State-of-the-art review of FRP composites for major

Int. J. Sustainable Materials and Structural Systems, Vol. 1, No. 3, 2014

State-of-the-art review of FRP composites for major construction with high performance and longevity Zhishen Wu*, Xin Wang, Xing Zhao and Mohammad Noori International Institute for Urban Systems Engineering, Southeast University, 2 Sipailou, Nanjing 210096, China Fax: +86-25-83793232 Fax: +86-25-83793831 E-mail: [email protected] E-mail: [email protected] E-mail: [email protected] E-mail: [email protected] *Corresponding author Abstract: This paper first identifies the need for high performance and longevity of major engineering structures focusing on the problems in current civil infrastructure. Subsequently, it reviews the state-of-the-art research of FRP in structural retrofitting and strengthening and identifies the challenges facing further development of FRP in civil engineering. In order to address the above background, several key scientific issues and corresponding research directions are introduced according to the newly granted National Key Basic Research Program in China, which comprises of: 1) fracture/failure control and probabilistic design of FRP composites and large FRP-reinforced concrete structures; 2) long life-cycle fatigue and creep characteristics as well as service life controllability design of FRP-reinforced structures subjected to multi-field coupled actions; 3) performance of FRP-reinforced structures subjected to extreme environments and extreme loadings as well as methods for performance control; 4) key technologies and their integration for the application of FRP composites in major engineering structures. Keywords: fibre-reinforced polymer; FRP; retrofitting; strengthening; major structures; high performance; longevity. Reference to this paper should be made as follows: Wu, Z., Wang, X., Zhao, X. and Noori, M. (2014) ‘State-of-the-art review of FRP composites for major construction with high performance and longevity’, Int. J. Sustainable Materials and Structural Systems, Vol. 1, No. 3, pp.201–231. Biographical notes: Zhishen Wu is a Professor at Southeast University, China. His research interests include FRP composite technologies, advanced sensor technologies, and structural health/risk/disaster monitoring and control. He is the author or co-author of over 500 papers in refereed journals and international conference proceedings including over 50 keynote or invited papers. He has led over ten important research projects in both Japan and China, and is now leading a National Key Basic Research Program (973 Program) on “the use of FRP composites to achieve high performance and longevity for major engineering structures” (2012–2017).

Copyright © 2014 Inderscience Enterprises Ltd.

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Z. Wu et al. Xin Wang is an Associate Professor at the International Institute for Urban Systems Engineering (IIUSE), Southeast University (SEU), China. He received his Bachelor and Master degree in Civil Engineering from SEU, and PhD in Structural Engineering from Ibaraki Univ., Japan. His research topics comprise long-term behaviour evaluation of FRP composites, advancement of FRP composites, and hybrid FRP system in long-span structures. He has published more than 40 papers in refereed journals. He is leading two NSF projects related to the fatigue behaviour of FRP cable for long-span cable supported bridges. Xin Zhao is a PhD student at the International Institute for Urban Systems Engineering (IIUSE), Southeast University (SEU), China. Her research focuses on the long life-cycle fatigue characteristics and life controllability design of FRP-reinforced composites subjected to multi-field coupled actions. Mohammad Noori’s research has been in non-linear random vibrations and hysteresis, smart materials, seismic isolation and diagnostics in structural health monitoring. He was the Higgins Professor and Head of Mechanical Engineering at WPI, the RJ Reynolds Professor and Head of Mechanical and Aerospace at NC State and the Dean of Engineering at Cal Poly, where he is currently a Professor of Mechanical Engineering. He is also affiliated with Southeast University. He is an ASME Fellow, has received a JSPS Fellowship, has published over 200 refereed and technical papers, serves as the associate editor and editorial board member of seven journals.

1

Introduction

1.1 Problems facing major engineering structures Currently, China is in a period of significant development of urbanisation. Enormous civil infrastructures are under planning and construction, such as major bridges, high rise buildings, and so on. It is reported that the annual amount of civil infrastructure work in China is now greater than the annual sum of all other countries in the world combined. Major engineering structures are mega-high-rise buildings, long-span bridges (especially cross-sea bridges), variety of long-span bridges on highways and high-speed railways, other engineering structures of great strategic significance (such as marine structures, nuclear plants, structures that can withstand major natural hazard lodgings, and other critical infrastructure). The achievement of high performance and longevity for major engineering structures is required and essential for the sustainable development and mitigating natural and other disasters. High performance and longevity mean that not only major engineering structures have a high degree of safety and performance, but also the recoverability in the whole life cycle in extreme environments (such as strong corrosion, fire) and under extreme loads (strong earthquakes, explosions, etc.) are drastically reduced in order to realise the objective of full life cycle cost (LCC) minimisation (less maintenance costs than traditional structures of equal service life, or equivalent maintenance costs with longer service life). In recent years, increasing number of structural disasters has occurred due to various factors such as corrosion, fatigue, earthquake, blast, etc. A few examples are shown in

State-of-the-art review of FRP composites for major construction

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Figure 1. Thus, in recent years, significant attention has been focused on safety and sustainability. The scope of this concern includes structural durability, lightweight requirements, the recoverability after disasters and the related economical and recyclability issues. In the opinion of the authors the following four areas are the major research themes that need to be addressed. Figure 1

Typical damage of major structures (see online version for colours)

Bridge collapsed due to corrosion of joints

RC box girder bridge’s severe cracks

Large deflection of girder bridge

Low recoverability after earthquake

Damage by tsunami

Damage by blast

Source: Photos from web resources.

1.1.1 Demand for prolonged service, safety, and durability There is a critical need for prolonging the service, safety and durability of major structures. The traditional design methods set the safety and suitability of the structure as the main indicator, with no consideration of the time variability of the structural resistance and lack durability failure criteria and design methods. These shortcomings have resulted in a profound worldwide problem of inadequate infrastructure durability. For example, the steel truss I-35W bridge, with only 43 years of service, in Minnesota, USA collapsed entirely in 2007 (http://en.wikipedia.org/wiki/I35W_Mississippi_River_bridge) due to the fatigue and corrosion of a joint. The financial losses due to corrosion of structures in marine environment reaches 700 billion USD globally and 100 billion USD for China every year (Ke, 2003). Therefore, there is an urgent need to further enhance the safety and durability major engineering structures (including existing and new construction).

