in the field, these structures and their applications in various fields could be developed more.
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/ ► FULL TEXT (Open Access):
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- http://arxiv.org/abs/1510.03933 
( https://arxiv.org/ftp/arxiv/papers/1510/1510.03933.pdf ) ;
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. Kamyar Esmaeili: "Elastic Composite Reinforced Lightweight Concrete as a Type of Resilient Composite Systems";
The Internet Journal of Innovative Technology and Creative Engineering (IJITCE); 2012; 2(8): 1-22.
- http://ia800305.us.archive.org/34/items/IJITCE/vol2no801.pdf [Also archived at: http://www.webcitation.org/6B2pFPpBh ] ;
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- https://www.scribd.com/doc/11530978/Elastic-Composite-Reinforced-Lightweight-Concrete-ECRLC-as-a-type-of-Resilient-Composite-Systems-RCS-http-arxiv-org-abs-1510-03933 ; 
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- https://sites.google.com/site/NEWSTRUCTURE1 ;
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- https://sites.google.com/site/newstructure1/publications-page/ELASTIC%20COMPOSITE%2C%20REINFORCED%20LIGHTWEIGHT%20CONCRETE%20AS%20A%20TYPE%20OF%20RESILIENT%20COMPOSITE%20SYSTEMS.pdf ;
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- http://www.pdf-archive.com/2015/09/22/elasticcomposite-reinforcedlightweightconcreteasatypeofrcs/elasticcomposite-reinforcedlightweightconcreteasatypeofrcs.pdf ;
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- The link to the document in PDF format on this site:
file:///C:/Users/pc5/Downloads/ELASTIC_COMPOSITE_REINFORCED_LIGHTWEIGHT.pdf ;
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Ferrous metals are often seen as antagonists of timber in buildings, since their gradual spread in structural elements has led to the progressive decrease of timber structures diffusion. However metal elements were and still are used in timber structures and have significantly influenced their evolution in time. On the basis of information found in treatises, historical handbooks and – for more recent times –technical journals, of archival sources, of modern historical investigations, and of direct survey, the paper attempts a critical historical reconstruction of the technological evolution of metal elements used in timber trusses between Middle Ages and the mid-20th century, making explicit its influence on the evolution of trusses typology. The paper also deals concisely with the diffusion of metal elements in strengthening works of existing timber structures, especially with reference to the last century of the analyzed period.
In Middle Ages carpentry joints and constructional types of trusses were generally designed so as not to require metal elements because of their high cost. Between 13th and 15th century, the evolution of iron industry allowed a drop in the cost of ferrous metals. In trusses the use of wrought iron in the form of nails and brackets grew, therefore a series of changes took place, including the gradual abandonment of “closed-joint” trusses in favour of “open-joint” ones. In 18th and 19th century, iron and steel industry revolution led to an exceptional production increase: new metal elements spread allowing the creation of the steel-timber trusses and of entirely metal ones. Since the second half of 19th century, the transition from empiricism to structural mechanics and a progressive loss of building traditions led designers to strengthening decayed timber structures using metal ties or rolled beams. In early decades of 20th century, further innovations in the field of hot and cold steel working allowed the invention of new elements and connection systems for timber structures (e.g. bolts, split rings, toothed rings, spiked plates) leading to the creation of new types of timber roof structures (reticular beams and portals).

Until the mid-19th century timber trusses were empirically designed thanks to centuries-old experience. Since the early 19th century the theory of statically-determinate trusses had been elaborated for the analysis of metal trusses, but this could not be used for timber trusses, because loads were not applied in joints, a hypothesis required to ignore static indeterminacy. In the late 1850s a specific analysis method was developed for timber trusses: it considered rafters as continuous beams on rigid supports, thus it did not satisfy constitutive and strain-displacement equations. However, theoretical developments of the 1870s allowed the exact calculation of statically-indeterminate structures, thus engineers often continued to resort to empiricism, or simplified methods.