Reinforcement Coupler for mechanical Splices of Bars in Concrete
What is Reinforcement Coupler ?
Rebar coupler creates couplers joint between reinforcing bars to connect together , whose bar ends are in contact and parallel.
Benefits of Mechanical Splices or Rebar coupler:
1.Improved structural integrity
Mechanical splices maintain load path continuity of the reinforcement, independent of the condition or existence of the concrete. To use splices in tensile regions, they must be able to develop the full strength of the rebar and not create a weak point.
2. No reliance on concrete for load transfer
In coastal regions, rebar corrosion can produce concrete delamination and spalling. Since lap splices transfer load through the surrounding concrete, when the concrete is gone, the lap splice in effect has failed. Mechanical splices do not rely on the concrete for load transfer and therefore maintain the structural integrity.
3. Elimination of lap splice calculations
Mechanical splicing does away with the tedious calculations needed to determine proper lap lengths and the potential calculation errors.
4. Reduced material costs
Because mechanical splices do not overlap, less rebar is used, reducing some of the material costs. This cost savings can be particularly significant for jobs requiring expensive epoxy- coated or galvanized bars, since building codes require up to 50% longer splice laps for these bars than for standard rebars.
5. Reduced rebar congestion
Important Points about Rebar Coupler
1. Mechanical Splice
Complete assembly of a coupler, or an end bearing sleeve including any additional intervening material or other component providing a splice of two reinforcing bars.
Actual length of the reinforcement coupler including all load transferring parts, if more than one, and including lock nuts, if any.
4. Length of Mechanical Splice
Length of reinforcement coupler plus two times the nominal bar diameter at both ends of the coupler.
NOTE — This is a conventionally accepted definition to take into account the affected zone in an approximate way.
- Slip : The permanent extension of a mechanical splice after being loaded to a defined load level.
- Slip Measurement Device :The assembly constituted by the extensometer and any system used to fix it to the mechanical splice.Rebar couplers, also known as mechanical splices, are used to join lengths of rebar together. Most building code requirements for masonry construction, now require longer lap lengths for some bar sizes.
This has resulted in making construction more difficult. To help solve this issue, builders can either use open-cell blocks, which are more expensive, or use mechanical rebar couplers to get rid of the lap. Reinforcing bar coupling has all of the features desirable in a rebar joining system combined with ease of installation.
Types of Mechanical Splices for Rebars
- Compression only mechanical splices or end bearing splices
- Tension and compression mechanical splices
- Mechanical lap splices or tension only mechanical splice
- Dowel bar mechanical splices
Classification of coupler:
End anchors: A convenient alternative to hooked bars or development length to provide end anchorages in congested areas. standard anchorage heads are circular but can also be made to order in other shape or dimension as per requirement and also save steel, by avoiding the bending and remove the risk of rebar embrittlement, especially on large diameters
Rebar Threading :
|Threaded Rebar coupler|
CUTTING : The end of the reinforcement bars is sawn square
COLD FORGING : The essence of the system consistsin a method of enlarging the end of the reinforcementbar by cold forging, thus increasing its core diameter.
Rebar Threading Process:
Step 1:The end of the reinforcing bar is sawn square
Step 2:The sawn end of the rebar is then enlarged by a cold forging process. The core diameter of the bar is increased to a pre-determined diameter.
Step 3:Finally, the enlarged end of the rebar is threaded to the required length.
Easy connection by bar rotation until full thread engagement No risk of thread mis-match No risk of cross-threading In Type A threading, Rebars shall be rotated to form the joint
Even when both bars cannot be turned, The coupler is fully engaged onto the extended thread of the connecting bar (step 1). The assembly is simply completed by butting the bars end to end and screwing back the coupler onto the first bar until full engagement (step 2)
The above pitch is been tested and complies with the conditions of acceptance under code AC133, ACI
318,ACI 439 and IS 1786.
a) Static tensile test
b) Slip test
c) Cyclic tensile test
d) Low cycle fatigue test and
e) High cycle fatigue test for Class H couplers only.
Yield Strength of Steel
Yield Strength of Steel (N/mm2) = Load at Yield/Cross Sec. Area The calculated yield strength of steel is given in table 2. As per cl. 8.1 of IS
1786 – 2008, minimum required yield strength of Fe 500 D grade steel is 500 N/mm2.
Ultimate Tensile Strength of Steel
Ultimate Tensile Strength of Steel (N/mm2) = Load at Ultimate Failure/Cross Sec. Area The calculated ultimate tensile strength of steel is given in table 3. As per cl. 8.1 of IS 1786 – 2008, minimum required ultimate tensile strength of Fe 500D grade steel is 565 N/mm2
3. Percentage of Elongation
As per cl. 9.2.1, 9.2.2 and 9.4 and Annex B of IS 16172 – 2014, the percentage of elongation of steel is calculated.
Percentage of Elongation = (Final Gauge Length – Initial Gauge Length (lg) × 100 / Initial Gauge Length (lg)
4. Slip Test
(ΔLS) = L1 – L2
L1 = Length of the mechanical splice measured after loading
L2 = Length of the mechanical splice measured before loading
1. Maximum Load : 0.6 × fy × A
2. Minimum Load : 20
fy = Yield Strength of steel
A = Cross sectional area of steel bar
As per cl. 9.3 of IS 16172 – 2014, the total slip value measured in accordance with the test procedure described in Annex C of IS 16172 – 2014 shall not exceed 0.10 mm. The tested specimens are satisfying the requirement of IS
16172 – 2014.