Rehabilitation and maintenance of buildings - 01 Karel Mikeš

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

Properties of material SAHC - SA5 Steel structures 2010 Properties of material Cast iron Wrought iron since 1785 until 1892 – 1905 after 1905 only exceptionally Mild steel since 1905 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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) T.Vraný, CTU in Prague

Properties of material SAHC - SA5 Steel structures 2010 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) T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

Causes of failures of steel structures - phases SAHC - SA5 Steel structures 2010 Causes of failures of steel structures - phases Errors in design Fabrication, erection Operation corrosion fatigue high temperature Additional temperature loading Fire accidental events T.Vraný, CTU in Prague

Causes of failures of steel structures - phenomenons SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

Malfunction of structure SAHC - SA5 Steel structures 2010 Malfunction of structure Partial collapse Excessive deformations T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 Tay bridge 1879 Collapse in wind storm with train 75 died T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 St. Lawrence, Quebec 1907 Flexural buckling of compression member Underestimation of dead load Errors in the design of joints T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 St. Lawrence, Quebec 1907 Collapse in construction stage 86 died T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 Hasselt 1937 Brittle fracture Bad selection of steel Wrong welding process  large residual stresses T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 Hasselt 1937 Collapse when tram crossed T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 Tacoma Narrows 1940 Aerodynamics Suspension bridge, span 853 m New bridge in 1950 Nowadays 2 bridges (2007) T.Vraný, CTU in Prague

Tacoma Narrows Assembly SAHC - SA5 Steel structures 2010 Tacoma Narrows Assembly 24 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 Collapse http://www.youtube.com/watch?v=AsCBK-fRNRk http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_Collapse 25 T.Vraný, CTU in Prague

Collapse due to plate buckling SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 Milford Haven (Wales) 1970 Eccentric load of diaphragm Imperfections Insufficient stiffening of diaphragm  capacity  50% of actions 4 died T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 Koblenz 1971 Buckling of unstiffened plate 9 died T.Vraný, CTU in Prague

Failure of roof at Opatovice power station SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

Failure of roof at Opatovice power station SAHC - SA5 Steel structures 2010 Failure of roof at Opatovice power station T.Vraný, CTU in Prague

Failure of roof at Opatovice power station Causes SAHC - SA5 Steel structures 2010 Failure of roof at Opatovice power station Causes 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 T.Vraný, CTU in Prague

SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

Reasons for refurbishment of steel structures SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

Types of refurbishment SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

Utilization of capacity reserves of structure SAHC - SA5 Steel structures 2010 Utilization of capacity reserves of structure Detection and improvement of loading Pernament loading Climatic loading Service loading Real material properties More precise calculation T.Vraný, CTU in Prague

Utilization of capacity reserves of structure Material properties SAHC - SA5 Steel structures 2010 Utilization of capacity reserves of structure Material properties Tensile tests Real fy, fu Plastic reserve Bi-linear stress-strain relation MNA – plastic hinges T.Vraný, CTU in Prague

Utilization of capacity reserves of structure More precise calculation SAHC - SA5 Steel structures 2010 Utilization of capacity reserves of structure More 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 T.Vraný, CTU in Prague