Method of forming a concrete structure with a recess to receive an anchorage

#In the construction of many concrete members and particularly floor slabs and slab walls it has been found to be particularly advantageous to use a prestressed concrete construction. Tupicaly, a plurality of tendons and tendon anchorages are placed within the concrete forms and the concrete is then poured with the tendon and anchorage being cast-in-place. The forms are then removed and the tendons are tensioned. It also has been found to be desirable in many applications to have the tenson anchorage located in a recess in the end of the concrete member, which recess is subsequently grouted so that the anchorage is completely contained within the finished prestressed concrete member. When this type of construction is used, the tendon anchorage must be located and positioned in fixed spaced relation to the concrete form by means of apparatus which, after casting of the concrete member, afford access to the anchorage for tensioning of the tendon.

#Several anchorages have been previously employed in order to provide an anchorage construction which can be cast-in-place at a position interiorly of the ends of the concrete member. Two such anchorage constructions are illustrated in U.S. Pat. Nos. 3,293,811 and 3,399,434. Another approach has been to provide a unitary anchorage member which is formed with screw threads or a bayonet-type socket on the side of the anchorage facing the form. A mounting member is then screwed into the front of the anchorage and extends therefrom to and through the form.

#Prior cast-in-place anchorage systems have been found to have several disadvantages. Primary among these disadvantages is the inflexibility of the system for mounting the anchorage in spaced relation to the concrete form. As will be readily understood, the prestressing reqirements of various concrete members may differ considerably. For example, the depth to which a cast-in-place anchorage must be placed in the concrete member may under different construction codes vary from state to state or locality to locality. Similarly, tensioning forces may require various sizes or shapes of bearing surfaces in order to properly distribute the axial loading of the tendon or tendons. Moreover, close grouping of tendons may result in special bearing plate requirements. Still further, special wedge containing anchor members may be required for given stress conditions. Thus, prior tendon anchorages hve lacked an interchangeability or flexibility of the elements in the systems which would allow the structural engineer maximum flexiblity of design.

#FIG. 1 is a fragmentary, side elevational view, in cross section, of a tendon anchorage constructed in accordance with the present invention and secured to a concrete form for casting of the anchorage into a concrete member.

#FIG. 2 is a fragmentary, side elevational view, in cross section, of the anchorage illustrated in FIG. 1 after casting of the concrete member, removal of the concrete form and tensioning of the tendon.

#FIG. 3 is a fragmentary, side elevational view, in cross section, of an alternative embodiment of the tendon anchorage of the present invention suitable for anchoring a tendon inclined to the form board.

#Referring now to FIGS. 1 and 2, there is illustrated a tendon anchorage constructed in accordance with the present invention which is particularly well suited for use as a cast-in-place type of tendon anchorage for prestressing applications. The anchorage is comprised of a bearing plate 111 and bearing plate locating device consisting of tubular member 113 and spacing or block-out member 114, which are urged against form board 116 by nut 117 and threads 118 at the small diameter end of bore 136 in the bearing plate. As above described mounting member 113 is formed with externally threaded outer end 119 and inner end 121, which are preferably threaded over a substantial portion of the ends to afford continuous axial adjustment at both ends to bring the assembly into close abutting relation with form board 116. Tendon 122 is here illustrated as a strand type of prestressing tendon having a cable-like construction, but wires and bars may be similarly secured. The strand can be wrapped in paper 133 and conveniently taped or otherwise blocked by member 124 against entry of concrete into the end 121 of mounting means 113.

#In order to insure that bearing plate 111 is cast into the concrete 138 in a proper orientation with respect to tendon 122, tapered bore 136 terminates in a threaded end 118 which mates with threaded inner end 121 of mounting tube 113. Thus, the axis of bore 136 is coaxially aligned with the axis of mounting tube 113 with the result that the bearing plate is secured in perpendicular relation to the mounting tube. Mounting tube 113 is further formed with an internal diameter or bore dimensioned to receive tendon 122 in general coaxial alignment therewith resulting further in the perpendicular orientation of bearing plate 111 to tendon 122, which is highly desirable in order to minimize any bending of the tendon at the anchorage.

#Bearing plate 111 in this configuration further acts as an anchor member by being formed with a frusto-conical bore 136. As above described, mounting means 113 can be inserted through openings or bores 132 and 133 in the spacing member and form, respectivey, and past the frusto-conical portion of the mounting means and screwed into the teeth 118 in bearing plate 111.