Blade assembly for a wind turbine blade, wind turbine and method for building a wind turbine blade

A blade shell assembly configured for forming a wind turbine blade shell, the blade shell assembly comprising:

• a first element configured as a main spar element for placement along a length of the blade shell, the first element having a first mating surface along a longitudinal side thereof;
• a second element configured as a core material for placement along the length of the blade shell adjacent the first element, the second element having a second mating surface along a longitudinal side thereof opposed to the first mating surface;
• wherein the first mating surface and the second mating surface are configured to butt against each other in an assembled state of the wind turbine blade shell;
• the second element comprising a spring effect section having one or more grooves displaced from the second mating surface such that the spring effect section is compressible and expandable in a cross-sectional direction of the second element substantially perpendicular to the second mating surface;
• and
• wherein the second element is configured for placement adjacent the first element in a blade shell mold with the first and second mating surfaces transverse to the blade shell mold and opposed to each other and with the spring effect section in a compressed state, wherein the spring effect section may remain in the compressed state in abutting engagement with the first mating surface or expand such that the second mating surface moves across a gap between the first and second elements and into abutting engagement with the first mating surface.