55 research outputs found
Assessment of the tensile behavior of twisted steel connectors for masonry retrofitting
No full textThe paper presents an experimental investigation on the tensile behavior of twisted stainless-steel bars considering
different parameters that could affect their performance, namely the bar diameter (8, 10, 12 mm), the embedment
depth, the position within the wall (installed into brick or in a T-mortar joint), the strength of the masonry
and the type of loading (monotonic or cyclic load). Experimental results showed very good performance
with reliable results associated to low coefficient of variation of the loads and very limited damage of the base
material. The load–displacement curves showed a good ductility, an excellent superposition between monotonic
and cyclic tests and an extended plateau at ultimate load. Among the different investigated parameters, the position
within the wall was the most influential one, with higher loads associated to mid-brick location of the bar.
Finally, based on the experimental results a user-friendly equation is proposed to predict the ultimate tensile
load
Seismic vulnerability and retrofitting of a historical masonry building
No full textThe paper presents the assessment of the seismic vulnerability of a historical masonry building located in Milan. After the identification of the mechanical properties by means of in-situ tests and Italian Technical Code indications, a finite element plate model has been implemented to analyse the dynamic behaviour of the building through a modal analysis. The masonry has been considered as a homogeneous material. The intermediate floors, realized with steel beams, did not match the requirements to be considered as rigid diaphragms. Therefore, they have been modelled as plates with appropriate thickness and stiffness. Even if the analysis results showed a good behaviour in terms of vibrational modes and participating masses, the introduction of new floors has been considered to guarantee a proper distribution of loads and improve the box behaviour of the structure. A modal analysis of the retrofitted configuration has been performed and the results compared with the ones of the initial configuration. The retrofitted configuration has been also studied using the equivalent frame approach. A nonlinear static analysis has been performed to evaluate the capacity of the structure and estimate the seismic risk index
Numerical approches for soil-structure interaction in a historical industrial masonry building
No full textDifferent numerical approaches were considered to investigate the possible causes of the structural damages detected in the masonry walls of an historical industrial building built at the beginning of the XX century in Italian Lombardia region; the building has a strategic role working as part of a drainage plant used for the reclamation of an extensive area close to the Po River. The structural analyses were performed with two different levels of complexity. In the first approach, structural finite element model and geotechnical one were implemented, independently. From the structural model, the forces transmitted to the soil are evaluated and applied to the geotechnical model. Consequently, the evaluated soil displacements are applied back to the structural model considering different boundary conditions: with fully restrained nodes, with base springs, and with imposed displacements. In such first approach the materials properties are linear. The second approach considered the implementation of a coupled model with both the building and the soil, modelled with solid elements having nonlinear properties. In the second approach, construction stage analysis was performed to evaluate the effects of the soil settlements occurred over time on the masonry structures and the foundation. A comparison between the results obtained by the two approaches is presented and the results are discussed to determine the causes leading to the cracks
A constitutive model for rubble masonry allowing for spread micro-cracks and localized macro-cracks
No full textStarting from a discussion on the experimental results obtained from diagonal compression tests executed on in-situ masonry panels, the paper presents a constitutive model, together with a numerical formulation, to describe the cracking phenomena in rubble masonry structures. A classical finite element discretization is assumed with the hypothesis of a homogenous continuum material. The adopted constitutive model identifies three different phases: (i) the elastic phase; (ii) the micro-cracking phase, in which the formation of microcracks, spread in the structural members, is accounted assuming a plastic material with a strain hardening stable behavior; (iii) the macro-cracks phase, in which the formation of macrocracks, developing along the edges of finite elements, are simulated by means of localized softening plastic deformation. While the numerical description of spread plasticity in the finite element framework is a topic that has been widely addressed in the past, the representation of localized plastic deformation and its implementation in a finite element code is an original contribution of the authors. From a computational point of view, the value of plastic deformations (i.e. crack openings) is found by solving a parametric linear complementarity problem (LCP) using mathematical programming algorithms. The main advantage of using an LCP method is its ability to deal also with configurations in which instability and a multiplicity of solutions are possible (e.g. softening behavior). The numerical simulation of a diagonal
compression test and the comparison of the results with the experimental evidence are presented to validate the model
Effect of size on the shear strength between old to new concrete interface
No full textThe retrofitting of the existing RC structures with added concrete layer crossed by post installed rebars is strongly related to the behavior of the interface between the new and the old concretes. The overall strength of the connection depends on several mechanisms such as friction and dowel action between the two concrete layers as well as the type of loading. In the past, attention was given to understand these mechanisms considering several types of specimens, usually characterized by small dimensions. Nevertheless, it is well known that size effect is often crucial in concrete elements. In this paper, with reference to a specimen geometry already employed for assessing the shear strength between old to new concrete interface, the influence of the size effect on the overall response is analyzed. Based on the results of an experimental campaign, a numerical model is adopted and validated. Therefore, specimens with three different dimensions were numerically analyzed to define the suitable specimen size
Analytical formulation for the design of steel reinforced plaster
