Name of OHTL


Voltage of OHTL



Linuhönnun (now EFLA) technical assistance for design

Duration of assignment

04.2003 - 05.2004

Value of service

70 k€

The aim of the project was the design of a temporary leg installed between the fork and the upper beam of an existing 400kV double circuit latticed steel tower (A4AB3_W type) in order to simplify the erection of new anti cascading tower on 400kV double circuit lines.

A preliminary design led HECLA's engineer to model the tower equipped with its leg with TOWER software (POWERLINE SYSTEM Inc.) for all construction work's stages in order to get the design load cases.

Design complied with the following constraints: assembly of elements no longer than 3m, whose weight did not have to exceed 600daN. The width of the temporary leg did not have to exceed 2m. Leg connections had to allow easy assemblies and dismantling because these operations had to be carried out close to a live circuit. The design itself had to comply with numerous handlings.

The sizing of leg was then able to be optimized, in particular the cross sections of main legs and braces, the steel class according to the actual transferred loads. Some of the connection parts were particular: use of welded connections, requiring a specific check made in accordance with NF P 22-470 standard, use of a 65mm diameter bolt. Workshop drawings have then been realized, and HECLA supervised the trial assembly at the supplier factory.

A real size test has been successfully carried out on 2x400kV OHTL Granzay – Les Jumeaux, in France.