Repair methods for wooden structures

Rak-43.3312 Repair Methods of Structures II (4 cr)

Esko Sistonen

Damage to wooden structures

-mold-decay-fire-cracking

*overload*shrinkage

-joint damage

Repair of timber structures

-Strengthening of timber structures*Damaged load-bearing structure*Undamaged load-bearing structure, increase of load bearing capacity demanded*Strengthening the connections

- Strengthening (intermediate floor) the framework *Additional beams

- Strengthening the Grid*Supporting rods, in particular the bearing of the buckling of the top chord *Strengthening the connections

-Repair of damage of supports of glued timber structures (Transverse tension, cracking of the joint area)

- Repair of damage of log structures

-Repair methods for structures suffering from mould growth damage

Repair of timber structures

*Strengthening the timberwork-adding new beams and retaining existing beams -next to, between, under, upon (suspension supports)

*additional beam-wooden beam

-timber-glue wood- glued laminated beam-  thin-web bed beam

-steel bar-I-bar-RHS-profile

Plastering

Strengthening of Grids

*strengthening of bars (struts) with bolted rigging rods

*strengthening in the joint area with plywood

*the buckling of the top chord-temporary suppor-chrods in the longitudinal direction of the

building between chrods in positions where construction assembly buckling supports located -> support both the upper and lower chord.

*a new grid alongside the old trusses

http://www.ymparisto.fi/download.asp?contentid=74103&lan=FI

Ref. YM 11/629/2006

diagonal stiffener Horisontal grid

Ref. YM 11/629/2006

Buckling support: diagonal reef

Buckling support: bar supported from two points

Liimapuukannatteiden vaurioiden korjaaminen (Poikittainen veto, liitosalueen halkeilu)

Cracks located in the lower and the upper surface of glued wooden beam is harmless. Cracks located on side of the beam are harmless if the depth of cracks are not more than 15% of the width of the beam and are not located at glued joints or in hazardous areas presented later on.

The straight and a few meters long cracks located at glued joints can be gluing fault and therefore structure should be repaired.

It is essential relative to load-bearing capacity, - How deep are cracks, and- The position at which cracks are located.

Repair of glued wooden cantilever damage(transversal tensile, cracking of annexed area

Ref. YM 11/629/2006

Poor suspension joint: cracking of wood due to tensile strain perpendicular to wood fibre

Best suspension at left, good at the middle, and poor at right

Ref. YM 11/629/2006

1. In the top of the beam at approximately mid-height2. Close the hole3. at the bottom of the notch close to the Support in the case when, the notch is located at the bottom of the beam

Most dangerous cracksSupport type

Straight beam

Pitched  and ridge beam 1. In the shallow end of the pitched beam at approximately half height and at the top of the beam2. In the ridge beam at the end of the beam approximately in the middle of the height and in the ridge area3. In addition, at the reversed ridge beam in the entire bottom when laminae at the bottom are cut obliquely in relation to direction of the wood fibre

Ref. YM 11/629/2006

Curved beam and a curved ridge beam

1. At a curved beam in the middle of the span, close supports, especially when laminae at the bottom are cut before they are reaching the support2. At a curved beam (i.e. boomerang beam) in the middle of the span, close supports, in particular when laminae at the bottom are cut before they are reaching the support. The curved central portion of the boomerang beam is more sensitive to cracking the ordinary curved beam.

Ref. YM 11/629/2006

A timber frame with three joints

1. The crack located at the head area of the beam in the outer edge of the column can be dangerous, if at the outer edge of the column the laminae are cut obliquely in relation to the direction of the wood fibre (cf. ‘belly’ beam)2. The crack located at the ridge area is dangerous, if the connecting ridge is formed so that timber structures are in contact with the top of the joint, and there is a gap at the bottom of the connection.3. The crack located at the bottom of the frame can be dangerous, if the lower edge of the beam is sawn in relation to the direction of the wood fibre

Ref. YM 11/629/2006

Installation, oval holes

Installation, tight holes

Drying, uncracked

Drying, cracked

Connection of the beam at the support. Steel plate is used as fastening, which is connected with bolts or similar to the side of the beam.

Ref. YM 11/629/2006

Incorrect repair methods of cracks:-filling the cracks with filler or glued wooden rods are not repair method for the load-bearing structure - the main risk of the repair of the cracking by bolting is the wood's moisture deformations

Areas prone to cracking caused by uneven drying

Repair of log structures

*Replacing the first row of logs (‘Shoeing’)-house is to be raised up on the jack wall section at a

time, old log is removed and replaced to a new one-can be changed the entire length of a log or do scarfing of

log.-For more information:

http://www.ouka.fi/pora/tietopankki/kengitys.pdf

*Patching up gaps-Connect logs to the opening edges of the gaps with wooden spindles (http://wikikko.info/wiki/Hirsiseinän_aukot)- repair with substructure

*Repair of Uneven settlement of log walls  -enough space for settlement

Fig. Jari Virta

Cladding damage

Cladding damage

Fig. Jari Virta

Repair methods for structures suffering from mould growth damage

*The priority should be to remove the rotting materials and remove causes of damage.*In the alternative, the structure of the encapsulation, sealing, vacuum bagging, air cleaners.*Dry rot control:

-chemicals are not an alternative-can serve as a advance protection, to prevent the spread

of mold and to regenerate-carbamates, urea and triazine derivatives,  isothiazolines,

  boric acid, borates, PHMG and PHMB [harmful substances]

-organic mercury and tin compounds, and pentachlorophenol has been abandoned because of toxicity

*ozone treatment to deodorize (odour) and eliminate micro-organism at the moment, but the problem persists once and for all, if the conditions of growth of microbes such as the structure is not removed from inside.

Fig. Kosteus- ja homevaurioituneen rakennuksen korjaus. Ympäristöopas 29

Basement structures

Fig. Kosteus- ja homevaurioituneen rakennuksen korjaus. Ympäristöopas 29

Bathroom structure before and after repair