Francesco Focacci

Structural Behavior of Arch Models Strengthened Using Fiber-Reinforced Polymer Strips of Different Lengths

The authors address the structural behavior of masonry arches strengthened through carbon-fiber-reinforced polymer (CFRP) strips at intrados or extrados surfaces and subjected to horizontal forces. The paper reports and compares results from experimental tests on 1:2-scale arches and from an analytical model that considers no-tensile strength, infinite rigid, and infinite compressive strength material. Under the assumption that the structure fails because of the formation of a four-hinge collapse mechanism, the model allows the calculation of the collapse load and the evaluation of the load-displacement diagram. The model is based on the equilibrium conditions and considers finite displacements. Results provide an evaluation of the dependence of arch structural behavior on the length of CFRP strengthening. In particular, the postpeak behavior is evaluated in the perspective of performance-based seismic design criteria, which regard the ultimate displacement as a key parameter for seismic capacity. The evaluation shows that, for the considered case study, an increase of intrados reinforcement length produces an increase of maximum load but a decrease of the ultimate displacement.

Effects of Thermal Loads on Concrete Cover of Fiber-Reinforced Polymer Reinforced Elements: Theoretical and Experimental Analysis

This paper analyzes fiber-reinforced polymer (FRP) reinforced concrete elements under thermal loads. Nonmetallic reinforcing bars present high values of transverse coefficients of the thermal expansion with respect to concrete; as a result, when temperature increases, tensile stresses occur within the concrete that may produce splitting cracks and, eventually, the concrete cover failure if the confining action is not sufficient. An analytical model is proposed to determine values of temperature increase corresponding to the first appearance of the cracking phenomenon and to the concrete cover failure. An experimental investigation conducted on concrete specimens reinforced with FRP reinforcing bars is described, and the results obtained are compared with theoretical predictions.

Fiber Reinforced Composites with Cementitious (Inorganic) Matrix

Fibre reinforced composite systems are increasingly used in civil engineering infrastructure applications for strengthening and rehabilitation of reinforced concrete (RC) structures. Composite materials represent a sustainable alternative to new construction because they allow for an extension of the original service life and therefore prevent demolition of existing structures. Promising newly-developed types of matrix that potentially represent a valid, sustainable, and durable alternative to epoxy, employed in fibre-reinforced polymer (FRP) composites, are the so-called inorganic matrices. Within the broad category of inorganic matrices, cement-based mortars have raised some interest in recent years. This chapter intends to highlight the potentials of this new category of fibre-reinforced composites as a viable alternative to traditional FRP systems. The latest advancements in this field and the new challenges that researchers will face in the future are presented and discussed.

A Study of the Fracture Process at the FRP-Masonry Interface: The Role of the Periodic Pattern of Bricks and Mortar Joints

This paper sheds light into the effect of the periodic pattern of bricks and mortar joints on the load-carrying capacity of the interface between fiber-reinforced polymer (FRP) composites and masonry. Two simplified cohesive material laws are proposed for the FRP-mortar and FRP-brick interfaces, which allow for the computation in closed form of a finite effective bond length Leff of the interfaces. The aforementioned simplified interfacial laws are employed to compute the load response of the FRP-masonry interface, and to obtain the interfacial shear stress, the FRP axial strain, and the slip profiles along the bonded length. The results indicate that length of the stress-transfer zone (LSTZ) of the FRP-masonry interface varies periodically as its location shifts with respect to the position of the mortar joints. Furthermore LSTZ can be different from the effective length of the FRP-brick interface and is influenced by the size of the bricks and mortar joints.

FRCM composites for strengthening of brick masonry arches

This paper examines the structural behavior of masonry arches strengthened at the intrados with fabric reinforced cementitions matrix (FRCM) composites. Textiles made of poliparafenilenbenzobisoxazole (PBO) and carbon fibers are considered. The experimental results are compared with those obtained on un-strengthened arches and arches strengthened with a carbon fiber reinforced polymer (C-FRP) composite. The tested arches are analyzed with the approach of the limit analysis of the collapse mechanisms.

Strengthening Historical Masonry with FRP or FRCM: Trends in Design Approach

Over the past two decades, composite materials, in forms of Fiber Reinforced Polymers (FRP), have been widely spread worldwide in the field of civil and monumental construction. Design guidelines and provisions were developed and provided by national and international institutions. In the last years, a new generation of materials, named Fabric Reinforced Cementitious Matrix (FRCM) were introduced as strengthening devices for concrete and masonry structures. Their application in the field of historical masonry has grown as a result of the recent Italian earthquakes. In this paper, starting from a retrospective on what has been done in recent years in the field of FRP applications, insights will be discussed for future research and applications of FRP and FRCM in heritage buildings. Some differences between FRP and FRCM materials will be highlighted, in terms of fiber-matrix interface and delamination mechanisms. The different micromechanical behavior in terms of fracture energy will be highlighted, and the macro-mechanical implications in terms of ductility will be pointed out, as a first attempt to quantify this complex problem. By considering the last innovative and pioneering applications of FRP/FRCM in heritage buildings, criteria for structural enhancement will be shown and discussed. This is done with a special focus on the ability, shown by these new technologies, to inhibit failure mechanisms in masonry artifacts.