1,720,985 research outputs found
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
Full text linkThis 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
Fragility curves for the seismic vulnerability of a stock of Italian highway bridges
Full text linkThe 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
Seismic Vulnerability Evaluation of a Historical Masonry Tower: Comparison between Different Approaches
Full text linkThroughout the last few decades, the scientific community has paid great attention to the structural safety of historical masonry constructions, which have high vulnerability with respect to seismic activities. Masonry towers are very widespread in Italy and represent an important part of the built heritage to be preserved. Different numerical methods with different levels of refinement were developed in the literature to evaluate their seismic performance. The present study shows a practical application of the seismic vulnerability evaluation of a masonry tower using different approaches. The aim is to provide practical suggestions to engineers for the successful evaluation of the performance of masonry towers under seismic loads. An in situ survey was performed to characterize the geometry of the structure and its constitutive material. All the collected information was introduced in a building information model, later used to generate different finite element models for the structural analyses. The global capacity of the structure was evaluated using three different models with different levels of complexity: the first simplified model is made of beam elements with cross-sections discretized in fibers; the second model is made of shell elements and uses a concrete damage plasticity model to describe the nonlinear masonry behavior; the third model adopts solid elements with a concrete smeared crack constitutive law. A preliminary eigen-frequency analysis is performed on the shell model to obtain some basic information about the structural behavior. Nonlinear static analyses were carried out for each model to understand the response of the tower under seismic loads, highlighting the main differences between the approaches. The behavior factor was evaluated on the basis of the analyses results and compared with the ones suggested by the Italian building code. The results showed that the towers do not satisfy the seismic demand required by the standards for all the considered models. Furthermore, the behavior factor calculated according to the Italian design code is overestimated, while the one evaluated by the simplified model is underestimated due to the neglection of the shear behavior. From all the analyzed configurations, the shell model resulted as a good compromise between reliable results and computation efficiency
Cyclic behavior of masonry walls retrofitted with post-installed twisted bars or bonded rebars
Full text linkThe damage observed after the recent earthquakes showed that the most common failures for masonry buildings involve out-of-plane mechanisms associated to the ineffective connection between walls. For this reason, retrofitting techniques aiming to achieve a box-like behavior are of great interest. This paper presents the results of an experimental study conducted to investigate two different retrofitting solutions used to improve the structural connection between orthogonal walls: a mechanical connection by means of twisted bars and a fastening solution with rebars and injection mortar. Two full-scale T-shaped masonry specimens were realized in solid clay brick, with a “weak” connection between the front and the back wall. The specimens were tested in unreinforced and strengthened configurations, considering different retrofitting layouts. An out-of-plane load was applied on the front wall, together with a vertical prestress to simulate the gravity load coming from the floors and walls above. Each specimen was tested in three consecutive runs: a monotonic one on the unreinforced masonry, a first cyclic run with the wall intersection reinforced with twisted bars, and a second cyclic run on the wall retrofitted with rebars and injection mortar, after the removal of the twisted bars. The twisted bar solution resulted in a significant increase of the dissipative capacity of the wall despite the number of adopted bars, while, in the case of rebars and adhesive, a higher resistance was achieved together with a perfect box-like behavior
Diagonal compression cyclic testing of unreinforced and reinforced masonry walls
No full textSteel reinforced plasters (SRP) are a traditional strengthening solution of existing masonry structures. SRPs consist of a thin layer of cementitious mortar or concrete (jacket) that incorporates a steel reinforcing mesh tied to a series of steel bent connectors embedded in the underlying masonry. Despite the recent development of more innovative retrofitting methods, SRPs are still widely adopted because of their low costs and effectiveness in terms of improved performance. In the present paper, a comprehensive experimental program on brickwork masonry walls is presented. The results are intended as a contribution to the knowledge of in-plane behavior of masonry strengthened with SRPs. Unreinforced and plastered masonry walls were subjected to cyclic diagonal compression loading under displacement control. Different thicknesses of walls (2 and 3 wythes) and plasters (30 and 50 mm) were selected. The performances of the plastered and non-plastered specimens were analyzed and compared. The results showed that the SRPs increased considerably the performance of the walls in terms of both strength and deformation capacity. The plaster's thickness had limited effects on the load carrying capacity of the walls, whereas it had a significant effect on their ductility. Finally, the connectors used to tie the steel mesh to the masonry walls played an essential role and avoided large out-of-plane displacements of the plaster layer after its detachment, thus preventing instability phenomena
