A nonlinear macroelement formulation for the seismic analysis of masonry buildings

A macroelement is presented for the nonlinear dynamic analysis of masonry structures under seismic actions. The macroelement, developed in the framework of the equivalent frame model, has a force-based formulation and accounts for flexural and shear failure mechanisms, by means of two flexural hinges at the ends and a shear link, respectively. The flexural hinges are formulated according to the Bouc-Wen model to describe the progressive development of cracks and the hysteresis loops under load reversals. The shear link, in addition to the aforementioned effects, accounts for the strength/stiffness decay and is formulated adopting the Bouc-Wen-Baber-Noori model. Numerical comparisons with experimental tests on masonry piers are presented, showing the suitability of the presented macroelement

An investigation of the beneficial effects of adding carbon nanotubes to standard injection grout

Mortar grouting is often used in masonry constructions to mitigate structural decay and repair damage by filling cracks and voids, resulting in an improvement in mechanical properties. This paper presents an original experimental investigation on grout with added carbon nanotubes (CNTs). The samples were prepared with different percentages of CNTs, up to 1.2 wt% with respect to the binder, and underwent three‐point bending tests in crack mouth opening displacement mode and compressive tests. The results showed that very small additions (up to 0.12 wt% of CNTs) increased not only flexural and compressive strengths (+73% and 35%, respectively, in comparison with plain mortar) but also fracture energy (+80%). These results can be explained on the basis of a reduction in porosity, as evidenced by mercury intrusion porosimetry, as well as by a crack bridging mechanism and by the probable formation of nucleation sites for hydration products, as observed through scanning electron microscopy

Performance of a school hosted within a historical complex affected by the 2016 seismic sequence

Immediately after the August 24th, 2016, earthquake in Central Italy, universities have been asked to inspect schools and assess their usability, under the coordination of ReLUIS (Rete Laboratori Universitari Ingegneria Sismica = Earthquake Engineering University Laboratories Network). Later on, about one hundred schools deemed as unfit to use have been evaluated in order to establish if it was possible to repair them before September 2017 or if it was more appropriate to build a new school. Among investigated buildings there are not only those in the epicentral area, but also some located even 30-45 km from the epicentres of the main events. One of those is the music high school located in Teramo, Abruzzi region, housed within the former monastery of San Giovanni a Scorzone established in 1384. The seismic vulnerability of the building was investigated in 2014 according to the Italian Building Standard. Based on the documentation produced therein, observations made after the August event, and a new inspection carried out in December 2016, the building has been assessed according to the procedure proposed after the Emilia 2012 Earthquakes. Despite ground shaking not being very severe, due to high vulnerability, the performance was that of a damage level 2 (damage between significant and severe), with important distress to non-structural elements. Such performances call into question the suitability of housing critical functions in historical buildings that, however, can suffer an accelerated decay if left unused and, thus, unmaintained

Analysis of seismically-isolated two-block systems using a multi–rocking-body dynamic model

A novel multibody rocking model is developed to investigate the dynamic response of two stacked rigid blocks placed on a linear base isolation device. The model is used to investigate the dynamic response of a realistic statue-pedestal system subject to pulse-like ground motions. The analysis shows that, in general, base isolation increases the safety level of the rocking system. However, for large period pulses or small size blocks, the isolator can amplify the ground motion, resulting in a lower minimum overturning acceleration than for the nonisolated system. Further, the amplification or shock spectrum of a linear mass-dashpot-spring oscillator, was found to be the reciprocal of the minimum nondimensional overturning acceleration of the investigated rocking system. Novel rocking spectra are obtained by normalizing the frequency of the pulse by the frequency of the isolator. The analysis also demonstrates how the dynamic response of the two stacked blocks is equivalent to that of a single-block configuration coincident with the whole system assumed monolithic or the upper block alone, whichever is more slender

Integration of ground-penetrating radar, ultrasonic tests and infrared thermography for the analysis of a precious medieval rose window

Abstract. The integration of high-resolution, non-invasive geophysical techniques (such as ground-penetrating radar or GPR) with emerging sensing techniques (acoustics, thermography) can complement limited destructive tests to provide a suitable methodology for a multi-scale assessment of the state of preservation, material and construction components of monuments. This paper presents the results of the application of GPR, infrared thermography (IRT) and ultrasonic tests to the 13th century rose window of Troia Cathedral (Apulia, Italy), affected by widespread decay and instability problems caused by the 1731 earthquake and reactivated by recent seismic activity. This integrated approach provided a wide amount of complementary information at different scales, ranging from the sub-centimetre size of the metallic joints between the various architectural elements, narrow fractures and thin mortar fillings, up to the sub-metre scale of the internal masonry structure of the circular ashlar curb linking the rose window to the façade, which was essential to understand the original building technique and to design an effective restoration strategy

