Influencia de la conductividad y fuerza iónica de soluciones sintéticas que simulan la fase acuosa del hormigón en el fenómeno de la corrosión de armaduras

Polarization Resistance (Rp) has been the electrochemical technique employed to study quantitatively the influence of Cl- and OH- ions on the corrosion of steel reinforcing, in a synthetic aqueous medium of similar composition to those of the concrete pore solution. Ionic strength, resistivity and their variations in function of CI- and OH- concentration have been chosen as more interesting solution parameters, together with intensity and potential corrosion measurements. The results showed the clear antagonistic role played by CI- and OH- ions on the corrosion process, which decreased as ionic strength increased.Este trabajo presenta el estudio cuantitativo, mediante la técnica de Resistencia de Polarización (Rp), de la influencia de los iones Cl- y OH- en la corrosión de armaduras de acero, en un medio acuoso sintético de similar composición al contenido en los poros del hormigón. Fuerza iónica, conductividad (resistividad) y sus variaciones en función de la concentración de dichos iones, han sido los parámetros de interés escogidos para la evaluación del proceso, además de las medidas de intensidad y potenciales de corrosión. Los resultados muestran claramente el antagonismo de los iones Cl - y OH- , cuyo carácter agresivo o protector disminuye a medida que aumenta la fuerza iónica del medio

Single-ion and exchange anisotropy effects and multiferroic behavior in high-symmetry tetramer single molecule magnets

We study single-ion and exchange anisotropy effects in equal-spin $s_1$ tetramer single molecule magnets exhibiting $T_d$, $D_{4h}$, $D_{2d}$, $C_{4h}$, $C_{4v}$, or $S_4$ ionic point group symmetry. We first write the group-invariant quadratic single-ion and symmetric anisotropic exchange Hamiltonians in the appropriate local coordinates. We then rewrite these local Hamiltonians in the molecular or laboratory representation, along with the Dzyaloshinskii-Moriay (DM) and isotropic Heisenberg, biquadratic, and three-center quartic Hamiltonians. Using our exact, compact forms for the single-ion spin matrix elements, we evaluate the eigenstate energies analytically to first order in the microscopic anisotropy interactions, corresponding to the strong exchange limit, and provide tables of simple formulas for the energies of the lowest four eigenstate manifolds of ferromagnetic (FM) and anitiferromagnetic (AFM) tetramers with arbitrary $s_1$. For AFM tetramers, we illustrate the first-order level-crossing inductions for $s_1=1/2,1,3/2$, and obtain a preliminary estimate of the microscopic parameters in a Ni$_4$ from a fit to magnetization data. Accurate analytic expressions for the thermodynamics, electron paramagnetic resonance absorption and inelastic neutron scattering cross-section are given, allowing for a determination of three of the microscopic anisotropy interactions from the second excited state manifold of FM tetramers. We also predict that tetramers with symmetries $S_4$ and $D_{2d}$ should exhibit both DM interactions and multiferroic states, and illustrate our predictions for $s_1=1/2, 1$.Comment: 30 pages, 14 figures, submitted to Phys. Rev.

Comportamiento frente a cloruros de un hormigón autocompactable de alta resistencia con mezclas ternarias de nano y micro sílice

