Common Structural Forms of Anchor Cables and Bolts in Flexible Bracket Edge Structures (Issue 7)

Anchor Rods and Anchor Cables in the Edge Structure

In the edge structure of a flexible bracket, the pros and cons of anchor cables and anchor rods are critical to overall safety. This issue focuses on the common structural forms of anchor rods and anchor cables used in flexible bracket edge structures.

I. Anchor Rods

Anchor rods for flexible brackets mainly take the following forms:

1. High-strength ribbed rolled thread steel. The most widely used specification in flexible brackets, with yield strengths of 830 MPa and 930 MPa and diameters of 20 mm, 25 mm, 28 mm and 32 mm. In practice, this high-strength ribbed steel has sometimes fractured because its high strength is accompanied by a lack of toughness. A scientific, rational selection of the anchor rod is therefore recommended to reduce accidents.

2. HPB300 steel bar. This must be processed in the factory and then installed on site; common diameters are 25 mm and 27 mm. This anchor rod has almost never fractured in service, making it a comparatively safe choice. Anchor rods are widely used in buildings, bridges and mines and are a mature product. Applied to PV flexible brackets, its advantages are low elongation, small influence on the bending moment of the edge pile, and fast, convenient installation. Its disadvantages are higher cost and poorer corrosion resistance — it is not suitable for high-humidity, high-salt-mist marine environments, and is especially not recommended for offshore flexible brackets, because it seriously shortens their service life.

II. Anchor Cables

Anchor cables fall into two sub-categories:

1. Galvanized steel strand. Mostly 15.2 mm and 17.8 mm in diameter, used singly or in pairs, made of 82B steel with strengths mostly at 1860 MPa. The anchor cable assembly of this structure is similar to an anchor rod, with the advantage of relatively low cost.

2. Galvanized unbonded strand and filled epoxy strand. Flexible bracket anchor cables built from these strands are low in cost and can be used in high-humidity, high-salt-mist and highly corrosive environments; offshore flexible brackets can safely use this type of strand as their anchor cable. The key technology is ensuring the anti-corrosion treatment of the strand and the anchor, and the sealing and anti-corrosion performance of the connection between the anchor and the strand. After years of development, the manufacturer has produced a range of anti-corrosion anchors for offshore flexible brackets that do not leak even under a 10-metre underwater pressure environment; this technology has won multiple national patents. This anchor cable assembly has a certain elongation; the solution is to strictly follow the tensioning procedure in the flexible bracket strand installation manual during construction, which completely avoids the edge-pile bending moment caused by the horizontal force from anchor elongation, achieving a force balance between the flexible bracket's strands and the pile foundation.

III. Basalt Fibre Anchor Rod Devices

Anchor rod devices built from basalt composite fibre reinforcement or basalt composite pipe are suitable for offshore flexible bracket plants, offering high strength and extremely strong corrosion resistance. Because the connection technology and installation process of basalt composite fibre reinforcement anchor rods are difficult and require very high safety standards — the connection head of the anchor uses 316 stainless steel or aluminium alloy sleeve crimping followed by anti-corrosion treatment, which is also very costly — this type has not yet been put into use. Should detailed technical parameters be needed, please contact us directly.

Key Takeaways

• HPB300 anchor rods are the safest conventional choice on land; avoid them in marine environments.
• For coastal and offshore projects, galvanized unbonded or filled epoxy strand anchor cables with properly sealed anti-corrosion anchors are the proven solution.
• Follow the standard tensioning procedure to eliminate edge-pile bending caused by anchor cable elongation.