P-D Effects on the Reliability of Oil Offshore Jacket Platforms in Mexico

Given the important economic consequences of an oil platform failure, all the aspects of its structural behavior and safety issues need to be carefully considered. In particular, P-D effects on the deck legs of marine offshore jacket platforms may be relevant when the deck height and the vertical load are significant. In this paper, the impact of the moment amplification, due to lenderness of the deck legs, on the platform safety is examined and appraised from he viewpoint of the structural reliability. The formulation is applied to a typical tall deck marine platform under the environmental loading at the Bay of Campeche, Mexico, and its reliability index is calculated with and without the P-D effect. The results presented herein may be sed to improve the current practice in the design and assessment of offshore marine platforms in Mexico and to update the current version of the code

ESTIMACIÓN DEL IMPACTO DEL TIEMPO DE CORROSIÓN EN LA EVOLUCIÓN DEL RIESGO DE ESTRUCTURAS DE CONCRETO REFORZADO

En las últimas tres décadas, se ha observado un incremento en agrietamientos y delaminaciones en elementos de estructuras de concreto reforzado, relacionados con la corrosión del acero de refuerzo, bajo la acción de los efectos ambientales, que ha provocado el deterioro prematuro de muchas de ellas a nivel mundial. Esto implica que, además del diseño por resistencia, se consideren aspectos de durabilidad que ayuden a prevenir este deterioro, tal que, la probabilidad de tener un comportamiento satisfactorio de la estructura durante su vida útil, sea aceptable. Con lo anterior, adquiere relevancia evaluar el riesgo que presentan este tipo de estructuras sujetas a corrosión en el tiempo y, en función de ello, adoptar las medidas preventivas que permitan garantizar su durabilidad. Para tratar esta situación, en el presente trabajo se estudia la relación entre el tiempo de corrosión del acero y la evolución de riesgo de una estructura de concreto reforzado, mediante el desarrollo de un modelo para estimar la variación del índice de confiabilidad durante el tiempo de inicio y propagación de la corrosión del acero, a partir de la modificación de un modelo de deterioro existente. Con el modelo propuesto en este trabajo, se obtuvo un perfil de confiabilidad de una estructura de concreto reforzado sujeta a daño por corrosión (caso de un puente vehicular), mediante la estimación cuantitativa del agrietamiento del recubrimiento de concreto y su evolución en el tiempo en varios de sus elementos estructurales dañados por corrosión. A partir de ello, se determinó la disminución del diámetro de las barras de acero de cada uno de los elementos, su correspondiente pérdida del área de su sección transversal y la disminución de la capacidad de carga, con el consiguiente aumento y reducción de su probabilidad de falla e índice de confiabilidad, respectivamente. Con el desarrollo del ejemplo y los resultados obtenidos, se observó que los elementos dañados por corrosión, presentaron cambios de rigidez y una reducción en su momento de fluencia nominal, durante el periodo de propagación de la corrosión, lo que provocó una disminución en su índice de confiabilidad a valores menores de 2 para acciones sísmicas, además de presentar una reducción de la vida útil de 15%, para la condición más crítica de falla (falla simultanea de dos elementos estructurales). Así, se probó la hipótesis del trabajo, referente a que una estructura de concreto reforzado sujeta a corrosión en el tiempo, presenta cambios en la rigidez de sus elementos estructurales y reduce su capacidad para resistir cargas, disminuyendo su índice de confiabilidad a valores menores de 2 para acciones sísmicas, acortando en un 20% o más su vida útil, aunque para el caso estudiado la reducción fue del 15% únicamente. Finalmente, se realizó una comparación de los resultados del perfil obtenido con el modelo desarrollado, y los de un perfil de confiabilidad utilizando un modelo de durabilidad existente, para la estructura estudiada, obteniendo resultados similares, del tiempo de inicio de la corrosión, del tiempo de propagación de la corrosión y del tiempo para el cual la estructura supera su estado límite último, para la condición más crítica de falla.Over the last three decades an increase in cracks and spalling of concrete in elements of reinforced concrete structures has been observed. These damages are related to the corrosion of reinforcing steel under the action of environmental effects, which have normally caused worldwide premature deterioration of structures. This implies that, apart from strength, durability should be considered to prevent this deterioration, such that the probability of satisfactory performance of the structure during its lifetime is acceptable. Consequently, it becomes relevant to assess the risk posed by this type of structures subject to corrosion over time and, accordingly, adopt preventive measures to ensure their durability. To address this situation, this piece of research deals with the relationship between the steel corrosion time and the evolution of risk for a reinforced concrete structure, by developing a model to estimate the reliability index variation during both the initiation time and the corrosion propagation process, by means of the modification of an existing deterioration model. With the proposed model, the reliability index of the reinforced concrete structure subject to corrosion damage (considering the case of a vehicular bridge) was obtained. To do so, it was required to carry out the quantitative estimation of the cracking of concrete cover and its evolution over time, analyzing several of its structural elements damaged by corrosion. Following on from this, the reduction on diameter of the steel bars of each of the elements was determined, along with the corresponding loss of its cross-sectional area and the load decrease, thus increasing the likelihood of failure and reducing the reliability index. With the example developed and the results obtained, it was observed that the corrosion damaged elements showed reductions not only in stiffness but also in its nominal yield moment, during the propagation of corrosion. This led to reductions on the structure reliability index (achieving values lower than 2 for seismic action), and in its lifetime of 15%, for the most critical failure (presented simultaneously in two structural elements). Thus, the working hypothesis has been proven, showing that a reinforced concrete structure subject to corrosion over its lifetime, has changes in its structural rigidity and reduces their ability to withstand loads, reducing its reliability index to values lower than 2 for seismic actions, and shortening by 20% or more of its lifetime (although for the studied case the reduction was only 15%). Finally, a comparison was made of the results obtained with the developed model, and the reliability index estimated by using a durability existing model for the studied structure. The results were similar in terms of the corrosion initiation time, the corrosion propagation time, and the time for which the structure exceeds its ultimate limit state, for the most critical failure

