Level Of Structural Reliability Research Articles

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.

A Dynamic Reliability Prognosis Method for Reusable Spacecraft Mission Planning Based on Digital Twin Framework

Abstract Reusable spacecraft has great potential in reducing space launch cost. Structural reliability evaluation is critical for mission planning of reusable spacecraft. A dynamic reliability prognosis method based on digital twin framework is proposed for mission planning in the paper. In this method, Uncertainties integration and dynamic model updating are implemented through a dynamic Bayesian network. A maintenance point is set when the predicted structural reliability level is lower than a threshold or unexpected conditions such as landing impact occur. Then, inspected data can be assimilated by the framework to dynamically update the structural reliability. Thus, it supports dynamic adjustment of maintenance interval, early warning of structure failure, and mission planning with quantified risk. A numerical example considering single point crack growth under fatigue load and landing impact of a simplified spacecraft structure is used for demonstration. Results show that the crack size predictions can be calibrated by inspected data and its uncertainties can be reduced. The proper selection of landing impact probability in reliability prediction is helpful to control the maintenance interval. The reliability of the spacecraft can be increased through model updating with new inspected data, representing a potential lifetime extension can be realized by the proposed method.

Modern import substitution technologies and quality control of workpieces

An expert assessment of the quality of reclamation castings is presented to identify the level of structural reliability. Visual-instrumental and capillary control made it possible to establish technological flaws that caused product defects. The introduction of electronic accompanying information systems with intermediate digital control of casting manufacturing is justified by the inconsistency of the appearance of casting defects. It is proposed to use the concept of product lifecycle management as a basic one in ensuring the quality of various components of technological machines in the strategy of import substitution. Keywords: casting, quality, defect, control, management, digital environment. nssevr@yandex.ru, a.apatenko@rgau-msha.ru

Design of Steel Fibre Reinforced Concrete Structures According to the Annex L of the Eurocode-2 2023

The Annex L of the new Eurocode – 2 gathers -for the first time- provisions for the design of Steel Fibre Reinforced Concrete (SFRC) structures. This response to the necessity of the construction sector for provisions and regulations of this composite material within the European space and this Annex is supported by the solid background derived from consistent research and experiences carried out along the last two decades. The existence of these design provisions could both favour competitiveness and enhance sustainability performance within the construction sector since new concrete reinforcement alternatives could be considered while ensuring the structural reliability level accepted for traditional reinforced concrete structures. This paper is aimed to cover -not exhaustively- all those features concerning SFRC included into the EC-2 and complement those -when considered necessary- with scientific literature.

Gaussian process regression-based surrogate modelling for direct loss-based seismic design of low-rise base-isolated structures

Seismic base isolation has gained popularity in the last decades. As a result, many structures are now equipped with base isolation systems to offer enhanced seismic performance and meet the needs of risk-aware stakeholders. However, a robust performance-based seismic design of these types of structures is generally not carried out due to the iterative nature of common design approaches and the time/computational resources required for such iterations, which are incompatible with the preliminary design phase. Indeed, seismic risk/loss is often just assessed at the end of the design process as a final verification step. This paper offers an overview of a simplified methodology for the seismic design of low-rise structures equipped with a base isolation system to achieve a predefined level of earthquake-induced economic loss while complying with a predefined minimum level of structural reliability. The main advantage of the proposed methodology is that it requires no design iterations. The procedure is enabled by Gaussian-process-regression-based surrogate probabilistic seismic demand modelling of equivalent single degree of freedom systems (i.e., the probability distribution of peak horizontal displacements and accelerations on top of the isolation layer conditional on different ground-motion intensity levels). Combined with simplified loss models for the base isolation system and the structural and non-structural components of the superstructure, this approach allows mapping a range of structural configurations to their resulting seismic loss. A designer can then select one of the identified combinations of the strength of the superstructure and properties of the isolation system conforming with the loss target, and reliability requirements, and consequently detail the superstructure and isolation system accordingly. This paper introduces the implemented surrogate probabilistic seismic demand models and provides an overview of a tentative Direct Loss-based Design procedure for low-rise base-isolated structures.