In this paper, the influence of additions of nanosilica (nSi) and microsilica (mSi) on the behav­iour of binary and ternary mixtures in chloride environments is studied. The main objective is to obtain high-performance self-compacting concrete (HPSCC) with a high durability which can meet specific demands in such aggressive environments. Ten blends were manufactured using Portland cement (CEM I 52.5 R) and additions of nSi and mSi in binary and ternary mixtures. The results of three tests frequently used to evaluate resistance to chloride penetration– electrical resistivity, migration and chloride diffusion –were studied and compared. Both binary and ternary mixtures presented significant improvements in chloride resistance, generally in proportion to the total content of the addition. In all the ternary mixtures, high resistivity is obtained, which indicates that such mixtures have a notably low chloride penetrability. Furthermore, these mixtures provided extremely low chloride diffusion coefficients even at small addition ratios.En este artículo se estudia la influencia en el comportamiento frente a cloruros de la adición de nanosílice (nSi) y microsílice (mSi) en mezclas binarias y ternarias. El principal objetivo es obtener un hormigón autocompactante de altas prestaciones con una alta durabilidad frente a estos ambientes agresivos con cloruros. Se prepararon diez dosificaciones usando cemento Portland (CEM I 52.5 R) y adiciones de nSi y mSi en mezclas binarias y ternarias. Se estudiaron y analizaron tres ensayos frecuentemente utilizados para evaluar la resistencia a la penetración de cloruros, resistividad eléctrica, migración y difusión de cloruros. Tanto las mezclas binarias como ternarias presentaron mejoras significativas en la resistencia a cloruros, en general proporcional al contenido de adición. En todas las mezclas ternarias se ha obtenido alta resistividad, indicando una penetrabilidad a cloruros notablemente baja. Estas mezclas proporcionaron un coeficiente de difusión de cloruros extremadamente bajo, incluso para bajos contenidos de adición

Measuring progress in sustainable food cities: An indicators toolbox for action.

Despite the growth of urban food policies across the globe, a key challenge remains around measuring the impact of these initiatives in building more sustainable and just cities. The literature identifies as the main barriers to progress food system assessments the lack of clear definitions of sustainability, insufficient data, the low applicability of global conceptualisations to local conditions and vice versa and low levels of actor involvement. We aim to address these gaps by co-developing a sustainability assessment framework to evaluate food systems performance in UK cities. The framework emerging from this collaborative process overcomes key limitations of previous exercises by providing a place-based and participative definition of sustainability aligned with global conceptualisations, building on the experiences and needs of a wide range of practitioners and taking a holistic but non-prescriptive approach to understanding food system outcomes. However, its application to the city of Cardiff reveals new challenges, mostly regarding the need to incorporate underrepresented stakeholders as well as account for multiscalar food system interdependencies and their positive but also negative impacts. Results show the need to embed critical perspectives in sustainable food assessments that actively expand their transformative capacity by developing further inclusive, participatory, place-based and whole-systems approaches

Large Eddy simulations of isolated and installed jet noise using the high-order discontinuous Galerkin method

A recently developed computational framework for jet noise is used to compute the noise generated by an isolated and installed jet. The framework consists of two parts. In the first part, the spectral/hp element framework Nektar++ is used to compute the near-field flow. Nektar++ solves the unfiltered Navier-Stokes equations on unstructured grids using the high-order discontinuous Galerkin method. The discrete equations are integrated in time using an implicit scheme based on the matrix-free Newton-GMRES method. In the second part, the Antares library is used to compute the far-field noise. Antares solves the Ffowcs Williams - Hawkings equation for a permeable integration surface in the time domain using a source-time dominant algorithm. The simulations are validated against experimental data obtained in the Doak Laboratory Flight Jet Rig, located at the University of Southampton. For the isolated jet, good agreement is achieved, both in terms of the flow statistics and the far-field noise. The discrepancies observed for the isolated jet are believed to be caused by an under-resolved boundary layer in the simulations. For the installed jet, the flow statistics are also well predicted. In the far-field, very good agreement is achieved for downstream observers. For upstream observers, some discrepancies are observed for very high and very low frequencies

An eco-physiological and biotechnological approach to conservation of the world-wide rare and endangered aquatic liverwort Riella helicophylla (Bory et Mont.) Mont.

