ISOMAT DOCUMENTATIE

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Transcript of ISOMAT DOCUMENTATIE

  • PROF. THANASIS C. TRIANTAFILLOU UNIVERSITY OF PATRAS

    DEPARTMENT OF CIVIL ENGINEERING STRUCTURAL MATERIALS LABORATORY

    STRENGTHENING AND SEISMIC RETROFITTING OF REINFORCED CONCRETE STRUCTURES WITH

    FIBER-REINFORCED POLYMERS (FRP)

    PATRAS, GREECE

    2005

  • iii

    page

    PREFACE i

    CONTENTS iii

    CHAPTER 1 INTRODUCTION 1 1.1 General 1

    1.2 Structure of the book 3

    CHAPTER 2 MATERIALS AND TECHNIQUES 5 2.1 Materials 5

    2.1.1 General 5

    2.1.2 Fibers 5

    2.1.3 Matrix 7

    2.1.4 Composite materials 7

    Example 2.1 9

    2.1.5 Adhesives 10

    2.2 Strengthening systems 11

    2.2.1 Wet lay-up systems 11

    2.2.2 Prefabricated elements 12

    2.3 Basic strengthening technique 13

    CHAPTER 3 BASIS OF DESIGN 15 3.1 General 15

    3.2 Material constitutive laws 15

    3.2.1 Calculation of resistance full composite action 15

    3.2.2 Calculation of resistance - debonding 17

    3.2.3 Serviceability limit state 17

    3.3 Bond at the FRP concrete interface 17

    3.3.1 General, behavior 17

    3.3.2 Analytical model 19

    Example 3.1 20

    CONTENTS

  • iv

    page

    CHAPTER 4 FLEXURAL STRENGTHENING 21 4.1 General 21

    4.2 Initial situation 22

    4.3 Ultimate limit state failure modes 23

    4.4 Ultimate limit state - calculations 25

    4.4.1 Full composite action 25

    4.4.2 Loss of composite action 27

    4.5 Ductility considerations 30

    4.6 Summary of design calculations ultimate limit state 31

    4.7 Example 32

    4.8 Servicability limit state 34

    4.9 Columns 35

    CHAPTER 5 SHEAR STRENGTHENING 39 5.1 General 39

    5.2 Shear carried by FRP 41

    5.3 Summary of design procedure 44

    Example 5.1 45

    Example 5.2 47

    Example 5.3 47

    5.4 Beam-column joints 48

    CHAPTER 6 CONFINEMENT 51 6.1 General 51

    6.2 Behavior and constitutive modeling of FRP-confined concrete 52

    6.2.1 Behavior 52

    6.2.2 Design model 54

    Example 6.1 58

    6.3 Chord rotation and ductility 58

    Example 6.2 63

    6.4 Lap-splices 64

    6.4.1 Behavior and design 64

    Example 6.3 66

    6.4.2 Effect of lap-splices on chord rotation 67

    6.5 Rebar buckling 68

    Example 6.4 69

  • v

    page

    6.6 General comments on FRP-jacketed columns 69

    CHAPTER 7 DETAILING AND PRACTICAL EXECUTION 71 7.1 General 71

    7.2 Detailing 71

    7.2.1 Flexural strengthening 71

    7.2.2 Shear strengthening 73

    7.2.3 Confinement 74

    7.3 Practical execution 76

    CHAPTER 8 DURABILITY 79 8.1 General 79

    8.2 Temperature effects 79

    8.3 Moisture 79

    8.4 UV light exposure 80

    8.5 Alcalinity and acidity 80

    8.6 Galvanic corrosion 81

    8.7 Creep, stress rupture, stress corrosion 81

    8.8 Fatigue 81

    8.9 Impact 82

    REFERENCES 83

    APPENDIX THE PROGRAM Composite Dimensioning 87

  • vi

  • i

    This document is based on the book by Prof. Thanasis C. Triantafillou Strengthening of

    Reinforced Concrete Structures with Fiber Reinforced Polymers (in Greek), published in 2003,

    and covers basic design aspects of strengthening and seismic retrofitting of concrete with

    advanced composite materials. This relatively new strengthening/retrofitting technique offers, in

    many cases, several advantages compared with traditional techniques, but is rather unknown to

    many designers, especially with respect to the relevant calculations. It is this gap that the present

    document intents to fill, through explanatory text (including simple examples) and a simple to use

    software package Composite Dimensioning described in the Appendix and included in the

    accompanied CD.

