•Non-linear 3D FE pushover analyses on eight existing masonry towers.•Preliminary modal analyses on complex 3D FE discretizations.•Comparison with simplified approaches suggested by Italian ...Guidelines on Cultural Heritage.•Utilization of elasto damaging 3D models for seismic vulnerability evaluation.•Comparative seismic analyses of masonry towers with different geometric features.
The seismic vulnerability assessment of eight historical masonry towers, located in the North-East region of Italy, is carried out by means of simplified approaches. Three-dimensional finite element models of the eight towers are created on the basis of geometrical data deduced from both existing available documentation and insitu surveys. First, preliminary eigen-frequency analyses are performed in order to obtain some basic information about the structural behavior of the different towers. Then, a simplified approach based on non-linear static pushover analyses is adopted for the seismic verification of the global performance of the eight towers. In order to avoid unnecessary complications due to the utilization of orthotropic damaging models requiring many material parameters, a damage plasticity approach is used for masonry. The essential aspects of the masonry material are reproduced with sufficient care, namely the very low tensile strength, damage in tension and crack-crushing in compression. From an overall analysis of the results, it can be observed that almost all the towers are able to resist the seismic action corresponding to Sag=0.1g, whereas the majority are unsafe at least along one geometric direction for Sag=0.2g. Finally, this study presents the evaluation of the seismic safety Index by means of the simplified sectional approach suggested by Italian Guidelines on Cultural Heritage. The collapse accelerations for the towers under consideration are compared and it is found that the results obtained with the different approaches are in a good agreement with a slight conservative trend for the simplified procedure proposed by Italian Guidelines.
•Hybrid base isolation of a historical masonry church.•Unbonded fiber reinforced elastomeric isolators and shape memory alloy wires.•Increase of the energy dissipation capacity.•Detailed 3D FE models ...to characterize the cyclic behavior of UFREIs.•Abaqus user element (UEL) to represent the 3D behavior of the isolators for global analyses.
One of the most promising devices for seismic base isolation of structures is the Unbonded Fiber Reinforced Elastomeric Isolator (UFREI) due to its low manufacturing cost and horizontal stiffness. This paper investigates the possibility of combining UFREIs and shape memory alloy (SMA) wires to increase the energy dissipation capacity of the isolation system for the seismic protection of a historical masonry church. Detailed 3D finite element (FE) analyses are performed to characterize the response of UFREIs under cyclic displacements. The behavior of SMA is simulated through a thermomechanical constitutive model implemented in a user-defined material (UMAT) subroutine available in the software package Abaqus. To reduce the computational effort in non-linear dynamic analyses of large isolated structures, an Abaqus user element (UEL) is developed to represent the 3D behavior of the isolation system proposed in this study. Non-linear dynamic time history analyses are then carried out to evaluate the seismic response of a historical masonry church in different configurations (fixed-base model and model equipped with different base isolation systems) for moderate and severe seismic intensity levels. Numerical results show that the damage observed in the masonry church can be considerably reduced through the insertion of UFREIs. The utilization of SMA wires with a specific pre-strain significantly increases the energy dissipation capacity of the base isolation system and decreases the horizontal displacements of the masonry church.
A series of simplified approaches are evaluated for their effectiveness to estimate the seismic vulnerability of historical masonry towers. First, collapse loads are evaluated on sixteen “idealized” ...benchmark cases with different slenderness and shear area. Both analytical and computational approaches are used, namely the analytical procedure proposed by the Italian Guidelines on the Built Heritage and pushover analyses conducted using the commercial codes UDEC and 3Muri. The sixteen towers are representative cases which can be encountered in practice. Their geometry is idealized into parallelepiped blocks with hollow square cross-sections, thus favoring the utilization of 2D approaches, beneficial to drastically reduce the effort required for repeated computations. In addition, a Monte Carlo MC upper bound limit analysis strategy is proposed, in order to have an insight into the possible failure mechanisms for the different cases investigated. Deliberately is avoided the introduction of any form of irregularity and they are supposed isolated from the neighboring buildings, to obtain results exclusively dependent from geometric features. Among all the possible collapse mechanisms, five of them are selected according to the probability of occurrence based on past earthquake experiences. Five million cloud points of collapse accelerations are obtained by carrying the height, slenderness and shear area of the idealized towers. The approach is very fast and allows identifying different regions where single mechanisms are active. The results are confirmed repeating MC simulations with a triangular FE upper bound limit analysis discretization of the idealized towers. A series of equations are provided in order to assist engineers and practitioners to obtain a preliminary estimation of their expected collapse acceleration. For validation purposes, the results obtained previously with refined full 3D FE models of 25 towers located in the Northern Italy are reported. Satisfactory agreement between the predictions provided by simplified methods and sophisticated analyses are obtained.
