Daniel TW Looi is Senior Lecturer and the Discipline Leader of Civil Engineering at Swinburne University of Technology (Sarawak), Malaysia. Ray KL Su is an Associate Professor of Structural Engineering at the University of Hong Kong, Hong Kong. Emad Gad is a Professor and the Dean of the School of Engineering at Swinburne University of Technology, Australia.
A STATE-OF-THE-ART GUIDE FOR POST-INSTALLED REINFORCEMENT
A STATE-OF-THE-ART GUIDE FOR POST-INSTALLED REINFORCEMENT provides comprehensive coverage on installation, design, and assessment guidelines for postinstalled reinforcements, a unique technology used very commonly in the construction industry. Previously published in Hong Kong, this Malaysian edition includes new EOTA technical reports and European Assessment Documents, fundamentals for post-installed reinforcements, design proposals, as well as unique design examples, all of which is specifically tailored for the Malaysian context.
ISBN 978-967-5492-74-7
9 7 8 9 6 7 5 4 9 2 74 7
Daniel TW Looi
Ray KL Su
Emad Gad
Daniel TW Looi Ray KL Su Emad Gad
Copyright © 2023 by Sunway University Sdn Bhd Published by Sunway University Press An imprint of Sunway University Sdn Bhd No. 5, Jalan Universiti Bandar Sunway 47500 Selangor Darul Ehsan Malaysia press.sunway.edu.my All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, now known or hereafter invented, without permission in writing from the publisher.
ISBN 978-967-5492-74-7
Perpustakaan Negara Malaysia
Cataloguing-in-Publication Data
Looi, Daniel T. W. A State-of-the-Art Guide for : POST-INSTALLED REINFORCEMENTS / Daniel T.W. Looi, Ray K.L. Su, Emad Gad. ISBN 978-967-5492-74-7 (hardback) 1. Civil engineering. 2. Reinforced concrete. 3. Structural engineering. 4. Structural design. I. Su, Ray K. L. II. Gad, Emad. III. Title. 624
Edited by Nicholas Hoe Designed and Typeset by Rachel Goh Printed by Vinlin Printing Sdn Bhd, Malaysia
Extracts of this book have been reproduced or adapted with permission from Hong Kong University Press.
Disclaimer The information in this book is true and complete to the best of the authors’ knowledge. The authors disclaim liability for any injury and/or damage to persons or properties, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the book. All information in this publication is correct at the time of printing and may be subject to changes.
Cover image: Yurii Andreichyn/Shutterstock.com Image used under licence from Shutterstock.com
Contents Preface
vii
Abbreviations
viii
Symbols
ix
1. Introduction to Post-installed Reinforcement
1
1.1 Overview
1
1.1.1 International qualification and design standards for PIR
3
1.1.2 Documents relevant for practice in Malaysia in a post-British Standards era
4
1.1.3 Quick guide to the naming convention of EOTA EAD
5
1.2 Concrete-to-Concrete Connection
5
1.2.1 Local load transfer mechanism in PIR
5
1.2.2 Failure modes for PIR
7
1.2.3 Shear stress transfer at the interface of new and existing concrete
8
1.3 Material for PIR 1.3.1 Adhesive systems 1.3.1.1 Adhesive types 1.3.1.2 Temperature effects on adhesives 1.3.1.3 Design working life 1.3.1.4 Selecting the right adhesive system 1.3.2 Base materials 1.3.2.1 Concrete 1.3.2.2 Others (e.g., rock) 1.3.3 Reinforcement
2. Installation Process for Post-installed Reinforcement
9 9 9 11 12 13 15 15 15 15
16
2.1 General 2.1.1 Installer competency 2.1.2 Installation process
16 16 17
2.2 Location for Safe Drilling
18
2.3 Roughening of Existing Concrete Surface 2.3.1 Roughening area 2.3.2 Requirements according to BS 8110-1 (1997) 2.3.3 Requirements according to MS EN 1992-1-1 (2010)
19 19 19 19
iii
iv
Contents
2.3.4 Requirements for surface roughening construction works according to TR 066 (2020) 2.3.5 Methods of surface preparation
20 21
2.4 Hole drilling 2.4.1 Hole drilling requirements 2.4.2 Hole drilling methods 2.4.3 Hole drilling aids
24 24 24 26
2.5 Hole cleaning
28
2.6 Adhesive injection 2.6.1 Inspection before injection 2.6.2 Types of dispensing tool 2.6.3 Injection process
29 29 29 30
2.7 Rebar insertion and setting 2.7.1 Rebar preparation 2.7.2 Rebar insertion
31 31 31
3. Qualification of Post-installed Reinforcement
33
3.1 Basic principles
33
3.2 Introduction to EAD 330087-01 (2020), EAD 332402-v01 (2021), and AC 308 (2019)
35
3.3 Resistance under fire exposure 3.3.1 Fire rating requirement in Malaysia according to the Uniform Building By-Laws (1984) 3.3.2 Fire exposure assessment as per EAD 330087-01 (2020)
40
3.4 Seismic actions requirement 3.4.1 Introduction to the seismic environment in Malaysia, MS EN 1998-1 (2015), and Malaysia National Annex (2017) 3.4.2 Seismic assessment by cyclic test as per EAD 330087-01 (2020)
42
44
3.5 Recommendation for providing qualifications for PIR in Malaysia
45
4. Proposed Design Procedure for Post-installed Reinforcement 4.1 Anchorage design: Cast-in rebar anchorage method, improved bond-splitting behaviour method or bonded anchor design method?
