Abstract: A very lightweight tubular building element for the construction of reinforced concrete floors and roofs; providing the formwork for the casting in place of the structural concrete and a high quality finished ceiling at the same time. It is a single component that can be installed easily and efficiently without heavy equipment or special craftsmanship; afterward the component is not removed, but stays permanently integrated in the concrete floor or roof. It forms a deck that is impervious, eliminating cumbersome cleaning during construction and leakage afterward, saving the common need of a costly waterproofing membrane over the slab. The formwork deck, composed of a plurality of the invention component, weighs less than four (4) pounds per square foot; and a single component for a common 15 feet span weighs less than 30 pounds, which can be easily handled by only one laborer.

Abstract: A structural member includes side walls, a top wall connecting a top region of the side walls, a bottom wall connecting side wall bottoms and extending beyond the side walls to form wings each having one portion of a connector for connecting members to one another, a span connected to the side walls, and truss configurations each connected to the span and the bottom wall and respectively to one side wall. Side walls, top wall, and span define an upper interior chamber and span, truss configurations, and bottom wall define a lower interior chamber. Each truss configuration has a vertical wall and two intermediate walls. An assembly of members interlock with one another in series by connecting a first portion of the connector with a second portion of another member. These interlocked members form a structure for receiving concrete as a base for a ribbed concrete slab.