Seismic Retrofit Design and Construction Guidelines for Existing Reinforced Concrete Buildings and Steel Encased Reinforced Concrete Buildings Using Continuous Fiber Reinforced Materials

Published by the Japan Building Disaster Prevention Association

Edited by the Building Guidance Division, Housing Bureau, Ministry of Construction

Editorial Supervisors Message

Seismic retrofitting techniques using continuous fiber reinforced materials is (receiving attention as) one of the most effective techniques for accelerating the retrofitting of buildings due to its high strengthening effectiveness and excellent workability. (Particularly in recent years, a construction method that makes buildings available for use even during retrofitting work has been widely anticipated, which accounts in large part for the attention this technique is receiving as it contains the possibility of meeting such a requirement.) However, this technique has the characteristics of using materials that have not been widely employed before in the construction industry and also of not offering high performance of the continuous fiber reinforced materials until the continuous fiber sheet is impregnated with impregnate adhesive resins at the work site. Consequently, conventional seismic retrofit design and construction methods can not be used for the continuous fiber reinforcement-based technique. Thus, this document is intended to complement the seismic diagnostic standards and seismic retrofit design guidelines for existing reinforced concrete buildings and steel encased reinforced concrete buildings. It is essential to properly understand these guidelines to implement adequate seismic retrofitting strategies them to correctly applied them in the field.

The Great Hanshin and Awaji Earthquake, which occurred early in the morning of January 17, 1995, attacked highly populated areas and caused the greatest disaster of the postwar period, 6,400-odd fatalities, 43,000-odd injures and a total number of earthquake-damaged houses of about 440,000. As a result, the Ministry of Construction created the Survey Committee for Damaged Buildings composed of academic and professional entities investigated the conditions of earthquake results and reviewed the causes of damage and corrective measures to be taken in the future. As a result, this committee concluded and reported that it is urgently necessary to carry out seismic retrofit and reconstruction of existing buildings and other countermeasures. In light of this situation, the Law for Promoting Seismic Retrofit of Buildings was promulgated on October 27, 1995 and has been in effect since December 25 of the same year. In addition, based on this law, it is stipulated that seismic diagnostic and seismic retrofit design guidelines be notified and the basic concepts, judgment criterion and precautions etc. of seismic diagnostics and seismic retrofit be defined. This document contains recommendations on seismic retrofitting design and construction methods using continuous fiber reinforced materials in reinforced concrete buildings and steel encased reinforced concrete buildings, and should be very useful for preparing proper seismic repair strategies.

The present document includes the latest research results and reports based on many wide ranging studies and investigation concerning this field. The efforts of all those who were

engaged in these activities are highly recognized. Also, we express our deep gratitude to the committee members for helping in the production of this document.

It is expected that this document will be widely utilized, and that seismic retrofitting using fiber reinforced materials in addition to more traditional seismic retrofitting techniques will provide and adequate retrofit of buildings.

September, 1999

Jin Matsuno Director Building Guidance Division Housing Bureau Ministry of Construction

Introduction

The development of the FRP technology, which uses materials mainly constituted of carbon fibers or aramid fibers was initiated in the 1980s. The original uses were mainly as bars or rods being an alternative for internal reinforcement due to their high durability. Also, the FRP materials were broadly used as tendons for prestressed concrete, for increasing the durability of concrete structures, thereby improving their endurance under extreme conditions. In the early 1990s, design recommendation using continuous fiber reinforced materials were being proposed in international meetings held on the basis of many research results and the prospect that bar type continuous fiber reinforced materials would become commercially practical was established, the development aim started to shift to the application of technology to continuous fiber sheets instead of bar-typed reinforcements. The purpose is to strengthen and repair existing buildings by attaching continuous fiber sheets with impregnate bond resins such as epoxy resins on the surface of reinforced concrete or steel encased reinforced concrete members. This was the starting point for the development and commercialization of a new seismic retrofit method for existing buildings. In 1994, the FRP-Hybrid Committee (1994-1997) was formed by the Building Research Institute with the theme of Research on Hybrid Structures Using Continuous Fiber Reinforced Materials. The activities led by this committee provided an opportunity to systematize research on continuous fiber reinforced materials. This committee focused on establishing the application of continuous fiber sheets as an effective technique for the strengthening and repair of existing reinforced concrete buildings.

In the midst of this technological movement, the Hyogoken-Nanbu Earthquake (Kobe Earthquake) occurred on January 17, 1995 damaging many existing buildings. As a result, the social needs for seismic evaluation and seismic strengthening techniques increased, and leading to the increase of seismic retrofitting using carbon fiber or aramid fiber.

Experimental programs were conducted by many institutions to evaluate the performance of strengthened structural element. As their results were generated, the design and construction guidelines for using continuous fiber reinforced materials as seismic reinforcements were developed by each organization and certified by either the Japan Building Disaster Prevention Association or the Japan Building Center, which allowed the development phase of the practical technologies to be continued. As a result of the earthquake, the following three organizations were established; the cooperative research Development of Technology for Improving Structural Earthquake Resistance under the Ministry of Constructions (comprehensive) research and development project (1996-1998), the related Review Committee for Continuous Fiber Sheet Construction Methods (1996-1998) and the Review Committee for Seismic Retrofit of Housing and Urban Development Corp. And a seismic

reinforcement structure and construction method based on continuous fiber reinforced materials was examined and its research results reported.

At this stage, a committee to develop these and to prepare the Seismic Retrofit Design and Construction Guidelines for Existing Reinforced Concrete Construction and Steel Encased Reinforced Concrete Buildings Using Continuous Fiber Reinforced Materials was established. These guidelines were based on each previous committees report and the accumulated research results. The committee, which is composed of relevant members of the previous committees involved in research activities, decided to prepare the guidelines available in the current phase.

Chiefly, the guidelines, show a design method for seismic repair using continuous fiber reinforced materials wrapped around existing independent columns and attached to a concrete surface with impregnate adhesive resins. For other members, it summarizes basic techniques of design and construction for using continuous fibers as a seismic reinforcement which include relevant precautions. In addition, it incorporates related techniques and construction work cases so that the actual situation regarding this method can be understood.

Finally, we wish to express our deep gratitude to the above mentioned committees for allowing us to make use of their research results, to each member of the committee for creating these guidelines for their hard work in carrying out their duties under a tight schedule, and to the Japan Building Disaster Prevention Association for their great assistance in regard to the publication of this document.

Committee for Developing Seismic Retrofit Design and Construction Guidelines for Existing Reinforced Concrete Buildings and Steel Encased Reinforced Concrete Buildings Using Continuous Fiber Reinforced Materials

Chairman, Yasuhiro Matsuzaki

Committee for Developing Seismic Retrofit Design and Construction Guidelines for Existing Reinforced Concrete Buildings and

Steel Encased Reinforced Concrete Buildings Using Continuous Fiber Reinforced Materials

Chairman: Yasuhiro Matsuzaki Professor, Faculty of Architecture, Engineering Department, Science University of Tokyo

Manager: Hiroshi Fukuyama Senior Researcher, International Institute of Seismology and Earthquake Engineering, Building Research Institution, Ministry of Construction

Member: Hisayoshi Ishibashi Vice Director, Building Structure Group, Technical Research and Development Institute, Kumagai Gumi Co., Ltd. Shunsuke Otani Professor of Architecture, Engineering Research Department, Graduate School, University of Tokyo Hideo Katsumata Senior Researcher, Technical Research and Development Institute, Obayashi Corp. Soichi Kawamura Director of Seismic Promotion, Sales Promotion Headquarters, Taisei Corp. Shigeharu Kitamura Assistant Manager, Building Guidance Division, Housing Bureau, Ministry of Construction Kazuaki Shimada Former Assistant Manager, Building Guidance Division, Housing Bureau, Ministry of Construction Shunsuke Sugano Director of Basic Research Department, Technical Research and Development Institute, Takenaka Corp. Hideyuki Suzuki Senior Researcher, Technology Institute, Ando Corp. Toshio Takahashi Director of Technology, Altes Co., Ltd. (Senior Researcher, Technology Institute, Kashima Corp.)

