Structuri Cadre Lemn Comparatie

8/12/2019 Structuri Cadre Lemn Comparatie

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82 Revista Romn de Materiale / Romanian Journal of Materials 2012, 42 (1), 82 - 93

ANALIZA COMPARATIV A PERFORMAN ELOR A DOU SISTEMESTRUCTURALE REALIZATE DIN LEMN

COMPARATIVE ANALYSIS OF TWO WOOD STRUCTURAL SYSTEM

PERFORMANCES

DORINA ISOPESCU

, IULIAN ASTANEI Universitatea Tehnica "Gheorghe Asachi" Ia i, Bd. Dimitrie Mangeron nr. 43, 700050 Ia i, Romnia

Articolul prezint o analiz comparativ privindevaluarea a dou sisteme constructive pentru structuri derezisten realizate cu elemente din lemn. Analiza esterealizat pe un modul structural utilizat frecvent laexecutarea construc iilor, parter cu pod, cu func iunea delocuin temporar .

Analiza structural cu elemente finite eviden iaz st rile de tensiuni, deforma iile i deplas rile pentru

elementele portante caracteristice, subliniind avantajele idezavantajele utiliz rii pentru fiecare sistem.n ultima parte sunt formulate concluziile pe baza

rezultatelor ob inute, perspective i recomand ri pentrudezvolt ri ulterioare.

The article presents a comparative analysis on theevaluation of two building systems for strength structuresmade with timber. The analysis is performed on a structuralmodule commonly used for execution of construction,ground floor and attic, with temporary housing function.

Structural finite element analysis evaluates tensions,deformations and displacements for the characteristicstructural elements, highlighting the advantages and

disadvantages of using each building system.In the last part are drawn conclusions based onresults, outlooks and recommendations for furtherdevelopments.

Keywords: wood, conventional structure, framing structure

1.Introducere

Lemnul i piatra au fost materialele deconstrucii folosite de om nc din cele mai vechitimpuri. Apariia oelului, a cimentului i mai trziu amaterialelor compozite, au determinat o diminuarea utiliz rii n construcii a acestor dou materiale.Lemnul ns , cu toate fluctuaiile privind utilizarealui n construcii, pozitive sau negative, a r masunul din cele mai atractive materiale de construcii.Spre deosebire de concuren ii s i, cum ar fi piatra,c r mida, oelul i materialele compozite, care sunttoate derivate din resurse epuizabile, lemnulprezint o particularitate care este unic printrematerialele de construc ii: este un material biologiccare poate fi obinut prin cultur , oriunde i oricnd[1 - 4].

Pentru orice construcie, structura derezisten reprezint un set de elemente asamblateastfel nct s asigure stabilitatea i durabilitateaacesteia. Proiectarea structurii de rezisten a uneicldiri este un proces complex i soluia aleas trebuie s ndeplineasc un set de cerin e de baz i anume:

inginere ti - siguran satisf c toare n ceeace prive te rezistena i stabilitatea;

arhitecturale - structura trebuie s asigurefunciuni i s prezinte calit i estetice;

privind protecia mediului - folosireamaterialelor locale i mai puin a celorenergofage, consumuri i pierderi energeticeminime.

1. Introduction

Wood and stone have been the constructionmaterials used by man since ancient times. Theemergence of steel, cement and later thecomposite materials have led to a decrease inconstruction use of these two materials. Wood,however, remains one of the most attractiveconstruction materials, despite all the fluctuationson its use in construction, positive or negative.Unlike its competitors, such as stone, brick, steeland composite materials, which are all derived fromexhaustible resources, wood has a feature that isunique among construction materials: it is abiological material that can be obtained as a crop,anywhere and anytime, [1 - 4].

For any building, the strength structurerepresents a set of elements assembled to ensureits stability and sustainability. The design of abuilding strength structure is a complex processand the chosen solution must fulfill a set of basicrequirements, namely:

engineering satisfying safety in terms ofstrength and stability;

architecture the structure must ensure thefunctionality and provide aesthetic qualities;

environmental protection use of localmaterials and a less usage of energy-intensive consumption and minimum energyloss.The importance of knowing the strength

properties of the material as well as the configu-

Autor corespondent/Corresponding author ,Tel. +4 0722 374 034 , e-mail:[email protected]


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D. Isopescu, I. Astanei / Analiza comparativ a performan elor a dou sisteme structurale realizate din lemn 83

Cunoa terea propriet ilor de rezisten alematerialului, precum i ipotezele i modul deaplicare a nc rc rilor sunt eseniale pentruproiectare. Lemnul, fiind un material biologic, arestructur cu caracteristici fizico-mecanice variabile.Variabilitatea propriet ilor mecanice ale lemnuluica material poate fi considerat un dezavantaj. Aceast variabilitate poate fi ns un avantaj prinfaptul c utilizatorul va gsi ntotdeauna un produsadecvat unui anumit scop.

