PROTECTION AND STRENGTHENING OF THE WOODEN ELEMENTSAGENTS OF WOOD DEGRADATION

Existing wood constructions, sometimes of hundreds of years, show that even if wood is a natural product, it may last a very long time without noticeable degradation under optimum exploitation conditionsIn order to identify the proper preventive measures that reduce risks of the initial design or for the rehabilitation of wood structures is important to find out main factors that may produce degradation (total or partial) with effects on the structure. There is a wide range of actions and factors, related mainly to the exploitation conditions which may affect durability of wood and degradation.The speed of damage occurrence and expansion may be controlled through the design of elements and use of the wood, leading to this respect to more main strands that must be taken into account:- design and detailing of elements and joints such that all kind of humidity sources will be avoided- avoid water collection in certain areas (hips, supports, etc.);- ensure proper ventilation of wood when water collection is impossible to be avoided;- selecting the type of wood with natural durability with respect to the environment;- applying an initial and in time treatment suitable for wood conservation.

Of all the factors leading to degradation the most important are those related to the service conditions. Apart from these, some additional factors may occur: earthquakes, high temperatures and fire, changes of functions, additional charges, etc.

Humidity actionHumidity represents the main factor influencing all the physico-mechanical properties of wood and further, on its sustainability in time. Humidity has a significant effect on the metallic elements used in the joints.

It is very important that wood put in work have a moisture percentage close to the estimated humidity equilibrium and moisture variations in time to be as limited as possible. If not, cracks from contraction may occur leading to conditions for water infiltration, mushroom spawn, larvae of insects, and finally to decay.

The concept of wooden structures must take into account the effect of environment moisture conditions and also other situations that can cause a large increase in humidity percentage:

-contact between wood and soil or between wood and other parts of the building (masonry, concrete elements, etc.);

-the presence of wood in a hot and humid atmosphere such as poorly ventilated areas,-vapour condensation inside the elements (walls, floors);-accumulation of snow in some areas and water infiltrations from wet areas (showers, bathrooms, kitchens);-water entering the wood, during storage on site or during the installation of the elements before they do cover

construction.Whereas the water infiltrartion in wood is made according to the direction of the fibres is very important to ensure the protection of the extremities by keeping them at a certain distance from the wet area, so as to avoid absorption through capillarity or treating them with different substances and protections that stop the rise of humidity.

In terms of the level of exposure to humidity, EUROCODE 5 and national codes differentiate 3 classes of service and five classes of risk.

European standards EN 335-1 relating to the sustainability of wood and wood-derived materials and the national norm SREN 335-1 defines the following classes of risk:

Risk class 1 — situations in which wood or wood products are protected and covered, totally protected from the weather and away from all the possibilities of wetting;

Risk class 2 - situations where the wood or wood products are protected and covered, totally protected from the weather but where high humidity environment may result in occasional wetting;

Risk class 3-situations in which wood or wood-based products are outside, not covered, but not in contact with the ground, they can be continuously exposed to weathering or can be protected from the weather but exposed to frequent soaks;

Risk class 4-situations in which wood or wood-based products are in contact with the ground or fresh water being constantly exposed to moisture;

Risk class 5-situations in which wood or wood-based products are continuously exposed to salt water.

Aggressive environment action

The anatomical composition of wood makes it resistant in aggressive environments in comparison with steel or concrete, placed in the same conditions. While steel structures require periodic application of materials and protection of concrete structures require permanent verification of their condition, wooden structures used in aggressive environment require very low maintenance, located mainly at the joining elements.

The natural strength of wood is sufficient to avoid chemical attack and no special measures are necessary.If a chemical attack occurs at the surface (corrosion) the decrease in its strength occurs in 10 ...20 mm depth,

while the rest of the section remains intact.A particular action of a chemical attack and effect on mechanical behaviour of wood may need to be involved in

areas where there is a contact between wood and metal parts (elements of) on the larger surface. In these cases it is recommended that the metal parts are galvanized, coated with protective substances or to be made of stainless steel.

High temperatures actionDue to the internal structure and thermal characteristics it can be said that high temperatures do not affect the

properties of the wood and its behavior.For temperature below 60 ° C the effect on the resistance of the wood can be ignored and temperatures around

100 ° C, while leading to a change to the brown coloration does not affect the strength of the wood. Strength changes occurs at temperatures above 150 ° C and the acceleration of the process occurs at 250 ° C, the decrease progressing from the outside inwards due to the low thermal conductivity of wood.

The simultaneous action of high temperatures and humidity favors the reduction of resistance and rigidity.

Radiation actionThe action of solar radiation and generally the action of ultraviolet rays change the structure in a superficial surface area (max. 1 mm thick) in a grey surface coloration, as a pseudo-charring.

The effect of solar radiation can manifest by heating the wood and moisture variations lead in deformations occurence.

WOOD PROTECTION measures aims to preserve the wood and wood derivatives and to protect against damage caused by fungus and insects.

