Repair of Fire Damage

Rak-43.3313 Repair Methods of Structures, exercise (4 cr)

Esko Sistonen

Learning outcomes• Building materials: wood, concrete,

steel; behaviour, and deterioration in fire

• Condition survey of fire damage • Repair of fire damage

Ref.: YM ympäristöopas 39

Wood

http://www.puuinfo.fi/sites/default/files/content/info/fire-safety-timber-buildings-technical-guideline-europe-kasikirja/technical-guideline-summary-sp-info-2010-36-finland.pdf

Temperature rise of wood

http://customers.evianet.fi/woodfocus/index.php?woodfocusid=2&vr=630&anonymous=nobody

Temperature

Normal wood Pyr

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In addition, fire design of steel connectors and junction elements

Solid wood chars by burning about 0.8 mm per minute, layer glued wood 0.7 mm per minute

Fig. Schaffer E.L. (1967). ‘Charring rate of selected woods – transverse to grain.’ US Forest Service Research Paper FPL69, Forest Products Laboratory, Madison, USA.

Ref.: Wood Handbook. Wood as an engineering material. General Technical Report 113.Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 463 p.

Temperature area ° C Predominant reaction Reaction type

20...300 100…200*)

Pore water exits Water exits

300...490 Chemically adsorbed water exits

Calcium silicate decomposes to calcium

oxide and silica

Water exits

Decomposition

490...540 >400*)

Decomposition of calcium hydroxide

Decomposition

573 Transformation of quartz crystal form

Transformation

580...750 Formation of ß-dicalcium silicate

Decomposition

Concrete structures: cement stone and the temperature rise

Ref. BY 501 and Ted Kay Assessment and renovation of concrete structures.

Critical temperature of cement stone and steel reinforcement bar is about 400 - 500 °C.

The maximum temperature of the reinforced concrete structure caused by fire, can be up to 400-500 °C

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Temperature

The effect fire on strength properties of concrete • Once heating to about 200 °C and

subsequent slow cooling reduces the final strength of the concrete 25%.

• About at 400 °C the strength of the reinforcing steel is about 90% of the original.

• About at 700 ° C the strength of the reinforcing steel is about 20% of the original.

• Once the heating to about 700 °C and subsequent cooling, reduces the final strength of the concrete to 70%.

• Prestressed steel looses 50% of its strength at about 400 °C.

• Slow cooling maintain the stiffness

Temperature Colour

> 300°C Reddish

> 600°C Greyish

> 900°C Brownish, yellowish

Effects of fire on the viability of the reinforced concrete structure

Loss of strengthcement stone (compressive strength, tensile

strength)reinforcing steelssteel tendons

Cracking (microcracking, internal cracks, surface cracks) and spallingExplosion-like exit of water from the concrete at the beginning of fire

cooling effect of extinction water Thermal Expansion

Steel and the temperature riseSteel (hot rolled) starts to lose its strength about at 300 °C.

At 500-600 °C (flame temperature) strength drops to about one-third of the original

300 ° C is reached in fire surprisingly quickly

Changes in the structures begin to occur

Condition and eligibility of building structures exposed to fire should always be researched

Fire damage

Limiting post-damage effects

-clearance work

Isolation modes

(negative pressure)

-drying

ventilation

-surface cleaning

Damage inspection

-structures

-goods

-equipments

Condition survey of structures suffering from fire damage

Primary damage:

-damage caused by fire

Secundary damage:

-damage caused by extinction water

-damage caused by fire-released chemical compounds

-In PVC combustion chlorine gas is formed, which reacts with water as hydrochloric acid

corrosion

-organic and inorganic compounds (smell)

-dust of soot (carbon)

-PCB

-asbestos

-fire-fighting chemicals

Cleaning soot damage with dry ice blowing

In dry ice blowing high pressure air is blown by means of dry ice or frozen carbon dioxide to the cleaned surface. dissolved dirt is left after cleaning, because dry ice turns directly to harmless gas as it hits the surface

Also suitable for sensitive surfaces.

Applicable for fire and mold damage removal

Condition survey of structures suffering from fire damage

Strength evaluation

-make the acquaintance of drawings

-assessment of damage

-clarifying causes of damage

-determination of material properties (cross-sections may have changed, and material properties diminish)

-determination of the original geometry of the structure (the cross-sectional size, deflection)

-test loading

-evaluation of the structure usability

-statement

-the draft of the suggested measures

Repair of fire damaged structure

• demolition and rebuild

• changing the loading

• changing the purpose of use

• strengthening and/or repairing

• further clarification

Concrete fire damage

-surface cracking

-cracking

-changes in the strength of the concrete

changes in the steel strength

-damage caused by thermal expansion

-damage of joints and fastenings, (e.g. rubber bearing burns off)

-secondary defects (no heat), for example PVC

-bonding decreases

-reduction of the prestressing force

-an increase of deflections

Research methods of characteristics of concrete structures:

-destructive methods

Concrete

-drilling testing samples (cylinders, minimum six pieces)

-compressive strength

-density of concrete

-frost resistance

-tensile strength

-concrete composition

-sphere of influence of corrosion

Reinforcing steel-detach testing samples

-yield limit state-ultimate strength-elongation at ultimate limit state-metric weight

Stressed steels-the amount of strength of

tendons

Research methods of characteristics of concrete structures:

-non-destructive research methods

Concrete

-Methods based on the hardness of the surface

-ultrasound

ftp://ftp.stru.polimi.it/corsi/Felicetti%20-%20Structural%20assessment%20and%20residual%20bearing%20capacity/documents%20%26%20papers/Fire%20damage%20assessment/New%20NDT%20techniques%20for%20the%20assessment%20of%20fire-damaged.pdf

Structural repair of the fire damaged concrete

Repairing spallings

-concrete batch repair

-patch repair

-shotcreting

-plastic repair

-prepakt method of concrete repair

-dry packing method

Ref.: NISTIR 7094 Structural Collapse Fire Tests:Single Story, Wood Frame Structures

Madrid, Fire of Windsor tower

Ref.: Betoni, 3/2005

Several internet links…http://www.vtt.fi/inf/pdf/publications/2002/P459.pdfhttps://noppa.aalto.fi/noppa/kurssi/rak-43.3121/luennothttps://noppa.aalto.fi/noppa/kurssi/rak-83.3110/luennothttp://www.puupaiva.com/sites/default/files/slides/C%20Ostman%20Birgit.pdfhttp://www.sbi.se/uploaded/filarkiv/EC1-1-2%20%20EC3-1-2%20PVR%202010%20new.pdfhttp://www.mace.manchester.ac.uk/project/research/structures/strucfire/DataBase/http://www.bca.gov.sg/SustainableConstruction/others/sc_fire_protection_guide.pdfhttp://www.tatasteelconstruction.com/file_source/StaticFiles/Construction/Library/Fire%20resistance%20of%20steel%20framed%20buildings2006.pdfhttp://asfp.associationhouse.org.uk/default.php?cmd=210&doc_category=293