Marianovella Leone

Review Study on the Durability of FRP-Confined Concrete

AbstractThe use of fiber-reinforced polymer (FRP) composites has recently experienced a steep increase in civil engineering applications because of the high mechanical and low-density properties of such materials. Over the last few decades, concrete columns externally confined with FRP sheets have been widely investigated for their use in structural rehabilitation and the seismic strengthening of civil constructions. There is much scientific literature based on experimental results and analytical or empirical theoretical models. In fact, several numerical models and analytical procedures are able to predict the behavior of FRP-confined structural elements subjected to axial or seismic loads, and researchers worldwide have experimentally studied and analytically calibrated a wide range of significant variables. Nevertheless, there are still few results concerning the durability of FRP-confined concrete exposed to severe environmental conditions, despite being an important issue in design and safety assessm...

Modeling of the Behavior of Concrete Tension Members Reinforced with FRP Rods

The paper is devoted to the analysis of cracking and deformability of concrete tension members reinforced with fiber-reinforced polymer (FRP) rods. A theoretical nonlinear model, derived from a cracking analysis founded on slip and bond stresses, is adopted for evaluating the crack width, crack spacing, and elongation of tension members. The procedure takes into account the local bond-slip law, experimentally determined by means of pullout tests, and allows us to evaluate the influence of tensile stiffening. The analysis is performed with considering all parameters influencing the behavior of tension members, such as the concrete strength, the kind of FRP rebars, the surface treatment of FRP rebars, and the concrete cover thickness. The theoretical predictions are compared with available experimental results, obtained on cylindrical concrete specimens reinforced with carbon FRP (CFRP) rods, and with predictions of the traditional models usually adopted for design purposes.

Experimental Study on Bond Behavior in Fiber-Reinforced Concrete with Low Content of Recycled Steel Fiber

AbstractThe use of recycled steel fibers from waste tires as reinforcement in concrete matrix appears to be a promising solution, thanks to the performance of the material in terms of toughness and postcracking behavior. The main objective of this paper is to analyze the bond behavior of recycled steel fiber–reinforced concrete (RSFRC) and steel bars, and compare the results with those of industrial steel fiber–reinforced concrete (ISFRC). The paper focuses on the characterization of the mechanical properties of concrete reinforced with short steel fibers from waste tires and on the results of pull-out tests executed both on RSFRC and ISFRC. The experimental results, in terms of failure mode, maximum bond stress, and bond stress versus slip behavior are analyzed and discussed. Finally, a theoretical analysis of the bond-slip behavior was performed. The experimental results show that most of the known performance of the ISFRC can be extended to RSFRC. Referring to the bond performance, an improved behavior...

Concrete Reinforced with Recycled Steel Fibers from End of Life Tires: Mix-Design and Application

The manufacturing technology of reinforced concrete with the use of steel fibers to improve its mechanical properties is well-known and commonly used in civil engineering. Generally, steel fibers as discontinuous reinforcement of the concrete matrix are used to limit the cracking growth following the load application. Thus, the obtained concrete is characterized by an improvement of the typically brittle behavior of the ordinary matrix, mainly referring to toughness and post-cracking behavior. In this paper the results of a recent experimental campaign carried out at the University of Salento will be discussed. It was designed to study the optimization of concrete mixtures reinforced with recycled steel fibers from end of life tires (ELTs) to be used for the realization of precast panels. This experimental campaign is part of a wider research project aimed to validate the idea that the constituent elements of the ELTs, especially rubber and steel, can be effectively reused in concrete mixtures. Taking into account the high annual amount of ELTs generated around the world and their negative impact on the global environmental sustainability, the recovery of their constituent materials and their reuse as raw materials in different technologies, is certainly an excellent way for a sustainable development.

