Reinforced concrete structures are designed to behave monolithically. Properly designed splices of individual reinforcing bars are a key element in transmitting forces through the structure and creating a load path. The architect/engineer provides location, lap length, and related information on structural drawings.
Simple Lap Splice
A lap splice is the predominant method used for splicing reinforcing bars. Bars may be spaced apart or in contact. For lap splices, contact splices are preferred for the practical reason that, when wired together, they are more easily secured against displacement during concrete placement. Non-contact lap spliced bars should not be spaced too widely apart, permitting a zigzag crack in the concrete between bars.
The length of a lap splice varies with concrete strength, type of concrete, the yield strength (grade) of the reinforcing bars, bar size, bar spacing, concrete cover, and the amount of ties or stirrups. Lap splice lengths are always shown on placing drawings and will be found either in the details, lap charts, or in the general notes. Additional information on lap splices can be found here.
Welded Lap Splice
In general, CRSI recommends against manual arc welding in the field. However, if necessary, field-welded splices are accomplished by electric arc welding the reinforcing bars together. For projects of all sizes, manual arc welding will usually be the most costly method, due to direct and indirect costs of proper inspection. Properly engineered and constructed welded splices require more considerations than a simple statement in the contract documents, “All welded splices shall conform to ‘Structural Welding Code – Reinforcing Steel’ (AWS D1.4/D1.4M:2011).”
While the welding code is a comprehensive document, other important items such as securing chemical analysis of the steel, field inspection, super-vision, and quality control are required for a project with welded reinforcement. CRSI recommends against connecting crossbars by small arc welds, known as “tack welds.” Tack welding is a factor associated with brittle failure of rebar assemblies.
Coupler for Thread-Deformed Bar
This is a mechanical splice that requires special bars with thread-like rolled, deformations over their entire length which meets ASTM A615. Splices are assembled with lock nuts and threaded couplers, then the nuts are tightened to a specified torque. Alternatively, the lock nuts can be omitted when the bars can be torqued together. Special hardware permits use for end anchorages in concrete or connection to structural steel members. Bars may be flame or saw-cut.
Upset Straight Thread Coupler
This is a mechanical splice consisting of a coupler with internal straight threads at each end that joins two upset end reinforcing bars with matching external threads. Upsetting the bar ends permits the cross-sectional area in the threaded portion to be greater than the bar cross-sectional area.
This type of splice can either be in three pieces (the two bar ends and internally threaded coupler) or in two pieces with the coupler integrally forged or pre-assembled onto the bar end. These systems are also available as weld-on couplers, transitional couplers, positional couplers, and headed bars.
Non-Upset Straight Thread Coupler
This is a mechanical splice consisting of a coupler with internal straight threads at each end that joins two reinforcing bars with matching external threads. Because the cutting of threads reduces the net cross-sectional area of the reinforcing bar, some manufacturers use bars one size larger while other manufacturers use bars with tensile and yield strengths sufficient to overcome the loss of net area by thread cutting.
This type of splice is in three pieces (the two bar ends and the internally threaded coupler). These systems are also available as weld-on couplers, transitional couplers, and positional couplers.
Cold-Swaged Threaded Coupler
The cold-swaged threaded coupler consists of pre-threaded male and female components, which are swaged onto the reinforcing bars using a swaging press with special dies. No threads are required on the bar ends. Splicing of the bars is completed by installing one pre-threaded component into the other. A three-piece position coupler is available for splicing bent bars that cannot be rotated. Optional details include transition couplers for splicing different bar sizes, couplers used to connect bars to structural steel members, and couplers with flanges having nail holes. Threads are sealed and protected for future extension applications.
This is a mechanical splice consisting of a taper threaded coupler that joins bars with matching tapered threads. The coupler is installed by turning the the bar or sleeve with wrenches to the manufacturer’s specified torque. For splicing bent or curved bars, special position couplers with collars are used. Adaptations permit the use for end anchorages in concrete or connection to structural steel members. Bar ends may be shear-cut or saw-cut. Bar ends require taper threading over a specified length.
Straight Threaded Coupler with Upset Rebar Ends
This is a mechanical splice consisting of forming heads on the ends of the bars to be connected using a hydraulic machine from the splice manufacturer, which is designed to fit between closely-spaced bars. The upset bar ends are butted to each other and are held in place using a male and female straight-threaded coupler that is positioned onto the bars prior to forming the heads. The coupler is installed by turning either the male or female component and tightening to the manufacturer’s recommended torque; no rotation of the bar is required. Bent or curved bars can be spliced with teh same device. Adaptations permit use for end anchorages in concrete or connection to threaded rod.
Grout-Filled Coupling Sleeve
The double-frustrum-shaped coupling sleeve is filled with a cement-based, non-shrink, high-early strength grout. Reinforcing bars to be spliced are inserted into the sleeve and butt at the center of the sleeve. The space between bar and sleeve is filled with non-shrink grout to transfer forces between the deformed surface of the bars and the deformed interior surface of the sleeve. No special end preparation of the bars is required except for normal cleaning. The relatively wide sleeves also can accommodate minor bar misalignments, and combinations of different size bars.
