In Japan, many reinforced concrete bridge structures collapsed in the recent severe earthquakes such as the 1995 Hyogoken Nanbu Earthquake and the 2004 Niigataken Tyuetsu Earthquake were designed and constructed before the introduction of the new seismic resistant design codes in 1980. Following the lessons learnt from these severe earthquakes and the continuous advancements of the state of the art and practice, further stringent performance based earthquake resistant design codes for both highway and railway bridge structures are recently enforced in Japan. For many existing structures, to meet the requirements of these new codes, proper strengthening schemes must be implemented. Among various strengthening techniques, the application of fiber reinforced polymer (FRP) has recently drawn a wide attention due to its advantages such as high strength to weight ratio, corrosion resistance, and ease of execution. This paper introduces the current issues related to the deficient reinforced concrete structural members in Japan and provides an overview of latest innovations and advancements in the technology and application of FRP sheets in structural retrofitting. The focus of this paper is mainly on the retrofitting of bridge superstructures and substructures including decks, girders, frames, and columns

Aravinthan, Thiru

Mutsuyoshi, Hiroshi

Pandey, Govinda Raj

Shinozaki, Hiroo

University of Southern Queensland ePrints

Advancements in Retrofitting Reinforced Concrete Structures in Japan using FRP Sheets   H. Shinozaki   T. Aravinthan   G. R. Pandey   H. Mutsuyoshi Senior Researcher Associate Professor Lecturer  Professor Mitsui Sumitomo Corp. Uni. of Southern Qld. James Cook Uni. Saitama University Japan   Toowoomba  Townsville  Japan     Synopsis: In Japan, many reinforced concrete bridge structures collapsed in the recent severe earthquakes such as the 1995 Hyogoken Nanbu Earthquake and the 2004 Niigataken Tyuetsu Earthquake were designed and constructed before the introduction of the new seismic resistant design codes in 1980. Following the lessons learnt from these severe earthquakes and the continuous advancements of the state of the art and practice, further stringent performance based earthquake resistant design codes for both highway and railway bridge structures are recently enforced in Japan. For many existing structures, to meet the requirements of these new codes, proper strengthening schemes must be implemented. Among various strengthening techniques, the application of fiber reinforced polymer (FRP) has recently drawn a wide attention due to its advantages such as high strength to weight ratio, corrosion resistance, and ease of execution. This paper introduces the current issues related to the deficient reinforced concrete structural members in Japan and provides an overview of latest innovations and advancements in the technology and application of FRP sheets in structural retrofitting. The focus of this paper is mainly on the retrofitting of bridge superstructures and substructures including decks, girders, frames, and columns.  Keywords: structural rehabilitation, retrofitting, concrete structures, FRP materials,   Introduction  Japan lies in an active seismic zone. The 1995 Hyogoken-Nanbu earthquake showed a widespread damage of reinforced concrete structures. Most structures that were damaged during this earthquake were designed based on the older JSCE (Japan Society of Civil Engineers) standards existed before 1980. The 1995 Hyogoken-Nanubu earthquake has been the main driver for the need of strengthening of RC structures.  Various technologies have been developed since including use of steel jackets/plates, concrete jackets, external post-tensioning and fiber reinforced polymer (FRP) sheets etc.    The application of Fiber Reinforced Polymer (FRP) in civil engineering structures was first introduced in Japan about two decades ago with the development of FRP reinforcement and tendons. Japan had been a pioneer in the research and development of FRP materials for reinforced and prestressed concrete structures especially in the bridge engineering.  The first JSCE standard specification for the design of FRP reinforcement was published in 1997, which has been adopted in various other countries (JSCE, 1997). Since then, a wide range of applications of FRP materials have been implemented including strengthening of deteriorated structures using FRP sheets and using FRP rods as reinforcement instead of steel rods. There has been a remarkable increase in the use of FRP sheets, especially carbon and aramid sheets since 1996, as a result of strengthening RC structures (Ueda, 2005).  