Repairing of timber and fire-damaged structures€“ wooden beams • Timber glue wood • glued...

Repairing of timber and fire-damagedstructures

Mon 02.05.2016

Rak-43.3313 Repair Methods of Structures, exercise (4 cr)Esko Sistonen & Fahim Al-Neshawy

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Introduction& Conservation

Repair methodsof the roofing

structures

Repair methodsof the windowand the door

structures Buildinginformation

modelling BIM

Strengthening ofbuilding

structures

Repair methodsfor woodenstructures

Repair of firedamage

The use of ICT forcondition assessment of

structures

Course Content

HVAC-renovation

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Outlines

Repair of timber structures• Introduction• Deterioration of timber structures• Condition inspection of the timber

structures• Repair of timber structures:

– load-bearing timber structures– timber floors– timber grids– glued timber structures– wood damaged by rot and

mould– Wood cladding

Repair of fire damaged-concretestructures• Deterioration due to fire• Assessment of fire damage• Fire damage classification• Repair methods of fire-damaged

concrete structures

Repair of timber structures

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Introduction

Uses of timebr in construction– Building construction– Construction of house posts– Construction of beams– Construction of rafters– Construction of bridges– Construction of piles, poles

and railway sleepers

posts and beams

http://www.everything-log-homes.com/post-and-beam-construction.html

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Timber deterioration

Problems in timber structures can bedefined in terms of three things:

– the timber material itself– the way it's put together

(connections),– the way it is functioning

Wood deteriorating factors• Moisture

– influence on physical-mechanical properties of wood

– creates favourable growingconditions for agentsresponsible for wooddegradations.

– Bellow the fiber saturationpoint, the wood will shrinkwhen losing moisture andswallow when absorbingmoisture

• Temperature– When exposing wood to

temperatures higher than 150°C,its strength will be affected

• Loading stresses– Bending moment, tensile,

compressive and shear forces– Torsion, creep, fatigue

• Biological agents– Fungi and insects or, in some

cases, by some marine borers

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Damage to timber structures

Common damage are:• Natural defects in timber elements• Fungi (brown and white rot)• Insects (termites etc.)• Decay• Delamination of glulam beams• Fire• Impact or collisions• Abrasion or wear• Overstress• Weathering or warping• Cracking (overload or shrinkage)• Connections damage

Firedamage

Shakesandcracks

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Damage to timber structures

Voichita Bucur (2011)Delamination in Wood, Wood Productsand Wood-Based Composites

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Condition inspection of the timber structures

The inspection should include asa minimum the following:1. Assessment of the condition of

each timber member including:a) Significant checkingb) Broken membersc) Member splittingd) Water and decay damagee) Fire damagef) Member warpingg) Other damage

2. Assessment of the condition ofeach timber connection.

3. Moisture content determination ofrepresentative members.

4. Assessment of all loadssupported by timber membersincluding:

a) Roof dead loadsb) Roof live/snow loadsc) Ceiling dead loadsd) Floor dead loadse) Floor live loadsf) Mechanical unit loadsg) Other applied loads

5. Assessment of timber memberconfiguration and sizes

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Repair of timber structures

1. Strengthening of load-bearingtimber structures

– Damaged load-bearing structures– Increasing the load bearing

capacity of non-damagedstructures

– Strengthening the connections

2. Strengthening of timber floors– Adding additional beams

3. Strengthening of timbertrusses– Supporting rods– buckling of the chords– Strengthening the connections

4. Repair of glued timberstructures– Transverse tension– Cracking of the joint area

5. Repair of wood damaged byrot and mould

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Strengthening of load-bearing timber structures

• Classical strengthening methodsimplying traditional materials:– case of compressive loads

• reduce the deformations• enhance the rigidity of the

member– elements subjected to tension

• using cover plates made ofwood

• connected with rods– elements subjected to bending

• stop crack propagation or toenclose it

• use of metallic elements

https://www.fhwa.dot.gov/publications/research/infrastructure/structures/04098/14.cfm

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Additional beams– wooden beams

• Timber glue wood• glued laminated beam• thin-web bed beam

– Steel beams• I-beams• Rectangular Hollow Sections

(RHS) beams


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• Strengthening wood elementsusing Fiber Reinforced Polymer(FRP) composite materials

• Reinforcing the wood memberswith very thin FRP sheets bondedonto their tension faces hasresulted in the increase of theelements strength, stiffness andductility characteristics.