It can be said that in optimal conditions of exploitation wood may last for long periods without presenting any noticable decay and without special measures of protection. However, if working conditions are not adequate wood requires special protective treatments against biological agents. Must be made for and against other agents or fire.

These measures may be constructive or in the form of chemical treatments of protection.Planning of protective measures, and their implementation particularly in the case of chemical treatments must

bear in mind the following:

-the nature and gravity of the risks (influence of humidity, fire risk, etc.); -the type of wood and its correlation with the destination; -the type of treatments carried out previously; -the side effects that used chemicals may have -the place and time of execution of the treatments -accessibility of the elements for a possible further treatment; -contractors expertise; -the conditions of checking the protection measures

Structural preventive measures

Structural preventive measures aime at structural limitation of wood humidity content by reducing the risk of moisture and by creating conditions for the rapid evacuation of water (in the case of temporary situations) in order to avoid overrunning moisture content of 20% or limit humid areas.

Structural measures should be preceded by the initial measures such as:-wood drying up at an optimal moisture content before putting in the work;-development of optimal conditions of transportation, storage and installation which do not allow a large increase

of moisture content in these phases.Bearing in mind that the wood humidity results from a balance between absorbed and discharged water is

particularly important that the meassures taken avoid or delay water penetration and facilitate the evacuation.If in some cases it is impossible to stop the water penetration it is necessary to provide a system of rapid

water evacuation to avoid exceeding 20% humidity. This can be done for example by adopting joints with decompression to improve ventilation (fig. 7.1).

Fig.7.1. Realizarea îmbinărilor între panourile pentru pereţi de lemna - îmbinarea etanşă la aer; b- element de îmbinare mecanică;

c - îmbinare de decompresie.

a) Măsuri preventive structurale a lemnului folosit la exterior.Când lemnul este folosit la exterior în zone de influenţă a precipitaţiilor nu este suficient să se realizeze numai

măsuri de protecţie chimică şi trebuie luate măsuri pentru eliminarea umezirii, cum ar fi:- realizarea unor streaşine suficient de largi;- evacuarea corespunzătoare a apelor de pe acoperiş cu prevederea de jgheaburi şi burlane;- realizarea unei distanţe de minimum 30 cm dintre partea superioară a solului şi partea inferioară a peretelui din

lemn, pentru evitarea stropirii;- executarea elementelor şi realizarea îmbinărilor între elemente expuse precipitaţiilor astfel încât apa să se scurgă

fără a atinge elementele situate în vecinătate sau sub acestea; - evitarea sau acoperirea colţurilor, canturilor şi îmbinărilor unde se poate acumula apa;- alegerea profilelor corespunzătoare pentru construcţii şi placaje;- asigurarea condiţiilor ca umezite să se usuce rapid;- acoperirea suprafeţelor orizontale şi oblice;- protejarea tuturor extremităţiilor lemnului care ies spre exterior;- utilizarea de elemente metalice zincate sau din metal inoxidabil pentru fixare;- realizarea unor îmbinări de elemente care să permită lucrul şi deformarea fără consecinţe dăunătoare. În cazul lemnului folosit la exterior o atenţie deosebită trebuie acordată îmbinăriilor dintre elemente pentru a evita

pătrunderea apei în aceste zone precum şi pentru asigurarea condiţiilor de ventilare a lor.În toate cazurile de placaj exterior este recomandabil să fie asigurată aerisite acestuia pe toată suprafaţa interioară

prin crearea unui strat de aer interior. În fig. 7.2 şi 7.4 sunt prezentate soluţiile de placări exterioare care asigură un strat de aer continuu vertical pe faţa interioară atât în situaţia scândurilor aşezate vertical cât şi a celor aşezate orizontal.

Depărtarea placajului de la suprafaţa elementului şi realizarea unor orificii de intrare şi evacuare asigură circulaţia de jos în sus a aerului din stratul interior favorizând evacuarea umezelii. Este recomandabil ca orificiile de intrare a aerului, plasate la partea inferioară şi cele de evacuare de la partea superioară să aibă o suprafaţă de minimum 1/500 din suprafaţa peretelui.

Amplasarea verticală a scândurilor de placare este mai avantajoasă şi este preferată deoarece dă o posibilitate de ventilaţie şi prin circulaţia orizontală a aerului şi asigură o evaporare mai rapidă a apei. Scândurile pot fi fixate simplu fără o prelucrare deosebită a îmbinărilor verticale (fig.7.2a), prin folosirea diferitelor tipuri de îmbinări cu piese suplimentare (fig.7.2b) sau prin prelucrarea canturilor (fig.7.2b,c).

a) Structural preventive measures of the exterior wood elements.

