A composite structural element has a main steel beam having a web and at least two flanges extending therefrom, having oppositely directed outer faces, having outer edges generally defining a plane and defining with the web a recess open away from the web between the outer edges. A mass of concrete fills the recess substantially to the plane, the outer flange faces being exposed and substantially free of concrete. Another profiled steel beam is fixed to the web of the main beam and wholly imbedded in and covered by the concrete mass. Typically the main beam is an H- or I-beam and has two such channels provided with such other beams and filled with respective such masses. The other beams can be of T-section or each other beam can be an I- or H-beam. In addition it is possible to provide longitudinally extending steel reinforcing bars imbedded in the concrete mass. Steel fibers can also be imbedded as reinforcement in the concrete mass, and this mass can be at least partially of colloid concrete.

An concrete filled steel tube column and method of constructing same. The concrete filled steel tube column includes a steel tube having an inner face; a concrete core disposed within the steel tube; and a separating layer interposed between the inner face of the steel tube and the concrete core for separating the concrete core from the inner face of the steel tube so that the steel tube may not be bonded to the concrete core. After the separating layer is formed on the inner face of the steel tube, the concrete is charged into the steel tube to form a concrete core.

A composite bearing column comprises a solid metallic core of circular or polygonal section free from reentrant recesses. The core is embedded in an intermediate layer of mortar which is compatible both with metal and with concrete. An external concrete mass surrounds the intermediate layer. Metallic bars are longitudinally distributed around the central core in that concrete mass and extend lengthwise of the column parallel to the core. The bars are welded at their opposite ends to a base plate and to a head plate. In one embodiment, mounting rings are secured to the base and head plates and extend toward each other; and a metallic wire helically surrounds the bars.

A centrifugally cast hollow fiberglass reinforced plastic (FRP) column having angled corners and straight sides. Interiorly of the column adjacent each corner are angled corner fillers that have straight angled sides adhered to straight interior wall surfaces of the column adjacent the respective corners. During molding, the corner fillers are supported within the mold with their straight sides in parallel spaced relation to the straight interior walls of the mold adjacent the respective mold corners a distance slightly greater than the desired minimum wall thickness of the column, whereby when the mold is rotated, uncured FRP material within the mold will flow by centrifugal force into engagement with the interior walls of the mold and around the corner fillers into the space between the corner fillers and interior walls of the mold adjacent the respective mold corners to form a column having a substantially uniform FRP wall thickness.

A method and apparatus for retensioning the development length of strands of an elongated prestressed concrete member is provided in which the ends of the strands are exposed, a metallic plate having tapered holes therein is placed over the ends of the strands, retaining wedges are inserted into the tapered holes of the plate to grip the ends of the strands, and a predetermined amount of tension is applied to the strand and maintained in the strand by the retaining wedges. A jack is provided to apply the tension to the strand. The prestressed concrete members such as piling, may be spliced together by using the apparatus on adjoining ends of piling.