•Resisting model uncertainty safety factor for seismic NLFE analyses is proposed.•Several NLFE analyses of r.c. members subjected to cyclic loads are performed.•Different reinforced concrete shear ...walls are considered.•Different software codes and constitutive laws for concrete are adopted.•Probabilistic analysis of the model uncertainties through a Bayesian approach.
This study assesses the partial safety factor corresponding to the resistance model uncertainties in the use of non-linear finite element analyses (NLFEAs) for reinforced concrete systems subjected to cyclic loads. Specifically, various walls experimentally tested are considered for this investigation and are simulated through two-dimensional (i.e., plane stress) finite element (NLFE) models. The comparison between the global resistances from the plane stress NLFE structural models and the experimental tests is carried out considering the possible modelling hypotheses available in relation to the mechanical response of reinforced concrete structural systems subjected to cyclic loads. After that, a probabilistic processing of the abovementioned epistemic uncertainties is carried out in line with a Bayesian updating. In detail, each prior distribution of the resistance model uncertainty related to a specific combination of the modelling hypotheses is computed and successively updated with the data achieved from the other models to estimate the posterior distribution. Hence, the coefficient of variation and the mean value of the resistance model uncertainties are evaluated and the corresponding partial safety factor is assessed in line with the NLFEA safety formats of reinforced concrete systems for seismic analyses.
This paper presents a probabilistic framework to derive the safety factors for fatigue of steel and composite steel concrete road bridges. Engineering models are used for the design and the safety ...factor is derived in such a way that the design meets the target reliability set by international Eurocode and ISO standards, estimated using measured data and advanced probabilistic models. Engineering model uncertainties and dynamic amplification factors are established through comparison of measurements and models. The value of visual inspections is quantified based on observations from practice and expert opinions. The safety factors are derived for Eurocode’s Fatigue Load Model 4 and Eurocode’s tri-linear S-N curve. The study shows that the safety factors for fatigue as currently recommended by the Eurocodes need to be raised.
•A method is proposed to derive safety factors for the fatigue design of bridges.•Engineering model uncertainty is determined by comparing modelled with measured strain.•Dynamic amplification through road bridge–vehicle interaction appears small.•The safety factor of Eurocode’s Fatigue Load Model 4 must be raised from 1 to 1.1.•Visually inspected bridges demand 10% lower safety factors than noninspected bridges.
•Machine learning -based shear strength models are proposed for SFRC beams.•The models are in close alignment with the experimentally observed shear strength and the existing models.•The models ...provide more accurate and unbiased predictions.•Partial resistance safety factors are proposed for the uncertainties related to shear design of SFRC beams.•Sensitivity of SFRC beam shear models to shear span to depth ratio is a cause for concern.
Shear failure in reinforced concrete beams poses a critical safety issue since it may occur without any prior signs of damage in some cases. Many of the existing shear design equations for steel fiber reinforced concrete (SFRC) beams include significant uncertainty due to failure in reflecting the phenomenology of shear resistance accurately. Given these, adequate reliability evaluation of shear design provisions for SFRC beam is of high significance, and increased accuracy and minimisation of variability in the predictive model is essential. This contribution proposes machine learning (ML) based methods - Gaussian Process regression (GPR) and the Random Forest (RF) techniques - to predict the ultimate shear resistance of SFRC slender beams without stirrups. The models were developed using a database of 326 experimental SFRC slender beams obtained from previous studies, utilising 75% for model training and the remainder for testing. The performance of the proposed models was assessed by statistical comparison to experimental results and to that of the state-of-practice existing shear design models (fib Model Code 2010, German guideline, Bernat et al. model). The proposed ML-based models are in close alignment with the experimentally observed shear strength and the existing predictive models, but provide more accurate and unbiased predictions. Furthermore, the model uncertainty of the various resistance models was characterised and investigated. The ML-based models displayed the lowest bias and variability, with no significant trend with input parameters. The inconsistencies observed in the predictions by the existing shear design formulations at the variation of shear span to effective depth ratio is a major cause for concern; reliability analysis is required. Finally, partial resistance safety factors were proposed for the model uncertainty associated with the existing shear design equations.
•Partial safety factor of the resisting model uncertainties for NLFEAs is proposed.•Several NLFE analyses of reinforced concrete members are performed.•Different r.c. members with different ...behaviours and failure modes are considered.•Different software codes and constitutive laws for concrete in tension are adopted.•Probabilistic treatment of the model uncertainties through a Bayesian approach.
This work evaluates the partial safety factor related to the resistance model uncertainties in non-linear finite element analyses (NLFEAs) for reinforced concrete structures. Various experimental tests concerning different typologies of structures with different behaviours and failure modes, i.e., walls, deep beams, panels, are simulated by means of appropriate two-dimensional finite elements (FE) structural models (i.e., plane stress configuration). Several FE structural models are defined for each experimental test to investigate the model uncertainty influence on the 2D NLFEAs of reinforced concrete structures in terms of global resistance, considering different modelling hypotheses to describe the mechanical behaviour of reinforced concrete members (i.e., epistemic uncertainties). Subsequently, the numerical results are compared to the experimental outcomes. Then, a consistent treatment of the resistance model uncertainties is proposed following a Bayesian approach. Specifically, the prior distributions of the resistance model uncertainties for the different modelling hypotheses are evaluated and then each one is updated on the basis of the data obtained from the other models to evaluate the posterior distributions. After that, the mean value and the coefficient of variation characterizing the resistance model uncertainties are identified. Finally, in agreement with the safety formats for NLFEAs of reinforced concrete structures, the partial safety factor related to the resistance model uncertainties is evaluated.
