A Detailed Explanation of Design Codes and Construction Requirements for Stirrups in Prefabricated Concrete Shear Walls

As a core system of modern building industrialization, prefabricated concrete shear wall structures have been widely adopted in high-rise residential and public engineering projects. Compared to traditional cast-in-place structures, the prefabricated system significantly improves construction quality and accelerates project timelines through standardized factory prefabrication and efficient on-site assembly. However, since precast components must be connected through sleeve grouting, grout-anchored joints, and post-poured joints to achieve a monolithic load-bearing system, the construction requirements for their internal reinforcement are far more stringent than those of traditional structures. As key components that constrain the core concrete, prevent buckling of longitudinal reinforcement, and resist shear forces, the quality of stirrup placement directly determines the seismic ductility of prefabricated joint areas and the overall structural safety. In accordance with national standards (GB 50010 “Code for Design of Concrete Structures,” JGJ 1-2014 “Technical Specifications for Prefabricated Concrete Structures,” JGJ 3-2010, and the 15G365 series of design manuals), this paper systematically reviews the technical standards and key on-site quality control points for stirrups in prefabricated shear walls.

1. Material and Fabrication Requirements for Precast Shear Wall Hoop Reinforcement

1.1 Reinforcement Grade and the Trend Toward Higher Strength

In precast concrete shear wall structures, stirrups typically use high-strength ribbed reinforcing bars such as HRB400 or HRB500. In areas with high seismic intensity or in high-rise buildings, the use of HRB500-grade high-strength reinforcing bars can effectively reduce the stirrup placement ratio in edge members and alleviate the problem of reinforcing bar crowding in areas with dense sleeves, thereby ensuring the flowability and fullness of the grout.

1.2 Requirements for 135° Seismic Hooks and End Straight Sections

To prevent the ends of stirrups from disengaging under seismic loads, which could lead to core concrete instability, all seismic confinement stirrups must strictly adhere to the 135° hook fabrication requirement. The length of their end straight sections must simultaneously satisfy the following conditions: no less than 10d (where d is the stirrup diameter); and an absolute length of no less than 75 mm. During factory fabrication, CNC automatic rebar bending equipment should be used for centralized forming to ensure consistent straight-end lengths.

2.1 Construction Requirements for Composite Closed Stirrups

Lap Zone Placement: Lap joints for open stirrups must be located away from zones subjected to maximum bending moments and shear forces, and should instead be placed in the compressed zone of the structure or in core areas with lower internal forces.

Hook Anchorage: The 135° hooks at both ends of the composite stirrups must be fully anchored into the core concrete of the wall to form an effective closed confinement loop.

Anchorage and Lap Length: The length of the composite lap section must strictly comply with the seismic design provisions in relevant national standard drawing collections to prevent joint detachment under tensile loads.

3. Reinforcement Standards for Precast Edge Elements (Hidden Columns/End Columns)

The edge elements at both ends of shear walls (structural edge elements GBZ and constrained edge elements YBZ) serve as the first line of defense against seismic forces.

3.1 Volume Stirrup Ratio and Densification Requirements for Constrained Edge Elements (YBZ)

Volume stirrup ratio (rho): It shall not be less than 1.2% for Seismic Grade I and not less than 1.0% for Seismic Grade II.

Stirrup spacing control: The maximum spacing of stirrups within the shaded area shall not exceed 100 mm and shall not exceed 6–8 times the diameter of the longitudinal reinforcement. In the reinforced areas at the base of shear walls and in the first-story joint zones, spacing is often further reduced to 80 mm in engineering practice.

Placement of Tie Bars and Stipple Spacing: For Seismic Class I, the stipple spacing of stirrups should not exceed 200 mm; for Seismic Classes II and III, it should not exceed 250 mm. When these limits are exceeded, tie bars must be added; these tie bars should be placed close to the longitudinal reinforcing bars and hooked around the stirrups.

3.2 Code for Structural Perimeter Members (GBZ)

The stirrup spacing in reinforced areas of structural perimeter members should be 100 mm, and 150 mm in non-reinforced areas; furthermore, the minimum stirrup diameter must not be less than 8 mm.

4. Special Design for Hoop Reinforcement in Prefabricated Connection Joint Areas

The “equivalent to cast-in-place” effect in joint areas depends on the effective confinement of the grout and the subsequently poured concrete by the hoop reinforcement.

4.1 Transverse Confinement in the Bottom Sleeve Grouting Area

In the sleeve grout connection zone, high-stress reinforcement can easily cause splitting of the base concrete due to pull-out forces; therefore, the outer side of the bottom sleeve of the precast wall panel must be provided with transverse confinement stirrups, continuous spiral stirrups, or specialized reinforcement mesh. The spacing of confinement stirrups within the height of the sleeve must be strictly controlled between 50 mm and 100 mm.

4.2 Requirements for Vertical Joints and Composite Wall Hoops

Vertical joints for cast-in-place hidden columns: When tying the hoop reinforcement for the cast-in-place section on-site, the bent ends of the horizontal distribution reinforcement protruding from the precast wall panel must extend precisely into the interior of the cast-in-place hidden column and be completely enclosed by the hoop reinforcement on the outer side of the hidden column.

Double-sided composite shear walls: Within the cast-in-place cavity between the double-sided precast panels, connecting tie bars and anti-blowout stirrups must be installed in conjunction with the truss reinforcement to ensure that the formwork does not expand during grouting and to achieve coordinated load-bearing between the new and old concrete.

5. Construction Quality Control and BIM Detailing Practices

BIM 3D Clash Detection: Since prefabricated wall panels integrate sleeves, grouting pipes, embedded parts, and dense reinforcement, 3D detailing using BIM must be performed prior to construction. Special attention should be given to verifying the clear dimensions inside the stirrups and the positions of the sleeves to prevent on-site installation failures.

Control of Cover Thickness: The cover thickness on the outer side of the stirrups in precast edge components is generally no less than 15 mm; for precast exterior wall panels installed in open-air or humid environments, it is recommended to increase the cover thickness to 20 mm–25 mm to ensure durability.