40 40
42
46
46
Contents
4.2 Design provisions for PIR in MS EN 1992-1-1 (2010) 4.2.1 Fundamental derivation of anchorage length 4.2.2 Required anchorage length 4.2.3 Design anchorage length 4.2.4 Lap length 4.2.5 Simplified detailing rules 4.2.6 Summary of bond strength as per MS EN 1992-1-1 (2010) 4.3 TR 069 (2019) to harmonise MS EN 1992-1-1 (2010) and EN 1992-4 (2018) 4.3.1 PIR yielding failure 4.3.2 Cone failure 4.3.3 Bond-splitting failure 4.4 TR 066 (2020) for application of shear connector in concrete overlay 4.4.1 ULS design actions at the shear interface 4.4.1.1 Determining longitudinal shear and tensile force due to external forces 4.4.1.2 Determining longitudinal shear and tensile force due to restraint at the perimeter 4.4.1.3 Non-superposition checking of shear stress and tensile force 4.4.2 Shear interface capacity 4.4.3 Tensile capacity of the connector at the shear interface 4.4.4 Minimum interface reinforcement and constructive interface reinforcement 4.4.5 Disregard presence of stirrups or hoops 4.4.6 Fatigue and seismic actions provisions 4.5 Recommended PIR design method for Malaysia 4.5.1 Proposal 1: Strut-and-tie method to calculate actual design stress 4.5.2 Proposal 2: Options for bond stress 4.5.3 Proposal 3: Impose minimum anchorage and lap length 4.5.4 Proposal 4: Impose minimum cover and edge distance 4.5.5 Proposal 5: Introduce cone and bond-splitting check as per TR 069 (2019) 4.5.6 Proposal 6: Special application – Shear friction check for concrete overlay as per TR 066 (2020)
v
49 49 49 50 52 52 54 54 55 55 58 60 60 61 62 62 62 63 64 69 69 69 70 70 72 76 76 77 77
vi
Contents
4.6 Design examples 4.6.1 Shear action 4.6.2 Bending and shear action 4.6.3 Special application
5. Quality Control of Post-installed Reinforcement in Malaysia
81 80 95 106
118
5.1 Supervision, inspection and certification 5.1.1 Supervisor 5.1.2 Supervision 5.1.3 Inspection 5.1.4 Certification
118 118 119 120 120
5.2 On-site testing 5.2.1 Tester 5.2.2 Verification of installation quality 5.2.3 Test report
121 121 122 123
5.3 Tender specification
123
6. Concluding Remarks
125
6.1 Summary of the Guide
125
6.2 Additional notes for design consideration
126
6.3 Software design tools
126
6.4 Additional readings
127
References
128
Index
133
About the Authors
135
Acknowledgements
135
Preface In Malaysia, post-installed reinforcements (PIR) are widely used in construction to connect reinforced concrete elements cast at different times. For years structural designers have relied on product suppliers for specialist designs as no PIR design guideline has been specially written for Malaysia following the Eurocodes. Moreover, the development of PIR designed according to European standards has been rapid since 2010, and picking up a large pool of knowledge within a short period is arduous. A State-of-the-Art Guide for Post-installed Reinforcement (hereafter named the Guide) is written specifically for Malaysia. Compared to other books on PIR, this Guide is significantly enhanced with new European Organisation for Technical Assessment (EOTA) Technical Reports (TR) and European Assessment Documents (EAD). Highlights of the Guide include: (1) Introduction to the fundamentals of PIR qualification, design, installation, and quality control (2) Six recommended proposals to design concrete-to-concrete connections; discussion of state-of-the-art technologies, i.e., the design of starter bars with improved bond-splitting behaviour as per TR 069 (2019) and shear friction interfaces as per TR 066 (2020) (3) Five unique and comprehensive PIR design examples to guide readers in following the design steps according to the proposals This Guide serves as a helpful reference for civil engineering communities in Malaysia (and other countries using the European Standards), i.e., structural designers, contractors, and installers. It is hoped that the Guide will eventually contribute to a Malaysian standard of practice for PIR. Daniel TW Looi PhD (HKU) MIEAust CPEng (Structural)
vii
Abbreviations ACI AEFAC BSI CEN EAD
American Concrete Institute Australian Engineering Fasteners and Anchors Council The British Standards Institution European Committee for Standardization European Assessment Document (documentation of EOTAaccepted methods and criteria applicable for the performance assessment of the essential characteristics of a construction product) EOTA European Organisation for Technical Assessment ETA European Technical Assessment (a document detailing an independent Europe-wide procedure for assessing the essential performance characteristics of non-standard construction products) ETAG European Technical Assessment Guidelines (valid until 30 June 2013) fib Fédération internationale du béton (International Federation for Structural Concrete) GPR Ground-penetrating radar ICC-ES International Code Council Evaluation Service LEED Leadership in Energy and Environmental Design MPII Manufacturer’s published installation instructions PIR Post-installed reinforcement RC Reinforced concrete STM Strut-and-tie model TR Technical report UBBL Uniform Building By-Laws ULS Ultimate limit state
viii
Symbols Ac Ac,N A0c,N c,N A0c,Nb c,Nb A0p,N p,N Ah Ai Ak As As,rqd As,rqd,m As,min As,prov As,prov,m As,surface Ast Ast,min CEd D Ec Fbond FEd Frebar I K Ktr MEd
Cross-sectional area of concrete Actual projected area of the group of tensioned rebars Reference projected area for concrete cone failure Reference projected area for an individual fastener with edge distance c1 Reference projected area for pull-out failure Load-bearing area of the head of the fastener Area of the joint A product-dependent factor for improved bond-splitting resistance, available in product ETA qualified with EAD 332402-v01 (2021) Area of reinforcement crossing the interface, including ordinary shear reinforcement in shear friction calculation; or, cross-sectional area of rebar in other application Cross-sectional area of the rebar required Cross-sectional area of the rebar required at midspan Minimum cross-sectional area of the rebar Cross-sectional area of the rebar provided Cross-sectional area of the rebar provided at midspan Lateral surface area of a steel bar bonded with concrete base material Cross-sectional area of a transverse rebar Minimum cross-sectional area of a transverse rebar Compression force Diameter of anchor Young’s modulus of concrete Resistance of anchorage bond Axial force in rebars Compression or tension force experience in a steel bar Second moment of area of the composite section Factor for beams and slab in MS EN 1992-1-1 (2010) in the calculation for α3 Normalized ratio to consider the amount of transverse reinforcement crossing a potential splitting surface defined by fib Model Code for Concrete Structures 2010 Bending moment
ix
x
Symbols
NEd N*Ed,j Ed,j NRd NRd,c NRd,cb NRk,cb 0 N Rk,cb Rk,cb NRk,c 0 N Rk,c Rk,c NRd,p NRk,p 0 N Rk,p Rk,p NRd,sp NRk,sp NRd,y NRk,y Q Rr Rt Sd VEd VEd,i V*Ed,j Ed,j Wsp ai av b
