Rehabilitation and maintenance of buildings - 01 Karel Mikeš

2 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

3 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

4 Properties of material  Cast iron  Wrought iron  since 1785  until 1892 – 1905  after 1905 only exceptionally  Mild steel  since 1905

5 Cast iron  Fragile  Suitable for compression, worse for bending  High contents of C (2,1%)  Mechanical properties:  E ~ MPa (N/mm 2 )  f u ~ 120 ÷ 140 MPa

6 Wrought iron  Production  Temperature  1000 o C  doughy state  Low charge – kg  Mechanical reduction of undesirable elements   Large scatter of mechanical properties  Layered anisotropic structure  Local defects

7 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

8 Wrought iron  Mechanical properties in rolling direction  E = ÷ MPa (N/mm 2 )  f y ~ 230 MPa (mean)  f u ~ 340 ÷ 370 MPa  Lower ductility but still sufficient

9 Mild steel  Production  Liquid state  Larger charges  Since 1905 properties similar to present steel  E = MPa  f y, f u similar to present S235 (Fe360)

10 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)

11 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

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

13 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

14 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

15 Malfunction of structure  Partial collapse  Excessive deformations

16 Tay bridge1879  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 bridge1879  Collapse in wind storm with train  75 died

18 St. Lawrence, Quebec1907  Flexural buckling of compression member  Underestimation of dead load  Errors in the design of joints

19 St. Lawrence, Quebec1907  Collapse in construction stage  86 died

20 Hasselt1937  Brittle fracture  Bad selection of steel  Wrong welding process  large residual stresses

21 Hasselt1937  Collapse when tram crossed

22 Tacoma Narrows1940  Aerodynamics  Suspension bridge, span 853 m  New bridge in 1950  Nowadays 2 bridges (2007)

23 Tacoma Narrows Assembly

24 Collapse

25 Collapse due to plate buckling  Vienna1968  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 Koblenz1971  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 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

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 structure Material properties  Tensile tests  Real f y, f u  Plastic reserve  Bi-linear stress-strain relation  MNA – plastic hinges

36 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