When wood is used in areas outside is not enough only to realize chemical protective measures but measures should be taken to avoid moisturising, such as:

-construction of wide enough eaves;-proper evacuation of water from roof gutters and downspouts;- at least 30 cm parapet between the top of the soil and the bottom of the wooden wall, in order to avoid splashing;-the execution of joint between elements exposed to rainfall so that the water can drain out without touching the

elements situated in the vicinity or beneath them; -avoid or cover corners, edges and joints where water can accumulate;-choice of appropriate profiles for construction -ensuring that humid elements dry quickly;-cover horizontal and oblique surfaces;-protection of all wood extremities-use of metal elements in zinc plated or stainless steel fasteners;-development of joints that do not introduce harmful efforts and distortion. In the case of exterior wood special attention must be paid joints in order to avoid water accumulation in these

areas and for ensuring a proper ventilation. In all cases of exterior plywood is recommended to ensure ventilation along all inner surface by creating a layer of

air inside, see fig.7.3 and 7.4.The locationof the coating away from the surface of the element and providing entrance and exhaust vents ensure bottom-up movement of the air in the inner layer moisture evacuation favoring. It is recommended that the air entrance openings, placed at the bottom and the outlet at the top to have an area of not less than 1/500 of the wall surface.

The vertical location of the sockets of the coating is more advantageous and is preferred because it gives a possibility of horizontal circulation and ventilation of air and ensures a more rapid evaporation of water. The boards can be fitted without special processing of the vertical joints (fig. 7.2) using various types of joints with additional elements (fig. 7.2 (b)) or by selective edge processing (fig. 7.2 b, c).

Fig.7.2 – Placări cu scânduri asezate verticala- îmbinare simplă cu scânduri aşezate pe două rânduri şi fără prelucrarea cantului;

b- îmbinarea scândurilor aşezate pe un rând cu elemente de îmbinare şi cu prinderea vizibilă sau cu agrafe invizibile; c- îmbinare cu lambă şi uluc.

1 - agrafă metalică; 2 - element de fixare (cui, horşurub,etc.);3 - baghetă de îmbinare(din lemn, mare plastice, etc.); 4 - rigle orizontale; 5 – scânduri; 6 - scânduri verticale prelucrate pe cant; 7 - scânduri verticale cu lambă şi uluc.

Vertical joints can be done having tongue and groove processing of edges using visible fasteners or invisible clips (fig. 7.2 c).

Special attention should be given, in the case of coating with vertical boards to the joints at the corners. (fig. 7.3)

Fig.7.3 - Soluţii de realizare a îmbinărilor la colţuri1 - rigle orizontale; 2 - rigle verticale; 3 - scânduri verticale.

Fig. 7.4- Placări cu scânduri aşezate orizontal1 - riglă verticală; 2 - scânduri orizontale simple sau având un cant prelucrat; 3- elemnnt de fizare (cui, horşurub); 4-elemnnt

de fixare la partea inferioară; 5- şipcă distanţer

Fig. 7.5 Realizarea rosturilor verticale la scânduri asezate orizontala- cu fâşie de etanşare din lemn rezistent; b- cu profil cu gol interior;

c- cu profil din metal sau mase plastice; d- cu material elastic de etanşare.1 - rigle verticale; 2 - scânduri orizontale; 3 - material de etanşare a rostului.

Fig. 7.6 Realizarea îmbinărilor la colţuri la scânduri asezate orizontal1- riglă verticală; 2- scânduri orizontale ; 3 - riglă verticală de colţ.

Using planks placed horizontally it is advisable only overlaying them on a distance of at least 12% in width and not less than 10 mm (fig. 7.4).

Vertical joints between the boards stacked horizontal are also areas which require special treatment. Mainly it is advisable that the sockets flush against will not be processed and left empty in order to be able to be controlled at all times and if necessary can be dealt with later. The joints between the boards are closed with different sealing materials which should allow any small movements.(Figure 7.5). the corners of Joints horizontal elements is carried out according to the same principles as the boards mounted vertically (fig. 7.6)

Fig. 7.7 Placări cu scânduri asezate în V

b) Măsuri preventive structurale la contactul lemnului cu alte materiale.Pentru prevenirea infiltraţiilor de apă provenite de la alte materiale este necesară o izolare, hidrofugă a lemnului

în zonele de contact (fig7.8, fig.7.9) între:- grinzi, stâlpi sau panourile de lemn şi zidărie sau beton;- părţile masive şi elementele planşeelor realizate din lemn.

b) Structural preventive measures at the contact of wood with other materials.Preventing seepage of water from other materials vapor barrier a required, and waterproofing of wood in contact

areas (Figure 7.8, fig. 7.9) between:-beams, columns or wooden panels and masonry or concrete;-massive parties and an accompanying set elements made of wood.

Fig.7.8. Realizarea rezemării grinzilor pe elemente masive (zidărie, beton)

1 - grindă; 2 - perete; 3 - hidroizolaţie; 4 - termoizolaţie; 5 - strat de aer.

Fig.7.9 Protecţia hidrofugă a lemnului la contactul cu elemente masive (ziduri, fundaţii)a - planşeu pe un suport masiv; b - planşeu cu zonă de aer între elementul masiv (teren, beton) şi elemente din lemn; c -

panouri de pereţi rezemate pe fundaţii; d - pane de streaşină rezemate pe centurile zidurilor;1 - elemente de lemn; 2 - element masiv (placă de beton, teren, fundaţii, zidării); 3 - izolaţie hidrofugă; 4 - orificii de ventilare (minimum 1/500 din suprafaţa

zonei de sub planşeu); 5- zona de aer.