Axial force (direct axial or resulted from bending) Resulting constraint peeling or uplift tensile force (perpendicular to the shear interface) at the perimeter due to moment Design values of the tensile resistance of the shear connector as per TR 066 (2020) Design concrete cone capacity Design blowout capacity for a headed shear connector Characteristic blowout capacity for a headed shear connector Characteristic blowout resistance of a single fastener not influenced by adjacent fasteners or further edges Characteristic concrete cone capacity Characteristic resistance of a single PIR placed in concrete without the influence of adjacent reinforcement or edge Design pull-out capacity of PIR; or, design combined pull-out and concrete capacity as per EN 1992-4 (2018) Characteristic pull-out capacity of PIR Characteristic resistance of a single bonded anchor without the influence of geometry or load eccentricity Design capacity for improved bond-splitting as per TR 069 (2019); or, design capacity of splitting as per EN 1992-4 (2018) Characteristic capacity for improved bond-splitting as per TR 069 (2019); or, characteristic capacity of splitting as per EN 1992-4 (2018) Design yield capacity of PIR Characteristic yield capacity of PIR First moment of area of new concrete overlay Relative rib area of tested reinforcing bar Peak to mean roughness (in millimetres) Ultimate design load Transverse shear force in shear friction calculation; or, design shear force in other application Ultimate shear force at the composite section considered Restraint shear force at the perimeter of new concrete overlay Section modulus Clear spacing of longitudinal rebars confined inside a stirrup and near to a bend Shear span Width of the concrete section
Symbols
bcol bi bwall c
xi
Width of the column Width of the interface Width of the wall A factor that depends on the roughness of the interface in shear friction calculation; or, smallest edge distance (cover thickness) in other application c 1 and c 2 Thickness of side cover in orthogonal directions 1 and 2 ca Coefficient for adhesive bond resistance in an unreinforced interface ccr,N Characteristic edge distance for ensuring the transmission of the characteristic resistance of a single fastener for concrete cone, given in the relevant ETA ccr,Np Characteristic edge distance for ensuring the transmission of the characteristic resistance of a single fastener for pull out, given in the relevant ETA ccr,sp Characteristic edge distance for ensuring the transmission of the characteristic resistance of a single fastener for splitting, given in the relevant ETA cd Minimum concrete cover cr Coefficient for adhesive bond resistance in a reinforced interface cs Top or bottom concrete cover; or, clear spacing between longitudinal rebars in values of km defined in fib Model Code for Concrete Structures 2010 cx and cy Thickness of side cover in orthogonal directions x and y cmax Maximum thickness defined in the improved bond-splitting resistance calculation in TR 069 (2019) d Effective depth of the beam or slab; or, diameter of the connector according to EN 1992-4 (2018) dh Diameter of the head of a headed rebar/connector eN Eccentricity of the resultant tension force of tension anchors with respect to the centre of gravity of tensioned rebars drough Circular area diameter for surface roughening of the carbonated layer on concrete surface f bd Design bond stress under static loading used in MS EN 1992-1-1 (2010) f bd,α2 Design bond stress under static loading with consideration of splitting coefficient 𝛼2 f bd,α2' Design bond stress under static loading with consideration of splitting coefficient 𝛼2' f bd,ETA Design bond stress under static loading according to specific ETA f bd,seis Design bond stress under seismic loading
xii
Symbols
f bm,req fc fcd fck fck,new fcm fctd fctk,0.05 fctm fcu,k fh frebar fsd fstrut fyd fyk fuk gk h hbeam hcol hmin hnew hslab k2 k3 k5 kb lb lb1
Required bond resistance of post-installed systems Characteristic cylinder compressive strength capacity of concrete Design cylinder compressive strength capacity of concrete Characteristic cylinder compressive strength capacity of concrete Characteristic cylinder compressive strength capacity of new concrete overlay Mean cylinder compressive strength capacity of concrete Design tensile strength of concrete, taken as the characteristic tensile strength at 5% fractile with consideration of partial safety factor (fctk,0.05/γm = 1.5) Characteristic tensile strength of concrete at 5% fractile Mean tensile stress capacity of concrete Characteristic cube compressive strength of concrete Bond strength perpendicular to the roughened surface Stress experience in the rebar Design stress Compressive stress of strut in the strut-and-tie model Design yield stress capacity of a steel rebar connector Characteristic yield strength of a steel rebar or PIR Nominal tensile strength of a steel rebar Dead load General depth or thickness of concrete as base material in PIR application Depth of beam Depth of column Minimum allowed thickness of a concrete member given in the ETA Thickness of new concrete overlay Depth of slab Factor is 7.5 and 10.5 for cracked and uncracked concrete, respectively, according to EN 1992-4 (2018) Factor is 7.7 and 11.0 for cracked and uncracked concrete, respectively Factor is 8.7 and 12.2 for cracked and uncracked concrete, respectively Reduction factor in Section 2.2.2 of EAD 330087-01 (2020) Embedment length or anchorage length A product-dependent factor for improved bond-splitting resistance, available in product ETA qualified with EAD 332402-v01 (2021)
Symbols
l bd l b,min l b,rqd le
xiii
Design anchorage length Minimum anchorage length Required embedment length Surface roughness-dependent distance to the perimeter forming an area to consider perimeter restraint forces in TR 066 (2020) ln Span length lo Lap length lo,min Minimum lap length lv Setting anchorage depth of rebars as per EAD 330087-01 (2020) n Number of bonded anchors nb Number of anchored or lapped bars in a potential splitting surface nt Number of stirrup confinement legs crossing a potential splitting surface p Transverse pressure (in megapascals (MPa)) at the ultimate limit state along the design anchorage length ptr Transverse pressure perpendicular to the longitudinal axis of PIR qk Live load s Spacing of bars sb Spacing between confining stirrups s1 and s2 Distance between rebars in orthogonal directions 1 and 2 scr,N Characteristic spacing of PIR for concrete cone resistance scr,Np Characteristic spacing of PIR for pull-out resistance scr,sp Characteristic spacing of PIR for splitting resistance sp1 A product-dependent factor for improved bond-splitting resistance, available in product ETA qualified with EAD 332402-v01 (2021) sp2 A product-dependent factor for improved bond-splitting resistance, available in product ETA qualified with EAD 332402-v01 (2021) sp3 A product-dependent factor for improved bond-splitting resistance, available in product ETA qualified with EAD 332402-v01 (2021) sp4 A product-dependent factor for improved bond-splitting resistance, available in product ETA qualified with EAD 332402-v01 (2021) th Thickness of the head of the headed connector t wall Wall thickness ν Shear strength reduction factor for cracked concrete; or, concrete strength reduction coefficient v' Strut efficiency factor v Ed,i Design longitudinal shear stress due to an external force