1.1.2 Reducing the weight of major engineering structures Reducing the weight of major engineering structures is an effective way to enhance the structural safety and to extend their lives. The self-weight of high-rise buildings

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accounts for 85% of the total stress in structural members. The huge weight also means a huge size, huge cost and huge energy consumption during the construction process. According to various statistics, approximately 70% of the energy consumption during the construction phase is for the heavy lifting and moving. Thus, reducing the dead weight of the building is a significant factor. There are numerous ways to reduce the weight. The utilisation of new types of lightweight and high strength construction materials for load-bearing walls or the partition walls is one of the most effective ways. Moreover, alternative application of construction materials can also be an effective ‘decompression’; for instance the column-filled steel tubular columns within the concrete in a three-way compression state can significantly reduce the size of the column section under the same load carrying capacity conditions, as compared with ordinary concrete columns. The vertical load-bearing elements of three 44 to 62-story high-rise buildings in Seattle, USA are the column-filled steel tubular columns. As for large span bridges, the typical span of the railway bridge in 2008 has exceeded 500 meters, but still difficult to meet the societal needs and the rapid economic development. For long-term development plans, China intends to build some cross-sea bridges in the three Straits ‘(Bohai Strait, the Taiwan Strait, the Qiongzhou Strait)’, in the two Gulfs (Hangzhou Bay, Lingdingyang) as well as in a series of bays (Liaoning Dalian Bay, Qingdao Jiaozhou Bay). The single span of bridges has now increased by more than 1,000 metres, reaching a maximum span of 1,991 m. However, for hundreds of kilometres across a strait or gulf, this is clearly insufficient. Large spans will be a major goal for future development in bridge construction, but the dead weight of steel is one of the bottlenecks. Thus, it is clear that more massive engineering structures need new lightweight, high strength structural materials as a key component of their construction.

1.1.3 Improving the recoverability It is critical to improve the recoverability of major engineering structures. Large infrastructures and massive structures need to be safe, secure and survive during disasters, such as earthquakes and other natural disasters hazards, as well as explosions and terrorist attacks. Over the last two decades, the world has experienced a growing number of catastrophic earthquakes that have taken huge tolls on human lives and civil infrastructures. Wenchuan earthquake, Haiti earthquake, Chile earthquake all occurred in recent years. The Great East Japan earthquake occurred on 11 March 2011, which resulted in massive casualties and economic losses. Those large earthquakes show the importance of protecting major lifeline systems such as power grids, telecommunications, water supplies, gas supplies and flammable, explosive, toxic, and nuclear plants and facilities. These critical infrastructures not only require high level of safety performance and measures during the earthquake, they also require a higher degree of survivability in order to function reliably after the earthquake. They also need to have minimum post-disaster repair requirements. The recoverability of major engineering structures, in particular, has become a major concern. It is predicted that by 2020, China will lose up to 43 billion RMBs per day if the traffic comes to a standstill in Beijing for one day. If the structures can be quickly recovered, or can be self-recovered, and continue to be used after a disaster, that can result in significant savings in the economic and social costs. For instance, since the steel bar is an elastoplastic material and its stiffness after yielding is close to zero, traditional reinforced concrete (RC) structures that incorporate steel rods


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can hardly tolerate damage that is controllable and repairable. Thus, there is a need to develop new materials and new techniques to achieve higher levels of recoverability.

1.1.4 Full LCC minimisation The cost minimisation of full life cycle of infrastructure is a critical factor for building a resource-saving, energy saving and environmental-friendly society. The maintenance and upgrading costs in traditional design life (50–100) of huge infrastructures have become a serious obstacle to the sustainable development of nations. On the other hand, the long service cycle of the infrastructure and steel corrosion continue to result in huge financial losses worldwide. Experience and lessons reveal that traditional RC infrastructure reinforcement corrodes severely in harsh environmental conditions, resulting in performance degradation, early retirement, huge maintenance costs and can even lead to serious catastrophic accidents. Europe, the US, Japan and other developed countries have proposed to implement the design philosophy of minimising the full LCC (including construction, custody, use, dismantling the economic costs and environmental costs, early stage of project construction or reinforcement of the social costs, etc.) in order to reduce the huge costs of infrastructure maintenance management. The input costs required for a large reduction in the cost of subsequent service process and significantly increasing the structural design life would only modestly increase. However, the design life can be increased as high as more than 100 years for some important structure leading to a huge reduction in LCC. Scholars have elaborated the importance of the LCC with the ‘five times rule’: saving $1 of durability in the design stage means an additional $5 for the steel corrosion repairing; an additional $25 for repairing of cracks in the concrete surface along the rebar; and an additional $125 for repairing serious damage. Long life design (more than 100 years) has been recognised as one of the most effective methods and the update costs can be significantly reduced, while the resource consumption is greatly reduced. The American Society of Civil Engineers Structural Engineer Institute (ASCE SEI) Sustainability Committee was established in 2005, with the main objective to explore the sustainability planning, design and management of civil engineering structures. The world bridge structures association (IABSE) has frequently set structural engineering sustainability as the theme of their annual meeting since 2000. In mid-1990s, the infrastructure investment budget of Japan reached 50 trillion yen, and the size of the investment budget has continued to decrease after 2005. In the future this budget can only be maintained at a scale of 30 trillion yen, while it only meets existing project management, maintenance, repair and update requirements. According to the data provided by the United States Federal Highway Administration (FHWA) in 2008, among the more than 600,000 bridges in the USA, 26.9% have structural or functional defects. The repair and maintenance of these bridges would require an annual investment of $17 billion for 50 years, but only $10.5 billion annual investment is available. China is still in the peak period of construction of infrastructure and needs to learn from the experience and lessons of the developed countries to achieve the minimum LCC by employing new materials, new technology, and research and development of new structures with integrated applications, in order to reduce the consumption of energy and resources, prevent waste generation, and the damage to the ecological environment. This means there is an urgent need to build a resource-saving, energy saving and environmentfriendly society.

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It is reported that the ore reserve in China is only 11.5 billion tons, but the exploitation is reaching more than 0.6 billion tons each year. All these problems which pose a potential crisis, indicate that the durability of structures need to be greatly enhanced and in order to improve structural safety, the self-weight of structures should be lowered to reduce stresses in structural members and to extend the structural service lives, and to reduce the LCC. In order to fundamentally address the above problems, a promising solution is offered by using fibre-reinforced polymer (FRP) composites, which have obvious advantages in comparison with conventional steel elements, such as high strength, light weight, good resistance to fatigue and corrosion, ease of forming, and so on (Wu et al., 2010b, 2010c; Bakis et al., 2002; Keller, 2003). Such potential replacement has a number of benefits, including: 1

easing the severe pressure created by the shortage of iron ores and other traditional mineral products and the need to reduce carbon emission

2

providing a reliable technology for improving the safety and durability of major existing and new engineering structures so that truly realise engineering structures with a super-long service life and minimise their LCC

3

enabling the damage controllability design of structures subjected to extreme loads/effects so that to ensure their recoverability to meet different levels of demands

4

offering an effective solution for the construction of lightweight structures.

