Gian Piero Lignola

Structural Evaluation of Full-Scale FRP-Confined Reinforced Concrete Columns

The external confinement of RC columns by means of externally bonded fiber-reinforced polymer (FRP) laminates is a well established technique for strengthening and retrofitting purposes. This paper presents a pilot research that includes laboratory testing of full-scale square and rectangular RC columns externally confined with glass and basalt-glass FRP laminates and subjected to pure axial load. Specimens that are representative of full-scale building columns were designed according to a dated American Concrete Institute (ACI) 318 code (i.e., prior to 1970) for gravity loads only. The study was conducted to investigate how the external confinement affects peak axial strength and deformation of a prismatic RC column. The results showed that the FRP confinement increases concrete axial strength, but it is more effective in enhancing concrete strain capacity. The discussion of the results includes a comparison with the values obtained using existing constitutive models.

Nonlinear Behavior of a Masonry Subassemblage Before and After Strengthening with Inorganic Matrix-Grid Composites

Past experimental tests on a full-scale masonry wall with an opening evidenced the key role of the spandrel panel in the in-plane nonlinear response of the system. Recent seismic codes do not provide specific criteria to assess and to strengthen existing masonry spandrel panels with inorganic matrix-grid (IMG) composites. Numerical finite-element (FE) analyses are used to deepen the knowledge about the nonlinear response of masonry walls and the role of the IMG strengthening system. The comparison of experimental and numerical results contributes to the development of a simplified analytical model to assess the influence of the external reinforcement system on the in-plane seismic response of masonry wall systems. Some hints about the strengthening design that could change the failure mode from brittle shear to ductile flexure are given. Finally, a further enhancement of the IMG strengthening system is proposed to avoid the undesirable splitting phenomena attributable to compression forces and to exploit ...

Nonlinear Analyses of Tuff Masonry Walls Strengthened with Cementitious Matrix-Grid Composites

Previous experimental studies, conducted by some of the authors, on in-plane response of tuff masonry walls strengthened with an innovative cementitious matrix composite grid (CMG) system confirmed that the CMG system could satisfy basic design requirements such as compatibility with the tuff masonry support (i.e., in terms of good bond properties), reversibility of the intervention and strengthening effectiveness. However, very large scatter was found in the experimental outcomes. Micromodeling and some parametric analyses were adopted to understand the contribution of basic material (mortar, tuff blocks and CMG strengthening) and the effect of the workmanship defects on the structural behavior of a natural stone wall. In order to conduct the analyses, finite-element method models of the elements have been compared to experimental data and they were found to be in good agreement with the test data. Significant improvements of strength and in the postpeak response were achieved installing different layouts of the CMG system. However the strengthening intervention had a negligible influence on the initial stiffness of the walls and this means that it has a reduced impact on the behavior of the existing structure.

Nonlinear Analysis of Cross Sections under Axial Load and Biaxial Bending

Biaxial bending moments can reduce the cross section capacity in terms of both strength and ductility. In this paper, a method and an integration procedure is presented that specifically targets the analysis of cross sections under biaxial bending and axial load. The method is applicable to regular or irregular shaped cross sections of various materials internally or externally reinforced by mild steel, prestressing tendons, and fiber-reinforced polymers. Surface integration of meshed cross sections allows moment-curvature relationships to be computed using nonlinear constitutive relationships and three-dimensional interaction domains to be drawn. Iteration procedures and convergence criteria are proposed to rapidly solve the highly nonlinear problem. Numerical tests showed fast convergence of the algorithm and good agreement with experimental results elsewhere. Comparisons between the numerical outcomes and the simplified expressions available in the literature have been performed to indicate the current limits of the formulas in currently available design codes.

Numerical Investigation on the Influence of FRP Retrofit Layout and Geometry on the In-Plane Behavior of Masonry Walls

Unreinforced masonry (URM) structures have shown their vulnerability to major events like as earthquakes, severe wind, blast, and impact. The present work started from experimental programs available in scientific literature related to masonry walls made of clay or natural stone units. The finite-element method (FEM) was used to describe the global behavior of tested specimens in terms of shear/displacement curves, shear capacity, and cracking pattern. FEM, and particularly detailed micromodeling, was adopted as a numerical simulation tool for masonry walls. International design codes underline that some fiber reinforced polymers (FRP) dimensions (e.g., width, thickness, and spacing of FRP strips applied as external strengthening of URM walls made of different brickworks) may influence the global behavior of strengthened masonry. The present work, starting from experimental programs by other research groups, related to walls made of solid and hollow clay units as well as natural tuff units subjected to compression/shear loading aims at identifying the actual influence of those dimensions. Diagonal and horizontal strips were investigated. Different brickwork panels having the same FRP strengthening (quantity and geometry) showed different behaviors. Present outcomes highlighted that the influence of some FRP strengthening parameters (e.g., strip spacing) is not so meaningful if compared to FRP total amount even if the code formulations predict significant differences.

Seismic Strengthening of Masonry Vaults with Abutments Using Textile-Reinforced Mortar

AbstractInnovative materials and technologies have been developed to limit the effects of earthquakes on structures, and the use of composite materials has been shown to be effective in existing buildings. In view of this background, experimental tests can provide a contribution to the interpretation of available strengthening interventions. The results of experiments with an innovative strengthening system are presented herein. The strengthening technique used is based on a textile-reinforced mortar (TRM) system coupled with traditional strengthening approaches, and was applied to a type of full-scale masonry vault that is typically found in the roofs of religious buildings. The experiments consisted of several shaking table tests, both before and after the application of the strengthening system. The seismic behavior of the vault after strengthening was significantly improved. The instrumental response of the vault started to change before the initial visible damage, which only occurred when the peak gr...

