Lab Testing - Evaluation of TMT Rebars and Reinforcement Couplers

TCR Engineering Services, based in Mumbai, specializes in the testing and evaluation of TMT (Thermo-Mechanically Treated) rebars and reinforcement couplers. As the construction industry shifts towards modern methodologies, mechanical splicing of reinforcement bars using couplers has emerged as a reliable technique.

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Importance of Mechanical Splicing

Mechanical splicing involves the end-to-end joining of two reinforcement bars using couplers. This technique is particularly advantageous in structures subjected to cyclic loading and where inelastic yielding may occur, such as multi-story buildings and bridges. The use of couplers reduces congestion during concreting, accelerates construction timelines, and ensures a more efficient load transfer between bars. To ensure safety and reliability, the quality of both the couplers and the TMT rebars must be rigorously assessed, considering factors such as material compatibility and construction standards.

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Relevant Standards

TCR Engineering conducts testing in accordance with several established standards, including:

• IS 16172: 2023: This standard outlines the requirements for mechanical splices of reinforcement bars.

• IS 1786: This specifies the requirements for TMT rebars, including their mechanical properties.

• IS 16651:2017: Standards for TMT made of SS material.

• ASTM A1034: This standard specifies the requirements for mechanical splicing of bars.

• ISO 15835-2: This standard covers the testing procedures for mechanical couplers.

• BS 4999: This standard includes guidelines for testing the mechanical properties of reinforcement couplers.

 

Testing Methods and Procedures

TCR Engineering utilizes a variety of testing methods to ensure the integrity and performance of TMT rebars and their couplers:

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TMT Testing - IS 1786:2008

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• Static Tensile Test: Determine the tensile strength and elongation of TMT rebars (Grades Fe 500 D, Fe 415 D/S, up to 45 mm diameter) per IS 1786.

• Bend and Re-Bend Tests: Evaluates ductility and flexibility by bending specimens to specified angles and then straightening to inspect for cracks or failure.

• Spectro/Wet Chemical Analysis: Confirms chemical composition of TMT rebars as per IS 1786 and IS 16651 (for SS materials).
   

Rebar Coupler Testing - IS 16172:2023

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• Static Tensile Test: Evaluates tensile strength on static machines.

• Slip Test: Measures permanent extension post-loading (performed before cyclic testing).

• Cyclic Tensile Test: Evaluates splice behavior under cyclic loads, typically 100 cycles at stress levels from 5% to 90% of yield stress, according to relevant standards, without loss of static tensile strength.

• Low Cycle Fatigue (LCF) Test (10,000 Cycles): Tests endurance under alternating loads of the splice in such a way that they should withstand 10,000 cycles of alternating tension and compression without failure.

• High Cycle Fatigue (HCF) Test (2 million Cycles): Measures durability under extensive cyclic loads with parameters including:

  • Minimum Stress: 30 MPa

  • Maximum Stress: 130-350 MPa

  • Frequency: 3-10 Hz

• Reporting: S-N curve documentation.

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Material Grades and Machines
Common Material Grades: EN8D and 45C8 for rebar couplers.
Equipment: Tests are conducted on advanced machines, static tensile and slip test performed on a static machine and fatigue tests (cyclic, LCF, HCF) on a dynamic machine. Closed-loop servo-hydraulic dynamic UTM machines enable testing frequencies from 0.035 to 30 Hz, ensuring precision and reliability.
 

Coupler Sizes and Standards

TCR conducts rebar coupler testing across diameters from 12 mm to 40 mm, ensuring compatibility with rebar grades like Fe415, Fe500, and Fe550, in compliance with standards such as IS 16172. All tests align with TCR’s NABL accreditation (ISO/IEC 17025:2017), emphasizing the company’s dedication to quality and accuracy.

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TCR Engineering stands at the forefront of material testing for TMT rebars and couplers, ensuring that the structures built using these materials meet the highest safety and performance standards. With over five decades of experience, TCR continues to support the construction industry with rigorous testing protocols, advanced technologies, and adherence to stringent quality standards, solidifying its role as a trusted partner in the field of materials testing.