Produsele din lemn prezint propriet imecanice dependente de direc ia fibrelor, deexistena defectelor naturale din perioada biologic de formare, de ac iunea factorilor din mediul nconjur tor (umiditate i temperatur ), precum i osensibilitate la aciunea factorilor biologici (insecte,ciuperci etc.).

Fiecare structur ia na tere din speran ele ivisele viitorilor ocupani aduse la realitate delimit rile bugetului i cerinele antierului. Astzi,construirea structurilor din lemn la cele mai naltestandarde necesit o mai bun nelegere a teoriei i mult practic combinat cu puin creativitate iflexibilitate. Produsele noi de construcii din lemn idin compozite pe baz de lemn, precum imetodele noi de construire au determinat nlocuirea sistemelor structurale tradiionale cusisteme structurale din cadre u oare, schimbnd,astfel, perspectiva asupra caselor din lemn.

Structurile de rezisten din cadre din lemnalc tuite din stlpi i grinzi, (figura 1), sunt realizateprin tehnologii tradiionale, n final rezultnd uncadru rigid spaial care asigur structura portant acldirilor. Cu un num r relativ redus de elementestructurale din lemn, dar care prezint n sec iunetransversal dimensiuni mari, aceast tehnologiede execu ie poate crea structuri portante puternice,care pot fi completate pentru nchideri icompartiment ri, fie prin umplerea cu diversemateriale a golurilor create de cadrele din lemn,sau prin nvelirea complet a cadrelor cu ovarietate de alte materiale sub form de panouri.

Structura de rezisten din cadre uoare dinlemn, cunoscut n literatura de specialitate castructura framing, (figura 2), are mai multe ncomun cu proiectarea i realizarea mobilierului dinlemn dect cu procedurile de construc iiconvenionale. Structura framing este o soluietehnic de structur care presupune realizareaunui sistem portant spa ial realizat din cadretransversale sub forma unor grinzi Vierendeelformate din stlpi/montani, grinzi i cpriori, decare se ata eaz celelalte elemente de completarea sistemului portant. n esen , structurile framingcreeaz un schelet pentru cldire care secompleteaz cu materiale termoizolante ifonoabsorbante, precum i cu plci pentrurealizarea nvelitorii i a compartiment rilor

interioare. Alegerea lemnului n locul altor materialeeste adesea bazat pe form i aspect, dar eco-

ration of applied loads are determinant for design.Wood is a biological material which has variablephysical and mechanical characteristics. Variabilityin the mechanical properties of wood as a materialcan be considered a disadvantage. This variabilitymay however be an advantage in that the user willalways find a suitable product for a particularpurpose.

The wood products have mechanicalproperties which are dependent on the graindirection, the existence of natural defects from thegrowth period, the action of the environmentalfactors (humidity and temperature) and have, also,a sensitivity to the action of biological factors(insects, fungi, etc.)

Each frame arises from the hopes anddreams of the future occupants brought down toearth by budget limitations and site requirements.Today to build wood structures to the higheststandards requires a broad understanding oftheory and good practice and all combined withsome creativity and flexibility. New constructionwood and wood-based composites products, aswell as the new construction techniques havedetermined the replacement of the conventionalstructural systems with light framing systems,changing in such way the perspective on thewooden houses.

Conventional wood frame strengthstructures made of pillars (posts) and beams,(Figure 1), are built using ancient methods, and, inthe end, the result is a rigid spatial frame whichprovides the strength structure of the building. Witha relatively small number of heavy-duty woodelements, but which have large cross-sections; thistechnology can create strong load-bearingstructures, which can then be completed forclosures and partitions by either filling the gapsbetween the wooden structural members, orcompletely wrapping the frames with a variety ofother materials in the form of blocks or panels.

Wood light framing strength structure,known in the technical literature as framingstructure, (Figure 2), has more in common withdesigning and making wooden furniture than it haswith conventional building procedures. Framingstructure is a building technique which involves aspatial strength structure made of bearing cross-frameworks as Vierendeel trusses made of studs, joists, and rafters, and between these frameworksare attaching the bracings elements onperpendicular direction. Basically, framingstructures creates a skeleton for the buildingwhich is completed with thermo-insulating andsound absorption materials, as well as, with coverpanels to make the roof and the walls.

The selection of wood over other materialsis often made on the basis of aesthetics, but

economy, durability, and ease of maintenance alsoplay important roles in determining the choice.Designer must carefully specify wood materials for


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84 D. Isopescu, I. Astanei / Comparative analysis of two wood structural system performances

Fig. 1 - Structur pe cadre tradi ionale din lemn realizat dinstlpi, grinzi i cpriori/Conventional wood framestrength structures made of pillars, beams and rafters

Fig. 2 Structur pe cadre u oare realizat din montani, rigle i cpriori/Wood light framing strength structure madeof studs, joists and rafters

nomia de energie nglobat n material,durabilitatea i uurina ntreinerii joac deasemenea un rol important n evaluare i decizie.Proiectantul trebuie s aleag cu grij produseledin lemn destinate construirii, iar aceasta nseamn a se asigura c lemnul specificat estedisponibil, c produsele respect cerinele deconformitate n scopul satisfacerii exigenelorutilizatorilor, i c structura n asamblul ei asigur realizarea i meninerea, pe ntreaga durat deexisten a construc iilor, a cerinelor esen iale.

n continuare se va prezenta o analiz privind capacitatea portant pentru elementeleprincipale ale celor dou tipuri de structuri derezisten ntlnite frecvent la construciile dinlemn, pentru a evidenia avantajele idezavantajele utiliz rii acestora.Studiul se va realiza pentru o structur parter i pod, cu destinaia de cas de vacan .

