Design of FRP and Steel Plated RC Structures

Retrofitting Beams and Slabs for Strength, Stiffness and Ductility

Deric Oehlers, Rudolph Seracino

• Publisher: Elsevier Science
• Year: 2004
• Print ISBN: 9780080445489
• eBook ISBN: 9780080472447
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

There are a large and ever-increasing number of structures and buildings worldwide that are in need of refurbishment, rehabilitation and strengthening. The retrofitting of beams and slabs for this purpose is now recognized as the most cost-effective and environmentally sustainable method of carrying out this essential renovation work. The authors of Design of FRP and Steel Plated RC Structures are both acknowledged world experts on these techniques and their book has been designed to provide the reader with a comprehensive overview of the established techniques and their applications as well as thorough coverage of newly emerging methodologies and their uses. The comparison of FRP and steel is a particular focus and the authors provide practical examples of where one material might be used in preference to another. Indeed practical, worked examples of how, when, and why specific solutions have been chosen in real-world situations are used throughout the text and provide the user with invaluable insights into the decision-making process and its technical background. Just as importantly these examples make the understanding and application of these techniques easier to understand for the student and the practitioner. The book is international in appeal, as while no reference is made to specific local codes the authors' approach always follows that of the more advanced structural codes worldwide. As such it will remain an essential resource for many years to come. Design of FRP and Steel Plated RC Structures is an important reference for a broad range of researchers, students and practitioners including civil engineers and contractors, architects, designers and builders. - Contains detailed worked examples throughout to aid understanding and provide technical insight - Covers all types of metal plates and all types of FRP plates - Uses design philosophies that can be used with any mathematical model - Provides coverage of all main international guidelines

Chapter 1

Introduction

1.1 Introduction

Existing reinforced concrete structures are often in need of strengthening, stiffening, improving the ductility or repair. A common form of retrofitting is to adhesively bond plates or sheets to the surfaces. However, tests have shown that these plates are prone to premature debonding, as has occurred to the tension face plate in Fig.1.1, which can inhibit the use of this retrofitting technique. The aims of this book are to:

Figure 1.1 Premature failure of adhesively bonded plate

• provide a comprehensive overview of all types and forms of plating

• provide an insight into the various plate debonding or peeling mechanisms

• compare, comment and apply the numerous design procedures or guidelines that are currently available in Australia, Europe, Hong Kong and the USA

• show where adhesively bonded plates can be safely applied, where they should not be applied and where bolted plates should be used instead of adhesively bonded plates

• clearly distinguish between the behaviours of metal and FRP plated sections

• provide comprehensive information so that retrofitting by plating can be used with safety and confidence and, hence, extend the use of all types of plating

• provide engineers with the design tools to develop their own unique plating systems and to decide on appropriate techniques specific to their retrofitting problems

This book covers the mechanics of retrofitting reinforced concrete (RC) beams and slabs using externally bonded longitudinal plates. The plates can be made of FRP, steel, aluminium or any metal; they can have any shape such as flat plates, channels or angle sections; they can be bonded to any surface such as the tension face, sides or compression face; and they can be either adhesively bonded or bolted. Methods of analysis are illustrated and applied to determine the strength, stiffness and ductility of plated structures and design procedures for preventing premature debonding are compared.

In this chapter, the large variety of forms of longitudinal plating available to the designer is first described. This is then followed by a description of the premature failure mechanisms that can occur and have to be designed for, and how these failure mechanisms can affect the choice of plate material and size. Design guides are then compared which shows that there is general agreement on the failure mechanisms.

1.2 Forms of plating beams and slabs

Forces can be transmitted to the external plates from the RC structure through an adhesive bond, through bolts or through wrapping. Plates can be placed on any surface of the beam or slab and they can have any shape such as flat plates, channels or angle sections.

1.2.1 Bonding or joining techniques

1.2.1.1 Bolted and adhesively bonded plates

It is common practice to adhesively bond plates to the tension faces of slab structures as in Fig.1.2(a). Plates can also be adhesively bonded to the sides of beams as in Section A-A in Fig.1.3. However, if a ductile connection is required or if the adhesively bonded plate is prone to premature debonding or peeling, then the plate can be bolted as shown in Figs. 1.2(b) and 1.3. Although plates can be bolted to the tension face as in Fig.1.3, this may be difficult in beams due to congestion of the longitudinal tension reinforcement, in which case the plates can be bolted to the sides of the beam where only the stirrups have to be avoided.

Figure 1.2 Retrofitting bridges

Figure 1.3 Bonding plates by adhesion and/or bolting

Plates can be both bolted and adhesively bonded but it should be remembered that each bonding technique works independently of the other; they do not enhance each other as bolts form a ductile connection that requires slip, whereas, adhesion forms a stiff but brittle connection. For additional safety, a plate can be designed as both bolted and adhesively bonded so that the bolts take over should the adhesive deteriorate. Bolts act as shear connectors in the composite plated structure so that they can be designed using the principles applied to stud shear connectors in composite steel and concrete beams (Oehlers and Bradford 1995, 1999) that are available in national standards. A bolted FRP plate is probably more expensive to install than an adhesively bonded FRP plate, but bolting does allow the full strength of the plate to be achieved, whereas, adhesively bonded FRP plates often debond at strains between one-quarter to one-third of their fracture strain.

1.2.1.2 Wrapping and mechanical end anchorage

An alternative technique to bolting and/or adhesion for transferring the force into the plate is wrapping as shown in Fig.1.4 where the plate is both adhesively bonded and vertically wrapped around a rounded corner. The most efficient form is to fully wrap the cross-section as shown in A-A. This is a common practice in columns. The vertical wrap neither prevents nor inhibits the plate from debonding but takes over transferring the force, such as at C, after debonding. It is a very efficient system for increasing the vertical shear capacity of a beam with stirrups, as the fully wrapped section has sufficient ductility to allow the stirrups to yield or at least get significantly stressed whilst the wrap is still resisting vertical shear force. However, it is a difficult system to apply as the plate has to penetrate the flange of the beam. An alternative approach is to partially wrap as in B-B but, in this case, the resistance to the force D is generally low and the system is also brittle so that it is likely that the plate will debond before there is any significant stressing of the stirrups. A good compromise is...

Table of contents

• Cover image
• Title page
• Table of Contents
• Elsevier Internet Homepage - http://www.elsevier.com
• Copyright
• Preface
• Notation
• Chapter 1: Introduction
• Chapter 2: Intermediate Crack (IC) Debonding
• Chapter 3: Flexural Strength and Ductility
• Chapter 4: CDC Debonding of Tension Face Plates
• Chapter 5: Generic Rules for CDC Debonding
• Chapter 6: Plate End (PE) Debonding
• Chapter 7: Design Examples
• Index