Abstract: A mechanical coupler for the reinforcing bars depending on the original male deformations of the reinforcing bars. The coupler comprising a pipe split along its longitudinal axis into two portions. The inner surface of each portion is grooved to form female grooves that exactly matching the reinforcing bar male deformations. The coupler is formed of one or two halves of the pipe portion assembled over the ends of the axially aligned reinforcing bars allowing for the bars male deformations to exactly enter into the pipe portion female grooves without any clearance or filling material to be added. Five techniques are applicable to tightly close the sleeve over the connected reinforcing bars ends. The outer surface of the pipe portions is processed to be used according to the technique of closing either one or two pipe portions over the reinforcing bars ends.

Abstract: A mechanical coupler for reinforcing bars is made of a sleeve divided into two halves split (13, 14) along its longitudinal axis. Each half is grooved (being a “female” 16) along its inner surface to match with the deformations “male” (10) on the reinforcing bars (1, 2). The sleeve is adopted to connect the ends of the two reinforcing bars in which the deformations of the reinforcing bars “male” (10) fitted into the groves “female” (16) made in the inner surface of the sleeve (13, 14). Three methods for closing the two halves in order to make the sleeve with the bars connection behaving as one unit are presented. The sleeve parts can be manufactured using casting or forging or rolling methods. The coupler does not affect the effective cross-section area of the reinforcing bars as in case of threading or concentrate stresses at certain points as in case of notching. The coupler as presented could allow for connecting reinforcing bars ends with different diameters.

Abstract: A technique and apparatus for retrofitting the concrete elements using external prestressing is presented. The method is more applicable in columns with rectilinear cross-section. This technique increases the strength and ductility of the reinforced concrete elements without significantly increasing the dimensions or weights of these elements, or even harming the concrete section. The technique is simple, easy to use, and does not need special hardware in rectilinear cross-sections. In addition, the technique reduces the lateral strains, internal cracking, and volume increase when adding more loads on the concrete element. Global external prestressing is provided along the whole length or the required part of the element to be strengthened through a set of elongated members using the special apparatus presented hereinafter.