Semi-probabilistic Approach Research Articles

Contribution to Adjustment of Partial Safety Factors for RC Water Tank Design

Traditionally, the optimisation of civil engineering structures is conducted by a deterministic approach based on global safety factors recommended by the dimensioning codes, such as the Algerian seismic code (RPA) and the Eurocode (EN 1990). These factors are applied to take into account the uncertainties related to the most important parameters of the structure as well as the actions and their effects, and implicitly provide a target level of reliability. The use of these factors aims to introduce a sufficient margin of safety in order to increase the safety of the structure design and to reduce the role of uncertainties on the performance of the optimised structure. In this research, the authors propose to use the semi-probabilistic method in the limit state design of the top ring beam of a Reinforced Concrete (RC) water tank placed on the ground for assessing the partial safety factors of both loadings and materials strength. The reliability approach is first conducted using a computer code developed with Matlab© software based on the Monte Carlo simulation method and on the First Order Reliability Method (FORM). Two random variables are considered, i.e. the static live load and the concrete compressive strength, both modelled by normal distribution laws. In the second part of this work, partial safety factors are adjusted in order to achieve the target reliability in a range of performance of the civil engineering structure. This semi-probabilistic approach is applied to a case study of an RC tank of capacity 250 m3 in order to adjust safety factors so as to obtain a compatible probability of failure with the appropriate target value as a function of consequence class. The results of the study conclude that this semi-probabilistic method allows adjusting adequate partial safety factors according to target reliability.

Risk assessment of multiple pesticide residues in Agrocybe aegerita: Based on a 3-year monitoring survey

The presence of pesticide residues in Agrocybe aegerita has raised an extensive concern. In this paper, based on a 3-year monitoring survey, the dietary exposure risks through A. aegerita consumption for different population subgroups were assessed using both deterministic and semi-probabilistic approaches under the best-case and the worst-case scenarios. Among the 52 targeted pesticides, 28 different compounds were identified in the concentration range of 0.005–3.610 mg/kg, and 87.4 % of samples contained one or more pesticide residues. The most frequently detected pesticide was chlormequat, followed by chlorfenapyr and cyhalothrin. The overall risk assessment results indicated extremely low chronic, acute, and cumulative dietary exposure risks for consumers. Using the ranking matrix, intake risks of pesticides were ranked, revealing endsoluran, chlorpyrifos, and methamidophos to be in the high-risk group. Finally, considering various factors such as the toxicity and risk assessment outcomes of each positive pesticide, use suggestions were proposed for A. aegerita cultivation.

Probabilistic Design Methods for Gust-Based Loads on Wind Turbines

The IEC 61400-1 standard specifies design load cases (DLCs) to be considered in the design of wind turbine structures. Specifically, DLC 2.3 considers the occurrence of a gust while the turbine shuts down due to an electrical fault. Originally, this load case used a deterministic wind event called the extreme operating gust (EOG), but the standard now also includes an approach for calculating the extreme response based on stochastic simulations with turbulent wind. This study presents and compares existing approaches with novel probabilistic design approaches for DLC 2.3 based on simulations with turbulent wind. First, a semiprobabilistic approach is proposed, where the inverse first-order reliability method (iFORM) is used for the extrapolation of the response for electrical faults occurring at a given rate. Next, three probabilistic approaches are formulated for the calculation of the reliability index, which differs in how the aggregation is performed over wind conditions and whether faults are modeled using a Poisson distribution or just by the rate. An example illustrates the methods considering the tower fore-aft bending moment at the tower base and shows that the approach based on iFORM can lead to reductions in material usage compared to the existing methods. For reliability assessment, the probabilistic approach using the Poisson process is needed for high failure rates, and the reliabilities obtained for designs using all semiprobabilistic methods are above the target level, indicating that further reductions may be obtained via the use of probabilistic design methods.