Deformability of Reinforced Concrete Hollow Columns Confined with CFRP

Many reinforced concrete (RC) bridges with hollow section piers were built in Europe between the 1950s and the 1970s. These bridges are now in need of a seismic upgrade to improve their response under earthquake conditions. This paper reports on a study to investigate the upgrade and retrofit of existing RC piers with rectangular hollow cross section using fiber reinforced polymer (FRP) materials applied in the transverse direction. To study the behavior of rectangular hollow cross sections subjected to combined axial load and bending, 7 scaled specimens representing, in reduced scale, typical square hollow bridge piers were tested. The paper discusses the outcomes of the performed tests focusing on the analysis of cross section curvature, member deformability, specific energy, and model restraints. Results showed that the failure of hollow members was strongly affected by the occurrence of premature mechanisms such as compressed bars buckling and concrete cover spalling. The FRP confinement delayed these mechanisms, increasing strength and ductility.

Shaking table tests on a full-scale unreinforced and IMG-retrofitted clay brick masonry barrel vault

The recent earthquakes in Italy demonstrated the extreme vulnerability of historical and cultural structures. Masonry vaults, which represent artistically valuable elements of these constructions, have been recognised among the most vulnerable elements. Traditional vault retrofit methods, such as buttresses or ties, are still widely adopted. These retrofit methods prevent differential displacements between vault supports (e.g., abutments, masonry piers and loadbearing walls). However, the pier differential displacement is not the only vulnerability source for vaults, and in many cases, further retrofit interventions are needed. Innovative retrofit methods based on inorganic matrixes, such as IMG, are aimed to prevent hinge mechanism failures. Such methods are suitable to be applied on vaults already retrofitted using traditional methods. The knowledge of the seismic behaviour of a vault, once the differential displacement between the supports is prevented, can be crucial to the assessment of potential further vulnerabilities of vaults already retrofitted with traditional methods. However, a deep knowledge of vault seismic behaviour is still lacking from an experimental point of view. Indeed, to date, few dynamic experimental studies have been conducted. Therefore, to investigate the seismic behaviour of masonry barrel vaults, several shaking table tests were performed on a full-scale specimen before and after the retrofit interventions. The tests investigated the main seismic properties of the tested structure and clarified the cracking mechanisms and capacity improvement due to the retrofit interventions. A comprehensive overview of the main results of the experimental tests has been presented.

Analysis of RC Hollow Columns Strengthened with GFRP

Reinforced concrete (RC) hollow piers in bridges withstand high moment and shear demands ensured with reduced mass and lower stress on foundations compared with solid piers. Failure of hollow columns is typically affected by premature buckling of reinforcing bars and concrete cover spalling. At present, no guidelines are available for the design of their upgrade, and few research investigations can be found on hollow columns strengthened by using fiber-reinforced polymer (FRP) materials. This paper discusses an experimental program carried out on purely compressed RC hollow columns externally wrapped with glass-fiber-reinforced polymer (GFRP). Three specimens were tested: one specimen was unstrengthened and used as the benchmark; the other two specimens were GFRP-wrapped with different confining reinforcement ratios. Each specimen was designed according to dated codes (i.e., prior to 1970) accounting only for gravity loads. In particular, steel longitudinal bars cross section and steel tie-spacing were designed with the minimum amount of longitudinal reinforcement and minimum tie area at maximum spacing. Tests results highlight that the GFRP-jacket mainly provided ductility increases before low strength increments could be obtained. Refined and simplified numerical models for hollow square RC columns, previously proposed by the authors, herein extend to hollow rectangular members. Comparisons of experimental results and theoretical predictions on the basis of both refined and simplified confinement models were performed and showed good agreement. In the case of the simplified model, a value for the effective ultimate FRP strain was suggested.

Military Quarters in Nola, Italy—Caserma Principe Amedeo: Damage Assessment and Reconstruction of a Partially Collapsed XVIII Century Complex

A methodological approach is presented for the structural restoration of a highly damaged XVIII century building complex, the former military quarters, called Caserma Principe Amedeo, in view of their reutilization as House of Justice in the city of Nola, near Naples, Italy. The complex was designed by one of the most important architects that operated in Naples at that time: Ferdinando Fuga. Today the structure is extremely damaged with many parts being collapsed. In the reconstruction phase of the vaults, particular attention was paid to the formwork for the vault timbering matching the specific geometry of the existing vaults. This implied extensive and in-depth historical investigations on the construction techniques of that period to reconstruct the vaults following the design rules, the manufacturing techniques, and the materials of XVIII century in that area. A non-linear finite element analysis of the vault was performed with reference to the effective geometric and mechanical properties. The numerical modeling was validated by means of a real scale pilot vault tested on-site, and two tests on existing vaults. This investigation made possible the redesign of an architectural layout that appears to be neat and functional for the future building utilization. It was possible to restore construction techniques applicable to materials and geometries perfectly correlated to the original design. This restoration allows the reconstructed part of the building smoothly fading into the architectural equilibrium of the original structure.