• Fiber reinforcements could also bevery advantageous in regions ofstress concentration (like boltedjoints), as well as with tensile andflexural members

a) (0°/90°, –45° /+45°) FRP fabricsb) Spiral stripsc) Parallel stripsd) Straight stripse) fabric confinement FRP rods


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Strengthening of timber floors

Strengthening or repair of timberfloor joists by the addition of steelsections• As in the case of frames, the

strengthening of wooden floors bythe addition of steel sections is asuitable solution:– to reinforce damaged

structures (rotten or worm-eaten),

– to withstand increased loads.• The strengthening sections are

supported by the existingstructure or a supplementarystructure (walls, beams…)

http://www.constructalia.com/english/renovation_with_steel/iii_beam_reinforcement_techniques

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Strengthening of timber floors (Video)

https://www.youtube.com/watch?v=2RJIJL9emY8

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Strengthening of timber floors

http://www.constructalia.com/english/renovation_with_steel/iii_beam_reinforcement_techniques

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Strengthening of timber trusses

http://wadsworth.net.au/wp-content/uploads/2014/02/TrussFactBook_AUS_2010-web.pdf

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• Strengthening of struts with boltedrigging rods

• Strengthening of joints withplywood

• Buckling support of the upper andlower chords (bracing)

• Adding new grids alongside the oldtruss

Strengthening of the struts

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Buckling support:Bracing

Ympäristöministeriö, YM35/612/2006:http://www.ymparisto.fi/download/noname/%7B53248464-F5C4-49BD-B319-DB59785EEF6E%7D/100789

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Repair of glued-laminated (glulam) timber structures

• Glued-laminated timbers are madeof wood laminations glued togetherto form a specific piece of wood fora specific load.

• Decrease product variability• Less affected by natural growth

characteristics like knots.• Offers almost unlimited possibilities

of shape and design forconstruction

• Widely used for load bearingstructures in houses, warehouses,pedestrian bridges, etc.

http://publications.lib.chalmers.se/records/fulltext/40294.pdf

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Alann A. (2006). Fibres for Strengthening of TimberStructures. Luleå University of Technology

Repair of gluing surfaces• The gluing surfaces on glulam beams

can give way either:– under excessive loads– due to ageing– poor application of the glue.

• Resins reinjection of the surface• Timber slats can be reassembled

using glass or carbon fibre pins.• By restoring the internal cohesion of

the beam's structure, shearing stressesbetween slats are supported perfectlyand the bearing capacity is restored.


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Increasing the bearing capacity

• To increase the inertia of a glulambeam, and thus its bearing capacity, awood prosthesis can be consolidatedwith the beam's soffit using timber resin

• The wood prosthesis is linked to theoriginal beam using glass fibrecomposite rods sealed with resin.


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External prosthesis made of treatedwood• Rotting effects can often be observed

at the bases of glued-laminated bearingarches or columns located outdoors

• it is recommended to amputate thestructure by sawing off thecontaminated part and then replacing itwith treated wood.

• The prosthesis shall be connected tothe existing structure by a series ofpinning sites sealed with glulam timberresin and carried out with compositerods (glass or carbon fibre according tothe magnitude of stresses) that areinsensitive to climatic changes andcorrosion.

• A wood preserving coating is thenapplied onto the restored external partsand a capping, such as a ventilatedcap, is mounted to preventcondensation on contact with thetimber.

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Repairing wood damaged by rot and mould

• Repairing mold damage is not a lastingsolution. If the conditions for mold toregrow exist (moisture, warmth, and afood source), mold will simply resumegrowing on your new wood over time

• Before removing and replacing rottingwood, follow these steps:– Removing water leakage sources:

(plumbing issues, groundwaterleaking etc.)