A semi-probabilistic approach for assessing material and model uncertainty in the out-of-plane response of URM structures

A procedure tailored for a practical calibration of partial safety factors (PSF) related to input material properties is presented. The methodology addresses the propagation of material and model uncertainty through a FORM-based calibration, resulting in a noteworthy reduction in computation time compared to full probabilistic approaches. The novelty lies on the introduction of the Star Design with Central Point (SDCP) method for the computation of sensitivity coefficients and corresponding partial safety factors for material uncertainty. A calibration example is reported with reference to unreinforced masonry structures under out-of-plane failure. The effect of considering different geometries, failure modes, and modelling approaches is explored. A comparative analysis involving different approaches to propagate uncertainties emphasize the promising potential of the proposed procedure.

Structural reliability of a RC beam considering different preliminary designs

In the last decades, most of the structural designs around the world have been made by employing semi-probabilistic approaches based on partial safety factors. These practical methods allow the engineer to deal with the safety of structures without the need to directly address the uncertainties involved. The simplicity of these approaches depends on the fact that the same values of the safety factors must be applicable to a large number of different cases; this typically leads to dispersion in the structural reliability levels. The present paper aims at quantifying such dispersion within a specific scenario, regarding RC structures, in a way different from those found in the literature. It focuses on a simple residential building, for which seven preliminary design solutions are proposed by different engineers, and seven different structures are obtained from these solutions, considering the specifications given by the Brazilian structural design code ABNT NBR 6118:2014. The structural reliability indexes of a continuous beam, common to all solutions, are assessed and compared. The results indicate that, even in this specific case, the variability related to the safety levels is significant. Furthermore, in some cases the reliability index is found to be below the target levels provided by international structural standards.

Analysis of modern approaches to assessing reliability in construction

Introduction. The study considers modern strategies for ensuring the reliability of building structures in Russian and foreign regulations, including probabilistic, risk-informed and semi-probabilistic criteria of reliability assessment, at all stages of the life cycle of the structure. The advantages and disadvantages of prescriptive and parametric approaches are analyzed and ways of their further improvement are suggested.Aim. To clarify the terminology of parametric regulation in construction, to analyze the existing differences in its interpretation, and to develop an innovative strategy for further development of Russian regulation based on a comparative analysis of domestic and foreign approaches to reliability assessment.Materials and methods. The methodology involved studying the structure of Russian and foreign regulatory documents in the field of reliability and performing their comparative analysis. The study considered the main approaches to technical regulation in the construction industry.Results. The analysis outlined the criteria underlying the fastest introduction of innovations and ensuring the safety of technical solutions. The study demonstrated the difference between the meaning of the term “parametric regulation” in Russian strategy and its foreign interpretation. The regulation standards of the Russian Federation are based mainly on a semi-probabilistic approach and specification of partial reliability factors, i.e. individual parameters of strength and loads, while in the foreign standards, notably in ISO 2394:2016 and Eurocodes, the emphasis is shifted to qualitative and probabilistic criteria for assessing reliability. However, all social, economic and performance criteria should be observed only after all requirements for the reliability and safety of people have been met. Thus, both Russian and foreign approaches to regulation demonstrate no fundamental contradictions. The approaches are gradually moving towards convergence while maintaining continuity in the development of the regulatory framework.Conclusions. The principles of ensuring the reliability of the designed buildings and structures in Russian, international and foreign regulation standards are quite close and are based on the limit state method with a reasonable combination of mandatory and recommended parameters. The main criterion consists in ensuring the safety of human life. Under contemporary conditions, traditional semi-probabilistic approaches to regulation should be accompanied by mechanisms for rapid introduction of innovations and new technologies in construction. In terms of reliability, these mechanisms involve additional probabilistic reliability criteria and risk assessment methods. The reliability criteria will contribute in choosing the optimal design and technological solutions for the construction of unique buildings and structures, higher criticality structures, as well as in assessing existing structures during their life cycle.