Combo Grout-Filled/Threaded Sleeve
Primarily used for precast construction, this type of mechanical splice combines two common mechanical splicing techniques. One end of the sleeve is attached and secured to a reinforcing bar (rebar) by means of threading. The splice is then completed when the other bar end is inserted into the sleeve and the space between the bar and the sleeve is filled with high-strength grout. The wide mouth opening of the sleeve allows for minor bar misalignment during erection. The wide mouth also allows for transitioning between different bar sizes.
Steel-Filled Coupling Sleeve
The steel-filled coupling sleeve is a mechanical splice in which molten metal or “steel filler” interlocks the grooves inside the sleeve with the deformations on the reinforcing bar. Special details permit use as end anchorages or connections to structural steel members. Shear-cut, flame-cut, or saw-cut ends of the bar can be used as the “steel filler” fills the space between the ends of the bar. However, a bar-end check is recommended.
Cold-Swaged Coupling Sleeve
The cold-swaged coupling sleeve uses a hydraulic swaging press with special dies to deform the sleeve around the ends of the spliced reinforcing bars. This produces a positive mechanical interlock with the reinforcing bars. Bars to be spliced are inserted equal distances into the sleeve. Bars may be shear-cut, flame-cut, or saw-cut, however, a bar-end check is recommended. Bars of different sizes can be spliced with this system. This mechanical splice can also be used for joining reinforcing bars to structural steel members. Longer sleeves are required for splicing epoxy-coated reinforcing bars.
Shear Screw Coupling Sleeve
This type of mechanical splice consists of a coupling sleeve with shearhead screws which are designed to shear off at a specified torque. The reinforcing bars are inserted to meet at a center stop in the coupling sleeve and the screws are tightened. The tightening process embeds the pointed screws into the bars. For one splice type, the srews force the bars into contact with the internal gripping rails. For the other type of splice, the screws force the bars to wedge into the coupling sleeve’s converging interior walls. The screws can be tightened using a standard socket wrench or pneumatic impact wrench. For making a splice between two fixed bars, coupling sleeves without a center stop are available.
Extruded Coupling Sleeve
This type of mechanical splice is produced by cold extruding a coupling sleeve over both bar ends in one operation. The coupling sleeve is then centered over the butted bar ends and is connected to one bar by tightening a set screw. A hydraulic press, designed to fit between closely-spaced bars of reinforcing steel, then pushes a drawing die over the entire length of the coupling sleeve. The coupling materials flow tightly around the bar deformations, which creates a splice.
Extruded transition coupling sleeves for splicing two different size reinforcing bars are also available. Bars may be shear-cut, flame-cut or saw-cut; however, a bar-end check is recommended.
Coupling Sleeve with Double Wedge
This coupling sleeve consists of a ductile iron sleeve with two internal wedges. Two series of cone-pointed screws are arranged a long the sleeve length, opposite a wedge-shaped profile in the sleeve. Each reinforcing bar extends out of the sleeve by approximately one bar diameter. No special bar end preparation is required. As the screws are tightened, they indent into the surface of the bars, and wedge the bars into converging sides of the sleeve profile. Screws can be tightened using suitable impact wrenches or hand-held ratchet wrenches. The heads of the screws are designed to shear off at a prescribed tightening torque. Bar sizes #3 through #6 [#10 through #19] plus bars of different sizes either uncoated or epoxy-coated can be spliced using this coupling sleeve.
Coupling Sleeve with Shear Bolt/Wedge
Designed primarily for splicing smaller bars, sizes #3 through #6 [#10 through #19], the coupling sleeve is oval in cross-section permitting the overlapping of two reinforcing bars of the same diameter in the sleeve. Each bar extends out of the sleeve about one bar diameter. After the sleeve is correctly positioned, a wedge-shaped round pin is driven through a hole in the flat face of the sleeve. The wedge passes between the bars and extends through a hole opposite the hole of insertion. The wedge pin is driven with a hand-held hydraulic ram.
Dowel Bar Mechanical Splice
Dowel bar mechanical splices are used to prevent bars from penetrating or protruding from forms and reinforced concrete structures. All of the various systems available consist of several components. The coupling component is internally threaded and another component is externally threaded. The internally threaded component is normally designed to fasten directly to the form face and is usually encased in the first concrete placement. These systems are available in a variety of designs, configurations, sizes and shapes.
Compression-Only Mechanical Splices
The use of end-bearing to transfer compression from bar to bar requires the ends of the bars be cut within 1-1/2 degress of square to the longitudinal axis of the bars. In field assembly, such mechanical splices must fit within 3 degrees when erected. Commercial devices are used to ensure concentric bearing.