ASTM A1061, A416 Multi-Wire Steel Prestressing Strand Tensile Elongation Test

Information on the most widely used ASTM standards within the materials testing industry

Descriptions of the most prominent lSO standards within the materials testing industry

Standards including EN, DIN, JlS, and more

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ASTM A1061/A1061M : Standard Test Methods for Testing Multi-Wire Steel Prestressing Strand

ASTM A416/A416M: Standard Specification for Low-Relaxation, Seven-Wire Steel Strand for Prestressed Concrete

ASTM A1061 test methods describe procedures for testing the mechanical properties of multi-wire steel prestressing strand. It are intended for use in evaluating specific strand properties prescribed in specifications for multi-wire steel prestressing strand, but they do not quantify acceptance criteria specified in the applicable specification for the strand being tested. The breaking strength and elongation of the strand are determined by one or more tensile tests in which fracture of the specimen ideally occurs in the free span. ASTM A1061 tensile test for breaking elongation stress relaxation on steel wire deals with the standard types and grade requirements of seven-wire, uncoated steel strands for use in the construction of pre-tensioned and post-tensioned pre-stressed concrete.

Overview and Relationship:

ASTM A416/A416M is the material specificationfor "Steel Strand, Uncoated Seven-Wire for Prestressed Concrete." It defines the chemical, mechanical, and dimensional requirements for the strand itself (the product). It states whatproperties must be met (e.g., minimum tensile strength) and whichtest methods to use.

ASTM A1061/A1061M is the test method standardfor "Testing Multi-Wire Steel Strand for Pre-Stressed and Post-Tensioned Concrete." It provides the detailed, standardized procedures for howto perform the mechanical tests (like tension an elongation) on the strand.

In generally: A strand manufacturer uses ASTM A1061 to test their product to prove it conforms to the requirements of ASTM A416.

Kinds of test for ASTM A1061, A416 Multi-Wire Steel Prestressing Strand:

Static Tensile

The steel strand undergoes elongation until it fractures. Steel strands are composed of multiple wires twisted together, and they tend to untwist when subjected to tensile loads.

Throughout the tensile test, both the force applied to the specimen and its elongation are measured. Testing machines designed for high test loads are predominantly utilized because prestressing steel is a high-strength steel.

Dynamic Tests

In the high cycle fatigue test on steel strands, the specimen must withstand two million test cycles at a maximum frequency of 20 Hz without fracturing.

specimen fractures near or in the grip, the test is considered invalid and needs to be repeated. Invalid tests are very costly, as the fatigue test lasts several days. Prestressing steel strands, being highly stiff, are particularly sensitive to notching.

Steel Strands Relaxation Test

Relaxation test of steel strands is a test to measure the degree of deformation of steel strands after long-term stable loading.

In this test, the steel strand first needs to be subjected to a constant load to ensure that it reaches a "steady state".

After being subjected to a certain amount of load for a certain period of time, measuring the elongation generated by the steel strand can determine its performance under that load.

This experiment can simulate actual usage conditions, thereby more accurately evaluating the service life and safety performance of steel strands.

ASTM A1061, A416 Multi-Wire Steel Prestressing Strand Tensile Elongation Test

Big length jaws for steel strand

(length 150mm, width 120mm)

Steel strand fixture used on

the universal testing machine

Jaws for 9.5, 11.10, 12.7,

15.2, 17.8mm steel strand

ASTM A1061/A1061M: Test Methods for Multi-Wire Steel Prestressing Strand:

This standard specifies procedures to determine yield strength, breaking strength, elongation at fracture, stress relaxation properties, and elastic modulus of multi-wire steel prestressing strand. It is used to evaluate properties required by product specifications like ASTM A416.