•We present a coal-gas outburst hypothesis model, which describes the progressive failure process of gas-bearing coal based on strength reduction theory.•Considering gas adsorption and seepage, the ...yield failure criterion and limit instability criterion of gas-bearing coal are established respectively.•Simulate the fluid-structure coupling characteristics under strength reduction.•Then the correlation between (limit) safety factor and outburst risk is explained, and verified by laboratory tests.
Coal is a kind of natural pore-fracture dual medium, which determines the diffusion and seepage characteristics of gas inside under the stress conditions. In turn, the gas migration has an effect on the mechanical damage properties of coal and is closely related to the occurrence of coal-gas outburst. The occurrence of outburst is inevitably accompanied by the instantaneous displacement mutation of gas-bearing coal, which is difficult to explained by conventional plastic zone analysis. And the process from plastic failure to instability is still vague, which makes the instability critical of outburst difficult to determine. Therefore, aiming at the outburst in the working face, we put forward a progressive failure and outburst hypothesis model based on the limit analysis method of strength reduction theory. Then, the limit instability criterion of gas-bearing coal is modified, and the coal-gas outburst in the strength reduction process is simulated by using the cyclic calculation method of COMSOL software. It describes the characteristics of fluid–structure coupling and progressive failure instability of gas-bearing coal. Finally, we use the limit safety factor to describe the outburst criticality and the outburst risk. We find that the initial uncovering coal area, stress and gas pressure play an important role in controlling outburst, especially the coal stability is extremely sensitive to gas pressure changes under high stress. And based on these, the outburst prevention and control measures are put forward. The method has potential application value for the risk assessment and prevention of outburst on site.
The purpose of this paper is to discuss the safety of ship berthing operations at port dock. Based on the features of ship’s berthing operations and the relevant literature, the safety factors (SFs) ...of ship berthing at port docks are first investigated. A gap assessment model based on Fuzzy AHP is then proposed to assess the perceived differences on those SFs between port marine pilots and shipmasters. Finally, the ships’ berthing operations at Kaohsiung Port in Taiwan were employed to illustrate the model’s practical application. The result may provide practical information for both marine pilots and shipmasters to improve the safety performance of ship berthing operations at port docks.
Based on limit analysis and pseudo-dynamic methods, a proposed method for evaluating slope stability under seismic conditions that considers dynamic changes in the axial force of the anchor cables is ...presented. The case study shows that compared to the computational conditions that neglect the dynamic changes in axial forces, the dynamic safety factors obtained by the proposed method are greater, whereas the dynamic variation amplitudes of the dynamic safety factors obtained by the proposed method are smaller. The better anti-seismic effect of the anchor cables due to considering the dynamic changes in axial forces is reflected by the proposed method.
This article aims to analyze the implementation of teleworking as a security practice to face the crisis resulting from the Covid-19 disease. The present paper provides both theoretical and practical ...results. From a theoretical standpoint, the Baruch and Nicholson approach is extended with environmental, safety, and legal factors that explain telework. From a practical perspective, a database of companies that have introduced telework as a measure to face coronavirus in a crisis context has been obtained. In short, the Covid-19 crisis demonstrates how teleworking has been used by companies to ensure their employees’ safety and to provide continuity to economic activity. Consequently, safety factors are relevant in the study of teleworking and should be considered in further research.
•Basis of design principles for cross laminated timber.•Uncertainties related to the production procedure of CLT.•Difficulties of non-standardized test procedure of CLT.
The design of cross laminated ...timber (CLT) structures is not included in the current version of European structural timber design standards of EN 1995 (Eurocode 5, EC 5). Due to the increasing importance of CLT, in different applications such as complete wall or floor elements as well as girders, it is one of the main goals of the currently ongoing revision of EC 5 to provide design principles for CLT structures. In the present paper some general aspects, relevant for the implementation of CLT in European standards in order to be consistent with the general philosophy of the Eurocodes are summarized and discussed. The differences between standard test specimens and structural components as well as the uncertainties related to the production procedure of CLT and the non-standardized test procedure are discussed. An investigation of 12 different test series from five different producers clearly indicates a large variation between different production series. Based on the investigation from the test series a reliability analysis is performed. The results indicate that the same partial safety factor as recommended for glued laminated timber (GLT) is appropriate in order to achieve an acceptable reliability. However, the analysis also indicates the potential for a smaller partial safety factor in the future, in case that the production of CLT is standardized and appropriate standardized test methods for the individual material properties exist.
PDF
