Assembly, comprising: - a first member and a second member that are tubular members of a wind turbine support structure, wherein; - the second member has a fork-shaped cross section with a main body arranged between two substantially parallel walls that each comprise at least one through hole (13, 14); - the first member is arranged between the two walls of the second member, having the through hole (13, 14); - wherein a through hole of the first member and the through holes (13, 14) of the second member define a channel; - a connector that is axially insertable in said channel to an end position and consecutively expandable radially relative to said channel, to connect the first member and the second member relative to each other; characterized by - an actuator configured to move said connector in an axial direction in said channel, and further configured to consecutively; - insert said connector into said channel from a first side, - move said connector in the axial direction in said channel to the end position, and - actuate the connector from the same first side to expand the connector radially relative to said channel and thereby connect the first member and the second member relative to each other; and - wherein the connector, in an expanded state thereof, pushes the first member in a radial direction relative to said channel against a face of the main body of the second member to define a clamping contact and thereby a pre-tensioned connection in said radial direction relative to said channel between a face of the first member and the face of the main body of the second member. - a first member and a second member that are tubular members of a wind turbine support structure, wherein; - the second member has a fork-shaped cross section with a main body arranged between two substantially parallel walls that each comprise at least one through hole (13, 14); - the first member is arranged between the two walls of the second member, having the through hole (13, 14); - the second member has a fork-shaped cross section with a main body arranged between two substantially parallel walls that each comprise at least one through hole (13, 14); - the first member is arranged between the two walls of the second member, having the through hole (13, 14); - wherein a through hole of the first member and the through holes (13, 14) of the second member define a channel; - a connector that is axially insertable in said channel to an end position and consecutively expandable radially relative to said channel, to connect the first member and the second member relative to each other; - an actuator configured to move said connector in an axial direction in said channel, and further configured to consecutively; - insert said connector into said channel from a first side, - move said connector in the axial direction in said channel to the end position, and - actuate the connector from the same first side to expand the connector radially relative to said channel and thereby connect the first member and the second member relative to each other; and - insert said connector into said channel from a first side, - move said connector in the axial direction in said channel to the end position, and - actuate the connector from the same first side to expand the connector radially relative to said channel and thereby connect the first member and the second member relative to each other; and - wherein the connector, in an expanded state thereof, pushes the first member in a radial direction relative to said channel against a face of the main body of the second member to define a clamping contact and thereby a pre-tensioned connection in said radial direction relative to said channel between a face of the first member and the face of the main body of the second member.