Compensation Factors for Bridges Built With a Reinforced Concrete Strength Below Its Nominal Value and Located on Seismic Hazard Zones

Sometimes, in the absence of a strict supervision, bridges are built with a reinforced concrete strength below its nominal value. If the difference is not so high to consider the bridge demolition, a question arises about how much the compensation should be. In this paper, a rational basis to orient negotiations, taken as the ratio between expected life-cycle costs for the actual and nominal concrete strengths is proposed and illustrated for a bridge in Mexico City. The calculation of the expected life-cycle cost includes the bridge annual failure probability under the dead, live and seismic loads and the costs of failure consequences. Uncertainty is considered only on the seismic load. The bridge annual failure probability is calculated by FORM approximation and by considering scenario ground accelerations and the seismic hazard curve for the bridge site. With the total probability theorem, the overall bridge annual failure probability is approximated and the expected life-cycle costs are calculated. The process is repeated for several values of reinforced concrete strength and the compensation factors are calculated and plotted for several costs of consequences. In order to explore several cases, two reinforced concrete strength, two pier heights: 4 and 8 m, three sites in Mexico with different seismicity and three levels of failure consequences, are considered. In these examples, the dominant failure mode is the pier axial load-bending moment interaction as a result of the acting loads combination. As expected, the factors increase for a larger difference of concrete strengths, for the higher piers, for a stronger seismicity and for larger costs of failure consequences. The factors were calculated for a nominal concrete strength of 200 Kg/cm2, and variations of 180 and 160 Kg/cm2, and for a nominal strength of 420 Kg/cm2, and variations of 400 and 380 Kg/cm2

Retos en la protección y resiliencia de comunidades susceptibles a desastres por deslizamiento de laderas

Se presentan las causas, tipos y medidas de mitigación para deslizamiento de laderas