2. Structura de rezisten pe cadre tradi ionaledin lemn

n dispunerea cadrelor tradiionale se vaurm ri modularea deschiderilor pentru a crea ooarecare simetrie n plan i elevaie. Structura are, n direcie longitudinal , patru deschideri culungimea L = 4,20m fiecare, iar n direcietransversal , trei deschideri cu urm toarelelungimi: L1 = 2,10m; L2 = 3,00m i L3 = 2,10m. n varianta de structur pe cadre tradi ionalese vor amplasa stlpi din lemn masiv cu sec iunep trat la interseciile axelor, pe care se vorrezema celelalte elemente structurale (figura 3).Pentru construc ia cadrelor este necesar un volumde 14,5 m3 de elemente din lemn.

Din predimensionare, stlpii au rezultat cusec iunea (b x h) de (250mm x 250mm), grinzileprincipale i panele au sec iunea de (200mm x300mm), iar grinzile secundare i cpriorii ausec iunea de (100mm x 150 mm).

Materialul a fost definit ca fiind ortotrop(propriet i diferite dup fiecare ax /direcieprincipal ). Avnd n vedere c pentru lemn,

the construction and this means to insure that thespecified timber is available, that the materialrespects the quality compliance requirements tomeet user requirements and that the wholestructure can assure the achievement and themaintenance, throughout the construction life, ofthe essential requirements.

In the next chapters there shall bepresented an analysis on the bearing capacity forthe main structural elements of the two types ofstrength structures commonly encountered, tohighlight the advantage and disadvantage of theirusage.

The study will be made for a ground floorand attic structure, serving as holiday home.

2. Conventional wood frame strengthstructures

In the conventional wood frames disposal,the spans should be modulated to create certainsymmetry in plan and elevation. The structure has,in the longitudinal direction, four spans with thelength L = 4.20m each, and in the transversedirection, three openings with the followinglengths: L1 = 2.10m; L2 = 3.00m and L3 = 2.10m.

In the conventional wood frame structurecase, at the axes intersections, will be placedwooden pillars with square section, on which willlean on the other structural elements, Figure 3. It isnecessary a volume of 14.50m 3 of wood elementsto build the strength structure.

From the pre-design phase, the pillarscross-section, (b x h), will be (250mm x 250mm),the main beams and the purlins have (200mm x300)mm cross-section, and the secondary beamsand rafters have (100mm x 150)mm cross-section.

The material was defined as orthotropic(different properties on each axis/main direction).Due to the wood similar properties in the tangentialand radial directions, there will be defined, relatedto grain direction, only two main directions:

longitudinal direction, with=0 transverse direction, with=90


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raportat la direcia tangen ial i la cea radial propriet ile sunt asemn toare, se vor defini doar2 direcii principale:

direcia longitudinal , cu =0 direcia transversal , cu =90

Fig. 3 - Elementele de rezisten ale structurii tradiionaleConventional wood frame strength structure'selements.

Pentru ambele structuri se va folosi clasa derezisten a lemnului C24, cu caracteristicileevaluate conform standardului de proiectare SREN 1995-1-1:2004/A1:2008. mbin rile ntreelementele structurale se realizeaz prin chertarefolosind i tije metalice (sau din lemn) pentrupreluarea eforturilor de forfecare din nod sau prinutilizarea sistemelor metalice de fixare la poziie i

rigidizare prin plcue multi-cui. Varianta de mbinare prin rezemare i fixare cu agrafe sauscoabe este mai pu in uzitat , proiectanii apelndla ea doar n cazuri rare (de exemplu pentrucrearea unei simple rezem ri sau articulaii n nod).

Apariia unor eforturi reduse n elementelecare se mbin impune ca nodurile, n general, s fie considerate n proiectare ca fiind rigide. n acestsens pentru realizarea mbin rilor rigide, lastructurile din lemn se folosesc piese i sistememetalice care mpiedic depls rile i/sau rotirile.

