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TYPES OF CONNECTIONS FOR STRUCTURAL ELEMENTS

ROUNDWOOD USED IN BRAZIL

Leandro Dussarrat Brito1, Carlito Calil Junior2

ABSTRACT: Wood connections must be considered as key points in the safety of timber structures. The use ofstructural elements of roundwood from reforestation in Brazil has grown in recent years due to the research that had

been conducted at universities, in order to make it a sustainable material more competitive relative to other materialsused as structural function. However the joining of the structural elements of roundwood timber, are usually more

difficult to be made than the connections made in sawn planks. In some cases, the raw timber connections have to besawed by hand to facilitate and ensure that the connections will fit and work properly. The major problem of usingroundwood in construction is that people have resistance against it because the work of preparing the connections iscarried out by hand and depends upon the expertise of the construction sites carpenter, which in some cases can result

in less efficiency and poor quality connections. With the aim to promote more efficient use of the joints connecting thestructural elements of roundwood timber, the purpose of this paper is to present the main types of connections used inthese structural and construction systems.

KEYWORDS:sustainable buildings; structural systems; roundwood treated; connections between structural elements;reforestation.

1 INTRODUCTION 123

The joints, also known as connections, should beconsidered as key points in the safety of timberstructures. The use of structural elements fromreforestation roundwood in Brazil has grown in recent

years because of research conducted at universities, inorder to make it a sustainable material more competitiverelative to other materials used as structural function inconstruction, BRITO (2010) [2]. However, connections to

the structural elements of roundwood construction areusually more difficult to manufacturing than connectionswith sawn timber. In some cases part of roundwoodneeds to be cut manufacture artisanal to facilitate theconnection and guarantee the best performance amongthe structural connections. This is the major problem in

the resistance of using roundwood to build in Brazil. Theprocess of implementing the connections is made by

artisanal methods and troublesome enough, often with

only carpenters practice work. Generally the buildingwithout adequate knowledge cases problems as loweffectiveness connections. This kind of thing happensbecause as they dont know or dont have the procedures

1 Leandro Dussarrat Brito, Laboratory of Wood and Timber

Structures, Department of Structural Engineering, School ofEngineering of So Carlos, University of So Paulo. Labour

Socarlense Avenue, 400, Downtown, CEP: 13566-590, POBox 359, So Carlos, SP, Brazil. Email: dussarrat@sc.usp.br

2 Carlito Calil Junior, Laboratory of Wood and TimberStructures, Department of Structural Engineering, School of

Engineering of So Carlos, University of So Paulo. LabourSocarlense Avenue, 400, Downtown, CEP: 13566-590, PO

Box 359, So Carlos, SP, Brazil. Email: calil@sc.usp.br

to follow, they execute based on their practice, instead oftechnical methods and as a consequence, they do itimproperly. In order to promote more efficient use of theconnections between the structural elements ofroundwood, specially those from reforested wood, thegoal of this article is to present the main usual types of

connections used in structural systems and constructioncommonly used in Brazil for the elaboration of structural

design of projects with this material, BRITO (2010) [2].

2 TYPES OF JOINTSFOR ROUNDWOOD

In this research, it was categorized the main varieties ofconnections with roundwood for structural elements,each corresponding to its function, such asnotches in thewood, wooden dowel, threaded rods with washers and

nuts, dowel nut, steel plate external fixed with screws,steel plate internal fixed with screws, galvanized

perforated steel plate and nailed,steel straps woven into,

steel rings with threaded rods fixed with washers andnuts, steel connectors for structures mixed roundwoodand concrete, details on the interface of the timberstructure with masonry, Connections log home walls,connections in parts compressed, connections to bases ofcolumns and other, CALIL & BRITO (2010) [3].The connections in the construction of structures with

plump pieces of wood are more difficult to be made thanthe connections with lumber. In some cases it isnecessary to cut the roundwood to facilitate theconnection of the joints and to ensure the best behaviorof the structural elements in the connections.Consequently, it is important to emphasize the major

problem of building using pieces of roundwood, wherethe process of implementing the connections are madeby artisanal methods and troublesome enough, which insome cases have low efficiency.

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Thus, the use of roundwood timber treated as aconstructive solution without project prepared by aprofessional with specific knowledge and without usingskilled labor and raw materials selected, may result inenhancement of the final cost of construction, and non-warranty safety of the structure.

