Product Technical Guides : US-EN Post-Installed Rebar Guide - Page 4

Post-Installed Reinforcing Bar Guide
The assumption of bar development is perhaps the most fundamental distinction separating post-installed reinforcing bars from adhesive anchors . Although instances do arise where post-installed reinforcing bars are designed for an applied force as described by equation 1 , the typical case conforms to the assumption of bar development .
This Guide provides information regarding the design , detailing and installation of post-installed reinforcing bars . It does not address their design as governed by ACI adhesive anchor qualification and anchoring-to-concrete provisions .
As noted above , post-installed reinforcing bars are typically used to facilitate connections between new and existing concrete elements or structures . Post-installed reinforcing bars are used in both retrofit work and in new construction and are suitable for a wide range of applications ( i . e ., as adhesive anchors ) outside of the context of bar development .
Figure 3 — Post-installed reinforcing bar . drilled hole
post-installed reinforcing bar
( E ) concrete ( N ) concrete
roughened interface
Perhaps the most common class of applications for postinstalled reinforcing bars is the extension of existing reinforced concrete ( R / C ) structural elements such as slabs , walls , and columns ( Figure 4 ), either to facilitate expansion of floor space or to address other functional changes in the use of the structure . Such applications usually involve the placement of large numbers of bars with close spacing . In some cases the post-installed reinforcing bars are installed close to the surface of the concrete ( e . g ., at close to minimum cover distance ) whereby the presence of existing reinforcing must be taken into account . Where applicable , such as in a column or extension , it is generally preferable to place the post-installed reinforcing bars inside of the existing reinforcing bar cage , both to minimize spalling during drilling and to ensure adequate cover . Avoidance of existing reinforcing is facilitated by use of reinforcing detection equipment , such as the Hilti PS 300 or Hilti PS 1000 scanning systems ( Figure 5 ).
Another class of applications involves the strengthening of existing concrete structures , often to improve performance under earthquake loads ( Figure 6 ). These applications are simplified by the fact that the bars typically do not carry gravity loads , are not subject to fire design considerations , and often involve doweling into concrete elements without close edge distances . On the other hand , the required embedments for development and splicing of bars subject to seismic loads may be greater than for bars designed only for static or wind loads .
A third application class with unique requirements is the extension , rehabilitation , and strengthening of existing concrete bridges and other civil engineering structures ( Figure 7 ). These applications are often distinguished by the need for enhanced resistance to corrosion and temperature extremes . Hilti has developed unique shear-friction solutions for bridge deck overlays 4 and offers hybrid adhesives ( e . g ., Hilti HIT-HY 200 V3 ) with superior resistance to elevated temperatures .
Since the required embedments to satisfy development length provisions of the building code ( typically 25 to 40 bar diameters ) often exceed typical anchoring embedment lengths ( generally limited to 20 bar diameters 5 ), special measures may be necessary to ensure that the holes are straight and that the drilling process does not damage the concrete , existing reinforcing or other embedded elements . These may include the use of specialized tools such as the Hilti drilling alignment system and Hilti ferric- and GPR-based detection systems .
Post-installed reinforcing bars are designed to transfer tension loads only . Extensive research programs have been conducted 6 at laboratories in Europe and the U . S . to verify that post-installed reinforcing bars installed with Hilti adhesive systems ( HIT-HY , HIT-RE ) demonstrate load transfer and load vs . displacement behavior comparable to cast-in-place reinforcing .
When installed well away from edges ( i . e ., where splitting does not limit the strength ), post-installed reinforcing bars typically exhibit higher pull-out strength than cast-in-place bars of equivalent bar diameter and embedment .
4 ) Contact Hilti for further information . 5 ) See ACI 318-19 17.3.3 . 6 ) See references and suggestions for further reading : [ 8 ], [ 10 ], [ 11 ], [ 12 ], [ 17 ], [ 18 ], [ 19 ], [ 20 ].
2 2021