Informe COTEC: situación y evolución de la economía circular en España

Tercera entrega de este informe bienal analiza la evolución y la situación actual de la economía circular en España respecto a Europa.La economía circular es una de las grandes transiciones en las que Cotec está inmersa y una de sus líneas prioritarias en las que está centrando sus esfuerzos. Con este tercer informe, Cotec quiere mantener su contribución al análisis de la situación de la economía circular en España y analizar las políticas puestas en marcha desde los distintos niveles administrativos. Esta entrega además incorpora un estudio detallado de las competencias y capacidades disponibles a nivel nacional para impulsar la transición circular, así como de las barreras y los elementos facilitadores para dicha transición. La economía circular ofrece una alternativa al actual modelo de producción, basado en una cadena de valor lineal que genera residuos en todas las etapas, desde la extracción de materias primas hasta la generación de residuos, pasando por las fases de fabricación, distribución y consumo. La alternativa consiste en prolongar la vida económica útil de los materiales y los recursos tanto como sea posible, reduciendo al mínimo la generación de residuos.Peer ReviewedPostprint (published version

Repositioning of the global epicentre of non-optimal cholesterol

High blood cholesterol is typically considered a feature of wealthy western countries(1,2). However, dietary and behavioural determinants of blood cholesterol are changing rapidly throughout the world(3) and countries are using lipid-lowering medications at varying rates. These changes can have distinct effects on the levels of high-density lipoprotein (HDL) cholesterol and non-HDL cholesterol, which have different effects on human health(4,5). However, the trends of HDL and non-HDL cholesterol levels over time have not been previously reported in a global analysis. Here we pooled 1,127 population-based studies that measured blood lipids in 102.6 million individuals aged 18 years and older to estimate trends from 1980 to 2018 in mean total, non-HDL and HDL cholesterol levels for 200 countries. Globally, there was little change in total or non-HDL cholesterol from 1980 to 2018. This was a net effect of increases in low- and middle-income countries, especially in east and southeast Asia, and decreases in high-income western countries, especially those in northwestern Europe, and in central and eastern Europe. As a result, countries with the highest level of non-HDL cholesterol-which is a marker of cardiovascular riskchanged from those in western Europe such as Belgium, Finland, Greenland, Iceland, Norway, Sweden, Switzerland and Malta in 1980 to those in Asia and the Pacific, such as Tokelau, Malaysia, The Philippines and Thailand. In 2017, high non-HDL cholesterol was responsible for an estimated 3.9 million (95% credible interval 3.7 million-4.2 million) worldwide deaths, half of which occurred in east, southeast and south Asia. The global repositioning of lipid-related risk, with non-optimal cholesterol shifting from a distinct feature of high-income countries in northwestern Europe, north America and Australasia to one that affects countries in east and southeast Asia and Oceania should motivate the use of population-based policies and personal interventions to improve nutrition and enhance access to treatment throughout the world.Peer reviewe

Contributions of mean and shape of blood pressure distribution to worldwide trends and variations in raised blood pressure: A pooled analysis of 1018 population-based measurement studies with 88.6 million participants

© The Author(s) 2018. Background: Change in the prevalence of raised blood pressure could be due to both shifts in the entire distribution of blood pressure (representing the combined effects of public health interventions and secular trends) and changes in its high-blood-pressure tail (representing successful clinical interventions to control blood pressure in the hypertensive population). Our aim was to quantify the contributions of these two phenomena to the worldwide trends in the prevalence of raised blood pressure. Methods: We pooled 1018 population-based studies with blood pressure measurements on 88.6 million participants from 1985 to 2016. We first calculated mean systolic blood pressure (SBP), mean diastolic blood pressure (DBP) and prevalence of raised blood pressure by sex and 10-year age group from 20-29 years to 70-79 years in each study, taking into account complex survey design and survey sample weights, where relevant. We used a linear mixed effect model to quantify the association between (probittransformed) prevalence of raised blood pressure and age-group- and sex-specific mean blood pressure. We calculated the contributions of change in mean SBP and DBP, and of change in the prevalence-mean association, to the change in prevalence of raised blood pressure. Results: In 2005-16, at the same level of population mean SBP and DBP, men and women in South Asia and in Central Asia, the Middle East and North Africa would have the highest prevalence of raised blood pressure, and men and women in the highincome Asia Pacific and high-income Western regions would have the lowest. In most region-sex-age groups where the prevalence of raised blood pressure declined, one half or more of the decline was due to the decline in mean blood pressure. Where prevalence of raised blood pressure has increased, the change was entirely driven by increasing mean blood pressure, offset partly by the change in the prevalence-mean association. Conclusions: Change in mean blood pressure is the main driver of the worldwide change in the prevalence of raised blood pressure, but change in the high-blood-pressure tail of the distribution has also contributed to the change in prevalence, especially in older age groups

