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Rehabilitation and maintenance of buildings - 02 Karel Mikeš.

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Presentation on theme: "Rehabilitation and maintenance of buildings - 02 Karel Mikeš."— Presentation transcript:

1 Rehabilitation and maintenance of buildings - 02 Karel Mikeš

2 List of lessons 1. Errors in the design of structures and modern reconstruction 2. Mechanical properties of cast iron, mild iron and mild steel 3. Causes and analysis of steel structural failures 4. Assessment of bearing struct. and reasons for refurbishment 5. Overview of codes for design and actions on structures 6. Inspections and material testing 7. Introduction of basic methods of reinforcing steel structures 8. Strengthening of individual members subjected to axial load 9. Strengthening of individual members subjected to bending 10. Strengthening of members subjected to combinations 11. Strengthening of riveted/bolted/welded connections 12. Repair and reconstruction of civil structures

3 3 Objectives of the lecture Introduction History of using iron and steel Cast iron Wrought iron Mild steel Properties of materials from ISO (Bases for design of structures – Assessment of existing structures) History of joints - RIVETING Retrofitting, replacement possibilities Case study – Casaratta bridge Design of replacement Material tests

4 Introduction Steel structures have an important role in civil engineering Since the end of the 18th century, first cast iron, then wrought steel and finally steel has increasingly been used as a construction material. Gradually, as industrial processes progressed, various steel products became available, (rolled members, cold-formed elements…). From the beginning, the fields of application of structural steel material included structures such as: - Buildings, - Bridges (first bridge made of cast iron and built near Coalbrookdale -UK) - Industrial plants.

5 Introduction – cont. Increasing economic and ecological pressure influences the need for reconstruction works and maintenance Use of appropriate method of recontruction is key point of the whole process It is usually complicated to obtain background information about the structure (material properties, static scheme, type of used elements, joints, bracing system…) This increases the financing and design responsibilities Steel structures provide the widest range of reconstruction possibilities than the other materials

6 6 History of using iron and steel Cast iron Wrought iron since 1785 until 1892 – 1905 after 1905 only exceptionally Mild steel since 1905

7 7 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 Cast iron bridges The use of cast iron for structural purposes began in the late 1770s, when Abraham Darby III built the Iron Bridge in the village Ironbridge /renamed by the bridge/ (Shropshire, England)Abraham Darby IIIIron BridgeIronbridgeShropshireEngland

8 8 Cast iron Cast iron usually refers to grey cast iron, but identifies a large group of ferrous alloys, which solidify with a eutectic.grey cast ironferrousalloyseutectic

9 9 Properties of cast iron [1] Name Nominal composition [2] Form and condition Yield strength [3] Tensile strength [4] Elongation [5] Hardness [6] Uses Cast grey iron (ASTM A48)ASTM C 3.4, Si 1.8, Mn 0.5 Cast Engine blocks, fly-wheels, gears, machine-tool bases White C 3.4, Si 0.7, Mn 0.6 Cast Malleable iron (ASTM A47) C 2.5, Si 1.0, Mn 0.55 Cast (annealed) Axle bearings, track wheels, automotive crankshafts Ductile or nodular iron C 3.4, P 0.1, Mn 0.4, Ni 1.0, Mg 0.06 Cast Gears, cams, crankshafts Ductile or nodular iron (ASTM A339) Cast (quench tempered) Ni-hard type 2 C 2.7, Si 0.6, Mn 0.5, Ni 4.5, Cr 2.0 Sand-cast55550Strength Ni-resist type 2 C 3.0, Si 2.0, Mn 1.0, Ni 20.0, Cr 2.5 Cast272140Resistance to heat and corrosion 1. Lyons, William C. and Plisga, Gary J. (eds.) Standard Handbook of Petroleum & Natural Gas Engineering, Elsevier, 2006; 2. percent, balance being Fe; % offset, 1000 lb /in²; lb /in²; 5. in 2 inches, percent; 6. Brinell scaleBrinell scale

10 10 The Fe-C phase diagram

11 Ironbridge

12 Crack and repairs in bridge Cracked supports Just a few years after the construction of the bridge, cracks were appearing in the masonry abutments, caused by ground movement. Some of the present-day cracks in the cast iron may date from this time, although others are probably casting cracks

13 Coalport – another old cast iron bridge was built in 1818

14 14 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

15 15 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

16 16 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 Commercially pure iron, having a very small carbon content (not more than 0.15 percent), but usually containing some slag. It is tough, malleable, and ductile and is easily welded. However, it is too soft for blades and the cutting edges of swords.

