Product Technical Guides : US-EN Post-Installed Rebar Guide - Page 22

Post-Installed Reinforcing Bar Guide
5.0 DEVELOPMENT OF DESIGN DATA
5.1 BACKGROUND
At the reinforcing bar-adhesive interface , load is transferred by adhesion and mechanical interlock . At the adhesive concrete interface , load is transferred by adhesion and micro mechanical interlock . Bond strength is typically defined as the maximum average bond over embedded length of bar .
Tension load [ lb ]
50000
40000
30000
20000
10000
2d b 2.5d b 6d b
~ 1100 psi
Splitting failures Concrete failure / bar rupture Bar rupture
~ 2100 psi
# 6 Gr . 60 bar @ 12d b embedment – HY 200-R V3
0
0.0
1.0
2.0
3.0
4.0
5.0
Edge distance [ in .]
Figure 39 — Unconfined tension failure load as a function of edge distance .
Over the past two decades , extensive investigations have been conducted to evaluate post-installed reinforcing bar connections subjected to a variety of loading conditions . Much of this work has been conducted at leading research institutions in Europe and the U . S . 13 The tests have consistently shown that post-installed reinforcing bars installed with qualified systems exhibit performance that is at least equivalent to cast-in reinforcing bars under similar conditions .
Figure 39 plots tension failure loads for increasing edge distance for a # 6 reinforcing bar embedded to a depth of 12 bar diameters in a Hilti HIT hybrid adhesive . Near-edge bond strength is limited by the splitting strength of the concrete and is on the order of 1100 psi . At larger edge distances , the average ultimate bond strength increases to approximately 2100 psi .
In 2006 , the European Organization for Technical Approvals ( EOTA ) issued TR023 Assessment of Post-installed Reinforcing Bar Connections [ 7 ]. This document provides a path for verifying that post-installed reinforcing bar connections performed with a specific system will exhibit comparable behavior to cast-in-place reinforcing bar connections in terms of load and displacement behavior .
In 2013 , ICC-ES amended their acceptance criteria 14 to include testing to verify adhesive anchor systems for post-installed reinforcing bar applications . These qualification provisions include the procedures developed for TR023 and add additional tests to check cyclic tension performance ( seismic ) and near-edge performance over deep embedment depths .
5.2 ESTABLISHMENT OF REQUIRED SYSTEM PERFORMANCE ( QUALIFICATION )
The suitability of an adhesive system for post-installed reinforcing bar applications is dependent on many factors . Systems that may be otherwise appropriate for anchoring applications will not necessarily fulfill the requirements for safe and reliable reinforcing bar installations .
A critical aspect of adhesive systems intended for post-installed reinforcement is the behavior of the system in configurations where splitting controls . Figure 40 shows tension testing of # 8 bars embedded 35 bar diameters in the corner of a column . These tests , which were developed specifically for qualification of post-installed reinforcing bar systems under AC308 , directly compare cast-in and post-installed bar behavior under conditions where splitting is the limiting failure mode . If the adhesive is too stiff , excessive shear lag can lead to zipper-like failure of a near edge bar . If the bond is too " soft ", relaxation of the post-installed bar may permit excessive opening of the joint between old and new concrete , leading to loss of shear transfer or corrosion .
35 in .
( 875 mm )
Figure 40 — Test for bond / splitting behavior per AC308 [ 9 ].
Figure 41 lists the full range of tests required to qualify adhesive anchor systems for post-installed reinforcing bar applications as provided in Table 3.8 of AC308 .
38 in . ( 965 mm )
Confined test setup , see Fig . 4.5 . Bearing plate to cover entire surface .
1.5 in .
( 38 mm )
# 3 ( 10 mm ) closed tie
A
# 3 ( 10 mm ) closed tie
A
4.75 in . ( 120 mm )
13 ) See references and suggestions for further reading : [ 8 ], [ 10 ], [ 11 ], [ 12 ], [ 17 ], [ 18 ], [ 19 ], [ 20 ]. 14 ) AC308 — Acceptance Criteria for Post-installed Adhesive Anchors in Concrete Elements , approved October 2017 ( Editorially revised March 2018 ), ICC Evaluation Service , LLC . [ 9 ].
20 2021