Current precast concrete diaphragm design may not necessarily protect the diaphragm from a non-ductile shear failure in an overload situation. As evidence exists that diaphragms can attract large inertial loads during strong ground motion, it may be advisable to develop the diaphragm flexural strength. However, the performance target desirable or achievable in design may depend on a number of other factors. An analytical study examines precast diaphragm performance for diaphragms of different shear strength relative to flexural strength over the range of several design parameters. The primary objective of the study is to determine the required shear reinforcement design overstength (relative to the flexural reinforcement) in the precast diaphragm to produce good performance. A number of key parameters are examined including diaphragm shear overstrength, diaphragm span, aspect ratio and the tension deformation capacity of reinforcing details.