17 17 Properties of wrought iron The fibers in wrought iron give it properties not found in other forms of ferrous metal. Hammering a piece of wrought iron cold causes the fibers to become packed tighter, which makes the iron both brittle and hard. Furthermore, wrought iron cannot be bent as sharply as steel, for the fibers can spread and weaken the finished work. It becomes soft at white heat and it can be easily forged and welded.white heatforgedwelded It can be used to form temporary magnets, but cannot be magnetized permanently.magnets It fuses with difficulty. It cannot, therefore, be adopted for making castings.castings It is ductile, malleable and tough.ductilemalleabletough It is moderately elastic.elastic It is less affected by saline water than steel, and resists corrosion better.saline watercorrosion Its fresh fracture shows clear bluish colour with a high silky luster and fibrous appearance.fibrous Its melting point is about 1500 °C.melting point Its specific gravity is about 7.8.specific gravity Its ultimate compressive strength is about 2000 kgf/cm² (200 MPa).compressive strengthkgf/cm²MPa Its ultimate tensile strength is about 4000 kgf/cm² (400 MPa).tensile strength

18 Iron pillar of Delhi built at the time of Chandragupta Vikramaditya (375–413 n.l) Chandragupta Vikramaditya Eiffel Tower (designer Gustave Eiffel) The tower was built as the entrance arch to the 1889 World's Fair.

19 19 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) called also Carbon steel (2.1% carbon; low alloy)

20 20 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)

21 FIRST STEEL STRUCTURE - Forth Bridge The Forth Bridge is a cantilever railway bridge over the river named Firth of Forth in the east of Scotland, to the east of the Forth Road Bridge, and 14 kilometres west of central Edinburgh. It was opened on 4 March 1890.

22 Characteristic and design strength values for steel

23 History of joints - RIVETING Rivets were the most commonly used fastener in the early days of steel construction They ensure tight fit connection with no slip Many riveted bridges are still in service and their replacement is uneconomical Retrofitting of riveted connections to improve remaining service life Recommend possibilities for rivet replacement 23

24 Modern history (18 th – 60s in 20 th century) First riveted structures in Russia (~1830) Eiffel tower -built in 1889 in wrought iron -2,5 mil. rivets Firth of Forth Bridge -built in 1890 in steel -over 8 mil. rivets 24 …Golden Gate Bridge, G. Washington B., Trans Bay B. …

25 Rivet installation 25 Blacksmith riveting – early days of steel construction Pneumatic hammers and press machines

26 European bridge data are presented 26 Retrofitting

27 Riveting was used for all bridges built before 1900 (category 100>) 50% of bridges in category 50–100 years (welding introduced) At least riveted bridges are in service in western Europe 27 Retrofitting

28 Replacement possibilities Rivets Fit bolts Preload bolts Lockbolts Injection bolts 28

29 29 Rivets Pros:convenient for historical construction Cons:virtually dead technology, expensive, labor intense, many tempered rivets, high quality demands Replacement possibilities

30 30 Fit bolts Pros:Easy bolt removal and inspection Cons:Expensive drilling machines, Difficult to drill a hole with such accuracy, Labor intense, Slip, Low vibration resistance Replacement possibilities

31 Preload bolts Pros: Low labor intense, Very stiff, resistance to alternating forces, good performance under fatigue loading, tamper resistant, no special tool required Cons:Re-torquing, Not suitable for slippy surfaces 31 Replacement possibilities

32 Injection bolts Pros: Oversized or slotted holes, Compact connections, No slip in case of overload, requirements for contact surface, internal corrosion Cons: Preparation of bolts, washers and resin, Dismantling, Prize 32 Design of replacement

33 Lockbolts Pros: High speed assembly, Tamper resistant, Vibration resistance, High fatigue life, Comparable to preload bolts Cons: Special installation tool needed, Cant be removed easily (in case of round collars), Not widespread, Relatively expensive 33 HeadPinCollarBreakneck groove Pintail Design of replacement

34 Material test Seven rivets extracted from 98 years old bridge near Karlovy Vary 34

35 35 Material test

36 36 f y,k = 338 MPa; Characteristic yield strength f u = 426 MPa; Ultimate limit strength

37 Results were compared to tests found in literature and structural codes Tested rivets were made of better quality steel than the producer declared (10370 steel with f u = 370 MPa) American and Czechoslovak codes are both conservative They can be used for repair works with sufficient safety 37 MethodInstitutionf u,range [MPa]f u,k [MPa]Diff. Tests CTU % UM % Codes ČSN % AISC % Material test

38 The purpose of the work in this thesis was to give general information about riveting and to investigate the rivet replacement possibilities. Many riveted bridges are still in service Increasing traffic demands Replacement of all riveted bridges is not possible Nowadays, more than half of the budget for the development of infrastructure in Europe is for maintenance and modernization of the existing infrastructure 38 Conclusion

39 All suggested replacement possibilities except fit bolts can be successfully used for rivet replacement. However, each of them is suitable for different conditions Rivets should be always used on historical structures Preload bolts are convenient in most cases Lockbolts are suitable for replacement of high number of rivets Injection bolts have very high resistance and durability Fit bolts are not suitable for rivet replacement 39 Conclusion

40 Literature and backgrounds Kocourek,J – Wald, F.: Retrofitting Of Riveted Shear Connections, powerpoint presentation 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

41 Thank you for your attention 41


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