Member: Masaharu Tanigaki Senior Researcher, Technical Research and Development Institute, Mutsui Construction Co., Ltd. Hideo Tsukagoshi Senior Researcher, Technical Research and Development Institute, Shimizu Corp. Masaomi Teshigawara Head of Structural Division, Structural Engineering Dept., Building Research Institute, Ministry of Construction Kenichi Nakamura Director, Test No. 2, Tsukuba Building Test Laboratory, Better Living Hiroyuki Nakamura Director, Building Research Office, Technical Research and Development Institute, Tokyu Construction Co., Ltd. Takashi Nireki Vice Head, Tsukuba Building Test Laboratory, Better Living Hisahiro Hiraishi Director, Codes and Evaluation Research Center, Building Research Institute, Ministry of Construction Shigeru Fujii Associate Professor of Environment Earth Engineering, Engineering Research Department, Graduate School, Kyoto University Tadashi Fujisaki Senior Researcher, Technical Research and Development Institute, Shimizu Corp. Kiyoshi Masuo Director, Structure Division, General Building Research Corporation of Japan Kenji Motohashi Director, Maintenance and Modernization Division, Building Materials and Components Dept., Building Research Institute, Ministry of Construction Susumu Imaizumi General Director, Japan Building Disaster Prevention Association

Secretariat: Yoshinori Takahashi

Director, General Affairs Division, Japan Building Disaster Prevention Association Naomi Kawashima Manager, Operating Section, General Affairs Division, Japan Building Disaster Prevention Association

Contents

Introduction Outline of Seismic Retrofit Method Using Continuous Fiber Reinforced Materials ............................................................................................................. 2

1. Method Features ............................................................................................................... 2 2. Construction Overview ..................................................................................................... 5

Chapter 1 General .................................................................................................................. 11 1.1 Scope and Terms ............................................................................................................. 11

1.1.1 Scope ..................................................................................................................... 11 1.1.2 Terms ..................................................................................................................... 12

1.2 Materials ......................................................................................................................... 14 1.3 Basic Policy for Strengthening Design ........................................................................... 16

1.3.1 Target Seismic Performance and Earthquake-resistance Index of Structures ....... 16 1.3.2 Properties of Continuous Fiber-reinforced Materials and Retrofit Plans .............. 21 1.3.3 Strengthening Design Procedures ......................................................................... 22 1.3.4 Construction of Retrofit Work ............................................................................... 24 1.3.5 Fireproofing Efficiency ......................................................................................... 24

Chapter 2 Characteristics of Continuous Fiber Reinforcements ........................................... 31 2.1 Characteristics of Continuous Fiber Reinforcements ..................................................... 31

2.1.1 Continuous Fiber Sheets and Continuous Fiber Reinforcements .......................... 31 2.1.2 Impregnate Adhesive Resin ................................................................................... 34 2.1.3 Primers ................................................................................................................... 37 2.1.4 Ground Mending Materials ................................................................................... 39 2.1.5 Cross Section Repair Materials ............................................................................. 41

2.2 How to Evaluate the Material Characteristics of Continuous Fiber Reinforcement ...... 43

Chapter 3 Design of Reinforcing Members and Parts ........................................................... 51 3.1 Strengthening of Independent Reinforced Concrete Columns ....................................... 51

3.1.1 Overview ............................................................................................................... 51 3.1.2 Strengthening Methods and Structural Details ...................................................... 51 3.1.3 Evaluation Methods for Strength and Toughness .................................................. 55

3.2 Strengthening of Reinforced Concrete Beams ................................................................ 83 3.2.1 Overview ............................................................................................................... 83 3.2.2 Strengthening methods and structural details ........................................................ 83 3.2.3 Evaluation methods for strength ............................................................................ 87

3.3 Strengthening of Steel-Encased Reinforced Concrete Columns ............... (Not translated) 3.4 Considerations ................................................................................................................ 92

3.4.1 Strengthening without Removing Finishing Mortar ............................................. 92 3.4.2 Adhesion of Ends of Continuous Fiber Reinforcements ..................................... 108 3.4.3 Strengthening of Columns with Wing Walls ....................................................... 116 3.4.4 Strengthening of Columns with Low Partitions .................................................. 123 3.4.5 Strengthening of Reinforced Concrete Walls ...................................................... 128

Chapter 4 Construction of Strengthening Work .................................................................. 141 4.1 Work specifications ....................................................................................................... 141

4.1.1 General ................................................................................................................ 141 4.1.2 Carbon fiber/epoxy resin work method ............................................................... 143

4.1.3 Carbon fiber/methacrylate resin work method .................................................... 145 4.1.4 Aramid fiber/epoxy resin work method .............................................................. 149

4.2 Construction procedure ................................................................................................. 150 4.2.1 General ................................................................................................................ 150 4.2.2 Construction plan ................................................................................................ 153 4.2.3 Construction procedure ....................................................................................... 155 4.2.4 Preparation ........................................................................................................... 156 4.2.5 Temporary work .................................................................................................. 159 4.2.6 Removing existing finish materials ..................................................................... 162 4.2.7 Ground treatment ................................................................................................. 165 4.2.8 Applying a primer ............................................................................................... 172 4.2.9 Ground mending .................................................................................................. 176 4.2.10 Marking ............................................................................................................... 180 4.2.11 Wrapping continuous fiber sheets ....................................................................... 182 4.1.12 Curing .................................................................................................................. 195 4.2.13 Finishing .............................................................................................................. 196

4.3 Safety, health and quality management during construction ........................................ 199 4.3.1 General rules ........................................................................................................ 199 4.3.2 Construction management system ....................................................................... 199 4.3.3 Safety and health management ............................................................................ 200 4.3.4 Quality management ............................................................................................ 203 4.3.5 Inspection ............................................................................................................ 207 [Appendix to Section 4.3] Quality management items ................................................ 218

Introduction Outline of Seismic Retrofit Method Using Continuous Fiber Reinforced Materials

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Introduction Outline of Seismic Retrofit Method Using Continuous Fiber Reinforced Materials

Continuous fiber reinforced materials have material characteristics different from those of the conventional steel and concrete construction materials. Therefore, their treatment requires special construction methods. In this section, characteristics and construction outlines of seismic retrofit methods using continuous fiber reinforced materials are introduced.

1. Method Characteristics

The seismic retrofit method for existing reinforced concrete and steel framed reinforced concrete construction buildings using continuous fiber reinforced materials is a technique that strengthens and repairs existing buildings by wrapping continuous fiber sheets (mainly contains materials like carbon fiber and aramid fiber) with impregnate adhesive resins such as epoxy resins on the surface of reinforced concrete or steel encased reinforced concrete members. Figure 1 illustrates the classification of fibers described in these guidelines. The carbon fibers shown in parenthesizes are excluded from these guidelines. Details of materials are shown in section 1.2.

PAN-family high strength type

Carbon fiber [PAN-family high stiffness type]*

Fibers [PITCH-family] *

Aramid fiber (Aromatic polyamide fiber)

Aramid 1: One kind of amine components belongs to a mono-polymer family

Aramid 2: Two kinds of amine components belong to a copolymer family.

* Items in [ ] are excluded from these guidelines.

Figure 1 Fiber Classification

The specific gravity of any fiber is lower than that of steels by approximately 1/4-1/5. Fibers have a high tensile strength of approximately 3000 MPa or more. For these reasons, expectations are high for the new technique using fibers to replace the conventional seismic retrofit methods based on steels and concrete. Also, other methods using relatively low cost glass fibers and polyacetal fibers in addition to the fibers shown in Figure 1, are being considered and developed for commercialization.

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Photo 1 Carbon Fiber Sheet

Photo 2 Aramid Fiber Sheet

Continuous fiber sheets used in seismic retrofitting are processed in a thin sheet shape. A carbon fiber of 0.2 mm or less in thickness and an aramid fiber of 0.3 mm or less are often used. A carbon fiber sheet is shown in Figure 1 and an aramid fiber sheet in Figure 2. These are worked into a sheet shape by aligning very thin continuous fibers of approximately 5-20 m in diameter in a given direction. Some of the continuous fibers worked into a sheet shape which have relatively narrow widths may be called continuous fiber tape. However, in this guidelines, they are collectively called a continuous fiber sheet. Each of these fibers can be shaped to suit a concrete surface and wrapped on it due to their high flexibility.

One-way preimpregnation type

One-way reinforced sheet One-way textile (including tape)

Shapes of continuous fiber sheet

One-way sheet

Two-way reinforced sheet Two-way textile

Figure 2 Shape Classification of Continuous Fiber Sheets

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The shape classification of continuous fiber sheets is shown in Figure 2. Continuous fiber sheets are classified into one-way or two-way types depending on their direction. Depending on the process used for maintaining them in a sheet shape, the fibers are classified based on preimpregnation type which wraps bundles of continuous fibers on a removable adhesive paper, the type of continuous fibers processed into a textile shape, and the type of continuous fibers formed into a sheet shape with auxiliary resins. For continuous fibers processed into a textile shape, two textile types exist. One is the two-way textile manufactured by weaving reinforced fibers placed in two directions and the other is a one-way textile manufactured by placing reinforced fibers in one direction and auxiliary and low cost fibers in another direction, as shown in Figure 3.

