Abstract: A structural panel having a thin-walled outer layer of high tensile strength and/or high modulus of elasticity material preformed as a large area trough open at the top and of a depth substantially the thickness of the panel, into which is poured a low tensile strength and/or a low modulus of elasticity material in metered quantities, which is compacted and hardened therein, in such a manner to form a composite with the trough where the trough is an externally disposed reinforcement member for the panel. The trough has a peripheral flange around the open top with accurately positioned apertures therethrough, or accurately positioned apertures through the bottom of the trough near the corners for connecting a plurality of the panels in alignment to external supports. The accurately positioned apertures are formed at the same time the trough is formed. The open top of the trough may be closed by a horizontal stress transmitting cover plate connected to the peripheral flange.