When specifying mechanical rebar couplers for a reinforced concrete project, one of the first decisions an engineer must make is whether a Type 1 or Type 2 splice is required. This classification, defined by ACI 318 (Building Code Requirements for Structural Concrete), is not merely a label — it determines the performance threshold the coupler must meet, where it can be placed within a structure, and ultimately, how the connection will behave under extreme loading conditions such as earthquakes.
The ACI 318 Classification System
ACI 318-19 defines the two types of mechanical splices in Clauses 25.5.7.1 and 18.2.7.1. The distinction centres on the tensile capacity each splice must develop relative to the connected reinforcing bar.
Type 1 Mechanical Splice
A Type 1 mechanical splice must develop at least 125% of the specified yield strength (fy) of the connected bar in both tension and compression. For ASTM A615 Grade 60 reinforcement, this translates to a minimum tensile capacity of 75 ksi (1.25 × 60 ksi). Type 1 splices are intended for use in structural members where the coupler is not expected to experience significant inelastic deformation — that is, locations away from plastic hinge zones and yielding regions.
Type 2 Mechanical Splice
A Type 2 mechanical splice must satisfy all Type 1 requirements and, additionally, develop the full specified tensile strength (fu) of the spliced bar. For ASTM A615 Grade 60 reinforcement, the specified tensile strength is 90 ksi. In practice, this means a Type 2 splice must be strong enough that the reinforcing bar itself will fracture before the coupler fails — commonly referred to as a "bar-break" criterion. This higher performance threshold is essential in regions of a structure where the reinforcement may be subjected to stresses approaching its ultimate capacity during a seismic event.
Side-by-Side Comparison: Type 1 vs Type 2
| Requirement | Type 1 Splice | Type 2 Splice |
|---|---|---|
| ACI 318-19 Reference | Clause 25.5.7.1 | Clauses 25.5.7.1 + 18.2.7.1 |
| Minimum Tensile Strength | ≥ 125% fy (yield strength) | ≥ 125% fy AND ≥ 100% fu (ultimate tensile strength) |
| Compression Strength | ≥ 125% fy | ≥ 125% fy |
| For Grade 60 (A615) — Tension | ≥ 75 ksi | ≥ 90 ksi |
| Failure Mode | Coupler may slip or deform before bar breaks | Bar breaks before coupler fails (bar-break) |
| Placement in Special Moment Frames | NOT within 2× member depth from column/beam face | Permitted at any location (Grade 420); ≥ h/2 from beam joint face |
| Placement in Yielding Regions | Not permitted | Permitted (Grade 420 reinforcement) |
| Seismic Ductility Demand | Low — non-yielding regions only | High — designed for inelastic deformation zones |
| Typical Applications | Standard columns, walls, foundations, non-seismic zones | Seismic moment frames, shear walls, plastic hinge zones, transfer structures |
| Relative Cost | Lower | Higher |
Why the Distinction Matters
The commentary to ACI 318-19 (R18.2.7) explains the rationale clearly: during an earthquake, the tensile stresses in reinforcement within yielding regions may approach the tensile strength of the reinforcement itself. If a mechanical splice in such a region can only develop 125% of the yield strength, it may fail prematurely — leading to bar pullout, coupler fracture, or a loss of structural ductility at the worst possible moment.
Type 2 splices eliminate this risk by ensuring the coupler is stronger than the bar. The bar will yield, strain-harden, and ultimately fracture in the free length — but the coupler connection remains intact. This is why ACI 318 permits Type 2 splices on Grade 420 reinforcement at virtually any location in a special moment frame, while Type 1 splices are restricted to regions at least twice the member depth away from critical sections.
Key takeaway: Type 1 splices are suitable for non-yielding regions and offer a cost-effective solution for standard structural connections. Type 2 splices are mandatory in yielding regions of seismic-resistant structures, where the splice must be stronger than the bar itself.
Placement Restrictions at a Glance
Clause 18.2.7.2 of ACI 318-19 provides specific placement rules that directly affect project detailing:
- Type 1 splices (any grade): Must not be located within a distance of 2× the member depth from the column or beam face in special moment frames, or from critical sections where yielding is likely.
