Rehabilitation and maintenance of buildings - 01

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Rehabilitation and maintenance of buildings - 01

• Karel Mikeš

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References

1. Errors in the design of structures and modern
   reconstruction
2. Mechanical properties of cast iron, mild iron and
   steel at historical structures
3. Causes and analysis of steel structural failures
4. Assessment of load bearing structures and reasons
   for refurbishment of steel structures
5. Overview of codes for design and actions on
   structures
6. Inspections and material testing
7. Introduction of basic methods of reinforcing
   steel
8. Strengthening of individual members subjected to
   axial load (tension, compression) elastic and
   plastic check procedures
9.  Strengthening of individual members subjected to
   bending
10. Strengthening of individual members subjected to
    combination of effects elastic and plastic
    check procedures
11. Strengthening of riveted/bolted/welded
    connections
12. Repair and reconstruction of civil structures

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References

• Agócs Z., Ziolko J., Vican J., Brodniansky J.
  Assessment and Refurbishment of Steel Structures,
  Spon Press, 2005.
• Mazzolani F. Refurbishment by steelwork,
  ArcelorMittal, Luxembourg
• Spal L. Refurbishment of Steel Structures,
  SNTL, Praha, 1968.
• Vašek M. Strengthening of steel structures, DOS
  T 3, No. 04, CKAIT, 2000
• Háša P., Jerábek L., Rosenkranz B., Vašek M.
  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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Malfunction of structure

• Partial collapse
• Excessive deformations

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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?vAsCBK-fRNRk http/
/en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_Colla
pse
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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
• Extensive research in 1970s
• 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
• 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

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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