Method of assembly and installation of an offshore support structure for a wind turbine

In the assembly of the support structure (3) of a wind turbine (2), N sets of a first tubular brace (11) and a second tubular brace (12) extend from a tower support (8). For each set, the second braces (12) are connected at one or both of their end parts (12A, 12B) by a casted connection. The first brace (12) or the tower structure (8) has a casting cavity (16) for accommodating an end of the corresponding second brace (12). In order to assemble the construction, the second brace (12) is inserted into the cavity (16), after which the end (11A) of the first brace (11) is lifted until the end of the second brace is inserted deeply enough into the respective cavity.