1.2 Development and application of FRP and the existing challenges Commercial applications of fibre-reinforced composite materials especially carbon fibre reinforced polymers (CFRP), began in the 1970s, initially being used in the field of sporting goods. In the 1980s, the FRP materials gradually started to be used in the field of transportation engineering. In the mid-1990s, because Japan’s Kobe earthquake resulted in a great deal of civil transportation infrastructure disasters, FRP quickly developed into an important means for seismic reinforcement. Since then, structural application of FRP’s has been widely studied and explored and extensive research has been carried out in the area of important physical and in-service properties of FRP and its reinforcement applications. The incorporation of FRP has evolved from the initial retrofitting and reconstruction to building new structures, as shown in Figure 2. A wide range of FRP products have developed from FRP fabric/plate, to a variety of forms of fibre composite cables, grating and shapes. The range and forms of applications of FRP’s are being more and more widely explored on internal reinforcements, externally bonded reinforcements, structural shapes and bridge decks (Bakis et al., 2002). For example, the number of applications involving composites as strengthening/repair or retrofit materials worldwide has grown from just a few applications ten years ago to several thousands today (Bakis et al., 2002). FRP also provides a good choice as a building material for civil engineering structures and facilities with comprehensive performance and for the reinforcement of the existing engineering facilities (Czigány, 2005, 2006; Liu et al., 2006). The larger fabricating firms, which already had experience of manufacturing FRP composite units for other industries, entered the building industry with the fabrication of semi-load


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bearing and infill panels for houses and larger constructions. The main large building examples of these systems in the UK are the classroom structure at Fulwood, Lancashire, the Mondial House, London and the Amex House in Brighton (Hollaway, 2010). FRP has also demonstrated a wide range of applications in transportation engineering. The first pedestrian FRP bridge was built in Tel Aviv, Israel in 1975. Since then, others have been constructed in Asia, Europe, and North America. Many innovative pedestrian bridges have been constructed using pultruded composite structural shapes. Due to the lightweight materials and the ease in fabrication and installation, it has been made possible to construct many of these bridges in inaccessible and environmentally restrictive areas without having to employ heavy equipment. Some bridges have been carried to the sites in one piece by helicopters; others have been disassembled and transported by vehicles and assembled on site (Hollaway, 2010). Depending on the application purpose, FRP can mainly be divided into two categories: 1

for the reinforcement and restoration of existing structures; and a substitute for reinforcing bars in RC structures

2

for the development of new FRP-concrete or FRP-steel composite structures.

FRP reinforcement technology started to be placed in use in the 1980s. Not only can FRP’s result in eliminating the long, difficult, high cost construction cycle, resolve the uneasy reinforcement of complex structures and address other shortcomings, they do not noticeably increase the original size of the structure either. Moreover, they do not add much to the self-weight of structures, and do not need large-scale construction equipment and ample space for construction. Therefore, FRP has considerable advantages in the rehabilitation and upgrading of RC and steel structures and buildings and subsequently over the past several years it has attracted the focus of many research groups. The reinforcement and transformation technology of FRP are quite mature now to meet a variety of needs for a variety of structures. FRP, in addition to being used as structural reinforcement and transformation material in the past 20 years, continues to be used to enhance new structures. For instance, researchers at home and abroad (especially in Northern Europe, the USA, Canada and other countries and regions where a large amount of salt is used to melt the snow in winter) are actively pursuing FRP composite materials instead of traditional steel production for utilisation in concrete structures (such as FRP bars embedded in concrete) in order to avoid the harm of steel corrosion in concrete (Serbescu et al., 2008). In Europe, China, Japan and the USA, a variety of FRP materials composite structures combining traditional building materials, such as FRP-concrete composite beam-slab structure, FRP pipe concrete columns, FRP-concrete-steel composite structure, are being employed (Serbescu et al., 2008). The combined structures enhance the characteristics of a variety of materials, to obtain a comprehensive high performance. In addition, preliminary studies of FRP as a separate structural unit, such as FRP tube grid structure, FRP woven structure, FRP cable large span cable-stayed structure, FRP profiles bridge panel and box girders, have also found applications and new grounds. These structures can significantly reduce the weight of the original structure, enhance the durability and long-term safety of the structure, and can reach the span requirements that cannot be achieved by conventional materials (Serbescu et al., 2008; Sim et al., 2005; Tan and Zhou, 2008; Wu et al., 2010a).

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Z. Wu et al. Application of FRP in construction, (a) FRP for structural retrofitting (b) FRP for new construction (see online version for colours) FRP bonded or wrapped

Beam or plate

FRP profiles

Chimney

Seismic strengthening

FRP tubes for piers

FRP bars or tendons

FRP cable externally strengthening

FRP NSM

(a) FRP replace steel bar

FRP-RC composite column/beam

FRP light roof

FRP bar

FRP 混凝土 R

混凝土

R C

FRP

C FRP cable structure

Offshore platform

FRP desulfurization chimney

FRP tanks

(b) Source: Photos from web resources

With the increasing efforts of scholars and engineering practitioners, some of above results are now reflected in improving the technical aspects and guidelines for building engineering structures globally. The USA (ACI 440.1R-06, 2006; ACI 440.2R-08, 2008) Europe (fib, 2001, 2007), Japan (ISIS Canada, 2001a, 2001b), Canada (JSCE, 1997, 2001) and other countries have enacted the design and construction guidelines for new


