1,721,012 research outputs found
ENHANCEMENT OF THE SEISMIC PERFORMANCES OF HISTORIC MASONRY BUILDINGS THROUGH GLASS FIBER-REINFORCED MORTAR
No full textThe study investigates on the behavior of a strengthening technique for unreinforced masonry based on the application, on both the sides of the wall, of a 30 mm thick mortar coating with Glass Fiber-Reinforced Polymer meshes embedded. The effectiveness of this technique, called Glass Fiber Reinforced Mortar (GFRM), for the enhancement of both the in-plane and out-of-plane performances of masonry walls is proved through experimental tests and numerical simulations, which are here described and discussed in detail.
In particular, a contextualization of the study is presented in the introduction section (2), describing briefly the behavior of historic unreinforced masonry buildings subjected to seismic actions and evidencing the main critical aspects to be considered so to ensure an adequate safety against horizontal loads. Furthermore, an overview on the state-of-art in the field of reinforcement techniques for masonry structures is reported, focusing, in particular to modern strategies employing composite materials.
In section 3, the considered reinforcement method is described and the experimental results of different characterization tests are shown.
Section 4 concerns the in-plane behavior of GFRM reinforced masonry. The characteristic and the results of a wide number of diagonal compression tests carried out in laboratory field are presented and discussed. Some considerations on the influence of different parameters on the technique effectiveness, based on experimental evidences, are also reported. The tests permit to investigate on the reinforced masonry equivalent diagonal tensile strength, shear modulus and deformation capacity. Analytical formulation, based on the experimental findings, are then proposed to predict the stiffness and the resistance of reinforced masonry specimens; a simple numerical Finite Element model is elaborated so to check the influence of some parameters. At last, a preliminary study aimed to the evaluation, at the whole building scale, of the seismic performance improvement due to the application of the reinforcement is performed by applying a simplified modeling method (Equivalent Frame Method). The application of the modified Capacity Spectrum Method permitted to compare the performances of reinforced and unreinforced structures also in terms of maximum resisting ground acceleration.
In section 5, the out-of-plane behavior of GFRM reinforced masonry is investigated. In analogy with the approach adopted for in-plane behavior, the results of some experimental tests (four-point bending) on unreinforced and reinforced full-scale masonry samples of different types are presented and compared, allowing an evaluation of the technique effectiveness in terms of both resistance and displacement capacity. The interpretation of the results permits also to purpose simple formulations for the evaluation of the cracking and ultimate bending resistance of reinforced masonry walls. A numerical Finite Element model is then presented to simulate the experimental tests and perform a parametric analysis, varying the main masonry and reinforcement parameters (such as thickness, stiffness and resistance). Some typical configurations of masonry walls of historic buildings subjected to out-of-plane bending are also analysed numerically to evaluate the actual performance improvements. Moreover, the numerical model is applied for the numerical simulation of the behavior of unreinforced and GFRM reinforced masonry vaults subjected to horizontal loads acting in the transversal direction.
Each section ends resuming the respective contents and results. Moreover, the main findings of the study, the final remarks and the future developments of the research are summarised in the conclusion section (6)
SEISMIC BEHAVIOUR OF POST-AND-BEAM TIMBER BUILDINGS BRACED BY TIMBER SHEAR WALLS
No full textAn evaluation of the seismic behaviour of post-and-beam timber buildings braced with timber shear walls by means of numerical simulations performed with non-linear elastic analysis is presented in the paper. Three different structural configurations are considered: two storeys and three storeys regular buildings and two storeys non-regular in plan building. The dissipative capacities of the systems were localized in correspondence of the connections; their non-linear behavior was assessed experimentally, numerically or analytically. The results evidenced good seismic performances in terms of global ductility and resisting ground acceleration and evidenced a similar behavior for the three analysed buildings
Characterization tests of GFRM coating as a strengthening technique for masonry buildings
Full text linkFiber Reinforced Mortars (FRM) represents a promising technique for the in-plane and out-of-plane reinforcement of existing masonry buildings, coupling effectiveness with compatibility needs. The paper focuses on a technique consisting in the application on the masonry surface of a 30 mm thick mortar coating with Glass Fiber-Reinforced Polymers (GFRP) meshes embedded, presenting and discussing the results of several characterization tests (pull-out, lap-splice, bond and tensile tests) performed so to investigate on the tensile properties and bond performances of the strengthening system, useful for correct design procedures and suitable also for numerical modeling
Experimental and analytical study to evaluate the effectiveness of an in-plane reinforcement for masonry walls using GFRP meshes
Full text linkThe paper collects the results of diagonal compression tests to compare the in-plane behavior of unreinforced masonry (URM) and of masonry strengthen with a GFRP reinforced mortar coating. Experimental tests concern square wallettes of different masonry types and thickness; different mortars are considered for the coating. Significant increasing both in resistance and ductility emerges in reinforced masonry (RM). The principal tensile strengths are derived from experimental results and an analytical formulation is proposed for the RM resistance prediction. The formulation evidences that the contribution of the reinforced mortar coating is influenced by the characteristics of both the masonry and the reinforcement
Seismic performances and behavior factor of post-and-beam timber buildings braced with nailed shear walls
No full textA procedure to assess the behavior factor of post-and-beam timber structures based on the Capacity Spectrum Method is herein presented and the results of numerical simulations performed on three different building configurations, two and three storey buildings regular in plan and a two storey building non-regular in plan, are shown. The procedure assumes that the dissipative capacity of the structure is concentrated in the nailed connections of the components, whose non-linear behavior is derived by means of experimental tests. The results obtained, concerning the three types of buildings with three different proportioning criteria for the connections, are compared in terms of force–displacement capacity curves, global ductility, maximum resistant ground acceleration and behavior factor q. The global ductility ranges from 1.8 to 2.4. The values of the behavior factor q of the two storey buildings ranges from 2.4 to 3.8, depending on the shear redistribution amount among the shear walls; higher values (3.0–4.4) were obtained for the three storey buildings. Moreover, a nail distribution at each level according to the storey demand increases the dissipative capacity of the structure. The results of the study evidence that the maximum value of the behavior factor allowed in Eurocode 8 for timber structures with nailed shear walls and nailed diaphragms, connected with nails and bolts (q = 5) is in general not possible for post-and-beam timber buildings braced with nailed shear walls