Pe lângă separarea propriu-zisă a zonelor de contact cu folii hidroizolatoare este recomandabil să se ia măsuri constructive ca aerul să poată circula la suprafaţa părţilor din lemn (capete de grinzi sau stâlpi). În acest sens la capetele grinzilor încastrate în elemente masive (zidărie, beton) se prevede un strat de aer ventilat de 1÷2 cm iar la capătul grinzii se va realiza o izolaţie termică (fig. 7.8 ).

La stâlpii care se reazemă pe fundaţii este recomandat ca să se realizeze o distanţă între capătul lor şi fundaţie iar când se folosesc piese metalice acestea nu trebuie să închidă complect baza stâlpului, pentru a asigura o ventilaţie corespunzătoare a lemnului (fig.7.10).

In addition to the actual separation of the areas of contact with waterproofing sheets it is advisable to take constructive measures that the air can circulate on the surface of the wooden parts (heads of beams or pillars). To this respect, the ends of the beams embedded in massive elements (concrete, masonry) require a ventilated air gap of 1 ÷ 2 cm and at the end of the beam a heat insulation will be created(fig. 7.8).

At the columns end towards the foundations it is recommended to create a distance and when using metal elements, they don't need to completely close the column end, in order to ensure proper ventilation of the wood (Figure 7.10).

Fig.7.10 Soluţii de realizare a rezemării stâlpilor pe fundaţii1 - stâlpi de lemn; 2 - fundaţii; 3 – elemente metalice exterioare;

4 - elemente metalice de rezemare interioară; 5 - buloane.

INTERVENTION ON WOOD ELEMENTS

The decision for the necessary work on existing wooden structures need to consider cooperation between experts, architects, timber designers, historians, construction authorities, officials in charge of cultural preservation, owners and building managers.

The factors involved are taking into account:-the identification of the objectives, requirements and limitations;-the degree of intervention that may include structural interventions or interventions for maintenance and

preservation.Decisions should be made after diagnosing the construction aiming to mainly:-causes that determined humidity and decay;-the possible attacks of insects;-the evolution of elements strength.

Identifying the objectives, requirements and limitations

The works of reparation or consolidation can and must respond, based on the objectives, to one or more requirements namely:

-preservation of original material and structural concept;-preserve the appearance and structural elements of the solution;-bringing the elements and structures at initial bearing capacity;-improving or changing the bearing capacity, rigidity, or work in service;-compliance with the technical regulations in force concerning the different requirments (seismic behavior and

resistance, fire resistance, etc.).Parallel with the stated objectives, other issues must be taken into account such as economic considerations,

environmental situations, prevention of future degradations, compatibility between wood and materials used for repairing or strengthening, etc.

Preservation of original material and structural concept and often artistic need is based on historical and cultural conditions which are far more important than the economic aspects which may be taken as priorities when decide intervention measures.

Restoring original capacity must take into account primarily the extent of degradation and resilience compared with the current structural requirements

Improving or changing the bearing capacity can be achieved through consolidation of structural elements with the purpose of meeting the requirements and performance required by the use of construction and modification of the structure.

Wooden structural elements comply with the new regulations on the requirements of construction start from the fact that many wooden structures were designed and made in periods with little knowledge in certain areas (e.g. seismic protection). It should be noted, however, that a number of provisions in the wood constructions have been developed without sufficient knowledge about the structure of this material and how to work them. Specific regulations in many countries, based on research, have brought a number of improvements including for example the proper behavior of wooden structures to seismic action and ceasefire.

Great importance in taking the decision on intervention solution comes fron the compatibility of wood with other materials especially in terms of deformations and effect of chemical factors. Thus, for glued or rigid joints a special attention should be paid to avoiding the occurrence of additional efforts caused by differential deformations (difference between contraction and nonhigroscopic materials, differentiated contraction on different areas, different thermal enlargements between wood and other materials, with different structural elements between different stiffness).

Based on the analysis of the objectives pursued, one of the following decisions ca be taken:-continued use of construction with or without intervention or interventions reduced;-keeping the structure after changes and consolidations;-demolition and reconstruction of parts of the building.