The goal of this paper is to analyze the aging behavior and the mechanism evolution of nano-Al2O3 (NA)-reinforced styrene-butadiene-styrene (SBS) asphalt under different thermal-oxidative aging ...conditions. First, NA/SBS-modified asphalt and SBS-modified asphalt with different aging levels were prepared. Second, the viscosity and high temperature rheological performance of the specimens were tested and the property-related aging indexes were calculated and compared. Third, a Fourier transform infrared (FTIR) test of the specimen was conducted and the chemical group-related aging indexes were calculated and analyzed. Fourth, gel permeation chromatography (GPC) was used to analyze the molecular weight of the specimens under different aging levels. Then, an atomic force microscope (AFM) was adopted to analyze the microsurface morphology of different specimens. Finally, correlation analysis between property-related indexes and chemical group indexes was conducted. The results show that NA can enhance the thermal-oxidative aging resistance of SBS asphalt. NA can inhibit the increase in sulfoxide groups and the degradation of the SBS polymer with the increase in aging. NA can slow down the formation of large molecule during the aging process. The degree of change in both the bee structures and micromorphological roughness of NA/SBS asphalt is lower than that of SBS asphalt under different aging levels.
•Failure analysis with advanced numerical FE computing on an outstanding historical palace.•Utilization of full 3D FE non-linear dynamic analyses to reproduce damage.•Comparison between non-linear ...static behaviour of a 3D model and equivalent frame.•Damage-plasticity with softening in tension and compression material used to model masonry.•N2 method to assess vulnerability after preliminary modal analysis.
The paper addresses the failure analysis under horizontal loads of the most ancient body of the National Palace of Sintra, Portugal: the Bonet building. This is a URM construction built on top of Arabic foundations during the reign of King Denis of Portugal around 1281; since then, few alterations have been made to the building. Due to the exemplary conservation of the whole palace, a few crack patterns are identified only on the top floor of the Bonet building, an area that is not open to visitors and that will soon undergo restoration works. The seismic vulnerability assessment of this building is carried out following two different approaches, enacted in two distinct numerical models: the so-called Equivalent Frame Method (EFM) and the Finite Element Method (FEM) developed in 3Muri and ABAQUS software, respectively. Both approaches adopt a numerical procedure based on the use of nonlinear static analyses, introducing “equivalent” boundary conditions that are defined to consider, approximately and conventionally, the possible interaction effects among the different parts of the structure. To minimize the multiple uncertainties usually existing in complex masonry buildings, whether related to geometry or masonry mechanical properties, a detailed structural survey is conducted through the laser scanning technology as well as in situ experimental tests. Different types of experimental tests are carried out, both non- and semi-destructive, including a Ground Penetrating Radar test, ambient vibration tests, flat-jack tests, and the collection of masonry samples. All these tests are important to adequately characterize the building and to calibrate the numerical models. Moreover, these tests enable the extraction of values for the mechanical properties of the rubble stone masonry that are used in the later numerical simulations on the Bonet building and, most importantly, can be used as a reference for future works regarding historical Portuguese monuments of the same period. Afterwards, the results obtained from the nonlinear static analyses with the two different software 3Muri and ABAQUS are presented and discussed. Specifically, the differences in modelling strategies and characterization of materials between the two software are considered with special regard to their feasibility, required computational effort, data availability and applicability to large scale structures. Efforts to calibrate and obtain the same behavior of the building for the different software are made, involving geometry, boundary conditions and characterization of the material constitutive laws. Eventually, a nonlinear dynamic analysis is carried out in ABAQUS to further assess the seismic vulnerability of the Bonet building; a spectrum-compatible accelerogram is applied to the numerical model, and the time-history of displacements in relevant control points of the buildings are extracted and discussed.
The renaissance bell tower of San Benedetto in Ferrara (Italy) has been investigated to understand its nonlinear dynamics correctly with the Non-Smooth Contact Dynamic (NSCD) method. The masonry ...structure has been modeled with the Discrete Element Methods (DEM), assuming rigid blocks and frictional joints, with the aim to recreate the tower in the actual configuration with the inclination and in a fictitious perfect vertical shape in order to assess the influence of the initial slope on its dynamics. The contacts between blocks are governed by the Signorini's impenetrability condition and by dry-friction Coulomb's law. Both configurations have been analyzed inducing real seismic excitations of various types and intensities, corresponding to the six main seismic events of the last few decades in Italy. Thus, the seismic vulnerability of the examined tower is clearly expressed in the numerical results, proving the effects due to the inclination on the amplification of the vulnerability and the several possible collapse mechanisms. Moreover, the NSCD has demonstrated to be a powerful numerical technique to obtain highly accurate results in the structural analyses of masonry structures in the nonlinear range.
► Dynamic non-linear analyses on 10 masonry structures in four seismic zones. ► Utilization of Rigid Body, Spring and Mass models (RBSM). ► Comparison with safety factors provided by Limit Analysis ...and codes of practice models. ► Influence of geometrical properties of the towers on the seismic response.
Ten existing masonry towers, located in the coastal Po Valley (Italy), are analysed in the presence of seismic excitations. They show some affinities which justify a comparative analysis: they are located in the same region and made of masonries having similar mechanical properties, and the majority of them are almost coeval. On the other hand, they exhibit different geometries (e.g. slenderness, thickness of the perimeter walls, height, percentage of perforations, etc.) which may be responsible for their different structural response to the same seismic excitations. Therefore, the aim of the work is to study the effect of the geometry on the seismic behaviour of such towers by assuming as mechanical properties for masonry the ones provided by the technical literature for existing towers in the coastal Po Valley.
