Transcript steel.fsv.cvut.cz

Rehabilitation and maintenance
of buildings - 01
Karel Mikeš
References
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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
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Contents
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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
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Properties of material
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Cast iron
Wrought iron
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since 1785
until 1892 – 1905
after 1905 only exceptionally
Mild steel
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since 1905
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Cast iron
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Fragile
Suitable for compression, worse for bending
High contents of C (2,1%)
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Mechanical properties:
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E ~ 100 000 MPa (N/mm2)
fu ~ 120 ÷ 140 MPa
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Wrought iron
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Production
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Temperature  1000oC  doughy state
Low charge – 200-600 kg
Mechanical reduction of undesirable elements
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Large scatter of mechanical properties
Layered anisotropic structure
Local defects
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Wrought iron
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Chemical composition
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Large scatter
Lower contents of C
High contents of P (phosphorus) – could be problem
Problems
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Uncertain weldeability
Low strength through thickness  Lamelar tearing
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Wrought iron
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Mechanical properties in rolling direction
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E = 180 000 ÷ 200 000 MPa (N/mm2)
fy ~ 230 MPa (mean)
fu ~ 340 ÷ 370 MPa
Lower ductility but still sufficient
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Mild steel
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Production
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Liquid state
Larger charges
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Since 1905 properties similar to present steel
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E = 210 000 MPa
fy , fu similar to present S235 (Fe360)
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Properties of material
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Time of construction  Type of material
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How to determine:
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from documentation (rarely)
verification by tests is recommended
using tests
Mechanical properties of iron/steel are NOT time
depending
(except fatigue)
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Contents
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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
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Causes of failures of steel structures phases
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Errors in design
Fabrication, erection
Operation
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corrosion
fatigue
high temperature
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Additional temperature loading
Fire
accidental events
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Causes of failures of steel structures - phenomenons
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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
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Typically Failure = more than one cause
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Causes of failures of steel structures - phenomenons
Discrepancy of model and reality
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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
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Tay bridge
1879
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Underestimation of load: wind load not considered
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Bad material: piers – cast iron, bracing – wrought iron with slag
Train speed 60 km/h instead of 40 km/h
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Tay bridge
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1879
Collapse in wind storm with train
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75 died
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St. Lawrence, Quebec 1907
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Flexural buckling of compression member
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Underestimation of dead load
Errors in the design of joints
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St. Lawrence, Quebec 1907
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Collapse in construction stage
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86 died
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Hasselt 1937
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Brittle fracture
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Bad selection of steel
Wrong welding process  large residual stresses
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Hasselt 1937
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Collapse when tram crossed
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Tacoma Narrows 1940
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Aerodynamics
Suspension bridge, span 853 m
New bridge in 1950
Nowadays 2 bridges (2007)
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Tacoma Narrows
Assembly
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Collapse
http://www.youtube.com/watch?v=AsCBK-fRNRk
http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_Collapse
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Collapse due to plate buckling
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Vienna
1968
Milford Haven (Wales)
1970
West Gate Bridge (Melbourne) 1970
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35 died
Koblenz (Germany)
1971
 Extensive
research in 1970‘s
 New codes with new procedures
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Milford Haven (Wales) 1970
Eccentric load of diaphragm
 Imperfections
 Insufficient stiffening of
diaphragm
 capacity  50% of actions
 4 died
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Koblenz
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1971
Buckling of unstiffened plate
9 died
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Failure of roof at Opatovice power station
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Structure from 1957
Main frame:
fixed columns + truss girder,
27,5 m span
Collapse: 11/2002
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during reconstruction of roof
snow load
Original documentation:
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Just part was found
Calculations missing
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Failure of roof at Opatovice power station
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Failure of roof at Opatovice power station
Causes
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Overloading by dead load
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Additional layers of concrete, water-proofing layers
Originally under-dimensioned structure
Very poor quality of welds
Not-functional dilatation detail
 collapse
of whole roof
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Contents
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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
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Reasons for refurbishment of steel
structures
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Malfunction of structure
Need of change
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Increased loading
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Change of use
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Bridges
Buildings
Need of free space
Bridges – new clear profile
Other reasons, e.g.:
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local situation (neighbour buildings)
war
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Types of refurbishment
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Strengthening
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Strengthening/enlargement of elements/joints
Change of static scheme
Prestressing
Coupling with concrete
Indirect strengthening
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Restoration/Repair
Replacement
Extension
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Utilization of reserve of structure
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Utilization of capacity reserves of structure
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Detection and improvement of loading
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Pernament loading
Climatic loading
Service loading
Real material properties
More precise calculation
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Utilization of capacity reserves of structure
Material properties
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Tensile tests
 Real fy, fu
Plastic reserve
 Bi-linear stress-strain relation
 MNA – plastic hinges
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Stress, MPa
300
360 MPa
235
200
0,03
100
E = 2,1 *E5 MPa
Strain
0
0
0,05
0,1
0,15
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0,2
0,25
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Utilization of capacity reserves of structure
More precise calculation
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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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