Force Analysis of Lattice Steel Tube Concrete Wind Power Tower

Literature Overview

This 2010 paper by Liu Xiang, Wang Min, and Li Jian, published in Journal of Wuhan University of Technology, investigates the structural behavior of lattice steel tube concrete (CFST) wind power towers. The study provides analytical formulations for the strength, stiffness, and stability of CFST columns used in lattice tower configurations. The research is significant for the growing wind energy industry, where cost-effective and durable tower structures are essential for economic wind power generation.

Core Technical Content

The lattice CFST wind tower combines the benefits of tubular steel members with the confinement effect of concrete infill. The analytical study covers three primary design checks:

Design Check	Governing Formula Type	Key Parameters	Result
Strength (compressive capacity)	N ≤ φfA_c + f_sA_s	Concrete strength, steel yield, area	Satisfies requirements
Stiffness (deflection)	δ ≤ L/500 (typical)	EI equivalent, span, loading	Satisfies requirements
Stability (buckling)	N ≤ N_cr (Euler/Flexural)	Slenderness ratio, effective length	Satisfies with margin

The example calculations demonstrate that the lattice CFST tower configuration provides adequate strength, stiffness, and stability with a conservative design margin. This conservatism may offer opportunities for material optimization in practical design.

Steel Tube Manufacturing and Welding Considerations

For the steel tubes used in lattice CFST wind towers, the following technical considerations are important:

Tube geometry and tolerances: Lattice towers use relatively small-diameter steel tubes (typically 168-457 mm OD) with wall thicknesses of 6-16 mm. The dimensional tolerances per ASTM A671 or GB/T 6725 must be strictly controlled, as variations in wall thickness directly affect the confinement effectiveness and structural capacity.
Welding of lattice connections: The gusset plate connections in lattice towers are critical welded joints. The following welding practices are recommended:

Weld Type	Process	Key Requirement
Gusset-to-tube fillet weld	GMAW or SAW	Full throat penetration, no slag inclusion
Gusset-to-gusset butt weld	SAW	Full penetration, RT inspection
Tube-to-tube lap weld	GMAW	Consistent gap control

Concrete placement in tubes: The concrete infill in CFST lattice members requires careful placement to ensure full compaction without voids. The tube diameter-to-aggregate-size ratio should be maintained at a minimum of 3:1 to prevent blockage during pumping.

Quality Control Framework

Applying a systematic quality control approach to the lattice CFST tower fabrication:

Plan: Establish acceptance criteria based on GB 50935 (Code for design of concrete-filled steel tubular structures) and applicable welding standards (GB/T 19866 for welding procedure qualification).
Do: Implement in-process inspection including weld visual examination, UT for critical welds, and concrete slump/air content testing during placement.
Check: Conduct post-fabrication NDT including RT for butt welds, MT for fillet welds, and dimensional survey of the assembled lattice frame.
Act: Document nonconformances and implement corrective actions. Maintain traceability records for all steel tube batches and weld operator certifications.

Engineering Practice Integration

The lattice CFST configuration offers several practical advantages for wind tower applications:

The concrete infill provides excellent fire resistance, eliminating the need for expensive fireproofing coatings.
The increased mass of CFST members reduces wind-induced vibration amplitudes compared to hollow steel tubes.
The lattice configuration provides efficient material utilization with good torsional stiffness for wind loading.

However, the increased dead load from concrete infill must be carefully balanced against the structural benefits. For tall towers (>100 m), the self-weight contribution to base moment becomes significant, and the designer must optimize the CFST member sizing to achieve the best overall structural efficiency.

Study Insights and Conclusions

This paper provides a solid analytical foundation for the design of lattice CFST wind power towers. The demonstrated conservatism in the example calculations suggests that further research into the actual load-bearing behavior of CFST lattice members could lead to more economical designs. For steel pipe engineers, the key takeaway is that the confinement effectiveness of CFST members depends critically on the tube's geometric regularity and material uniformity. Manufacturing quality directly translates to structural performance, and investment in quality control at the fabrication stage yields significant benefits in terms of structural reliability and service life.