1. Rehabilitation and maintenance of buildings - 01
Karel Mikeš

2. 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

3. 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

4. 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

5. 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

6. SAHC - SA5 Steel structures
2010
Cast iron
Fragile
Suitable for compression, worse for bending
High contents of C (2,1%)
Mechanical properties:
E ~ MPa (N/mm2)
fu ~ 120 ÷ 140 MPa
T.Vraný, CTU in Prague

7. SAHC - SA5 Steel structures
2010
Wrought iron
Production
Temperature  1000oC  doughy state
Low charge – kg
Mechanical reduction of undesirable elements 
Large scatter of mechanical properties
Layered anisotropic structure
Local defects
T.Vraný, CTU in Prague

8. 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

9. SAHC - SA5 Steel structures
2010
Wrought iron
Mechanical properties in rolling direction
E = ÷ MPa (N/mm2)
fy ~ 230 MPa (mean)
fu ~ 340 ÷ 370 MPa
Lower ductility but still sufficient
T.Vraný, CTU in Prague

10. SAHC - SA5 Steel structures
2010
Mild steel
Production
Liquid state
Larger charges
Since 1905 properties similar to present steel
E = MPa
fy , fu similar to present S235 (Fe360)
T.Vraný, CTU in Prague

11. 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

12. 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

13. 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

14. 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

15. 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

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

17. 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

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

19. 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

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

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

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

23. 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

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

25. SAHC - SA5 Steel structures
2010
Collapse 25
T.Vraný, CTU in Prague

26. Collapse due to plate buckling
SAHC - SA5 Steel structures
2010
Collapse due to plate buckling
Vienna
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

27. 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

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

29. 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

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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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