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Rehabilitation and maintenance of buildings - 02

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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 Objectives of the lecture
SAHC - SA5 Steel structures 2010 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 T.Vraný, CTU in Prague

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 History of using iron and steel
SAHC - SA5 Steel structures 2010 History of using iron and steel Cast iron Wrought iron since 1785 until 1892 – 1905 after 1905 only exceptionally Mild steel since 1905 T.Vraný, CTU in Prague

7 SAHC - SA5 Steel structures
2010 Cast iron Fragile Suitable for compression, worse for bending High contents of C (2,1%) Mechanical properties: E ~ 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 Bridge in the village Ironbridge /renamed by the bridge/ (Shropshire, England) T.Vraný, CTU in Prague

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

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) C 3.4, Si 1.8, Mn 0.5 Cast 25 0.5 180 Engine blocks, fly-wheels, gears, machine-tool bases White C 3.4, Si 0.7, Mn 0.6 450 Malleable iron (ASTM A47) C 2.5, Si 1.0, Mn 0.55 Cast (annealed) 33 52 12 130 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 53 70 18 170 Gears, cams, crankshafts Ductile or nodular iron (ASTM A339) Cast (quench tempered) 108 135 5 310 Ni-hard type 2 C 2.7, Si 0.6, Mn 0.5, Ni 4.5, Cr 2.0 Sand-cast 55 550 Strength Ni-resist type 2 C 3.0, Si 2.0, Mn 1.0, Ni 20.0, Cr 2.5 27 2 140 Resistance 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; 3. 0.2% offset, 1000 lb /in²; 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 – another old cast iron bridge was built in 1818

14 SAHC - SA5 Steel structures
2010 Wrought iron Production Temperature  1000oC  doughy state Low charge – kg Mechanical reduction of undesirable elements Large scatter of mechanical properties Layered anisotropic structure Local defects T.Vraný, CTU in Prague

15 SAHC - SA5 Steel structures
2010 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 T.Vraný, CTU in Prague

16 SAHC - SA5 Steel structures
2010 Wrought iron Mechanical properties in rolling direction E = ÷ 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 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. T.Vraný, CTU in Prague

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. 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 kgf/cm² (200 MPa). Its ultimate tensile strength is about kgf/cm² (400 MPa).

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

19 SAHC - SA5 Steel structures
2010 Mild steel Production Liquid state Larger charges Since 1905 properties similar to present steel E = MPa fy , fu similar to present S235 (Fe360) called also Carbon steel (≤2.1% carbon; low alloy) T.Vraný, CTU in Prague

20 Properties of material
SAHC - SA5 Steel structures 2010 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) T.Vraný, CTU in Prague

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 Bridges on main rail lines are completely replaced nowadays. However, there is a large number of them on secondary lines.

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 First riveted structures occured in ~1830 in Russia …Golden Gate Bridge, G. Washington B., Trans Bay B. …

25 Rivet installation Blacksmith riveting – early days of steel construction Pneumatic hammers and press machines Blacksmith riveting – insufficient quality, labor intensive, low speed of installation, many tampered rivets. The resistance of a rivet was highly dependent on the installation quality. The rivet length was adjusted before insertion into the hole (Fig. 3 in blacksmith riveting).

26 Retrofitting European bridge data are presented

27 Retrofitting Riveting was used for all bridges built before 1900 (category 100>) and it was used until ~1960 (category 50 – 100). Welding was introduced in about 1920 and soon became popular. It’s estimated that 50% of bridges in category 50–100 years are riveted and the second half welded or assembled by different technology. As the result, at least riveted bridges are in service in the Western Europe. 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

28 Replacement possibilities
Rivets Fit bolts Preload bolts Lockbolts Injection bolts There are presented five options for rivet replacement in the work. The advantages and disadvantages are also discussed.

29 Replacement possibilities
Rivets Pros: convenient for historical construction Cons: virtually dead technology, expensive, labor intense, many tempered rivets, high quality demands Cons: High quality demands, High energy consumption, High tamper rate, Special equipment needed

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 The hole dimension tolerance might be only 0.3 mm larger in diameter than the nominal bolt shank diameter

31 Replacement possibilities
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 Per one shear plane

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 resin

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 resin

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
The biggest measured ultimate strength is 482 MPa (specimen 7). On the contrary, the lowest is 405 MPa (specimen 5) which means difference 77 MPa. This difference is very high in comparison with today’s standards. fy,k= 338 MPa; Characteristic yield strength fu = 426 MPa; Ultimate limit strength

37 Material test 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 Method Institution fu,range [MPa] fu,k [MPa] Diff. Tests CTU 405 482 426 0% UM 378 415 11% Codes ČSN - 346 19% AISC 310 386 348 18%

38 Conclusion 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

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 resin

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

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