Paper 9.1 - Steel Innovations Conference 2013 Christchurch-Ver4.pdf

The Performance and Remnant Life of Structural
Steel in an Earthquake Damaged Building
W. G. Ferguson 1 , H. Nashid 2 , G.C. Clifton 3 ,
M V Kral 4 , S. Lopert 5 and G MacRae 6
PART A
W. George Ferguson
Department of Chemical & Materials
Engineering

Pacific Tower
Steel Framed Building
22 Storied
Eccentrically Braced Framed
(EBF) Seismic resisting system

Eccentrically Braced Frame (EBF)
K - Type

Earthquake Resistant Construction
• Steel framed structures performed well during the Christchurch
• Inelastic/plastic deformation was less than predicted
• A design philosophy is to have structural elements (eg. EBFs’)
deforming plastically and absorbing energy
• Some EBFs’ sustained significant plastic deformation
• How much more plastic strain can these elements absorb?
• The question is “to replace the deformed EBF or not to replace the
deformed EBF” that is the question?
• This aspect is examined in the Pacific Tower

Structural Steel
• 153 years since Bessemer set up a Steel Company in Sheffield
• Steel more plentiful, less expensive and available for structures
• Open Hearth method used for higher quality steel
• Electric Arc and Oxygen processes are modern methods
• Late 1800’s, maximum limits for phosphorous, P, & sulphur, S
• Early 1900’s impact tests for toughness in use
• After WWII increased weldability important
• Also need for increased strength, ductility & toughness

Modern Structural Steel
• Strengthening structural steel by
- grain refinement (reduce size)
- solid solution strengthening
- precipitation hardening
• Increase Toughness & reduce Transition Temp. by
- grain size reduction
• These achieved by Al treatment, addition of micro-alloying
elements, Nb, V & Ti together with controlled rolling.

Lamellar Tearing – RBNZ 1974
Sulphur reduction & inclusion shape control
• Beam-Column Joint doubler plate weld doubler plate
•
Weld HAZ Fracture Surface

AS/NZS 3678:2011 Structural Steel (plates & slabs)

Certificate of Analysis and Mechanical Test

Plastic Strain Determination
Determine plastic strain in a deformed Structure
• Strain gauges and extensometers – when deforming
• Digital imaging – no pattern on beam
• Magnetic Barkhausen Noise – not developed
• Hardness Test – material must work harden
- Rockwell & Leeb (portable) Hardness Testers
- Hardness tests show scatter
- Method has established use in Nuclear Industry
- Steel deformed to various plastic strains
hardness measured
hardness correlated with either strain or flow stress

Hardness Technique
Grade 300Mpa steel
Tensile specimens
Plastic strained
Rockwell B hardness

Rockwell B Hardness – Plastic strain
Correlation

EBF – Web Plastic Strain
- testing zones A B, & C
- tensile specimen locations
- hardness test grid pattern for zones A, B & C

Rockwell B versus Grid Numbers
for Zones A, B & C ( Leeb tester)

Hardness versus Normalised Beam Depth
for Zones A, B & C (Rockwell & Leeb testers)
Note: - for zones B & C plastic strain near flanges
- for zone A plastic strain constant across web

Stress – Strain Curves
for zones A, B & C
- tensile test results confirm hardness behaviour
- as received plastic strain near flanges of about 3%
- active link, zone A, plastic strain about 7 – 7.5%

- paint peeled off centre of web
- plastic strain in centre of web
Active Link

Beam X–Section Hardness Traverse
- results Tide 16
- as received plastic strain caused by cold flange straightening

Toughness of Pre-strained Steel
• Steel 310UC158 G300+
Specimens taken from
25mm thick column flanges
• Steel pre-strained in
uni – axial tension
– 4.9%, 9.8% & 17.7%
• Specimens prepared from
pre-strained material for:
Charpy V-Notch CVN,
tensile and CTOD, testing at
various temperatures.
• Naturally Aged for at least
2 months
C Mn Si S P Ni V Nb Ti Al N
0.17 1.47 0.10 0.014 0.017 0.007 0.001 0.001 0.001 0.025 0.0064
Table 1 Mill certificate chemical analysis of 300Plus 310UC158, wt-%

Charpy V – Notch Transition Curves
- effect of plastic prestrain
- transition temperature increases with increasing prestrain

Conclusions
• Need knowledge of Standards & Steel Mill Certificates
• Hardness technique for determining plastic strain is credible
• Portable Leeb hardness tester can give consistent results
• The hardness variations in EBF link confirmed by tensile tests.
• Testing must be done in the centre of the beam web
• There was about 7 – 7.5% plastic strain in the active link beam.
• Pre-existing plastic strain near the flanges produced by low
temperature roll straightening of the flanges - strain was about 3%.
• Steel plastically deformed 7.5% would still just meet 70 J at 0˚C

Thank you

Tensile Properties
-at 10˚C
- significant increase strain aged yield stress
4.9 %
9.8%
17.7%