Breakthrough in Anchor Technology Makes Flexible Brackets Safer (Issue 8)

Why Anchors Are the Most Critical Component

How can the safety and durability of a flexible bracket be guaranteed? The key lies in the edge structure — and the most critical part of the edge structure is the anchor. The anchor accounts for only a small share of flexible bracket cost, yet its safety performance is vital: it directly affects the service life and safety of the whole bracket. Whether the anchor matches the flexible bracket, how long it lasts, and whether the anchors used are qualified can all be judged by referring to flexible bracket plants that have already been completed and connected to the grid.

Basic Knowledge of Anchors

Anchors are widely used in bridges, civil buildings, mines and wind-power concrete towers — they are mature products developed through years of practice. Anchors are mainly divided into two types:

1. Extrusion anchors. The structure is an extrusion sleeve plus an extrusion spring. During installation, the spring is placed between the strand and the extrusion sleeve, and a hydraulic cylinder squeezes them together so they bond with the strand. This type of anchor has a high pass rate in break tests and 2-million-cycle fatigue tests and performs stably — which is why some flexible bracket companies insist on using it. Its drawback is higher material and installation cost.

2. Wedge (grip) anchors. The technology was imported from abroad and has many types. After decades of domestic development and use, the main structures and parameters are basically standardized, with complete national and industry standards. Flexible brackets commonly use single-hole anchors, consisting of an anchor ring and wedges. The ring and wedges are precision-matched conical parts, typically with a taper of 6–7°, and the contact face between the wedge and strand is serrated. The wedge tooth shape and pitch are matched to the strand diameter and specification and are basically standardized. The working principle: after the strand is prestressed, the wedges are pulled into the anchor ring by the axial force of the strand; under the huge axial tension, the tapered structure creates a positive pressing force between wedges and ring, producing a large biting force that locks the strand.

The Problem: Copying Bridge Anchor Parameters into Flexible Brackets

Although anchors and strand belong to the same family of cable-anchor technology, they are actually two different industries: strand producers rarely make anchors, and anchor producers rarely make strand. Anchors are not well known in hardware manufacturing, but total sales are large — top producers range from tens of millions to hundreds of millions in annual output. Anchor development is difficult and slow, and the industry has basically formed a standardized production model. Developing a new anchor product takes a long time from design and trial samples to testing, and carries considerable safety risk. Most flexible bracket companies therefore directly borrow existing prestressed anchor technology.

But the key question is whether simply copying the parameters of existing prestressed anchors is scientific and can meet flexible bracket requirements. Bridge and flexible bracket anchor structures and parameter values differ greatly. Applying conventional anchors to equipment with such different design parameters inevitably causes a huge gap between the actual cable parameters and the design data — dangerous and unscientific in cable engineering. For example, in bridges and other construction projects, the tensioning ratio of the strand is 50%–70% of the breaking standard value, while the tensioning value of flexible bracket strand is mostly 10%–20% of the breaking value. Under such low strand tension, the positive pressure between the anchor ring and wedges is very low, so the biting force between the wedges and the strand fails to meet design and practical needs, and does not comply with national standards for anchors and strand. Moreover, the flexible bracket anchor belongs to an external cable structure whose vibration frequency and amplitude are far greater than a bridge's, which can cause the flexible bracket to collapse because the anchor loosens and the strands slip.

Remedies Attempted by the Industry

Faced with the hidden dangers of these structural defects, industry experts proposed several remedial options:

1. Adding a lock nut outside the anchor ring to try to lock the wedges and prevent strand slippage. But the actual parameters of conventional anchors require more than 13 tonnes of pressure to achieve wedge self-locking — no one can manually tighten a nut to even 1 tonne, let alone 13 tonnes of torque. Yet this anchor product remains the mainstream product of the flexible bracket industry, showing how blindly anchors are applied. After years of practice, the loosening and slippage problem remains unsolved.

2. Adding a sleeve (spacer tube) and an extrusion anchor at the tail of the installed anchor to avoid the safety hazard of wedge slippage. However, this increases material cost, a large amount of installation labour, and extends the construction period.

Flexible brackets are the most profitable link in the PV industry chain, attracting many players — central SOEs, module manufacturers, listed companies, design institutes and many bracket factories — all investing heavily. Yet looking at flexible bracket plants completed by the end of 2024, the progress of flexible bracket anchor technology has been slow.

Proposed Solution 1: Custom-Matched Anchors

According to the strand tensioning values in the project's flexible bracket drawings, and combined with the tensioning value and strand type, calculate the correct parameters of the anchor ring and wedge taper, wedge tooth shape and pitch, and custom-order anchors matched to the project. In more detail, refer to the deflection ratio of the main strand in the drawings: early advanced flexible bracket designs used deflection ratios from 1/200 to 1/100, and the most common is 1/50. After review by experts from industry associations, the 2025 deflection ratio of the main strand of flexible brackets may be set at a minimum of 1/30. Different main-strand deflection ratios and different strand types (galvanized, non-galvanized, filled epoxy, etc.) require different anchor parameters. In this complex situation, one must not use the same anchor product for everything. The scientific approach is to custom-order matching anchor products according to the design drawings and the strand type. The inner bore of the anchor ring, the wedge taper and the wedge tooth shape of such custom anchors all match the overall design data of the flexible bracket, achieving a safe, durable whole. Such matched anchors can be installed in one step on the flexible bracket, eliminating the cumbersome process of installing spacer tubes and secondary extrusion anchors, greatly saving construction time and material cost. Custom anchor production requires solid anchor expertise, rich practical experience and a complete production supply chain.

Proposed Solution 2: A Multi-Function Tensioning Jack

This is an industry-first product. Besides tensioning the strand, it can also jack the wedges of the anchor. Although bridge construction has similar equipment, it differs fundamentally from this multi-function jacking-tensioning jack. The jack consists of two hydraulic cylinders of different sizes:

• One cylinder for strand tensioning — 10 tonnes of pull (adjustable), 200 mm working stroke.
• One cylinder for jacking — 20 tonnes of jacking force (adjustable), 10 mm working stroke.

Its structural feature is a quick-connect device at the front of the cylinder that connects to the anchor ring of the flexible bracket anchor. The complete set consists of one pump station configured with one or two jacks; two jacks are used to balance the pull of two module strands when tensioning the flexible bracket module cables. The working procedure:

1. After tensioning is complete and the strand tension loss has stabilized, connect the quick-connect device at the front of the jack to the anchor ring, grip the ring and jack the wedges inside it.
2. Alternatively, jack the wedges in the anchor ring immediately after the module cable tensioning is completed.

After jacking, the working state of the anchor wedges and ring reaches the working state of a bridge-environment anchor — that is, consistent with the working state of bridge cable structures. In nearly one hundred reverse-withdrawal checks over nine months on strands that had completed the jacking process, the values were all 8–12.8 tonnes — far exceeding the forward tensioning value of the flexible bracket strand. In other words, the forward tension of the flexible bracket strand is lower than the reverse-withdrawal value after jacking. This technology easily solves the problem of low positive pressure between ring and wedges caused by insufficient axial strand tension — the root cause of anchor loosening and strand slippage — and contributes to technical improvement, cost reduction and safety assurance for the flexible bracket industry.

Key Takeaways

• Bridge-type anchors operated at flexible bracket tension levels cannot self-lock properly — the mismatch is a root cause of collapses.
• Custom-matched anchors designed to the project's tension and deflection data install in one step and meet national standard requirements.
• The multi-function jacking-tensioning jack restores the anchor to bridge-grade working state, eliminating wedge slippage.