Composites in Construction: A Reality

Recent economic and social changes have affected the level of collaboration between research and industry. The role of Institutions and their decisions can be crucial in stimulating and promoting such relationships. This paper summarizes the presentation that the author made on the main programs and goals that the Regional Government of Campania is trying to achieve for local Universities and Research Centres. Its relevance for the academic world is that a new protocol in the relationship between University and Industry is proposed, which could also become a model to be implemented and improved upon in other countries. The author believes that the achievement of the fixed objectives and the development of similar political programs are key factors for the research of the next years and for the diffusion of composites in construction.

This paper covers the latest developments in the preparation of design guidelines, construction specifications, and inspection and quality control recommendations related to the use of composites in construction. The forms of FRP composites addressed are limited to bars and laminates for reinforcement of concrete and masonry structures (new construction and repair/rehabilitation). FRP bars are being used as the internal reinforcement in concrete members when the conventional steel bars may be undesirable for a host of reasons (e.g., corrosion), and principles for design and construction have been established and proposed to industry by the American Concrete Institute (ACI). Conversely, strengthening of concrete members with externally bonded FRP composites in the form of laminates or near surface mounted (NSM) bars can now be considered an "acceptable practice." Also in this case, the design and construction principles for use in practice are being finalized by ACI. The drivers for FRP strengthening technology are several, but perhaps the most relevant one is the ease of installation. On the wave of historical structures restoration projects conducted in Europe, there is an increasing interest in masonry-type applications even though no institution-sanctioned guidelines are available at present.

Nowadays, there is a considerable interest in FRP (fibre reinforced polymer) reinforcement and structural shapes for building construction. Especially, the use of FRP for externally bonded reinforcement (EBR) to repair and strengthen existing structures is becoming more and more established world-wide. Although much research has been done and many applications already exist in various countries, the lack of codes of practice incorporating advanced materials is still seen as a barrier for its more extensive use. In 1996 the International Federation for Structural Concrete (fib) established Task Group 9.3, with the objective of developing guidelines for the design of concrete structures, reinforced, prestressed or strengthened with advanced composites. In December 1997 the EU TMR Network, ConFibreCrete, has been established and operates in support of the fib Task Group 9.3. In this article an overview is given of the European guidelines proposed for the use of FRP in structural applications.

Fiber-reinforced polymers (FRP) are increasingly used in Singapore and the surrounding region, in particular in repair and strengthening works. This paper presents the current status and potential application of FRP in the region, and discusses the code-related issues, in particular design concepts. Suggestions for a unified code on the structural use of FRP are made.

This paper introduces briefly the Japanese codes and standards for FRP as reinforcement of new concrete structures and reinforcing material for upgrading existing structures. Some information on shaped FRP structural material is also provided.

An overview of the state of the FRP Rebar industry is given describing key milestones accomplished. Experiences of the author in terms of the construction, use and handling of GFRP bars are sited along with sales volumes in terms of lineal footage of GFRP rebar supplied. A discussion of the economics of GFRP rebar with specific examples from a bridge deck application noted as well as the successful implementation of GFRP rebar in the restoration of a dry dock at Pearl Harbor Hawaii. Future industry needs and barriers to further adoption of GFRP Rebar are discussed. Breakthroughs that would be beneficial to the composites industry in terms of infrastructure applications are expressed.

The state-of-the-art for applications of fiber reinforced polymers (FRP) in civil engineering is illustrated, highlighting the advantages achievable in the strengthening and static improvement of structures by using these innovative materials compared to traditional systems. Possible future developments in their applications are then discussed. Limitations, barriers, and problems to be solved for the diffusion of FRP materials in construction are also outlined.

This paper discusses issues relating to the use of composite materials for the construction of infrastructure projects. Some of the practical construction problems encountered in the field are presented in the context of a demonstration project built in Dayton, Ohio. In addition to site adaptation problems, field support by the composite deck panel manufacturers proved to be a very important aspect of the project. From a management perspective, new project delivery formats such as Design-Build (DB) contracts offer a framework for innovation and the use of new materials and techniques.