Auxiliary fiber(glass fibers etc.)

One-way textile Two-way textile

Continuousfiber

Continuousfiber

Continuousfiber

Figure 3 One-way Textile and Two-way Textile

One-way reinforced sheets are often employed for seismic repair. For instance, shear reinforcement can be ensured by wrapping these sheets to columns and beam members perpendicularly to the longitudinal, while bending strength can be reinforced by wrapping these sheets in their longitudinal direction. Also, since impregnate adhesive resins impregnated into continuous fiber sheets also serve as an adhesive between the sheets, it is possible to lap them in multiple layers. Therefore, two-way reinforcement is possible by lapping the sheets over each other at right angles, and high strengthening effectiveness can be attained by lapping them in the same direction.

Good workability: Lightweight and welding-free

Advantages of continuous fiber reinforcement-based method

Shortening of construction period: Preprocess-free and a few construction items

Increased design flexibility: Invariant section dimension and building weight

Improved durability: Prevention of concrete neutralization and steel corrosion

Figure 4 Advantages of Continuous Fiber Reinforcement-based Seismic Retrofit Method

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Figure 4 shows the advantages of the continuous fiber reinforcement-based seismic retrofit method over the conventional steel jacketing when the two methods are compared. Construction features of the former method include: construction by manpower only is possible since continuous fiber sheets are lighter than steel materials, easy construction can be achieved even in work environments not accessible to machines and heavy equipment. Also, special skills in welding and other operations are not required, fires are not required, and there is little generation of noise or dust. The steel jacketing method requires the obtaining of prior measurement of reinforcement members and processing steel plates, but continuous fiber sheets can be cut to the size and shape of the members on-site. Such good construction features allow shortening of the construction period using the former method. Since shortening of the construction period becomes a key cost factor particularly when seismic retrofit work causes suspension of building use, the advantages of the former method are apparent. Also, because the amount of increase in the buildings weight of building weight following construction is negligible, building serviceability is not disrupted and the increase in weight can be ignored from a design viewpoint. In addition, it does not have effect on the balance of member rigidity due to little variation of member stiffness in shear reinforcement. Little maintenance work such as periodic painting is required for durability since wrapping members prevents concrete neutralization and there is no risk of steel corrosion in continuous fiber reinforced materials.

Though continuous fiber reinforced materials are more expensive than steels on the basis of material cost, the continuous fiber-based method is often cheaper than the conventional steel jacketing in terms of total costs including construction conditions and construction period.

On the other hand, when continuous fiber sheets are closely wrapped around members, the corner edges of members must be rounded so as to reduce centralized stress on bending areas. Noise and dust are produced when chamfering these edges and correcting the unevenness of member surfaces, and offensive odors are generated during the application of primers and impregnate adhesive resins. For these reasons, a method that eliminates dust and odors during such construction is required while a building is in use.

Continuous fiber sheets are bonded to a concrete surface with impregnate resins. To ensure their strengthening effectiveness, the sheets must be close looped to the circumference of members or the sheet edges must be completely anchored.

In addition to seismic retrofit using continuous fiber reinforced materials processed into a sheet shape, these guidelines also propose some other continuous fiber-based reinforcement methods.

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Some methods considered in the past include machine looping columns with impregnate adhesive resins impregnated into strand fibers, on-site wrapping of L-shaped or U-shaped continuous fiber reinforced materials and filling the gaps between the concrete and the fibers with grouts or resins, and on-site assembly of precast concrete slabs whose insides are wrapped with continuous fiber sheets.

Apart from carbon fibers and aramid fibers, the use of glass fibers and polyacetal fibers is considered. The latter fibers are cheaper than the former, and their strengthening effectiveness evaluation methods and durability are being researched and developed. The methods and materials excluded from these guidelines are referred to in this documents appendix.

2. Construction Overview

The general procedures for continuous fiber reinforcement-based seismic retrofit are shown in Figure 5. The construction overview is as follows:

Surface treatment: If the surface has irregularities, when wrapping continuous fiber sheets, this will produce rising and waving. Surface smoothing is critical work since rising and waving substantially reduce strengthening effectiveness. Corner edges should be roundly chamfered. The chamfering diameter ranges from approximately 10 to 30 mm. It does not matter that the edge-chamfering diameter in aramid fibers is smaller than that in carbon fibers. Primers are applied to improve the adhesion of impregnate bond resins to the concrete surface.

Wrapping of continuous fiber sheets: Continuous fiber sheets and tapes can be easily cut with scissors or cutters. The cutting is done taking into consideration member dimensions, sheet allocation and the required wrapping length. The required amount of impregnate adhesive resins is applied for rough coating and finish coating respectively. It is important to impregnate continuous fiber sheets with impregnate bond resins and remove excessive foams. This process should be repeated when overlapping the sheets.

Curing: The hardening time of impregnate bond resins depends on atmospheric temperatures. Particularly in outdoor construction, it is necessary to cure the resins so that sand, dirt and dust can not bond to them. When using epoxy resins as impregnate adhesive resins, if the atmospheric temperature drops during hardening, there is a possibility of defective hardening of the bond resins. Therefore, it may be required to perform curing in line with the atmospheric temperature. Since epoxy resins are not generally suitable for construction work below 5C, methacylic (MMA) resins with excellent low-temperature hardening have recently become commercially practical. If the

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resins have become wet with water before hardening, low strength resins may be formed. For this reason, operation should be stopped during rainfall or fog in outdoor construction, and in indoor work prevention of dew condensation during curing is required.

Finishing: Finishing is done in consideration of surface appearance, protection and fire resistance. All work starts after hardening of the impregnate bond resins.

Surface treatment Smoothing of concrete surface by scouring and sanding Putty-based unevenness correction of concrete surface Roundly chamfer corner edges Application of primers

Bonding of continuous fiber sheets

Cutting of continuous fiber sheets Rough coating with impregnate bond resins Wrapping and impregnating of continuous fiber sheets Finish coating with impregnate bond resins Impregnating and removing foams

Curing Cure impregnate bond resins without the adherence of rain, sand or dust before hardening.

Cure epoxy impregnate bond resins while ensuring the atmospheric temperature does not fall below 5C.

Finishing Conduct finishing with mortars and paints after verifying that impregnate bond resins have dried.

Figure 5 General Procedures for Continuous Fiber Reinforcement-based Seismic Retrofit

Photo 3 Surface Treatment with a Sander Equipped with a Dust Collector

Photo 4 Chamfering of Corner Edges

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Photo 5 Application of Primers Photo 6 Putty-based Unevenness Correction

Photo 7 Cutting of Carbon Fibers Photo 8 Cutting of Aramid Fibers

Photo 9 Rough coating with impregnate bond resins

Photo 10 Sheet wrapping (carbon fiber sheet)

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Photo 11 Sheet wrapping (aramid fiber tape)

Photo 12 Finish coating with impregnate adhesive resins

Photo 13 Resin impregnating and removing foams

Photo 14 Spraying of silica sands for finish coating after the completion of wrapping

The seismic repair method features better workability than that of existing methods. However, their strengthening effectiveness depends largely on construction work conditions. Rising and loosing between a concrete surface and the continuous fiber reinforced materials substantially reduce its effectiveness. The fiber reinforcement-based method requires all the processes including surface treatment, wrapping of continuous fiber sheets, resin impregnating and curing, etc. to obtain the strengthening effects expected in the design.

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Chapter 1 GENERAL

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Chapter 1 General

1.1 Scope and Terms

1.1.1 Scope

These guidelines, that cover independent columns and beams of existing reinforced concrete buildings and existing steel-encased reinforced concrete buildings, apply to the seismic retrofit design and construction methods that use continuous fiber-reinforced materials, except for design and construction based on special studies. The items not contained in these guidelines are based on related standards and criterion such as the Guidelines for Seismic Retrofit of Existing Reinforced Concrete Buildings, the Guidelines for Seismic Retrofit of Steel-Encased Reinforced Concrete Buildings published by the Japan Building Disaster Prevention Association.

[Comments]

These guidelines apply to seismic retrofit design and construction methods for existing reinforced concrete buildings and existing steel-encased reinforced concrete buildings that use continuous fiber-reinforced materials. A seismic retrofit method that covers independent columns and rectangular beams is employed to improve their capacity or ductility by attaching continuous, fiber-reinforced materials to their surfaces.

These guidelines focus on construction methods and materials investigated to date by research results. When employing construction methods, materials, and details not contained in these guidelines, strengthening effectiveness must be confirmed based on laboratory data and new experiments. However, the items not contained in these guidelines, should be in accordance with related standards, criteria, and guidelines such as the Guidelines for Seismic Retrofit of Existing Reinforced Concrete Buildings, the Guidelines for Seismic Retrofit of Steel-frame Reinforced Concrete Buildings, and the criteria and standard specifications related to various kinds of structural calculations and construction presented by the Architectural Institute of Japan (AIJ), as well as the guidelines cited.