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FRP reinforced structures and for utilising FRP’s for reinforcing existing structures. International Standardization Organization (ISO) TC71 Working Group, based on the experience and the opinions of different states, have also recently developed a draft design guide for FRP reinforced structures (including new structures and existing structures). Although in terms of wide implementation of FRP and the necessary studies for FRP reinforced structures, China is relatively lagging behind the advanced industrial countries, however, the National Science Foundation Committee of China has supported more than 70 related projects since 1999, and in 2010 the national code of ‘Technical code for infrastructure application of FRP composites’ (GB50608-2010) was issued. Hong Kong began research in this field from the mid-1990s, and ‘Technology Guide of FRP RC structure of Hong Kong’ is also nearly completed. Those projects and guidelines/code have solved many problems that occurred on the component level of FRP reinforcement, and promoted the application of FRP in civil engineering. It is worth mentioning, as a pioneer country in the world, in the field of energysaving, environmental protection and disaster prevention, in 2004 Japan organised major domestic production, and education and research forces to establish an FRP Application Research Commission in civil engineering. In their 2005 report, the Commission introduced new prospects for FRP applications in the fields of marine structures, ports, bridges, underground structures, earthquake disaster prevention engineering, and more importantly pointed out that the lack of a long-term performance study of FRP reinforced structures, the design of the life cycle, and a lack of globally accepted guidelines have limited a wider range of FRP applications in civil engineering. Meanwhile, some other countries have also started key or large research projects in order to promote FRP for infrastructure applications. For instance, the project of ISIS Canada focused on the massive fundamental and application study of FRP, which attracted 14 universities and 190 organisations. Another example is the European Tans-IND plan for promoting FRP in transportation applications which involves nine European countries and 21 research institutions. All these efforts for the development of design standards of FRP and FRP reinforced structures indicate the importance and broad prospects of FRP application in the field of civil engineering. However, FRP materials should warrant separate treatment in standards and codes on account of their lower modulus and ductility in comparison with conventional materials such as metals (Bakis et al., 2002). These extensive efforts have not yet resulted in a satisfactory progress towards addressing the need for high performance and long life requirements for critical FRP applications. This is in addition to the fact that the performance of FRP has not been proven for the public and the initial cost of FRP is higher than the traditional structural materials. The fundamental reasons that have limited a wider range of FRP applications are as follows: First, the current research achievements have not been able to be reflected in or to quantify the advantages of FRP reinforced structures, especially in large-scale structures. Subsequently, a large variation exists in the same design models. Second, deficiencies exist in the design methods for assuring long-term durability, fatigue/creep, fire resistance, the LCC and performance. Third, the existing design specifications and related background research have basically followed the safety and performance design theory for traditional RC structures, therefore, they have failed to essentially establish new damage control design theory for FRP reinforcement materials and components, structures, systems and there is a lack of

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theoretical support for the scientific design of major projects and their overall performance (especially safety, durability). The fourth is the lack of key technologies that can fully utilise and integrate the advantages of FRP and efficiently apply them to the structures.

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Key issues

Based on the aforementioned discussions on the current limitations, several key issues have been identified by the authors and are discussed in the following. By focusing on these issues, it is the authors’ hope that the current limitations of FRP can be overcome and the ultimate goal of achieving high performance and longevity for major engineering structures can be achieved.

2.1 Design theory and system integrity of FRP reinforced large structures and their system integrity Design theory of FRP reinforced large structures and their system integrity is a critical issue that needs be further improved. Over the past three decades, design theories for both newly built as well as existing FRP reinforced structures (concrete structure) (Teng et al., 2002) has been established. However, the applicability of most existing design theories and codes/guidelines for FRP reinforced structures (such as giant FRP confined RC members, FRP reinforced long-span bridges, the combined system of large FRP member and the traditional structure) are still of low accuracy and unclear. Some new models have been established to address different aspects of this low accuracy issue for instance above in different aspects like interface, confinement and shear capacity.

2.1.1 FRP-concrete interfacial debonding prediction Teng et al. (2002) have studied rupture of FRP reinforced ordinary concrete structures and debonding mechanism of FRP-concrete interfacial for the past ten years. Their research provides strong support for the breakthroughs in design theory of FRP reinforced large concrete structures based on fracture mechanics and probability theory. Through analysing the probability distribution of material properties, the geometry, calculation mode as well as resistance, and the parametric analysis of cross-sectional dimensions of the beam, the effective height of the steel bars, FRP configuration and material properties, Shi at Southeast University evaluated the corresponding target reduction factor meeting a reliable indicator for different models, as listed in Table 1. Table 1

The corresponding target reduction factor meeting a reliable indicator

Prediction model Reliable indicator

Wu and Niu Said and Wu (2007) (2008)

ACI 440_2R (2008)

GB 50608 (2010)

Teng et al. (2003)

βT = 3.7

0.825

0.85

0.80

0.75

0.825

βT = 4.2

0.80

0.825

0.70

0.675

0.775


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2.1.2 Stress-strain relationship of FRP confined concrete Fahmy and Wu (2010) presented a new model with high accuracy to predict stress-strain response of confined cylinder size column varied from small-test to large-scale specimens. Diameter (d) and height (L) range from 70 mm to 407 mm and 140 mm to 813 mm, respectively. The distribution of the percentage ratios of the predicted-toexperimental second stiffness according to the different models are shown in Figure 3 and Table 2, from which it is clear that the new model predicts the second stiffness of FRP-confined concrete with a reasonable accuracy. Figure 3

Predicted-to-experimental ratio of E2 by Fahmy and Wu model

Table 2

Statistical results of the studied models

Source of models in Fahmy and Wu (2010)

Avg. (%)

SD (%)

COV (%)

Karbhari and Gao

33.8

25.8

76.4

Samaan et al.

63.3

23.9

37.7

Hosotani and Kawashima

40.7

48.3

118.6

Lam and Teng

96.4

37.9

39.4

Wu et al.

125.9

60

47.6

Mohamed and Wu

100.5

27.5

27.4

Source: Fahmy and Wu (2010)

2.1.3 Shear capacity prediction of FRP reinforced RC beam Sayed et al. (2013) developed a finite element analysis based simulation approach and a new model that accounts for all parameters that affect the ultimate shear capacity such as beam width, beam depth, shear span-to-depth ratio and height of the FRP sheet. The model has been proved with high accuracy compared with the experimental results obtained from 274 RC beam tests collected from the literature, covering a wide range of test geometries, structural variations, and shear-strengthening configurations. Table 3 shows the average value, the correlation coefficient r, and the coefficients of variation COVs of the ratio VExp/VPred for side bonding, U-jacketing and complete wrapping

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validation configurations, both separately and in a total validation set. The proposed new model has the best average for VExp/VPred, the corresponding coefficient of variation is less than the other models and the coefficient of correlation is higher than the other models for beams strengthened with side bonding, U-jacketing and complete wrapping. Table 3

Average, r and COV of VExp/VPred for different models

Side bonding

U-jacketing

Complete wrapped

Total set of validation

ACI440

Tri. and ant.

Matthys and Tri.

Täljsten

Sayed et al.

