University of Minho Czech Technical University in Prague University of Padova Technical University...

University of Minho Czech Technical University in Prague

University of Padova Technical University of Catalonia ARCCHIP- ITAM

300 mm

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250 mm250 mm

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500 mm

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Perfil HEM140Localização do antigo soalho 250 mm

Localização das novas vigas secundárias em castanho

Investigation of the Use of Iron in Construction from Antiquity to the Technical Revolution

Anastasios Drougas

Universitat Politècnica de Catalunya

Department of Construction Engineering

Barcelona, Spain

[email protected]

Contents

1. Introduction2. History of the Use of Iron in Construction and Restoration3. Iron in Ancient Greek Architecture4. Material Properties5. Material Identification6. Deterioration7. Inspection8. Repair and Maintenance9. Case Study – The Parthenon10. Conclusions

A. Drougas – Investigation of the Use of Iron in Construction from Antiquity to the Technical Revolution

History of the Use of Iron in Construction and Restoration


• Alloy Types• Historical Production Techniques• Application Typologies in Construction• Extent of Use and Examples• Iron as a Restoration Material• Further Aspects of Iron Production and Use


• Transition from meteoric to terrestrial iron Iron Age c. 2000BC

• First iron type to be manufactured

• Largely replaces copper

Wrought Iron


Wrought Iron – Production Techniques

• Smelting in bloomeries

• Introduction of coke

• Osmond process

• Finery Process

• Puddling + Rolling

• Clamps and dowels in masonry


Wrought Iron – Structural Uses

• Connections in timber



• Gothic architecture



• Reinforcement of masonry assemblies



• Riveted wrought iron members




• First produced in China 6th century BC

• Introduced in Europe 13th century AD

Cast Iron

• Smelting in presence of phosphorus

• Chinese puddling

• Water powered bellows

• Blast furnace


Cast Iron – Production Techniques

• Arched bridges and aqueducts


Cast Iron – Structural Uses



• Columns, piers and beams



• Skeletal structures


Steel• Produced as early as wrought iron

• Much more expensive and time consuming to produce

• Wrought iron was preferred as a structural material


Steel – Production Techniques

• Smelting in bloomeries• Melting of wrought with cast iron• Cementation process• Bessemer process• Open-hearth process


Steel – Structural Uses

• Mixed systems with wrought or cast iron

• Replacement of wrought iron in all applications


Iron as a Restoration Material - Historical Applications

• Tension ties in arches – Replacement of timber ties• Crack bridging in masonry with clamps• Bracing and repair of timber members and trusses• Mechanical pinning• Fire proofing of textile mills• Strengthening of cast iron bridges with wrought iron

or steel girders• Historically, opinions of experts clash


Iron as a Restoration Material - Modern Applications

• Its use encouraged in steel frames and R.C. rebars by the Athens Charter (1931)

• Criticized by the Venice Charter (1964)


Iron as a Restoration Material - Modern Applications

• Confining straps in adobe• Tension ties in brick and stone masonry• Steel connection plates in timber trusses• Bracing trusses in damaged R.C. structures• Temporary bracing


Further Aspects of Iron Production and Use• Production rates• Production cost• New structural needs• Grasp of material properties• Design and analysis methods• Building methods and construction management• Development of structural systems• Attained spans and heights• Rapid development in all fields

Historical Application ExampleAncient Greek Architecture


• Introduction of iron to Greek territory

• Production techniques

• Application typologies

• Development of applications

• Structural role

• Iron as a restoration material


Introduction of Iron to Greek Territory

• Forceful import from the East (Caucasus) after the 11th century

• Rapid development after 7th century; possible influence from central Europe

• Indications of knowledge of rudimentary heat welding and iron alloy casting


Iron Production Tecniques

• Advanced form of smelting for items of high quality


Iron in Ancient Greek Architecture

• Horizontal connections• Vertical connection• Structural reinforcement• Various minor uses


Horizontal Connection


Vertical Connection


Structural Reinforcement


Structural Role of Iron in Ancient Greek Architecture

• Relieves stresses from stone blocks• Prevents overall structural movement• Allows greater spans• Reduces self weight of superstructure• Prevents relative movement of stone blocks

during construction and in the final setup• Stressed near its elastic limit


Experimental and Numerical Investigation

• Mainly associated with restoration projects• Verification of design approaches for structural

intervention• Restoration of tensile connecting elements often

reduces risk of collapse• Dowel influence in joint strength is often very

small


Iron in Historic Restoration of Ancient Greek Architecture

• Ancient practices only partially followed in restoration of connecting elements



• Use of iron frames and rebars in R.C.



