Numerical study on the reduction of the seismic vulnerability of historical industrial buildings with wide timber roofs

In the paper are presented the results of a preliminary numerical study concerning the evaluation of the effectiveness of interventions for the reduction of the seismic vulnerability of buildings with traditional multiple sloping timber roofs laid on masonry walls along the building perimeter and on columns internally. In particular, the effects of three different strengthening strategies are analyzed: the bracing of the roof diaphragm by means of wooden-based nailed panels, the addition of steel portal frames and the reinforcement of the masonry through the application of a mortar coating with composite meshes embedded. To take into account the different interventions effects, a simplified numerical procedure, based on non-linear-static analysis, is proposed and a case study is analyzed numerically to compare, in terms of resistant ground acceleration, ag,res, the effects of the different reinforcement techniques. Typically, the absence of the roof diaphragm determines the out-of-plane collapse of the longitudinal walls, for very low seismic actions. The roof stiffening induces a redistribution of the seismic load from the longitudinal walls to the transversal ones; however, as they are not dimensioned for horizontal loads, very modest benefits emerged in terms of ag,res. The addition of two steel portal frames or the reinforcement of the walls with the reinforced mortar technique permits to reach values of the resistant acceleration considerably higher than that of the unreinforced configuration (1.91 and 2.73 times higher, respectively)

Experimental and analytical study to evaluate the effectiveness of an in-plane reinforcement for masonry walls using GFRP meshes

The 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

Masonry vaults subjected to horizontal loads: Experimental and numerical investigations to evaluate the effectiveness of a GFRM reinforcement

The paper investigates the effectiveness of a modern reinforcement technique based on a Glass Fiber-Reinforced Mortar (GFRM) for the enhancement of the performances of existing masonry vaults subjected to horizontal seismic actions. In fact, the authors recently evidenced, through numerical simulations, that the typical simplified loading patterns generally adopted in the literature for the experimental tests, based on concentrated vertical loads at 1/4 of the span, are not reliable for such a purpose, due to an unrealistic stress distribution. Thus, experimental quasi-static cyclic tests on full-scale masonry vaults based on a specific setup, designed to apply a horizontal load pattern proportional to the mass, were performed. Three samples were tested: an unreinforced vault, a vault reinforced at the extrados and a vault reinforced at the intrados. The experimental results demonstrated the technique effectiveness in both strength and ductility. Moreover, numerical simulations were performed by adopting a simplified FE, smear-crack model, evidencing the good reliability of the prediction by comparison with the experimental results

Masonry vaults strengthened with a GFRP reinforced mortar coating: evaluation of the resisting peak ground acceleration

The reinforcement of existing masonry vaults against seismic actions is an extremely timing issue and it has already involved many researchers in experimental testing and numerical modelling. However, up to now, the results of the research have been expressed and compared in terms of load-displacement capacity curves. But the designers, in the practice, need to assess the resisting peak ground acceleration of the vault (PGA), so to compare it with the seismic demand. In the paper, a strategy to evaluate this parameter, based on the modified Capacity Spectrum Method and accounting for the level of the vault in the building is proposed. The procedure is applied to a case study of a masonry building with barrel vaults, comparing the performances of plain vaults and vaults strengthened with a GFRP (Glass Fiber Reinforced Polymer) reinforced mortar coating. The results evidenced significant improvements in terms of PGA after the reinforcement, attaining to values from 3.1 to 3.3 times that of the unreinforced vault

Out-of-plane behavior of reinforced masonry walls: Experimental and numerical study

In the paper, the results of an experimental and numerical study on the out-of-plane bending effectiveness of a modern strengthening technique applied to existing masonry walls are presented. The technique consists in the application, on both wall faces, of a mortar coating reinforced with glass fiber-reinforced polymer (GFRP) meshes. Four point bending tests of full scale masonry samples (1000 width, 3000 mm height) were carried out considering three types of masonry (solid brick, 250 mm thick, rubble stone and cobblestones, 400 mm thick). The performances of plain and reinforced specimens were analysed and compared. It emerged that strengthened specimens are able to resist out-of-plane bending moments almost 4\u20135 times greater than those of plain specimens; moreover they can overcome deflections more than 25 times higher, due to the presence of the GFRP mesh, which contrasts the opening of cracks. The cracking and the ultimate bending moments of reinforced samples can be analytically predicted using relationships quite close to those used in the design of reinforced concrete beams subjected to combined axial and bending actions. The results of nonlinear static analyses performed on a 2D numerical model were also presented, so to comprehend the mechanical behaviour of reinforced masonry walls. Their agreement with the experimental results proved the reliability of the simulations; moreover, the extension of the 2D model to a 3D one, necessary to analyze the behavior of perforated walls, was also made