Interventions and structural repairmentsRepairments and structural consolidation are diverse and must be analyzed on a case by case basis since there are

noy two similar situations.Interventions are based on the structural elements state and take into account:-a reduction in sections due to various causes (rot, insects, fire, or damage due to requests, cracks, fractures, etc.)

requiring replacements or consolidations;-the partial destruction of the joints-excessive deformations.Of particular importance in adopting different solutions is the aim purpose:-maintaining the same functions as the original structure by replacing some parts, or after a consolidation;-achieving an enhanced structural bhaviour by use of additional elements of consolidation;-maintenance of the aesthetic, architectural conditions and historical fatures and the structural functions will be

taken over by other load-bearing elements (wood, concrete or metal).Whatever the purpose is it must take into account the following:-the work done must constitute a coherent whole;-Consolidations must be compatible with existing structures;-technical solutions should be easy work.Repairs may be carried out by different levels and refers to: isolated elements, material, structural units, structures

as a whole, between wood joints or connections with external elements.For the isolated elements repairs can take into account all the item or only parts of it , For structural units or

structures strengthening can be made for each structural element or the entir structural systemstructural system.

a) Consolidarea materialului.Sub influenţa mediului (climat, insecte, ciuperci) pot să apară degradări de suprafaţă, fisuri, găuri, etc. În aceste

cazuri se pot aplica tipuri de tratamente cu scop preventiv sau cu scop de reparaţie.Tratamentele preventive, asemănătoare cu cele aplicate lemnului nou (v.cap.7.2.3), se aplică elementelor de lemn

folosite pentru consolidări sau înlocuiri. Aceste tratamente trebuie corelate şi trebuie să fie compatibile cu metodele de îmbinare ulterioară şi cu metodele folosite pentru protecţia finală.

Tratamentele de reparaţii se aplică elementelor existente şi constau în injectarea în lemn de răşini destinate de a optura golurile , găurile sau fisurile şi permit refacerea caracteristicilor mecanice ale lemnului. Tehnica de punere în operă este asemănătoare cu cea aplicată şi la alte materiale de construcţii (zidărie, beton, etc.) iar soluţia poate fi combinată şi cu alte măsuri de consolidare (bare de oţel, poliesteri armaţi cu fibre de sticlă, etc.).to Strengthen the material.)

Under the influence of the environment (climate, insects, fungi) surface degradation may occur by, together with cracks, holes, etc. In these cases, prevention or repairing treatments may be used.

Preventive treatment, similar to that applied to new wood elements (see Chapter 7.2.3) is applied to wood used for consolidation or replacement. These treatments should be correlated and must be compatible with the methods further used and with the methods used for the final protection.

Repair treatments applied to existing elements consist of the injection resins for wood to the gaps, holes or cracks and allow recovery of the mechanical properties of wood. The technique of work is similar to that applied to other construction materials (masonry, concrete, etc.) and the solution can be combined with other measures to strengthen (steel bars, polyesters reinforced with glass fibers, etc.).

b) Consolidarea grinzilor.Consolidarea grinzilor se poate realiza pe toată lungimea lor sau pe zone degradate (capete de grinzi, zone

curente) şi au ca scop aducerea lor la capacitatea portantă iniţială sau creşterea capacităţii portante.Cele mai frecvente degradări întâlnite la grinzi sunt:- putrezirea capetelor, provocată în special de absorbţia apei din elementele de reazem sau de umiditatea

provenită de la apa meteorică ;- degradări cu apariţia unor fisuri şi crăpături în câmpul grinzilor;- deformaţii excesive provocate de modificarea încărcărilor sau de creşterea deformaţiilor sub încărcări de lungă

durată. Consolidarea capetelor de grinzi are în vedere mărimea degradărilor iar capetele grinziilor se pot păstra sau pot fi

îndepărtate, adoptându-se următoarele soluţii:- consolidarea cu răşini epoxidice cu îndepărtare parţială sau fără îndepărtarea capătului grinzi (fig.7.11); - îndepărtarea capetelor degradate şi înlocuirea cu altele noi. Consolidarea cu răşini epoxidice se realizează după mai multe tehnologii şi în mai multe faze funcţie de gradul de

degradare şi anume :- îndepărtarea zonei degradate şi curăţarea zonei unde lemnul nu este atacat mecanic; - impregnarea lemnului mai puţin atacat şi consolidarea lui cu răşină epoxidică pură;

- forarea unor goluri, prin lemnul sănătos şi prin cel consolidat, pentru a introduce armături (poliesteri întăriţi cu fibre, metal, etc.);

- introducerea armăturilor în goluri până în zona în care lemnul a fost îndepărtat;- formarea capătului grinzi cu un beton compus din răşină, agregate şi eventual cuarţ;- injectarea golurilor din jurul armăturilor cu răşină şi praf de cuarţ.

b) strengthening beams.Strengthen the beams can be done throughout their length or degraded areas (beams, heads the current areas) and

are aimed at bringing their initial or increase the load bearing capacity.The most common degradation encountered the beams are:

-rot, caused, in particular, heads of water absorption of the support elements or moisture of meteoric water;-degradation with the emergence of cracks and cracks in the beams;-deformations caused by excessive workload or modification of growth deformations under loads of long

duration. Strengthening the ends of beams considering size degradărilor and grinziilor heads can keep or can be removed,

the simplification of the following solutions:-strengthened with epoxy resin with partial removal removal of the cod-end beams or not (fig. 7.11); -removal of degraded and replacing with new ones. Consolidation with epoxy resin is achieved after several technologies and in several phases depending on the

degree of degradation, namely:-the removal of degraded area and clean the area where the wood is not attacked mechanically; -impregnation less attacked and his building with pure epoxy resin;

-drilling of holes through the wood and healthy through the strengthened to insert fittings (fortified polyesters with fiber, metal, etc.); -introduction of armatures in goals to the area where the wood has been removed;-formation of beams with a concrete compound resin, quartz and aggregates;-injecting dips around armatures with resin and quartz powder.