Datorit caracterului higroscopic al lemnului,continuitatea elementelor n nodurile structurii nu

se poate considera ideal ; umfl rile i contraciile(longitudinale i transversale), care apar datorit varaiei umidit ii din mediul nconjur tor vor slbi n timp orice tip de mbinare utilizat, permindapariia unor uoare rosturi n zona de nod. Pentruvalori reduse ale eforturilor n cmp, mbin rileclasice ale elementelor din lemn sunt proiectatepentru a fi rigide. n realitate ele nu pot ficonsiderate astfel, a a c pentru a simula ct maibine comportarea real , rigiditatea capetelor debar s-a redus la jum tate.

Structura se consider ncastrat la nivelulcotei 0.00, datorit stlpilor ancorai n fundaiile

pahar prefabricate (sistemul de funda ii izolateprefabricate fiind cel mai corespunz tor sistem defundare pentru o astfel de structur ).

For both structures will be used C24strength class timber with the characteristicsevaluated according to SR EN 1995-1-1:2004/A1:2008 standard. Joints betweenstructural elements are achieved by wood carvingand using metal rods (or wooden rods) for takingthe shear efforts from the node or by using metalfixing systems for fastening into place andreinforcing by using pre-punched metal plates orhangers. Overlap jointing and fastening usingclasps or staples is a less commonly used method,designers turning to it only in rare cases (as forcreating a simple support or a hinge joint to thenode).

The occurrence of low values of the effortsin the field, generally requires that the nodes areregarded as rigid in design. In order to achievethese stiff joints, metallic parts and systems areused for the wooden structures to preventdisplacements and/or rotations.

Due to the hygroscopicity of wood, theelements continuity in the structure nodes can notbe considered ideal, swelling and shrinkage (onthe longitudinal and transverse direction), whichcan occur due to moisture variation in theenvironment, in time will weak any type of jointsused, allowing the emergence of light gaps in thenode area. For low values of the efforts in the field,the classical elements of wood joints are designedto be rigid. In reality they can not be regarded thisway, so that, for a better simulation of the realbehavior, the end of the bars rigidity is halved.

The structure is considered embedded atthe level 0.00, due to the pillars anchored into theprefabricated slab foundations (the isolatedprecast foundation system being the mostappropriate foundation system for such astructure).

For this construction system, a significantrotation (to consider a node as a hinge) would behindered by the other elements of the node and,therefore, in the modeling process, even at thelevel of the embedded base, the rigidities at theends of the elements (at the entry in the node) willbe halved.

To take into account the eccentricitieseffect, in the static calculation will be taken intoaccount the eccentricities of positioning theunderpinning element relative to the bearingsupport: rafters on purlins, main beam on thecolumns head, eccentricities of positioning on themain beam of the secondary beam, with theremark that the back side of the secondary beammust be in the same plane with the main beamback side.

As a result of the vibration analysis, itappears that the structure is a flexible one, featurehighlighted by the fundamental period of vibration

of 0.342s, value close to that of a concrete framewith the same level of height.


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La acest sistem constructiv, o rotiresemnificativ (pentru a considera nodul articulat)este mpiedicat de celelate elemente din nod i nconsecin , n procesul de modelare, chiar i lanivelul ncastr rii bazei, se vor reduce rigidit ileelementelor la extremit i (la intrarea n nod) la jum tate din valoarea efectiv .

Pentru a lua n considerare efectulexcentricit ilor, n calculul static se vor lua nconsiderare i excentricit ile de poziionare aelementelor portante n raport cu cele de reazem:cpriorii pe pane, grinda principal pe capulstlpului, precum i excentricit ile de poziionare agrinzilor secundare pe cele principale, cuobservaia c extradosul grinzii secundare trebuies fie n acela i plan cu extradosul grinziiprincipale.

n urma analizei modurilor proprii de vibraii,se observ c structura este una flexibil ,caracteristic evidentia de valoarea perioadeifundamentale de vibraie de 0,342s, valoareapropiat de cea a unui cadru din beton cu acela iregim de n lime.

3. Structura de rezisten pe cadre u oare dinlemn de tip framing

Dup cum este sugerat i n denumire,cadrele uoare sunt structuri de rezisten ,alc tuite din panouri portante cu o greutatesuficient de redus nct doi oameni s le poat manevra cu uurin n timpul execuiei imontajului.

Structura mai este denumit i structur pecadre dese, deoarece stlpii pozi ionai la distanede c iva metri la cadrele din lemn tradiionaledevin montani poziionai la distana de 45 cm, darcu acela i rol principal de preluare i transmitere lafundaii a nc rc rilor gravitaionale. Cldirea estecompartimentat cu pere ii portani din lemn,realizai din panourile prezentate n figura 4, mbinate rigid. Orice modificare ulterioar afuncionalului poate afecta rezistena i stabilitateaansamblului constructiv.

Panoul este alc tuit din dou componente:- rigla, element orizontal sau nclinat, careeste talp superioar i inferioar de cuplare amontanilor i buiandrug de sus inere a golurilor deu i i ferestre. n cadrul structurii ea are rol delegare a panourilor la extremi i i de asemenearol de grind sau pan acolo unde nu exist peretede sus inere la intrados;

- montantul , element vertical solicitat axial,preia doar nc rc ri gravitaionale, iar mpreun cucelelalte elemente ale panoului particip lapreluarea nc rc rilor orizontale (figura 4).

