The influence of the geometrical features on the seismic response of historical churches reinforced by different cross lam roof-solutions

Recent Italian earthquakes have shown the seismic vulnerability of many typical historical masonry churches characterized by one nave and wooden roofs. Under transverse earthquake, the nave transverse response of this kind of churches can be influenced by the geometrical and material features. To increase the seismic performance, strengthening interventions aimed to pursue the global box-behavior by the realization of dissipative roof-structure represent a valid strategy, especially to avoid out-of-plane mechanisms. In this way, the roof structure must be able to represent a tool for the damped rocking of the perimeter walls. Cross-laminated timber (CLT) panels with calibrated metal connections have been recently adopted in experimental tests as a valid solution to obtain a roof-diaphragm with ductile behavior, satisfying the conservative restoration criteria at the same time. In this paper, after a description of the numerical approach for the damped rocking mechanism for one nave configuration church, the effectiveness of different CLT based roof-diaphragms in the nave transverse response is investigated for four historical churches. The seismic responses are performed by comparative dynamic nonlinear analyses and the results are shown in terms of displacements and shear actions transferred to the façade. The influence of the geometrical features of the churches on the nave transversal response is deepened by sensitivity analyses with the aim to predict the displacements and shear variations under the same earthquake excitation

The use of fly ash in high strength concrete mix design

In this paper the use of fly ash for particular High Strength Concrete (HSC) realizations is investigated. The use of fly ash as a partial replacement of Portland cement in HSC seems a valid solution in particular for a sustainable construction design, considering the interesting HSC performances and the economic aspects. Obviously the advantages demonstrated for the underground constructions can be also evaluated for the structures in elevation. In this paper the most important technical regulations about the use of fly ash for the concrete mix design are discussed and it’s shown the increase of the mechanical resistance and the better protection against the chemical agents attacks and against the freezing and thawing cycles using fly ash. Moreover, in comparison to the fresh concrete, it’s presented the benefits related to the minor ratio water/cement (defined by w/c) in the same conditions of workability. Additional considerations are carried out about the hydration process: the mixture produces less heat for the lowering of the C3A and C3S percentages using fly ash. Finally, a greater concrete impermeability obtained using fly ash, due to the presence of a lower hydrolysis content, which leads to an increment of the cement paste porosity, has been evidence

The advantages of fly ash use in concrete structures

In this paper the use of fly ash for particular High Strength Concrete (HSC) realizations is investigated. The use of fly ash as a partial replacement of Portland cement in HSC seems a valid solution in particular for a sustainable construction design, considering the interesting HSC performances (in terms of strength and durability) and the economic aspects (in terms of waste material's reuse from industrial process). Fly ashes have been employed in the past especially for underground structures. Nowadays, their use is under evaluation also for elevation structures. In this paper, the most important technical regulations about the use of fly ash for the concrete mix design are discussed. The increase of the mechanical resistance, the better protection against chemical agents attacks and freezing - thawing cycles using fly ashes are also show. Moreover, in comparison to the fresh concrete, the benefits related to the minor water/cement (w/c) ratio are presented, in the same workability conditions. Additional considerations are carried out about the hydration process: the mixture produces less heat for the lowering of the C3A and C3S percentages using fly ash. Finally, a greater concrete impermeability obtained using fly ash, due to the presence of a lower hydrolysis content, which leads to an increment of the cement paste porosity, has been evidenced. All of mentioned benefits shows the fly ash use in the High Strength Concrete (HSC) is a valid solution against many problems interested negatively the concrete mix - design and the mix - production

Construction Stage Analysis for a New Mixed Structure Building in Milan

In this study the Construction Stage Analysis (CSA) of a new mixed structure building is discussed in order to identify the best timing and execution activities scheduling. The building is part of a new university campus that will be realized close to the center of the city. The CSA is carried out by the implementation of two models: the finite element model for the structural analyses and the BIM model for controlling the sequence of the construction phases. Once fixed the structural model, in the preliminary design phase, different sequences are analyzed in order to optimize the construction management in terms of timing and costs. Moreover, the optimization of the construction phases is set by considering the creep and shrinkage of the concrete material

Seismic Vulnerability Evaluation of a Historical Masonry Tower: Comparison between Different Approaches

