Simultaneous　topology,　shape　(form-finding)　and　size　optimization　of　steel　arched　trusses　was　performed　under　vertical　multi-loading　case　and　seismic　action.　To　bear　vertical　multi-loading　cases,　optimum　truss　arches　were　optimized　by　shaping　the　two　chords　in　order　to　suitably　convert　bending　moments　acting　along　the　truss　arch　into　axial　forces　in　each　arched　chord,　thus　allowing　to　bear　highly　different　multi-loading　cases.　The　chord　shape　is　identified　by　defining　the　form　of　the　arched　chords　through　Cubic　Rational　Bezier　curves.　Similarly,　when　considering　the　seismic　action　too,　two　arched　chords　arc　still　considered,　but　lying　on　different　planes.　For　this　purpose,　the　upper　chord　of　the　truss　arch　has　been　supposed　to　lie　on　the　horizontal　plane,　while　the　lower　chord　was　shaped　as　an　inclined　arch.　The　two　arches　are　connected　by　a　bracing　system,　thus　collaborating　to　bear　the　external　loading.　The　horizontal　arch　primarily　resists　to　the　earthquake　action　that　mainly　determines　its　shape,　while　the　vertical　loads　are　transferred　to　the　inclined　arch,　thus　mainly　affecting　its　shape.