Montanii, t lpile i buiandrugii vor avea n

sec iune transversal dimensiuni (b x h) de (50mmx 150mm), iar grinzile dimensiuni de (50mm x240mm). La intersecia axelor structurale, stlpii cu

3. Wood light framing strength structure

As suggested by the name, "light frames",are strength structures, made up of bearing panelswith a mass low enough that two people canhandle them easily during construction andinstallation.

The structure is also called "thick framestructure" because the pillars positioned atdistances of several meters from the traditionalframeworks become studs spaced 45 cm, but withthe same main role to take over the gravitationalloads. The building is compartmented with bearingwooden walls, made at their turn from the panelsreferred in Figure 4, joined together rigidly. Anysubsequent changes to functionality can affect thestrength and stability of the whole construction.Panel is made up of two components:

- the thick plank, as a horizontal or tiltedelement, that in the panels composition is the topand bottom plate coupling the timber studs andlintel of the doors and windows span. Within thestructure it serves for "binding" together the panelsends and also it acts as a joist or purlin wherethere is no wall to soffit;

- the stud, as vertical element loaded withaxial force, takes over only gravity loads, and withthe others elements of the panel is participating intaking horizontal loads (Figure 4).

Fig. 4 Schema constructiv a panoului de perete(elementulde rezisten a structurii framing/Wall panelsconstructive scheme (framing structure strengthelement).

The studs, the bottom and top plates, andthe lintels will have the cross-section dimensions(b x h) of (50 x 150)mm, and the beams sizes of(50 x 240)mm, to fulfill the rigidity condition. At theintersection of the structural axes, the pillars withrectangular section from the conventional strengthstructure are apparently replaced with composed-section studs, as shown in Figure 5.

Joints between the small dimensions

elements (at least one side less than 100mm) canbe considered continuous in the static calculationbecause node efforts are much lower than those


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Fig. 5 Sec iune transversal efectiv a stlpului i a montantului pentru determinarea efortului secional n cazul celor dou structuristudiate/The effective cross-section of the pillar and the stud for determining the sectional efforts of the two studied structures.

sec iune rectangular de la structura tradiional sunt nlocuii aparent de stlpi cu o sec iunecompus , aa cum este prezentat n figura 5.

mbin rile dintre elementele din lemn cudimensiuni mici (cel puin o latur mai mic de100mm), pot fi considerate continue n calcululstatic, deoarece eforturile din nod sunt mult maimici dect n cazul nodurilor cadrelor tradiionale,iar elementele de tip tij utilizate au arii suficient demari (comparativ cu seciunea) pentru a prevenistrivirea local .

n plan vertical elementul care confer structurii rezisten i rigiditate este panoul , iar nplan orizontal, plan eul . Grinzile principale deplaneu din structura tradiional , sunt nlocuite derigle mai zvelte (rezemate pe panourile de pere i),pe care vor rezema grinzile secundare (prinintermediul unor piese metalice). Cadrul orizontalal planeului va fi rigidizat n totalitate cu plcirigide stratificate alc tuite din achii de lemnorientate OSB (ca i panourile de perei), avndaceea i comportare la aciuni.

Suprastructura se ncastreaz n fundaii cuancore metalice.

Considernd reale aceste ipoteze, nmodelarea cu elemente finite s-a considerat c structura este alc tuit din elemente liniare culungimea de 0,5m ncastrate la ambele capete, nc rcate conform schemelor de ncrcarepredefinite.

Conform P 100/1-2006 structura se ncadreaz la categoria structur din panouri din

lemn cu fee mbinate cu cuie pe scheletul dinlemn.Perioada de vibraie cu efectul decontravntuire este de aproximativ 0,105s, funciede caracteristicile placajului. Utilizareacontravntuirilor are ca efect reducerea perioadeide vibraie de la 0,842s (structur f r contravntuiri) la aproximativ 0,105s (structur cucontravntuiri).

Volumul de lemn necesar pentru ridicareascheletului cldirii l dep este pe cel pentrucadrele tradiionale, ajungnd la 22 m3 de lemn der inoase.

4. Analiza rezultatelorPentru simularea pe calculator a ambelor

efforts in conventional structure nodes, and theelements like utilized rods of any types havesufficient cross-sectional area (in comparison withthe building element cross-section) to prevent thelocal crushing.

In the vertical plane, the element that givesthe structures strength and rigidity is the paneland in the horizontal plane, the deck. The mainfloor beams from the traditional structure arereplaced by more slender thick planks (leaning onwall panels), on which will lean the side beams (byusing metal fasteners). The entire horizontalframework will be fully reinforced with orientedstrand board OSB (as the wall panels), havingthe same behavior to actions.

The superstructure is locked into thefoundations with metal anchors.