Then, in order, to promote more efficient use of the linksbetween structural elements with pieces of wood, the

objective of this paper is to present the most commontypes of connections to these structures, used today inBrazil.

2.1 NOTCHES IN THE WOOD

The links are slots types of connections frequentlyadopted for beam-column system in Brazil, and is a

fitting concave at the top of the column and sometimeswith the addition of fixed vertical bar of galvanized steelor wooden dowel to prevent separation of parts, figure 1to figure 3.

According to NBR 7190:1997 [1], the connections ofpieces of wood can be made by means of metal pins,wooden pegs and or connectors.

2.2 THREADED RODS, WASHERS AND NUTS

Connections using threaded steel rods attached with

washers and nuts on the extremities have been widelyused in structural connections between elements inroundwood in Brazil, figure 4.

2.3 DOWEL NUT

This type of connection is a system with threaded steelbar, metal pin. In a transverse hole passing through the

axis of the beam near the column connects the metal pinthat has a female threaded hole compatible with thethread diameter of the steel bar to fix it, figure 5 andfigure 6.

Figure 1:Connection with the notch at the top of thepiece: Preparation of the notch with drill (Handicraft

system). CALIL & BRITO (2010) [3].

Figure4:Connection with threaded steel rodsattached with washers and nuts.

CALIL & BRITO (2010) [3].

Figure5:Connection dowel nut.CALIL & BRITO (2010) [3].

Figure 3:Connection with the notch at the top of thepiece completed. CALIL & BRITO (2010) [3].

Figure 2:Connection with the notch at the top of the

piece: Making the notch with a chisel.CALIL & BRITO (2010) [3].

Figure 6:Connection dowel nut: System ofconnection beam-column.CALIL & BRITO (2010) [3].

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2.4 CONNECTIONS WITH EXTERNAL METAL

PLATES BOLTED

The connections roundwood structural elements ofwood, metal plates carried out with external may also bereferred to as metal splints. The connection is performed

via a threaded steel rods that traverse across the plates

and pieces of roundwood. With the tightening of nuts onthe ends of the steel bars, crash the system bycompressing the wood pieces. Usually this type ofconnection is common to modify the slicing wood plumptwo external faces so as to become flat and continuousjoining to adequately close to the faces of the plate. Thefigure 8 illustrates a rigid connection apparently because

they have four screws in each part with externalconnecting sheet metal parts, forming the ridge of the

roof of a gantry system shed.

2.5 CONNECTIONS WITH INTERNAL METAL

PLATES BOLTED

These types of connections consist of metal plates withsystems which are imputed into the cleft longitudinal

axis of the pieces of roundwood, usually at the ends ofthese parts and the thickness of metal sheet. Theconnection also runs through threaded steel bars,crossing across the plates and pieces of roundwood.With tightening of the nuts on the ends of the steel bars,the lock system compressing the inner faces of the woodwith the faces of metal sheet. The figure 9 and figure 10illustrates details of the connection runs the project

coverage LaMEM tower, making a call from the cornerof a cover system and the metal tube that supports thissystem is connected to the column and attached bythreaded steel bars, washers and nuts.

2.6 CONNECTIONS WITH FOILS EXTERNAL

METALLIC GALVANIZED PERFORATED

AND NAILED

The connectors of galvanized perforated sheet metal andnailed (figure 11 e 12) are efficient components forconstruction of rural sheds, using roundwood withdifferent diameters, designed to make connectionsbetween the parts in a simple manner, and provide short-run time in assembling the structure. These connectorsare typically manufactured by specialized companies.

The GANG-NAIL Brazil is an online provider of

connectors, and unique pieces made of special steel hotdip galvanized with 1.95 mm thick, welded or seamless,ensuring technical links between the pieces, figure 12.

Figure 10:Connections with internal metalplates bolted: Systems Beam-Column

connection. CALIL & MOLINA (2010)[5].

Figure7:Connections withexternalmetal platesbolted: System of connection Beam-Column.

Cited in BRITO (2010)[2].

Figure11:Connections Beam-column withfoils external metallic galvanized perforated and

mailed.Cited in BRITO (2010)[2].

Figure8:Connections withexternalmetal platesbolted: System of connection Beam-Beam.

Cited in BRITO (2010)[2].