Test Method	Purpose	Key Parameters
Monotonic Tension Test	Measures yield strength, breaking strength, and elongation	Loading rate: 1.0–10 MPa/s (145–1450 psi/s) up to yield; post-yield per ASTM E8/E8M
Yield Strength Determination	Measures the load at 1% extension under load (specific to strand)	Preload: 10% of minimum breaking strength; attach extensometer, adjust to 0.1% gauge length, load to total 1.0% extension
Elongation Test	Measures total elongation at fracture	Gauge length: 500 mm (20 in) for strand ≤15.2 mm (0.60 in); 750 mm (30 in) for larger diameters
Stress Relaxation Test	Evaluates loss of stress under constant strain over time	Temperature: 23 ± 2°C (73.4 ± 3.6°F); initial stress: 70% of minimum breaking strength; duration: 1000 hours minimum
Elastic Modulus Test	Determines the modulus of elasticity.	Load between 10–40% of minimum breaking strength; calculate from stress-strain curve slope

ASTM A1061 Specimen Composition & Preparation

Material: Multi-wire steel prestressing strand (typically seven-wire, uncoated) matching the product specification.

Length: Sufficient to allow gripping and gauge length (minimum 600 mm / 24 in for 500 mm gauge length).

Preparation: No mechanical damage (bending, abrasion, nicking) before/during testing; avoid excessive heating during specimen collection. Accurately mark the original gauge length (L₀) on the parallel section of the specimen using a dotting machine or a scriber.

Number of Specimens: Minimum 3 specimens per test batch.

Main Testing Equipmen and Fixture:
Universal Testing Machine: Must have sufficient tonnage (usually 1000 kN or above) with an accuracy level of no less than grade 1.
Extensometer (speccial): Used for accurately measuring deformation within the gauge length, it is a key device for determining specified plastic elongation strength and elastic modulus. Contact or non-contact types (video extensometers) are commonly used.

ASTM A1061, A416 Multi-Wire Steel Prestressing Strand Tensile Elongation Test

Fixtures: Specialized wedge-type fixtures for steel strands. The design of the fixtures is crucial and must ensure that the steel strands neither slip nor break prematurely during tensile testing.

Gauge Marking Equipment: Used to mark the original gauge length on the specimen.

ASTM A1061: Test Method for Steel Strand:

Tension Test	Purpose: To determine the ultimate tensile strength, yield strength at 1% extension (EL1.0%), and total elongation.
	Test Specimen: A straight length of strand. The ends are often "socketed" (potted in metal cones with zinc or a resin) to prevent slippage and jaw breaks in the wedge grips of the testing machine.
	Procedure: The specimen is mounted in a universal testing machine. An extensometer is attached to a 24-inch (610 mm) gauge length within the straight section to measure elongation. The strand is loaded continuously until it fractures. The load at the 1.0% extension under load is recorded as the yield strength. The maximum load achieved is recorded as the tensile strength. The total elongation (plastic + elastic) over the 24-inch gauge length at fracture is measured.
Relaxation Test	Purpose: To measure the strand's loss of stress (relaxation) under constant length and temperature over time—a critical property for long-term performance of prestressed concrete.
	Test Specimen: A length of strand long enough to be anchored in a specialized relaxation testing frame, typically several feet long.
	Procedure: The specimen is mounted in a frame and loaded to an initial force (a specified percentage of its actualtensile strength, typically 70% or 80%). The length of the test frame is locked (held constant). The specimen is held in a controlled temperature environment (20°C ± 2°C / 70°F ± 3.6°F) for 1000 hours. As the metal micro-creeps, the force in the strand drops. The force is monitored periodically. The percentage loss of the initial force after 1000 hours is calculated as the relaxation value.

ASTM A416/A416M: Low-Relaxation, Seven-Wire Steel Strand for Prestressed Concrete:

This product specification covers two grades (Grade 250 [1725] and Grade 270 [1860]) of low-relaxation, seven-wire, uncoated steel strand for use in prestressed concrete construction. It defines acceptance criteria for mechanical properties, which are tested per ASTM A1061.