- Type 2 splices on Grade 420 reinforcement: Permitted at any location, except not closer than h/2 from the joint face of beams (per Clause 18.9.2.1(c)).
- Type 2 splices on Grade 550 or Grade 690 reinforcement: Subject to the same restrictions as Type 1 splices, because higher-grade bars may develop stresses exceeding the splice capacity even at Type 2 levels.
Bosa Technology's Coupler Range
At Bosa Technology, we manufacture mechanical couplers for both Type 1 and Type 2 applications, giving engineers the flexibility to specify the right splice for every location in a structure.
Type 1: SERVISPLICE
SERVISPLICE is our flagship Type 1 coupler — a simple, effective, and high-performance mechanical splice using fully automated CNC parallel threading. With a threading time of approximately 30 seconds per bar end, zero material wastage (100% of rebar length is used), and no special assembly skills required, SERVISPLICE is the most cost-effective coupler in the Bosa range. It is suitable for standard column, wall, and foundation splicing in non-yielding regions, and is compliant with HK CoP 2013 Cl. 3.2.8.3, AC133, and BS8110.
Type 2: SEISPLICE
SEISPLICE is Bosa's flagship Type 2 coupler — a CNC parallel-threaded mechanical splice designed specifically for seismic ductility zones. Like SERVISPLICE, it uses CNC parallel threading, making it a true like-for-like upgrade when a project requires Type 2 performance. SEISPLICE achieves ≥100% fu (bar-break) under both static and cyclic testing, ensuring the reinforcing bar itself will fracture before the coupler fails. It is suitable for special moment frames, shear walls, transfer structures, and any location where inelastic deformation is expected during a seismic event.
SERVISPLICE vs SEISPLICE: Head-to-Head
Because both couplers use the same CNC parallel-threading mechanism, the comparison is straightforward. The key difference is the performance threshold — and consequently, where each coupler can be placed in a seismic-resistant structure.
| Feature | SERVISPLICE (Type 1) | SEISPLICE (Type 2) |
|---|---|---|
| ACI 318 Classification | Type 1 Non-Ductility | Type 2 Ductility |
| Mechanism | CNC parallel thread | CNC parallel thread |
| Tensile Requirement | ≥ 125% fy | ≥ 125% fy AND ≥ 100% fu |
| Bar-Break Guarantee | No — coupler may slip before bar breaks | Yes — bar fractures before coupler fails |
| Bar Range | Ø12 – Ø50 mm | Ø12 – Ø50 mm |
| Permitted in Yielding Regions | No | Yes (Grade 420) |
| Seismic Ductility Demand | Low — non-yielding regions only | High — plastic hinge zones, moment frames |
| Best For | Standard columns, walls, foundations | Seismic moment frames, shear walls, transfer structures |
| Relative Cost | Lower | Higher |
Bosa also manufactures ISPLICE (cold-swaged) and GROUTSPLICE (grout-filled sleeve) couplers for specialised applications such as congested reinforcement zones, retrofit projects, and precast/MIC connections. Contact our team for guidance on these products.
Choosing the Right Splice for Your Project
The decision between Type 1 and Type 2 is driven by the structural design requirements — specifically, whether the splice location falls within a region expected to undergo inelastic deformation during a seismic event. In many projects, a combination of both types is the most economical approach: Type 2 couplers in the critical seismic zones (plastic hinge regions, beam-column joints, transfer structures) and Type 1 couplers in standard non-yielding locations (mid-height column splices, foundation connections, wall panels away from boundary elements).
With over 1,000 projects delivered across Hong Kong and expansion underway into Australia, the United States, and Southeast Asia, Bosa Technology's engineering team can help you determine the optimal splice specification for your project — balancing code compliance, structural performance, and cost efficiency.
Need help specifying the right coupler?
Our engineering team can review your project drawings and recommend the optimal Type 1 / Type 2 coupler configuration. Get in touch for a free technical consultation.
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