• Resulted in further damage, loss of architectural fabric and structural authenticity

• Main problems caused by corrosion and mechanical strain

• Iron use influenced by contemporary construction practices in building engineering


Iron in Modern Restoration of Ancient Greek Architecture

• Largely replaced by other materials, such as titanium, FRP and stainless steel

• Restoration projects focus on removal of corroded iron

• Minor applications include temporary bracing with steel frames and confinement


Properties of Iron

• General properties of each alloy• Effect of properties in every alloy’s adoption

for specific historical structural uses


Wrought Iron

• Orthotropic behaviour, high strength Replaces timber in several applications

• Properties depend on raw material and shaping process

• Strength is more consistent than ductility• May have superior corrosion resistance than that

of steel


Cast Iron

• Strong in compression, weak in tension Replaces masonry in several applications

• High fire resistance Used for fireproofing of industrial buildings

• High corrosion resistance


Steel

• Isotropic behaviour, high strength and elastic modulus, production methods produce different batches of highly consistent properties Has replaced all other iron alloys in construction

• May corrode easily• Properties require careful chemical control

during production, carbon content is the chief parameter


Material Identification

• Visual inspection and historical knowledge• Member typologies• Spark test• Breaking test

• Microstructure investigation• Chemical testing


Historical Iron Deterioration

• % of affected material Electrochemical>Chemical>Mechanical

• Development Speed Mechanical>Chemical>Electrochemical

• Frequency Electrochemical>Mechanical>Chemical

• Biological deterioration usually aggravates corrosion

• Iron deterioration greatly affects neighbouring historical materials


Historical Iron Inspection

• Historical data often available

• Historical testing techniques Percussion, spark test, liquid penetrant method, hardness test, tension test, impact test


Historical Iron Deterioration

• Historical data often available

• Historical testing techniques Percussion, spark test, liquid penetrant method, hardness test, tension test, impact test


Historical Iron Repair & Maintenance

• Historical MethodsReplacement & complementingCold repair of members, mixing of alloysProtective coatings: painting, electroplating, Bower-

Barff methodCathodic protection

• Modern methodsCompatibility established by chemical methodsMild steelWeldingPassivation layer


Case Study – The Parthenon

• Structural layout and brief historical overview• Description of connecting element types• Pathology of connecting elements• Restoration of connecting elements• Restorations incorporating iron


Structural layout and brief historical overview


Description of connecting element types

• Clamps and dowels



• Placement along the length of the stone assemblies



• Sufficient tension anchoring area



• Investigation to determine mechanical properties



• Structural function Invisible substitute for mortar Prevent small movement during placement Clamps also work in shear and dowels also work in tension Dynamic loads on assemblies cause such deformations that

clamps primarily function in shear and not in tension Relative displacements are larger in horizontal joints; dowels are

more stressed than clamps


Pathology of Connecting Elements

• Corrosion



• Forced removal and loss



• Mechanical failure


Stone Pathology due to Iron

• Stone fails first in shear


Restoration of Iron Elements

• Historical efforts Iron/lead ratio larger than in original structureLonger tension elements usedJoints not securely closedMechanical pinning


Restoration of Iron Elements• Modern efforts

Iron replaced by titaniumDesigned according to Ultimate State philosophyElements fail after anchoring areaMaterial ductility Elements function when deformed


Iron in Restoration of the Monument• Joining of fragmented stones with iron clamps• Mechanical pinning• Rebars in R.C. anchored in original marble• Stainless steel rejected in modern efforts


Conclusions • Chemical compatibility is satisfactory, new material is appropriate• Mechanical properties of material for intended function are

appropriate• Marginal understanding of structural function when restoration was

compiled, only on a local level and not on the structure as a whole• ULS without safety level assessment• Experimental and numerical approaches have not completely

verified design approach• Restoration of iron elements may perpetuate the deterioration

mechanisms it aims to remedy• Elements do not contribute to preservation of architectural or

structural authenticity• Contribution of elements to safety against earthquake action is null

for some assemblies, such as walls• A rethinking of the design and execution approach for connecting

elements is necessary

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