    PREFACE

  • ii

  • INTRODUCTION

    STRENGTHENING AND SEISMIC RETROFITTING OF RC STRUCTURES WITH FRP T. C. Triantafillou

    1

    1.1 General

    The issue of upgrading the existing civil engineering infrastructure has been one of great importance for over 15 years or so. Deterioration of bridge decks, beams, girders and columns, buildings, parking structures and others may be attributed to ageing, environmentally induced degradation, poor initial design and/or construction, lack of maintenance, and to accidental events such as earthquakes. The infrastructures increasing decay is frequently combined with the need for upgrading so that structures can meet more stringent design requirements (e.g. increased traffic volumes in bridges exceeding the initial design loads), and hence the aspect of civil engineering infrastructure renewal has received considerable attention over the past few years throughout the world. At the same time, seismic retrofit has become at least equally important, especially in areas of high seismic risk.

    Recent developments related to materials, methods and techniques for structural strengthening and seismic retrofitting have been enormous. One of todays state-of-the-art techniques is the use of fiber reinforced polymer (FRP) materials or simply composites, which are currently viewed by structural engineers as new and highly promising materials in the construction industry. Composite materials for strengthening of civil engineering structures are available today mainly in the form of: (a) thin unidirectional strips (with thickness in the order of 1 mm) made by pultrusion, (b) flexible sheets or fabrics, made of fibers in one or at least two different directions, respectively (and sometimes pre-impregnated with resin). Central to the understanding of composites bonded to concrete is the fact that stresses in these materials are carried only by the fibers, in the respective directions.

    The reasons why composites are increasingly used as strengthening materials of reinforced concrete members may be summarized as follows: immunity to corrosion; low weight (about of steel), resulting in easier application in confined space, elimination of the need for scaffolding and reduction in labor costs; very high tensile strength (both static and long-term, for certain types of FRP materials); stiffness which may be tailored to the design requirements; large deformation capacity, which results in substantial member ductility; and practically unlimited availability in FRP sizes and FRP geometry and dimensions. Composites suffer from certain disadvantages too, which are not to be

    CHAPTER 1

    INTRODUCTION

  • INTRODUCTION

    STRENGTHENING AND SEISMIC RETROFITTING OF RC STRUCTURES WITH FRP T. C. Triantafillou

    2

    neglected by engineers: contrary to steel, which behaves in an elastoplastic manner, composites in general are linear elastic to failure (although the latter occurs at large strains) without any yielding or plastic deformation, leading to reduced (but generally adequate) ductility. Additionally, the cost of materials on a weight basis is several times higher than that for steel (but when cost comparisons are made on a strength basis, they become less unfavorable). Moreover, some FRP materials, e.g. carbon and aramid, have incompatible thermal expansion coefficients with concrete. Finally, their exposure to high temperatures (e.g. in case of fire) may cause premature degradation and collapse (some epoxy resins start softening at about 50-70 oC). Hence FRP materials should not be thought of as a blind replacement of steel (or other materials) in structural intervention applications. Instead, the advantages offered by them should be evaluated against potential drawbacks, and final decisions regarding their use should be based on consideration of several factors, including not only mechanical performance aspects, but also constructability and long-term durability.

    Composites have found their way as strengthening materials of reinforced concrete (RC) members (such as beams, slabs, columns etc.) in many thousands of applications worldwide, where conventional strengthening techniques may be problematic (e.g. steel plating or steel jacketing). For instance, one of the popular techniques for upgrading RC elements has traditionally involved the use of steel plates epoxy-bonded to the external surfaces (e.g. tension zones) of beams and slabs. This technique is simple and effective as far as both cost and mechanical performance is concerned, but suffers from several disadvantages (Meier 1987): corrosion of the steel plates resulting in bond deterioration; difficulty in manipulating heavy steel plates in tight construction sites; need for scaffolding; and limitation in available plate lengths (which are required in case of flexural strengthening of long girders), resulting in the need for joints. Replacing the steel plates with FRP strips provides satisfactory solutions to the problems described above. Another common technique for the strengthening of RC structures involves the construction of reinforced concrete (either cast in-place or shotcrete) jackets (shells) around existing elements. Jacketing is clearly quite effective as far as strength, stiffness and ductility is concerned, but it is labour intensive, it often causes disruption of occupancy and it provides RC members, in many cases, with undesirable weight and stiffness increase. Jackets may also be made of steel; but in this case protection from corrosion is a major issue, as is the rather poor confining characteristics of steel-jacketed concrete. The conventional jackets may be replaced with FRP in the form of sheets or fabrics wrapped around RC members, thus providing substantial increase in strength (axial, f