ACI 318-14 provides comprehensive requirements for splicing reinforcing bars in concrete structures. Rebar splices are necessary when continuous bars are not practical due to transportation limitations, construction sequencing, or design requirements. The code covers three main types of splices: lap splices, which rely on concrete bond to transfer forces between overlapping bars; mechanical splices, which use devices like couplers to connect bars; and welded splices, which join bars through welding. Each type has specific requirements to ensure structural integrity and proper force transfer.
Tension lap splices in ACI 318-14 are categorized into two classes: Class A and Class B. Class A splices require a lap length equal to the development length, and are permitted only when the area of reinforcement provided is at least twice what's required by analysis, and when no more than 50% of the bars are spliced within the required lap length. Class B splices require a lap length of 1.3 times the development length, and are used when Class A conditions aren't met. The development length depends on multiple factors including concrete strength, bar yield strength, bar diameter, concrete cover, and confinement conditions. The minimum lap splice length in any case is 12 inches or 300 millimeters.
Compression lap splices in ACI 318-14 have different requirements than tension splices. The basic compression lap splice length is calculated as 0.073 times the yield strength in psi times the bar diameter in inches, when concrete strength is at least 3000 psi. For lower strength concrete, this length must be multiplied by the ratio of 3000 divided by the concrete strength. When the yield strength exceeds 60,000 psi, the lap length must be increased proportionally. The minimum compression lap splice length is 12 inches or 300 millimeters. A notable advantage of compression splices is that they can be reduced to 83% of the calculated length when sufficient transverse reinforcement, such as ties or stirrups, is provided throughout the splice length.
ACI 318-14 also provides requirements for mechanical and welded splices. Mechanical splices are categorized as Type 1 or Type 2. Type 1 splices must develop at least 100% of the specified yield strength of the bar in tension, while Type 2 splices must develop at least 125% of the yield strength. Type 2 splices are required in critical locations such as tension-controlled regions, areas where yielding is expected, and in seismic applications. Welded splices must conform to AWS D1.4, the Structural Welding Code for Reinforcing Steel, and like Type 2 mechanical splices, must develop 125% of the yield strength in critical regions. Welding is generally not permitted for high-strength bars such as Grade 75 or 80 unless their weldability has been confirmed through testing.
To summarize the ACI 318-14 requirements for rebar splices: First, splices are necessary to transfer forces between bars when continuous reinforcement isn't practical. For tension lap splices, Class A requires a length of 1.0 times the development length, while Class B requires 1.3 times the development length. Compression lap splices are calculated as 0.073 times the yield strength times the bar diameter, with a minimum length of 12 inches. Mechanical splices are categorized as Type 1, developing 100% of the yield strength, or Type 2, developing 125% of the yield strength. Welded splices must conform to AWS D1.4 requirements. Critical locations in structures require stronger splice types, typically Type 2 mechanical or welded splices. Finally, it's good practice to stagger splices when possible to avoid concentrating them in one location.