How to Judge Flexible Bracket Quality and Durability from Structure: Refer to Suspension Bridge Design (Issue 10)

Learn from the Suspension Bridge

Before designing a flexible bracket, it helps to understand the basic structural knowledge of a suspension bridge. A suspension bridge mainly consists of main cables, towers, anchorages, the main deck (girder) and hangers. The hangers are evenly distributed between the main cables and the main girder; their function is to transmit the girder load to the main cable to keep the bridge structure stable. A hanger consists of three parts: steel strand, an upper cable clamp, and an anchor connecting it to the bridge.

The U-Bolt Problem: A Hidden Risk in Flexible Brackets

Flexible brackets have developed for nearly ten years, yet in some projects the strand and the main girder are still fixed with U-bolts. The contact area between a U-bolt and the strand is extremely small — at most five points, with a total area of less than five square millimetres, about one-thousandth of the standard contact area of a strand clamp. Does this design meet the relevant national standards and specifications for anchor-cable structures?

Using U-bolts to fix the strand has obvious defects:

• Contact area is too small to withstand the compression and friction damage to the structure caused by wind and snow loads and wind-induced resonance that a PV flexible bracket faces.
• If the strand has an unbonded PE sheath, the U-bolt easily crushes and ruptures the sheath, destroying the strand protection layer, causing rapid local rusting and fracture, and shortening the service life of the flexible bracket.

Strand Clamps: The Irreplaceable Basic Component

Comparing the structures above shows that the strand clamp is crucial to the performance and safety of cable-structure engineering — it is an irreplaceable basic structure and product. There are many kinds of strand clamps for flexible brackets, all of which can remedy the defects of U-bolt fixing. Somewhat more complex is the clamp used for flexible brackets on mountains and hills. This issue introduces one such combined strand clamp for mountain and hill flexible PV brackets: it consists of a round-tube beam, upper and lower cable clamps, and U-bolts. Its friction contact area with the strand is about 1,000 times that of a single U-bolt. It was the only universal-joint combined clamp for flexible brackets exhibited at the 2024 Shanghai PV Exhibition, with a 360° working range of connection. It effectively solves the structural defect of single-horizontal-angle strand installation of mountain flexible brackets and flexibly meets the multi-angle strand fixing requirements of mountain and hill terrain. This flexible bracket strand clamp has been installed in several flexible PV bracket power plant projects. Practice has proved that it effectively reduces wear at the strand connection and fixing points, increases strength, avoids quality hazards caused by excessively large turning angles, and significantly improves the quality and safety performance of flexible PV brackets.

Key Takeaways

• Judge flexible bracket quality by comparing its strand fixing structure with suspension bridge cable-clamp practice.
• U-bolt fixing of strand does not meet anchor-cable national standards and creates rust and fracture risks.
• Universal-joint combined clamps raise contact area about 1,000-fold and handle multi-angle mountain terrain.