Rehabilitation and maintenance of buildings - 01

Karel Mikeš

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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

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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

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Properties of material Cast iron Wrought iron

since 1785 until 1892 – 1905 after 1905 only exceptionally

Mild steel since 1905

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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

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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

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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

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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

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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)

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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)

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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

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Causes of failures of steel structures - phases Errors in design Fabrication, erection Operation

corrosion fatigue high temperature

Additional temperature loading Fire

accidental events

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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

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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

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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

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Tay bridge 1879 Collapse in wind storm with train

75 died

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

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St. Lawrence, Quebec 1907 Collapse in construction stage

86 died

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Hasselt 1937 Brittle fracture

Bad selection of steel Wrong welding process large residual stresses

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Hasselt 1937 Collapse when tram crossed

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

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Tacoma NarrowsAssembly

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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 Vienna 1968 Milford Haven (Wales) 1970 West Gate Bridge (Melbourne) 1970

35 died Koblenz (Germany) 1971

Þ Extensive research in 1970‘sÞ 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 1971

Buckling of unstiffened plate 9 died

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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

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Failure of roof at Opatovice power station

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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

Þ collapse of whole roof

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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

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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

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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

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Utilization of capacity reserves of structure Detection and improvement of loading

Pernament loading Climatic loading Service loading

Real material properties More precise calculation

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Utilization of capacity reserves of structureMaterial properties

Tensile tests Real fy, fu

Plastic reserve Bi-linear stress-strain relation MNA – plastic hinges

360 M P a

E = 2 ,1 *E 5 M P a

235

0

100

200

300

0 0 ,05 0 ,1 0 ,15 0 ,2 0 ,25

0 ,03

S tre ss , M P a

S tra in

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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