xiv
Symbols
wstrut z
Strut width in the strut-and-tie model Lever arm of section
𝛼
Inclination angle formed by the longitudinal axis of the rebar with the contact interface, limited between 45 and 90-degree angles Coefficient for the form effect of the bars assuming adequate cover Coefficient for the effect of minimum concrete cover to consider splitting failure Coefficient to consider for effect of minimum concrete cover Coefficient to account for confinement effects by transverse reinforcement Coefficient to account for the effect of the pressure transverse to the plane of splitting along the design anchorage length Coefficient of the percentage of lapped bars (p1) relative to the total cross-section area within 0.65lo from the centre of the lap length Product-specific factor for ductility, used in the calculation of shear interface derived in accordance with EAD 332347-v01 (2021) Product-specific factor for geometry, used in the calculation of shear interface derived in accordance with EAD 332347-v01 (2021) Amplification factor for minimum anchorage length in accordance with EAD 330087-01 (2020) Ratio of sustained actions to total actions considered at the ultimate limit state Ratio of the longitudinal force in the new concrete area to the total longitudinal force either in the compression of tension zone, both calculated for the section considered in the calculation for shear friction; or, bond stress coefficient according to BS 8110-1 (1997) Surface roughness-dependent factor that ranges from 0.3 to 0.5 as per TR 066 (2020) Factor for the rise in design bond strength with increasing related concrete cover due to different mortar types Material safety factor for concrete according to MS EN 1992-1-1 (2010) Installation safety factor Material safety factor for steel according to MS EN 1992-1-1 (2010) Material safety factor for concrete cone resistance according to EN 1992-4 (2018) Material safety factor for steel according to MS EN 1992-1-1 (2010) Material partial safety factor for improved bond-splitting resistance
𝛼1 𝛼2
𝛼2' 𝛼3 𝛼5 𝛼6
ακ1 ακ2 𝛼lb
𝛼sus β
βc δ γc γinst γs γMc γMs γMsp
Symbols
κ1 κ2 λ μ η1 η2 Ωcr Ωp,tr ϕ ρ ρ1 ρmin σn σs ψec,N ψec,Np ψec,Nb ψg,Nb ψg,Np ψh,sp
xv
Interaction coefficient for tensile force activated in the shear connector Interaction coefficient for bending resistance in the shear connector Ratio of the excess transverse reinforcement area to the longitudinal reinforcement area A friction coefficient that depends on the roughness of the interface derived in accordance with TR 066 (2020) Coefficient for bond condition according to MS EN 1992-1-1 (2010) Coefficient for the influence of rebar diameter according to MS EN 1992-1-1 (2010) Reduction factor if a cracked concrete condition is assumed in the improved bond-splitting resistance calculation in TR 069 (2019) Multiplication factor due to transverse pressure can be applied in the improved bond-splitting resistance calculation in TR 069 (2019) (also mentioned in fib Model Code for Concrete Structures 2010) Diameter of rebar Ratio between the area of reinforcement (As) crossing the interface, including ordinary shear reinforcement, to the area of the joint (Ai); or, shear connector reinforcement ratio crossing the interface Percentage of the lapped bar relative to the total cross-section area within 0.65 lo from the centre of the lap length Minimum amount of reinforcement ratio Stress per unit area caused by the minimum external normal force across the interface that can act simultaneously with the shear force, positive for compression and negative for tension Steel stress associated with the relevant failure mode as per EN 19924 (2018) Factor to cater for the eccentricity between the point of application of tension force and the centre of gravity on group rebars (for cone resistance) Factor to cater for the eccentricity between the point of application of tension force and the centre of gravity on group rebars (for pullout resistance) Factor to account for a group effect when different loads act on the individual shear connectors of a group (for blowout resistance) Factor to account for the group effects of the number of shear connectors n in a row parallel to the edge Factor to account for the effect of closely packed fasteners Distinct parameter to account for the influence of the actual member thickness on splitting resistance
xvi
Symbols
ψM,N ψre,N ψre,Np ψs,Nb ψs,N ψs,Np ψsus o ψsus
τEd τEdi τ*EdEd τRd τRdi τRk τRk,sp τRk,cr τRk,ucr
Factor to consider the effect of compression stress resulting from moment-resisting actions of the concrete cone capacity Shell spalling reduction factor for closely spaced reinforcement with an anchorage length of less than 100 millimetres (considered in concrete cone capacity) Shell spalling reduction factor for closely spaced reinforcement with an anchorage length of less than 100 millimetres (considered in pullout capacity) Factor to account for the disturbance effect of distribution stress due to a corner proximity to concrete members Factor to account for the disturbance effect of distribution stress due to the edge of concrete members (considered in concrete cone capacity) Factor to account for the disturbance effect of distribution stress due to the edge of concrete members (considered in pull-out capacity) Factor to account for the effects of sustained loads as per EN 1992-4 (2018) Factor taken from product ETA or assumed at 0.6 as per EN 1992-4 (2018) Demand of shear stress at the concrete interface as per TR 066 (2020) Demand of shear stress at the concrete interface as per MS EN 1992-1-1 (2010) Restraint shear stress at the perimeter of new concrete overlay Design capacity of shear stress at the concrete interface as per TR 066 (2020) Capacity of shear stress at the concrete interface as per MS EN 19921-1 (2010) Characteristic bond strength in either uncracked or cracked concrete Characteristic capacity of improved bond-splitting as per TR 069 (2019) Characteristic bond resistance in cracked concrete assessed following the provisions of EAD 330499-01 (2020) Characteristic bond resistance in uncracked concrete assessed following the provisions of EAD 330499-01 (2020)
1
Introduction to Post-installed Reinforcement
Preview This introductory chapter initiates the discussion on post-installed reinforcement (PIR) and summarises the various qualification and design standards of PIR relevant to Malaysian practice. The chapter also discusses the fundamental mechanism of load transfer and the materials used for PIR: adhesive, base material, and reinforcement.
