<p>This paper presents a tunable elastic metamaterial structure with periodically arranged resonators. The resonator consists of two beams and a moveable lumped mass block. The dynamical model of the proposed structure is established in frequency domain. The frequency responses are obtained by applying the spectral element method and finite element method. The influences of the structural and material parameters on the wave properties are explored. It is shown that the movement of the mass blocks has great relationships with the bandgaps, such as frequency shift and broadening effects. The parameter optimization is given by using genetic algorithms in order to improve the obtained results. The optimal positions of the mass blocks are addressed and ultra-wide bandgaps are revealed. An experimental platform is designed and performed to validate the bandgap characteristics.</p>