ASTM A416/A416M mandates testing per ASTM A1061/A1061M for the following properties:

Property	Acceptance Criteria	Test Method (A1061)
Breaking Strength	Grade 250: ≥250 ksi (1725 MPa); Grade 270: ≥270 ksi (1860 MPa)	Monotonic Tension Test
Yield Strength	≥90% of breaking strength (for low-relaxation strand)	Yield Strength at 1% Extension
Elongation	≥3.5% for Grade 250; ≥3.0% for Grade 270 (500 mm gauge length)	Elongation at Fracture
Stress Relaxation	≤2.5% stress loss after 1000 hours at 70% of breaking strength	Stress Relaxation Test
Bond Strength	Average pull force from six tests ≥8000 lbf (35.6 kN); individual minimum ≥6800 lbf (30.2 kN)	ASTM A981/A981M (separate bond test)

Test Specimen Requirements (per A416/A416M referencing A1061):

Material: Seven-wire, uncoated, low-relaxation steel strand matching Grade 250 or 270

Sampling: Random samples from each production lot (lot size defined by manufacturer)

Specimen Dimensions: Same as A1061 requirements (minimum length for gauge length + gripping)

Preparation: Same as A1061—no damage, proper handling to preserve mechanical properties.

In General Comparison of ASTM A1061 and ASTM A416:

Feature	ASTM A416 (Material Spec)	ASTM A1061 (Test Method)
Primary Role	Defines the product requirements for steel strand.	Defines the laboratory procedures to test that strand.
Key Contents	Grades, diameters, chemical limits, minimum strength/elongation values, maximum relaxation loss.	Step-by-step instructions for performing tension tests, relaxation tests, and bond tests.
Test Specimen	Specifies required properties and general gauge length (24 in).	Details specimen preparation (e.g., socketing), exact gauge length marking, and extensometer attachment.
Output	A product that can be certified as "ASTM A416 Grade 270."	A test report with measured values (e.g., "Tensile Strength = 275 ksi").

UnitedTest Steel strand tensile testing machine can perform tension test for the steel strand, 7-wire strand for the reinforcement and prestressing of concrete, reinforcing bars, wire rod and wires.

United Test make Universal Testing Machines are known for their long lasting trouble-free performance and highest quality material used in the manufacturing process. The Hydraulic universal testing machine can perform tension, compression, flexure/bending and shearing test for kinds of specimens. Suitable for metal and nonmetal material, such as iron, steel, steel bar, rebar, cement, concrete, rod and so on. Specially design for production, research, student training and industrial laboratory. Available in wide range of loadframe capacities (300kN to 2000kN)/(10Ton to 200Ton) and with combination of control panels (Digital, Computerized) makes United Test product range suitable for every customer requirement.

Steel Strand Extensometer is a high-precision electronic instrument specifically designed for measuring the deformation (strain) of steel strands, prestressed tendons, and similar elongated specimens during tensile tests.

Steel Strand tensile stress relaxation testing machine made by UNITEDTEST, adopt servo control, computer data collection and processing, close loop control and high precision measuring. Consist of frame, servo control system, measuring system, test fixture etc., max. load is 500KN.

UnitedTest UT1027 Video extensometer, is a non-contact real-time high-precision strain measurement system, which is based on a separate camera and real-time image processing algorithm, by taking images of the experimental process, analyzing image characteristic changes, dynamically measuring the strain changes of the specimen, accurately and quickly realizing the functions of traditional extensometers.

1, Abnormal Fracture Location:
When the fracture is less than 20mm from the fixture face, check for the following:
1.1, Uneven clamping force: asynchronous wedge block movement causing unilateral stress concentration
1.2, Specimen bending: fracture risk increases by 57% when straightness deviation >1mm/m
1.3, Jaw contamination: oil reduces friction coefficient μ < 0.15 (standard requires μ ≥ 0.2)

2, Force Fluctuations:
When hydraulic system pressure pulsation >0.5% (ISO 7500-1:2018), it can cause:
Yield point determination errors up to ±15MPa
Solution: Increase accumulator damping, keep oil temperature at 40 ± 5℃

3, Extensometer Slippage:
Clamping extensometers tend to slip when strain >2%; using a non-contact type can reduce abnormal data rate to below 0.3%.

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