The high demand of FRP materials in the construction industry has demanded the development of innovative strengthening technologies considering practical applications.  This paper introduces some of these technologies used especially in bridges and highway structures.  While various FRP materials have been used for structural rehabilitation, the scope of this paper is limited to the application of FRP sheets.  The relative merits of using different types of FRP sheets are discussed.  These technologies are discussed through selected case studies using aramid sheets.      Properties of FRP sheets Fig. 1 shows the stress strain behaviour of different kinds of FRP sheets and are compared with steel. In retrofitting practice, carbon fibres, aramid fibres and glass fibres are the most commonly used ones. Carbon fibre has the highest stiffess and strength. Its stiffness is comparable with elastic stiffness of steel but has a very high strength. Aramid fibres possess lesser strength and stiffness compared to carbon fibres however their advantage in handling and execution has made it popular in retrofitting and rehabilitating concrete structures. Glass fibres are also popular in many countries due to its low cost. In Japan however glass fibres are not widely used largely due to its durability concerns. 010002000300040000.0 1.0 2.0 3.0 4.0Strain(%)Stress(N/mm2 )Carbon1Carbon2Aramid1Aramid2Grass Fig. 1 Stress strain relationship  Comparison of AFRP sheets with CFRP and GFRP Table 1 and Table 2 compare the properties of Aramid Fibre Reinforced Polymers (AFRP) sheets with Carbon Fibre Reinforced Polymers (CFRP) sheets and Glass Fibre Reinforced Polymers (GFRP) sheets respectively. Mechanical properties of CFRP sheet is the best amongst all. When it comes to practical application, however, there are issues related to processing, rounding of corner angles, impregnation of resin, work speed and influence of electrical equipments, AFRP sheets have distinct advantages. Especially, while strengthening RC beams and columns, rounding off corner angles takes a lot of time and effort. Using AFRP sheets the use of disk sander is sufficient to round off the corner angles and saves a lot of time and cost. GFRP sheets are very economical but due to its inferior mechanical properties and poor resistance to alkali and acid, AFRP sheets are widely used in Japan.   Table 1 Comparison of CFRP sheet and AFRP sheet           Carbon Sheet Aramid Sheet PROPERTIES   TENSILE STRENGTH（N/mm2） 1900～3,400 2,060～2350 YOUNG’S MODULUS (kN/mm2) 245～640 78～118 TENSILE CAPACITY （kN/m） 380～570 392～1,176 ELONGATION (%) 1.5 1.8 PROCESSING Moderate Easy Rounding of corner angles R>40mm R>10mm (only disk sander) Impregnation of resin Moderate Easy Work speed One ply per day Multi-plies per day Influence of electrical equipment Create troubles with chop of fibre No troubles Durability Long term Long term Direct Expense (In Japan) 120t/m sheet $404/m2 120t/m sheet $322/m2 Table 2 Comparison of AFRP sheet and GFRP sheet ITEM Aramid Sheet Glass Fibre Sheet CHARACTERISTICS OF FIBER  DENSITY （g/cm3） 1.45 2.6 TENSILE STRENGTH (N/mm2） 2,840 2450 YOUNG'S MODULUS (kN/mm2） 109 73 ELONGATION （％） 2.4 4.0 CHARACTERISTICS OF SHEET WEIGHT （g/m2） 830 (AK-120) 344 (MG300) TENSILE STRENGTH (N/mm2） 2,060 1,400 YOUNG'S MODULUS (kN/mm2） 118 72 TENSILE CAPACITY (kN/m） 1,176 (AK-120) 71 (MG300) ELONGATION （％） 1.8 2.0 ALKALI - RESISTANCE  EXCELLENT WEAK ACID - RESISTANCE  EXCELLENT WEAK  Table 3 shows the properties of various AFRP sheets available for application. The properties basically depend of the thickness of FRP sheets. AK-120 is the thickest sheet available and it is often used in retrofitting. If one layer of sheet is insufficient, a number of layers can be applied to meet the required strengthening performance.  Table 3 Properties of AFRP sheets WEIGHT TENSILESTRENGTHYOUNG'SMODULUSTENSILECAPACITYDESIGNTHICKNESSg/㎡ N/mm2 kN/mm2 tf/m（kN/m） mmAK-40 280 2,060 118 40（392） 0.193AK-60 415 2,060 118 60（588） 0.286AK-90 623 2,060 118 90（882） 0.430AK-120 830 2,060 118 120(1,176） 0.572CODE   Comparison with other retrofitting methods A number of methods are being used for retrofitting RC structures. The most common ones are the use of concrete lining, steel plates and FRP sheets. Table 4 compares the merits, demerits, working period and cost of all these methods. Concrete lining has distinct advantage of being durable but it significantly increases dead weight, it requires access for concreting and it requires a long period. Though steel plates used in retrofitting are lighter than the concrete lining, it still requires the use of crane to handle it. It also requires the use of welding to connect plates which increases the working period. On the other hand AFRP sheets are noncorrosive, durable and processing is so easy and convenient that no crane and access space is required and hence the working period is very short.  