A natural fiber-based, engineered beam assembly comprising opposing top and bottom surfaces, opposing first and second side surfaces and a longitudinal axis. Loads applied to the beam assembly are normal to the top surface. Substantially parallel layers of flattened bamboo or vegetable cane culms are stacked and laminated together. Each layer is formed by at least one culm, and each culm has fiber bundles extending substantially parallel to the longitudinal axis and are impregnated with a binder. The density of the fiber bundles in the culm decreases across the culm's thickness from the exterior surface to the interior surface. At least a plurality of the culms have a common orientation, wherein the exterior surfaces face toward a same one of the top, bottom, first or second side surfaces.