Fig.7.11 Consolidarea capetelor de grinzi cu răşini epoxidice 1 - lemn sănătos; 2 - lemn impregnat cu răşină; 3 - zonă de lemn îndepărtat; 4 - goluri pentru armături; 5 - beton de consolidare; 6 - armături.

Fig.7.12 Consolidarea capetelor de grinzi cu înlăturarea zonei degradate1 – grindă de lemn existentă; 2 - lemn de complectare;

3 – eclisă de lemn; 4- oţel sau fibră de sticlă; 5 – profile metalice

Pentru consolidarea capetelor de grinzi atunci când pe zona degradată lemnul se îndepărtează se pot adapta următoarele soluţii (fig. 7.12):

- dispunerea unor elemente noi de lemn la partea superioară sau inferioară a grinzii, când funcţionalitatea clădirii permite mărirea gabaritului grinzilor (fig.7.12a);

- dispunerea unor eclise din lemn amplasate lateral, antiseptizate şi solidarizate de grindă (fig.7.12b) sau a unor eclise metalice;

- prevederea unor soluţii metalice folosind profile sau elemente sudate; amplasate la feţele grinzi (fig.7.12c) sau în interiorul lor;

- realizarea unor elemente speciale din oţel (grinzi cu zăbrele);- realizarea unor reazeme noi (grinzi din lemn sau metalice, console) pe porţiunea sănătoasă a grinzi, modificând

modul de rezemare iniţial;- realizarea unor consolidări de capete cu bare de oţel sau fibre de sticlă şi răşini epoxidice (fig.7.12d).Lucrările de consolidare a capetelor grinzilor pot să fie însoţite de lucrări de îmbunătăţire a rezemări grinzi şi a

ancorări ei în elementele portante verticale .Repararea unei grinzi în secţiune curentă prin consolidare locală se realizează pentru oprirea fisurilor, pentru

oprirea şi închiderea unei fisuri sau pentru consolidarea unei eventuale rupturi (fig.7.13).

In order to reinforce the ends of beams when on the degraded wood is removed can adapt the following solutions (Figure 7.12):-the layout of the new wood elements at the upper or lower part of the beam, when the building's functionality allows increasing gauge beams (Figure 7.12) (2);

-arrangement of wooden pads placed laterally, and antiseptizate joined together of girder (fig. b 7.12) or metallic pads;

-the provision of metal solutions using profiles or welded elements; the faces of beams (Figure 7.12 c) or inside them;

-development of special steel elements (girders);-development of new supports (metal or wooden beams, brackets) on healthy portion of beams, by changing how

the original abutments;-completion of consolidation ends with steel bars or glass fiber and epoxy resins (Figure 7.12 d).The work of strengthening of beams can be accompanied by works to improve the rezemări beams and anchoring

them in the vertical load-bearing elements.Repair a beam in the current section through local consolidation is done to stop cracks, for stopping and closing of

cracks or to strengthen a possible rupture (Figure 7.13).

Fig.7.13 Consolidarea locală a grinzilor1- găuri; 2 - colier; 3 - fisură; 4 - platbandă; 5 - buloane

Intervenţiile locale pentru oprirea propagări unei fisuri sau închiderea ei se realizează cu ajutorul unor elemente metalice (fig.7.13a) care în anumite cazuri pot să creeze o compresiune perpendiculară pe fisură. Pentru limitarea propagări fisurii soluţia cea mai simplă este realizarea, la capetele ei a unor găuri perpendiculare pe direcţia fisurii.

Tehnicile clasice constau în dispunerea de o parte şi alta a elementului a unor platbenzi sau profile metalice legate între ele cu buloane.

Pentru repararea unor rupturi sau fisuri perpendiculare pe axul grinzii se pot utiliza soluţii locale cu elemente din lemn sau metal sub formă de eclise amplasate lateral (fig.7.14c), deasupra sau sub element (fig.7.14a,b).

Local interventions for stopping the spread of cracks or closing them is carried out by means of metallic elements (Figure 7.13 a) which in some cases can create a compression perpendicular to the crack. To limit the spread of the fissure, the simplest solution is the realization, at the ends of her holes perpendicular to the direction of the fissure.

Classical techniques consist in disposition of one side and the other of the prodct or metal profiles linked together with bolts.

For repair of ruptures or cracks perpendicular to the beam axis, you can use local solutions with wood or metal in the form of clips placed laterally (fig. 7.14 c), above, or below the item (fig. 7.14 a, b).