Throughout 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

Vulnerabilità sismica di viadotti autostradali

Negli ultimi anni la comunità tecnico-scientifica ha rivolto un interesse crescente nei confronti delle tematiche inerenti alla valutazione della vulnerabilità sismica delle costruzioni esistenti. In quest’ampio panorama spiccano, per importanza strategica e complessità tecnica, i viadotti della rete autostradale. La maggior parte di questi manufatti è stata realizzata tra gli anni ’60 e ’70 con approcci progettuali che ignoravano le attuali conoscenze nel campo dell’ingegneria sismica. Pertanto, è emersa la necessità di indagare con moderne tecniche di analisi le effettive capacità resistenti di queste strutture, traendone conclusioni circa il loro livello di sicurezza in occasione di un terremoto. Nell’applicazione sistematica a più manufatti di una rete, è stato adottato un approccio basato sull’analisi “pushover” multi-modale che permette di tenere in conto sia il comportamento non lineare, dovuto ai complessi fenomeni di ridistribuzione delle azioni che avvengono in campo post-elastico, sia la complessità della risposta dinamica del sistema, dovuta alle diverse forme modali significative della struttura. A tal proposito, si è implementata una routine automatica che, appoggiandosi ai risultati ottenuti dal software FEM, esegue in automatico le combinazioni modali e le verifiche degli elementi costruttivi, riducendo in modo considerevole i tempi di lavoro e garantendo un maggiore controllo dei risultati. Gli indici di rischio così ottenuti vengono riassunti in opportune schede di analisi di vulnerabilità sismica (fornite e raccolte dalla Protezione Civile)

Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector

This paper presents a measurement of b-jet production in Pb+Pb and pp collisions at sqrt(s_NN)=5.02 TeV with the ATLAS detector at the LHC. The measurement uses 260 pb^{−1} of pp collisions collected in 2017 and 1.4 nb^{−1} of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti-kt algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters R=0.2 and R=0.4, and only R=0.2 jets are used in Pb+Pb collisions. For comparison, inclusive R=0.2 jets are also measured using 1.7 nb^{−1} of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, R_{AA}, is calculated for both b-jets and inclusive jets with R=0.2 over the transverse momentum range of 80-290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet R_{AA} to inclusive jet R_{AA} is also presented and suggests that the R_{AA} for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions

Measurement of muon pairs produced via γγ scattering in nonultraperipheral Pb+Pb collisions at sqrt(s_NN)=5.02 TeV with the ATLAS detector

Results of a measurement of dimuon photoproduction in nonultraperipheral Pb+Pb collisions at sqrt(s_NN)=5.02 TeV are presented. The measurement uses ATLAS data from the 2015 and 2018 Pb+Pb data-taking periods at the LHC with an integrated luminosity of 1.94 nb^{−1}. The γγ→μ+μ− pairs are identified via selections on pair momentum asymmetry and acoplanarity. Differential cross sections for dimuon production are measured in different centrality, average muon momentum, and pair rapidity intervals as functions of acoplanarity and k⊥, the transverse momentum kick of one muon relative to the other. Measurements are also made as a function of the rapidity separation of the muons and the angle of the muon pair relative to the second-order event plane to test whether magnetic fields generated in the quark-gluon plasma affect the measured muons. A prior observation of a centrality-dependent broadening of the acoplanarity distribution is confirmed. Furthermore, the improved precision of the measurement reveals a depletion in the number of pairs having small acoplanarity or k⊥ values in more central collisions. The acoplanarity distributions in a given centrality interval are observed to vary with the mean pT of the muons in the pair, but the k⊥ distributions do not. Comparisons with recent theoretical predictions are made. The predicted trends associated with effects of magnetic fields on the dimuons are not observed

Correlations between flow and transverse momentum in Xe+Xe and Pb+Pb collisions at the LHC with the ATLAS detector: A probe of the heavy-ion initial state and nuclear deformation

The correlations between flow harmonics v_n for n=2, 3, and 4 and mean transverse momentum [pT] in 129Xe+129Xe and 208Pb+208Pb collisions at sqrt(s)=5.44 and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are potentially sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from nonflow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and an event-activity selection based on particle production at very forward rapidity. The v_n−[pT] correlations show strong dependencies on centrality, harmonic number n, pT, and pseudorapidity range. Current models qualitatively describe the overall centrality- and system-dependent trends but fail to quantitatively reproduce all features of the data. In central collisions, where models generally show good agreement, the v_2−[pT] correlations are sensitive to the triaxiality of the quadruple deformation. Comparison of the model with the Pb+Pb and Xe+Xe data confirms that the 129Xe nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the 129Xe nucleus from high-energy heavy-ion collisions

Production of Υ(nS) mesons in Pb+Pb and pp collisions at 5.02 TeV

A measurement of the production of vector bottomonium states, Υ(1S), Y(2S), and Υ(3S), in Pb+Pb and pp collisions at a center-of-mass energy per nucleon pair of 5.02 TeV is presented. The data correspond to integrated luminosities of 1.38 nb^{−1} of Pb+Pb data collected in 2018, 0.44 nb^{−1} of Pb+Pb data collected in 2015, and 0.26 fb^{−1} of pp data collected in 2017 by the ATLAS detector at the Large Hadron Collider. The measurements are performed in the dimuon decay channel for transverse momentum p^{μμ}_T<30 GeV, absolute rapidity |y^{μμ}|<1.5, and Pb+Pb event centrality 0–80%. The production rates of the three bottomonium states in Pb+Pb collisions are compared with those in pp collisions to extract the nuclear modification factors as functions of event centrality, p^{μμ}_T, and |y^{μμ}|. In addition, the suppression of the excited states relative to the ground state is studied. The results are compared with theoretical model calculations