Rehabilitation and maintenance of buildings - 02

1. Rehabilitation and maintenance of buildings - 02 Karel Mikeš

2. List oflessons • 1. Errors in the design of structures and modern reconstruction • 2. Mechanical properties of cast iron, mild iron and mildsteel • 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. Objectives of the lecture • Introduction • Historyofusing iron and steel • Castiron • Wroughtiron • Mildsteel • Propertiesofmaterialsfrom ISO 13 822 (Bases for design of structures – Assessment of existing structures) • Historyofjoints - RIVETING • Retrofitting, replacementpossibilities • Case study – Casaratta bridge • Design of replacement • Material tests

4. Introduction • Steel structureshaveanimportant role in civil engineering • Since the end of the 18th century, first cast iron, then wrought steel and finally steelhasincreasingly been used as a construction material. • Gradually, as industrial processesprogressed, various steel products became available, (rolled members, cold-formedelements…). • From the beginning, the fields of application of structural steel material includedstructuressuch as: • - Buildings, • - Bridges (first bridge made of cast iron and built 1777-1779 near Coalbrookdale-UK) • - Industrialplants.

5. Introduction – cont. • Increasingeconomic and ecologicalpressureinfluencestheneedforreconstructionworks and maintenance • Use ofappropriatemethodofrecontructioniskey point ofthewholeprocess • Itisusuallycomplicated to obtain background informationaboutthestructure (materialproperties, static scheme, type ofusedelements, joints, bracingsystem…) • Thisincreasesthefinancing and design responsibilities • Steel structuresprovidethewidestrangeofreconstructionpossibilitiesthantheothermaterials

6. Historyofusingiron and steel • Cast iron • Wrought iron • since 1785 • until 1892 – 1905 • after 1905 onlyexceptionally • Mildsteel • since 1905

7. Cast iron • Fragile • Suitableforcompression, worseforbending • Highcontentsof C (2,1%) • Mechanicalproperties: • E ~ 100 000 MPa (N/mm2) • fu ~ 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 Bridgeinthevillage Ironbridge /renamed by thebridge/ (Shropshire, England)

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

9. Properties of cast iron[1] 1. Lyons, William C. and Plisga, Gary J. (eds.) Standard Handbook of Petroleum & Natural Gas Engineering, Elsevier, 2006; 2. percent, balance being Fe; 3. 0.2% offset, 1000 lb /in²; 4. 1000 lb /in²; 5. in 2 inches, percent; 6. Brinell scale

10. The Fe-C phase diagram

11. Ironbridge

12. 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 Cracked supports Crack and repairs in bridge

13. Coalport– anotherold castiron bridgewas built in 1818

14. 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

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. 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 • 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. 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. It can be used to form temporary magnets, but cannot be magnetized permanently. It fuses with difficulty. It cannot, therefore, be adopted for making castings. It is ductile, malleable and tough. It is moderately elastic. It is less affected by saline water than steel, and resists corrosion better. Its fresh fracture shows clear bluish colour with a high silky luster and fibrous appearance. Its melting point is about 1500 °C. Its specific gravity is about 7.8. Its ultimate compressive strength is about 2000 kgf/cm² (200 MPa). Its ultimate tensile strength is about 4000 kgf/cm² (400 MPa). Properties of wrought iron

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

19. Mild steel • Production • Liquidstate • Largercharges • Since 1905 propertiessimilar to presentsteel • E = 210 000 MPa • fy , fusimilar to present S235 (Fe360) • calledalsoCarbon steel (≤2.1% carbon; low alloy)

20. Properties of material • Timeofconstruction Type ofmaterial • How to determine: • fromdocumentation (rarely) verification by testsisrecommended • usingtests • Mechanicalpropertiesof iron/steel are NOT timedepending(exceptfatigue)

21. FIRST STEEL STRUCTURE - Forth Bridge The Forth Bridge is a cantilever railway bridge over the rivernamedFirth 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 strengthvaluesforsteel

23. Historyofjoints - 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

24. Modern history (18th – 60’s in 20th 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 …Golden Gate Bridge, G. Washington B., Trans Bay B. …

25. Rivetinstallation • Blacksmith riveting – early days of steel construction • Pneumatic hammers and press machines

26. Retrofitting • European bridge data are presented

27. Riveting was used for all bridges built before 1900 (category 100>) • 50% of bridges in category 50–100 years (welding introduced) • At least 23 000 riveted bridges are in service in western Europe Retrofitting

28. Replacementpossibilities • Rivets • Fit bolts • Preload bolts • Lockbolts • Injection bolts

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

30. Replacement possibilities • 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

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 • Replacement possibilities

32. Design of replacement • 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

33. Design of replacement • Lockbolts • Pros: High speed assembly, Tamper resistant, Vibration resistance, High fatigue life, Comparable to preload bolts • Cons: Special installation tool needed, Can’t be removed easily (in case of round collars), Not widespread, Relatively expensive Pintail Breakneck groove Collar Pin Head

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

35. Material test

36. fy,k= 338 MPa; Characteristic yield strength fu = 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 fu = 370 MPa) • American and Czechoslovak codes are both conservative They can be used for repair works with sufficient safety 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 Conclusion

39. Conclusion 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

40. Literature and backgrounds • Kocourek,J – Wald, F.: Retrofitting Of Riveted Shear Connections, powerpointpresentation • Agócs Z.,Ziolko J., Vičan J., Brodniansky J.: Assessment and Refurbishmentof Steel Structures, Spon Press, 2005 • Spal L.: Rekonstrukce ocelových konstrukcí (Refurbishmentof Steel Structures), SNTL, Praha, 1968

41. Thank you for your attention