Fig.7.14 Repararea rupturilor la grinzi 1 - zona degradată; 2 - buloane; 3- eclise; 4- profile metalice

Lungimea ecliselor se determină din condiţia de transmitere a eforturilor de încovoiere prin tijele de îmbinare. Ameliorarea secţiunii şi lucrul ei ca şi un element compozit oţel-lemn trebuie realizată încât să se asigure o foarte

bună transmitere a lunecării la interfaţa oţel lemn.O soluţie modernă de consolidare locală a grinzilor se obţine prin plasarea la partea inferioară a grinzii a unor armături

oblice în goluri impregnate cu răşini (fig.7.15).

Link length is determined from the condition of bending efforts through the joint rods. Improvement of the section, and her work as a composite steel-wood element must be carried out to ensure a very

good transmission of the lunecării lemn steel interface.A modern solution to strengthen local breeds is obtained by placing the bottom edge of the beam of oblique

fittings in goals with resins (fig. 7-15).

Fig.7.15 Consolidare locală cu bare oblice din oţel 1 – bare din oţel; 2 – zonă impregnată; 3- element consolidat

Consolidarea totală a grinzilor se impune din necesitatea refacerii sau creşterii capacităţii portante a grinzilor, atunci când are loc schimbarea destinaţiei construcţiei şi se realizează prin:

- schimbarea secţiunii transversale; - consolidarea secţiunii fără mărirea ei;- realizarea unei noi scheme statice. Schimbarea secţiunii transversale se obţine prin consolidarea cu elemente noi din lemn, metal sau din beton care

se alătură elementelor existente. Funcţie de structura din care face parte grinda de consolidat noile elemente pot fi plasate lateral, deasupra sau sub elementele existente.

Consolidarea cu elemente noi din lemn se face de obicei prin amplasarea acestora la intradosul sau lateral la grinzile existente (fig. 7.16). Amplasarea elementelor de consolidare la intradosul grinzilor existente are avantajul că nu influenţează mult asupra elementelor secundare şi asupra planşeului. Elementele suplimentare au lăţimea grinzilor existente şi se leagă de acestea cu ancoraje metalice (fig.7.16a).Elementele de lemn amplasate lateral au aceeaşi înălţime cu grinda iniţială şi se leagă de aceasta cu ancoraje metalice (fig.7.16b).Total building beam requires the restoration of or increase in bearing capacity of beams, when there is change of construction and is achieved by:-changing cross section;

-strengthening of the section without raising them;-establishment of a new static schemas. Changing cross section is obtained by consolidating with new items made of wood, metal or concrete which joins

the existing elements. Based on the structure of the steel beam strengthened with new elements can be placed laterally, above, or below existing elements.

Consolidation with new wooden items is usually done by placing them at intradosul or lateral to the existing beams (fig. 7.16). The location of the intradosul building on existing beams has the advantage that it does not influence much on secondary elements and on the floor. Additional elements have width of existing beams and link them with metal anchors (fig. 7.16 to).Wood items placed side have the same height with the original beam, and link to it with metal anchors (fig. 7.16 (b)).

1-

Fig.7.16 Consolidare grinzilor cu elemente din lemn1- grindă existentă; 2 - grindă nouă; 3 - grindă secundară;

4 - ancoraj metalic; 5 - strat de aer; 6- grinzi laterale.

Consolidarea cu elemente metalice se realizează cu platbenzi sau profile laminate.Platbenzile metalice se amplasează sub grindă sau lateral de aceasta şi se prind de ea cu elemente de fixare (fig.

7.17).The metallic elements strengthening the prodct or laminated profiles.

Metal Platbenzile placed under the beam or to one side of it and catch it with fasteners (fig. 7.17).

Fig.7.17 Consolidare grinzilor cu platbenzi metalice1- grindă existentă; 2 - platbandă metalică; 3- element de prindere

Consolidarea cu profile metalice se poate realiza cu elemente amplasate sub grindă, lateral sau deasupra acesteia (fig.7.18 )

Strengthening with steel profiles can be made with items located under beam laterally or above (fig. 7.18)

Fig.7.18 Consolidare grinzilor cu profile metalice1-platbanda; 2 - profil metalic; 3 – traversă metalică;

3- buloane de prindereÎn cazul amplasări laterale a profilelor grindă consolidată se poate reazema pe toată lungimea pe profile,

intermediar prin traverse metalice sau poate transmite încărcarea prin buloane de legătură.In the case of lateral profiles locations the beam can be strengthened along the entire length on reazema profiles, metal sleepers or the intermediary can transmit loading by connecting bolts.

Amplasarea profilelor metalice la partea superioară se realizează atunci când modul de alcătuire a elementelor secundare sau gabaritele necesare nu permit amplasarea laterală sau sub grindă a acestora. Legarea de grinda de lemn se realizează cu ajutorul unor coliere din platbandă.

Profilele metalice de consolidare se reazemă pe pereţi prin intermediul unor reazeme de beton armat.Consolidarea grinzilor din lemn cu elemente din beton se face cu ajutorul unor grinzi monolite din beton realizate

deasupra grinzilor din lemn. Legătura între grinda din lemn şi cea din beton se realizează cu ajutorul conectorilor metalici şi prin locaşurile practicate în grinda de lemn.