The only demerit is that in cold climate when temperature is under 5OC, it requires heating.          Table 4 Comparison of retrofitting techniques   Application of AFRP sheets Applying AFRP sheets on concrete surface usually have four steps as shown in Fig. 2. First of all, surface treatment has to be done on the member where FRP sheet has to be applied. The idea is to remove surface laitance which are weak. A coat of primer is applied on the surface which is then followed by a layer of epoxy resin. Fibre sheets are then wrapped on the surface by removing trapped air with roller. Final coat of epoxy resin and other protective coats are applied. This method is called wet lay up and it is extensively used in retrofitting existing structures.       (a) Surface  treatment    (b) coating primer        (c) Wrapping sheet and      (d) coating epoxy resin                                          and epoxy resin               removing air with roller      and protective coating.  Fig. 2 Process of application of AFRP sheets  While retrofitting columns, FRP sheets can be wrapped by either of the two methods shown in Fig. 3. In sheet method columns are wrapped by FRP sheet of certain width and with a certain overlap. In tape method sheets are applied continuously without the need of any overlap. The second method is effective because it reduces the cost of construction by saving materials and also it is stronger because it does not have any joint.  Method Concrete Jacketing Steel Jacketing AFRP sheets Outline After installing re-bar & form, concrete is placed to surface of existing concrete.  After setting steel plate with anchor bolt, epoxy resin is injected the space.  AFRP sheet is bonded to  concrete with epoxy resin.  Merit ・Concrete is durable. ・Has been used widely.  ・Has been used widely ・Steel plate is lighter than concrete  ・AFRP sheet is non-corrosive and durable. ・Processing is easy, requires no crane & access space.  Demerit ・Deadweight increase    (minimum thickness of concrete is 25cm) ・Requires access for concreting.  ・Steel plate is heavy and requires crane (minimum thickness of concrete is 6mm for welding procedure) ・Require welding machine  ・When temperature is under 5OC requires heating.  Working period LONG  MODERATE  SHORT Direct expense (in Japan) at 25cm concrete thickness and re-bar ( D22, pitch 17cm) used  ¥30,000/ m2  at 6mm steel plate ¥70,000～90,000/ m2  at AK-120,1ply ¥35,000/m2  SHEET METHOD TAPE METHODKevlar TapeOverlapKevlar sheetSheet is wrapped horizontally.Overlap is necessary each step.Tape is wrapped in spiral shape. Fig. 3 Wrapping methods for AFRP sheets Construction Examples AFPR has been widely used in Japan in retrofitting RC structures. Especially after the 1995 Hyogoken Nanbu earthquake, design codes in Japan were modified. To meet the requirements of new design codes, a large number of existing structures have been retrofitted. Fig. 4 shows the application of externally bonded AFRP sheets for the seismic retrofitting of highway piers in Saitama city. Fig. 5 and Fig. 6 shows the application of AFRP sheets in flexural strengthening of slab and beam, respectively     Fig. 4 RC bridge piers retrofitted by AFRP sheets.       Fig. 5 Strengthening of slab    Fig. 6 Strengthening of beam  A number of buildings have also been retrofitted using AFRP sheets. Building structures are mainly retrofitted to meet the requirement of new design codes. Another reason for strengthening is the change in design load on structures due to the alteration of usage such as installing a heavy equipment in a structure designed for normal use. Fig. 7 shows the application of AFRP sheets in building structures in various parts of Japan                   Fig. 7 Application of AFRP sheets in building structures   Applications of AFRP sheets are not limited to building and bridge structures. Many other structures have been repaired and retrofitted using FRP sheets. Fig. 8, Fig. 9 and Fig. 10 show the examples of application of AFRP sheets in retrofitting chimney, tunnel and reservoir, respectively. These examples show the versatility of this method. They also demonstrate that this method does not require heavy machines and does not add additional dead load to the structure.     