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Mechanical splicing of reinforcement steel


As we know, the reinforcement steel length is limited. For long structural members, the reinforcement steel bars should be overlapped or spliced to produce the required length of reinforcement. Mechanical splicing of reinforcement is used widely in the construction industry. Threaded couplers are a widespread type of mechanical splicing. Threaded couplers are sub-categorized into taper and parallel threaded couplers. The cross-section and length of the coupler will depend on the grade of the reinforcement rebar.

Taper Threaded Couplers: in taper threaded couplers, the threaded on the rebar is carried out at a slight incline. The threads of coupler and rebar should be kept at the same slope to ensure the engagements of all threads simultaneously in the coupler joint. Taper threaded coupler is the simplest type of threaded coupler. This type of coupler can be used for columns and horizontal applications. But it is difficult to in rafts or other applications where it is difficult to turn and tighten the rebars. In general, the length of taper threaded couplers is more than parallel couplers. Taper threaded couplers are designed, taking into ac­count defects of the rebar such as undersizing, skewness, and oblongness of the rebar. 


Figure 1

Roll Threaded Couplers: roll threaded coupler is a type of parallel threaded coupler where the threads are formed by pressing the rebar end by a set of rollers. The end of the rebar should be cut vertically before threading as there is no allowance for additional threads inside the couplers. Tightening the rebar and coupler will require more turns due to parallel threads. This system will take more time for installation compared to the taper threading coupler system. This system can be used for vertical and horizontal applications such as columns and rafts. 


Figure 2


Cold Forged Couplers/Upset Parallel Threaded Couplers: in this type of couplers, the end of rebars are enlarged by 10-30% by hydraulic pressure before cutting parallel threads on the enlarged rebar ends. This type of coupler is suitable for vertical and horizontal applications. The installation of cold-forged couplers will take a longer time compared to tapered threading coupler due to parallel threads. Used steel should possess sufficient ductility to prevent the formation of microcracks during the enlarging process of the end of rebars. Precautions that are needed for cold-forged couplers include ensuring that there is no play between the threads formed in this process and the coupler. Gauges are used to provide tolerance of the threads in such cases. It is vital. 

Figure 3

Non-Threaded Couplers: There are various sub-types of non-threaded couplers, which are used mainly for the installation of couplers in loca­tion where it is not possible to use threaded couplers or for specialized applications. This category includes but is not limited to crimple/swage couplers, welded couplers, Bolted couplers, couplers with injected sleeves, friction-weld cou­plers.

Using mechanical splice can offer various advantages such as:

  • Reinforcement bars spliced by couplers will act as a continuous bar. Unlike the lapping of reinforcement, overlapped rebars will act dependently inside the concrete. Using the coupler will eliminate the errors due to provide a smaller overlapping or the reduction of overlapping due to using of reduced concrete strength of concrete segregation.
  • Reduce steel wastage by saving the lap length.
  • Using steel coupler can reduce steel congestion, which prevents the formation of honeycombs in casted concrete.
  • It is possible to easily verify joint strength in the case of Cou­plers as compared to lap splices where the testing is cumbersome and not regulated.

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