Average

1.16

0.98

1.18

1.18

1.03

r

0.89

0.94

0.88

0.87

0.96

COV %

28.4

24.7

54.7

32

18.9

Average

1.22

1.11

1.16

1.33

0.98

r

0.9

0.88

0.87

0.78

0.95

COV %

25.5

22.5

24.3

25.6

17

Average

1.67

1.06

1.19

1.08

1.03

r

0.83

0.88

0.85

0.86

0.95

COV %

23.8

28.1

32.6

29.1

18.3

Average

1.32

1.06

1.17

1.22

1.01

r

0.87

0.91

0.89

0.86

0.96

COV %

30.3

25.1

38.7

29.5

18.1

Source: Sayed et al. (2013)

Another issue that should be indicated and studied is the size effect. The specimens in the past studies have been usually of small size and small scale, such as in the British Standard (Concrete Society 2004). For instance, the design formulas of FRP confined rectangular cross-section column has been mainly limited to a column with short side of section below 200 mm, which is far from the demand in major constructions. Moreover, several studies have shown that when the cross section or the length of the FRP specimen changes, the fracture strain and tensile strength have significant size effect (Teng et al., 2002; Wisnom and Atkinson, 1997; Wisnom et al., 2008). For instance, strengths of FRP laminated plies are plotted against gauge section volume in Figure 4 (Wisnom et al., 2008); the interfacial de-bonding strains of externally bonded FRP vary with the dimension of the strengthened beams, as shown in Figure 5 (Shan et al., 2007; Leung, 2006; Wu and Niu, 2007; Said and Wu, 2008; Teng et al., 2003; American Concrete Institute, 2008; CNR-DT 200/2004; GB 50608, 2010); comparisons for the effect of column size is plotted in Figure 6. As shown in Figure 6(a), the normalised compressive strength of square concrete columns with a given corner radius (r = 3, 5 and 10) and CFRP volumetric ratio (0.5% and 3.0%) declines as the column size increases. Similarly, as shown in Figure 6(b), the ultimate axial strain of square concrete columns with a given corner radius and CFRP volumetric ratio declines as the column size increases. However, column size has no effects on normalised compressive strength and ultimate axial strain of columns with a given CFRP volumetric ratio and column side to corner radius ratio (D/r) (Yeh and Chang, 2012). Thus, the mechanism and the design theory of large FRP reinforced structures must be verified for the application in large structures.

State-of-the-art review of FRP composites for major construction Figure 4

Size effect in scaled unidirectional laminated FRP plies

Figure 5

Size effect of debonding strain (see online version for colours) Leung (2006) Exp_Leng(2004) Said & Wu 2008 Italian Code 2004 Chinese Code 2010

0.015

Wu &Niu 2007 ACI 2008 Teng 2003

200

0.012 0.009

1800

0.006 0.003 0.000 400

3600

600

800

800

3600

Depth 200 Clear span 1800

Figure 6

unit: mm

400

Debonding strain

0.018

213

7200

7200

Effect of column size (D) on (a) normalised compressive strength and (b) ultimate axial strain for columns with B/D = 1 and fco = 27.47 MPa

(a)

(b)

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To figure out the fracture mechanism and the size effect of FRP large structures, the studies carried out in the field of aerospace are good resources. It is reported that fracture size effect of FRP has become an important branch of the composite material science (NASA 1994). Unfortunately, in the field of civil engineering, the size effect of FRP fracture and its impact on fracture properties of large FRP reinforced members are rarely studied. In addition, all FRP reinforced structural design codes have adopted traditional material partial factor (or similar) to consider the safety reserves of FRP material, but the values of these coefficients are neither taken full account of the failure mechanism of FRP structure (such as material or interface fracture), nor have been based on a rigorous system reliability analysis. Most importantly, they fail to take into account the different safety requirements of infrastructure and other structures. As a result, existing design methods may underestimate the FRP brittle fracture in some cases, or may be too conservative, resulting in a waste in the use of these materials. Thus, design of FRP reinforced structures needs to be studied more thoroughly and valuable lessons can be learned from the design of aircrafts, as shown in Figure 7. The development stems from static strength design, which is empirically determined by static strength of material and its relation to the actual number of flights without considering fatigue and corrosion to safe life design which is based on S-N diagram of material. Therefore, this rarely considers the fracture size effect. Moreover, this leads to fail-safe design which adopts multiple traditional material partial factors, and results in damage tolerant design, which can allow local damage when it is lower than damage limit, taking into account the different requirements of different members. Finally, this process leads to damage control design which uses the failure mechanism of structure and detection methods to analyse and detect the damage that can develop. Figure 7

Design evolution of composites in airplane (see online version for colours)

Static strength design

Safe life design

Fail-safe design

Damagetolerant design

Damage control design

empirically determined by actual number of flight.

based on S‐N diagram and the airworthiness

Multiple safety redundancy

Local damage is allowed but lower than damage limit

active damage identification by fracture mechanics and detection methods.

initial stage

Figure 8

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late 1950s

late 1970s

after 1985

L-D curves of FRP strengthened RC beams (see online version for colours) RC beam strengthened with prestressed FRP sheets

FRP rupture P Limited reinforcement effect （Load） Initiation of Debonding FRP debonding failure Great enhancement of of FRP Sheets steel yielding load Py’’ Py ’ Py Pcr ’’ Pcr

σcr (Cracking)

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σy (Steel yielding)

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Scholars recognise that mechanical characteristics of FRP reinforced structures are quite different from that of traditional ductile members or completely elastic member. The load-displacement curve of FRP reinforcement member has a secondary stiffness stage as shown in Figure 8. Thus, the ductility design methods of traditional structures are no longer suitable for FRP reinforced structure. How to balance load capacity and deformation capacity of the FRP reinforced structures in order to perform the capacity and ductility design of structures has become an important issue. Some scholars have carried out extensive original researches on the ductility improvement using hybrid brittle FRP (Tan and Zhou, 2008; Bakis and Nanni, 2001; Wu et al., 2011, 2010c, 2008; Wu, 2004; Dai et al., 2005; Xue et al., 2008; Teng et al., 2007; Wang et al., 2010). Bakis and Nanni studied seven types of hybrid FRP bar for concrete applications achieving pseudo-ductile status and they concluded that hybridisation of unidirectionally reinforced composites using low-elongation piezo resistive fibres and high elongation inert fibres is a viable method for obtaining pseudo-ductile tensile behaviour (Bakis and Nanni, 2001). According to their findings, pultruded rods with low concentration of dispersed carbon tows were better able to sustain further loading following first failure of the carbon tows, like the case in type D, F and G rods. The scheme of hybrid FRP is shown in Figure 9. High modulus fibres are designed to ensure the enhancement of initial stiffness. The mixture of high modulus and high strength fibres presents a certain strain hardening behaviour until the rupture of the high strength fibres, which may be used to control the deformation of structures with a good recoverability. In addition, the ductility can be guaranteed by mixing with ductility fibres in certain proportions (Wu et al., 2008). Figure 9

Hybridisation of various fibres (see online version for colours) σ

Ductility behavior

Strain hardening behavior for controlling deformation

fm

To exceed steel （E≧Es） fy

⊿f ( to be controlled) Initial yielding(rupture) of high strength fibers ⊿f ( to be controlled )

fyo

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Final rupture of High ductile Fibers ε

εyo

εy

High modulus Fibers

εm

High strength Fibers

εu

High ductile Fibers

εf

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In addition, new innovative technology of pre-stressed FRP (Xue et al., 2008) has been developed, which realises high efficiency of construction and relieves stress concentration in the anchorage zone. Another innovative structure is FRP-steel-concrete composite double-walled hollow members (typical sections is shown in Figure 10) proposed by Teng et al. (2007). Compared to the steel-concrete DSTC, the advantages of the new column include: 1

a more ductile response of concrete as it is well confined by the FRP tube which does not buckle

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no need for fire protection of the outer tube as the outer tube is required only as a form during construction and as a confining device and additional shear reinforcement during earthquakes

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no need for corrosion protection as the steel tube inside is well protected by the concrete and the FRP tube.

