Post-Installed Reinforcing Bar Guide
1.0 POST-INSTALLED REINFORCING BARS — WHAT ARE THEY ?
a . Bridge widening b . Bridge deck rehabilitation c . Bridge deck augmentation d . Bridge deck augmentation Figure 7 — Applications in bridge rehabilitation with post-installed reinforcing bars .
For near-edge bars subjected to tension loads ( see Figure 8a below ) the ultimate limit state behavior is characterized by splitting of the concrete along the bar or splice in response to the hoop stresses developed around the bar . Provided that the adhesive used can accommodate redistribution of stress along the bar length in a manner similar to cast-in-place bars , post-installed reinforcing bars exhibit ultimate strengths that are on a par with those obtained for cast-in-place bars . Figure 8 depicts typical applications for post-installed reinforcing bars . Some of these applications have been verified experimentally while others have been investigated using advanced simulation ( FEM ) techniques .
These applications may be categorized as follows :
a . Non-contact lap splices or extensions in which tension loads are transferred between adjacent bars via compression struts and hoop stresses in the concrete directly surrounding the spliced bars ( see Figure 8a ).
b . Shear dowels used to resist interface shear across a shear plane , usually the roughened joint between existing and new concrete ( see Figure 8b ). The primary shear mechanism , friction across the irregular surface , is enabled by the reinforcing bars ( shear dowels ) that hold the surfaces together , and as such the usual design assumption , e . g ., in the shear friction concept utilized by ACI , is that the shear dowels are placed in direct tension as the irregular shear plane is translated laterally . To a much lesser degree , or in the case of a smooth interface , shear may also be transferred by dowel action ; that is , bearing of the concrete on the reinforcing bars . c . Structural joints which are typically used to resist tension and shear forces across beam-to-column and column-to-foundation joints . Structural joints are oriented perpendicular to the primary reinforcing of the existing concrete member in which they are installed . In castin-place construction , rebar for structural joints are usually hooked . Post-installed rebar for structural joints are straight , and as such their design must be based on straight bar development length provisions ( see Figure 8c ).
It should be noted that with the sole exception of dowel action as noted in ( b ) above , the method of load transfer between post-installed reinforcing bars and the concrete in which they are anchored is bearing of the reinforcing deformations ( lugs ) on the adhesive surrounding them . These bearing stresses in turn are transferred from the adhesive to the surrounding concrete via adhesion and micro-friction , whereby the lateral dilation of the adhesive layer in response to the bearing stresses enhances the friction mechanism . The concrete in turn develops circumferential ( hoop ) stresses around the bars that can result in splitting cracks at certain load levels . This response is identical to that observed for cast-in-place reinforcing bars loaded in tension .
Note : Where it is has been verified through appropriate qualification testing ( in accordance with AC308 or similar procedures 7 ) that a given post-installed reinforcing bar system results in similar bond strength and displacement behavior as cast-in-place reinforcing bars , the design of post-installed reinforcing bar connections employing that system can proceed using the provisions for cast-in-place reinforcing bars .
7 ) Hilti HIT-RE and HIT-HY adhesives have been verified as suitable for post-installed reinforcing bar applications through extensive research and testing .
4 November 2022