Rehabilitation and maintenance of buildings - 01
Karel Mikeš
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References Agócs Z.,Ziolko J., Vičan J., Brodniansky J.: Assessment and
Refurbishment of Steel Structures, Spon Press, 2005 Spal L.: Rekonstrukce ocelových konstrukcí (Refurbishment
of Steel Structures), SNTL, Praha, 1968 Refurbishment by steelwork, ArcelorMittal, Luxembourg Vašek M.: Zesilování ocelových konstrukcí (Strengthening of
steel structures), DOS T 3, No. 04, ČKAIT, 2000 Lectures of prof.Macháček to subject YSMK, CTU in Prague,
2009 Háša P., Jeřábek L., Rosenkranz B., Vašek M.: Havárie střechy
kotelny elektrárny Opatovice nad Labem (Collapse of boiler house roof of the power station in Opatovice), Konstrukce No.3, 2004
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Contents Properties of material Failures of steel structures Types of refurbishment Methods of reliability verification Basis of design of steel structures Assessment of steel structures Strengthening of members Strengthening and refurbishment of structures Refurbishment of masonry structures using
steelwork Seismic upgrading using steel structure
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Properties of material Cast iron Wrought iron
since 1785 until 1892 – 1905 after 1905 only exceptionally
Mild steel since 1905
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Cast iron Fragile Suitable for compression, worse for bending High contents of C (2,1%)
Mechanical properties: E ~ 100 000 MPa (N/mm2) fu ~ 120 ÷ 140 MPa
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Wrought iron Production
Temperature 1000oC doughy state Low charge – 200-600 kg Mechanical reduction of undesirable elements
Large scatter of mechanical properties Layered anisotropic structure Local defects
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Wrought iron Chemical composition
Large scatter Lower contents of C High contents of P (phosphorus) – could be
problem
Problems Uncertain weldeability Low strength through thickness Lamelar tearing
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Wrought iron Mechanical properties in rolling direction
E = 180 000 ÷ 200 000 MPa (N/mm2) fy ~ 230 MPa (mean) fu ~ 340 ÷ 370 MPa Lower ductility but still sufficient
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Mild steel Production
Liquid state Larger charges
Since 1905 properties similar to present steel
E = 210 000 MPa fy , fu similar to present S235 (Fe360)
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Properties of material Time of construction Type of material
How to determine: from documentation (rarely)
verification by tests is recommended using tests
Mechanical properties of iron/steel are NOT time depending(except fatigue)
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Contents Properties of material Failures of steel structures Types of refurbishment Methods of reliability verification Basis of design of steel structures Assessment of steel structures Strengthening of members Strengthening and refurbishment of structures Refurbishment of masonry structures using
steelwork Seismic upgrading using steel structure
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Causes of failures of steel structures - phases Errors in design Fabrication, erection Operation
corrosion fatigue high temperature
Additional temperature loading Fire
accidental events
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Causes of failures of steel structures - phenomenons
Underestimation of loading Discrepancy of model and reality Defective or inadequate material Stability of compression members (or beams) Stability of plates Brittle fracture Weak joints Aerodynamics Fatigue
Typically Failure = more than one cause
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Causes of failures of steel structures - phenomenons Discrepancy of model and reality
Wrong selection of details, not correspondng to assumption (fixed/hinged)
Unconsidered eccentricity in joints Different load application points Omitted effects (torsion, secondary moments) Non-considered reduction of cross-section
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Tay bridge 1879 Underestimation of load: wind load not considered Bad material: piers – cast iron, bracing – wrought iron with
slag Train speed 60 km/h instead of 40 km/h
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Tay bridge 1879 Collapse in wind storm with train
75 died
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St. Lawrence, Quebec 1907 Flexural buckling of compression member Underestimation of dead load Errors in the design of joints
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St. Lawrence, Quebec 1907 Collapse in construction stage
86 died
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Hasselt 1937 Brittle fracture
Bad selection of steel Wrong welding process large residual stresses
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Hasselt 1937 Collapse when tram crossed
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Tacoma Narrows 1940 Aerodynamics Suspension bridge, span 853 m New bridge in 1950 Nowadays 2 bridges (2007)
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Tacoma NarrowsAssembly
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Collapse
http://www.youtube.com/watch?v=AsCBK-fRNRk
http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_Collapse
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Collapse due to plate buckling Vienna 1968 Milford Haven (Wales) 1970 West Gate Bridge (Melbourne) 1970
35 died Koblenz (Germany) 1971
Þ Extensive research in 1970‘sÞ New codes with new procedures
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Milford Haven (Wales) 1970
Eccentric load of diaphragm
Imperfections Insufficient stiffening of
diaphragm capacity 50% of
actions 4 died
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Koblenz 1971
Buckling of unstiffened plate 9 died
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Failure of roof at Opatovice power station
Structure from 1957 Main frame:
fixed columns + truss girder, 27,5 m span
Collapse: 11/2002 during reconstruction of
roof snow load
Original documentation: Just part was found Calculations missing
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Failure of roof at Opatovice power station
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Failure of roof at Opatovice power stationCauses
Overloading by dead load Additional layers of concrete, water-proofing layers
Originally under-dimensioned structure Very poor quality of welds Not-functional dilatation detail
Þ collapse of whole roof
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Contents Properties of material Failures of steel structures Types of refurbishment Methods of reliability verification Basis of design of steel structures Assessment of steel structures Strengthening of members Strengthening and refurbishment of structures Refurbishment of masonry structures using
steelwork Seismic upgrading using steel structure
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Reasons for refurbishment of steel structures Malfunction of structure Need of change
Increased loading Bridges Buildings
Change of use Need of free space Bridges – new clear profile
Other reasons, e.g.: local situation (neighbour buildings) war
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Types of refurbishment Strengthening
Strengthening/enlargement of elements/joints Change of static scheme Prestressing Coupling with concrete Indirect strengthening
Restoration/Repair Replacement Extension
Utilization of reserve of structure
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Utilization of capacity reserves of structure Detection and improvement of loading
Pernament loading Climatic loading Service loading
Real material properties More precise calculation
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Utilization of capacity reserves of structureMaterial properties
Tensile tests Real fy, fu
Plastic reserve Bi-linear stress-strain relation MNA – plastic hinges
360 M P a
E = 2 ,1 *E 5 M P a
235
0
100
200
300
0 0 ,05 0 ,1 0 ,15 0 ,2 0 ,25
0 ,03
S tre ss , M P a
S tra in
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Utilization of capacity reserves of structureMore precise calculation Calculation in accordance with
present knowledge present (valid) codes
3D complex models Shell elements
Joints Shell structures (silos, pipelines ...)
Interaction of elements Connections
Semi-rigid connections – new standards enable to determine joint stiffness
Column bases Stochastic methods of the reliability verification