The rare aquatic liverwort Riella helicophylla (Bory et Mont.) Mont., inhabitant of temporary shallow ponds around the Mediterranean basin, is considered threatened throughout its distribution range. In addition, little is known of its biology and ecology or of its role in such an important ecosystem where envi- ronmental conditions vary yearly in unpredictable ways. In these variable habitats, due to the seasonal fluc- tuation of water levels, there is no guarantee of yearly spore input into the spore bank. Spore germination rate and the effects of different culture media in an axenic culture establishment, as well as propagation proce- dures of R. helicophylla, were tested. New insights into the ecology and biology of R. helicophylla are given. Spore dormancy is documented, and the protocols for the in vitro culture establishment, propagation and ac- climatization of this liverwort are developed. Dry storage at 20 ± 2 °C for about three months broke the dor- mancy of spores, which subsequently germinated in a high percentage (over 90%). A two phase (solid and liquid) culture media system was developed for the purpose of achieving fully developed gametophytes. The liquid phase contained electrolytes simulating brackish water

Load limiters on temporary shoring structures: Tests on a full-scale building structure under construction

[EN] Temporary shoring structures are used in the construction of reinforced concrete buildings to transmit the loads of newly poured slabs onto the lower floors. The main problems involved in the use of shores/props are: a) the possibility of having higher loads than those initially foreseen, and b) the structural efficiency and cost of the system, which is normally over-sized due to being designed to bear the maximum load of the most demanding building operation. This paper describes a test carried out on a full-scale one-story building to analyze the behaviour of load limiters (LLs) installed on shores under actual construction loading conditions. The theoretical approach and development of this new LL concept were described in previous papers. As these LLs still had not been tested in actual buildings, this paper covers the existing need for a test in the form of a "proof of concept". It also includes computer simulations and recommendations for the use of LLs.The authors would like to express their gratitude to the Spanish Ministry of Education, Culture and Sport for funding received under the FPU Program [FPU13/02466], to the Generalitat Valenciana [GV/2015/063] and also to the Levantina, Ingenieria y Construcción S.L. and Encofrados J. Alsina S.A. business companies for their invaluable cooperation.Buitrago, M.; Calderón García, PA.; Moragues, JJ.; Alvarado, YA.; Adam, JM. (2021). Load limiters on temporary shoring structures: Tests on a full-scale building structure under construction. Journal of Structural Engineering. 147(3):1-9. https://doi.org/10.1061/(ASCE)ST.1943-541X.0002948S191473Adam, J. M., Buitrago, M., Moragues, J. J., & Calderón, P. A. (2017). Limitations of Grundy and Kabaila’s Simplified Method and Its Repercussion on the Safety and Serviceability of Successively Shored Building Structures. Journal of Performance of Constructed Facilities, 31(5), 04017040. doi:10.1061/(asce)cf.1943-5509.0001038Adam, J. M., Parisi, F., Sagaseta, J., & Lu, X. (2018). Research and practice on progressive collapse and robustness of building structures in the 21st century. Engineering Structures, 173, 122-149. doi:10.1016/j.engstruct.2018.06.082Alvarado, Y. A., Calderón, P. A., Adam, J. M., Payá-Zaforteza, I. J., Pellicer, T. M., Pallarés, F. J., & Moragues, J. J. (2009). An experimental study into the evolution of loads on shores and slabs during construction of multistory buildings using partial striking. Engineering Structures, 31(9), 2132-2140. doi:10.1016/j.engstruct.2009.03.021Buitrago, M., Adam, J. M., Alvarado, Y. A., Calderón, P. A., & Gasch, I. (2016). Maximum loads on shores during the construction of buildings. Proceedings of the Institution of Civil Engineers - Structures and Buildings, 169(7), 538-545. doi:10.1680/jstbu.15.00089Buitrago, M., Adam, J. M., Alvarado, Y. A., Moragues, J. J., Gasch, I., & Calderón, P. A. (2016). Designing construction processes in buildings by heuristic optimization. Engineering Structures, 111, 1-10. doi:10.1016/j.engstruct.2015.12.009Buitrago, M., Adam, J. M., Calderón, P. A., & Moragues, J. J. (2018). Load limiters on shores: Design and experimental