No full textAmong the available techniques to improve the performance of existing masonry structures, steel reinforced plaster (SRP) is largely adopted to retrofit common residential masonry buildings. The adoption of the method is mainly due to its simple technology, which recurs to ordinary and cheap materials, associated with its high effectiveness. Even if several technical codes suggest it as a possible retrofitting intervention for existing masonry, satisfactory theoretical models to be used for the practical design are not available in the scientific literature. This paper proposes an analytical method to predict the strength of SRP-retrofitted masonry walls. The aim is to define a general design formulation, which considers the main parameters that affect the performance of the strengthened wall (e.g., thickness and mechanical properties of the plaster, number of connectors), to be used in daily structural engineering practice. The method was developed starting from a database of experimental results of diagonal compression tests conducted on unreinforced and retrofitted masonry specimens. The proposed formulation is able to approximate the experimental values with an acceptable level of accuracy, being on the safe side in most of the cases. It should be noticed that the experimental data used in the assessment process were limited to specific masonry types. For this reason, further experimental results should be acquired to extend the validity of the proposed method to other masonry base materials and confirm the good trend of the prediction model
Masonry retrofitting with steel reinforced plaster: experimental and analytical study
No full textThis paper presents the results of an experimental program aimed at assessing the effectiveness of steel reinforced plaster in improving the performance of masonry walls under cyclic loads, analysing the effect of the main design parameters. Diagonal compression tests were performed under displacement control. Unreinforced specimens were also tested as reference. The investigated parameters were: the masonry thickness (250 or 380 mm), the overlay thicknesses (30 or 50 mm), the type of mortar used for the overlay (cementitious or lime-based), and the number of connectors (8 or 12 for each side of the specimen). An analytical approach, previously presented by the authors, is recalled and further validated using the new experimental data, and a parametric study is performed to better discuss the effect of some design parameters. The results show that the load capacity of specimens retrofitted with lime-based plaster resulted at least equivalent to the one retrofitted using the most common cementitious one, and in some cases superior, with higher displacement at the ultimate load. Higher overlay thickness has a positive effect in terms of post-peak ductility for the cementitious plaster, and higher load bearing capacity for the lime plaster. An increasing number of connectors does not affect the ultimate load but results in a late detachment of the plaster layers. The analytical method results still valid by considering the new presented experimental data. The parametric study confirms that the strength and thickness of the overlay are crucial for the load bearing capacity of the specimen, while the number of connectors does not affect significantly the ultimate load
Experimental behaviour of full-scale C-wall under out-of-plane loading
No full textEarthquakes are among the major threats of existing masonry buildings, as proved by the damage recorded after recent seismic events. Out-of-plane failure mechanisms were often observed, which were strictly related to the lack of an effective connection between the load resisting elements. For this reason, the retrofitting interventions aimed to achieve a box-like behaviour of the building are of great interest. This paper presents an experimental campaign focused on the strengthening technique using fasteners to retrofit wall intersections. Full scale tests on masonry C-wall brickwork of solid clay bricks strengthened with twisted stainless-steel bars and bonded fasteners were executed. The unreinforced specimen was built with weak bonding at the two orthogonal wall intersection and out-of-plane loaded until cracking and corresponding load drop. After that, the cracked wall intersections were strengthened using the different fasteners, with deep embedment and different angles, bridging the cracks. Additional bars were used to stitch bending cracks on the front wall. The wall was cyclically loaded out-of-plane. The test results showed a significant increase both in load capacity and ductility which can be achieved depending on the type of fasteners used
Fragility curves for the seismic vulnerability of a stock of Italian highway bridges
No full textThe present study aims to analyze a stock of highway bridges of the Italian motorway network for the determination of analytical fragility curves, based on nonlinear modal pushover analyses. Fragility curves represent a valid and reliable tool for seismic risk evaluation and allow to correlate the probability of damage exceedance to the earthquake intensity, here represented through the peak ground acceleration. Fragility curves are fundamental in bridge management software to evaluate possible intervention scenarios and to schedule maintenance or retrofitting works by optimizing the economic resources. The obtained results showed a recurrent failure sequence: for increasing values of the peak ground acceleration, a shear failure of the pier is detected at first, followed by the bending failure of the base section of the pier and the unseating of the deck. Furthermore, the behavior in the transverse direction of the bridge results more critical, especially for long viaducts. The fragility curves were also compared with the ones presented in the scientific literature by other researchers for different bridge stocks. The curves result in agreement with the ones determined by other researchers with nonlinear static analyses, while they result conservative with respect to those determined with nonlinear time history analyses
Experimental behavior of fastener strengthened full scale T-wall
No full textRecent earthquakes showed the vulnerability of unreinforced masonry buildings as the integrity of the structures is often affected by insufficient resistance of wall interconnections. Due to this reason, many strengthening solutions aim to achieve a box-like behavior to improve the overall resistance of the building. This paper presents an experimental campaign focused on the strengthening technique using fasteners to strengthen wall intersections. Full-scale masonry testing on T-walls made of solid clay bricks using twisted stainless-steel bars and bonded fasteners as strengthening method was carried out. The unreinforced specimens were built with a weak connection at the orthogonal wall intersection and loaded out-of-plane until cracking and corresponding load drop. After the cracked wall intersection was strengthened using different fasteners with deep embedment bridging the cracks, the specimen was cyclically loaded out-of-plane. The test results showed that a significant increase both in load capacity and ductility can be achieved depending on the type and number of fasteners used
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