Figure 9:Models of the connections with internalmetal plates bolted. CALIL & MOLINA (2010)[5].

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2.7 CONNECTIONS WITH METAL RINGS,

STEEL BARS, WASHERS AND NUTS

A type of connection to composite parts with higher loadcapacity is that which employs the metal rings (figure13) that are inserted into grooves previously executedparts. The transmission of efforts between parts tends tocause the shear hard wood internal to the ring andcompression between the wood and the ring, CALIL et

al (2003) [6].The metal rings with steel bars, washers and locking nutsto allow unification of composite beams, suitable forlarge spans and high loads.

Given this context, a important research in this area wasperformed at the Laboratory of Wood and WoodStructures (LaMEM), using rings cut from water pipes,galvanized, with diameters ranging from 2 "to 8". Closed

rings were studied, parties and split, figure 13.

HELLMEISTER (1978) cited in CALIL & BRITO

(2010) [3] presented a system in which the BridgePensil Tiete, in So Paulo, Brasil tray longitudinalbeams are designed with two circular sections, connectedwith metal rings and steel bars threaded and secured withwashers and nuts on the ends, figure 14.

The figure 15 illustrates the connection, with metalrings, steel bars, washers and nuts, for a connectionfor the composition of double circular beam,

HELLMEISTER (1978) cited in CALIL & BRITO(2010)[3].

.

HELLMEISTER (1978) cited in CALIL & BRITO(2010) [3] presented a system for beam compositebridge structures, the beams using two unified by doublecirculars cross section metal rings, as details ofconnections in Figure 16.

Figure 15:Connections with metal rings, steelbars, washers and nuts.

HELLMEISTER (1978) cited in CALIL & BRITO(2010)[3].

Figure 16:System two double circular beam.HELLMEISTER (1978) cited in CALIL &

BRITO (2010)[3].

Figure12:Connections GANG-NAILBRAZILwith foils external metallic galvanized

perforated and mailed.

(a) (b) (c)Figure 13:(a) Ring Party; (b) Ring double Party; (c)

Closed ring. MATTHIESEN (1987).

Figure 14:Bridge Pensil Tiete, in So Paulo,Brasil: Connections with metal rings, steel

bars, washers and nuts.HELLMEISTER (1978)cited in CALIL & BRITO (2010)[3].

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According LOGSDON (1982) mentioned in CALIL &BRITO (2010) [3], can also be the union of severalhorizontal cylindrical logs of wood by using rings andmetal bars bolted to form plate elements. The figure 17shows a scheme with links to metal rings and bars inbridge structures in single card.

According MATHIESSEN (1987) mentioned in CALIL& BRITO (2010) [3] presents a mixed system of aleveling concrete and asphalt unified with the union ofseveral horizontal logs of roundwood using metal rings

and flat steel bars screwed, which behaves plate system,reinforced with ribs of double circular sections, alsoconnected with metal rings and bolted steel bars, figure18 and figure 19.

2.8 STEEL CONNECTORS FOR STRUCTURES

MIXED ROUNDWOOD AND CONCRETE

In structures mixed roundwood and concrete, to ensure

adequate adhesion of the concrete structural element ofwood, facilities are required connectors bolted steel with

epoxy adhesive into holes in roundwood.

The figure 20 and figure 21 presents details of projectboard connectors for steel bridges of roundwood incomposite structures, reinforced concrete. The mainfeature of this system is the uniform distribution of theload applied on the whole CALIL et al (2006) cited inCALIL & BRITO (2010) [3].

2.9 CONNECTIONS IN PARTS COMPRESSED

The compressed parts may be simple or compound. They

may be present in parts of trusses, bracing systems, aswell as isolated columns or porches. The figure 22 showsexamples of amendments in parts compressed axially,BRITO (2010)[2].

Figure 20:Steel connectors for structures mixedroundwood and concrete. CALIL et al (2006)[4].

(a) (b) (c) (d) (e) (f)

(g) (h) (i) (j)Figure 22:Connections in elements compressed.

CALIL & BRITO (2010)[3].

Figure 17: Connections with metal bars and rings(arranged in horizontal position), combining thestructural elements of cylindrical logs of wood,forming the deck of the bridge structure in singlecard. LOGSDON (1982) cited in CALIL & BRITO(2010)[3].