1.1 Overview PIR system is a specialised fastening technology utilising techniques that drill holes into cured concrete of an existing structure to bond newly inserted rebars with a qualified adhesive system. Protruded rebars usually act as starter bars to create lap splicing with the reinforcement in new concrete structures or a lapped joint with the reinforcement already present in the existing member (see Figure 1.1).
Adhesive injection for PIR
Base material (concrete)
PIR
Figure 1.1 PIR system
1
2
Introduction to Post-installed Reinforcement
Despite the wide use of PIR, many (if not all) Malaysian engineers are unfamiliar with PIR technology—qualification documents, material, design standards, installation process, and control requirements. This Guide is written to discuss the state-of-the-art development of PIR, with emphasis on its relevance to Malaysian practice. The post-installation of anchors and rebars technology has been around since the 1940s, ranging from chemical glass capsules to foiled epoxy. Figure 1.2 illustrates how post-installation technology has evolved over the years.
Design Technology
Uncracked concrete Grout to chemical glass capsule
Soft capsule
Cracked concrete
Seismic consideration
Hard cartridge
Soft and dual cartridge
Timeline ∼1940–1980 Standards
1990
British Standards
BSI
2000 ETAG
2010
2020
Eurocodes, Country National Annex, and EAD
EOTA
Eurocodes
EOTA
STANDARDS Malaysia
Figure 1.2 Post-installation technology advancement
PIR technology can be designed according to the cast-in rebar anchorage provision for concrete-to-concrete connection. Some recent attempts showed PIR designed to anchor theory (Mahrenholtz et al., 2015). However, it should be noted that anchor theory is more reasonable to be applied to steel-to-concrete connection mainly because it holds conservative consideration of combined concrete cone and pull-out failure and splitting failure modes. Unlike anchor theory, reinforced concrete (RC) design usually does not utilise the tensile strength of concrete. PIR can be applied in constructing a new RC slab or beam onto existing RC shear wall and column, RC slab extension, RC column into the foundation, and RC structural retrofitting through new concrete overlay. Some of these applications are shown schematically in Figure 1.3.
Introduction to Post-installed Reinforcement
3
(Rebars at top column are not shown for clarity) Chemical adhesive
Existing slab
New slab
New beam
Existing column
Roughened surface (b)
(a) New overlay New wall
Roughened surface
Chemical adhesive
Existing foundation (c)
Existing slab (d)
Figure 1.3 Typical application examples of PIR: (a) End anchor of a new slab/beam into walls/columns; (b) Lap splice of a new slab to an existing slab; (c) Momentresisting connection; (d) New concrete overlays
1.1.1 International qualification and design standards for PIR Prior research (static loading by Spieth, 2002; seismic loading by Simons, 2007) showed that an equivalent or more superior load-slip performance than castin rebar can be achieved for PIR installed with a qualified system. The design provisions of end anchorage for cast-in reinforcement can be extended to PIR connections formed using qualified products. Some notable documents were published to qualify PIR designed using rebar anchorage theory, e.g., European Assessment Document (EAD) 330087-01 (2020), and modified anchor theory for rigid connection, e.g., EAD 332402-v01 (2021), which references the anchor theory used for steel-to-concrete connection in EAD 330499-01 (2020). A special design application of PIR as shear connectors was documented in Technical Report (TR) 066 (2020), which should be used for products with European Technical Assessment (ETA) qualified using EAD 332347-v01 (2021). Literature review shows no holistic design provision for PIR systems explicitly given in modern international structural design codes, e.g., EN 1992-1-1 (2004). However, some design philosophies can be rationally traced in the codes based
4
Introduction to Post-installed Reinforcement
on associated failure modes; for instance, provisions for cast-in rebar anchorage length design (Cl. 8.4 in EN 1992-1-1, 2004) and lap splicing length (Cl. 8.7 in EN 1992-1-1, 2004). Anchor theory is given in EN 1992-4 (2018), where more detailed discussions can be referred to Charney et al. (2013) and Morgan (2015). TR 066 (2020) was developed for the special application of shear connectors in concrete overlay strengthening. TR 069 (2019) was recently published for rigid PIR connection using formulation analogical to the anchor design method. 1.1.2 Documents relevant for practice in Malaysia in a postBritish Standards era Malaysia adopted Eurocodes as regulatory design standards after the 2010 withdrawal of the British codes in the United Kingdom. Table 1.1 shows a list of relevant and updated documents for PIR qualification, mostly issued by the European Organisation for Technical Assessment (EOTA). Some engineers may be familiar with older documents (Looi & Ng, 2019), e.g., the superseded EOTA TR 023 (2006) and Part 5 of ETAG 001 (2013). Table 1.1 is essential to introducing the latest qualification documents, such as EAD 330087-01 (2020), EAD 332402-v01 (2021), and EAD 332347-v01 (2021). It is noted that PIR connections also use adhesives, just like bonded anchors fastening; hence, the Table 1.1 List of EOTA documents for PIR qualification and design
Qualification document
Roles and functions
Design documents
EAD 330087-01 (2020)
Qualification of PIR connections with mortar under static, seismic loading, and fire exposure
Design as per MS EN 1992-1-1 (2010), MS EN 1998-1 (2015), and Malaysia National Annex to MS EN 1998-1:2015 (2017)
EAD 330499-01 (2020)
Qualification of bonded fasteners for use in concrete
Design as per EN 1992-4 (2018)
EAD 332402-v01 (2021)
Qualification of PIR with improved bond-splitting behaviour under static loading for rigid connection (with provision of 100 years working life)
Design as per TR 069 (2019)
EAD 332347-v01 (2021)
Qualification of connector to strengthen existing structure by concrete overlay
Design as per TR 066 (2020)
Introduction to Post-installed Reinforcement
5