Compared with the FRP-concrete DSTC, the advantages of the new column include: 1

ability to support construction loading through the use of the inner steel tube

2

ease of connection to beams due to the presence of the inner steel tube

3

savings in fire protection cost as the outer tube is required only as a form during construction and as a confining device and additional shear reinforcement during earthquakes

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better confinement of concrete as a result of the increased rigidity of the inner tube.

Similarly, the new column also has significant advantages over other composite/hybrid columns including concrete-filled steel tubes, concrete filled FRP tubes and concreteencased steel columns in many applications. The axial compression and flexural test results of double-skin tubular members is also provided in Figure 11, where the number of the FRP plies varies and indicted in the specimen numbers (Teng et al., 2007). These test results have confirmed a very ductile response of the new members, which result from the effectively confined concrete and additional shear resistance provided by the two tubes and the delayed or suppressed local buckling of the inner steel tube by the surrounding concrete. Figure 10 Typical sections of double-skin tubular members (see online version for colours)

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Figure 11 Test result of double-skin tubular members, (a) axial load-axial strain behaviour of DSTCs (b) load-deflection curves of beams

(a)

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2.2 FRP reinforced structures in the extreme environments Consideration of the durability evaluation, promotion, life prediction and control methods for FRP reinforced structures in the extreme environments is another important issue. FRP fatigue and creep damage in most cases determine the service life of FRP reinforced structures. However, FRP fatigue and creep strength design that the guidelines recommend are too conservative. For instance, design stress of CFRP, AFRP and GFRP is not higher than 55%, 30% and 20% of its strength (ACI 440.2R-08, 2008), in which material is used with low efficiency. In addition, because factors that influence fatigue and creep properties of FRP and FRP reinforced structures are varied, the studies so far are far from answering multiple factors regarding FRP fatigue/creep mechanism and long-term performance. Fatigue, creep and freeze-thaw performance of FRP can be addressed in the design process (Wu et al., 2010c). For instance, hybridisation of fibres can effectively improve the FRP fatigue strength (Figure 12) (Tan and Zhou, 2008) and mechanical performance under freeze-thaw action (Figure 13) (Wu et al., 2010c; Shi et al., 2011), but there is still need for further investigation of fatigue and creep damage mechanism of different types and forms of FRP and for establishing the appropriate life prediction models for civil engineering applications. In the field of aerospace, fatigue and creep performance study of FRP is most mature (Degrieck and Paepegem, 2001), but it is different from that of civil engineering with respect to FRP materials preparation techniques, scale and service environment. As a result, the research results cannot be directly applied to the field of civil engineering, but they provide useful references. Superior durability of FRP materials in a highly corrosive environment is an advantage of FRP over structural steel, but the history of FRP applications in civil engineering is relatively short. Although there are a large number of studies of performance degradation of FRP reinforced structures in a highly corrosive environment, most studies have been limited to apparent and macro-scale performance tests and predictions (Bencardino et al., 2006; Yang et al., 2008; Asaro et al., 2009), with no indepth study of the mechanism changes in the macroscopic properties, or the type of material and structure. In addition, the extreme conditions of service studied are also

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limited. Accelerated testing based FRP durability study (Chen et al., 2007; Karbhari and Abanilla, (2007) cannot fundamentally reveal the relationship between the experiment chamber accelerated environment and the real service environment. More than 20,000 hours of accelerated testing in the laboratory (Wu and Niu, 2007) have proved that FRP and its reinforced structure in highly corrosive environments (such as sea water, alkali, acid, etc.) have excellent durability, but longer-term performance (for example, more than 100 years) degradation mechanism and the behaviour of FRP in the actual highly corrosive environment are not clear. This makes the design for the durability of FRP in a highly corrosive environment become one of the key issues that circumvents a wider range application of FRP materials (Bakis and Nanni; 2001; Saadatmanesh et al., 2010; Bai et al., 2008a; Belarbi and Bae, 2007). Based on the similarity of the FRP material degradation mechanism, establishing a short-term acceleration-durability test combining with long-term monitoring method will be potential breakthroughs on long-term durability design of FRP and its reinforced large structures as shown in Figure 14 (Xian, 2008). Figure 12 Fatigue behaviour of hybrid FRP (see online version for colours)

max stress/tensile strength

110%

S=1.011-0.042logN

100% 90% 80% CFRP

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74% fu

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BFRP C/GFRP

50%

55% fu

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1

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5

6

Log of number of cycles（LogN）

Figure 13 Freeze-thaw behaviour of hybrid basalt and CFRP 1.2

Nomalized tensile strength

1.1 1.0 0.9 0.8

B C G B/C(1:1) B/C(2:1)

0.7 0.6 0.5

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Figure 14 Establishment of long-term performance prediction (see online version for colours)

Model correction

Accelerated laboratory experiments

Exposure experiments on real environment

The fire safety performance of FRP reinforced structures has been a great concern. Resin matrix of FRP composite has low glass transition temperature and may burn. And the performance of FRP rapidly degrades with temperature increasing from normal. Most existing codes/guidelines of FRP structures state that FRP in the fire has completely lost strength and stiffness (ACI 440.2R-08, 2008). However, in the study of fire resistance of FRP RC beams, columns, plates and other structures, the members after fire-resistant coating have met the stringent fire resistance rating requirements, such as up to four hours refractory limits (Kodur and Ahmed, 2010). Furthermore, after experiencing higher temperature than FRP glass transition temperature, the performance retention rate is more than 80% of their original capacity, indicating that the FRP reinforced structure has considerable safety attributes after the fire, as shown in Figure 15 (Cao et al., 2011) for the tensile strength and Figure 16 (Bai et al., 2008b) for the storage and loss modulus. The storage modulus of the composite material decreased, while the loss modulus increased, with increasing temperature. The rates accelerate when temperature is approaching Tg (the glass transition temperature determined by the peak point of the tandelta curve). However, when temperature exceeds Tg, the loss modulus starts to decrease. Figure 15 Tensile strength of BFRP tendons under elevated temperatures (see online version for colours) 112.29

