86,861 research outputs found
Seismic vulnerability of structures and infrastructures: Strategies for assessment and mitigation
No full textSeismic engineering is constantly looking for new strategies and methods that provide designers with the opportunity to get more and more efficient solutions both from the performance and from the economic point of view. In this context, the scientific community is called not to miss its support and to face the new challenges coming from the observation of the damage caused by the recent earthquakes. This Special Issue of “Ingegneria Sismica” collects some works focusing the theme of the seismic vulnerability, some of them specifically refer to mitigation strategies while others address modeling strategies. Obviously, for the multiplicity of aspects involving the theme of "seismic vulnerability", only a few issues have been discussed. In particular, some works deal with the theme of base isolation from the point of view of design and seismic reliability, others are focused on the theme of structural robustness considered as a further goal of seismic design. Further papers are deepening the problems of interaction between frames and masonry infills, providing simplified modeling strategies, suggesting criteria to reduce interaction effects, but above all by providing methods for the analysis of combined in-plane / out-of-plane behavior. The themes related to modeling are also addressed with particular care. Other papers in fact face the issues of model uncertainty and of the reliability of constitutive laws for normal and high strength confined concrete, being the latter of fundamental importance for the assessment of the rotational capacity of reinforced concrete structural elements under seismic actions. Moreover, the problem of the reliability of seismic vulnerability assessment methods is also discussed, with particular reference to multimodal "pushover" analysis. This Special Issues is composed of 10 paper produced by 29 authors, to whom we would like to address a special thank for the effort made during the editorial phases. Finally, the Guest Editors, Paolo Castaldo, Liborio Cavaleri e Fabio Di Trapani, wish to thank Prof. Gianmario Benzoni and Prof. Rosario Montuori for this opportunity and for their assistance
Cyclic response of masonry infilled RC frames: Experimental results and simplified modeling
No full textThe recentlargeinterestinnonlinearseismicanalysismethods,staticanddynamic,hasrequiredproper
strategiesofmodelingbasedonreliable,andatthesametimeeasytouse,constitutivelawsforthe
structural elements.Regardingthebehaviorofframedstructures,specialattentionhastobedevotedto
infills becauseofthekeyroletheyplayinmodifyingoverallstiffness,strengthandductilityunder
seismic excitation.Pointingouttheattentiononthistopicthepaperdiscussesacriteriaformodelingthe
structural behaviorofinfills basedonamacromodelingapproach,thatistosayonthesubstitutionof
infills withdiagonalpinjointedstruts.Ishereshownhowmultilinearplasticlinkelementsgoverned
by ahystereticPivotmodel,availableindifferentFEMcodes,canbeappropriatelyusedtomodelthe
equivalentstrutstoperformlinearornonlinearanalyses.Inordertoenlargeexperimentalknowledgeon
cyclicbehaviorofinfilled framesstructuresandasreferencefordevelopingtheabovementioned
modelingstrategy,anexperimentalcampaignonsingle-storey,single-bay,fullyinfilledframeswithdifferent
kindsofmasonryandsubjectedtolateralcyclicalloads,wascarriedout,andsomeothersavailableinthe
literaturearereferredto.ValidationofPivotmodeling approachwascarriedoutcomparingexperimental
resultsandcomputersimulationsoftheexperimentaltests.Inthepaperhysteresisparametersvalues
calibratingPivotlawarealsogivenforinvolvedmasonryinfills typologiesandsomeproposalsforcorrelation
betweenstrengthandstiffnessofinfilledframesandofmasonryinfillsareprovidedasatoolforthequick
calibrationofthePivotmodelinpracticalapplications
Out-of-Plane Behavior of URM Infill: Accuracy of Available Capacity Models
No full textThe aim of this paper is to check the accuracy of analytical capacity models available for the prediction of out-of-plane strength of unreinforced masonry (URM) infill walls. The accuracy of the available models is checked by detailed comparison with the existing experimental results. In doing so, both types of capacity models are evaluated: Type I for the prediction of the strength in the undamaged state, and Type II for the prediction of strength reduction in the in-plane damaged state. Results from the calculations are discussed, and the best among the available models are recommended. Furthermore, the influence of orthotropy of the infill masonry in the out-of-plane capacity predicted by the models is discussed. The paper also highlights the prospect of using the capacity models in the cases of infill-beam gap and infill with openings. In the paper, the best pairs of models (composed by a model for the prediction of the out-of-plane strength in the undamaged state and a model for the prediction of the reduction of the out-of-plane strength in the damaged state, not necessarily provided by the same author) for URM infill walls, are suggested for the first time
On the Effect of Downscaling in Inkjet Printed Life-Inspired Compartments