Fig. 8 Retrofitting chimney        Fig. 9 Retrofitting tunnel      Fig. 10 Retrofitting reservoir   Application of precast FRP sheets Though wet layup is an excellent method of bonding FRP sheet, due to space limitation and accessibility, it is not always possible. A concept of partially precasting FRP sheet has been used in such instances. Fig. 11 and Fig. 12 schematically illustrate the application of precast FRP sheets in beams and columns respectively. Precast portions are used in inaccessible region while wet layup is used in remaining portions. A gap is provided between precast sheet and concrete surface using spacers which is later filled by epoxy resin.    Pre-cast sheet Pre-cast sheet Beam Normal sheet   Fig. 11 Application of precast FRP sheet in beams        Fig. 12 Application of precast FRP sheet in columns       RC pier A construction under the girder Precast sheet Conventional   RC pier A construction under the girder spacer Fill with epoxy Precast sheet Future Directions While the above sections demonstrate the extensive use of FRP in structural rehabilitation of reinforced concrete structures, the trend is shifting towards the construction of FRP structures.  In the last decade, the research and development of all FRP structures in civil engineering has progressed substantially in several countries (Keller, 2003, VanErp, 2006). The first all FRP bridge in Japan was constructed in Okinawa prefecture in 2001 (Ueda, 2005).  This bridge is a two span continuous girder pedestrian bridge as shown in Figure 13, which is located in the road-park of Ikei-Tairagawa road. All the structural elements have been made with Glass Fiber Reinforcement Plastics (GFRP).  The all FRP solution was chosen for this bridge due to its heavily corrosive environment where the bridge is surrounded by the ocean.  As we believe that the innovative materials can be competitive to conventional materials in the near future when life cycle cost is taken into account, there is an urgent need for research and development of this cutting edge technology in Japan.  Recently, a research project sponsored by the Ministry of Ministry of Land, Infrastructure and Transport in Japan investigates the potential of using hybrid FRP girders in bridge engineering.  Initial investigations reveal there is huge potential for such hybrid girders in civil engineering, if some of the issues could be resolved (Mutsuyoshi (2007), Asamoto(2007)).  With such research and development, it is anticipated a use of FRP materials in the construction industry will further increase in the near future in Japan.      Figure 13   All FRP Pedestrian Bridge in Okinawa made of GFRP  Concluding Remarks The advancements in the retrofitting technologies for reinforced concrete structures using FRP sheets in Japan are discussed in this paper.  The main driver behind such application has been the effect of two major earthquakes in the recent years.  While various materials (aramid, carbon and glass) have been used for to produce the FRP sheets, the selection of appropriate material depends on the particular structure, cost and other considerations.  Research and development is emerging in Japan in the last five years in the application of all FRP structures in civil engineering. These provide evidence for the increasing demand and potential of FRP materials in the construction industry.   References:  Asamoto, S., Mutsuyoshi, H., Aravinthan, T. and Suzukawa, K. (2007). Experimental investigation of innovative hybrid composite girders with GFRP and CFRP, the fourth international structural engineering & construction conference (ISEC-4), (submitted). Keller, T. (2003). Use of Fiber Reinforced Polymers in Bridge Construction. International Association for Bridge and Structural Engineering. Zurich. JSCE (1997).   Recommendation for Design and Construction of Concrete Structures Using Continuous Fiber Reinforcing Materials, Concrete Engineering Series 23 Van Erp, G. (2006). Future Materials – The Use of fiber Composites in Civil Engineering. Proc. of Main Roads Technology Forum, Brisbane. Ueda, T (2005).  FRP for Construction in Japan. Proc. of JSCE-CICHE Joint Seminar, Mongolia Mutsuyoshi, H, Aravinthan, T, Asamoto, S and Suzukawa, K (2007). Development of New Hybrid Composite Girders Consisting of Carbon and Glass Fibers, Proc. of COBRAE CONFERENCE 2007 - Benefits of Composites in Civil Engineering, Stuttgart. (in print).  

Advancements in retrofitting reinforced concrete structures in Japan using FRP sheets

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Advancements in retrofitting reinforced concrete structures in Japan using FRP sheets

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