Strengthening of concrete structures with adhesive bonded reinforcement : design and dimensioning of CFRP laminates and steel plates

Design and construction in existing contexts is becoming increasingly important, and often the structures - sometimes of historical interest - can be preserved easily and at minimum cost by employing strengthening measures. Existing concrete members can be strengthened by using adhesives to bond additional reinforcing elements onto or into those members. This book explains the design rules, together with their background, and uses examples to illustrate their use, specifically for slabs, beams and columns. Concrete member strengthening measures can take the form of, for example, flexural strengthening with externally bonded (surface-mounted) CFRP strips, CF sheets and steel plates, flexural strengthening with CFRP strips bonded in slits (near-surface-mounted reinforcement), shear strengthening with externally bonded CF sheets and steel plates, and column strengthening with CF sheets as confining reinforcement.
The explanations and background information provided are mainly based on the new German guideline "Strengthening of Concrete Members with Adhesively Bonded Reinforcement" by the German Committee for Structural Concrete (DAfStb). This is the first European guideline to regulate this topic in the form of a supplement to the Eurocode. As it is planned to produce a document in a future Eurocode 2, the DAfStb guideline serves as a starting point.
The authors are extensively involved in the planning, design, operation and inspection of buildings for preservation and reconstruction, and in the updating of European Technical Approval Guidelines (ETAGs) and design rules.

Selected chapters from the German concrete yearbook are now being published in the new English "Beton-Kalender Series" for the benefit of an international audience.
Since it was founded in 1906, the Ernst & Sohn "Beton-Kalender" has been supporting developments in reinforced and prestressed concrete. The aim was to publish a yearbook to reflect progress in "ferro-concrete" structures until - as the book's first editor, Fritz von Emperger (1862-1942), expressed it - the "tempestuous development" in this form of construction came to an end. However, the "Beton-Kalender" quickly became the chosen work of reference for civil and structural engineers, and apart from the years 1945-1950 has been published annually ever since.

Author Notes

Prof. em. Dr.-Ing. habil. Dr.-Ing. E. h. Konrad Zilch studied civil engineering and gained his doctorate at TU Darmstadt in 1976. Following research posts at the University of California, Berkley, and the University of Western Ontario, Canada, he worked in the construction industry for many years. From 1988 to 1993 he was professor for structural analysis at RWTH Aachen University, and from 1993 to 2009 professor for concrete structures at TU Munich. He was a design certifying engineer for more than twenty years and is senior partner at Zilch + Mller Ingenieure, Munich.
PD Dr.-Ing. habil. Roland Niedermeier studied civil engineering and gained his doctorate at TU Munich in 2001. Since 1993 he has been involved in research at TU Munich and MPA BAU, the accredited authority for testing construction materials and products, where he has been the technical director of the Structural Engineering Laboratory since 2001.
Dr.-Ing. Wolfgang Finckh studied civil engineering and gained his doctorate at TU Munich in 2012. He has been a senior design engineer at Wayss Freytag Ingenieurbau AG (wf) since 2012.