Figure 18: Connections with metal bars and rings(arranged in horizontal and vertical positions),combining the structural elements of cylindrical logsof wood, forming the deck of the bridge structure inribbed plate with mixed system of a levelingconcrete and asphalt . MATHIESSEN (1987) cited inCALIL & Brito (2010) [3].

Figure 19:Cross Section: details of the connectionswith metal bars and rings (arranged in horizontaland vertical positions), combining the structuralelements of cylindrical logs of wood, forming thedeck of the bridge structure in ribbed plate withmixed system of a leveling concrete and asphalt .MATHIESSEN (1987) cited in Brito (2010)[3].

Figure 21:Concreting Bridge timber mixed concrete,Bridge II Exit Campus II, USP, So Carlos, Brazil.

CALIL et al (2006) cited in BRITO (2010)[3].

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Etam figure 22 illustrates the types of connectionscommon in Brazil, for splicing elements in tablets, withplump pieces of wood, cited in, Brito (2010) [2]:(a) amendment of the top with four sides splintsperforated sheet metal and screwed bars with threadedbushings, washers and nuts;

(b) amendment of the top with four sides splintsperforated sheet metal and screwed with self-tapping

screws;(c) amendment of the top, with four side splintsperforated sheet metal and fastened;(d) amended by cutting tilted with galvanized steelbrackets, bolts, washers and nuts;(e) amendment by cutting vertical bars and bolted withthreaded bushings, washers and nuts;(f) amended by cutting angled bars and bolted with

threaded bushings, washers and nuts;(g) section consists of three cylindrical logs,connections with steel threaded bushings, washers and

nuts;(h) section consists of four cylindrical logs, brought withspacers of roundwood;(i) section consists of four cylindrical trunks, with

special connections for attaching metal stretchers risers;(j) section consists of four cylindrical trunks, withspacers interposed pieces of lumber and metalconnections with special stretchers for fixing bolts.

2.10CONNECTIONS BUILDING SYSTEMS FOR

LOGHOME

Another type of connection using rods, washers and nuts,

are industrialized systems for buildings of wall typeloghome systems with roundwood turned (figure 23),overlapping fitting male and female. But they are speciallong bars, threaded ends, figure 24.

2.11CONNECTIONS TO BASES OF COLUMNS

One of the most economical ways of building withroundwood is the use of wooden columns embeddeddirectly into the foundation block, and this is a common

practice in several countries around the world. This type

of foundation is a system in which the column roundwood is installed in a hole in the ground borer type, withcircular section of diameter D greater than the diameterof the pole, and in the region of the blank surroundingthe base of the post is filled with concrete, or onlyoccasionally with gravel, as shown in figure 25. As aresult, costs for foundations of buildings with these

systems are mostly reduced PARTEL (1999) cited inCALIL & BRITO (2010) [3]. However, to enable the use

of this type of foundation, the soil should have adequatebearing capacity, which should be investigated "in situ"by engineer foundations. Also, for this type offoundation, one should be a guarantee adequate

preservative treatment of timber, according to the Classof Use 5. This type of system has been widely used in

constructions in Brazil.

Another alternative very efficient is to fix the base of thecolumn in the concrete block foundation through a metal

connector (base plate), avoiding contact of wood withsoil and moisture. One can, however, to design varioustypes of metal connectors (base plate), and the mostsuitable one that does not induce cracking of the partroundwood (Figure 26).

Figure 25:Columns embedded directly into thefoundation block. CALIL & BRITO (2010)[3].

Figure 23:System link to the type of building with logsturned loghome Cited in BRITO (2010) [2].

Figure 24:Special long bars, threaded ends, for wall

type loghome systems with roundwood turned.

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The figure 27 presented two distinct articulated baseplate, with masts for roundwood timber used in stiffstructures. The figure 28 is a picture of the base plateof

the pole of Eucalyptus Citriodora wood, the firstLatin American cable-stayed bridge constructed withprestressed curved board. This walkway, whose board issupported by distributed and you are set on top of thissingle column, which is hinged at the base, was the resultof the doctoral thesis of PLETS (2003) cited in CALIL

& BRITO (2010) [3], developed in LaMEM, School ofEngineering of So Carlos, University of So Paulo.

