How to Lap Rebar in Prefabricated Houses

The main methods for lapping rebar in prefabricated houses include rebar sleeve connections, rebar grout-anchored lap connections, welding or bolt connections, and rebar mechanical connections. The specific choice should be determined based on the load-bearing requirements of the components, on-site construction conditions, and the requirements for building components and fittings.

1. Rebar Sleeve Connections
This method connects the ends of two rebars using a specially made sleeve, where the inner wall of the sleeve and the surface of the rebar form a mechanical interlock through threading or extrusion. Common types include straight-thread sleeve connections and tapered-thread sleeve connections, with the former being widely used due to its high thread precision and stable connection strength. During construction, it is necessary to ensure that the ends of the rebars are flat, and after tightening the sleeve, the torque value should be checked to ensure it meets the specification requirements. This method is suitable for rebars with a diameter of 16mm or more, especially in scenarios where on-site space is limited or rapid installation is required.

2. Rebar Grout-Anchored Lap Connections
Insert rebar into the reserved holes in prefabricated components and achieve the connection by injecting high-strength non-shrink grout. The grout must meet requirements for fluidity, early strength, and slight expansibility to ensure full bonding between the rebar and the hole wall. During construction, strict control is required over the cleanliness of the holes, the mix ratio of the grout, and the curing time, which usually takes more than 7 days to reach the design strength. This method is suitable for connecting vertical components, such as the anchoring of prefabricated wall panels to foundations, but attention should be paid to the impact of ambient temperature on the setting speed of the grout.

3. Welding or Bolt Connections

• Welding: Includes arc welding, electroslag pressure welding, etc., which form a weld by melting the ends of the rebars at high temperatures. Arc welding is suitable for flexible on-site operations but requires control over the welding current and weld quality; electroslag pressure welding, on the other hand, uses conductive heating through molten slag and is suitable for connecting vertical rebars. After welding, visual inspection and sampling mechanical property tests should be conducted.
• Bolt Connections: Fix the steel plates connected to the ends of the rebars using high-strength bolts, which require pre-drilling holes and ensuring the bolt torque value. This method is convenient for disassembly but has a higher cost and is mostly used in temporary structures or nodes that require adjustment.

4. Rebar Mechanical Connections
In addition to sleeve connections, this category also includes new methods such as sleeve extrusion connections and tapered-sleeve locking joints. Sleeve extrusion connections use hydraulic equipment to compress the sleeve, tightly bonding the rebar and the sleeve; tapered-sleeve locking joints utilize the wedge action of a tapered sleeve to achieve self-locking. These methods offer high connection strength and fast construction efficiency but require specialized equipment and are suitable for large-diameter rebars or structures in high-intensity earthquake zones.

Construction Points:
All connection methods require concealed work inspection during the installation of components and fittings, focusing on checking the connection location, rebar spacing, and protective layer thickness. Temporary supports should be set up after the connection of main load-bearing components is completed, and they can only be removed after the connected parts reach the design strength (usually detected through condition-matched curing specimens). In addition, construction techniques should be adjusted according to the climatic environment, such as preheating before welding in low temperatures and preventing the grout from getting damp during the rainy season.