Fiber-reinforced polymer (FRP) materials have emerged as a practical alternative material for producing reinforcing rods and sheets for concrete structures. FRP reinforcing rods and sheets offer advantages over steel reinforcement in that FRP is non-corrosive and nonconductive. FRP rods include rods, grids and tendons for nonprestressed and prestressed concrete structures, respectively. FRP sheets are being used as external reinforcement for strengthening of existing concrete structures. Due to differences in the physical and mechanical behaviour of FRP materials compared to steel, unique test methods for FRP reinforcing rods and sheets are required. This paper provides test methods, which are being developed by ACI Sub-Committee 440K, and suitable test methods from ASTM standards, for determining physical and mechanical properties of FRP reinforcing rods for concrete structures.

Fiber reinforced polymer (FRP) reinforcements have some superior characteristics to steel reinforcements (especially they are non-corrosive), however, specific considerations may be needed for their behavior under long-term influences. Durability and time dependent mechanical characteristics of FRPs are essential parameters for design of concrete structures reinforced or prestressed with FRP. Based on an extensive literature review, present paper summarizes all aspects of FRP reinforcements considering durability (including effects of alkalis, chloride ions, UV radiation, water, elevated temperature and freeze/thaw cycles) as well as time dependent mechanical characteristics (such as creep, relaxation, fatigue) and their changes due to environmental effects.

This paper discusses the concrete environment and its affect on fibre-reinforced polymers (FRP) in terms of internal and external aggressive conditions that may affect its durability. The specific conditions considered are the effects of moisture, chlorides, alkali, stress, temperature, UV actions, carbonation and acid attack. The differences in performance between glass, aramid and carbon fibres and the polymers used to bind them have, where possible, been identified. However, higher variability in performance may be due to manufacturing techniques and details of some of the polymers and fibres tested are not disclosed in the literature. Notwithstanding the above, the potential degradation mechanisms are discussed with reference to internationally published research and some very general recommendations are given at the end of each section in an attempt to give some guidance to engineers when selecting FRP for construction.

Issues regarding the long-term durability of fibre reinforced polymer (FRP) strengthening and rehabilitation technologies are addressed. A brief overview of some recent research activities in this field is first presented. In particular, we discuss work related to performance in corrosive environments, applications in cold regions, and fatigue behaviour. On the basis of this review, some important needs for future investigation are identified. The importance of developing standardized accelerated laboratory test conditions, as well as of establishing appropriate field sites for calibrating results from accelerated tests, is emphasized.

Fiber-reinforced polymer (FRP) composite structural shapes and systems represent a significant opportunity to enhance national infrastructures through improved durability and by enabling rapid replacement techniques. We present an overview of the materials, component fabrication techniques, methods of analysis for stiffness and strength, component durability issues, and design codes and guidelines for these shapes and systems. The state-of-the-art is presented and suggestions for paths forward are outlined.

Fiber reinforced polymers (FRP) have recently been introduced into the construction market in various applications: rebars for concrete reinforcement, tendons for prestressed concrete, bolts for grouted anchors and more. In all the applications, the composite technology is used to produce a material that is as strong as steel, durable- with high resistance to aggressive environment, high strength to weight ratio and easy for handling and installation. Fibers of high properties, such as carbon, glass and Kevlar, are used for this purpose and together with a good polymeric matrix they can meet the above requirements. However, a weak link exists in the system that transfers the loads from the carrying fibers to the surrounding concrete, namely ‘bond'. In all the applications, the polymeric system at the surface of the rods is the one that transfers the loads between the two; therefore special demands are required from this system. An extensive study has been carried out in the last decade to establish the bond properties of FRP rebars and tendons as well as the load-slip relationship during pullout, effect of rod and tendon configuration on the bond, bond at the anchors and more. Part of this extensive study is covered by a review prepared by Cosenza et al., 1997, hence later data will be presented here. The understanding of these parameters can allow a better design of new FRP materials and accurate prediction of the behavior of reinforced and prestressed concrete members. The following paper presents a state of the art review on bond behavior of FRP rebars and tendons, the parameters affecting the bond with respect to rebars and tendon configuration, external parameters affecting the bond and models for bond behavior. Finally, points where lack of knowledge still exists and need further investigation in the future will be highlighted.

