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Rehabilitation and maintenance of buildings - 01

Rehabilitation and maintenance of buildings - 01. Karel Mikeš. References. Errors in the design of structures and modern reconstruction Mechanical properties of cast iron, mild iron and steel at historical structures Causes and analysis of steel structural failures

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Rehabilitation and maintenance of buildings - 01

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  1. Rehabilitation and maintenance of buildings - 01 Karel Mikeš

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

  3. References • Agócs Z., Ziolko J., Vičan 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, ČKAIT, 2000 • Háša P., Jeřábek L., Rosenkranz B., Vašek M.: Collapse of boiler house roof of the power station in Opatovice, Konstrukce No.3, 2004

  4. 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

  5. Properties of material • Cast iron • Wrought iron • since 1785 • until 1892 – 1905 • after 1905 only exceptionally • Mild steel • since 1905

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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)

  11. 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)

  12. 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

  13. Causes of failures of steel structures - phases • Errors in design • Fabrication, erection • Operation • corrosion • fatigue • high temperature • Additional temperature loading • Fire • accidental events

  14. 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

  15. 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

  16. 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

  17. Tay bridge 1879 • Collapse in wind storm with train • 75 died

  18. St. Lawrence, Quebec 1907 • Flexural buckling of compression member • Underestimation of dead load • Errors in the design of joints

  19. St. Lawrence, Quebec 1907 • Collapse in construction stage • 86 died

  20. Hasselt 1937 • Brittle fracture • Bad selection of steel • Wrong welding process  large residual stresses

  21. Hasselt 1937 • Collapse when tram crossed

  22. Tacoma Narrows 1940 • Aerodynamics • Suspension bridge, span 853 m • New bridge in 1950 • Nowadays 2 bridges (2007)

  23. Tacoma NarrowsAssembly 24

  24. Collapse http://www.youtube.com/watch?v=AsCBK-fRNRk http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_Collapse 25

  25. Collapse due to plate buckling • Vienna 1968 • Milford Haven (Wales) 1970 • West Gate Bridge (Melbourne) 1970 • 35 died • Koblenz (Germany) 1971 • Extensive research in 1970‘s • New codes with new procedures

  26. Milford Haven (Wales) 1970 • Eccentric load of diaphragm • Imperfections • Insufficient stiffening of diaphragm  capacity  50% of actions • 4 died

  27. Koblenz 1971 • Buckling of unstiffened plate • 9 died

  28. 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

  29. Failure of roof at Opatovice power station

  30. 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

  31. 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

  32. 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

  33. 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

  34. Utilization of capacity reserves of structure • Detection and improvement of loading • Pernament loading • Climatic loading • Service loading • Real material properties • More precise calculation

  35. Utilization of capacity reserves of structureMaterial properties • Tensile tests • Real fy, fu • Plastic reserve • Bi-linear stress-strain relation • MNA – plastic hinges

  36. 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

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