Structural Design of Long-Span Flexible Brackets: Truss Forms, Span-Wise Layout and Wind-Pressure Adaptation

This article carries out technical analysis on the basis of national policies, standards and codes, public data and the current state of the industry. It is intended purely as objective discussion, only to make the product structure sounder, and is not directed at anyone.

Many flexible brackets on the market have fundamental problems in their structural design. This article sets out the core keys to flexible bracket safety: by understanding and implementing the design logic described here, the safety of long-span flexible brackets can be greatly improved, and "swimming" oscillation, heavy vibration and swaying can be eliminated at the root.

Thanks to their long span, low bracket density and suitability for complex terrain, PV flexible brackets are widely used in large PV plants. Their structural stability, load-bearing safety and wind resistance directly determine the safety and service life of long-span flexible brackets, and depend on a scientific and reasonable structural layout and precise matching of actual conditions. This article systematically analyses the design logic of long-span flexible brackets in terms of structural forms, span-wise design, truss connections and wind-pressure adaptation, returning to the essence of structural mechanics.

I. Analysis of typical truss structural forms

Form 1: Series-connected independent triangular units

Composed of multiple independent triangular units connected in series by single members, without continuous top and bottom chords, it does not form a complete truss load-bearing system and relies only on local triangles for single-point stability. Force transfer is discontinuous and the capacity for overall coordinated work is weak; under lateral and repeated loads it is prone to deformation and displacement. At best this structure forms a chain-like linear connection and has essentially no rigidity, so it can play no effective role in the overall stability and wind resistance of the structure, seriously threatening the safety and service life of long-span flexible brackets.

Form 2: Statically indeterminate parallel-chord truss

This is a standard, complete truss structure with continuous top and bottom chords, together with cross diagonal webs and vertical webs, forming a geometrically stable system. Members work mainly in axial tension and compression, the load path is clear, structural redundancy and overall stiffness are high, and resistance to wind, torsion and deformation is strong. It is suitable for demanding conditions such as high loads, high wind pressure and long spans; the member quantity is ample and the cost is relatively high, but it can fully guarantee the safety and service life of long-span flexible brackets.

Form 3: Statically determinate Warren parallel-chord truss

This is a standard truss form commonly used in the industry. The top and bottom chords are continuous, and the web members are arranged as single diagonals, forming a continuous triangular lattice — a geometrically stable, statically determinate structure. The top chord is in compression, the bottom chord in tension, and the webs transfer shear effectively. It offers a good balance between stability and economy, with moderate stiffness and controllable deformation, and is a fairly general, reasonable structure for long-span flexible brackets.

Form 4: Series-connected diagonal braces without chords

Without continuous load-bearing chords, it consists only of scattered diagonal braces and short members lapped together, does not form a complete force-transfer system, and is overall a geometrically changeable system. Lacking core bending and lateral-force-resisting members, most members are in a compound stress state; overall stiffness is insufficient and resistance to lateral disturbance is weak. Its applicable conditions are limited, and it cannot meet the safety and service life requirements of long-span flexible brackets.

II. Key points of the bi-directional load design of flexible brackets

A long-span PV flexible bracket adopts a bi-directional structural system of east–west load-bearing cables plus rigid north–south truss connections; the two together determine overall stability.

(1) East–west long-span design

The east–west direction is the main span direction. The current mainstream long-span sizes in the industry cover three typical levels — 32 m, 50 m and 60 m — relying mainly on the coordinated work of load-bearing cables, main cables and stability cables:

The load-bearing cables carry the vertical loads of modules and equipment, controlling deflection through a reasonable sag ratio and pretension force;

The main cables maintain the shape of the cable network and ensure structural continuity;

The stability cables reduce wind-induced vibration and improve the resistance of the cable system to disturbance.

Long-span design must balance load-bearing capacity and deformation control. It is the foundation of structural safety and, even more, the core prerequisite for the safety and service life of long-span flexible brackets.

(2) North–south truss connection design

The east–west cable system itself has weak lateral stiffness. When multiple rows of arrays are arranged north–south, a single row of cables tends to sway and twist under wind load. The role of the north–south trusses is to connect multiple independent cable networks into a spatial structure working as a whole, achieving uniform load transfer, suppressing sway, and resisting lateral displacement and torsion — this is the key to overall stability. Truss spacing is not a fixed value and should be specially designed according to the project's actual wind load conditions.

III. Wind pressure and north–south truss spacing adaptation

The basic wind pressure is the core basis for determining truss spacing; the design follows the principle of densifying in high wind pressure and relaxing moderately in low wind pressure:

Low-wind-pressure regions (0.3–0.4 kPa): wind load has a small influence, and truss spacing can be 5–6 m;

Moderate-wind-pressure regions (0.5–0.7 kPa): wind effects are evident, and truss spacing should be controlled at 4–5 m;

High-wind-pressure regions (0.8–1.0 kPa, coastal and strong-wind areas): wind load and torsion effects are prominent, and truss spacing should be densified to 3 m or less, to ensure sufficient safety reserves against wind and torsion and to secure the safety and service life of long-span flexible brackets.

Structural calculation and model analysis should genuinely reflect actual conditions such as the project's wind pressure, restraint conditions and member layout, so that the calculation results are consistent with engineering reality. Drawing review and expert assessment should strictly check key indicators such as the load-bearing system, stiffness and wind resistance, so that procedural compliance is built on a structurally sound basis.

The long-term safety of a structure comes from a scientific and reasonable load-bearing system, sufficient stiffness and safety reserves under real conditions. A design divorced from mechanical logic and relying only on formal packaging and procedural documents can hardly guarantee the reliability of the structure in actual operation. Engineering safety is ultimately decided by the structure itself.

IV. Suggestions for the standardized development of the industry

Improve the standards system: it is suggested that the relevant standardization bodies, in light of different wind-pressure regions and different spans — especially the mainstream long-span conditions of 32 m, 50 m and 60 m — further refine technical requirements such as structural layout, truss spacing and cable system configuration, supplement and improve the design principles, and promote the standardized development of the industry.

Strengthen tendering technical constraints: it is suggested that owners and tendering parties clearly lock key indicators such as the structural system, truss spacing and wind-pressure adaptation requirements in tender documents and technical specifications, control design quality at the source, reduce later safety and O&M risks, and effectively guarantee the safety and service life of long-span flexible brackets.

Adhere to the origin of structural design: engineering design should return to the essence of mechanics, determine parameters from real conditions, ensure safety through a sound structure, and achieve safe and stable operation of PV plants throughout their life cycle through scientific, rigorous and pragmatic design.

V. Conclusion

The core of a long-span PV flexible bracket lies in the coordinated design of east–west load-bearing cables and north–south truss stability. All technical parameters should fit the actual load environment and the laws of structural mechanics, and precise adaptation is especially required for the 32 m, 50 m and 60 m long-span scenarios. With a scientific structure as the foundation, codes and standards as the guide, and source control as the guarantee, the industry can truly achieve high-quality development, continuously ensure the safety and service life of long-span flexible brackets, and provide solid support for the long-term reliable operation of PV plants.

We are willing to work with owners and design institutes on prudent selection, safeguarding the peace of mind and returns of projects.