Among different compatibility problems for FRP the tensile strength reduction due to uneven stress distribution in elastic fibers is discussed. Uneven stress in fibers, not fully straight fibers, shear lag also accentuated by creep, influence the tensile strength. Fracture at tension and creep of hybrid fiber rods and rotation capacity of concrete members are discussed. For laminate type application the confinement efficiency decreases with increasing number of plies due to increased non-linearity of fibers. These problems are logical but not always notified in code clauses.

Both the flexural and shear capacities of reinforced concrete (RC) beams can be increased by bonding fibre-reinforced polymer (FRP) composites. A variety of debonding failure modes are possible in these strengthened beams, and for reliable strengthening measures, these debonding failures must be designed against. This paper provides a review of existing research on debonding failures in FRP-strengthened RC beams. Various failure modes are identified, and for each failure mode, existing research is summarised, with particular attention to studies on strength models. Issues which require future research are also outlined.

While significant advances in the development of cost-effective and durable fiber-reinforced polymer (FRP) composite systems for reinforcing glulam structures have been achieved, there is a need to address relevant material, processing, and durability issues. The objective of this paper is to present a performance-based material evaluation methodology for FRP-glulam structures. Challenges and opportunities in the development of hybrid FRP-glulam composites as structural materials are analyzed in the context of specific construction applications. The ongoing research effort will develop a set of simple and integrated material stiffness, strength, toughness and durability test methods with associated performance limits, and will provide data and recommendations necessary to draft performance-based material specifications.

In the field of fiber reinforced polymer (FRP) reinforced concrete (RC) structures most of the available research works relate to the flexural behaviour. This paper covers the main issues affecting the flexural behaviour of FRP reinforced members: the most significant experimental results obtained from several researchers are summarized and provisions reported by the international codes are discussed. Finally, some research needs are suggested.

The work reported in this paper reviews modifications to existing codes to incorporate Fibre Reinforced Polymer (FRP) reinforcement in reinforced concrete (RC) structures focusing on shear resistance. Various approaches are examined ranging from the first recommendations proposed by the Japan Society of Civil Engineers to the latest work published by the British Institution of Structural Engineers and the American Concrete Institute. The inadequacies of these approaches are exposed and a new approach developed at the University of Sheffield based on experimental work is presented.

This paper discusses a general design philosophy for strengthening of concrete structures with FRP, which is in alignment with the proposed ACI 440F recommendations. The goal of the paper is to convey the main FRP design issues and several cautionary remarks to the engineering audience in the US. The paper focuses on several ley topics: minimum required pre-strengthened strength criterion to prevent collapse if the CFRP system is compromised due to uncontrollable events (fire, impact, etc.); limits on strength enhancement to maintain "pseudo-ductile" behavior; and appropriate φ ("reliability") factors and limits on FRP design strength.

Reinforced concrete members may be strengthened in flexure through the use of fiber reinforced polymer (FRP) composites epoxy-bonded to their tension zones, with the direction of fibres parallel to that of high tensile stresses (member axis). In this paper the authors present an overview of the design approach for flexural strengthening using FRP, according to recent developments of the working group within fib Task Group 9.3 on externally bonded reinforcement (EBR). Both ultimate limit state (including full composite action as well as bond failure modes) and serviceability limit state aspects are presented. Moreover, some special cases are discussed briefly: strengthening of post- or pre-tensioned concrete members, EBR in compression and strengthening with prestressed FRP. Finally, recommendations for future work related to flexural strengthening are given.

Nowadays, there is a considerable interest in FRP (fibre reinforced polymer) reinforcement for building construction. Especially, the use of FRP for externally bonded reinforcement (EBR) to repair and strengthen existing structures is becoming more and more established world-wide. Since first applications in the late 1980s, the commercial use of externally bonded FRP reinforcement (FRP EBR) is currently increasing exponentially in many countries, its use can be regarded well documented and strengthening with FRP EBR is becoming a standard technique in a fast way. Although a majority of the applications deal with flexural strengthening, also a deficient shear capacity often occurs. Due to its flexibility, FRP EBR is very attractive for shear strengthening. As demonstrated by several researchers, the use of FRP EBR for shear and torsion strengthening is feasible and efficient. Different calculation models have been proposed, which are still subject to further verification.