3 CONCLUSIONS

The LaMEM is one of the most important researchlaboratories of wooden structures in Brazil in recentyears has held several lines of theoretical andexperimental research of structural elements andconnections between structural elements withroundwood, especially from reforestation, as species of

eucalyptus and pine. In May 2010, Engineer CivilLeandro Dussarrat Brito, presented the dissertation of

master in structures engineering "Recommendations forthe Design and Construction of Structures withRoundwood from Reforestation", directed by teacher Dr.Carlito Calil Junior in the Department of StructuralEngineering School of Engineering of So CarlosUniversity of So Paulo. The chapter 4 of thedissertation deals with the connections betweenstructural elements in roundwoods structures. Therefore,

the purpose of this article is to present briefly, a

literature reference review of some major types ofconnections, between structural elements common toroundwood used in Brazil as suggestions in theapplication of models in design and construction withthis material. The aim of this study is to guide studentsand professionals in civil engineering and architecture,

presenting some of the most appropriate models ofconnections in order to provide enough information tohelp them to choose the most convenient structuralconstruction systems that use reforestations roundwood.For the types of connections shown, the natural taper ofthe parts affects the detailing of the buildings with plump

pieces of wood. A common practice is to modify the

slicing wood plump one hand, to provide a continuousplanar face, as well as making and holes or slots. Theflattened face allows for greater safety at the junction of

metallic connection with the structural elements. It mustbe remembered that the penetration of the preservative isgenerally limited to the sapwood, yet the planning mayresult in less protection than in any other part of the postis not flattened. All cutting and machining must bepreferably performed prior to preservative treatment.

ACKNOWLEDGEMENT

The authors acknowledge the CNPq for the scholarshipdoctorete, the researchers LaMEM/SET/EESC/USP, andthe organizing committee and scientific WCTE 2012.

REFERENCES

[1] ABNT NBR 7190:1997. Design of timberstructures. Rio de Janeiro, 1997.

[2] BRITO, Leandro Dussarrat (2010). Recommen-dations for the Design and Construction ofStructures with Roundwood from Reforestation. So

Carlos. 339 pg. Masters, SET/EESC/USP.

Download:

[3] CALIL JR., Carlito; BRITO, Leandro Dussarrat(2010). Manual of Design and Construction of

(a) (b)Figure 27:Models base articulated plates, galvanized

steel. PLETS (2003) cited in BRITO (2010)[2].

Figure 26:Column base plate fixed in theconcrete pad foundation through a metallicconnector (base plate). AM (2009) cited in

BRITO (2010)[2].

Figure 28:Base articulated plates for base pole.PLETZ (2003) cited in BRITO (2010)[2].

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Structures with Roundwood from Reforestation.SET/EESC/USP. So Carlos. 332 pg. Download: ISBN: 978-85-8023-000-0.

[4] CALIL JR., Carlito; et al (2006). Manual for designand construction of timber bridges. So Carlos:Suprema, 2006. 252p. ISBN: 85-98156-19-1.

[5] CALIL JR. Carlito; MOLINA, Julio Cesar (2010).Coberturas em estruturas de madeira: Editora PINI.So Paulo. 207 pg. ISBN: 978-85-7266-224-6.

[6] CALIL JR. Carlito; ROCCO LAHR, F.A.; DIAS,A.A. (2003). Dimensionamento de ElementosEstruturais de Madeira. Barueri-S.P.. EditoraManole. ISBN: 85-204-1515-6.

[7] HELLMEISTER, J. (1978). So Carlos, 85p. Pontesde eucalipto Citriodora. Tese (Livre docncia).Escola de Engenharia de So Carlos, Universidade

de So Paulo, So Carlos, 1978.

[8] LOGSDON, N. B. (1982) Contribuio ao Estudodas Pontes de Madeira. Dissertao de Mestrado.Escola de Engenharia de So Carlos daUniversidade de So Paulo.

[9] MATTHIESEN, J. A. (1987). Contribuio aoEstudo das Pontes de Eucalipto Citriodora. So

Carlos, 220p. Tese. Escola de Engenharia de SoCarlos, Universidade de So Paulo.

[10]PLETZ, Everaldo (2003). Passarela Estaiada com

Tabuleiro de Madeira Laminada Protendida emMdulos Curvos. Tese (Doutorado) - Escola de

Engenharia de So Carlos, Universidade de SoPaulo, So Carlos, 2003.