Arebar splicing device developed originally toconnect precast concrete members is now be-ing used for cast-in-place construction aswell. A metal splice sleeve is filled with gro u t

that provides a mechanical bond between rebar de-f o rmations and gro oves on the inside of the sleeve (seeFi g u re 1).

Structural continuity for precast membersIf precast concrete buildings must resist heavy wind

loads or moderate seismic forc e s, stru c t u ral continuity isre q u i red. The precast elements must function as a sin-gle unit and re i n f o rcing bars must be mechanicallys p l i c e d .

When used in precast members, the splice sleeves areattached to the main stru c t u ral re i n f o rcing bars at thep recasting plant and are embedded in the precast con-c re t e. Sl e e ves are installed at one end of the rebar and theopposite end of the bar pro t rudes from the precast piece.On the jobsite, the pro t ruding bars mate with the sleeve sas shown in Fi g u re 2.

If panels are erected with sleeves in the top of the pre-cast elements, grouting is done by pouring grout into thes l e e ve. This simple method, called pre - g routing, doesntmake efficient use of the cra n e. The panel must first beset to assure proper mating of the sleeves and bars, then

Grout-filled metal sleevesplices rebarsApplications include precast andpost-tensioned structures

Figure 2. When a pre-grouting method is used, grout ispoured into the metal sleeve and the precast member islowered into place. Members must be braced for at least24 hours after grouting. This procedure is used primarily forerecting precast columns.

Figure 3. When a post-grouting method is used, the member islowered into place and immediately braced. Grouting is donelater with a hand-operated grout pump. This method makesmore efficient use of crane time and is preferred over pre-grouting for most applications such as connecting shear wallsor connecting structural elements to foundations.

Figure 1. In this splicing device,hardened grout locks reinforcingbars inside a metal sleeve.

GROUT

DEFORMED BAR

DEFORMED BAR

SLEEVE

raised and held while grout is poured into the sleeve s.Too much crane time is wasted. A better method is calledp o s t - g routing. The sleeve is cast in the bottom of thep recast element and a low - p re s s u re grout pump is usedto force grout into the sleeve after the panels have beenjoined as shown in Fi g u re 3. In post-grouting, once thep recast piece has been lowe red into place on a layer ofbedding mortar and shims, braces are connected andthe crane can be released. Grouting can take place laterwithout having an effect on crane opera t i o n s.

Re g a rdless of whether pre- or post-grouting is used,members must be braced for 24 hours after joining to al-l ow the grout to harden and cure. The grout is a pre-mixed, high-strength, shrinkage-compensating form u-lation that reaches approximately 3000 psi compre s s i ves t rength in one day at 68 degrees F. About 20 percent wa-ter by weight of the dry ingredients is added on site andthe grout is mechanically mixed for 2 minutes.

Wet bedding is sometimes used instead of dry packingat joints between precast members. Less material isneeded than is used in dry packing and the re s u l t i n gjoints are thinner. If wet bedding is used when the pre -g routing pro c e d u re is employed, the same grout shouldbe used for filling the sleeves and for the bedding be-

t ween precast elements. Ot h e rwise there is a danger thatw o rkers will use the wrong grout to fill splice sleeve s. Theg rout used in splice sleeves costs more than the usualbedding materials but it can be installed ve ry quickly,thus reducing labor and crane time.

Post-tensioning applicationsThe sleeves have also been used to reduce re s t ra i n t

f o rces in post-tensioned slabs. Post-tensioned floorslabs or beams can induce high bending and shears t resses in walls or columns to which they are stru c t u ra l-ly connected. When post-tensioning cables are stre s s e d ,the beams or slabs shorten and exert hori zontal forc e son the ve rtical members. The forces can cause cra c k i n g .One way of reducing re s t raint forces is to delay makings t ru c t u ral connections until all of the elastic short e n i n gand much of the creep and shrinkage shortening havetaken place.

R i c h a rd We i n g a rdt Consultants In c. of De n ver deve l-oped the design detail shown in Fi g u re 4 for use withpost-tensioned slabs supported by cast-in-place con-c rete walls. In this application, splice sleeves we re usedon hori zontal bars and the construction sequence wasas follow s. A 10-inch-thick, one-story wall was cast andsmooth troweled on top. The floor slab was formed sothat the floor overlapped the wall by 4 inches. Pre s t re s s-ing tendons, rebar dowels and splice sleeves (Fi g u re 5)we re installed and then the floor was poured. Sp l i c es l e e ve s, howe ve r, we re nt grouted at this time. After thep roper curing period the tendons we re stressed and thenext level of the wall was formed and cast.

Figure 4. This detail permits delayed structural connectionbetween a post-tensioned floor and cast-in-place wall. Thedelay allows all elastic shortening and much of theshrinkage and creep shortening to take place in the floorwith minimal restraint from the supporting walls.

Figure 5. Splice sleeves are set in place to connect rebars inthe floor and wall after post-tensioning tendons have beenstressed. Grout is pumped into the inlet hole on the rightand comes out of the outlet hole when the sleeve is filled.

A waiting period of 60 days was specified before thesplice sleeves we re grouted to provide a stru c t u ral con-nection between the wall and floor. This delay perm i t t e dall of the elastic shortening and about 50 percent of thes h rinkage and creep shortening to take place in the floorwith minimal re s t raint from the supporting walls.

Other applicationsThe grout-filled sleeves have also been used in tilt-up

w o rk as moment connectors at the foundation, con-necting tilt-up panels to foundation dowe l s. Another ap-plication is in splicing rebars at the base of pre-tied col-umn rebar cages. The advantage is a saving in cra n e

t i m e, but a major drawback is that the cages must beg u yed and braced at least ove rnight and perhaps longerin cold we a t h e r.

This splicing method has gained acceptance by the In-t e rnational Co n f e rence of Building Officials and was re-cently used in a 21-story De n ver high-rise to form whatis believed to be the tallest precast concrete shear wallt ower featuring the system.

P U B L I C AT I O N # C 8 5 0 9 2 9Copyright 1985, The Aberdeen Gro u pAll rights re s e r v e d