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1.1.2 Terminology

The terminology used in these guidelines, unless specified otherwise, conform to the Standards for Evaluation of Seismic Capacity, Guidelines for Seismic Retrofit of Existing Reinforced Concrete Buildings, the Standards for Evaluation of Seismic Capacity, Guidelines for Seismic Retrofit of Steel-encased Reinforced Concrete Buildings published by Japan Building Disaster Prevention Association, and the criterion and standard specifications related to various kinds of structural calculations and construction presented by the Architectural Institute of Japan (AIJ).

[Comments]

Terms and their definition generally used in these guidelines are listed as follows:

Continuous fiber: Generic name for very thin, continuous fibers with a diameter of approximately 5-20 m. The continuous fibers are extremely strong with a high level of corrosion resistance, are lightweight and non-magnetic. The fibers are employed for seismic retrofit.

Continuous Fiber Sheet: These sheets use auxiliary materials to maintain their sheet shape. Those sheets that can be continuously closely wrapped around columns and beams due to a relatively small width is called continuous fiber tape.

Continuous Fiber Reinforcement: (FRP) (CFRP) (AFRP)

Those types of reinforcement formed by impregnating continuous fiber sheets with adhesive resins and letting them harden is called FRP. Some types of reinforcement use carbon fiber and are called CFRP and other reinforcements use aramid fiber and are called AFRP.

Carbon Fiber: (CF)

Carbon fibers, imperfect graphitic microcrystal aggregates, are classified into a PAN-family and PITCH-family depending on raw materials and manufacturing methods. PAN-family fibers are formed by heating and carbonizing polyacrylonitrile fibers, and PITCH-family fibers are formed by burning oil or coal pitches. The PAN-family has a diameter of approximately 5-8 m and the PITCHfamily has a diameter of approximately 9-18 m. The two types physical properties vary according to crystal orientations. The PAN-family includes extremely strong and highly stiffness products. It is very easy to manufacture highly stiffness products. These fibers are called

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Carbon Fiber or CF.

Aramid Fiber: (AF) (Aramid 1) (Aramid 2)

These fibers are synthetic fibers consisting of PAN-aromatic polyamide fibers that have the same amide links -CONH- as nylon. An aramid fiber has a mono-polymer family consisting of one kind of amine component and a copolymer family consisting of two kinds of amine components. These guidelines label the former fiber Aramid 1 and the latter fiber Aramid 2. Both of these kinds of fibers have a diameter of approximately 12 m and offer substantially greater tensile strength, stiffness, and thermal resistance when compared to other organic or synthetic fibers. They are called AF.

Impregnate Adhesive Resin:

These resins are used to impregnate continuous fiber sheets and tapes for incorporation into these fibers and bonding to a concrete surface. These resins are also used as an adhesive between reinforcements to lap continuous fiber sheets.

Amount of Continuous Fiber Reinforcement:

The mass of continuous fibers alone per unit area of continuous fiber-reinforced materials

Designed Thickness of Continuous Fiber Reinforcement:

The designed thickness represents a value calculated by dividing the density of continuous fibers into the amount of continuous fiber-reinforced materials.

Cross Section Area of Continuous Fiber Reinforcement:

The cross section area represents a value calculated by multiplying the designed thickness of continuous fiber-reinforced materials by the width of continuous fiber-reinforced materials taken at right angles to the continuous fiber orientation.

Standardized Tensile Strength of Continuous Fiber-reinforced Materials:

The tensile strength represents a value produced by reducing the maximum tensile stress of continuous fiber-reinforced materials in light of a given safety factor. It is called the Guaranteed Tensile Strength.

Designed Tensile Strength of Continuous Fiber-reinforced Materials:

The tensile strength of continuous fiber-reinforced materials used for design. It is determined by multiplying the standardized tensile strength of continuous fiber-reinforced materials by an effective coefficient.

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1.2 Materials

Continuous fibers, produced by forming carbon or aramid fibers in sheet or tape shapes, can be used for seismic retrofit. Epoxy-family or methacrylic (MMA)-family impregnated-adhesive resins should be employed.

[Comments]

These guidelines cover carbon and aramid fibers demonstrated to date by research results and are tried and true to some extent, although there are some kinds of continuous fibers that can be used for seismic retrofit.

An example of the stress-strain relationship for continuous fiber-reinforced materials and reinforcing bars is shown in Figure 1.2-1. The tensile strength of continuous fiber-reinforced materials is about ten times the yield strength and tensile strength of normal-strength steels, and fiber materials behave elastically until rupture by tension. However, when members strengthened by continuous fiber-reinforced materials reach ultimate capacity, the stress of the material does not always reach its tensile strength limit. To evaluate the structural performance of members for seismic retrofit, the fracture pattern and strengthening effectiveness of continuous fiber-reinforced materials must be thoroughly studied.

There are two types of carbon fibers: one has the almost the same Youngs modulus as steel, and the other is highly stiffness and its Youngs modulus is about twice that of steel. Since the strain at rupture of highly stiffness is lower than that of other continuous fibers, care must be taken to use the fibers as shear-reinforcement. The guidelines cover PAN-family and high-strength carbon fibers.

Normal Reinforcing Bar(SD295A)

Stre

ss (M

pa)

Carbon Fiber(stiffness type)

Carbon Fiber(high-strength type)

Strain (%)

Aramid 1Aramid 2

PC Tendon(C class)

Figure 1.2-1 Stress-Strain Relationship for Continuous Fiber-reinforced Materials and Reinforcing Bars

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Youngs modulus of Aramid fibers is about 1/2-1/3 that of steel and their strain at tensile strength is higher than that of carbon fibers.

The resins for impregnated bonding must be compatible with the temperature during construction work. Epoxy resins, which are often used as impregnated-adhesive resins, have hardening problems at low temperatures, i.e., below 5C. Therefore, using methacrylic (MMA)-family resins with excellent hardening at low temperatures is suggested for construction work in such environments. Recently, a technique to improve the hardening of impregnated-adhesive resins has been developed by pre-impregnating (prepreg type) continuous fiber sheets with the resins, wrapping them over a body, and heating them electrically.1)

Impregnated-bond resins generally are less fireproof. The post-hardening resins soften with heat and continuous fiber-reinforced materials tensile strength lowers. So, when fireproofing is desired for earthquake-proofing methods using continuous fiber-reinforced materials, proper fireproof coverage is required.

For reference, when using carbon and aramid fibers in seismic retrofit, research results indicate that the strengthening effectiveness of a combination of continuous fibers and impregnated-adhesive resins is limited. Construction methods from the guidelines are based on this combination, so this fact should be understood. When using continuous fibers and impregnated-bond resins by changing their combination, their strengthening effectiveness must be confirmed with testing, and future accumulation of research data is suggested.

1) Tomoaki Sugiyama, Yasuhiro Matsuzaki, Katsuhiko Nakano, and Hiroshi Fukuyama: Experimental Research on the Performance of RC Non-structural Walls Strengthened with Carbon Fiber Sheets, Report on Annual Papers in Concrete Engineering, Vo1.21, No.3, pp.1423-1428, 1999.7

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1.3 Basic Policy for Strengthening Design

1.3.1 Target Seismic Performance and Earthquake-resistance Index of Structures

When developing retrofitting plans, targeted seismic performance should be clearly defined.

[Comments]

(1) Seismic performance

When designing reinforcement for seismic, the value of RIS, the seismic resistance index for structures, a strengthening design target, should be set based on the Standards for Evaluation of Seismic Capacity and Comments for Existing Reinforced Concrete Buildings1) (hereafter referred to as RC Diagnostics Standards) or the Standards for Evaluation of Seismic Capacity and Comments for Steel-encased Reinforced Concrete Buildings2) (hereafter referred to as SRC Diagnostics Standards), or the Law for Promoting the Seismic Retrofit of Buildings (Law No. 123, 1995)3) (hereafter referred to as Seismic-retrofit Promotion Law). After the completion of strengthening design, earthquake-resistance diagnostics should be performed again and the attainment of target values should be confirmed.