Characterization tests of GFRM coating as a strengthening technique for masonry buildings

Fiber 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

ENHANCEMENT OF THE SEISMIC PERFORMANCES OF HISTORIC MASONRY BUILDINGS THROUGH GLASS FIBER-REINFORCED MORTAR

The 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)

A strengthening technique for existing masonry based on FRP mesh reinforced mortar coating. Influence of the strength of the mortar

Many 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 \u3b2, which depends on strength and stiffness of the coupled materials. A characteristic curve for \u3b2 in function of the tensile strength of the \u3b2 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

Numerical Simulation of the Out-of-Plane Performance of Masonry Walls Strengthened with a GFRP Reinforced Mortar

The enhancement of the wall bending resistance is often required in historical masonry buildings especially in upper storeys or in the occurrence of high floors (4- 5 m). An innovative technique is the application, on both sides of the wall, of a GFRP mesh reinforced mortar coating. Experimental tests (four point bending tests) performed on 1x3 m unreinforced and reinforced masonry walls made of solid brick (250 mm thick), rubble stones (400 mm) and cobblestones (400 mm) specimens proved the effectiveness of the technique. Moreover, for the cobblestone masonry, a hybrid technique, which couples the GFRP reinforced mortar coating, on one face, and a stainless steel reinforced repointing on the other, was also investigated. This paper presents the results of a numerical study, carried out utilising a twodimensional nonlinear model so as to comprehend the mechanisms that intervene in the out-of-plane bending behaviour of reinforced masonry walls. The reliability of the numerical simulations was proved by comparisons with experimental results. A numerical parametric study permitted the investigation of the influence of the mechanical characteristics of the employed materials on the cracking and on the ultimate load

Studio numerico sulla resistenza a flessione fuori piano di murature rinforzate mediante intonaco armato con rete in GFRP

La necessit\ue0 di incrementare le prestazioni strutturali degli edifici esistenti in muratura soggetti ad eccitazione sismica richiede frequentemente anche un incremento della resistenza fuori piano delle pareti murarie. Una possibile tecnica di rinforzo consiste nell\u2019applicazione di un intonaco armato con rete in materiale composito di fibre di vetro lunghe in matrice polimerica GFRP (glass fiber reinforced polymer). Nell\u2019articolo viene presentato un modello numerico agli elementi finiti 2D che consente, mediante un\u2019analisi non lineare statica, di stimare le prestazioni fuori piano di pannelli murari rinforzati con tale tecnica. Il comportamento della muratura \ue8 stato ricavato da prove sperimentali di flessione fuori piano eseguite su pannelli non rinforzati. Sono inoltre state eseguite alcune prove sperimentali di trazione su campioni di intonaco rinforzato per stimare la rigidezza dello stesso sia prima che dopo l\u2019inizio della fessurazione in modo da valutare correttamente l\u2019effetto irrigidente della malta dell\u2019intonaco teso tra le fessure (tension stiffening). L\u2019affidabilit\ue0 del modello numerico \ue8 verificata mediante confronto con alcune prove sperimentali di flessione fuori piano condotte su murature rinforzate. Il modello numerico \ue8 stato quindi utilizzato per la simulazione del comportamento di alcuni esempi di pareti reali. Sono state messe a confronto le curve che esprimono l\u2019andamento del carico orizzontale (uniformemente distribuito) in funzione dell\u2019inflessione fuori piano della parete: l\u2019incremento di resistenza dato dal rinforzo \ue8 risultato da 4 a 6 volte quello della parete non rinforzata, a seconda del tipo di muratura considerata. Inoltre, tutte le pareti rinforzate hanno mostrato una capacit\ue0 di spostamento fuori piano massimo pari a circa 1/65 dell\u2019altezza