No full textThe fabrication of size-scalable liquid compartments is a topic of fundamental importance in synthetic
biology, aiming to mimic the structures and the functions of cellular compartments. Here, inkjet
printing is demonstrated as a customizable approach to fabricate aqueous compartments at different
size regimes (from nanoliter to femtoliter scale) revealing the crucial role of size in governing the
emerging of new properties. At first, inkjet printing is shown to produce homogenous aqueous
compartments stabilized by oil-confinement with mild surfactants down to the hundreds of picoliter
scale [1]. Raster Image Correlation Spectroscopy allows to monitor few intermolecular events by the
involvement of protein-binding assays within these compartments [2]. Subsequently, in order to
reduce droplet size at values below the nozzle size, a theoretical model from Eggers et al. [3] is
experimentally reproduced permitting to obtain femtoliter-scale aqueous droplets from picoliter-scale
microchannels [4]. As a remarkable difference to picoliter scale droplets, downscaling at the
femtoliter-size triggers the spontaneous formation of molecularly crowded shell structures at the
water/oil interface stabilized by a mixture of biocompatible surfactants. The shells have typical
thickness in order of hundreds of nanometers, in accordance with theoretical models [5]. Molecular
crowding effects in these systems are tested by using fluorescence lifetime imaging under the phasor
plot approach [6], revealing different characteristic lifetimes of specific probe molecules in the
confined volumes with respect to bulk solutions. The femtoliter-scale compartments autonomously
trigger the formation of unique features (e.g., up-concentration, spatial heterogeneity, molecular proximity) that are mediated by the intermolecular interactions in these novel environments, ultimately permitting to mimic the native conditions of sub-cellular scale compartments. The crowding conditions in femtoliter-scale droplets do not to affect the conformation variation of a model DNA hairpin in presence of molecular triggers and of a CYP2E1-catalyzed enzymatic reaction. Our results can be a first step towards the fabrication of size-scalable lab-on-a-chip compartments mimicking sub-cellular environments.
References
1. G. Arrabito, F. Cavaleri, V. Montalbano, V. Vetri, M. Leone, B. Pignataro, Lab on Chip, 2016, 16,
4666.
2. M.A. Digman, C. M. Brown, A. R. Horwitz,W.W. Mantulin, and E. Gratton, Biophysical Journal,
2016, 94, 2819.
3. J. Eggers, Phys. Rev. Lett. 1993, 71, 3458.
4. G. Arrabito, F. Cavaleri, A. Porchetta, F. Ricci, V. Vetri, M. Leone, B. Pignataro, Adv. Biosys.
2019, 1900023.
5. M. Staszak, J. Surfactants Deterg., 2016, 19, 297.
6. C. Stringari, A. Cinquin, O. Cinquin, M. A. Digman, P.J. Donovan, and E. Gratton, Proc. Natl.
Acad. Sci. USA 2011, 108, 13582
Autonomous molecularly crowded confinement in inkjet printed femtoliter-scale aqueous compartments
No full textNatural evolution has chosen the localization of biomolecular processes into crowded sub-cellular femtoliter (fL) scale compartments for organizing complex biological processes. [1] Many synthetic biology platforms with life-like activities have been able to mimic these systems under different compartment sizes regimes. [2] However, the fabrication of crowded compartments down to sub-cellular scales is challenging, mainly because of high surface-volume ratio of these systems, finally compromising the stability of the encapsulated biomolecules. In this regard, we here bridge this gap by showing the possibility to produce femtoliter-scale aqueous droplets using a novel inkjet printing approach reproducing a theoretical model from Eggers et al. [3] The fL-scale droplets are spiked with non-ionic surfactants to stabilize the water/oil interface whilst not compromising ink viscosity and surface tension. [4] When injected into nL-scale mineral oil droplets, the fL-droplets form an almost-regular circular pattern at the border of mineral oil drops due to Marangoni flows (see Figure). Remarkably, downscaling at the fL-size induces the spontaneous formation of molecularly crowded shell structures at the water/oil interface, as observed by fluorescence microscopy, showing typical thickness in order of hundreds of nanometers, in accordance with previously reported models. [5] Molecular crowding effects are tested by using fluorescence lifetime imaging under the convenient phasor plot approach, [6] revealing different characteristic lifetimes of specific probe molecules in the confined volumes with respect to macroscopic solutions. The fL-scale compartments autonomously trigger the formation of unique features (e.g., spatial
heterogeneity, up-concentration, molecular proximity) that are mediated by the intermolecular interactions in these novel environments. Remarkably, the crowding conditions are observed not to affect the conformation variation of a model DNA hairpin in presence of molecular triggers and of a CYP2E1-catalyzed enzymatic reaction. Our results can be a first step towards the fabrication of lab-on-a-chip compartments for molecularly crowded confinement mimicking sub-cellular environments.
