短语词组短語main steel girder 鋼主梁main box girder 箱形主梁main hull girder 主船躰桁main longitudinal girder 主縱梁single -main-girder 單主梁box -main-girder 箱形主梁main girder webs 主梁腹板fetching material main girder 取料主梁main girder web 主梁腹板 返回 main girder