A rotor blade for a wind turbine includes a first blade segment and a second blade segment extending in opposite directions from a chord-wise joint. Each of the first and second blade segments includes at least one shell member defining an airfoil surface and an internal support structure. The first blade segment includes a beam structure extending lengthwise that structurally connects with the second blade segment. Further, the beam structure forms a portion of the internal support structure of the first blade segment. Moreover, the beam structure is formed, at least in part, of a first portion constructed of a first composite material and a second portion constructed of a different, second composite material. Further, the first and second portions are connected together via a scarf joint. In addition, the scarf joint includes a different, third composite material arranged between the first and second composite materials.