1000

102.29

900

92.29

800

82.29

700

72.29

600

62.29

500

52.29 0

50

100

150

200

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250

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(%)

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Figure 16 Storage and loss modulus normalised by the initial values at 25°C for each specimen, and tan-delta curves in longitudinal direction for three different heating rates (°C/min)

For structural level, the FRP covered structures may have superior durability such as T-shaped basalt-carbon fibre-concrete composite beam (Figure 17). The hybrid BFRP and CFRP on the bottom of the girder can increase the stiffness and maintain ductility and the shear reinforcement by BFRP can achieve sufficient shear strength and lower the cost. The test results (Figure 18) illustrates that 1

comparison of results of several bonding methods, including wet bonding, dry bonding and pre-bonded gravel, shows that each bonding method can achieve good results, in which not only can wet-bonding approach obtain good results, but also facilitates the rapid construction

2

the composite beams have obvious secondary stiffness after yielding of the longitudinal reinforcement and the ultimate load are greatly improved

3

the hybrid of CFRP and BFRP improve the ultimate strain of CFRP, and the layers of BFRP are directly proportional to this effect.

As a result, the material utilisation efficiency is improved. In addition, the wet-bonding plus shear studs composite beams were also investigated, which shows not only reliable bonding of interface between concrete and FRP can be achieved, but also superior flexural behaviour under the static and cyclic loading can be realised. Although a great deal of efforts and innovations have been invested in using FRP for durable structures, there is still an urgent need for the development of fundamental theories and constitutive laws that can better explain the physical behaviour of FRP structures. Moreover, further investigations on fire resistant design of RFP structures (such as residual strength based model as shown in Figure 19) are needed. A systematic study of performance degradation, smoke generation, interface and overall guarantee of FRP materials and products under the fire are important research areas. Figure 20 shows the models of the decomposition process of resin in


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composite materials collected and compared with experimental data by Bai et al. (2007). Based on the decomposition degree calculated from the decomposition model, a temperature-dependent mass transfer model could be obtained. Considering that composites are a combination of two different phases (undecomposed and decomposed material), the volume fraction of each phase could be directly obtained from the decomposition model and mass transfer model. The temperature-dependent thermal conductivity could be then estimated by the series model. Based on these results, the temperature responses can be predicted by assembling these models of thermo-physical properties into the final governing equation of thermal response models. It should be noted however, that researchers have successfully attempted to control and optimise fire performance, high temperature, and freeze-thaw resistance of FRP composite (Bai et al., 2007; Cao et al., 2009) for the specific requirements of civil engineering applications. This provides a more active choice for the design of FRP reinforced structures under extreme environmental performance. Figure 17 Schematic of fibre profiles-concrete composite beam

FRP anchorage BFRP: shear reinforcement Stirrup Wet bonding with external resins

Tensile steel rebars

CFRP: tensile reinforcement (strength, stiffness) BFRP: tensile reinforcement (ductility)

Figure 18 The tests results of wet-bonding U shape FRP-RC beams (see online version for colours)

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Figure 19 Residual strength based prediction model for various FRP (see online version for colours) σ =

2

1 1 ⎡ (T − (Tg + ΔT / 2) )⎤⎥ + 2 (σ 0 + σ r ) ⎣ ΔT / 2 ⎦

(σ 0 − σ r ) tanh ⎢ −

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CFRP-1

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CFRP-2

100 Normalized tensile strength (%)

Normalized tensile stregnth (%)

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Tes t

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Model

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0

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Tem perature (ºC)

with Matrix II

Figure 20 Decomposition degree from own TGA tests compared with results from four different modelling methods

2.3 Performance evaluation of FRP reinforced structural system Performance evaluation of FRP reinforced structural systems under extreme loads/effects (earthquake, impact, and explosion) is also an important area that needs to be studied. FRP tube systems for seismic strengthening of concrete columns have been relatively matured (Priestley et al., 1996; Xiao and Wu, 2000). Hunan University recently conducted a research about performance design and reinforcement control methods of FRP RC under seismic loads and other damages, and established the relationship between different degree of damage and the strain of outsourcing FRP reinforcement layer. The results showed that FRP reinforcement can effectively improve ductility and energy dissipation capacity without changing the stiffness of the column of structure and can be


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used for major structural damage reinforcement design (Shan et al., 2006). But these findings are still limited when compared with the study of concrete structures (Park and Ang, 1985). It has been suggested (Cao et al., 2009) that for the use of FRP own elastic recovery properties, as well as secondary stiffness of FRP reinforced structure after steel yielding, the damage controllable design can be preliminarily validated as shown in Figure 21. In addition, some methods realising the concept of recoverability have been proposed as shown in Figure 22, but system design theory still needs further investigation. Figure 21 Schematic of damage controllable and recoverable structures (see online version for colours)

H Serviceability State

H max

No Repair Major Shaking

Moderate Shaking

H theoretica l Minor Shaking

Damage Controllable State Dilatory Repair

Second Stiffness

Hy

H(δ)

Ultimate State Dilatory Repair

Requiring Repair

h Ultimate Point

Proposed DamageControllable RC Structure

Normal RC Flexural Structure

Concrete Cracking

δ

Recoverability limit

Residual Displacement < h/100

Figure 22 Two ways realising structural recoverability (see online version for colours)

纵筋

Longitudinal reinforcement

Hybrid 配筋 FRP bar

Hybrid FRP bar： SFCB

Concrete 混凝土

OR HS steel bar/FRP bar

Common steel bar

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Figure 23 Test setup

Figure 24 Antiknock experiment on a concrete wall strengthened with FRP sheets (see online version for colours)

Scholars outside China have thoroughly studied antiknock properties of externally bonded FRP RC structures (Jerome and Ross, 1997). Test results have proven that the FRP reinforcing method can significantly improve the structural antiknock bearing capacity and the structural ductility. After 11 September event, man-made explosion damage and progressive collapse of the structure attracted especial attention, followed by research to improve the antiknock performance of civil construction and indicated that using FRP reinforcement are worth pursuing (Mosallam and Mosallam, 2001). Research on the dynamic properties of concrete is relatively mature in China, but antiknock impact study of FRP RC columns and steel pipe concrete has been only recently investigated and


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with a limited scope (test setup is shown in Figure 23) (Shan et al., 2007). Some preliminary experimental studies on concrete wall strengthened with FRP sheets show obvious advantage in antiknock compared with conventional concrete wall as shown in Figure 24.

