Technical Specification of Bar coupler for reinforcement

Lapped joints are not always an appropriate means of connecting reinforcing bars. The use of laps can be time consuming in terms of design and installation and can lead to greater congestion within the concrete because of the increased amount of rebar used.

Couplers can simplify the design and construction of reinforced concrete and reduce the amount of reinforcement required. Lapped joints are dependent upon the concrete for load transfer. There are several manufacturers producing various types of couplers available in market. The main system for transferring load is by:

 Threaded couplers
 Swaged couplers
 Bolted sleeve couplers
 Combination of the above three types

Swaged type requires the coupler to be pressed onto the bar in
a factory. Each bar requires to be tested after swaging and hence the procedure is cumbersome.

Bolted type is less popular and there are doubts about its performance.

Threaded couplers are of two types, namely, parallel treaded and
tapered threaded. This specification recommends and shall cover the
requirements of threaded couplers, both, parallel and tapered.

References IS Codes you may find in our IS Codes Section

IS 456 Plain and Reinforced Concrete – Code of Practice
IS 1786 High strength deformed steel bars and wires for concrete
reinforcement – specifications
IS 2062 Hot Rolled Low, Medium and High Tensile Structural Steel

Testing

Chemical Properties:

The couplers shall be tested for chemical content by ladle analysis and finished product analysis as per IS 228 or ASTM A 751. The chemical composition shall be in accordance to the code to which the coupler metallurgy and its grade complies

Physical Properties:

The couplers shall have a defined minimum yield strength and tensile strength.The same shall be established using bars of strength higher than the couplers. The tests shall be done in accordance to IS 1786, IS 1608 and IS 2062 or as per ASTM A

The couplers shall satisfy the following requirements:
 The tensile strength of the coupler sleeve shall be more than that of rebars. When the rebar splice assembly with coupler is tested, the failure should occur by snapping of rebar outside the coupler.

 When the rebar splice assembly with coupler is tested, the total permanent elongation after loading to 0.6 times the specified yield stress of the bar shall not be more than 0.1mm.

 Couplers which have been tested and established for use with Grade 60 of ASTM A 706 bars may be used for Fe 415 and Fe 415D bars conforming to IS 1786

Inspection, Identification & Delivery

The supply of material, inspection & testing shall conform to IS 1387. Material shall not be dispatched from manufacturer’s or supplier’s premises prior to it being cleared by purchaser or his authorised representative/ TPIA.

The manufacturer shall provide the purchaser a test certificate duly signed by him mentioning that all the chemical and physical tests as stipulated herein have been carried out on the batch to be purchased and that all the material conforms to the codal provisions and is fit for use for the intended purpose.

Couplers tested after delivery if found not satisfying the requirements stipulated herein and the referred codes are liable to rejection. All the couplers shall have its name, type and other such identification marks permanently embossed on it. Each delivered
batch shall have:

 Description of the coupler system, dimensions, designations and material
specifications
 Certificates of acceptance by recognised/ BIS or International code
accredited institutes
 Relevant test certificate with sample identification, test date and duly
signed
 Tagging indicating material origin and production batch

 Chemical composition
 Diameter, length, thickness and thread properties
 Compatible threading and cold forging machine
 Rebar grade and diameter
 Installation procedure: It shall typically include the following:
 Cold forging treatment giving the forging process, amount of increase in bar diameter, length of cold forging for each bar diameter.

 Thread type, pitch, length and taper if any
 Colour/ code marking on couplers & their description
 Length upto which the bar should be engaged inside the couplers and permissible gap between the bars inside the couplers.
 Tightening/ torque requirement