The　poor　stiffness　and　strength　of　traditional　U-shaped　dampers　is　an　issue　that　is　addressed　in　the　present　work　by　the　development　of　a　new　form　of　T-section　metallic　damper,　termed　as　the　TSMD.　Theoretical　and　experimental　studies　are　carried　out　to　evaluate　the　seismic　performances　of　TSMD.　Based　on　the　principle　of　virtual　work　and　Castigliano＇s　second　theorem,　theoretical　formulas　of　yield　strength　and　initial　stiffness　of　TSMD　are　derived　and　verified.　Stiffness,　strength　and　energy　dissipation　capacity　of　TSMD　are　significantly　higher　than　those　of　the　U-shaped　damper　with　the　same　size　of　flange.　A　finite　element　model　which　can　capture　the　cyclic　responses　and　fracture　failures　of　TSMD　is　established.　Based　on　the　numerical　simulation　and　parametric　study,　the　effects　of　geometrical　dimensions　and　material　properties　on　the　seismic　performances　of　TSMD　are　quantified.　The　mechanical　characteristics　of　the　damper　are　significantly　affected　by　the　web　width,　height,　flange　width,　and　thickness　of　the　T-section　of　TSMD.　Shape　memory　alloy-made　TSMD　shows　stronger　strength　hardening　and　fracture　resistance　capacities　than　traditional　steel-made　TSMD　and　decreases　damper　residual　displacement　after　cyclic　loading.　This　study　aims　to　provide　valuable　insights　into　the　behavior　and　potential　applications　of　the　TSMD.