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
Temperature rise of wood In addition, fire design of steel connectors and junction elements Pyrolysis Normal wood Temperature Transition zone Char http://customers.evianet.fi/woodfocus/index.php?woodfocusid=2&vr=630&anonymous=nobody
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.
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
Relative modulus of elasticity, E [%] 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
Effects of fire on the viability of the reinforced concrete structure Loss of strength cement stone (compressive strength, tensile strength) reinforcing steels steel tendonsCracking (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 rise Steel (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 Damage inspection -structures -goods -equipments Limiting post-damage effects -clearance work Isolation modes (negative pressure) -drying ventilation -surface cleaning 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.pdf https://noppa.aalto.fi/noppa/kurssi/rak-43.3121/luennot https://noppa.aalto.fi/noppa/kurssi/rak-83.3110/luennot http://www.puupaiva.com/sites/default/files/slides/C%20Ostman%20Birgit.pdf http://www.sbi.se/uploaded/filarkiv/EC1-1-2%20%20EC3-1-2%20PVR%202010%20new.pdf http://www.mace.manchester.ac.uk/project/research/structures/strucfire/DataBase/ http://www.bca.gov.sg/SustainableConstruction/others/sc_fire_protection_guide.pdf http://www.tatasteelconstruction.com/file_source/StaticFiles/Construction/Library/Fire%20resistance%20of%20steel%20framed%20buildings2006.pdf http://asfp.associationhouse.org.uk/default.php?cmd=210&doc_category=293