A method of manufacturing a load-bearing structure. The method may include establishing overall dimensions and expected loading conditions of the load-bearing structure; determining a material density distribution within a solid model for the load-bearing structure based on the overall dimensions and the expected loading conditions for a predetermined objective end constraint; generating stress field data for the determined material density distribution based on the expected loading conditions; transforming the solid model into a spatially-graded mesh model having a plurality of three-dimensional cells based on orthogonal isostatic lines populated along principal stress directions of the stress field data;; and fabricating the load-bearing structure with truss members aligned according to the spatially-graded mesh model. A system for manufacturing a load-bearing structure and a load-bearing structure manufactured thereof.