This　study　deals　with　optimum　geometry　design　of　laterally　loaded　piles　in　a　Winkler＇s　medium　through　the　Fully　Stressed　Design　(FSD)　method.　A　numerical　algorithm　distributing　the　mass　by　means　of　the　FSD　method　and　updating　the　moment　by　finite　elements　is　implemented.　The　FSD　method　is　implemented　here　using　a　simple　procedure　to　optimise　the　beam　length　using　an　approach　based　on　the　calculus　of　variations.　For　this　aim　two　conditions　are　imposed,　one　transversality　condition　at　the　bottom　end,　and　a　one　sided　constraint　for　moment　and　mass　distribution　in　the　lower　part　of　the　beam.　With　this　approach　we　derive　a　simple　condition　to　optimise　the　beam　length.　Some　examples　referred　to　different　fields　are　reported.　In　particular,　the　case　of　laterally　loaded　piles　in　Geotechnics　is　faced.　Copyright　©　2018　Techno-Press,　Ltd.