RC Earthquake-resistance Diagnostics and SRC Earthquake-resistance Diagnostics standards express the earthquake-resistance performance of buildings as a structural earthquake resistance index IS and also set a target value for the product of a cumulative strength index and a shape index, CT SD, as well as a target structural earthquake- resistance index RIS. Also conforming to these concepts for earthquake resistance using continuous fiber reinforcement methods, properly applying these guidelines to repair methods means that the coefficient () associated with evaluation of strengthening effectiveness and construction reliability (Seismic Retrofit Design and Construction Guidelines for Existing Reinforced Concrete Buildings4) (hereafter referred to as RC Retrofit Design Guidelines) or Seismic Retrofit Design and Construction Guidelines for Existing Steel-encased Reinforced Concrete Buildings5) (hereafter referred as to SRC Retrofit Design Guidelines) may be 1.0. Namely, it is possible to set targets like the expressions in (1.3.1) and (1.3.2). For reference, expression (1.3.2) can be applied to the second and third diagnostics methods. This target value may be considered set in a similar way with the concurrent use of the reinforcement method with evaluation approaches in the RC Retrofit Design Guidelines and SRC Retrofit Design Guidelines and the continuous fiber reinforcement method.

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RIS ISO (1.3.1)

0.3 (RC buildings) CT SD 0.28 Z G U (SRC buildings consisting of partial steel members) 0.25 Z G U (SRC buildings consisting of full steel members)

(1.3.2)

Where RIS: Target value for the structural earthquake resistance index of

post-reinforcement buildings ISO: Structural earthquake-proofing determination index in earthquake-resistance

diagnostics (=EsZGU) Es: Basic earthquake-resistance performance index (0.8 for the first diagnostics

method and 0.6 for the second and third diagnostics methods) Z: Regional index, revision coefficient on the basis of regional seismic activity

levels and possible seismic strength G: Coefficient of the subgrade reaction, revision coefficient on the basis of

amplification properties, and topographic effectiveness of subsurface grounds and interaction between grounds and buildings

U: Importance coefficient, revision coefficient on the basis of function of buildings, etc.

CT: Cumulative capacity index for post-reinforcement buildings SD: Shape index for post-reinforcement buildings

In addition, the Earthquake-resistance Diagnostics and Earthquake-resistance Guidelines for Specific Buildings (Notification No. 2089 of the Ministry of Construction, on December 25, 1995), based on the provisions of the Earthquake-resistance Promotion Law, Article 3, express earthquake-resistance performance as an index q associated with a structural earthquake-resistance index RIS for an ultimate lateral strength of each story, providing expressions (1.3.3) and (1.3.4). When the requirements of these two expressions are met, the safety during an earthquake in key areas of earthquake proofing is evaluated as a slight possibility that buildings will collapse or fall due to seismic shakes and shocks. This is considered to be the same level of earthquake-resistance performance required by current seismic provisions as a minimum requirement.

RIS 0.6 (1.3.3) q 1.0 (1.3.4)

Where

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q: Index associated with the ultimate lateral strength of each floor = Qu / (Fes W Z Rt Ai St) Qu: Ultimate lateral strength of each floor Fes: Fes value (coefficient representing shape characteristics of each floor

determined with stiffness and eccentricity) defined by Article 82-4, No. 2, the Enforcement Ordinance, Building Standards Act

W: Sum of the fixed load and live load (plus the snow accumulation load in areas with heavy snow) in areas supported by appropriate floors when calculating the seismic force according to the provisions of Section 1, Article 88, the Enforcement Ordinance, Building Standards Act

Z: Z value (seismic zone coefficient) defined by the provisions of Section 1, Article 88, the Enforcement Ordinance, Building Standard Act

Rt: Rt value (coefficient of vibration characteristics due to soil condition) defined by the provisions of Section 1, Article 88, the Enforcement Ordinance, Building Standard Act

Ai: Ai value (distributed coefficient of the story shear force during an earthquake) defined by the provisions of Section 1, Article 88, Enforcement Ordinance, Building Standard Act

St: The value is defined according to structural types for buildings and is 0.25 for steel-building and steel-encased reinforced concrete building and 0.3 for other structural methods.

Earthquake-resistance performance was originally associated with overall basic structural performance: safety, reparability and serviceability of structural frames, building members, facilities and equipment, furnitures and ground in response to an earthquakes seismic tremors, but here only the safety of structural frames is covered in a limited sense. Frame safety can be assured by preventing frames from falling, collapsing, and disintegrating due to an earthquakes seismic tremors. To express the frame safety as a value, as mentioned above, a structural earthquake-resistance index for earthquake-resistance diagnostics, the product of a cumulative capacity index, and a shape index or an ultimate lateral strength-related index are used. The structural earthquake-resistance index represents the magnitude or strength of an earthquakes seismic tremors when the buildings structural frame reaction during an earthquake reaches safety limits (with situations that resulting in falls or collapse). The target value of earthquake-resistance performance is shown in equations (3.1.1) to (3.1.4). Refer to recommended values required by the RC Earthquake-resistance Diagnostics and SRC Earthquake-resistance Diagnostics standards or the target value defined by Earthquake-resistance Diagnostics and Earthquake-resistance Guidelines for Specific Buildings. Given cost efficiency, availability, and the features of earthquake-resistance

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methods using continuous fiber-reinforced materials, the target value must be set.

This construction method conforms to earthquake-resistance polices to ensure the earthquake-resistance performance necessary for buildings by preventing shear failure of existing members, increasing their ductility and improving the ductility of structural frames. Therefore, a construction method is recommended using ductility with resistance-based reinforcement or strength and ductility with resistance-based reinforcement, with the main aim of increasing the ductility index and performance of the bending yield priority of post-reinforced buildings. On the other hand, the method can be applied to strength and ductility resistance-based reinforcement that has the main aim of attaining higher member strength by increasing shear strength. In this case, the stiffness, balance with other members, and fracture patterns of overall buildings should be properly considered. In any case, it is important to make the owners understand that repairs and other work for earthquake-damaged members are required. For reference, this construction method can improve earthquake proofing without increasing the weight of the buildings and without increasing member stiffness due to small, growing sections of post-executed members.

To ensure the targeted earthquake-resistance performance of buildings, the concurrent use of this method and other repairing methods should be considered in depth. For this deliberation, it is important to select the most suitable construction method, given the seismic element balance in the same layer and balance in strength, ductility, and stiffness between each story and in accordance with basic earthquake-resistance polices as to the extent of strength and ductility that should be provided for reinforced buildings.

(2) Structural Earthquake-resistance Index (Is)

The RC and SRC Earthquake-resistance Diagnostics standards express earthquake-resistance performance of buildings as a structural earthquake-resistance index Is.

The structural earthquake-resistance index Is is determined from the product of three sub-indices, an ultimate performance basic index EO, a shape index SD and an aging index T (Is = EO SD T). The index EO is used to evaluate the buildings own earthquake-resistance performance based on the ultimate strength and fracture patterns/ductility of buildings. Ultimate strength is expressed with the C index (the ultimate lateral shearing force coefficient), and fracture patterns and ductility are represented by the F index (EO = C F). A shape index SD is a coefficient for correcting the imbalance of yield strength and stiffness and an aging index T for considering the effects of cracks, deformation, and aging on structural yield strength.

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(a) Improvement of the Ductility Index Value (Increasing the F index) When it is difficult to add seismic elements including increases in member sections and shear walls when planning, measures should be taken to meet the target value for earthquake resistance by raising the F index. When the shear strength is lower than the bending strength in members, improvement of the ductility can be accomplished by the increasing shear strength with continuous fiber reinforcement methods and transferring it to a bending yield pattern. The same effect as seen in increasing shear reinforcement can be obtained. In addition, as observed when increasing shear reinforcement, it is expected to increased ductilities by the concrete lateral confining effect will lead to growing compressive toughness of concrete, upgrading bond properties of reinforcing bars and concrete, and minimizing bond splitting failures. The F index is evaluated on the basis of the ratio of the shear strength to bending strength (the ratio of shear capacity to flexural capacity), the amount of shear reinforcement, an axial force ratio, and a shear span ratio. However, sufficient data has not been accumulated to evaluate the effects of these forces, and these effects are not presented in a positive manner.

(b) Improvement of the Capacity Index Value (Increasing the C index) This construction method is used mainly to increase the shear strength of members. The member strength is determined on the basis of shear failure, and can be expected to develop a bending strength that is greater than shear strength and an increase in ductility after reaching its bending strength. In this case, the earthquake-resistance reinforcement will be a strength and ductility resistance pattern that can improve both the C and F values. The method could be applied to reinforcement to increase the bending strength. But particular attention should be paid to problems due to the fact that continuous fiber-reinforced materials are elastic materials that are subject to brittle fracture. Problems are that the maximum strength is determined on the basis of rupture or anchoring fractures, that stress re-allocation as in reinforcing bars cannot be expected, and that the edges of continuous fiber-reinforced materials must be securely anchored. Also, to develop an assumed bending strength, shear reinforcement needs to be consistent with the same strength.