Considering this premises as being real, inthe finite element modeling was considered thatthe structure consists of linear elements with alength of 0.5m embedded at both ends, loadedaccording to load predefined schemes.

According to P 100/1-2006 the structure iscoming under category "wooden panels structurenail joined sides on the wooden frame."Thevibration period considering the bracing effect isaround 0.105s (usually higher) depending on thepanel characteristics. The bracing effect is thereducing of the vibration period from 0,842s(structure without bracings) to 0.105s (structurewith bracings).

The volume required for constructing the

buildings skeleton exceeds the volume of theconventional frameworks, reaching the value of22 m3 of softwoood.

4 . Analysis of design results

For computer simulation of both types ofstructures it was used the modeling and structuralanalysis program based on finite elements, withthe commercial code AXYS VM10 version 3g*.The finite element calculation model of thestructures was created with presented materialand cross section characteristics. The local andgeneral system coordinate axes are presented inFigure 6.

Structural analyses have led to obtain the


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Fig. 6 Coordonatele locale: x-rou, y-galben, z-verde/The local coordinates: x-red, y- yellow, z- green

Fig. 7 Elementele de compara ie din cele dou structuri/The strength structures elements to be compared

a) variaia tensiunii / the variation of tension b) variaia tensiunii / the variation of tension Fig. 8 Variaia tensiunilor and de-a lungul axei longitudinale a panei.

The variation of and tension on the purlins longitudinal axis.

tipuri de structuri s-a utilizat programul demodelare i analiz structural utiliznd elementefinite, cu denumirea comercial AXYS VM10 ediia3g**. Modelul de calcul cu elemente finite alstructurilor a fost creat cu materialele i seciuniletransversale prezentate. Sistemele de axe decoordonate locale i generale sunt prezentate nfigura 6.

following output results of the elements and nodes:maximum/minimum values for tensions related tolocal coordinates, values for the displacementsand deflections. In the Figures 8 - 11 arepresented the following variation diagrams alongthe elements length: the tensions anddisplacements or deflections, as appropriate, forthe two bearing elements from the analyzed struc-


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a) variaia tensiunii / the variation of tension b) variaia tensiunii / the variation of tension

Fig. 9 Variaia tensiunilor and de-a lungul axei longitudinale a stlpului/montantului/The variation of and tension on the pillars/studs longitudinal axis

a) deformare orizontal (pe direcia OY) b) deformare gravitaional horizontal deflection (on OY direction) gravitational deflection

Fig. 10 Deformarea axei longitudinale a panei/The purlins longitudinal axis deflection.


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a) deplasare orizontal (pe direcia OY)/horizontal displacement(on OY direction)

c) scurtare longitudinal /longitudinal shrinkage

b) deplasare orizontal (pe direcia OZ)/horizontal displacement(on OZ direction)

Fig. 11 Deplas rile axei longitudinale alestlpului/montantului/The pillars/studs longitudinalaxis displacements.

Analizele structurale au condus la obinereaurm toarelor rezultate pentru elemente i noduri:valori ale tensiunilor maxime/minime n coordonatelocale, valori ale deplas rilor i sgeilor.

n figurile 8 - 11 sunt prezentate diagramelede variaie pe lungimea elementului ale tensiunilor i deplas rilor sau sage ilor, dup caz, pentru dou

tures, the purlin and the pillar/corresponding studshown in figure 7. In figure 12 there are presentedthe values of gravitational forces transmitted to thefoundations by the pillars/corresponding studs.

5. Conclusions The framing structure, compared to the

Fig. 12 Valoarea for ei axiale pentruelementele verticale ale structurii

The axial force value for thestructures vertical elements.


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elemente portante din structurile de rezisten dinlemn analizate, pana i stlpul precizate n figura 7. n figura 12 sunt prezentate valorile for elor axialela baza elementelor verticale din structura derezisten .

5. Concluzii

Structura de rezisten de tip framing,comparativ cu structura de rezisten convenional , este o structur spa ial cuelemente portante i/sau reazeme suplimentare.Sub ac iunea nc rc rilor, prezena acestorelemente i reazeme modific n sens favorabileforturile, i implicit strile de tensiuni, care apar nelementele determinante pentru capacitateaportant a structurii n ansamblul ei, cu performanesatisf c toare pentru asigurarea cerin eloresen iale de rezisten i stabilitate.

