Alternative structural layouts for wind turbine blades are investigated with the aim to improve their design, minimize weight and reduce the cost of wind energy. To obtain the new concepts, topology optimization is performed on a 45 m wind turbine blade. Additionally, shape factors for non-symmetric sections under biaxial bending are developed to evaluate the results in terms of ability to minimize deflection and stress. The topology optimization results in a concept which transforms along the length of the blade, changing from a design with spar caps at the maximum thickness and a trailing edge mass, to a design with offset spar caps towards the tip. The shape factors indicate that the trailing edge reinforcement and the offset spar cap topology are both more efficient in minimising deflection and stress. In summary, an alternative structural layout for a wind turbine blade has been found and shape factors have been developed, which can quantitatively assess the structural efficiency under asymmetric bending.