Abstract: A collar for connecting a duct to a wall having a hole therein bounded by an edge having a predetermined thickness. The collar is constructed from a sheet of material having top, bottom, left and right edges, the sheet forming a tubular structure in which the left and right edges overlap. The sheet includes a groove for engaging the edge of the hole. The sheet also includes first and second detents spaced apart thereon. The overlap of the left and right edges at the top edge changes when the spacing between the first and second detents is changed. The collar also includes a first fastener for fixing the overlap of the left and right edges at the top edge when the edge of the hole is engaged in the groove and a second fastener for fixing the overlap of the left and right edges at the bottom edge. In the preferred embodiment of the present invention, the groove includes a layer of a sealing material for forming a seal between the sheet of material and the edge of the hole.

Abstract: A high-energy-absorbing prestressed concrete fender pile, and fendering sem using a plurality of such piles, constructed from high-strength concrete prestressed with longitudinal tensioned strands only partially prestressed such that the longitudinal strands remian elastic to provide high remaining material strength for absorbing high energy impact prior to reaching the yield strength of the strands; the longitudinal tensioned strands are wrapped with an outer spiral wire reinforcement, and the longitudinal strands are preferably stressed to remain elastic until the concrete reches a capacity of 0.003 inch/inch compression strain.