Tensiunile care apar n elementul orizontal,tip pan , analizat, figurile 8-a i 8-b, dinipotezele de nc rc ri considerate, prezint ,comparativ, variaii reduse privind valorile nsec iunile caracteristice. Pe prima parte agraficului, figura 8-a, pentru structuraframing, valorile tensiunilor normale sunt njum t ite datorit efectului de rezemaresuplimentar produs de un perete desp r itorcare, dup modul de realizare, produce efectediferite n cazul celor dou structuri: lastructura convenional se consider c peretele este unul neportant, n timp ce lastructura framing acela i perete realizat printehnologia specific acestui sistem cap t rolde perete portant. Aceea i observaie estevalabil i pentru tensiunile tangeniale, figura8-b. n cazul elementului vertical, tip stlp,figurile 9-a i 9-b, se observ c starea deeforturi care se dezvolt din aciunea nc rcrilor este de compresiune excentric pentru ambele structuri de rezisten .Diferenele care apar n valorile tensiunilorsunt generate de prezen a sistemului decontravntuiri, precum i de valorilecaracteristicilor geometrice ale sec

iunii

transversale ale stlpilor: tensiunile normalesunt mai mici la stlpii structurii de rezisten convenionale datorit ariei seciuniitransversale mai mari, n timp ce valoareatensiunii tangeniale este redus cu pn la50% n cazul structurii de rezisten de tipframing datorit sistemului de contravntuiriorizontale din planul pereilor.

Stabilitatea construciei este mai bun ncazul construciilor din lemn cu structura derezisten de tip framing datorit panourilor de nchidere la perei care au rol de contravntuiri. n

acest sens se observ : Figura 10-a reprezint nf ur toareasgeilor n planul orizontal al panei

conventional strength structure is a spatialstructure with bearing elements and / or additionalsupports. Under the action of loads, the presenceof these elements and supports change in a betterway the efforts, and therefore the tension states,which appear in the determined elements for thebearing capacity of the structure as a whole, withthe essential requirements to ensure satisfactoryperformance of strength and stability.

The tensions that arise in the horizontalelement, the analyzed purlin, figure 8-a and 8-b, in the considered load hypotheses, havecomparatively smaller variations of values incharacteristic sections. On the first part of thegraph, Figure 8-a, for the framing structure,normal stress values are halved due toadditional bearing position effect produced bya partition wall that, after the manner ofconstruction, produces different effects for thetwo structures: for the conventional structure isconsidered that the wall is a non-load bearingone, while the same wall in the framingstructure, achieved through role-specifictechnology for this system, gets a bearing role.The same observation is also valid for thetangential stresses, figure 8-b. In the case of the vertical element, theanalyzed pillar, figures 9-a and 9-b, it can beseen that the efforts state that develop fromthe loads action is the eccentric compressionfor both strength structures. The appearingdiferences in stress values are generated bythe presence of the bracing system, as wellas from the geometrical characteristics valuesfor the pillars cross - section: normal stressvalues are smaller for the conventionalstructure pillars due to a larger cross-sectionalarea, while the tangential tension value isreduced up to 50% in the framing strengthstructure due the walls horizontal bracingsystem.

The construction stability is better for thewood construction with framing type strengthstructure due to the walls closing panels that actas bracings. In these meaning, it can be noticed:

Figure 10-a represents the envelope ofdeflections in the horizontal plane of theanalyzed purlin, determined by the loadsgrouped together for the exploitation limitstates (including earthquake). The deflectionvalue does not start from zero because theyare combined with the displacements of theentire structure. For the framing structure,sets of deflection envelopes were made, fortwo cases: one is the structure without thecovering panels, and the other is the bracedversion (with the covering panels). From thechart in figure 10, it can be noticed that

deflection values in the horizontal plane aresignificantly reduced by the structuralcladding.


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determinate de nc rc rile grupate pentru st rilimit n exploatare (inclusiv seismul). Valorile sgeilor nu pleac din zerodeoarece sunt cumulate cu deplas rile ntregiistructuri. Pentru structura pe cadre dese(framing) s-au realizat nf ur tori alesgeilor pentru dou situaii: n varianta destructur liber f r panourile din care serealizeaz nvelitoarea pereilor i n variantacontravntuit (cu panourile de placare). Dingraficul din figura 10-a se observ c valorilesgeilor n planul orizontal sunt considerabilreduse de placarea structural . Inf ur toarea s geilor pe direciegravitaional a panei, eviden iaz deasemenea aportul pe care l au panourile deplacare ale pere ilor n cazul structurii derezisten de tip framing (figura 10-b).Valorile sgeilor din prima por iune agraficului sunt reduse n cazul structuriiframing datorit prezen ei peretului decompartimentare portant. n cazul stlpilor, n prima variant amodelului de calcul (cu montaniinecontravntuii) pe direcia slab amontantului (axa oy n coordonate locale), ncazul structurii de rezisten de tip framingse produce o deplasare de 10 ori mai maredect deplasarea pe aceea i direcie astlpului de la structura de rezisten convenional (figura 11-a). n cazuldeplas rilor pe direcia (oy) a structuriiframing cu montanii contravntuii depanourile pereilor nu se observ diferenesemnificative ntre valorile acestor deplas ri ideplas rile stlpilor din structura de rezisten convenional , deplas rile laterale alemontanilor devin foarte mici, valorile fiindapropiate de zero. Deplas rile pe direcia (oz), n sistemul de coordonate local prezint acelea i aspecte ca i la deplas rile pedirecia (oy). Datorit diferenei de for axial cu caresunt nc rcai stlpii din cazul structuriiconvenionale cu a montanilor n cazulstructurii framing, se pot oberva diferen

e

ntre valorile comprim rii n sens longitudinalale elementului vertical (figura 11-c).