research. Engineering Structures, 173, 1029-1038. doi:10.1016/j.engstruct.2018.07.063Buitrago, M., Alvarado, Y. A., Adam, J. M., Calderón, P. A., Gasch, I., & Moragues, J. J. (2015). Improving construction processes of concrete building structures using load limiters on shores. Engineering Structures, 100, 104-115. doi:10.1016/j.engstruct.2015.06.007Buitrago, M., Moragues, J. J., Calderón, P. A., & Adam, J. M. (2018). Structural failures in cast-in-place reinforced concrete building structures under construction. Handbook of Materials Failure Analysis, 153-170. doi:10.1016/b978-0-08-101928-3.00008-2Buitrago, M., Sagaseta, J., & Adam, J. M. (2018). Effects of sudden failure of shoring elements in concrete building structures under construction. Engineering Structures, 172, 508-522. doi:10.1016/j.engstruct.2018.06.052Buitrago, M., Sagaseta, J., & Adam, J. M. (2020). Avoiding failures during building construction using structural fuses as load limiters on temporary shoring structures. Engineering Structures, 204, 109906. doi:10.1016/j.engstruct.2019.109906Calderón, P. A., Alvarado, Y. A., & Adam, J. M. (2011). A new simplified procedure to estimate loads on slabs and shoring during the construction of multistorey buildings. Engineering Structures, 33(5), 1565-1575. doi:10.1016/j.engstruct.2011.01.027Carper, K. L. (1987). Structural Failures During Construction. Journal of Performance of Constructed Facilities, 1(3), 132-144. doi:10.1061/(asce)0887-3828(1987)1:3(132)Ellirtgwood, B. (1987). Design and Construction Error Effects on Structural Reliability. Journal of Structural Engineering, 113(2), 409-422. doi:10.1061/(asce)0733-9445(1987)113:2(409)El-Tawil, S., Li, H., & Kunnath, S. (2014). Computational Simulation of Gravity-Induced Progressive Collapse of Steel-Frame Buildings: Current Trends and Future Research Needs. Journal of Structural Engineering, 140(8). doi:10.1061/(asce)st.1943-541x.0000897Epaarachchi, D. C., Stewart, M. G., & Rosowsky, D. V. (2002). Structural Reliability of Multistory Buildings during Construction. Journal of Structural Engineering, 128(2), 205-213. doi:10.1061/(asce)0733-9445(2002)128:2(205)Gasch, I., Alvarado, Y. A., Calderón, P. A., & Ivorra, S. (2014). Construction loads using a shoring–clearing–striking process. Proceedings of the Institution of Civil Engineers - Structures and Buildings, 167(4), 217-229. doi:10.1680/stbu.12.00006Ghali, A., & Gayed, R. B. (2014). Sustainable Serviceability of Structural Concrete: Control of Deflection and Cracking. Journal of Structural Engineering, 140(7), 04014042. doi:10.1061/(asce)st.1943-541x.0000965Hadipriono, F. C. (1985). Analysis of Events in Recent Structural Failures. Journal of Structural Engineering, 111(7), 1468-1481. doi:10.1061/(asce)0733-9445(1985)111:7(1468)Hadipriono, F. C., & Wang, H.-K. (1987). Causes of falsework collapses during construction. Structural Safety, 4(3), 179-195. doi:10.1016/0167-4730(87)90012-9Karshenas, S., & Ayoub, H. (1994). Analysis of Concrete Construction Live Loads on Newly Poured Slabs. Journal of Structural Engineering, 120(5), 1525-1542. doi:10.1061/(asce)0733-9445(1994)120:5(1525)Liu, X., Chen, W., & Bowman, M. D. (1985). Construction Load Analysis for Concrete Structures. Journal of Structural Engineering, 111(5), 1019-1036. doi:10.1061/(asce)0733-9445(1985)111:5(1019)Qian, K., & Li, B. (2013). Performance of Three-Dimensional Reinforced Concrete Beam-Column Substructures under Loss of a Corner Column Scenario. Journal of Structural Engineering, 139(4), 584-594. doi:10.1061/(asce)st.1943-541x.0000630Sasani, M., Kazemi, A., Sagiroglu, S., & Forest, S. (2011). Progressive Collapse Resistance of an Actual 11-Story Structure Subjected to Severe Initial Damage. Journal of Structural Engineering, 137(9), 893-902. doi:10.1061/(asce)st.1943-541x.0000418Sasani, M., & Sagiroglu, S. (2008). Progressive Collapse Resistance of Hotel San Diego. Journal of Structural Engineering, 134(3), 478-488. doi:10.1061/(asce)0733-9445(2008)134:3(478)Schellhammer, J., Delatte, N. J., & Bosela, P. A. (2013). Another Look at the Collapse of Skyline Plaza at Bailey’s Crossroads, Virginia. Journal of Performance of Constructed Facilities, 27(3), 354-361. doi:10.1061/(asce)cf.1943-5509.0000333Zhang, H., Reynolds, J., Rasmussen, K. J. R., & Ellingwood, B. R. (2016). Reliability-Based Load Requirements for Formwork Shores during Concrete Placement. Journal of Structural Engineering, 142(1), 04015094. doi:10.1061/(asce)st.1943-541x.000136