Soluţia de consolidare cu grindă de beton poate fi cuplată cu realizarea unui planşeu monolit din beton.Consolidarea secţiunii transversale fără mărirea ei se realizează prin introducerea în interiorul grinzii a mai

multor plăci metalice cu înălţime mai mică decât grinda a unor grinzişoare cu zăbrele metalice sau prin folosirea unor tiranţi îngropaţi în grindă. Soluţia cu plăci metalice şi grinzişoare are avantajul protecţiei acestora împotriva focului şi a coroziunii iar elementele de consolidare pot prelua în totalitate sau parţial încărcările. Elementele metalice sunt protejate cu răşini epoxidice.

Execuţia consolidării comportă următoarele faze: - realizarea locaşului longitudinal pentru elementele metalice;- introducerea în locaş a unui prim strat de răşină şi apoi a elementelor metalice;- complectarea cu răşină a locaşului longitudinal .În cazul folosirii plăcilor metalice se poate realiza consolidarea şi fără răşini legătura efectuându-se cu ajutorul

unor şuruburi.O altă posibilitate de consolidare a grinzilor fără mărirea secţiunii transversale constă în folosirea unor tije

metalice îngropate în lemn (fig. 7.19).

Location of metallic profiles at the top is achieved when the composition of the side elements or dimensions required lateral location or do not allow the beam to them. Wooden beam linking is accomplished with the help of the necklaces flat. Metal strengthening profiles resting on walls by means of reinforced concrete supports.

Wooden beams strengthened with concrete elements is done with the help of monolithic concrete beams made of wood beams above. The connection between steel beam and concrete that is achieved by using metal connectors and snaps in the wooden beam.

Consolidation solution with concrete beam can be coupled with the development of a monolithic concrete slab.Strengthening its cross section without the increase is achieved by placing the beam inside of several metal plates

with a height smaller than the beam of the metallic lattice or regulated lags using tension rods buried in the beam. Solution with metal plates and regulated lags takes advantage of their protection against fire and corrosion and consolidation items can take over in full or partial loads. Metal items are protected with epoxy resin.

Implementation of consolidation involves the following phases:-completion of Groove metal elements for longitudinal;

-introduction in place of a first layer of resin and metal components;-Kitting-up with resin of the longitudinal slot.When using metal plates can be achieved without strengthening the link with resins by means of screws.Another possibility to strengthen the beams without increasing the cross section lies in the use of metal rods

buried in wood (fig., 7. 19).

Fig.7.19. Consolidarea grinzilor cu tiranţi îngropaţi la partea inferioară1-tirant; 2-grindă; 3- element de ancorare

Elementele metalice care lucrează ca tiranţi pot fi amplasate lateral de grindă sau la partea inferioară cu ancorare la capete sau la partea superioară a grinzii (fig. 7.19).

Pentru consolidarea grinziilor cu tiranţi se pot folosi şi solutiile de amplasare exterioară a tiranţiilor, lateral de grindă sau la partea inferioară, cu distanţarea lor de grindă funcţie de efectul care se doreşte a fi obţinut prin modificarea schemei statice (fig. 7.20).Metal working parts as tension bars can be placed on either side of the beam or to the underside with anchoring at the ends or at the top of the beam (fig., 7.19).

To strengthen grinziilor with tension rods and solutions may be used outside of the tiranţiilor location, beam laterally or at the bottom, with their alienation of beams based on the effect of which is to be obtained by changing the static scheme (fig. 7.20).

Fig.7.20 Consolidarea grinzilor cu tiranţi exteriori1- ghidaj de tirant; 2 - ancoraj ; 3 - element de tensionare

4- tirant; 5- distanţer; 6 - grinda.

c) Strengthening of tensioned elementsConsolidating of tensioned elements is made based on the values of loads and the way of their transmission

consolidation works.The tensioned elements for which temporary supporting cannot be achieved the consolidation is made with the

help of metal pretensioned elements The tensioned elements for which temporary supporting can be achieved, the consolidation is made adding bolt

fastened main and secondary elements

d) strengthening of compressed elements

Deformation of compressed elements is a particularly dangerous phenomenon because the solicitation becomes composed, is a compression with bending – eccentricaly compression- and additional efforts not considered initially can lead in time to the total compromise of the item.

Fig. E 7.21 – Consolidarea elementelor întinsea – cu tiranţi metalici; b – cu eclise şi fururi

1 – zonă degradată; 2 – tiranţi metalici; 3 – profile tip cornier;4 – eclise din lemn; 5 – fururi; 6 – buloane.

Strengthening aimes at the partial or total reduction of deformations and eventually increasing the rigidity in the bending plan. Items must be discharged and for bringing to the initial position the following methods may be used:-strengthening with rigid wooden elements fastened with clips or metal items and tightening with bolts to the original position;-consolidation with special systems, for upper and lower chords of trusses, -the use of jacks with special devices for straightening.

Strengthening the overall structural elements formed by both tensioned and compressed elements (e.g. truss) may be achieved by transforming them into other structural elements with behavior more favorable, according to the new conditions of exploitation.