Stress distribution among sheathing-to-frame nails of timber shear walls related to different base connections: Experimental tests and numerical modelling
No full textThe performances of nailed timber shear walls subjected to in-plane horizontal actions are numerically investigated in the paper. In particular, it focuses on the different behavior that the vertical diaphragm may perform if the wall base steel devices are connected to the timber frame with or without the interposition of the sheathing. Nonlinear static analyses were performed and the dissipative capacity is concentrated in the connections among the components (nails, hold-down, angle brackets, stud-joist node), whose behavior is calibrated by means of experimental tests and numerical simulations on connections. The reliability of the numerical model was proved by comparing the numerical results with the findings of five full-scale experimental tests performed on shear walls subjected to in-plane horizontal cyclic loads. It emerged that the different arrangements of the base connections influence significantly the distribution of the shear among the sheathing nails and, when the base steel devices are applied with the sheathing interposed and/or the panels are nailed to a base timber plate, the force distribution among the fasteners significantly differs from those suggested by the analytical methods proposed in the literature
Seismic enhancement of masonry buildings strengthened through GFRP reinforced mortar coating
No full textThe reduction of seismic vulnerability of existing masonry buildings through the application on the walls of a mortar coating reinforced with a GFRP (glass fiber reinforced polymer) mesh is studied and discussed. Numerous experimental tests, carried out by the authors, demonstrate
the effectiveness of this technique for enhancing the mechanical response of the walls, both subjected to in-plane and out-of-plane actions. In the study, the capacity curves of an existing unreinforced masonry building are compared with those of the same building strengthened with the GFRP reinforced mortar coating technique. An almost regular two storey building is considered in the numerical study and it is analyzed by adopting the method of the equivalent frame. Two different types of masonry are considered in the study: solid bricks and rubble stones. Static nonlinear analyses are carried out and the nonlinearity of the material of the wall elements (piers and spandrels) is considered through the introduction of plastic hinges in the plane of the masonry wall. The results evidence a significant increase in terms of shear resistance, displacement capacity and total strain energy. The collapse due to bending of piers in most cases of strengthened buildings occurred before than the ultimate shear drift was obtained
Rehabilitation of Masonry Buildings with Fibre Reinforced Mortar: Practical Design Considerations Concerning Seismic Resistance
No full textHistoric masonry buildings experience a high seismic vulnerability: innovative intervention strategies for strengthening, based on the use of fibre-based composite materials are gradually spreading. In particular, the coupling of fibre-based materials with mortar layers (Fibre Reinforced Mortar technique - FRM) evidenced a good chemical and mechanical compatibility with the historical masonry and proved to be effective for the enhancement of both in-plane and out-ofplane performances of masonry, contrasting the opening of cracks and improving both resistance and ductility. The resistant mechanisms that arise in FRM strengthened masonry walls subjected to inplane horizontal actions are analyzed in the paper and a practical design approach to evaluate their performances is illustrated, evidencing the dominant collapse mode at the varying of the masonry characteristics. Some masonry walls are analyzed numerically and analytically, as “case study”
A strengthening technique for existing masonry based on FRP mesh reinforced mortar coating. Influence of the strength of the mortar
No full textMany experimental tests were carried out on different types of masonry: solid brick masonry (different thickness), rubble stone masonry, cobblestone masonry, two-leaf brick masonry with very poor infill. The role of type of masonry mortar, type of reinforcement, number of connectors was also investigated.
The scope of the study was to check the influence of the resistance and the thickness of the mortar coating through a specific experimental campaign of diagonal compression tests. 16 different types of mortar, with tensile strengths ranging from 0.76 to 2.97 MPa, were considered.
The resistance of the reinforced masonry specimens is appreciably influenced by the mechanical characteristics of the mortar coating, but the dependence to each parameter is not known yet.
An analytical formulation for the calculation of the resistance of reinforced masonry was proposed: the summation of the unreinforced masonry resistance to that of the coating multiplied by a coefficient β, which depends on strength and stiffness of the coupled materials. A characteristic curve for β in function of the tensile strength of the β g coating was drawn: an exponential function with decreasing trend and with a horizontal asymptote at 0.8. For small thickness coating slightly better performances were found for equivalent reinforcement
Out-of-plane behaviour of masonry walls strengthened with a GFRP reinforced mortar coating
No full textA strengthening technique for masonry walls based on the application of a mortar coating reinforced with GFRP meshes was considered in the study, so to evidence its effectiveness for out-of-plane actions. The results of four point bending tests carried out on full scale masonry elements (1000 mm width, 3000 mm height) were presented and discussed. The specimens are made with three different masonry types (solid bricks, rubble stones, and cobblestones) and using lime and cement plaster. URM specimens were also tested as reference. The out-of-plane bending resistance was significantly increased (almost 5 times) and the mid-span deflection reached considerable values before the wall collapse (from 1/200 to 1/100 of the wall height). Results of plain specimens permitted the estimation of the flexural strengths of unreinforced masonry. The application of simplified analytical relations for uncracked and cracked sections lead to quite good predictions of first cracking and maximum resistances of RM
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