Wastewater surveillance of pharmaceuticals during the COVID-19 pandemic in Mexico City and the Mezquital Valley: A comprehensive environmental risk assessment

This study tracked five pharmaceutically active compounds (PhACs) in Mexico City's sewage, namely, famotidine, indomethacin, dexamethasone, azithromycin, and ivermectin, which were used to treat COVID-19. The monitoring campaign was carried out over 30 months (May 2020 to November 2022), covering the five COVID-19 waves in Mexico. In the Central Emitter, the main sewage outflow, famotidine displayed levels of 132.57 ± 28.16 ng L−1 (range from < LOQ to 189.1 ng L−1), followed by indomethacin (average 672.46 ± 116.4 ng L−1, range from 516.7 to 945.2 ng L−1), dexamethasone (average 610.4 ± 225.7 ng L−1, range from 233.4 to 1044.5 ng L−1), azithromycin (average 4436.2 ± 903.6 ng L−1, range from 2873.7 to 5819.6 ng L−1), and ivermectin (average 3413.3 ± 1244.6 ng L−1, range from 1219.8 to 4622.4 ng L−1). The concentrations of dexamethasone, azithromycin and ivermectin were higher in sewage from a temporary COVID-19 care unit, by a factor of 3.48, 3.52 and 2.55, respectively, compared with those found in municipal wastewater. In the effluent of the Atotonilco Wastewater Treatment Plant (AWWTP), which treats near 60 % of the Mexico City's sewage, famotidine was absent, while concentrations of indomethacin, dexamethasone, azithromycin and ivermectin were 78.2 %, 76.7 %, 74.4 %, and 88.1 % lower than those in the influent, respectively. The occurrence of PhACs in treated and untreated wastewater resulted in medium to high environmental risk since Mexico City's wastewater is reused for irrigation in the Mezquital Valley. There, PhACs were found in irrigation canals at lower levels than those observed in Mexico City throughout the monitoring. On the other hand, famotidine, indomethacin, and dexamethasone were not found in surface water resulting from the infiltration of wastewater through soil in Mezquital Valley, while azithromycin and ivermectin sporadically appeared in surface water samples collected through 2021. Using an optimized risk assessment based on a semi-probabilistic approach, the PhACs were prioritized as ivermectin > azithromycin > dexamethasone > famotidine > indomethacin.

The first harmonised total diet study in Portugal: Vitamin D occurrence and intake assessment

Vitamin D acts in calcium and phosphate homeostasis and also as an immunomodulatory hormone. To estimate the vitamin D intake by the ‘adults’ and ‘elderly’ Portuguese populations TDS methodology was used, since in the absence of skin UVB exposure, food and supplements are the only vitamin D sources. Vitamin D was quantifiable in 78 (24 from the fish group) of the 164 TDS samples. Sea bream contained the most vitamin D (13.8 µg/100 g), followed by plaice (9.2 µg/100 g). MCRA software (semi-probabilistic approach) was used to estimate the median vitamin D intake that ranged between 2.47 (‘adults’ ‘males’) − 1.45 (‘elderly’ ‘females’) µg/day, well below the Dietary Reference Values (5–15 µg/day). Plaice, sea bream and sardine were the main contributors to intake. A prevalence of 94% inadequate vitamin D intake for ‘adults’ and ‘elderly’ was found based on the estimated average requirement of 10 µg/day.

Reinforced Concrete Durability Design Through a Semi-probabilistic Approach

This study provides a semi-probabilistic approach to durability design of reinforced concrete structures, subjected to carbonation-induced corrosion. The method was developed from an existing approach and using comprehensive data collated from the literature. A statistical model for predicting accelerated carbonation coefficient, using as input variables mix proportions and test conditions was also generated. The performance of the proposed method was assessed and proved appropriate. Besides delivering a more consistent semi-probabilistic method to design for the avoidance of unforeseen carbonation-induced corrosion problems, the developed statistical model to estimate the accelerated carbonation coefficient is a useful tool on the mix design, from the standpoint of conforming with the accelerated carbonation coefficients obtained through the semi-probabilistic method.