Influence of Masonry Infills on the Shear Forces of RC Framed Structures

The damages observed during the earthquakes occurred in the last decades have clearly shown as the influence of infill panels on the seismic behaviour of Reinforced Concrete (RC) buildings should be taken into account; the global stiffness and the strength of the RC frames are significantly modified by the infills. In the present study the influence of infills in terms of shear forces has been analyzed by means of linear static analysis; a parametric study has been carried out to evaluate the behavior of infilled frames varying both modelling approach and the mechanical properties of the masonry infills. In terms of modelling approach the single and multi-strut models have been adopted; the Young modulus of masonry infills have been varied in the common range proposed in literature. The results show that multi-strut approach is able to predict both global and local behavior. In addition, the importance of the mechanical properties of masonry infills in the evaluation of the elastic period and shear force in the columns is underlined.

The Mechanical Behavior of a Pin-Loaded Hole in a Thermoplastic Composite Laminate

The paper deals with the structural response of mechanically fastened fiber-reinforced laminated thermoplastic composite joints. An experimental investigation was carried out to analyze the behavior of single-pinned joints made with woven glass-reinforced polypropylene composite laminates. A detailed experimental analysis was performed in order to predict the bearing response, failure strength, and failure mode of composite laminates containing a pin-loaded hole. The results obtained allow one to evaluate the influence of geometric parameters and the stacking sequence of laminates on the behavior of such joints.

The Interface Behavior between External FRP Reinforcement and Masonry

The need to guarantee higher safety levels of masonry structures under both short and long term conditions, have led to the use of new materials and technologies, in conjunction or in place of traditional ones. In this context, fiber-reinforced composite materials have gained an increasing success, mostly for strengthening, retrofitting and repair existing structures. As well known, the analysis of the interface performance of FRP (Fiber Reinforced Polymer) composites and masonry substrate is a critical problem as it influences the effectiveness of the technique. The present paper reports part of a large research project, still in progress, focused on the analysis of the bond performance between FRP sheet and different type of masonry substrates. The obtained experimental data were analysed in terms of bond strength and the kind of failure. The influence of the deformability of the strengthening material as well as the mechanical performance of the substrates are also discussed.

Modeling of Masonry Vaults as Equivalent Diaphragms

Recent seismic events that occurred in Italy revealed the vulnerability of masonry buildings with vaulted roof with respect to horizontal forces. Assuming that a large part of the architectural heritage is made by vaulted masonry buildings, measures aimed at improving the seismic response of such structures is a strategic objective. In the present work the behavior of masonry vaults is modeled through equivalent plane element (diaphragm), and a modeling procedure is proposed for design. Different types of vaulted structural roofs were studied, considering geometries with simple and double curvature. An extensive parametric analysis was conducted by varying significant structural parameters: vault thickness, in-plane dimensions, constraint conditions and presence or not of side walls. In the proposed model the complex geometry of the vault is replaced by an equivalent plate, with the intent of modeling the entire building as a frame being equivalent to the real structural with respect to the seismic response. The equivalent plate is defined as an element generally orthotropic with the same in-plane dimensions and same thickness of the vault from which it is derived.

Experimental Analysis on Bond Behavior of GFRCM Applied on Clay Brick Masonry

External bonded reinforcements (EBR), made by fibrous meshes embedded in a cementitious/hydraulic lime mortar, are getting a great deal of attention, mostly for strengthening, retrofitting and repair existing structures. In this context, the interest versus the FRCM (Fiber Reinforced Cementitious Matrix) is growing. The mechanical performance of these mortar-based reinforcements is not well known at the date and it needs to be investigated in terms of bond and tensile strength, strain and stiffness, in relation to the type of both substrate and fibers. The present work reports the results of an experimental study, still in progress, on different pre-cured GFRP grids embedded in inorganic matrices and applied on clay brick masonry. First, the mechanical properties of both pre-cured GFRP grid and GFRCM reinforcements were obtained through tensile tests. Then, the experimental investigation on bond behavior was carried out by direct shear bond test. The test results were collected and processed to evaluate bond strength, failure mode, load-slip relationship.