Presentation on theme: "Rehabilitation and maintenance of buildings - 02"— Presentation transcript:
1 Rehabilitation and maintenance of buildings - 02 Karel Mikeš
2 List of lessons1. Errors in the design of structures and modern reconstruction2. Mechanical properties of cast iron, mild iron and mild steel3. Causes and analysis of steel structural failures4. Assessment of bearing struct. and reasons for refurbishment5. Overview of codes for design and actions on structures6. Inspections and material testing7. Introduction of basic methods of reinforcing steel structures8. Strengthening of individual members subjected to axial load 9. Strengthening of individual members subjected to bending10. Strengthening of members subjected to combinations11. Strengthening of riveted/bolted/welded connections12. Repair and reconstruction of civil structures
3 Objectives of the lecture SAHC - SA5 Steel structures2010Objectives of the lectureIntroductionHistory of using iron and steelCast ironWrought ironMild steelProperties of materials from ISO (Bases for design of structures – Assessment of existing structures)History of joints - RIVETINGRetrofitting, replacement possibilitiesCase study – Casaratta bridgeDesign of replacementMaterial testsT.Vraný, CTU in Prague
4 IntroductionSteel structures have an important role in civil engineeringSince 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 maintenanceUse of appropriate method of recontruction is key point of the whole processIt 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 responsibilitiesSteel structures provide the widest range of reconstruction possibilities than the other materials
6 History of using iron and steel SAHC - SA5 Steel structures2010History of using iron and steelCast ironWrought ironsince 1785until 1892 – 1905after 1905 only exceptionallyMild steelsince 1905T.Vraný, CTU in Prague
7 SAHC - SA5 Steel structures 2010Cast ironFragileSuitable for compression, worse for bendingHigh contents of C (2,1%)Mechanical properties:E ~ MPa (N/mm2)fu ~ 120 ÷ 140 MPaCast iron bridgesThe 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 ironCast 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 NameNominal compositionForm and conditionYield strengthTensile strengthElongationHardnessUsesCast grey iron (ASTM A48)C 3.4, Si 1.8,Mn 0.5Cast—250.5180Engine blocks, fly-wheels, gears, machine-tool basesWhiteC 3.4, Si 0.7,Mn 0.6450Malleable iron (ASTM A47)C 2.5, Si 1.0,Mn 0.55Cast (annealed)335212130Axle bearings, track wheels, automotive crankshaftsDuctile or nodular ironC 3.4, P 0.1,Mn 0.4, Ni 1.0,Mg 0.06537018170Gears, cams, crankshaftsDuctile or nodular iron (ASTM A339)Cast (quench tempered)1081355310Ni-hard type 2C 2.7, Si 0.6,Mn 0.5, Ni 4.5,Cr 2.0Sand-cast55550StrengthNi-resist type 2C 3.0, Si 2.0,Mn 1.0, Ni 20.0, Cr 2.5272140Resistance to heat and corrosion1. 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
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 cracksCracked supportsCrack and repairs in bridge
13 Coalport – another old cast iron bridge was built in 1818
14 SAHC - SA5 Steel structures 2010Wrought ironProductionTemperature 1000oC doughy stateLow charge – kgMechanical reduction of undesirable elementsLarge scatter of mechanical propertiesLayered anisotropic structureLocal defectsT.Vraný, CTU in Prague
15 SAHC - SA5 Steel structures 2010Wrought ironChemical compositionLarge scatterLower contents of CHigh contents of P (phosphorus) – could be problemProblemsUncertain weldeabilityLow strength through thickness Lamelar tearingT.Vraný, CTU in Prague
16 SAHC - SA5 Steel structures 2010Wrought ironMechanical properties in rolling directionE = ÷ MPa (N/mm2)fy ~ 230 MPa (mean)fu ~ 340 ÷ 370 MPaLower ductility but still sufficientCommercially 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 2010Mild steelProductionLiquid stateLarger chargesSince 1905 properties similar to present steelE = MPafy , 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 structures2010Properties of materialTime of construction Type of materialHow to determine:from documentation (rarely)verification by tests is recommendedusing testsMechanical properties of iron/steel are NOT time depending (except fatigue)T.Vraný, CTU in Prague
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 constructionThey ensure tight fit connection with no slipMany riveted bridges are still in service and their replacement is uneconomicalRetrofitting of riveted connections to improve remaining service lifeRecommend possibilities for rivet replacementBridges 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. rivetsFirth of Forth Bridge- built in 1890 in steel- over 8 mil. rivetsFirst riveted structures occured in ~1830 in Russia…Golden Gate Bridge, G. Washington B., Trans Bay B. …
25 Rivet installationBlacksmith riveting – early days of steel constructionPneumatic hammers and press machinesBlacksmith 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).
27 RetrofittingRiveting 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 RivetsFit boltsPreload boltsLockboltsInjection boltsThere are presented five options for rivet replacement in the work. The advantages and disadvantages are also discussed.
29 Replacement possibilities RivetsPros: convenient for historical constructionCons: virtually dead technology, expensive, labor intense, many tempered rivets, high quality demandsCons: High quality demands, High energy consumption, High tamper rate, Special equipment needed
30 Replacement possibilities Fit boltsPros: Easy bolt removal and inspectionCons: Expensive drilling machines , Difficult to drill a hole with such accuracy, Labor intense, Slip, Low vibration resistanceThe hole dimension tolerance might be only 0.3 mm larger in diameter than the nominal bolt shank diameter
31 Replacement possibilities Preload boltsPros: Low labor intense, Very stiff, resistance to alternating forces, good performance under fatigue loading, tamper resistant, no special tool requiredCons: Re-torquing, Not suitable for slippy surfacesPer 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 corrosionCons: Preparation of bolts, washers and resin, Dismantling, Prizeresin
33 Design of replacement Lockbolts Pros: High speed assembly, Tamper resistant, Vibration resistance, High fatigue life, Comparable to preload boltsCons: Special installation tool needed, Can’t be removed easily (in case of round collars), Not widespread, Relatively expensivePintailBreakneckgrooveCollarPinHeadresin
34 Material testSeven rivets extracted from 98 years old bridge near Karlovy Vary
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 strengthfu = 426 MPa; Ultimate limit strength
37 Material testResults were compared to tests found in literature and structural codesTested 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 safetyMethodInstitutionfu,range [MPa]fu,k [MPa]Diff.TestsCTU4054824260%UM37841511%CodesČSN-34619%AISC31038634818%
38 ConclusionThe 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 serviceIncreasing traffic demandsReplacement of all riveted bridges is not possibleNowadays, more than half of the budget for the development of infrastructure in Europe is for maintenance and modernization of the existing infrastructure
39 ConclusionAll suggested replacement possibilities except fit bolts can be successfully used for rivet replacement. However, each of them is suitable for different conditionsRivets should be always used on historical structuresPreload bolts are convenient in most casesLockbolts are suitable for replacement of high number of rivetsInjection bolts have very high resistance and durabilityFit bolts are not suitable for rivet replacementresin
40 Literature and backgrounds Kocourek,J – Wald, F.: Retrofitting Of Riveted Shear Connections, powerpoint presentationAgócs Z.,Ziolko J., Vičan J., Brodniansky J.: Assessment and Refurbishment of Steel Structures, Spon Press, 2005Spal L.: Rekonstrukce ocelových konstrukcí (Refurbishment of Steel Structures), SNTL, Praha, 1968