Din punct de vedere al aciunii seismice,cadrele dese au o comportare unitar , toat structura fiind angrenat n preluarea ac iuniiorizontale. La polul opus, cadrele tradiionaleavnd elementele mai distan ate i mbin riledintre ele semirigide, rolul de preluare a sarciniiorizontale se transfer pe element. Consumul de material lemnos cre te cuaproximativ 20%-25% n cazul structurii derezisten de tip framing datorit num rului

crescut de elemente, care nu este compensatvolumetric de valorile reduse ale caracteristicilorgeometrice n sec iune transversal . Consumul

Deflection envelope for the gravitationaldirection also highlights the wall coveringpanels contribution to the framing strengthstructure, figure 10-b. Values from the firstpart of the graph are reduced in the framingstructure due the presence of the bearingwall. For the studs, in the first version of thecalculation model (with un-braced studs bywall panels) on the studs weak direction (theoy axis in the local coordinates system), inthe case of framing strength structure, adisplacement occurs, 10 times bigger thanthe displacement on the same direction forthe conventional frame structures pillar,figure 11-a. For the case with the studsbraced with the wall panels there can not benoticed significant differences between thevalues of the displacements for bothstructures and lateral displacement valuesbecome very small, values aiming to zero.Displacements on the (oz) direction, in thelocal coordinate system present the sameaspects as the displacements on thedirection (oy). The different values of axial forces whichload the pillars for the conventional structureand the framing structures studs producedifferences between the longitudinalcompression values for the element, figure11-c.

In terms of seismic action, thick framingshave a consistent behavior, all elements of thestructure being engaged in taking the horizontalaction. In contrast, at the conventional frameswith more spaced elements and semi-rigid joints,the horizontal load-taking role is transferred tothe element. The wood material consumption increasesaround 20%-50% more for the framing strengthstructure due to the number of elements, which isnot volumetric compensated by the lower valuesof cross-sectional geometric characteristics.Consumption of wood material can becompensated in the total cost of the building

since the partition walls are already made. Fire resistance is higher in traditionalstructures exposed to fire due to a smallerexposed to fire surface compared to the framingstructure. The problem can be solved troughconstructive measures and specific details:fireproofing, coating, etc. The conventional wood structures offers thefreedom to modify the position of the partitionwalls without affecting the strength or stability ofthe structure. The framing system has a better behavior toseismic load and a better distribution of efforts

(Figure 12), to the foundation soil.


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de material lemnos se poate compensa n costultotal al cldirii avnd n vedere c pere iidesp r itori sunt deja realizai. Rezistena la foc este mai mare lastructurile tradiionale avnd o suprafa expus la foc mai mic comparativ cu structura de tipframing. Problema aciunii focului se poaterezolva prin msuri i detalii constructivespecifice: ignifugare, placare etc. Cadrele din lemn tradiionale ofer libertatea recompartiment rii spaiului interior f r a afecta rezisten a sau stabilitatea structurii. Sistemul framing prezint o mai bun comportare la sarcina seismic i o distribuiemai eficient a eforturilor (figura 12), c tre terenulde fundare.

** Autorii in s mul umeasc firmei Consoft Romnia pentru sprijinul acordat n punerea la dispozi ie a programuluide modelare i analiz structural utiliznd elemente finite, cu

denumirea comercial AXYS VM10.

** The autors would like to thank the Consoft Romaniacompany for their support in providing the modeling andstructural analysis using finite elements program with comercialcode AXYS VM10

REFERENCES

1. D. Isopescu, Timber Structures, Ed. GH.ASACHI Ia i, 2002

2. xxx, Details for Conventional Wood Frame Construction, American Forest and Paper Association, Washington, 2001

3. xxx, Axis VM User's Guide

4. xxx, SR EN 1995-1-1: Design of timber structures Part 1-1:General Common rules and rules for building.

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MANIFEST RI TIINIFICE / SCIENTIFIC EVENTS

7th International Scientific Conference WOOD & FIRE SAFETY May 13 16, 2012

The Patria Hotel, trbsk Pleso, Slovakia

The traditional conference of fire-fighting experts, with the predominant interest in wood and wood-based materials .

The main conference aim is to bring new knowledge into this multidisciplinary branch.

Scientific topics

burning of materials, combustion tests, certification, fire modeling wood structures and properties (changes at burning) stages of wood burning (ignition, flaming, burning, charring, toxicity) fire retardant of wood and wood based materials fire safety in wooden buildings experience with liquidation (extinguishing fires in wooden buildings) forest fires

Contact: http://www.wfs2012.sk/en/

University of ilinaFaculty of Special EngineeringDepartment of Fire EngineeringUl. 1.maja 3201026 ilinaSlovakiatel. 041 5136750fax: 041 5136620e-mail: [email protected]

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