1 / 48

Rehabilitation and maintenance of buildings - 01

Rehabilitation and maintenance of buildings - 01. Karel Mikeš. List of lessons. 1. Errors in the design of structures and modern reconstruction 2. Mechanical properties of cast iron, mild iron and mild steel 3. Causes and analysis of steel structural failures

albin
Télécharger la présentation

Rehabilitation and maintenance of buildings - 01

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Rehabilitation and maintenance of buildings - 01 Karel Mikeš

  2. List oflessons • 1. Errors in the design of structures and modern reconstruction • 2. Mechanical properties of cast iron, mild iron and mild steel • 3. Causes and analysis of steel structural failures • 4. Assessment of bearing struct. and reasons for refurbishment • 5. Overview of codes for design and actions on structures • 6. Inspections and material testing • 7. Introduction of basic methods of reinforcing steel structures • 8. Strengthening of individual members subjected to axial load 9. Strengthening of individual members subjected to bending • 10. Strengthening of members subjected to combinations • 11. Strengthening of riveted/bolted/welded connections • 12. Repair and reconstruction of civil structures

  3. Objectives of the lecture Errors in the design of structures and modern reconstruction • Introduction • History • Basic terms • Principlesof the design • Assessmentofstructures

  4. Causesoffailures of steel structures - phases • Errors in design errors in theconceptional design ofthestructure errors in thedocumentation (calculations…) wrongselectionofconstructionalmaterials erros in solutionofconstructionaldetails wrongcalculation model (differentfromtherealbehaviour) • Fabrication, erection • Operation • corrosion • fatigue • hightemperature • Additionaltemperatureloading • Fire • accidentalevents

  5. 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

  6. 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

  7. 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

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

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

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

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

  12. Hasselt 1937 • Collapse when tram crossed

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

  14. Tacoma NarrowsAssembly 15

  15. Collapse http://www.youtube.com/watch?v=AsCBK-fRNRk http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_Collapse 16

  16. 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

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

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

  19. 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

  20. Failure of roof at Opatovice power station

  21. 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

  22. 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

  23. Refurbishmentofsteelstructurescanbedividedinto: • Reinforcement • Renovation • Extension • Replacement • Relocation • Specialarrangements • Utilizationofreserveofstructure

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

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

  26. 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

  27. Reinforcement • Reinforcement = adaptation to recoveroperationalfeatures; increaseloadingcapacity, reliability and serviceabilityofthestructure • Direct reinforcement – reinforced and reinforcing part constituteoneloadbearing element • Indirectreinforcement – reinforced and reinforcing part are constituted by separateloadbearingelements

  28. Renovation • = arrangement ofstructuralpartsorthewholestructureafterextraordinaryevents and accidents Extension • = extensionofanexistingsectionofthestructure Replacement • = replacestheoriginalstructureor a section by a newstructurelinked to anexisting layout

  29. Relocation • = a part oftheoriginalstructureorentireoriginalstructure are moved to another place Specialarrangements • Indirectreinforcing • Changes to the static system • Prestressing • Couplingwithconcrete • Reinstalationofthestrustureforotheruses

  30. Assesmentofsteelstructuresforrefurbishment • In designingtherefurbismentofanexistingstructureweshouldfollowthepresentvalidstandards and regulations • Previouslyvalidstandardscan serve only as informative background • Mustbeprovidedexaminationofthe reliability oftheoriginalstructure • First step = substandardanalysisofthesuitabilityofunsuitabilityofthestructureforthereconstruction; structuresunsuitableforthereconstructionwhenreplacement by thenewstructureisrecomendedinclude:

  31. Structuressignificantlydamaged by impactorexplosion • Structurestotallydamamgedordistorted by highteperatureduring a fire • Structurestotallycorroded • Structuresforwhichtheconditionofstressesorthehistoryofactingvariableloadingcannotbereliablydetermined • Structuresofwrought iron and otherlow-qualitymaterial (exeptofrarehistoricalstructuires) • Structuresforwhichis not possible to obtainnecessaryresultsofassessingexaminations (takingintoaccountthelevelofacceptablecostsforexaminingtheexistingloadbearingsystem