On the nonstationary identification of climate-influenced loads for the semi-probabilistic approach using measured and projected data

On the nonstationary identification of climate-influenced loads for the semi-probabilistic approach using measured and projected data

Simulation-Based Reliability Analysis of Steel Girder Railway Bridges

Bridges are an essential component of the transportation system and safety and sustainability of bridges are critical for the efficient operation thereof. Due to scarcity of resources, an economical way should be determined to design and maintain bridges and the transportation system in general. Reliability indexes are widely used in the analysis of these concepts within a semi-probabilistic approach. However, advances in computer technology allow implementing a fully-probabilistic approach. This study represents a simulation-based reliability analysis of steel girder bridges in the railway lines. Statistical parameters of the bridges are determined both analysing the existing body of knowledge available in the literature and conducting specimen tests. The Bayesian approach is used to update the statistical properties of the steel material. Basic Monte Carlo Simulation (MCS) is used to simulate the load and resistance of the bridge. The reliability of the bridges is determined according to their ultimate limit states and statistical load distribution. By using simulation, the consistency of the log-normal marginal distribution obtained is analysed herein.

The Post-fire Assessment of Steel Structures, a Reliability-Based Semi-probabilistic Approach

The Post-fire Assessment of Steel Structures, a Reliability-Based Semi-probabilistic Approach

Design-related reassessment of structures integrating Bayesian updating of model safety factors

In the semi-probabilistic approach of structural design, the partial safety factors are defined by considering some degree of uncertainties to actions and resistance, associated with the parameters’ stochastic nature. However, uncertainties for individual structures can be better examined by incorporating measurement data provided by sensors from an installed health monitoring scheme. In this context, the current study proposes an approach to revise the partial safety factor for existing structures on the action side, γE by integrating Bayesian model updating. A simple numerical example of a beam-like structure with artificially generated measurement data is used such that the influence of different sensor setups and data uncertainties on revising the safety factors can be investigated. It is revealed that the health monitoring system can reassess the current capacity reserve of the structure by updating the design safety factors, resulting in a better life cycle assessment of structures. The outcome is furthermore verified by analysing a real life small railway steel bridge ensuring the applicability of the proposed method to practical applications.

The first harmonised total diet study in Portugal: Nitrate occurrence and exposure assessment

A harmonised TDS methodology was used to assess the Portuguese population’s nitrate baseline dietary exposure and the risk of exceeding the Acceptable Daily Intake (ADI). Nitrate occurrence in 164 TDS samples pooled based on 20 FoodEx2 groups, representative of 18 to 75 years old population diet, was determined using UV-HPLC. The ‘vegetables’ group had the highest mean nitrate concentration (353 mg/kg), followed by ‘starchy roots’ (62 mg/kg), ‘composite dishes’ (53 mg/kg) and ‘fruits’ (46 mg/kg). Lettuce contained the most nitrates (1729 mg/kg). The estimated mean nitrate exposure of 1.17 mg/kg bw/day, with 3.18% of individuals exceeding the ADI, was assessed on a semi-probabilistic approach using the MCRA software. Lettuce (28%) contributed most to nitrate exposure followed by vegetable soup (13%). Processed meat contribution to exposure was 0.86% and 2.44% (overall population and consumers only). At population level the nitrate estimated exposure (mean and 95th percentile) revealed no reason for concern.

