MNL-3(20): Guide to the Code for Assessment, Repair, and Rehabilitation of Existing Concrete Structures

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Author: Updated by Khaled Nahlawi, ACI Distinguished Engineer, under the review and approval of an ACI/ICRI review group consisting of Chair Keith E. Kesner and members Tarek Alkhrdaji, Eric L. Edelson, and Fred R. Goodwin


Introduction to the ACI 562-19 Code

Advancements in the practice of assessment, repair, rehabilitation, and strengthening of concrete structures have developed through a collaboration of design professionals, contractors, suppliers, manufacturers, researchers, educators, and lawyers. The annual cost to owners for repair, protection, and strengthening of existing concrete structures is estimated between $18 and $21 billion (Vision 2020). Simply put, even sound concrete may require repair, rehabilitation, maintenance, or strengthening throughout the service life of a structure. Accordingly, from 2004 to 2006, the Strategic Development Council (SDC), an interindustry development group dedicated to supporting the concrete industry’s strategic needs, facilitated the development of “Vision 2020: A Vision for the Concrete Repair, Protection, and Strengthening Industry” to establish a set of goals that would improve the efficiency, safety, and quality of concrete repair and protection activities. One of the goals established by Vision 2020 was to create a concrete repair and rehabilitation code by 2015. The ACI 562-13 standard, “Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings and Commentary,” is the end result of that initiative. ACI 562-19 is the third edition of the Code with revisions, additions, and reorganized information to enhance the Code, providing more clarity and additional, updated information to assist the design professional.

The purpose of the ACI 562 Code is to provide minimum material and design requirements for the assessment, repair, and rehabilitation of structural concrete members. Like other ACI codes, ACI 562 is organized in a dual-column format, with mandatory code provisions to the left of each page, and nonmandatory commentary to the right to provide additional guidance and information on the content presented in the Code provisions. Unlike other ACI standards, ACI 562 includes both prescriptive and performance requirements. The performance requirements provide great latitude and flexibility to the licensed design professional in satisfying the requirements of ACI 562. Accordingly, ACI 562 serves to unify and strengthen concrete assessment, repair, and rehabilitation projects while accommodating the diverse and unique strategies and materials used in the industry.

In general, the overall use and function of ACI 562, with respect to existing concrete structures, can be compared to that of ACI 318-19, “Building Code Requirements for Structural Concrete and Commentary,” with new concrete construction. As with ACI 318 and the 2018 International Building Code (2018 IBC), plans are underway for ACI 562 an ANSI standard, to be adopted into the International Existing Building Code (IEBC) to address matters pertaining to assessment, repair, rehabilitation, and strengthening of concrete members within existing buildings. Local jurisdictions and building authorities can also adopt ACI 562 directly. Cities and states have both adopted ACI 562 and adopted use of ACI 562 on specific projects. Other jurisdictions are in the process of reviewing the Code for consideration and adoption. Accordingly, while ACI 562 currently defines the standard for the concrete assessment, repair, and rehabilitation industry, the code provisions of ACI 562 will likely then become mandatory requirements as part of the governing building codes that regulate work in existing buildings.

Overview of the guide to ACI 562 Code content

The primary purpose of this guide is to help licensed design professionals (LDPs) gain more knowledge, skill, and judgment to interpret and properly use the ACI 562 Code. Although specifically developed for LDPs, this guide also provides insight into the use and benefits of ACI 562 for contractors, material manufacturers, and building owners and building officials. To achieve this goal, the guide is separated into three main components: Chapter Guides including Appendix A, Project Examples, and Appendix B, providing an overall view of the new standard, ACI 563, “Specifications for Repair of Concrete in Buildings.”

The Chapter Guides and Project Examples are provided in tandem for clarity and understanding of the relative portions of ACI 562 Code. The Project Examples illustrate the process of carrying out a concrete building assessment, repair, rehabilitation, or strengthening project from inception through completion. This guide, including the Project Examples, is intended as a supplement to the ACI 562 Code and not as a “how-to” manual for performing concrete assessment, repair, rehabilitation, or strengthening. Several additional documents are referenced in ACI 562 Commentary and this guide to assist in evaluating the various options and approaches to performing successful concrete assessment, repair, rehabilitation, or strengthening projects. The intent of each Project Example is not to be a prescriptive formula for each of the project scenarios presented, but to illustrate how various sections of ACI 562 are applied together to execute the project. For convenience, related provision numbers from ACI 562 are given at the top of each corresponding paragraph of the project example text. Eight Project Examples are included within the guide:

1. Typical parking structure repairs

2. Typical façade repairs

3. Repair of historic structure for adaptive reuse

4. Strengthening of two-way flat slab

5. Strengthening of double-tee stems for shear

6. Concrete beam repair by section enlargement

7. Concrete repair by steel jacket

8. Beam repair with fire protection analysis:

a. Beam strengthening due to live load increase

b. Beam with inadequate existing concrete cover

In the third edition of this repair guide, a new chapter, Appendix B, was added to address specifications. This is another goal by Vision 2020 to create a concrete repair specification standard. The ACI 563-18 standard, “Specification for Repair of Concrete in Buildings,” is a reference standard that the LDP can apply to any construction repair and rehabilitation project involving structural concrete by citing it in the Project Specifications. It provides direction to the contractor and clearly defines the responsibilities and scope of the repair, rehabilitation, or strengthening. The specifications detail the work, material, and installation required to complete a project the way the client wants.

The Chapter Guides follow the general organization of ACI 562, broken down by the corresponding sections of ACI 562. Section numbers in Chapters 1 to 10 and Appendix A of this guide correspond to the provision numbers in ACI 562. The Chapter Guides include background information and an explanation of the various ACI 562 provisions, with particular insight into how the particular chapter and section of the Code fit within the project. Where applicable, flowcharts are provided to illustrate how to navigate the various provisions of ACI 562. References to Project Examples are provided where applicable to illustrate how specific provisions within each chapter of ACI 562 are incorporated into the design process. In some instances, additional limited-scope examples are included to better illustrate a point that is not covered by the Project Examples.

The first edition of ACI 562 was published in 2013, and was not available when the work for the projects discussed in the Project Examples was actually performed. All Project Examples assume that ACI 562 was available and accepted by local jurisdiction when the example projects were performed.

The second edition of ACI 562, published in 2016, includes additional definitions used in the Code for consistency with 2018 IEBC and other similar standards for existing structures. The title of ACI 562-16 was changed by replacing the word “Evaluation” with “Assessment.” The two terms, which are used interchangeably by other standards and the first version of this Code, have received distinct definitions in the second edition of ACI 562 (Stevens et al. 2016). Specific criteria requirements for assessment and design of repair and rehabilitation for varying levels of damage, deterioration, or faulty construction was added in Chapter 4 when using the Code with IEBC, and in Appendix A when using the Code as a stand-alone code. Chapters 1 and 4 were revised to include specific criteria requirements for assessment and design of repair and rehabilitation for varying levels of damage, deterioration, or faulty construction. Load combinations in Chapter 5, which define the minimum strength of a structure with unprotected external reinforcement, were revised. Chapter 6 directs the LDP to provide an assessment before rehabilitation of an existing structure. This chapter includes historical material property data to help the design professional in the assessment if existing documents related to the existing structure are not available or physical samples cannot be extracted, because of the historical value of the structure. The interface bond provisions in Chapter 7 were revised to provide specific requirements based on shear test, as well as when to provide interface reinforcement, and commentary in Chapter 8 was clarified.

The third edition of ACI 562, published in 2019, has:

(a) Added text to simplify use of new materials that have the equivalent of an ICC-ES evaluation report in Chapter 1;

(b) Simplified the requirements for the basis of design reported in Chapter 1;

(c) Clarified requirements related to detailing of existing reinforcing steel in Chapter 7; and

(d) Updated commentary in Chapter 8 to include a listing of exposure categories that may affect durability.

In addition, three new repair examples are added to demonstrate the flexibility of the Code and its applicability to different repair and strengthening methods. Example 6 is related to concrete beam repair by section enlargement, Example 7 addresses concrete frame strengthening by steel jacketing, and Example 8 focuses on the effect of fire on concrete members and possible protection based on two scenarios: scenario one—concrete structure subjected to increase in live load; and scenario two—reinforcement with low concrete cover.

Lastly, a summary of the various provisions of ACI 562, as well as the corresponding location where each provision is covered within the guide, is provided in the Provision Coverage Matrix at the end of this guide. This serves as a useful tool when searching for additional information to a specific provision of ACI 562.