– Fix any grade line & gutter issues– Eliminate termites, carpenter ants,

or other biological agents

Example rotting woodin crawl space

http://www.gothrasher.com/home-mold/repair-wood-damage.html

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Repairing wood damaged by rot and mould

• Three main challenges wheninspecting the damage:

1. Determining which wood must bereplaced

2. Assessing where wood can berepaired

3. Evaluating where repairs are notneeded

• Crawl space supports are used torepair the wooden posts that are rotting

• Crawl space supports support thewooden posts that are sagging due topoor supporting soils

• An additional beam of new wood maybe installed along the old rotten beamto add structural strength

http://www.gothrasher.com/home-mold/repair-wood-damage.html

Crawl space jack posts

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Repair of wood cladding

• Wood cladding is typically used inresidential and low rise buildingsthat have wood frame construction

• Maintenance and Repair:

– Re-Painting• Re-painting and re-staining of

wood siding is typicallyperformed approximately onceevery five to seven years.

– Replacement• Replace damaged boards• Replace the whole cladding

Photos: Jari Virta

Repair of firedamaged-concrete

structures

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Physical effects of temperature on concrete


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Phases of deterioration due to fire

http://www.mapei.com/public/GB/linedocument/Concrete_deterioration_-GB.pdf

The concrete withstandstemperatures of up to 650°C1 2

3 4

The first part to break off is the concretearound the reinforcement, which isfundamental in protecting the rods

Once the reinforcement rodsare exposed, heat propagatesmore quickly

If the structure is exposed to fire for aconsiderable time, the steel alsoloses its performance characteristics,causing the structure to collapse

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Assessment of fire damage

Materials– Effects of high temperature on

concrete strength and elasticmodulus

– Mineralogical changes inconcrete

– Cracking of concrete in fires– Spalling of concrete in fires– Residual thermal movement

cracks– Reinforcing and prestressing

steel

Testing of fire damaged reinforcedconcrete

– On-site inspection– Non-destructive testing (NDT)– Petrographic examination– Thermoluminescence tests– Core test– Tests on samples of

reinforcement– Other laboratory tests

Assessment of fire damagedstructures

– Assessment of fire severity– Heat transfer

The concrete Society, (2008). TR68: Assessment and repair offire-damaged concrete. (Camberley, UK: concrete.org.uk)

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Spalling of a slab soffit owing to fire-damage of embedded plastic

reinforcement bar spacers.

Explosive spallingView of floor below thefire showing thermalexpansion cracks on theslab soffit

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Fire damage classification

http://mosenltd.com/wp-content/uploads/2011/01/Concrete-Structures-in-Fire.pdf

Colour change of heated concrete

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Fire damage classification


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Repair methods of fire-damaged concrete

For reinforced concrete, the mainprocesses to be undertaken areas follows:

– Surface cleaning– Removal of damaged or

weakened concrete– Replacement of weakened

reinforcement– Replacement of concrete both

to reinstate the original formand to provide adequatestructural capacity, durabilityand fire resistance.

– Reinstatement of specialfinishes and appearance.

Removing small area of concreteusing hand-held equipment

hydro-demolition


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Repair methods of fire-damaged concrete

Repairing methods• Mortar / concrete – patch repairing• Flowable micro-concrete

– Flowable micro-concretes are self-levelling and self-compacting

• Sprayed concrete• Overcladding• Resins

– often been used for repairs tolightly spalled areas

– may perform quite satisfactorily innormal service

• Strengthening with fibre composites(FRP) Sprayed concrete

application

patchrepairing


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Repair methods of fire-damaged concrete (Video)

https://www.youtube.com/watch?v=XgKOSkqYAz4

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Summary

Lecture summary– Deterioration of timber

structures– Condition inspection of the

timber structures– Repair of timber structures– Deterioration due to fire– Assessment of fire damage– Fire damage classification– Repair methods of fire-

damaged concrete structures

Next Lecture:– 09.05.2016– The use of ICT for condition

assessment of structures

Repairing of timber and fire-damaged structures€“ wooden beams • Timber glue wood • glued...

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