qualification of post-installed anchors is included in Table 1.1. It should be noted that this Guide does not consider other standards (e.g., EN 1504-6, 2006) that allow products to be certified following different requirements, that do not address the most critical installation conditions, and that are not tied to available design building codes. 1.1.3 Quick guide to the naming convention of EOTA EAD In the discussion aforementioned, a few EADs were highlighted. EAD is a harmonised technical specification developed by EOTA as the basis for ETAs. For first-time readers, the EAD number can be challenging. EOTA codes the EAD number “ECNNNN-VS-PGSG-vXX” according to these principles:
EC = Product area, e.g., 33 for fixings including all PIR technology NNNN = Subsequent number in that product area, e.g., 0087 for PIR connections with mortar VS = Version number, e.g., 00 is the original version and 01 is a newer version PGSG = ETA product area code, e.g., 0601 is for fixation and sealing in concrete vXX = Variant number, e.g., v01 is the variant version
The full naming convention is not entirely written in this Guide, but a concise name is used. For instance, EAD 330087-01 (2020) is the concise name for EAD 330087-01-0601, while EAD 332402-v01 (2021) is the concise name for EAD 332402-00-0601-v01. It is important for readers to refer to the reference list for the complete document citation.
1.2 Concrete-to-Concrete Connection This section introduces several important concepts related to the load transfer mechanism (including associated failure mechanism) of PIR used in concreteto-concrete connection. 1.2.1 Local load transfer mechanism in PIR Bond strength is required for rebars to mobilise the surrounding composition of concrete effectively. A constant average bond stress distribution along the embedded length of the rebar is commonly assumed for design purposes (uniform bond model) for both cast-in bars and PIRs.
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Introduction to Post-installed Reinforcement
The bond force represents the force that tends to move a reinforcing bar along its longitudinal axis length with respect to the surrounding concrete and the maximum bond stress that can be sustained by a bar in concrete (ACI 408R, 2003). Figure 1.4 schematically shows the load transfer mechanism of a castin bar and a PIR under tension. For the cast-in rebar in Figure 1.4, the load is mainly transferred by mechanical interlock provided by the ribs at the rebarconcrete interface. The reaction forces within the concrete are assumed to be compressive struts inclined to the rebar axis. The vector-bearing forces can be decomposed into directions parallel and perpendicular to the rebar longitudinal axis. The sum of the parallel components is bond stress. On the contrary, the perpendicular radial components induce circumferential tensile stresses in the surrounding concrete. If the concrete cover is “small”, the radial forces may cause splitting cracks in the concrete. If the concrete cover is “large”, pull-out or rebar tensile failure may occur. RC standards do not take into account concrete cone failure as concrete is not supposed to take tensile forces. The tensile forces of reinforcement are transferred via local strut (i.e., splices) or global strut (i.e., idealised strut-and-tie models (STM)). For the PIR in Figure 1.4, the load transfer mechanism involves two steps. First, the load from the rebar is resisted by the surrounding adhesive, similar to the mechanism of cast-in rebars directly on concrete. Second, this load is then Tension
Tie Bond stress
Post-installed rebar
Strut
Strrut
Tensile stress
Micro-strut
Cast-in surrounding bars Adhesive
Concrete
Figure 1.4 Local load transfer mechanism of cast-in bar and PIR
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7
transferred from the adhesive to the surrounding concrete via adhesion and micro-friction. The lateral dilation of the adhesive layer due to the bearing stress enhances the friction mechanism. The concrete, in turn, develops hoop stresses around the rebar. A small concrete cover may lead to splitting failure (Randl & Kunz, 2012). Pull-out failure may occur between the rebar and the adhesive or the adhesive and the concrete interface depending on the strength of the individual layers. Steel failure might also occur for sufficiently deep embedment. 1.2.2 Failure modes for PIR In Figure 1.4, the resolved forces perpendicular to the longitudinal direction of the bars act as splitting forces—typically resisted by transverse reinforcement— with a negligible part of the splitting forces attributed to concrete tensile capacity. If the development length is not adequately designed, concrete splitting failure is highly possible, particularly at the near-edge bars. On the contrary, without lap splice, the splitting forces will be transferred directly to the concrete, which may result in typical failures in anchorage design, i.e., pull-out, steel rebar yielding, concrete cone, and splitting (see Figure 1.5).
(a) Pull-out (bond failure)
(c) Cone (short embedment)
(b) Rebar yielding (deep embedment)
(d) Splitting (small cover thickness)
Figure 1.5 Failure modes of PIR: (a) Pull-out failure; (b) Rebar yielding; (c) Cone failure; (d) Splitting failure
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Introduction to Post-installed Reinforcement
1.2.3 Shear stress transfer at the interface of new and existing concrete In post-installed concrete structures, the interface of new and existing concrete shall be properly roughened to bond them (see Figure 1.6). At the end of the beam, the shear force transfers tension stress to the bottom rebar through an STM. The concrete strut will preclude the potential formation of concrete cone failure. The top reinforcement bar should be checked for possible cone and bond-splitting failures in the absence of concrete strut confinement. In any case, as per general principles of RC theory, the reinforcing bars are assumed not to take up shear forces significantly, although dowel action is attributed to the presence of longitudinal bars. Readers are encouraged to refer to some established reference documents on examples of STM design, e.g., Fédération internationale du béton (2011b).
