Claudio Modena

Shear behavior of masonry panels strengthened by FRP laminates

Abstract The present experimental study, performed on brick masonry panels strengthened by Fiber Reinforced Polymer (FRP) laminates, was aimed to investigate the efficiency of an alternative shear reinforcement technique. A series of nine unreinforced masonry (URM) panels and 24 strengthened panels have been subjected to diagonal compression tests. Different reinforcement configurations were evaluated. Experimental results pointed out that FRP reinforcement applied only at one side of the panels did not significantly modify the shear collapse mechanisms (diagonal splitting) of the URM; while double-side configurations provided a less brittle failure and a noticeable ultimate capacity increase. Performances of the different reinforcement configurations are compared in terms of strength and mechanism of failure; finally, experimental results are also used to calibrate existing analytical formulations for ultimate shear strength prediction.

Fiber-Reinforced Polymer Shear Strengthening of Reinforced Concrete Beams: Experimental Study and Analytical Modeling

Fiber reinforced polymer (FRP) is used in many forms for strengthening reinforced concrete (RC), including side bonding, U-jacketing, and complete wrapping. This article reports on a study that investigated RC rectangular beams strengthened in shear with externally bonded U-wrapped carbon fiber-reinforced polymer (CFRP). The authors report on the complex failure mechanisms that characterize the ultimate shear capacity of RC members with transverse steel reinforcement and FRP sheets and show some mechanisms of interaction between the externally applied FRP sheets and the internal shear steel reinforcement with different static schemes. They note that this interaction is not considered in the actual code provisions but strongly influences the efficiency of the shear strengthening rehabilitation technique. The authors conclude by proposing an analytical model that allows the estimation of the interacting contributions to the shear capacity of the strengthened beams. This model is based on simplified hypotheses but can be used as a first step toward a comprehensive approach about the shear behavior of FRP-strengthened beams.

Repair and investigation techniques for stone masonry walls

Abstract The injection of appropriate grouts turns out to be a very valuable way to repair and strengthen stone masonry walls provided the materials (the existing and the new ones) are accurately controlled and selected, the technique is calibrated by means of preliminary in-situ injection tests and the efficacy of the injection, i.e. a substantial portion of the voids are filled, is ensured. As the experience demonstrates the fulfilment of the above issues requires, at the actual stage of knowledge, to classify masonry typologies and materials, and to put considerable investigation efforts, both in laboratory and in-situ. In this paper the state of the art is presented of a comprehensive research program which is cooperatively carried out since some years by the Polytechnic of Milan and the University of Padova, with the cooperation and the financial support of the Ministry of Research, CNR, the Ministry of Cultural Heritage, and occasionally of some industries (ITEA, ISMES). A methodology has been so far defined and implemented which is substantially based on three principal steps: (i) laboratory characterization of the materials sampled from the walls, and choice of grouts suitable for injection through an injectability test, (ii) injection on site of check points, (iii) control of the injection efficacy by flatjack test and survey of the penetration and diffusion of the grout.

Analytical Model for FRP Confinement of Concrete Columns with and without Internal Steel Reinforcement

The paper aims to contribute to a better understanding of the behavior of reinforced concrete columns confined with fiber-reinforced polymer (FRP) sheets. In particular, some new insights on interaction mechanisms between internal steel reinforcement and external FRP strengthening and their influence on efficiency of FRP confinement technique are given. In this context a procedure to generate the complete stress-strain response including new analytical proposals for (1) effective confinement pressure at failure; (2) peak stress; (3) ultimate stress; (4) ultimate axial strain; and (5) axial strain corresponding to peak stress for FRP confined elements with circular and rectangular cross sections, with and without internal steel reinforcement, is presented. Interaction mechanisms between internal steel reinforcement and external FRP strengthening, shown by some experimental results obtained at the University of Padova with accurate measurements, are taken into account in the analytical model. Four experimen...

Design choices and intervention techniques for repairing and strengthening of the Monza cathedral bell-tower

Abstract A presentation is given of the fundamental design choices and of the selection of the most appropriate materials and techniques which have been made for strengthening the Monza cathedral bell-tower, based on investigation and structural assessment carried out prior to and during the design process. The results of the experimental and numerical investigation will first be given in order to explain the reasons for the design choice.

