A spar assembly for a rotor blade of a wind turbine is disclosed. The spar assembly includes a first spar cap segment and a second spar cap segment. The first spar cap segment is configured on an interior surface of a first blade segment and the second spar cap segment is configured on an interior surface of a second blade segment. Each spar cap segment includes an end having a joint section that is joinable at a chord-wise joint. Each of the first and second joint sections includes a plurality of holes formed therein. Further, the spar assembly includes a plurality of pins inserted into the plurality of holes of the first and second joint sections to join the first and second blade segments so as to improve stiffness of the rotor blade.