Cyclic behavior of C-shaped masonry wall retrofitted with twisted bars or bonded rebars
Full text linkThe lack of effective connection between masonry walls is one of the most common reasons leading to the activation of out-of-plane failure mechanisms in masonry buildings during earthquakes. Thus, retrofitting interventions aimed at improving the box-like behavior of masonry structures are of primary importance. The paper presents the results of an experimental program aimed at investigating the effectiveness of two different fastening solutions to improve the joint connection of masonry walls in existing unreinforced masonry buildings. A full scale C-shaped clay brick masonry specimen was built featuring purposely weakened wall intersections. Vertical prestress was applied on top of the specimen to represent the weights of upper floors. The specimen was first tested in the unreinforced configuration under monotonic out-of-plane displacement, until a main crack was detected. Then, its corner connections were repaired using twisted bars, and tested under cyclic out-of-plane displacement. Lastly, the twisted bars were removed and replaced with bonded bars, and the specimen was tested again under cyclic out-of-plane displacement. The test results showed that both retrofitting solutions were able to recover the full capacity of the unreinforced wall, with higher displacement and dissipation capacity for the twisted bars solution, and higher resistance for bonded bars. The latter seems to be the most effective solution, especially in terms of monolithic behavior achieved; however, the large displacements associated to twisted bars could be a great advantage in case of earthquake actions
The new foundation system of the Basilica di Collemaggio's transept
No full textIn the seismic retrofitting of historical churches, the realisation of new foundations of collapsed elements represents an important aspect for the interaction with both the underground pre-existing structures and the new structural elements to be rebuilt. For the specific case study of the Basilica di Collemaggio, after an accurate geometrical survey and onsite geotechnical tests, a specific mixed structure foundation system is proposed in order to fulfil the seismicsafety requirements and the Cultural Heritage Office's conservation prescriptions. Nonlinear analyses are performed considering the interaction between the soil and the foundation system, together with the new couple of main pillars and the triumphal arch. The analyses are aimed to verify the capabilities of the new foundation system to bear the transversal seismic actions. The analyses are also completed by some experimental tests on micropiles, which represent the main underground-to-elevation connection elements
Experimental Behaviour of Fastener Strengthened Full Scale T-wall Under Out-of-Plane Loading
No full textRecent earthquakes have demonstrated the vulnerability of unreinforced
masonry buildings as the integrity of the structures is often affected by
insufficient resistance of wall interconnections. Regarding the large share of masonry
structures in the existing building stock, strengthening solutions increasing
their seismic performance to achieve a box-like behavior are of highest relevance.
This paper focuses on the strengthening technique using fasteners to strengthen
wall intersections. Although the general technique is widely used, no detailed
design approaches are available in scientific literature or codes. In order to fill
this gap and support designers in their daily work, an experimental campaign on
full scale masonry T-walls made of solid clay bricks using mechanical and
bonded fasteners as strengthening method was carried out to develop a design
concept, also considering recent developments in seismic qualification and design
of fastenings to masonry. The specimens were built unreinforced with a
weak connection at the orthogonal wall intersection and loaded out-of-plane until
cracking and corresponding load drop. After that, the cracked wall intersection
was strengthened using different fasteners with deep embedment bridging the
cracks and 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. The paper presents the main experimental
findings
Numerical investigation on pull-out behavior of twisted steel connectors for masonry retrofitting
No full textTwisted steel bars are often used to strengthen masonry buildings and, in particular, to improve the transverse connection between different structural elements. The performance of the retrofitted structure depends on several parameters such as the mechanical properties of the base material (masonry), the bar diameter, the pre-drilled hole diameter. The paper presents the numerical assessment of the tensile behavior of twisted stainless-steel bars installed in brickwork masonry. Nonlinear numerical models in Abaqus software were developed and validated on the basis of experimental results, considering different bar diameters (8, 10, 12 mm). A parametric study was conducted to examine the factors that could influence the performance, namely the embedment depth, the pre-hole diameter, and the mechanical properties of the base material. The outcomes reveal the sensitivity of the twisted bars to the aforementioned parameters. In particular, the twisted bars exhibited a higher capacity in stiffer base materials, with longer embedment and smaller pre-drilled hole. However, none of the above parameters proportionally affect the ultimate strength, but lead to a limited improvement in the ultimate capacity (up to 40% in the considered range)
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