Composite overwrap repair of pipelines-reliability based design framework

Considering the ages and need for repairment of the gas and oil transmission pipes in the world, in the past years, lab and field experiments were performed on fiber reinforced polymer (FRP) wrapping to steel pipes. Although this technology has widely been employed for decades, further improvement on the design guidelines is still needed. In this context, this study proposes a reliability structural design framework for the repairment of corroded pipelines using FRP composite wrapping. To be consistent with international structural design standards, reliability-based design framework is to be proposed within a semi-probabilistic approach by calibrating safety factors to account for the associated uncertainties in capacity and load effects to best meet the cost-safety balance in design. Currently, the repair design practice for corroded pipelines is based on a deterministic approach, and it cannot ensure the proper consideration of uncertainties and meeting a consistent level of target reliability in design. This study involves comprehensive experiments of FRP materials under two different environmental conditions for onshore and offshore pipes, which were used to propose the best-fit statistical models to the design parameters to realistically represent the random variables in the proposed safety factor based structural design framework. Through extensive reliability analyses, the values for the safety factors for composite and steel have been proposed according to the target reliability indices and the corrosion rate. The proposed design framework for corroded steel pipes with FRP overwrap repairment is expected to improve the current design practice and optimize the cost and safety by meeting the target reliability level.

Simplified expressions for reliability assessments in code calibration

First Order Reliability Methods (FORM) have been used by specification committees in the reliability analyses required for the calibration of resistance and safety factors for the past 40 years. However, these methods are iterative, require input information that may not be readily available, and make comparisons between different approaches or design frameworks difficult. This paper presents a set of simplified equations to estimate reliability indices β, resistance factors ϕ and partial safety factors γM based on simpler First Order Second Moment (FOSM) considerations for the US and Eurocode frameworks, which are particularized for different load cases, and on the semi-probabilistic approach prescribed in the Eurocode 0. The equations provide direct relationships between the reliability calibration results corresponding to different design frameworks, and can be used to estimate resistance factors as simple cross-checks for the US framework based on the partial safety factors derived for the Eurocode (or vice versa) from basic statistical input information and given target reliability, including when the data available in the literature is insufficient to perform FORM analyses. The accuracy of the proposed equations is assessed against reliability results derived using FORM techniques for an extensive database of steel and stainless steel frames subjected to gravity and combined gravity plus wind load cases collected from the literature, and limitations for their applicability are recommended. The results demonstrate that the set of equations proposed in this paper provides accurate estimations of the reliability index β, resistance factors ϕ and partial safety factors γM and can assist specification committees in the process of calibrating suitable ϕ and γM-factors.

Probabilistic Health Risk Assessment of Iodine Exposure in Bangladesh.

In this study, the concentrations of iodine in household salt samples (n = 690) were determined by following the iodometric titration method, and the health risks of Bangladeshi people were assessed based on the semi-probabilistic approach and the US Environmental Protection Agency (USEPA) deterministic model. After adjusting 20% of cooking losses, the iodine concentration (mean, range) in salt samples of Phultala, Dighalia, Terokhada, Rupsha, Batiaghata, Dumuria, Paikgacha, Koyra, Dacope, and KCC was (29.68 ± 8.67, 14.39-48.26), (31.05 ± 6.68, 15.24-43.18), (26.94 ± 5.57, 16.09-45.72), (24.33 ± 5.61, 12.70-37.26), (26.69 ± 6.73, 10.16-44.87), (27.20 ± 8.44, 9.31-53.34), (27.71 ± 8.09, 8.46-47.42), (28.39 ± 7.80, 11.01-46.57), (28.20 ± 7.97, 3.38-49.10), and (29.21 ± 6.62, 18.62-40.64) mg/kg, respectively. The iodine contents in 97.25% of samples were within the standard fortification level of Bangladesh (15-50mg/kg), while 2.61% of samples were below this limit. The semi-probabilistic risk assessment studies showed that 80.14% of samples at a low ingestion rate could provide optimal nutrition (150-299μg/day) to the whole population. Contrarily, at medium, moderate-high, and high consumption rates 34.93%, 65.22%, and 85.94% of samples, respectively, belonged to above the requirements to excessive exposure categories (300-1100μg/day), which might cause iodine-induced diseases. The target hazard quotient (THQ) values for the adults in most of the samples were within the threshold risk limit (THQ < 1.0), whereas THQ values in 6.82% to 85.97% of samples for the children at low to high ingestion rates, respectively exceeded this limit, which revealed that the adults were almost safe, but the children might face non-carcinogenic health effects. Therefore, regular monitoring of iodine concentration in iodized salts should be done to prevent iodine deficiency or iodine-induced disorders.