Flexural Strengthening of Real-Scale RC and PRC Beams with End-Anchored Pretensioned FRP Laminates

External fiber reinforced polymer (FRP) prestressing offers the potential to be a useful technique in strengthening existing reinforced concrete structures and reinforcing new elements, particularly in bridges. This paper presents results of experimental testing of real-scale reinforced concrete and prestressed reinforced concrete beams strengthened in flexure with FRP laminates. Externally bonded FRP reinforcement was applied in different ways with different types of end-anchorage devices and, in some beams, prestress transfer. After characterization of the single materials, four-point bending tests were executed and crack pattern and failure modes were studied, with particular attention to the behavior of the anchorages, consisting of two types of mechanical devices. Experimental results in terms of load deflection response were then compared with the predictions of an analytical model, taking into account prestressing effects due to both internal strands and external FRP laminates, based on trilinear behavior characterized by section flexural crack initiation, steel yielding, and ultimate capacity. Findings show that the increments of ultimate capacity due to FRP strengthening vary according to many parameters. Mechanical anchor devices increased the ultimate capacity of the structural element, delaying end and/or intermediate delamination. The trilinear analytical model appears to describe the experimental behavior reasonably well.

In-Plane Behavior of Clay Masonry Walls: Experimental Testing and Finite-Element Modeling

Extensive experimental research aimed at defining the in-plane cyclic behavior of three types of load-bearing masonry walls, assembled with perforated clay units, and various types of head and bed joints was carried out. Experimental behavior was modeled with four types of nonlinear finite-element models. Both macromodeling and micromodeling strategies, implementing either isotropic or orthotropic material laws, were adopted. Two simplified criteria were proposed for calibrating the models, one for defining orthotropic properties starting from perforated unit geometry and the other for defining expanded unit and interface element properties in micromodels. The procedures adopted for model calibration established the reliability of various modeling strategies. Results allow some conclusions to be drawn about the reliability of diagonal compression tests for large unit masonry, the stress distribution and different behaviors of masonry made with different head and bed joints, and the influence of unit strength on the in-plane behavior of masonry.

Seismic Assessment of Complex Historical Buildings: Application to Reggio Emilia Cathedral, Italy

The definition of structural safety of a historical masonry structure is still a concept that is somewhat difficult to interpret. Whereas for new masonry structures, it is possible to have useful indications about their structural behavior, as the analysis turns to “historical” constructions such a task became increasingly more difficult. Furthermore, the needs of preservation of the historical, cultural, and architectural essence of the building in many cases contrast with the needs of providing the “adequate” capacity to its structure, especially in order to withstand the design seismic loads. The study presented in the article is related to the definition of a knowledge and safety assessment path , concerning masonry religious buildings with a monumental character. A complex building, the Santa Maria Assunta (Our Lady of the Assumption) Cathedral in Reggio Emilia (Italy), is studied in order to evaluate its structural behavior thus defining its seismic vulnerability, by using different investigation and analysis methodologies.

Structural Aspects of The Conservation of Historic Masonry Constructions in Seismic Areas: Remedial Measures and Emergency Actions

Preservation of historic buildings is a demanding task, especially in seismic zones, where vulnerable constructions can suffer severe damages and losses. The last earthquake that struck the Abruzzo region in Italy in 2009 caused a particularly extensive damage. Lessons learned by previous experiences and the knowledge acquired through researches allowed facing the first emergency period involving universities, civil protection, and the Cultural Heritage Ministry. The result of this collaboration was the survey and the realization of emergency interventions for thousands of buildings in few months after the earthquake, waiting for the definition and design of definitive solutions.

Fatigue tests on riveted steel elements taken from a railway bridge

Assessment of structural integrity and remaining life are essential tools for the management of ageing infrastructures, especially bridges. Compared to bolted or welded structures, little attention has been devoted to the fatigue assessment of riveted details. To fill this gap, extensive experiments are conducted on a short-span two-lane riveted steel-girder railway bridge near Sacile, Italy. In service since 1918, it was dismantled in 2006 and moved to a structural laboratory. Within a fatigue assessment framework, first physical and physical–chemical tests were performed, characterising the material properties; then, static, cyclic and fatigue full-scale tests were carried out. The experimental investigation allowed to test in particular the safe condition of the short riveted diaphragm connections of the bridge, and to compare the current fatigue design curves with experimental results. Moreover, the current practice to equate the fatigue behaviour of rivets to that of non-preloaded bolts proved to be a safe comparison.