Editorial	p. ix
1 Introduction	p. 1
1.1 The reason behind this book	p. 1
1.2 Strengthening with adhesively bonded reinforcement	p. 1
2 DAfStb guideline	p. 3
2.1 The reasons for drawing up a guideline	p. 3
2.2 Preparatory work	p. 3
2.3 Work on the guideline	p. 4
2.4 The structure and content of the guideline	p. 4
2.4.1 General	p. 4
2.4.2 Design and detailing	p. 4
2.4.3 Products and systems	p. 4
2.4.4 Execution	p. 5
2.4.5 Planning	p. 5
2.5 Safety concept	p. 5
2.6 Applications	p. 6
2.6.1 Member to be strengthened	p. 6
2.6.2 Strengthening systems	p. 7
2.6.3 Ambient conditions	p. 7
2.6.4 Fire protection	p. 8
2.7 Relationship with other regulations	p. 9
2.8 Documents and assistance for practical applications	p. 10
3 Design of strengthening measures with externally bonded CFRP strips	p. 11
3.1 Principles	p. 11
3.2 Verification of flexural strength	p. 13
3.3 Bond analysis	p. 15
3.3.1 Principles	p. 15
3.3.2 Simplified method	p. 16
3.3.3 More accurate method	p. 17
3.3.3.1 General	p. 17
3.3.3.2 Determining the crack spacing	p. 19
3.3.3.3 Accurate analysis of concrete element between cracks	p. 20
3.3.3.4 Simplified analysis of element between cracks	p. 23
3.3.4 End anchorage analysis	p. 24
3.3.4.1 General	p. 24
3.3.4.2 End anchorage analysis at flexural crack nearest to point of contraflexure	p. 24
3.3.4.3 Anchorage analysis at an arbitrary concrete element between cracks	p. 26
3.3.4.4 End anchorage analysis with shear wrapping	p. 27
3.4 Shear force analyses	p. 29
3.4.1 Shear strength	p. 29
3.4.2 Shear strengthening	p. 30
3.4.2.1 Full wrapping in steel	p. 31
3.4.2.2 Full wrapping in fibre-reinforced material	p. 32
3.4.2.3 U-wrapping	p. 32
3.4.3 End strap to prevent concrete cover separation failure	p. 33
3.5 Fatigue analysis	p. 35
3.6 Analyses for the serviceability limit state	p. 36
3.7 Detailing	p. 36
3.7.1 Strip spacing	p. 36
3.7.2 Provision of shear straps	p. 37
3.7.3 Steel shear straps	p. 37
4 Example 1: Strengthening a slab with externally bonded CFRP strips	p. 39
44 System	p. 39
4.1.1 General	p. 39
4.1.2 Loading	p. 39
4.1.3 Construction materials	p. 40
4.1.3.1 Near-surface tensile strength	p. 40
4.1.3.2 Concrete compressive strength	p. 41
4.1.3.3 Type and quantity of existing reinforcement	p. 41
4.1.3.4 Position of existing reinforcement	p. 41
4.1.3.5 Strengthening system	p. 41
4.2 Internal forces	p. 42
4.3 Determining the prestrain	p. 42
4.4 Simplified analysis	p. 44
4.5 Accurate analysis	p. 46
4.5.1 General	p. 46
4.5.2 Verification of flexural strength	p. 46
4.5.3 Determining the crack spacing	p. 48
4.5.4 Accurate analysis of concrete element between cracks	p. 48
4.5.4.1 Determining the strip forces	p. 49
4.5.4.2 Determining the bond strength	p. 52
4.5.5 End anchorage analysis	p. 55
4.6 Analysis of shear capacity	p. 58
4.7 Serviceability limit state	p. 59
5 Design of strengthening with near-surface-mounted CFRP strips	p. 61
5.1 Principles	p. 61
5.2 Verification of flexural strength	p. 61
5.3 Bond analysis	p. 63
54 Shear Force Analyses	p. 65
5.5 Fatigue analysis	p. 66
5.6 Analyses for the serviceability limit state	p. 67
5.7 Detailing	p. 67
6 Example 2: Strengthening a beam with near-surface-mounted CFRP strips	p. 69
6 J System	p. 69
6.1.1 General	p. 69
6.1.2 Loading	p. 69
6.1.3 Construction materials	p. 71
6.1.3.1 Concrete compressive strength	p. 71
6.1.3.2 Type and quantity of existing reinforcement	p. 71
6.1.3.3 Position of existing reinforcement	p. 71
6.1.3.4 Strengthening system	p. 71
6.2 Internal forces	p. 72
6.3 Determining the prestrain	p. 72
6.4 Verification of flexural strength	p. 74
6.5 Bond analysis	p. 76
6.5.1 Analysis point	p. 76
6.5.2 Acting strip force	p. 78
6.5.3 Bond resistance	p. 79
6.5.4 Bond analysis	p. 80
6.6 Shear analyses	p. 80
6.6.1 Shear capacity	p. 80
6.6.2 Shear strengthening	p. 81
6.6.3 Check for concrete cover separation failure	p. 82
6.7 Analyses for the serviceability limit state	p. 84
7 Design of column strengthening with CF sheets	p. 87
7.1 Principles	p. 87
7.2 Properties of CF sheets relevant to design	p. 91
7.3 Load-carrying capacity of cross-section	p. 93
7.4 Load-carrying capacity of member	p. 98
7.5 Creep	p. 102
7.6 Analysis at ultimate limit state	p. 105
7.7 Analysis at serviceability limit state	p. 111
8 Example 3: Column strengthening	p. 115
8.1 System	p. 115
8.1.1 General	p. 115
8.1.2 Loading	p. 115
8.1.3 Construction materials	p. 116
8.1.3.1 Concrete	p. 116
8.1.3.2 Type and quantity of existing reinforcement	p. 116
8.1.3.3 Strengthening system	p. 117
8.2 Internal forces	p. 118
8.3 Determining the cross-sectional values	p. 118
8.4 Boundary conditions	p. 119
8.5 Verification of column load-carrying capacity	p. 120
8.5.1 Creep of confined concrete	p. 120
8.5.2 Properties of the CF sheet	p. 121
8.5.3 Distribution of transverse compression	p. 122
8.5.4 Multi-axial stress state in concrete	p. 122
8.5.5 Calculation of column load-carrying capacity	p. 123
8.6 Serviceability limit state	p. 127
9 Summary and outlook	p. 129
References	p. 131
Index	p. 145

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