Check for cone and bond-splitting
Roughened surface
External loading
Post-installed rebars New RC member
Strut and tie induced by V
Shear (V) translated from external loading
Existing support
Figure 1.6 PIR is designed to take tension force only and not shear force
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1.3 Material for PIR This section introduces the primary materials used for PIR, including adhesive systems, base material, and reinforcement. 1.3.1 Adhesive systems 1.3.1.1 Adhesive types
There are three typical structural adhesives available for PIR systems: polymer adhesives, cementitious grouts, and hybrid grouts (a combination of polymers and cementitious components). Polymer adhesives Polymer adhesives are usually two-component systems that can be delivered as (i) injection systems with soft or hard plastic cartridges, or (ii) capsule systems with soft or glass capsules. The polymer adhesives for injection systems are commonly pre-packaged in dual-plastic cartridges, requiring mixing with a static mixer before dispensing into the drilled hole through injection (see Figure 1.7(a)).
Polymer
Soft cartridge
Soft capsule
Hard cartridge (a)
Glass capsule (b)
Figure 1.7 Types of polymer adhesives: (a) Injection systems with soft or hard plastic cartridge; (b) Capsule systems with soft or glass capsule
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Introduction to Post-installed Reinforcement
Capsule systems, on the other hand, use adhesives encapsulated in a plastic foil (soft capsule) or glass capsule (see Figure 1.7(b)). The capsule is inserted into the drilled hole and mixed by direct hammer or boring to achieve rebar setting. Polymer adhesives can provide high bond strength with existing concrete. It is generally observed that an average bond strength (15 to 35 megapascals (MPa), without splitting failure) can be obtained for PIR installed in uncracked lowstrength concrete tested with a confined test setup of an embedment length of approximately 7 to 10 diameters. On the contrary, it is approximately 10 MPa for cast-in rebars. Polymer adhesives have high compression strength of about 50 to 100 MPa and high tensile strength, usually between 10 and 40 MPa. Various polymer adhesives have suitable viscosity to provide a void-free bond layer in the annular space between rebar and concrete if installed with a proper delivery system (see Chapters 3 and 5). These adhesives allow installation at all orientations (i.e., vertical downwards and upwards, horizontal and inclined directions) with superior bond strength under different use conditions. Despite the advantages of polymer adhesives, there are some known setbacks. Their coefficient of thermal expansion is different from that of the concrete base material. The noticeable difference of the modulus of elasticity for adhesive (usually higher) and concrete base material (usually lower) may induce cracks because of internal stresses. The problem can be circumvented through a qualified system, such as aggregate sieve grading, to optimise the proportion of polymers to be lesser, reducing the differences in natural properties (El-Reedy, 2008). Cementitious grouts While polymer adhesives give physical protection to steel reinforcement, cementitious grouts provide passive protection as they have the same properties as existing concrete. The alkalinity environment around the reinforcement is increased with cementitious grouts, offering corrosion protection for steel rebars. The advantage of cementitious grouts is their optimal use for corrosion repair. However, a larger drilled hole diameter is required to install cementitious grouts compared to other bonding materials. The low viscosity grout mix is typically limited to vertical down-hole application and cannot be used in horizontal and overhead applications. Cementitious grout cannot be used when water seepage is present. Hybrid grouts Hybrid adhesives are a combination of polymer and cementitious grout. Polymers are added to the cement mortar through liquid or powder to improve some properties of the cementitious grout, particularly to increase flexural
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resistance and elongation, reduce water permeability, strengthen the bond between old and new concrete, and raise operational effectiveness. 1.3.1.2 Temperature effects on adhesives
Adhesives are sensitive to temperature, so the effects of temperature must be considered before, during, and after installation to ensure an effective connection. The main temperature influences can be divided into three stages under ordinary circumstances (Gamache, 2017): (a) Storage temperature of the adhesive, which can influence its shelf-life (b) Temperature (low and high) of the concrete and adhesive at the time of installation (c) Temperature of the concrete during the service life of the reinforcement structures (elevated temperatures can markedly affect the bond strength of PIR structures) Special provisions should be applied to adhesives exposed to extremely high temperatures, such as fire. Storage temperature The manufacturer’s published installation instructions (MPII) commonly provide the storage temperature of the adhesive before installation. Always follow the temperature limit to avoid adhesive degradation before installation. Special consideration for storage at job sites (i.e., the amount of sun exposure for the lockboxes) may be required. High temperature may cause liquid separation and permanent adhesive degradation, while low, freezing temperature conditions may cause crystallisation. Degradation and crystallisation may significantly reduce the bond strength performance of PIR structures. Installation temperature Adhesives experience two stages of time—gel time and cure time—during PIR installation. Gel time is the working time that starts when dual adhesives are mixed to initiate the chemical reaction. In a static mixing nozzle system, gel time starts in the nozzle. During gel time, the adhesive can be worked and the rebar can be adjusted without affecting the in-service strength of the PIR system later. After gel time has elapsed, the adhesive (including the steel rebar element) must remain undisturbed until full cure time is achieved. Cure time is the period required for the mixed adhesive to achieve full strength before being subjected to withstand the desired loading. A general trend of gel time and cure time against temperature indicates that a low temperature induces longer gel and cure times. Conversely, a high temperature induces shorter gel and cure times. It should be noted that the gel time and cure
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Introduction to Post-installed Reinforcement
