Rehabilitation and maintenance of buildings - 02

Karel Mikeš

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

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Objectives of the lecture Introduction History of using iron and steel Cast iron Wrought iron Mild steel Properties of materials from ISO 13 822 (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

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 1777-

1779 near Coalbrookdale -UK) - Industrial plants.

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

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History of using iron and steel 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

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)

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Cast iron

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

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Properties of cast iron[1]

NameNominal

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

Cast — 25 0 450 —

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

Cast 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

Cast — 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; 4. 1000 lb /in²; 5. in 2 inches, percent; 6. Brinell scale

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The Fe-C phase diagram

Ironbridge

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

Coalport – another old cast iron bridge was built in 1818

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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

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.

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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 2000 kgf/cm² (200 MPa). Its ultimate tensile strength is

about 4000 kgf/cm² (400 MPa).

Iron pillar of Delhi built at the time of Chandragupta Vikramaditya (375–413 n.l)

Eiffel Tower (designer Gustave Eiffel)

The tower was built as the entrance arch to the 1889 World's Fair.

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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) called also Carbon steel (≤2.1% carbon;

low alloy)

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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)

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.

Characteristic and design strength values for steel

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

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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

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…Golden Gate Bridge, G. Washington B., Trans Bay B. …

Rivet installation

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Blacksmith riveting – early days of steel construction

• Pneumatic hammers and press machines

European bridge data are presented

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Retrofitting

0%

10%

20%

30%

40%

50%

60%

49%

19%

32%

Rehabilitation Strengthening Reconstruction

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

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Retrofitting

< 20 20 – 50 50 – 100 100 >05

1015202530354045

10

22

40

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Age

perc

en

tag

e [

%]

Replacement possibilities

Rivets

Fit bolts

Preload bolts

Lockbolts

Injection bolts

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Rivets• Pros: convenient for historical construction• Cons: virtually dead technology, expensive, labor intense,

many tempered rivets, high quality demands

Replacement possibilities

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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

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

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Replacement possibilities

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

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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

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HeadPinCollarBreakneckgroove

Pintail

Design of replacement

Material test

Seven rivets extracted from 98 years old bridge near Karlovy Vary

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35

4

X X2022

10 4 10 22

5013 50 to 75

Material test

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fy,k= 338 MPa; Characteristic yield strength

fu = 426 MPa; Ultimate limit strength

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

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Method Institution fu,range [MPa] fu,k [MPa] Diff.

TestsCTU 405 482 426 0%

UM 378 415 378 11%

CodesČSN - - 346 19%

AISC 310 386 348 18%

Material test

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

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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 replacement39

Conclusion

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

Thank you for your attention

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