3

Introduction of 973 Program

By focusing on the three key issues, discussed in Section 2.1 through 2.3, above, a National Key Basic Research Program (973 Project) was applied in 2011 by nine top universities and two major construction companies in China, including Southeast University, the Hong Kong Polytechnic University, Tsinghua University, Tongji University, PLA University of Science and Technology, Harbin Institute of Technology, Dalian University of Technology, Hunan University, Nanjing University of Technology, the MCC Building Research Institute Co. Ltd. and MBEC Co. Ltd. This project was finally granted in 2012, for which southeast university serves as the leading institution. 973 program focuses on the three key issues discussed above and plans to address the following three key scientific topics. 1

The statistical characteristics of FRP composite properties and FRP-reinforced structures, their fracture mechanism and the principles for the control of facture failure. This study encompasses the safety design of large FRP RC structures by considering multi-scale material properties of FRP, interface characteristics of FRP and concrete materials, the failure mechanism of large FRP RC elements, the size effect on the performance of components, ductility of large FRP reinforced structures as well as the overall stability of the system, and other important and relevant factors.

2

The laws of life-cycle temporal-spatial evolution and degradation of the performance of FRP composites and FRP-reinforced structures subjected to multiple environmental actions or extreme single environments. Creep and fatigue behaviour of FRP can be influenced by more parameters than that of structural steel, such as the brittleness of fibres and resins, the types of fibres, resins and their interfaces, the environmental and load coupling. There is a need to take full account of the above factors in particular, and the inherent complexities to reveal the fatigue and creep damage evolution laws of FRP and their reinforced structures in the long life cycle with multi-field coupling (such as high and low temperature fields, repeated or sustained load, corrosive environment fields, UV radiation fields, etc.).

3

The failure mechanisms and recoverability of FRP composites and FRP-reinforced structures subjected to extreme loadings. Major engineering structures during service may be subjected to extreme loads (earthquakes, explosions and travel impact, etc.). Such extreme dynamic and hazard loads will generate significant non-linear deformation and accumulation of damage. If structurally weak parts or critical components fail, that may cause the destruction of the surrounding components, which leads to the collapse of the entire structure and results in significant loss of lives and property. On the other hand, the recent earthquake disasters further show that although some major engineering structures do not collapse in the earthquake, but the traffic artery cannot be restored within a few days, and many buildings

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Based on the above three scientific topics, 1–3, the entire program is decomposed into five sub-topics as follows. By combining the achievements of five sub-topics, the three scientific topics are expected to be thoroughly understood and the final goal of high performance and longevity to be achieved. In the following the content of five sub-topics are listed and the corresponding Project leaders and organisations are introduced. 1

Fracture/failure control and probabilistic design of FRP composites and large FRP-RC structures This project focuses on studying the size effect of the FRP materials, will investigate the failure mechanism of large FRP RC elements and the influence of the FRP size effect on strength. Based on fully considering the discrete characteristics of the strength of FRP materials and FRP-concrete interface, are liability analysis will be utilised to establish rupture control and structural design theory for large FRP RC components, while local rupture, early detection and control mechanisms would also be developed. This project also plans to establish ductility control methodologies and related design approaches by using high strength characteristics and secondary stiffness characteristics of FRP.

2

Long life-cycle fatigue and creep characteristics and service life controllability design of FRP composites and FRP-reinforced structures subjected to multi-field coupling actions This sub-project focuses on investigating fatigue/creep damage evolution of FRP and its reinforced structure in multi-field coupling (high and low temperature field, circulation/sustained load, corrosion environment field, UV radiation field). It is expected this research should lead to the development of some fatigue/creep performance improvement methods based on surface treatment, resin-modified, hybrid design technology. It is also expected that this project would result in the development of fatigue life control mechanisms and design methods of FRP reinforced critical areas. Finally, it should establish a quantitative fatigue life prediction model and system design theory for FRP reinforced structures, and develop a professional software based on the life prediction model.

3

Performance of FRP composites and FRP-reinforced structures subjected to extreme environments as well as methods for performance control This sub-project is expected to reveal the micro/meso-scale performance degradation mechanism of FRP materials in a highly corrosive environment. It should lead to the development of an evaluation theory and methods for long-term performance of FRP materials in a highly corrosive environment, and should lead to the principles and methods for the performance control of high performance FRP materials under long-term service in highly corrosive environments. It is also expected that this project would reveal thermal matrix decomposition and failure mechanism of interfacial stress transfer of FRP under fire, and should establish fire damage analysis model of FRP reinforced structures.

State-of-the-art review of FRP composites for major construction 4

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Dynamic responses of FRP composites and FRP-reinforced structures subjected to extreme loadings as well as methods for response control This task focuses on revealing the characteristics of the interface between the FRP and other materials such as concrete or steel, studying mechanical properties and damage mechanism when subjected to dynamic loads for different strain rates, and would establish dynamic constitutive models considering different strain rates. It also focuses on the establishment of a hierarchical index system for seismic design and earthquake damage isolation and design methods. It should also lead to the establishment of antiknock and impact resistance design of FRP structural members, based on the concept of ‘partial sacrificial’ and ‘partial reinforced’.

5

Key technologies and their integration for the application of FRP composites in major engineering structures This sub-project will establish damage controllable composite column analysis and optimisation design methods for FRP cable suspension structures, FRP-concretesteel composite columns and FRP RC for high-rise buildings. It is expected this task should lead to the development of a series of critical applications, construction methods, standardisation systems and applications. It also focuses on the critical methods for the design of FRP reinforced and pre-stressed long-span bridges. Finally, it is expected that it would carry out the feasibility of the design schemes of a 2,000 m cross-sea cable-stayed bridge.

4

Conclusions

FRP reinforced structures for major constructions have broad application prospects. However, there are also a series of bottlenecks to be resolved. Research and engineering applications of FRP reinforced structures so far has laid the necessary foundation for the use of high performance FRP and longevity of major structures, however, the study of the failure mechanism, durability performance and life cycle design theory of large-scale FRP reinforced structures (especially under extreme loads and extreme environmental conditions) remains to be addressed. The project described in this paper intends to enhance the use of large-scale FRP component model tests and to develop advanced numerical simulation tools to clarify size effects and damage evolution under extreme load. Furthermore, the corresponding study of reinforced large-scale structures should reveal multi-scale deterioration mechanisms of FRP materials and reinforced large-scale structures and multi-field coupling effect. It is also expected this ongoing project would establish a reliable short-term accelerated durability test method for FRP reinforced structures, combined with long-term monitoring of the these structures for long-life application, and form the basis for the reliability design of FRP reinforced large-scale structures.

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Acknowledgements The authors herein acknowledge the scholars who were involved in the technical discussion of 973 Program (No. 2012CB026200) that resulted in these in the recommendations summarised in this paper.

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