Full non-linear dynamic analyses are performed by means of a specific Rigid Body and Spring Model (RBSM). This is based on a relatively refined 2D discretization obtained by assembling rigid quadrilateral elements interconnected by non-linear axial and shear springs, exhibiting softening and realistic energy dissipation under cyclic loads.
The geometry of the towers is deduced from both existing available documentation (cross-section, front and planar views) and in situ surveys. On the basis of such geometrical data an equivalent 2D mesh is built, where different thicknesses are assigned to adjoining elements, wherever necessary, in order to properly take into account the actual behaviour of the structure within a 2D approach.
Four artificial design consistent horizontal accelerograms are applied to the 2D models and the response in terms of collapse mechanisms and force–displacement histories are analysed in detail. Although this study is only a first attempt to analyse the relationship between some typological features of the chosen towers and the structural response they exhibit in the presence of seismic excitations, the results obtained and the comparative analysis that follows are enough to show clearly the strong dependence of the towers’ structural behaviour on their geometric characteristics (slenderness, base shear area, presence of belfry, big perforations, presence/absence of internal vaults, etc.).
The rubber material is widely used either for household or industrial needs. Since the prehistoric era, rubber has been involved in human life by exploiting the latex from specific trees. For ...elastomeric isolators, rubber pads have a central role. Damping performance is a prerequisite for isolation-bearing materials. Besides, the materials must have an excellent overall performance, such as high strength to resist damage. From a chemical point of view, it is paramount that the rubber used for assembling the devices is vulcanized correctly. It is crucial to determine the optimal vulcanization times and temperatures to properly create the polymer network and make the rubber capable of exhibiting good mechanical properties at large strains applied. All rubber mechanical properties are strongly affected by vulcanization. This study proposes a numerical model to predict the degree of vulcanization of a Fiber-Reinforced Elastomeric Isolator (FREI) made of a Natural Rubber (NR) – Ethylene Propylene Diene Monomer (EPDM) blend. The aim is to determine the optimal vulcanization time and temperature, taking the induction time into account, to obtain a homogeneous curing level distribution within the isolator.
The utilization of fiber-reinforced polymer (FRP) composites for building reinforcement has gained widespread acceptance. However, the bond behavior between externally applied composites and ...strengthened substrates, which are crucial for system efficacy, has primarily focused on flat surfaces. Yet, the challenge of curved substrates, common in masonry arches and vaults, remains less explored. This study introduces a classical analytical model addressing the bond behavior between FRP plates and curved substrates. This classical approach is structured upon a simplified model that concentrates all the non-linearities of the FRP–substrate interface. The interface is described through a universal multi-linear stress–slip relationship, with the influence of the curved substrate being considered by the normal stress that impacts the interface law. Closed-form solutions for distinct bond-slip law stages are derived and verified against the previous study. Through comparisons with existing experimental data and simulations, this approach is able to predict the maximum load, the trends of the global load-slip curves, and give insights into detailed local behavior. Additionally, the exploration of employing neural networks for determining the interface law exhibits promising outcomes.
In this paper the problem of seismic vulnerability of masonry churches is analysed with reference to the Nativity of Blessed Virgin Mary ecclesiastic complex in Stellata of Bondeno (Italy). This ...religious construction is composed of a church, two bell towers, a cloister and the Saint Domenico´s oratory. The church, made of masonry brick stones, is characterized by a single hall with chapels, which is divided into three parts by arches, and has an apse elevated by a few steps with reference to the hall. The study herein presented is carried out according to the Italian Standards and Guidelines on Cultural Heritage. In a first step, the seismic risk coefficients both at Damage Limit State (αDLS) and Ultimate Limit State (αULS) are evaluated by using the 3Muri calculation software for masonry structures. These coefficients indicate the ratio between the ground acceleration leading towards attainment of the two mentioned limit states and the PGAs of the site referred to a given reference return period. Afterwards, the variability of such coefficients is examined by changing both the masonry type and the seismic zone in order to detect the worst situations on the Italian land.
In a second analysis step a comparison among the seismic risk coefficients αULS and the damage index calculated through a fast method provided in a suitable form by the Italian Civil Protection Department is proposed.
Moreover, overturning mechanisms of facades are checked by using the 3Muri software with the ultimate goal to compare the predictive theoretical results with the real damages detected after the 2012 Emilia Romagna earthquake.
Finally, in order to obtain a more precise assessment of the seismic behaviour of the church under study, linear and non-linear dynamic analyses are performed on a 3D FEM model setup through the ABAQUS software package.
•The seismic vulnerability of the Nativity of Blessed Virgin Mary church is assessed.•The study is carried out according to the Italian Guidelines on Cultural Heritage.•Numerical analyses are performed by means of the 3Muri calculation software.•Overturning mechanisms of facades are checked under theoretical way.•Linear and non-linear dynamic analyses are performed through the ABAQUS software.
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