Strategies for structural strengthening in seismic areas with composite materials

The evolution of construction techniques, natural events of the past and innovation of knowledge and technologies allowed to improve the solutions adopted in structural design. At the moment it seems that the preservation of historical and strategic structures is the problem requiring new efforts in terms of research. Structures that were built in the past present a vulnerability against seismic events, due to old construction techniques, modifications of service conditions, degradation of materials or damage accumulated during the past. The use of composite materials such us Fibre Reinforced Polymers (FRP) for structural strengthening or retrofit of civil structures was studied since two decades. These materials usually present an epoxy matrix and a reinforcement phase which has the same length of the structural composite element, thus they are also called long-fibre composites. Several research studies and technical conferences furnished information to researches and practitioners. Design guidelines were also produced all over the world for the testing and design of structural strengthening with FRP composites. It is clear that research results and real applications improved in the last years, thanks to a widespread interest in this field inside the scientific community. Thus advantages and limits of the FRP-strengthening techniques may be considered well known, so the use of FRP with reference to a modern concept of structural design is ready to give reliable solutions. In the last decade an increasing interest was shown for cementitious composites (Fibre reinforced cements FRC) which include long and short fibre composites. Although the cement matrix has lower mechanical properties if compared to epoxy resin a proper use of FRC as strengthening material may improve the structural behaviour of deficient elements. In this paper the use of FRP and FRC is presented in order to show innovative solutions for the mitigation of seismic effects in civil engineering structures. A modern approach is followed, according to: the widespread knowledge in the field of FRP in civil engineering; a recent developed structural design concept in matter of seismic engineering. Structures will be considered as systems that are able to perform in terms of strength, stiffness and ductility, FRC and FRP composites will be considered as systems that are able to influence these three aspects of the structural behaviour. It will be shown that the use of FRP may increase the strength, without changing the stiffness and weight, but this is not always the solution required against seismic forces. An FRC system, in conjunction with FRP, may improve the seismic behaviour thanks to its dissipative capacity, which allows to have the required ductility necessary for the dissipation of seismic energy.