Direct finite element simulation of turbulent flow for marine based renewable energy

In this article we present a computational framework for simulation of turbulent flow in marine based renewable energy applications. In particular, we focus on floating structures and rotating turbines. This work is an extension to multiphase turbulent flow, of our existing framework of residual based turbulence modeling for single phase turbulent incompressible flow. We illustrate the framework in four examples: a regular wave test where we compare against an exact solution, the standard MARIN wave impact benchmark with experimental validation data, a vertical axis turbine with complex geometry from an existing turbine, and finally a prototype simulation of decay test in a coupled moving boundary rigid-body and two-phase fluid simulation.IEA-OES Task 1

Transmisión de cargas entre forjados y puntales en un edificio de forjado reticular de casetón perdido utilizando clareado

En el presente artículo se presentan los resultados de la instrumentación llevada a cabo durante la construcción de un edificio de viviendas resuelto con forjados reticulares de casetón perdido situado en Sabadell (España), en el que se ha empleado un proceso de cimbrado, clareado, descimbrado (CCD). Se han registrado las cargas debidas a las operaciones constructivas de CCD en puntales de los seis primeros forjados. Dichos registros han permitido analizar la transmisión de cargas entre forjados y puntales durante la construcción de este edificio, teniendo un proceso de CCD. El análisis de las medidas experimentales ha permitido concluir que la transmisión de cargas entre forjados y puntales difiere según las condiciones de contorno del vano estudiado. Asimismo, se han comparado las medidas experimentales con diversos métodos simplificados que permiten simular la operación del clareado, obteniendo que el método que mejor se ajusta es el Nuevo Procedimiento Simplificado.Gasch, I.; Alvarado Vargas, YA.; Calderón García, PA.; Torres Górriz, B. (2013). Transmisión de cargas entre forjados y puntales en un edificio de forjado reticular de casetón perdido utilizando clareado. Informes de la Construcción. 65(530):195-202. doi:10.3989/ic.12.046S1952026553

Nonlinear computations of heave motions for a generic Wave Energy Converter

A bench-marking activity of numerical methods for analysis of Wave Energy Converters (WEC) was proposed under the Ocean Energy Systems (OES) International Energy Agency (IEA) Task 10 in 2015. The purpose of the benchmark is to do a code-2-code comparison of the predicted motions and power take out for a WEC. A heaving sphere was used as a first simple test case. The participants sim- ulated heave decay and regular and irregular wave cases. The numerical methods ranged from linear methods to viscous methods solving the Navier-Stokes equa- tions (CFD). An overview of the results from the first phase of the benchmark was reported in [1]. The present paper focus on the simulations of the sphere using one fully nonlinear time-domain BEM one transient RANS method and one transient Direct FE method with no turbulence model. The theory of the three methods as well as the modeling of the sphere are described. Heave decay and heave motions for steep regular waves were selected as test cases in order to study and compare the capability to handle nonlinear effects. Computational efficiency and applicability of the three methods are also discussed