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3 Why is this Important? Construction growth implications for rebar: Increased volumes Increased strengths and sizes Increased use of stainless grades Mechanical coupler requirements
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Instron® – A World Leader in Materials Testing
An overview of recent changes and challenges facing rebar manufacturers, suppliers, and consumers
Challenges of Rebar Testing
2
Why Now?• Construction average annual growth rate projections to 2025
*QatarSource: Engineering News-Record
3
Why is this Important?• Construction growth implications for rebar:
• Increased volumes• Increased strengths and sizes• Increased use of stainless grades• Mechanical coupler requirements
4
How Does this Impact You?• Are additional testing systems required to meet increased testing
volumes?• Will a larger testing system (load capacity) be necessary to
accommodate increased strengths and/or sizes?• Can current gripping solutions withstand stainless grades?• Will you need to test mechanical couplers in the future?• Is your testing program prepared for these expected changes?
5
Steel Rebar Applications• Embedded in concrete to improve
tensile strength• Deformations on bar for better
adherence to the concrete• Thermal expansion properties similar
to concrete• Structural shapes formed by bending
rebar
6
Product Standards Linked to Testing Standards
ISO 6892-1 2009ASTM
E8M:2013
ASTM A370Standard Test Methods
and Definitions for Mechanical Testing of
Steel Products
ASTM A615Standard specification for Deformed and Plain Carbon-Steel Bars for
Concrete Reinforcement
ISO 15630-1Steel for the
reinforcement and pre-stressing of concrete –
Test Methods Part 1: Reinforcing bars,
wire rod and wire BS 4449Specification for Carbon
steel bars forthe reinforcement of
concrete
GB 1499Hot rolled ribbed steel
bars for the reinforcement of
concrete
JIS G3112Steel bars for
concrete reinforcement
AC133Mechanical Coupler
Test
Common Rebar and Testing Standards
7
Rebar Testing Challenges
• Violent Tensile Failures
• Irregular and Bent Specimens
• Automatic Tensile Results
• Strain and Elongation Measurement
• Cyclic Testing for Couplers
• Bend Testing
8
Challenge: Irregular Surface• Rebar’s irregular surface geometry and scaling during
elongation present several gripping challenges
9
Gripping Irregular Surface• Application-specific jaw faces
effectively prevent slippage and jaw breaks while still allowing for safe and easy removal of broken test pieces
• Internal components are shielded from falling scale – produced during rebar elongation – that reduces system maintenance costs and possible down time
10
Challenge: Bent Specimens• Rebar specimens are often cut from coiled material
and must be straightened prior to tensile testing. As a result, specimens are not always perfectly straight.
11
Gripping Bent Specimens• Grips accommodate slightly bent
specimens and will overcome small side-loads while still maintaining axial specimen alignment
• No need to reset (re-center) grip jaws between tests improves testing throughput
12
Challenge: Violent Failures• Rebar specimens exhibit violent failures with significant
recoil (up to 60G of acceleration), which can lead to increased system wear.
13
Absorbing High-Energy Release• Robust hydraulic grips and
load frames effectively absorb released energy preventing unwanted damage to the testing system
• Standard system capacities ranging from 300 - 3500 kN (67,500 - 800,000 lbf) easily accommodate any size and grade of rebar
14
Challenge: Measuring Strain• Non-machined rebar specimens require extensometers with
long gauge lengths• Extensometers must be able to attach to the uneven surface of
rebar and maintain contact during elongation• Automatic elongation results require instrument to remain
attached beyond maximum force or even failure
15
Suitable Strain Measurement - Manual
• Securely clamps to the irregular specimen preventing strain errors due to slippage or undesired movement on uneven surface
• Instruments are uniquely identified by testing software that prevents accidental use of the incorrect instrument or gauge length
Manual Clip-On
16
Suitable Strain Measurement - Automatic• Adjustable gauge length accommodates a
wide range of specimen diameters and gauge lengths with a single instrument
• Automatic clamping and release improves operator safety and reduces variability between operators
• Can remain attached through failure allowing for automatic recording of Ag, Agt, and A (Elongation after Fracture).
Automatic Contacting
Link to YouTube Video
17
Automatic Elongation Measurement• Test standards now allow for the automatic
measurement of elongation results from strain data if the testing system is capable
• Using an extensometer that remains attached through peak load and fracture will reduce the need for manually marking the specimen and allows the operator to focus on more value-added activities
18
Challenge: Automatic Test Results• Common test results for rebar include:
• ReH (Upper Yield, Halt of Force, Drop of Beam)
• Rp0.2 (0.2% Proof Strength, Offset Yield)
• Fm (Maximum Force, Peak Load)• Rm (Tensile Strength, Ultimate
Strength)• Ag, Agt (Elongation at Maximum
Force, Uniform Elongation)• A (Percent Elongation after Fracture)
• Historically, many of these results have required manual identification (ReH), measurement (A), or calculation (Ag).
19
Automatic Capture of Test Results• All calculation results can be automatically performed, saving
time and reducing operator and system variability
20
Challenge: Bend Testing• Rebar is frequently bent for use in concrete applications• Test standards require a bend test to determine if
cracks form on the outside of the bend
21
Bend Testing Rebar Effectively
• System testing stroke is long enough to perform entire bend on largest diameters eliminating the need for a separate bend tester
• Dual test space systems allow bend fixtures to remain in the machine during tensile testing, which reduces setup time and operator fatigue from moving heavy fixtures.
22
Challenge: Coupler Testing• Seismic testing couplers for slippage, which is
comprised of 2 pieces of rebar joined by a coupler, requires cycling the specimen
• Tests can be tension-tension cycling only or demand through-zero cycling like the requirements of AC133, CS2, or ISO 15835
Example test stages from AC133:
23
Cycle Testing Mechanical Couplers• High-pressure, side-acting grips provide a positive
clamping force to allow loading in both the tensile and compressive directions
• Testing software allows strain at yield stress to be recorded on initial cycle so it can automatically determine reversal points for remaining test cycles
Does this sound familiar?
Do you see the same challenges in your business?
www.instron.com for more information