Document Details

Pages: 224

ISBN: 9781641951210

Categories: Codes, Repair

Formats: Printed Document or Protected PDF/Web View

Table of Contents

Acknowledgments 6

Preface 7

About This Book 12

Chapter 1—General Requirements 13

1.1—General 13

1.2—Criteria for the assessment and design of repair and rehabilitation of existing concrete structures 14

1.3—Applicability of the Code 15

1.4—Administration 16

1.5—Responsibilities of licensed design professional 16

1.6—Construction documents 16

1.7—Preliminary assessment 16

Chapter 2—Notation and Definitions 19

2.1—Notation 19

2.2—Definitions 19

Chapter 3—Referenced Standards 21

Chapter 4—Basis for Compliance 23

4.1—General 23

4.2—Compliance method 24

4.3—Potentially dangerous structural conditions 25

4.4—Substantial structural damage 26

4.5—Conditions of deterioration, faulty construction, or damage less than substantial structural damage 26

4.6—Conditions of deterioration, faulty construction, or damage less than substantial structural damage without strengthening 30

4.7—Additions, 4.8—Alterations, 4.9—Changes in occupancy 30

Chapter 5—Loads, Factored Load Combinations, and Strength Reduction Factors 31

5.1—General 32

5.2—Load factors and load combinations 33

5.3—Strength reduction factors for repair design 33

5.4—Strength reduction factors for assessment 33

5.5—Additional load combinations for structures rehabilitated with external reinforcing systems 34

Chapter 6—Assessment, Evaluation, and Analysis 37

6.1—Structural assessment 37

6.2—Investigation and structural evaluation 38

6.3—Material properties 40

6.4—Test methods to determine or confirm material properties 44

6.5—Structural analysis of existing structures 45

6.6—Structural serviceability 45

6.7—Structural analysis for repair design 45

6.8—Strength evaluation by load testing 46

6.9—Recommendations 46

Chapter 7—Design of Structural Repairs 47

7.1—General 47

7.2—Strength and serviceability 47

7.3—Behavior of repaired systems 48

7.4—Interface bond 49

7.5—Materials 57

7.6—Design and detailing considerations 57

7.7—Repair using supplemental post-tensioning 58

7.8—Repair using fiber-reinforced polymer (FRP) composites 59

7.9—Performance under fire and elevated temperatures 60

Chapter 8—Durability 61

8.1—General 61

8.2—Cover 62

8.3—Cracks and deterioration of reinforcement and metallic embedments 62

8.4—Corrosion 63

8.5—Surface treatments and coatings 64

Chapter 9—Construction 65

9.1—General 65

9.2—Stability and temporary shoring requirements 65

9.3—Temporary conditions 66

9.4—Environmental issues 68

Chapter 10—Quality Assurance 69

10.1—General 69

10.2—Inspection 70

10.3—Testing of repair materials 70

10.4—Construction observations 70

Chapter 11: Commentary References 71

Appendix A—Criteria When Using ACI 562 as a Stand-Alone Code 73

A.1—General 73

A.2—Design-basis code criteria 73

A.3—Potentially dangerous structural conditions 75

A.4—Substantial structural damage 76

A.5—Conditions of deterioration, faulty construction, or damage less than substantial structural damage 76

A.6—Conditions of deterioration, faulty construction, or damage less than substantial structural damage without strengthening 78

A.7—Additions 79

A.8—Alterations 80

A.9—Changes in occupancy 82

Appendix B—Repair Guide 83

General 83

Section 1—General requirements 83

General procedures 84

Preinstallation conference 84

Quality assurance, quality control, testing, and inspection 85

Quality assurance (QA) 85

Advantages of quality assurance 87

Disadvantages of quality assurance 87

Quality control (QC) 87

Advantages of quality control 87

Disadvantages of quality control 87

Testing and inspection 88

Section 2—Shoring and bracing 90

Section 3—Concrete removal and preparation for repair 91

Section 4—Formwork 94

Section 5—Reinforcement and reinforcement supports 97

Section 6—Conventional concrete mixtures 99

Section 7—Handling and placing of conventional concrete 101

Section 8—Proprietary cementitious and polymer repair materials 102

Sections 9 and 10 102

Notes to Specifier (nonmandatory) 102

Checklists 102

Project Examples 104

Chapter 12: Project Example 1—Typical Parking Structure Repair 105

Description of structure 105

Project initiation and objectives 105

Governing building codes 106

Preliminary assessment 107

Investigation of existing site conditions 107

Capacity and demand of existing structure 108

Findings of preliminary assessment 108

Area 1 109

Area 2 111

Report to owner 113

Structural Assessment 113

Existing conditions 113

Structural analysis for repair design 114

Area 1 115

Area 2 115

Design of structural repairs and durability 116

Slab Area 1 116

Slab Area 2 and columns 117

Slab soffit repairs 118

Construction specifications 118

Construction 119

Quality assurance 119

Project close-out 120

Periodic maintenance 120

Record documents 120

Chapter 13: Project Example 2—Typical Façade Repair 121

Description of structure 121

Project initiation and objectives 122

Governing building codes 122

Preliminary observations and assessment 123

Observed concrete conditions 124

Laboratory findings 125

Findings 125

Structural assessment and repair design 126

Shear wall reveal strip repairs 126

North and south walls away from reveal strips and east and west slab and column edges 128