Probabilistic approach and fault-tree analysis for increased bucket wheel excavator welded joints reliability

The main part of this paper is consisted of presentation of a new method for determination of reliability of the structures. Presented method provides more knowledge and confidence when evaluating the construction of vital welded structures and determining the cause of their failure in service. The probabilistic and semi-probabilistic approaches have been defined for expressing the coefficient of validity (ν) and the coefficient of the welded joint weakening (η), while reliability (R) has been defined as a measure of quality of installed vital welded structures on bucket wheel excavators in service. The applied "fault-tree" analysis enables quantitative and qualitative analysis of the failure causes, diagnostics of behavior and structural degradation, evaluation of integrity and estimate of the service life of the vital welded structures that have a flaw in the welded joint, as well as creating a data base, by which the reliability of the bucket wheel excavators can be increased. The method also makes possible to efficiently test the welded joints, during the manufacturing, acceptance and assembling the new welded structures of the bucket wheel excavators, cranes or bridges.

Occurrence and risk assessment of pharmaceuticals and personal care products (PPCPs) against COVID-19 in lakes and WWTP-river-estuary system in Wuhan, China

The consumption of pharmaceuticals and personal care products (PPCPs) for controlling and preventing the COVID-19 would have sharply increased during the pandemic. To evaluate their post-pandemic environmental impacts, five categories of drugs were detected in lakes and WWTP-river-estuary system near hospitals of Jinyintan, Huoshenshan and Leishenshan in the three regions (J, H and L) (Regions J, H and L) in Wuhan, China. The total amount of PPCPs (ranging from 2.61 to 1122 ng/L in water and 0.11 to 164 ng/g dry weight in sediments) were comparable to historical reports in Yangtze River basin, whereas the detection frequency and concentrations of ribavirin and azithromycin were higher than those of historical studies. The distribution of concerned drugs varied with space, season, media and water types: sampling sites located at WWTPs-river-estuary system around two hospitals (Regions L and J) usually had relatively high waterborne contamination levels, most of which declined in autumn; lakes had relatively low waterborne contamination levels in summer but increased in autumn. The potential risks of detected PPCPs were further evaluated using the multiple-level ecological risk assessment (MLERA): sulfamethoxazole and azithromycin were found to pose potential risks to aquatic organisms according to a semi-probabilistic approach and classified as priority pollutants based on an optimized risk assessment. In general, the COVID-19 pandemic did not cause serious pollution in lakes and WWTPs-river-estuary system in Wuhan City. However, the increased occurrence of certain drugs and their potential ecological risks need further attention. A strict source control policy and an advanced monitoring and risk warning system for emergency response and long-term risk control of PPCPs is urgent.

Partial factors and reliability verification for the site load factor approach for the assessment of existing bridges

Fundamental concepts of the developed site load-factor approach for the assessment of existing bridges are introduced in this contribution. The method is complemented by the calibration of the partial factors accounting for uncertainties. The calibration is crucial for the simple application of the method in concordance with semi-probabilistic approaches commonly presented in design guidelines. As means of verification of the proposed methodology, a reliability analysis of the site load factor approach is offered to assure that the intended safety level required by codes is achieved. Results indicate that reductions of the static load effects mandated by design stipulations can be implemented, while maintaining the required safety levels. The methodology presented here is developed in the context of data collected in South Africa, nevertheless the framework is general and can be extrapolated to any other country or dataset.