Formwork Wall-Through Bolt: The Core Fastener Ensuring Concrete Wall Stability

1. What Is a Formwork Wall-Through Bolt?

Formwork Wall-Through Bolt also known as tie rod or through-wall screw, is a core fastener in the formwork support system. It connects the formwork panels on both sides to resist the lateral pressure generated during concrete pouring, ensuring precise wall thickness and stable structural forming. Penetrating the formwork, wall reserved holes, and support system, it is locked by nuts, washers, and other accessories to form a rigid fixed structure of "formwork-bolt-support". It is an indispensable key component in the construction of concrete walls such as high-rise buildings, bridges, and basements.

Wall-through bolts can be divided into carbon steel wall-through bolts (Q235, Q355), stainless steel wall-through bolts (304, 316) by material; ordinary wall-through bolts, three-section wall-through bolts, and water-stop wall-through bolts by structural form; non-water-stop type (for walls without waterproof requirements) and water-stop type (for waterproof projects such as basements and water pools) by function. Compared with traditional iron wire and ordinary screws, professional wall-through bolts have the advantages of strong bearing capacity, high reuse rate, and easy installation, which can effectively avoid quality problems such as formwork bulging, slurry leakage, and thickness deviation of concrete walls.

2. Core Functions and Application Significance

1). Resist Concrete Lateral Pressure and Prevent Formwork Bulging

During concrete pouring, huge lateral pressure is generated (when the pouring height of C30 concrete is 3m, the lateral pressure can reach 45kN/㎡). The wall-through bolt penetrates and locks the formwork on both sides, transmitting the lateral pressure to the support system to avoid formwork deformation and displacement. The bearing capacity of ordinary wall-through bolts is ≥15kN/piece, and the high-strength model can reach 30kN/piece, which can meet the construction needs of different grades of concrete and different wall heights. In the construction of the basement wall of a 30-story residence, three-section wall-through bolts made of Q355 material were used to successfully resist the lateral pressure of C40 concrete pouring. The wall verticality deviation was ≤3mm, and there was no formwork bulging.

2). Control Wall Thickness and Ensure Structural Precision

The length of the wall-through bolt strictly matches the designed wall thickness (common specifications: 200mm, 250mm, 300mm, 400mm, etc.). Used with positioning sleeves, it can accurately control the spacing between the formwork on both sides, ensuring the wall thickness deviation is ≤±5mm, which meets the requirements of Code for Acceptance of Construction Quality of Concrete Structures (GB 50204-2015). In the construction of shear wall structures, the spacing of wall-through bolts is usually 600-800mm, forming a uniform force grid to avoid uneven structural stress caused by local thickness deviation.

3). Waterproof Sealing (Exclusive Function of Water-Stop Wall-Through Bolts)

The water-stop wall-through bolt is equipped with a water-stop ring in the middle of the screw (steel plate water-stop ring thickness ≥3mm, width ≥40mm), which blocks the seepage path of groundwater or water along the screw gap. It is a core waterproof component for waterproof concrete walls such as basements, civil air defense projects, and water pools. According to Code for Acceptance of Construction Quality of Underground Waterproof Engineering (GB 50208-2011), the water-stop ring must be fully welded to the screw, and the weld height is ≥3mm to ensure waterproof sealing. A 316 stainless steel water-stop wall-through bolt was used in an underground utility corridor project. After a 24-hour water tightness test, the water seepage rate was 0, which fully met the first-class waterproof standard.

4). Reusability and Reduce Construction Costs

Through modular design, three-section and detachable wall-through bolts allow screws, nuts, washers and other components to be reused 100-200 times. Only the plastic sleeve or water-stop ring needs to be replaced, which saves more than 60% of material costs compared with disposable ordinary bolts. Taking the construction of a 100,000 ㎡ basement as an example, the use of three-section wall-through bolts can reduce steel consumption by about 80 tons, save 400,000-600,000 yuan in costs, and reduce the amount of construction waste, in line with the concept of green construction.

3. Types and Technical Specifications

1). Main Types and Application Scenarios

2). Core Technical Parameters