Balcony repairs 128

Performance under fire and elevated temperatures 130

Contract specifications 130

Construction 131

Quality assurance 131

Project close-out 132

Periodic maintenance 132

Record documents 132

Chapter 14: Project Example 3—Adaptive Reuse of Historic Depot 133

Description of structure 133

Project initiation and objectives 134

Governing building codes 134

Preliminary observations and evaluation 135

Concrete conditions 135

Material evaluation findings 137

Summary 137

Structural assessment 138

Requirement for structural assessment 138

Existing properties 138

Structural analysis 138

Structural analysis findings 139

Recommended repair program 140

Train deck rehabilitation 140

Column rehabilitation 142

Concrete repair details 144

Contract specifications 146

Construction 148

Quality assurance 148

Project close-out 148

Periodic maintenance 148

Record documents 148

Chapter 15: Project Example 4—Parking/Plaza Slab Strengthening 149

Description of structure 149

Project initiation and objectives 149

Governing building codes 149

Preliminary evaluation 150

Document review 150

Existing site conditions 150

Strength of as-built structure 150

Compliance method and design-basis code 153

Structural assessment 154

Requirement for structural assessment 154

Structural assessment 154

Structural analysis 155

Strengthening concepts 155

Strengthening Concept 1 155

Strengthening Concept 2 155

Assessment of strengthening concepts 156

Structural analysis for repair design 157

Design of structural repairs and durability 159

Contract specifications 160

Construction 163

Quality assurance 163

Load test 163

Test procedure 163

Test results 167

Project close-out 168

Periodic maintenance 168

Record documents 168

Chapter 16: Project Example 5—Precast/Prestressed Double-Tee Repair 169

Description of structure 169

Project initiation and objectives 169

Governing building codes 170

Preliminary assessment 171

Existing site conditions 171

Design strength of existing structure 171

Findings of preliminary assessment 171

Design-basis code 173

Structural evaluation 173

Existing site conditions 173

Structural analysis for evaluation 174

Structural safety 176

Repair/replacement options 176

Repair/replacement Option 1 176

Repair/replacement Option 2 177

Repair/replacement Option 3 177

Repair/replacement Option 4 178

Evaluation of repair/replacement options 179

Design of strengthening repairs 179

Structural analysis for repair design 179

Design of strengthening repairs 180

Design of structural repairs and durability 181

Development and bond of CFRP strips 181

Acceptance of CFRP repairs by the authorities having jurisdiction 182

Durability of repairs 182

Aesthetics of repairs 182

Contract specifications 182

Construction 183

Quality assurance 183

Project close-out 186

Periodic maintenance 186

Record documents 186

Chapter 17: Project Example 6—Concrete Beam Repair by Section Enlargement 187

Description of structure 187

Project initiation and objectives 187

Governing building code 188

Structural assessment 189

Structural analysis 189

Repair options 190

Design of repairs 191

Durability of repairs 192

Contract documents 193

Construction specifications 193

Construction 193

Quality assurance/construction observations 193

Project Close-out 194

Periodic maintenance 194

Record documents 194

Chapter 18: Project Example 7—Concrete Frame Strengthening by Steel Jacket 195

Description of structure 195

Project initiation and objectives 195

Governing building codes 196

Preliminary evaluation 196

Strengthening concepts 199

Structural analysis and repair design 199

Durability 200

Contract documents 200

Construction specifications 200

Construction 203

Quality assurance 203

Project close-out 204

Periodic maintenance 204

Record documents 204

Chapter 19: Project Example 8—Building Subjected to Fire 205

Description of structure 205

Project initiation, objectives, and remediation summary 206

Governing codes 208

Fire resistance rating calculations 208

Contract specifications 217

Construction 218

Quality assurance 218

Load test 218

Test procedure 218

Project close-out 219

Periodic maintenance 219

Record documents 219

References 219

Referenced Standards and Reports 221

Authored documents 224


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