(c) Improvement of the Shape Index Value (Increasing the SD Index) A continuous fiber reinforcement method makes earthquake resistance possible without increasing the section area and weight, but receiving the effects of controlling the stiffness of members with this construction method would be difficult. The balance of the average strength can be corrected by reinforcing lateral members with low and rising strength. This effect is not positively reflected in the SD index but provides a useful measure to correct odd-shaped buildings.

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(d) Improvement of the Aging Index Value (Increasing the T Index) The aging index T evaluates the effects of cracks, deformation, and aging on structural capacity. In applying this construction method to strengthening construction, cracks, deformation, and aging of members should be basically repaired. Members covered with continuous fiber-reinforced materials after earthquake resistance could retard the results of cracks, deformation, and aging.

(e) Diagnostics Order and Repair Policies The first diagnostics method may be employed for evaluating strength resistance-pattern reinforcement as an earthquake-resistance policy. The second and third diagnostics methods are required for ductility resistance-pattern reinforcement. When beam-retrofit is implemented, the third diagnostics method must be used. The diagnostics order will be more than the second diagnostics when employing a continuous fiber reinforcement method that often provides a ductility resistance-pattern repair policy.

(3) Earthquake-resistance Index for Non-structural Members (IN)

The earthquake-resistance index for non-structural members IN, a structural method index B, and an effect index H are important coefficients. The index for B is measured from performance following deformation and service performance, and the H represents the effects of fractures. This construction method can be often expected to improve deformation performance for structural members and to compensate for deformation to follow in non-structural members due to great interlayer deformation during a major earthquake. According to a review 6) of that concept, non-structural members are reinforced with a continuous fiber reinforcement method; performance following deformation in non-structural members has been shown to be substantially better. The earthquake-proofing index IN is a coefficient to diagnose the safety of human lives given that peeling and falling of non-structural members, and especially exterior walls, during an earthquake directly injure people and prevent their escape. Therefore, this construction method could be effective in improving the index.

1.3.2 Properties of Continuous Fiber-reinforced Materials and Retrofit Plans

Properties of continuous fiber-reinforced materials should be thoroughly considered in the strengthening plan.

[Comments]

The earthquake-resistance method using continuous fiber-reinforced materials has different properties with existing repair methods, as discussed here. Therefore, paying attention to

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these distinctive features, the areas where the materials are used should be selected and strengthening and construction planning should be developed.

(a) Continuous fiber-reinforced materials can attain great levels of strength with fiber orientation but are brittle at right angles to the fiber orientation.

(b) Continuous fiber-reinforced materials cause brittle fractures without yield phenomena after exhibiting elastic behavior.

(c) Continuous fiber-reinforced materials can attain strength after the fibers have been securely impregnating with resins.

(d) The corner areas of continuous fiber-reinforced materials may be subject to stress reduction due to intensive stress.

(e) The adherence of continuous fiber-reinforced materials to a concrete surface and lapping of the materials depend on resin-based bonding capabilities.

(f) Impregnated-bond resins, with their positive effect on construction performance and fireproofing, should be employed.

1.3.3 Strengthening Design Procedures

(1) Feasibility Studies When conducting strengthening design and construction planning, field studies should be conducted thoroughly and meetings with building owners should be held to confirm various conditions related to retrofit work.

(2) Strengthening Design Procedures Strengthening design procedures, basic design, detailed design, and strengthening effectiveness evaluation should be followed in proper order, and the procedures be repeated when earthquake-resistance performance cannot reach a target value.

[Comments]

(1) Feasibility Studies

Earthquake resistance using continuous fiber-reinforced materials is the most effective for members that can be close looped as in independent columns. However, actual columns often have appurtenant structures such as shear walls and non-structural walls, sashes and equipment, and it is generally difficult to wrap continuous fiber-reinforced materials closely around these members. Also, some surface of members to be reinforced may be in various finishings and uneven or sloping. Therefore, when cracks occur on earthquake-damaged concrete, cracks must be filled with resin and other fillers and repaired in advance. The members and their surrounding shapes, subject to repair,

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should be studied beforehand.

The continuous fiber reinforcement method is suitable for use with in-service buildings in comparison to existing steel-plate lining methods. Since dust, noise and offensive smells are given out during construction work, the in-service conditions of buildings during construction should be thoroughly studied and meetings with the owners should be held.

(2) Strengthening Design Procedures

Strengthening design procedures, (a) reinforcement plan, (b) basic design, (c) detailed design, and (d) strengthening effectiveness evaluation, should be conducted in proper order and procedures (a)-(d) should be repeated when post-reinforced earthquake-resistance performance cannot reach a target value. Review items at each phase are provided as follows:

(a) Reinforcement Plan A reinforcement target should be set and a basic policy about the extent of the strength and ductility provided to retrofitted buildings should be defined. In addition to the set target and policy, given the characteristics and important points for materials and construction work contained in Chapters 2 and 4, the construction method best suited to the target should be selected.

(b) Basic Design The required quantity of reinforcement (the section area of reinforcing members and their quantities) should be estimated and the layout of reinforcing members should be planned. The evaluation expressions of strength (the shear strength and bending strength) and ductility (ductility factor) are provided in Chapter 3. It is important to use these expressions after understanding the member strength and scope.

(c) Detailed Design Details including the arrangement of layout-planned reinforcing members and methods to bond new members to existing members should be designed in accordance with Chapter 3 of these guidelines and the RC or SRC Retrofit Design Guidelines. For reference, important points in strengthening design are presented in Section 3.4.

(d) Strengthening Effectiveness Evaluation Earthquake-resistance performance of earthquake-resistant buildings should be evaluated in accordance with the RC or SRC Retrofit Design Guidelines, and post-retrofit earthquake-resistance performance should meet the target value. It is recommended that diagnostics results for buildings prior to repair be used as much as possible. Based on these results, the mechanical properties of earthquake-resistant buildings should be considered and the validation of the reinforcement plan should

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be verified.

1.3.4 Construction of Retrofit Work

The construction of retrofit work should conform to the provisions in Chapter 4.

[Comments]

The construction of an earthquake-resistance method using continuous fiber-reinforced materials should be done in accordance with construction method specifications, construction instructions, safety and sanitation control, and quality control specified in Chapter 4. The concurrent use of this method and other construction methods should be referred to in RC and SRC Retrofit Design Guidelines.

1.3.5 Fireproofing Efficiency

(1) Basic Concepts Adequate measures should be taken as necessary so that members, earthquake-proof with continuous fiber-reinforced materials, meet fireproofing requirements.

(2) Ensuring Fireproofing (a) Control of an Increase in Combustible Materials In an earthquake-resistance method using continuous fiber-reinforced materials, the

excessive increase in combustible materials within buildings should be controlled. If an increase in combustible materials is not negligible, adequate fireproofing measures must be taken.

(b) Incombustibility of Interior Materials When members, earthquake-resistance with continuous fiber-reinforced materials in

accordance with the Building Standards Act, are subject to interior limitations, the surface areas in the interior should be finished with noncombustible, semi-noncombustible and other appropriate materials.

(c) Ensuring Structural Fireproofing When earthquake-resistance work causes section deficits in fireproof structural

members due to chamfering and slitting or reinforced materials on the surface of members may promote the spread of a fire, adequate measures should be taken to prevent these factors from reducing fireproofing.

(d) Fireproof Covering for Continuous Fiber-reinforced Materials When continuous fiber-reinforced materials used in earthquake resistance are subject

to fires and then intended for reuse, adequate fireproofing covers should be placed on their surfaces.

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(3) Repair and Reinforcement for Fire-damaged Materials When members strengthened with continuous fiber-reinforced materials are subject to fires, adequate repair and reinforcement should be performed according to the level of damage.

[Comments]

(1) Basic Concepts

Fireproof structures basically consist of noncombustible materials and originally did not promote the occurrence and spread of a fire. Fireproof columns continuously support vertical loads even if they are subject to a fires heat and have the capability to support loads necessary to prevent a building from falling. In addition, section members including fireproof walls and floors possess thermal shielding and flame shielding that prevent a fires heat, flames, and high-temperature gas from penetrating these structures. Functions for thermal shielding and flame shielding are needed to stop the spread of a fire. The incombustibility, capability to support loads, and thermal shielding/flame shielding (i.e., fireproofing as mentioned before), are original fireproofing capabilities. Fire safety for buildings with main structures such as columns, beams, floors, and walls that are fireproof is based on the fireproofing efficiency mentioned. Therefore, when applying the continuous fiber-reinforced materials-based construction method to fireproof members, measures contained in (2) should be taken as needed and the fireproofing efficiency of members should be ensured. According to Article 5 and the Enforcement Ordinance of the Earthquake-resistance Promotion Law (Decree No. 28 of the Ministry of Construction, 1995), the provisions of the Building Standards Act for fireproof buildings should not be applied to buildings equipped with fire alarm systems to promote earthquake resistance. The systems must effectively detect the occurrence of fire and notify a building superintendent.

