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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
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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
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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
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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
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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
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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.)
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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
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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
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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
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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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- 14 -
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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- 15 -
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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- 16 -
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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- 17 -
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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- 18 -
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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- 20 -
(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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- 21 -
(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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- 22 -
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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- 23 -
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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- 24 -
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.
-
- 25 -
(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
-
- 26 -
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.
-
- 27 -
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
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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