In　order　to　predict　the　ductile　fracture　of　welded　connections　in　steel　structures　due　to　earthquakes,　the　investigations　were　carried　out　on　the　calibrations　and　validations　of　micromechanics-based　fracture　models.　The　void　growth　model　(VGM)　and　the　stress　modified　critical　strain　(SMCS)　model　relate　the　micromechanism　of　ductile　fracture　(void　nucleation,　growth　and　coalescence)　to　macroscopic　stress　and　strain　fields.　The　VGM　and　SMCS　model　parameters　for　Q345　structural　steel,　the　corresponding　weld　and　heat-affected　zone　were　calibrated　by　using　the　available　tensile　tests　of　notched　round　bars　and　the　complementary　finite　element　analyses　(FEA).　Seven　local　welded　assemblies　of　beam-to-column　connections　were　tested　at　monotonic　tensile　loading,　and　the　fracture　critical　elongations　were　measured.　The　J-integral　based　fracture　mechanics　approach　and　micromechanics-based　model　VGM　and　SMCS　were　adopted　to　predict　the　fracture　critical　elongation　of　each　specimen　using　the　refined　finite　element　model　(FEM).　The　comparisons　between　FEA　predictions　and　experimental　measurements　in　fracture　critical　elongation　indicate　that　the　VGM　and　SMCS　models　could　predict　the　ductile　fracture　of　welded　connections　with　reasonable　accuracy,　while　the　J-integral　approach　obtains　quite　conservative　results.　A　general　method　that　is　only　material　dependant　is　proposed　for　the　ductile　fracture　prediction　of　welded　connections　in　steel　structures.　©,　2015,　Tsinghua　University.　All　right　reserved.