(2) Ensuring Fireproofing efficiency

(a) Control of an Increase in Combustible Materials Combustible resins used for continuous fiber-reinforced materials, which might burn in a fire, generally have no fireproofing problems since the amount of these materials used in earthquake resistance is much less than that of stored combustible materials. However, if many members are subject to earthquake resistance and the usage (the numbers of looped layers, etc.) of reinforced materials for members is greater in the same floor and section, combustible materials will increase. Therefore, an efficient construction plan, with a greater effect of earthquake resistance and decreased usage of reinforced materials, is desired. When fireproof buildings based on limited usage

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of combustible materials are earthquake-resisted after considering the effects of an increase in combustible materials on a fires characteristics, re-design may be required depending on the results.

(b) Incombustibility of Interior Materials Limitations for interior finishing for earthquake-resistance members should be compulsory in accordance with the Building Standards Act. The members used in interior surface areas must be fireproof materials such as noncombustible and semi-noncombustible ones according to the use, size, and structure of the building. Reinforced materials placed on the surface of members, containing a slight amount of resin, have little risk of catching fire even when exposed at the surface of the interior, but covering them with noncombustible materials is suggested even without the application of limitations for interior finishing. There are some methods to install interior materials, bonding them with adhesives, placing them on the base of lightweight steel frames and painting them with mortar after lathing. Work must be done to prevent the reinforced materials from being damaged.

(c) Ensuring Structural Fireproofing The Building Standards Act specifies that the thickness of cover concrete for reinforcing bars of reinforced concrete bearing walls, columns, and beams will be more than 3 cm. Fireproof, reinforced concrete members should also meet the requirements for the thickness of cover concrete. In addition, the minimum thickness of walls and the minimum minor diameter of columns and beams are defined to ensure fireproofing efficiency. On the other hand, earthquake resistance using continuous fiber-reinforced materials requires surface preparations including the removal of concrete member finishes, cutting of a body concrete surface, and chamfering of corner areas. With this preparation, for example, as shown in Figure 1.3-1, the cited cover thickness and size of the member section must be preserved. If required, the members must be repaired with the application of mortar so that they can meet the requirement for a given section size.

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Longitudinal Reinforcement

Chamfering

Shear Reinforcement

Figure 1.3-1 Preserving Cover Thickness

ColumnWall

Reinforced Material

Noncombustible

Wall

Mortar Backfill

Figure 1.3-2 Ensuring Fireproofing Efficiency in Fireproof Sections

With reinforcing for completely mounted columns that form fireproof sections, due to cutting slits in lapped areas of walls and columns and wrapping of reinforced materials around columns, a fire might spread to the side of the room that is not exposed through these slits or by the material burning. Therefore, to prevent a fire from spreading, as shown in Figure 1.3-2, the slits must be completely backfilled with mortar and concrete and then the surface of reinforced materials must be covered with noncombustible materials including mortar.

(d) Fireproof Cover for Continuous Fiber-reinforced Materials Notification No. 1675 of the Ministry of Construction, 1964, specified that RC and SRC construction members meeting given requirements have a fireproof structure. Continuous fiber-reinforced materials used for shear reinforcement have no difficulties in structural strength for long-term loading even if heat from a fire causes a deterioration in performance or they burn, since they do not contribute to the support of continuing loads. Therefore, it is not generally necessary to place

- 28 -

fireproof covers on the surface. However, when the re-use of materials damaged by fire is intended, fireproof covers will be placed on their surface to keep the temperature of the reinforced materials in a fire below a temperature where their performance might deteriorate. For example, reinforced materials using carbon fibers as fiber and epoxy resins as impregnated-bond resins are considered to lose tensile strength in heating hysteresis at approximately 260C. So, if the temperature of the reinforced materials in a fire is kept below 260C, re-use will be possible. These fireproof covers must be designed to ensure fireproofing efficiency while meeting the size requirements of possible fires (fire duration, fire temperature, etc.). In fact, adequate reinforced materials can receive fireproof covers in terms of 30 minutes to 3 hours for fireproofing performance in steel-encased fireproofing as specified by the Minister of Construction. Any work to install fireproof covers, as defined in (b), should be done to prevent the reinforced materials from be damaged. Specified fireproof covers in steel-encased fireproofing are designed for steel-encased members. For example, fireproof covers in 1-hour fireproofing do not always posses the same 1-hour fire resistance efficiency for continuous fiber-reinforced materials. According to a fireproofing test required to obtain the designation as fireproof, the steel temperature limit of steel-encased members averages about 350C for columns and beams. But, continuous fiber-reinforced materials generally suffer degradation even in heating hysteresis at lower temperatures. For reference, when earthquake proof members are exposed to fires, even if they are fireproof due to a coating, fireproof covers must be removed and the deterioration of continuous fiber-reinforced materials must be studied, except when fire damage is sensitive (the cover surface is contaminated with smoke).

(3) Repair and Reinforcement for Fire-damaged Materials

When members stiffened with continuous fiber-reinforced materials are subject to fires, fire damage such as rising, peeling, burning, cracking of the body concrete and cracks should be visually checked. If required, a tensile test for continuous fiber-reinforced materials should be conducted. If continuous fiber-reinforced materials suffer deterioration, degraded areas should be removed and earthquake resistance should be done again. When the fire damage also affects body concrete, repairs and reinforcing of members per se is required, and work such as the removal of concrete, additional placement of reinforcing bars, and additional casting of concrete will be done. In this case, in place of repeating the same earthquake-resistance method, it would be more efficient to plan the incorporation of repairs and reinforcement in earthquake resistance.

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1) Japan Building Disaster Prevention Association: Revised Edition, Standards for Evaluation of Seismic Capacity and Comments for Existing Reinforced Concrete Buildings, 1990.12

2) Japan Building Disaster Prevention Association: Standards for Evaluation of Seismic Capacity and Comments for Existing Steel-encased Reinforced Concrete Buildings, 1997.12

3) Japan Building Disaster Prevention Association, Japan Building Center : Regulation and its Comments on the Law Promoting the Earthquake-proofing of Buildings, 1996.1

4) Japan Building Disaster Prevention Association: Revised Edition, Standards for Evaluation of Seismic Capacity and Comments for Existing Reinforced Concrete Buildings, 1990.12

5) Japan Building Disaster Prevention Association : Standards for Evaluation of Seismic Capacity and Comments for Existing Steel-encased Reinforced Concrete Buildings, 1997.12

6) Tomoaki Sugiyama, Yasuhiro Matsuzaki, Katsuhiko Nakano, and Hiroshi Fukuyama: Experimental Research on the Performance of RC Non-structural Walls Strengthened with Carbon Fiber Sheets, Report on Annual Papers in Concrete Engineering, Vo1.21, No.3, pp.1423-1428, 1999.7

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Chapter 2 Characteristics of Continuous Fiber Reinforcements

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Chapter 2 Characteristics of Continuous Fiber Reinforcements

2.1 Characteristics of Continuous Fiber Reinforcements

2.1.1 Continuous Fiber Sheets and Continuous Fiber Reinforcements

Continuous fiber sheets are made using four different continuous fibers as shown in Table 2.1-1. The continuous fiber reinforcements are made by hardening them with impregnate adhesive resin. The specified values, shown in Table 2.1-2, must be used for the strengthening design and construction described in this guideline.

Table 2.1-1 Specifications of Continuous Fiber Sheets

Carbon fiber Aramid fiber 3400 MPa class 2900 MPa class Aramid 1 Aramid 2

Type of fiber PAN-class high-strength type Homopolymer Copolymer Sheet shape Unidirectional reinforcement type Unidirectional reinforcement type Weight per unit length 300 g/m

2 or smaller 623 g/m2 or

smaller 525 g/m2 or

smaller

Table 2.1-2 Specifications of Continuous Fiber Reinforcements

Carbon fiber Aramid fiber 3400 MPa class 2900 Mpa class Aramid 1 Aramid 2

Tensile strength 3400 MPa (35,000 kgf/cm2) 2900 MPa

(30,000 kgf/cm2)2060 MPa

(21,000 kgf/cm2) 2350 MPa

(24,000 kgf/cm2) Youngs modulus

230 GPa (2.34 106 kgf/cm2)

118 GPa (1.20 106 kgf/cm2)

78 GPa (0.80 106 kgf/cm2)

If materials other than the continuous fiber sheets shown in Table 2.1-1 are used, the characteristics of such materials must be examined thoroughly based on Section 2.2, Evaluating the characteristics of continuous fiber reinforcements and strengthening design and construction must be done using design and construction methods verified by experiments.

