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Architected materials can be synthesized to effectively control elastic wave propagation via bandgap engineering, which is essential for vibration mitigation and sound attenuation applications. Mechanisms for controlling elastic waves include Bragg scattering resulting from structural periodicity and local resonance effects, both of which were employed to create bandgaps. It is also shown that with careful design, the Bragg- and resonance-type bandgaps can be combined to achieve broader stopbands. Structures that use these bandgap mechanisms, especially those utilizing local resonators, add mass to the system, which could be highly undesirable for many engineering applications where mass considerations directly impact the system efficiency. To address this shortfall and advance the state of the art, this research proposes a mass-conserved design concept for metastructures that utilize both Bragg-type and local resonance bandgap mechanisms to create enhanced bandgap characteristics within the structure. The mass-conserved design is achieved by employing the existing system mass to create geometries that allow for bandgap generation, rather than adding mass to the structure as seen in traditional metastructure systems. The developed methodology shows that broader stopbands can be created without adding mass to the overall system, and this research identifies critical design parameters in order to achieve effective mass-conserved bandgap engineering compared to traditional metastructures designs. This method of mass-conserved metastructure design is shown to be effective when applied to various means of tuning that further enhance the bandgap regions, including the use of multiple-degree-of-freedom resonators and hybrid unit cells. These advancements provide a mass-constrained approach to bandgap engineering methods, expanding our ability to create lighter and more efficient structures with effective vibration control.