Çédille, revista de estudios franceses

Presentació

Worldwide trends in hypertension prevalence and progress in treatment and control from 1990 to 2019: a pooled analysis of 1201 population-representative studies with 104 million participants

Background Hypertension can be detected at the primary health-care level and low-cost treatments can effectively control hypertension. We aimed to measure the prevalence of hypertension and progress in its detection, treatment, and control from 1990 to 2019 for 200 countries and territories. Methods We used data from 1990 to 2019 on people aged 30–79 years from population-representative studies with measurement of blood pressure and data on blood pressure treatment. We defined hypertension as having systolic blood pressure 140 mm Hg or greater, diastolic blood pressure 90 mm Hg or greater, or taking medication for hypertension. We applied a Bayesian hierarchical model to estimate the prevalence of hypertension and the proportion of people with hypertension who had a previous diagnosis (detection), who were taking medication for hypertension (treatment), and whose hypertension was controlled to below 140/90 mm Hg (control). The model allowed for trends over time to be non-linear and to vary by age. Findings The number of people aged 30–79 years with hypertension doubled from 1990 to 2019, from 331 (95% credible interval 306–359) million women and 317 (292–344) million men in 1990 to 626 (584–668) million women and 652 (604–698) million men in 2019, despite stable global age-standardised prevalence. In 2019, age-standardised hypertension prevalence was lowest in Canada and Peru for both men and women; in Taiwan, South Korea, Japan, and some countries in western Europe including Switzerland, Spain, and the UK for women; and in several low-income and middle-income countries such as Eritrea, Bangladesh, Ethiopia, and Solomon Islands for men. Hypertension prevalence surpassed 50% for women in two countries and men in nine countries, in central and eastern Europe, central Asia, Oceania, and Latin America. Globally, 59% (55–62) of women and 49% (46–52) of men with hypertension reported a previous diagnosis of hypertension in 2019, and 47% (43–51) of women and 38% (35–41) of men were treated. Control rates among people with hypertension in 2019 were 23% (20–27) for women and 18% (16–21) for men. In 2019, treatment and control rates were highest in South Korea, Canada, and Iceland (treatment >70%; control >50%), followed by the USA, Costa Rica, Germany, Portugal, and Taiwan. Treatment rates were less than 25% for women and less than 20% for men in Nepal, Indonesia, and some countries in sub-Saharan Africa and Oceania. Control rates were below 10% for women and men in these countries and for men in some countries in north Africa, central and south Asia, and eastern Europe. Treatment and control rates have improved in most countries since 1990, but we found little change in most countries in sub-Saharan Africa and Oceania. Improvements were largest in high-income countries, central Europe, and some upper-middle-income and recently high-income countries including Costa Rica, Taiwan, Kazakhstan, South Africa, Brazil, Chile, Turkey, and Iran. Interpretation Improvements in the detection, treatment, and control of hypertension have varied substantially across countries, with some middle-income countries now outperforming most high-income nations. The dual approach of reducing hypertension prevalence through primary prevention and enhancing its treatment and control is achievable not only in high-income countries but also in low-income and middle-income settings