Comments:

(1) Specifications of continuous fiber sheets

Chapter 3 and subsequent chapters describe continuous fiber sheets and reinforcements that meet the specifications shown in Tables 2.1-1 and 2.1-2. They already have a good track record, and the impregnating ability of resin, workability, adhesion performance, material characteristics, strengthening performance, and so forth have been verified.

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Various types of carbon fiber sheet of different tensile strength and Youngs moduli have so far been made. This guideline describes only the PAN-class high-strength carbon fiber sheets because their strengthening effects have been experimentally demonstrated. For aramid fibers, this guideline describes both aramid 1 (homopolymer) and aramid 2 (copolymer).

Table 2.1-3 Quality Standards for Continuous Fiber Reinforcements

Carbon fiber Aramid fiber 3400 MPa class 2900 MPa class Aramid 1 Aramid 2

Type of fiber PAN-class high-strength type Homopolymer Copolymer

Tensile strength* 3400 MPa or

greater (35,000 kgf/cm2)

2900 MPa or greater

(30,000 kgf/cm2)

2060 MPa or greater

(21,000 kgf/cm2)

2350 MPa or greater

(24,000 kgf/cm2)

Youngs modulus*

230+4515 GPa (2.34+0.450.15 106 kgf/cm2)

11820 GPa (1.200.2 106

kgf/cm2)

7815 GPa (0.800.15 106

kgf/cm2) Weight per unit length To be greater than values shown on products

Fiber density 1.800.05 1.450.05 1.390.05 * Quality standard values of tensile strength and Youngs modulus are used to assess the results of

normal-condition tests but also heating and alkali immersion tests.

Table 2.1-4 Shapes of Continuous Fiber Sheets

(a) A bundle of continuous fibers is placed on a sheet of paper. The shape of the fibers is retained using a small amount of resin and shape-retaining meshes.

(b) Shape-retaining meshes with adhesives are placed on both sides or one side of a bundle of continuous fibers.

(c) The shape of a bundle of continuous fibers is retained in the form of fabrics using glass and nylon fibers.

(d) Nonwoven fabric made with thermoplastic resin is heat sealed on both sides or one side of a bundle of continuous fibers.

Tables 2.1-3 and 2.1-4 show the quality standards for continuous fiber reinforcements and the shapes of continuous fiber sheets respectively. The properties of continuous fiber reinforcements include the density of continuous fibers, the weight per unit length of continuous fiber sheets and the tensile strength and Youngs modulus of continuous fiber reinforcements. It is required that the specified tensile strength and Youngs modulus values of continuous fiber reinforcements remain unchanged after being subjected to heating and alkali immersion tests. The heating method and alkali immersion test conditions are shown in Section 2.2. The shapes of continuous fiber sheets are classified into four types, as shown in Table 2.1-4. All four types are unidirectionally

- 33 -

reinforced sheets and are already used in actual applications; the resin impregnating ability, workability and strengthening performance have already been verified. The weight per unit length of continuous fiber sheets affects the impregnating ability and bond performance of resin, as in the case of the shape. In this guideline, continuous fiber sheets having the weight per unit length shown in Table 2.1-1 are used because the strengthening performance of those in this weight range has already been verified.

Table 2.1-5 Specifications of Continuous Fiber Sheets

Name Weight per unit length

(g/m2)

Design thickness

(mm)

Sheet width (mm)

Specified tensile strength*

Specified Youngs modulus*

Carbon fiber sheets

3400 MPa class

200 0.111 250

330

500

3400 MPa (35,000 kgf/cm2) 230 GPa

(2.34 106 kgf/cm2)

300 0.167 2900 MPa

class 200 0.111 2900 MPa

(30,000 kgf/cm2) 300 0.167

Aramid fiber sheets

(aramid 1)

40-ton type 280 0.193 100 2060 MPa

(21,000 kgf/cm2) 118 GPa

(1.20 106 kgf/cm2)

60-ton type 415 0.286 90-ton type 623 0.430

300 Aramid fiber

sheets (aramid 2)

40-ton type 235 0.169 2350 MPa

(24,000 kgf/cm2) 78 GPa

(0.80 106 kgf/cm2)

60-ton type 350 0.252 500

90-ton type 525 0.378 * This tensile strength is not for continuous fiber sheet but for continuous fiber reinforcement.

For presently manufactured carbon and aramid fiber sheets, those that meet the specifications in Tables 2.1-1 and 2.1-2 are shown in Table 2.1-5. Carbon fiber sheets are classified based on the tensile strength of fiber, while aramid fiber sheets are named based on the tensile strength of a sheet having a width of one meter. They are further classified based on weight per unit length and named accordingly. Although sheets of up to 50 cm in width are available, the larger the sheet width, the more creases they have. It is important to choose an appropriate sheet width after due consideration of the workability.

(2) Specifications of continuous fiber reinforcements

The specifications for continuous fiber reinforcements shown in Table 2.1-2 are specified design values applicable for continuous fiber reinforcements that meet the standards shown in Table 2.1-3. In this guideline, tensile strength, Youngs modulus and other mechanical characteristics correspond to continuous fiber reinforcements that are made by impregnating fibers in resin and hardening them. This is based on the understanding that the performance of continuous fiber reinforcements hardened with impregnate adhesive resin is more important than the mechanical characteristics of continuous fibers themselves. A continuous fiber reinforcement is a composite material of a continuous fiber sheet and impregnate adhesive resin. If a certain continuous fiber reinforcement is

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made with the same continuous fiber sheet but different impregnate adhesive resin is used, this continuous fiber reinforcement must be considered as a different material. Tables 2.1-2 and 2.1-5 show the tensile strength and Youngs modulus of continuous fiber reinforcements made of epoxy resin, methacrylate resin and continuous fiber sheets which are described in Section 2.1.2, Impregnate adhesive resin.

The specified values shown in Table 2.1-2 are based on data obtained from the results of tensile strength tests conducted on 50 specimens in accordance with the tensile test methods described in Section 2.2, Evaluating the material characteristics of continuous fiber reinforcements. Specifically, as the tensile strength value, a value less than the one obtained by subtracting the number three times as large as the standard deviation from the average tensile strength value is adopted in consideration of variations in material characteristics. As the Youngs modulus, average values are adopted. The specified tensile strength shown in this table is the specified value of a material. It is also understood as the tensile strength having a certain safety margin defined with consideration given to material variations, which is sometimes referred to as the guaranteed tensile strength.

When an external force is applied to a member reinforced with continuous fiber reinforcement made of continuous fiber sheet, the stress intensity acting on this continuous fiber reinforcement varies, depending on the type of continuous fiber sheet, where the reinforcement is installed and the reinforcement method. In ultimate load conditions, the specified full tensile strength of the continuous fiber reinforcement is not necessarily delivered. Therefore, the design tensile strength values for continuous fiber reinforcements shown in Chapter 3 and subsequent chapters have been established by reducing the specified tensile strength values after considering of safety margins.

2.1.2 Impregnate Adhesive Resin

As impregnate adhesive resin either epoxy or methacrylate resin should be used. A type of resin that can be efficiently integrated with the continuous fiber sheet and increase the combined strength effectively must be used. Epoxy resin is used as impregnate adhesive resin to be applied to carbon or aramid fiber sheets. Methacrylate resin is used as impregnate adhesive resin to be applied to carbon fiber sheets.

If types of resin other than these are used, the material characteristics should be identified thoroughly and strengthening design and construction should be done using appropriate design and construction methods established based on experiments.

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Comment:

The functions of adhesive resin impregnated and hardened inside the continuous fiber sheet are to enable the continuous fiber reinforcement to function as a reinforced composite material by transferring stress among continuous fibers, and to transfer stress between the continuous fiber reinforcement and a reinforced structure. To enable impregnate adhesive resin to deliver the designed dynamic and strength characteristics, it must be thoroughly impregnated and hardened inside all cavities in the continuous fiber sheet.

There are example applications for epoxy and methacrylate resins as impregnate adhesive resin. The performance of these two resins when they are applied to continuous fiber sheets for reinforcement has been verified. Epoxy resin has so far been widely used as impregnate adhesive resin but methacrylate resin is also being increasingly used because it hardens more quickly than epoxy resin and is suited for use in cold environments.

Tables 2.1-6 and 2.1-7 show the quality standards for impregnating adhesive epoxy and methacrylate resins respectively. These quality standards show weight, viscosity and other characteristics which greatly affect useful life, workability and construction management, tensile strength after hardening, compression strength, Youngs modulus of compression and other mechanical characteristics. Becaus