Elevated Temperature Properties of ASTM A992 Steel

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Elevated Temperature Properties of ASTM A992
Steel

• Presenter Guanyu Hu
• Mohammed Ali Morovat, Jinwoo Lee and Michael D.
  Engelhardt
• The University of Texas at Austin

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Background and objective

• Increasing interest in a performance-based
  approach in building fire safety
• Mechanical properties of ASTM A992 at elevated
  temperatures
• Elevated temperature related properties (Static
  yielding behavior and effect of loading rates)
• First step of full investigation on structural
  steel material characterization at elevated
  temperatures (Future study will include
  compressive behavior and time dependent effect,
  etc)

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Test Equipment

• MTS 810 test frame
• MTS Model 653 furnace
• MTS Model 409.83 temperature controller
• MTS Model 632.54E-11 air-cooled high temperature
  extensometer (1 in gauge length )

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Test Specimens

• Cut from web of W30x99 steel
• girder (ASTM A992)
• Dimensions according to ASTM standard A70

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Test Procedure

• 1. All tests were thermal steady state
• Zero load during the heating process to allow
  free expansion
• 2. All tests were displacement control
• Two crosshead displacement rates 0.01 in/min
  (slow test) and 0.1 in/min (fast test)
• Static yielding and creep effect investigated for
  temperature at 700C

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Temperature Measurement
Problem Significant temperature variation over
the gauge length of the coupon
Solution Furnace control techniques
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Temperature Measurement
Problem Different cross-sectional
temperature reading
Solution Aluminum shield
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Strain Measurement

• Two ceramic rods of the extensometer attach to
  specimen

• Extensometer was reset when it approached the 10
  strain limit during tests.

Engineering stress F/Ainitial
Engineering strain ?L/Linitial
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Test results
Necking and elongation of the coupons
Cross-sections of the coupons at fracture
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I. Stress strain curve
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The full stress-strain curve
0.1 in/min(fast test)
0.01 in/min(slow test)
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Initial portion of stress-strain curve
0.1 in/min(fast test)
0.01 in/min(slow test)
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Comparison to Eurocode 3



500 C
Eurocode
600 C
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II. Strength and modulus
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Strength and modulus reduction factors
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0.2 offset yield strength reduction factors
Stress
0.2 yield strength
0.2
Strain
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0.5 yield strength reduction factors
Stress
0.5 yield strength
0.5
Strain
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2.0 yield strength reduction factors
Stress
2.0 yield strength
2.0
Strain
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Stress-strain curve comparison of 20 C and 400 C
0.2yielding 43 ksi
2yielding 57 ksi
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Ultimate strength reduction factors
Ultimate strength (fu,T/fy,20C)
Ultimate strength (fu,T/fu,20C)
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Reduction factors of elastic modulus and
proportional limit
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III. Effect of loading rate
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Stress-strain curve comparison at two loading
rates
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Static yield phenomenon at elevated temperatures
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Stress relaxation test at 700C
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Constant stress creep test at 700C
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Conclusions

• Testing steel coupons at elevated temperatures
  introduces difficulties that are not encountered
  in ambient temperature testing. Specialized
  equipment is needed and considerable care and
  experience is required
• The properties of A992 steel at elevated
  temperatures are similar with other structural
  steel
• The yield strength of steel at elevated
  temperatures up to about 600 C is highly
  dependent on the manner in which Fy is defined.
  More discussion on which definition of yield
  strength should be used is needed.
• Steel exhibits increasingly significant creep
  effects as temperatures increase and some future
  work is needed to fully characterize the time
  dependent effects on the elevated-temperature
  response of structural steel

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Acknowledgements

• Eric Schell
• Funded by NSF Award 0700682 and NSF Award No.
  CMS-0521086

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Comments and Questions?