Relevant issues regarding the behavior of concrete, either plain or reinforced, confined with FRP are presented. The paper describes the state of development of three research areas: experimental, analytical (modeling) and design-oriented. The achievements attained so far are recognized and the needs for further research and future advancements are indicated.

The aim of this paper is to discuss certain aspects concerning applications of FRP materials in strengthening historical masonry buildings. The discussion covers the objectives of the reinforcement and the design criteria. As FRP materials can be used in a number of ways for the structural strengthening of masonry buildings, it is impossible to consider all possible cases here; this paper discusses a few recurrent applications such as for strengthening masonry arches or barrel and cross vaults, the flexural and shear strengthening of panels, and the belting of buildings.

This paper deals with seismic strengthening with composites. A general overview on the basic concepts that drive the upgrade of structures located in seismic regions is provided; methods for improving their seismic performance or reducing the seismic demand are outlined. The discussion focuses on opportunities and reasons for using Fiber Reinforced Polymer (FRP) materials in the strengthening of both reinforced concrete (RC) and masonry structures. Possible local (i.e., columns, piers, beam-column joints) and global (i.e., frames and walls) applications are presented along with the most relevant conducted studies. Advantages of techniques utilizing FRP composites for the seismic upgrade of structures are summarized; limitations and needs to be solved and analyzed by future research are indicated.

The present paper summarizes the meaningful subjects of the structural behaviour of Fiber Reinforced Polymer (FRP) profiles. Material advantages are defined, underlining that it can be fruitfully used in infrastructure where durability is a controlling factor; many bridges have also been constructed designing specific shapes and systems. Three problems are analysed focusing the main points of each one: mechanical characterization, buckling and failure mode. References of experimental tests, modeling and design issues are discussed. The state-of-the-art shows many research needs especially due to the variety of products available in the market and the lack of general provisions for experimental tests and design.

Presented is an international perspective on analysis and design of bolted connections (no adhesive bonding) for structures of Pultruded Fiber Reinforced Plastic (PFRP) shapes and systems. It is observed that guidance in the manufacturers' design manuals has been written using in-house experience and technology transfer. The manuals are found to be limited and to give different guidance. Results of physical tests on single-bolted joints by academics are found to support parts of the pultruder's guidance. Advanced Ultimate Limit State (ULS) design (EUROCOMP Design Code relies on finite element stress analysis and failure analysis for one of the three distinct modes of net-tension, shear-out and bearing. Physical tests have shown that other failure modes (or combinations) exist and that, to design for Serviceability Limit State (SLS), there is ‘first' failure (initial material damage) at a load below maximum. Analysis by way of the finite element method is helping to determine how joint forces are distributed amongst a group of bolts and is starting to expose the local stress fields causing material failure and damage progression. Some observations are given on aspects of analysis and design that are priorities for future R&D.

The simple approach currently used to size the beams and columns of a number of small and large pultruded GRP braced frames is outlined. It is emphasised that frame design tends to be governed by serviceability and elastic buckling criteria, because of the flexibility of the GRP profiles and the assumption that all joints behave as if pinned. Semi-rigid design analysis is advocated as a rational alternative approach to frame design. It promises significant improvements in structural performance and lower costs. Recent research, which provides limited quantification of the potential benefits offered by the semi-rigid design approach, is cited. Finally, suggestions are made with regard to the experimental, theoretical/numerical and design research required for semi-rigid frame design to be adopted with confidence.

This paper was written at the conclusion of the International Workshop titled "Composites for Construction: A Reality," held in Capri, Italy, July 20–21, 2001. Its objective is to collect and summarize main ideas, opinions, evaluations, and proposals that emerged during the discussions held by the participants at break-up and general sessions. For simplicity, the reporting follows the order of such sessions and includes elements from the general sessions when applicable. The paper is intended to help professionals and scientists interested in the study and implementation of composites for the built infrastructure by providing a vivid snapshot of the state-of-the-art situation, opportunities, barriers, and needed research for the immediate future.