Mechanical testing of a new “node-and-bolt-based” assembly system using a full-scale tubular lattice tower module

Spanish OHL system, these constraints have driven the search for more cost-effective, compact, material-efficient, and visually integrated tower designs that remain compatible with existing regulatory frameworks.

Tubular lattice towers offer a promising alternative, providing improved buckling resistance for a given mass, reduced bracing density, and enhanced aerodynamic performance, while enabling more visually transparent structures. When combined with insulated cross-arms, these advantages contribute to tower compaction, lower material usage, and reduced right-of-way requirements. However, the widespread adoption of tubular lattice systems has been limited by the lack of a clearly established, cost-effective, and mechanically robust on-site connection solution suitable for large-scale transmission and distribution (T&D) infrastructures.

This paper reports the fabrication and full-scale experimental testing of a representative module derived from our proposed 400 kV double-circuit tubular lattice tower design [1]. The module is assembled using a novel node-and-bolt-based system with six-arm tubular nodes.

As the experimental campaign was performed on a unique partial structural assembly, an auxiliary frame was designed and employed to reproduce representative working conditions and prevent premature failure. A single finite-element-optimised load case was applied exclusively at the top nodes to approximate the most demanding tensile and compressive load effects at the six-arm nodes, corresponding to extreme 140 km/h lateral wind actions plus a 50

% safety margin in accordance with Spanish regulation. This strategy ensured that critical demand scenarios were captured within the scope of a feasibility assessment. The experimental campaign was conducted at a dedicated tower testing facility using calibrated force measurement devices, with loads applied incrementally from 10 % up to 150 % of the regulatory design loads. The tested module sustained 130 % of the design loads before failure, which was governed by bolt fracture at the tube–to–node arm connections, while no yielding or instability was observed in the tubular members or node bodies. These results demonstrate the structural feasibility of the proposed node-and-bolt-based system under realistic load conditions and support its further development toward future full-tower validation campaigns.