Download presentation
Presentation is loading. Please wait.
Published byGabriella Lewis Modified over 8 years ago
1
Rehabilitation and maintenance of buildings - 01 Karel Mikeš
2
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
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
4 Properties of material Cast iron Wrought iron since 1785 until 1892 – 1905 after 1905 only exceptionally Mild steel since 1905
5
5 Cast iron Fragile Suitable for compression, worse for bending High contents of C (2,1%) Mechanical properties: E ~ 100 000 MPa (N/mm 2 ) f u ~ 120 ÷ 140 MPa
6
6 Wrought iron Production Temperature 1000 o C doughy state Low charge – 200-600 kg Mechanical reduction of undesirable elements Large scatter of mechanical properties Layered anisotropic structure Local defects
7
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
8 Wrought iron Mechanical properties in rolling direction E = 180 000 ÷ 200 000 MPa (N/mm 2 ) f y ~ 230 MPa (mean) f u ~ 340 ÷ 370 MPa Lower ductility but still sufficient
9
9 Mild steel Production Liquid state Larger charges Since 1905 properties similar to present steel E = 210 000 MPa f y, f u similar to present S235 (Fe360)
10
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
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
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
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
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
15 Malfunction of structure Partial collapse Excessive deformations
16
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
17 Tay bridge1879 Collapse in wind storm with train 75 died
18
18 St. Lawrence, Quebec1907 Flexural buckling of compression member Underestimation of dead load Errors in the design of joints
19
19 St. Lawrence, Quebec1907 Collapse in construction stage 86 died
20
20 Hasselt1937 Brittle fracture Bad selection of steel Wrong welding process large residual stresses
21
21 Hasselt1937 Collapse when tram crossed
22
22 Tacoma Narrows1940 Aerodynamics Suspension bridge, span 853 m New bridge in 1950 Nowadays 2 bridges (2007)
23
23 Tacoma Narrows Assembly
24
24 Collapse http://www.youtube.com/watch?v=AsCBK-fRNRk http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_Collapse
25
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
26 Milford Haven (Wales)1970 Eccentric load of diaphragm Imperfections Insufficient stiffening of diaphragm capacity 50% of actions 4 died
27
27 Koblenz1971 Buckling of unstiffened plate 9 died
28
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
29 Failure of roof at Opatovice power station
30
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
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
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
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
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
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
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
Similar presentations
© 2024 SlidePlayer.com Inc.
All rights reserved.