Monolithic precast reinforced concrete (RC) frames with cast-in-place joint cores and grouted-sleeve splices are increasingly adopted in seismic regions, yet connection degradation is not carried through to system-level fragility: existing studies take hinge properties from code tables or one test, or stop at the joint. This study closes that gap with a reproducible transfer route in which the degrading, pinched M–θ hysteresis identified from a refined joint model becomes structure-level hinge parameters, with every intermediate quantity reported so that the route can be reproduced elsewhere. The joint model is an explicit finite-element interface-spring/contact strategy with Mohr–Coulomb interface behavior, tension cut-off, local spring failure, and sleeve–grout–rebar bond slip. Incremental dynamic analysis and fragility assessment of a six-story monolithic precast frame and a comparable cast-in-place frame show larger inter-story drift demands in the precast frame. At PGA = 0.40 g, its collapse exceedance probabilities are higher by 0.73 and 0.44 percentage points in X and Y, respectively. Global performance is broadly comparable, but the precast frame shows a consistent, modest unfavorable tendency caused by connection pinching and reduced ultimate rotation. Interface treatment, sleeve grouting quality, and connection-level ductility should therefore be explicitly considered in seismic performance assessment and design.