Bibliography
1. S. F. Banani et al., Nat. Rev. Mol. Cell Biol. 2017, 18, 285.
2. B. C. Buddingh’, J. C. M. Van Hest, Acc. Chem. Res. 2017, 50, 769.
3. G. Arrabito, F. Cavaleri et al. Adv. Biosys. 2019, 1900023
4. J. Eggers, Phys. Rev. Lett. 1993, 71, 3458.
5. M. Staszak, J. Surfactants Deterg. 2016, 19, 297.
6. C. Stringari et al. Proc. Natl. Acad. Sci. USA 2011, 108, 13582
Hand verification for flexural strength of existing R.C. floors subject to degradation phenomena
No full textIn the present paper, a simplified model for hand verification of the flexural and shear strength of existing corroded T beams cast in place of lightened R.C. orthotropic slabs forming floors is presented and discussed. Diffused and pitting corrosion on steel bars, compressive concrete strength degradation and concrete bond strength degradation are included in the model. The original contribution of the paper is evaluation of the flexural and shear strength considering both the cases of strain compatibility and absence of compatibility and considering the main parameters governing the corrosion process. An arch-resistant model for the calculus of the flexural and shear strength of the beam was adopted in the absence of strain compatibility, while the plane section theory was adopted for the case of strain compatibility. No punching shear is considered. This approach is simple and can be applied on the basis of the experimental information available (carbonation test, chloride content, measurement of the pitting in the bar, gravimetric method for general corrosion) or by utilizing analytical expressions calibrated on the knowledge of the corrosion current intensity determined by linear polarization resistance measurement (LPR). The model was also verified against experimental results recently obtained by the authors
Practical Calculation Models for Column Footing and Comparison with Experimental Data
No full textIn this paper, a simplified calculation model for the prediction of the load-carrying capacity of an RC column footing with a square cross section is presented. A detailed background of available experimental data and existing models for the prediction of the load-carrying capacity of slender and deep footings is presented. Cases of flexural failure and punching shear failures for slender footing and concrete strut crushing and tie yielding in deep members are analyzed. The aim of the paper is to propose a simple design formula for slender and deep footing verified by available experimental data and in agreement with other existing expressions. Expressions of the maximum mechanical ratio of main steel for slender and deep footing are defined to avoid brittle failure. The effects of the main parameters, such as the dimensions of the footing and column (depth, width) and the mechanical ratio of longitudinal steel and type of soil, were investigated both numerically and analytically. A comparison between analytical and numerical results shows good agreement
Prediction of the additional shear action on frame members due to infills
No full textInfill masonry walls in framed structures make a significant contribution to the
response under seismic actions. With special regard to reinforced concrete (RC) structures,
it is known that internal forces modifications caused by the frame–infill interaction may be
not supported by the surrounding frame because of the additional shear forces arising at
the ends of beams and columns. Such additional forces may lead to the activation of brittle
collapse mechanisms and hence their prediction is basic in capacity assessment, especially
for structures that disregard the details for seismic zones. In this paper a parametric study is
carried out addressed to the prediction of the shear forces mentioned before. The results of
this study can be used as a support when the simplified model is adopted consisting in the
substitution of infill with an equivalent pin jointed concentric strut, because in this case the
structural analysis fails in the prediction of the shear forces in question. Through the paper, in
which existing RC infilled frames designed only for vertical loads are discussed, analytical
laws, depending on the level of the axial force arising in a concentric strut equivalent to
infill, are proposed, the above analytical law allowing to correct the local shear forces in the
frame critical sections, which are not predictable in the case of substitution of infill with an
equivalent concentric strut
- …