Displacement-based design procedures for rigid block isolation

When subjected to earthquakes, many objects or structural elements behave like rocking rigid blocks. Computer servers, medical shelves, art objects, statues, and electrical transformers are frequently included in this category. Protection of these objects is an important task, considering that their value could be inestimable or their operation crucial during earthquakes; base isolation technology has been proven to be a viable option for this purpose. Initially, the dynamic model of a rocking rigid block placed on a base isolation device is reviewed. Then, two equivalent-static displacement-based procedures for designing the isolators for these types of objects are proposed, and the main steps are illustrated. The first procedure aims to determine isolator characteristics to prevent the initiation of rocking motion during the code-level earthquake event. The second procedure is aimed at designing isolators that allow a specified maximum rotation of the block during seismic events. The proposed procedures are validated by means of time-history analyses for a suite of spectrum-compatible accelerograms. The first displacement-based procedure appears particularly suitable for objects of small to medium size. The validation of the second procedure demonstrates that the equal displacement rule can be applied for this kind of systems, despite their softening. The results also indicate that the approach is particularly effective for medium to large structures/objects, if small oscillations are acceptable. The controlled rocking procedure offers a significant advantage by allowing for a reduction in the maximum displacement and period of the isolator, compared to situations where rocking motion must be prevented entirely

Vulnerability Assessment of Italian Unreinforced Masonry Churches Using Multi-Linear Regression Models

The extensive damage occurred to the Italian historical and architectural heritage during the 2016-2017 earthquake sequence, and particularly to unreinforced masonry churches, highlights the need to better recognize the vulnerability of religious buildings. A sample of 158 churches belonging to the four stricken regions is studied and their performance analysed statistically. Structural behaviour of these churches is described in terms of mechanisms affecting the so-called macroelements, being portions of the building behaving more or less independently. In order to define fragility curves correlating the damage related to each collapse mechanism against ground motion intensity and churches’ specific characteristics, the observed behaviour of the sample is herein analysed by means of statistical procedures accounting for possible local collapse mechanisms. Several regressions strategies are considered, accounting for vulnerability modifiers increasing/reducing the vulnerability of each macroelement, since the severity of shaking alone is not capable to fully explain the observed damage, strongly influenced by structural details that can worsen the seismic performance or improve it through earthquake-resistant elements. A synthetic damage index, purely based on observed data, is used to summarise the overall severity of damage related to relevant mechanisms, highlighting the contributions of ground shaking and building vulnerability. Results show the relevance of the proposed multi-linear regression models for the national heritage of churches and the advisability of extending mechanism-based regressions to other countries besides Italy. The proposed global damage index can be used as predictive tool to support seismic vulnerability mitigation at a territorial scale

Free energy methods in Coupled Electron Ion Monte Carlo

Recent progress in simulation methodologies and in computer power allow first principle simulations of condensed systems with Born-Oppenheimer electronic energies obtained by Quantum Monte Carlo methods. Computing free energies and therefore getting a quantitative determination of phase diagrams is one step more demanding in terms of computer resources. In this paper we derive a general relation to compute the free energy of an ab-initio model with Reptation Quantum Monte Carlo (RQMC) energies from the knowledge of the free energy of the same ab-initio model in which the electronic energies are computed by the less demanding but less accurate Variational Monte Carlo (VMC) method. Moreover we devise a procedure to correct transition lines based on the use of the new relation. In order to illustrate the procedure, we consider the liquid-liquid phase transition in hydrogen, a first order transition between a lower pressure, molecular and insulating phase and a higher pressure, partially dissociated and conducting phase. We provide new results along the T = 600K isotherm across the phase transition and find good agreement between the transition pressure and specific volumes at coexistence for the model with RQMC accuracy between the prediction of our procedure and the values that can be directly inferred from the observed plateau in the pressure-volume curve along the isotherm. This work paves the way for future use of VMC in first principle simulations of high pressure hydrogen, an essential simplification when considering larger system sizes or quantum proton effects by Path Integral Monte Carlo methods.Comment: Accepted for publication in Molecular Physic

Compilability of Abduction

Abduction is one of the most important forms of reasoning; it has been successfully applied to several practical problems such as diagnosis. In this paper we investigate whether the computational complexity of abduction can be reduced by an appropriate use of preprocessing. This is motivated by the fact that part of the data of the problem (namely, the set of all possible assumptions and the theory relating assumptions and manifestations) are often known before the rest of the problem. In this paper, we show some complexity results about abduction when compilation is allowed