Abstract:
Improved connections of preformed concrete construction elements wherein one or more metal pins, of any preferred cross-sectional shape, are cast in place, or grouted, extending into each of two elements to be connected, with an elastic grommet disposed between a portion of each pin, in an area on each pin nearest the joint, and the surrounding concrete or grout, whereby the load transfer capacity of the connection is increased about threefold.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an improvement in connections of precast concrete articles, such as girders, beams, columns or plates and particularly to building structures in high seismic areas having such improved connections of precast building elements. 
     Structural beams subjected to lateral or axial loads in addition to gravity loads must be connected in a way that will transfer these loads through the connection to the support. Transfer of lateral loads between precast or prestressed concrete members can be troublesome. Examples of some such lateral loads include loads from earthquakes, vibratory machinery, moving vehicles and wind. 
     SUMMARY OF THE INVENTION 
     This invention is a connector used to transfer loads, such as lateral or axial loads, from one element to another, such as from a precast concrete beam to a concrete column. The connector includes a metal pin, normally of a round or rectangular cross section and an elastic grommet around the metal pin. The metal pin and grommet are affixed within an end portion of a girder or within a column ledge, with a portion of the metal pin protruding outwardly of the girder or the column ledge, this outwardly protruding portion being affixed or slidably mounted within a beam or girder connected to the girder or ledge, respectively, depending on the type of loads anticipated. 
     It is a primary object of the invention to provide a novel connector for precast concrete structural elements. 
     A further object is to provide a connector for precast concrete structural elements which is particularly adapted for use in meeting the structural requirements in high seismic areas. 
     A still further object is to provide a novel connector for precast concrete structural elements which will increase the load transfer capacity of the connection by a factor of about three times the capacity of a similar connection without the elastic grommet of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages will be more readily apparent when considered in relation to the preferred embodiments, as set forth in the specification, and shown in the drawings, in which: 
     FIG. 1 is a vertical sectional view of a precast concrete column with opposed ledges affixed to and supporting oppositely directed precast concrete girders, all connected in accordance with the invention. 
     FIG. 2 is a diagrammatic view of the connection of FIG. 1. 
     FIGS. 3, 4, and 6 are diagrammatic views similar to FIG. 2 of modifications of the connection, in accordance with the invention. 
     FIG. 5 is a bottom view of the girder of FIG. 4 showing the special heel plate with the pin extending therethrough. 
     FIG. 7 is an end diagrammatic view of a girder, shown supported on a column ledge, with a still further modified form of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a short section of a precast concrete column 10 which has been formed with two opposed ledges 12, 12. Also, cast in place within each ledge 12 is a metal pin 14 and an elastic grommet 16. Metal pin 14 is of about two inches in diameter and twenty-eight inches in length, with sixteen inches embedded within ledge 12 and one foot protruding upward out of ledge 12. The elastic grommet 16 is a 70 durometer neoprene sleeve, having a wall thickness of 3/4 inch and being friction fit around the upper eight inches of the portion of metal pin 14 which is embedded within ledge 12. 
     Disposed upon, and supported by, each ledge 12 is a precast concrete girder 18, with a flexible bearing pad 20 disposed between ledge 12 and girder 18. A grout hole 22 is formed in girder 18 arranged to have located therewithin the upper one foot of metal pin 14, and of a diameter such that grout 24 within the hole 22 surrounds pin 14. 
     Hole 22 extends to the top of girder 18, to permit filling the hole with grout 24. A threaded rod 26 affixed within the top of hole 22 by grout 24, has a nut 28 and washer 30 sealing the top of grout hole 22. A metal heel plate 32 is firmly adhered to the bottom surface of girder 18, located to rest upon the bearing pad 20, and, preferably, cast in place during forming of the girder 18. A similar sole plate 34 is cast in place on ledge 12, for location under bearing pad 20. 
     Also cast in place in each girder 18 and in column 10, but not shown, are reinforcing rods, all located therewithin in accordance with known engineering principles. 
     FIG. 2 is a diagrammatic view of the structural connection shown in FIG. 1, including diagrammatically the elements which are essential in understanding the manner of transferring loads, including ledge 12, pin 14, grommet 16, girder 18, bearing pad 20, grout hole 22, grout 24, heel plate 32 and sole plate 34. 