time of adhesives depend on the temperature of the concrete base material (not the ambient air temperature) during installation. A low temperature in the base material may retard the curing process (longer gel and cure times) and elevate the viscosity of the adhesive, making it less workable during injection. In contrast, a high temperature in the base material may considerably shorten the gel time and cure time of the adhesive and reduce viscosity, causing the adhesive to run out in horizontal and overhead installations. The high-temperature environment in the base material, which causes accelerated curing, affects the use of PIR systems in deep embedment depth and large drilled holes. A non-universal but somewhat effective solution is to condition the adhesive to a temperature of approximately 20°C before use to allow optimal injectability. However, this measure is ineffective in influencing cure time, which is mainly related to the temperature of the concrete member where the reinforcing bar is installed. Service temperature The design of PIR, including the selection of adhesives, should cater to the service temperature in the base material (not the air temperature). The service temperature includes the minimum, maximum, and extreme temperature in transient and long-term exposure. In general, a high base material temperature reduces the bond strength of adhesives, but a low temperature has little negative impact on the bond strength as verified in freeze-thaw tests (Gamache, 2017). Fire exposure For PIR systems subjected to high temperature or fire, particular advice and data should be sought from the product manufacturer. The product manufacturer should provide the variation of adhesive bond strength with temperature obtained through tests (see EAD 330087-01, 2020). The temperature at a depth within the concrete will often be much lower than at the concrete surface. Therefore, an extended embedment depth to compensate for the loss of bond strength close to the concrete surface is beneficial in mitigating the effects of fire (Interim Advice Note 104/15, 2015; BS 8539, 2012). 1.3.1.3 Design working life
MS EN 1990 (2010) suggests the assumed periods a structure (or part of it) is still fit (without major repair work). For example, the design working life for temporary structures, common building structures, and infrastructures such as bridges are 10, 50, and 100 years, respectively. Readers are reminded to note the service life of a qualified product in ETA, particularly the long-term durability
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performance of PIR under sustained loading. The types and characteristics of the adhesive (polymer adhesive, cementitious grout, or hybrid grout) are essential parameters in the application for specific engineering purposes. For example, cementitious grout is known to have creep behaviour, which may not be appropriate for long-term bonding. 1.3.1.4 Selecting the right adhesive system
The choice of adhesive depends on its use, loading direction, environmental considerations, anchorage length, rebar diameter, drilling method, and job site conditions. It should be noted that some adhesives for anchor systems may not be used for PIR. Only approved adhesives for PIR by EAD 330087-01 (2020) (replacing EOTA TR 023, 2006) or AC 308 (2019) are suitable. Table 1.2 lists a generic form to facilitate the selection of a suitable adhesive system. Engineers can fill in the generic form and pass it to a specialist/ manufacturer of adhesives to suggest the most appropriate product. Table 1.2 Generic adhesive system selection considerations
No.
Considerations
1
What are the application conditions of the drilled hole? A. Dry B. Wet C. Water-filled/Flooded*
2
What is the diameter and depth of the drilled hole? Rebar diameter: Hole depth*#:
3
What is the direction of the drilled hole? A. Downward B. Horizontal
C. Overload
4
What is the drilling method?
5
Is the concrete cracked or non-cracked? A. Cracked concrete B. Non-cracked concrete
6
What is the concrete cylinder/cube strength?
7
What is the type of load on the post-installed reinforcement structures? A. Static load B. Quasi-static load C. Fatigue load D. Dynamic or seismic load E. Wind load
8
Should the adhesive be fire-resistant? A. Yes ( hours)
9
/
B. No
What is the chloride content† in concrete?
%
MPa
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Introduction to Post-installed Reinforcement
Table 1.2 (cont'd)
10
What is the expected gel time and cure time? Gel time: Cure time:
11
What is the expected service life of the adhesive?
12
Should the adhesive be non-shrink? A. Yes B. No
13
Storage temperature of adhesive: ___________ Working temperature of concrete: ___________ Service temperature range: from ___________ to ___________ Short-term temperaturea: from ___________ to ___________ Long-term temperatureb: from ___________ to ___________
14
Hole cleaning A. As per MPII
years
B. Inability to clean thoroughly due to site condition
15
Should the adhesive be chemical-resistant to the following products? Alkaline products: Drilling dust slurry PH=12.6; potassium hydroxide solution (10%) PH=14 Acids: Acetic acid (10%), nitric acid (10%), hydrochloric acid (10%), sulfuric acid (10%) Solvents: Benzyl alcohol, ethanol, ethyl acetate, methyl ethyl ketone (MEK), trichloroethylene, xylol (mixture) Products from job site: Concrete plasticiser, diesel, engine oil, petrol, oil for formwork Environment: Saltwater, demineralised water, sulphurous atmosphere (80 cycles)
16
Should the adhesive system have ETA approval (EAD 330087-01, 2020) or ICC-ES approval (AC 308, 2019)? A. ETA approval B. ICC-ES approval
Note: * Condition is not considered by EAD 330087-01 (2020) and AC 308 (2019), additional technical data from the supplier is needed # To be justified by the engineer † Example standards for chloride content tests are BS 1881-124 (2015) and EN 14629 (2007) a Short-term temperature: Where elevated concrete temperatures are transient or part of a regular cycle of heating and cooling, such as day-night temperature rise and fall b Long-term temperature: Where concrete temperatures may remain elevated over weeks or months
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1.3.2 Base materials Several base materials are suitable for adopting the PIR system, such as normalweight RC (cracked or uncracked), prestressed concrete, lightweight concrete, and masonry structure. This Guide only elaborates on the normal-weight RC structure as it is the most commonly used in Malaysia. 1.3.2.1 Concrete
This guideline applies to the use of PIR in normal-weight structural concrete grade C12/C15 to C50/C60 (characteristic cylinder/cube strength in MPa) conforming to EAD 330087-01 (2020). For higher grade concrete (over 70 MPa), the bond strength of PIR is capped at the limit of C60 (characteristic cylinder strength) unless justified by special technical data from the supplier. The minimum thickness of the concrete members in which the rebar will be installed should be greater or equal to the sum of the minimum anchorage length of the PIR and the minimum cover thickness. 1.3.2.2 Others
Other base materials, such as rock, is common in Malaysia for infrastructure projects, e.g., Mass Rapid Transit. No ETA is available for all types of rocks in the rock scenario, so an on-site pull-out test may be required. Readers are reminded that the results obtained from the on-site pull-out test may include coupled effects of workmanship during installation and not the actual PIR performance as tested in a laboratory. 1.3.3 Reinforcement Like concrete, steel reinforcement in this Guide should conform to the MS EN 1992-1-1 (2010) requirement. It should be noted that 250 MPa round bars do not apply to PIR systems.