  32. Proposalforreconstruction – structuremustbeexamined to establish: • Theconditionofthestructure as a whole • Propertiesofusedmaterials • Loadsthataffectthestructureorhaveaffectedstructure in the past • The influence oftheenvironment on thestructure • Documentationofthestructure

  33. Introduction • Steel structureshaveanimportant role in civil engineering • Since the end of the 18th century, first cast iron, then wrought steel and finally steelhasincreasingly been used as a construction material. • Gradually, as industrial processesprogressed, various steel products became available, (rolled members, cold-formedelements…). • From the beginning, the fields of application of structural steel material includedstructuressuch as: • - Buildings, • - Bridges (first bridge made of cast iron and built 1777-1779 near Coalbrookdale-UK) • - Industrialplants.

  34. Introduction – cont. • Increasingeconomic and ecologicalpressureinfluencestheneedforreconstructionworks and maintenance • Use ofappropriatemethodofrecontructioniskey point ofthewholeprocess • Itisusuallycomplicated to obtain background informationaboutthestructure (materialproperties, static scheme, type ofusedelements, joints, bracingsystem…) • Thisincreasesthefinancing and design responsibilities • Steel structuresprovidethewidestrangeofreconstructionpossibilitiesthantheothermaterials

  35. Historyofusingiron and steel • Cast iron • Wrought iron • since 1785 • until 1892 – 1905 • after 1905 onlyexceptionally • Mildsteel • since 1905

  36. Characteristic and design strengthvaluesforsteel

  37. Cast iron • Fragile • Suitableforcompression, worseforbending • Highcontentsof C (2,1%) • Mechanicalproperties: • E ~ 100 000 MPa (N/mm2) • fu ~ 120 ÷ 140 MPa • Cast iron bridges • The use of cast iron for structural purposes began in the late 1770s, when Abraham Darby III built the Iron Bridgeinthevillage Ironbridge /renamed by thebridge/ (Shropshire, England)

  38. Ironbridge

  39. Just a few years after the construction of the bridge, cracks were appearing in the masonry abutments, caused by ground movement. Some of the present-day cracks in the cast iron may date from this time, although others are probably casting cracks Cracked supports Crack and repairs in bridge

  40. Coalport– anotherold castiron bridgewas built in 1818

  41. 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

  42. 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

  43. 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

  44. Iron pillar of Delhibuiltat the time of Chandragupta Vikramaditya (375–413n.l) Eiffel Tower (designer Gustave Eiffel) The tower was built as the entrance arch to the 1889 World's Fair.

  45. Mild steel • Production • Liquidstate • Largercharges • Since 1905 propertiessimilar to presentsteel • E = 210 000 MPa • fy , fusimilar to present S235 (Fe360) • calledalsoCarbon steel (≤2.1% carbon; low alloy)

  46. Properties of material • Timeofconstruction Type ofmaterial • How to determine: • fromdocumentation (rarely) verification by testsisrecommended • usingtests • Mechanicalpropertiesof iron/steel are NOT timedepending(exceptfatigue)

  47. FIRST STEEL STRUCTURE - Forth Bridge The Forth Bridge is a cantilever railway bridge over the rivernamedFirth of Forth in the east of Scotland, to the east of the Forth Road Bridge, and 14 kilometres west of central Edinburgh. It was opened on 4 March 1890.

  48. References • Agócs Z.,Ziolko J., Vičan J., Brodniansky J.: Assessment and Refurbishmentof Steel Structures, Spon Press, 2005 • Spal L.: Rekonstrukce ocelových konstrukcí (Refurbishmentof Steel Structures), SNTL, Praha, 1968 • Refurbishment by steelwork, ArcelorMittal, Luxembourg • Vašek M.: Zesilování ocelových konstrukcí (Strengtheningofsteelstructures), DOS T 3, No. 04, ČKAIT, 2000 • Lecturesof prof. Macháček to subject YSMK, CTU in Prague, 2009 • Háša P., Jeřábek L., Rosenkranz B., Vašek M.: Havárie střechy kotelny elektrárny Opatovice nad Labem (Collapseof boiler house roofofthepower station in Opatovice), Konstrukce No.3, 2004

More Related