     FIG. 3 is a modification of the connection of FIG. 2 wherein the grommet 16 is friction fit onto the portion of pin 14 which is disposed within the girder 18. In this embodiment the pin is preferably first affixed within ledge 12, by being cast in place therein or grouted into a hole formed therein. After placement of the girder 18 on ledge 12, with the pin 14 and grommet 16 extending into hole 22, grout 24 is placed in hole 22 and surrounds pin 14 and grommet 16. 
     The pin 14 and grommet 16, in the connection shown in FIGS. 1-3 transfers a horizontal force in any direction. 
     FIG. 4 shows a slip connection which transfers a horizontal force in only one direction. The sole plate is omitted. The heel plate 36 is specially made with an elongate hole 38, as shown in FIG. 5. Elongate hole 38 has a width which is equal to the diameter of pin 14 and a length which is equal to the diameter of the grout hole 40 in girder 18&#39;. Elongate hole 38 has a long axis in the direction which pin 14 is to move freely without transferring any force, and grout hole 40 is either void or filled with a soft compressible material, such as loose vermiculite particles. 
     The structure of FIG. 4 could also be reversed, not shown, with the elastic grommet 16 located in girder 18&#39;, and with a sole plate having an elongate slot and a void hole therebelow, allowing movement of pin 14 in one direction, relative to ledge 12. With the elongate slot in a heel plate or a sole plate, movement is allowed in one direction, while forces normal to the axis of movement will be transferred from the girder 18&#39; to the ledge 12. 
     FIG. 6 shows a standard connection as in FIG. 2 used in combination with a top connection. This modification adds the function of restraining overturning of the girder 18&#34; due to a rotation about the longitudinal axis of the girder. The lower standard connection includes the ledge 12, pin 14, grommet 16, girder 18&#34;, bearing pad 20, grout hole 22, grout 24, heel plate 32 and sole plate 34. 
     A flat pin 42, with an elastic grommet 44, is grouted in a preformed pocket 46 near the top of the girder 18&#34; and extends out from the end of the girder 18&#34;, with the elastic grommet 44 surrounding the portion of pin 42 which is grouted into the girder 18&#34;. The protruding portion of flat pin 42 extends into a pocket 48 in column 10, through a face plate 50 having a slot 52 aligned with the vertical axis of the girder 18&#34;. Face plate 50 is affixed over the pocket 48. Pocket 48 can either be void or filled with a compressible material such as vermiculite particles. Flat pin 42 is thus free to move vertically within the slot 52, or in the direction of the longitudinal axis of the girder 18&#34;. 
     The structure of FIG. 6 could also be modified by replacing the lower standard connection, with a lower connection such as the slip connection of FIG. 4. 
     FIG. 7 is a diagrammatic end view of a girder 18&#34;&#39; with a modified connection wherein overturning is restrained, in accordance with the invention, by using a pair of metal pins 54, 54, each of which has a threaded top end 56 and a threaded bottom end 58. A nut 28 and a washer 30 is used as an anchor on each end. The bottom portion of each pin 54 is cast in place or grouted into ledge 12&#39; with an elastic grommet 16 friction fit around an upper portion of that bottom portion in ledge 12&#39;. The two pins 54, 54 are located equidistant from the end of girder 18&#34;&#39;, side by side, each spaced in from a side 60 of girder 18&#34;&#39; a distance of about 1/3 the width of girder 18&#34;&#39;. 
     Each pin 54 extends up through a grout hole 62 into a grout pocket 64 in girder 18&#34;&#39;. The grout hole 62 is filled with grout 66. The grout pocket 64 is also filled with grout 66. A lower portion 66&#39; of the grout 66 in grout pocket 64 is allowed to set prior to the upper nut 28 and washer 30 being placed and tightened by turn of the nut 28, compressing a bearing pad 68 between girder 18&#34;&#39; and ledge 12&#39;. The remainder of pocket 64 is then filled with grout 66&#34;. A heel plate 70 and a sole plate 72 may also be affixed to the girder 18&#34;&#39; and the ledge 12&#39;, respectively. 
     Tests have shown that the use of the elastic grommet around the pin or pins used to make preformed concrete structure connections increases the load transfer capacity of the connection by a factor which is on the order of three times the capacity of a similar connection without the grommet. If engineering analysis indicates that more pins or multiple top connections are required, then the use of an elastic grommet for each pin or plate should be required, in accordance with the invention. The advantages of this invention are of particular importance in structures located in active seismic areas. 
     Having completed a detailed disclosure of the preferred embodiments of our invention, so that others may practice the same, we contemplate that variations may be made without departing from the essence of the invention.