Stochastic Reliability-Based Design Optimization Framework for the Steel Plate Girder with Corrugated Web Subjected to Corrosion.

This paper proposes the framework for reliability-based design optimization (RBDO) of structural elements with an example based on the corrugated web I-girder. It tackles the problem of topological optimization of corroding structures with uncertainties. Engineering restrictions follow a concept of the limit states (LS) and extend it for stability and eigenfrequency assessment. The reliability constraints include all the LS; they are computed according to first- and second-order reliability methods. The RBDO example minimizes the bridge girder cross-section while satisfying the structural reliability level for the ultimate and the serviceability limit states, stability, and eigenfrequency. It takes into consideration two uncorrelated random effects, i.e., manufacturing imperfection and corrosion. They are both Gaussian; the first of them is applied at assembly time, while the second is applied according to the time series. The example confronts three independent FEM models with an increasing level of detailing, and compares RBDO results for three concurrent probabilistic methods, i.e., the iterative stochastic perturbation technique (ISPT), the semi-analytical method, and the Monte Carlo simulation. This study proves that the RBDO analysis is feasible even for computationally demanding structures, can support automation of structural design, and that the level of detailing in the FEM models influences its results. Finally, it exemplifies that reliability restrictions for LS are much more rigorous than for their deterministic counterparts, and that the fastest ISPT method is sufficiently accurate for probabilistic calculations in this RBDO.

Probabilistic Collapse Design and Safety Assessment of Sandwich Pipelines

This paper presents an approach for probabilistic design and safety assessment of sandwich pipelines under external pressure. The methodology consists of the categorisation of sandwich pipeline collapse strength models based on interlayer adhesion conditions. The models are validated by comparing their predictions against collapse test data of sandwich pipelines. The accuracy of the strength models and their prediction uncertainty are used to select the best model in each category. Regarding interlayer adhesion categories, uncertainty propagation of models’ predictions over a wide range is assessed by the Monte Carlo simulation method. The proposed methodology is demonstrated using a case study of a sandwich pipeline with adequate probabilistic modelling of the basic random variables. Different limit states are defined for three categories of sandwich pipelines, based on which structural reliability indices are estimated. In employing the First Order Reliability Method for sensitivity analysis, the importance of basic variables of the limit states is evaluated. Later, a parametric analysis is conducted, presenting reliability variations for several design and operational scenarios of sandwich pipelines. Finally, to achieve a uniform level of structural reliability of sandwich pipelines, a few suggestions are provided, and practical partial safety factors are calculated. The results of the present analysis can provide guidance on the probabilistic design and operational safety assessment of sandwich pipelines.

Buckling curves of stainless steel CHS members: Current state and proposed provisions

The study objective is to propose the optimal shape of the flexural buckling curves for stainless steel circular hollow cross-section (CHS) members. It has been pointed out by several researchers, that the currently utilized buckling curves do not fulfil the required structural reliability level, and several provisions have already been proposed. Following this research, our proposals are based on a numerical investigation of the ultimate limit state of geometrically imperfect stainless steel CHS columns of three different material grades (Austenitic 1.4307, Ferritic 1.4003 and Duplex 1.4462) using the statistical characteristics of input initial imperfections, material and geometric parameters. The statistical characteristics are considered according to the results of published research. The first-order reliability method (FORM) supported by the advanced finite element method – geometrically and materially nonlinear imperfect analysis (GMNIA) – is used. The values of the ultimate resistance obtained using FORM are compared with the values of the design resistance determined according to the corresponding European standards and are used to determine the optimal shape of flexural buckling curves. Additionally, the influence of linear correlation between the ultimate resistance of CHS stainless steel columns exposed to flexural buckling and input imperfections is discussed. Studies have shown that the maximum effect of initial axial curvature on resistance occurs at higher slenderness compared to carbon steels. The obtained results present provisions to optimize the flexural buckling curves of stainless steel CHS members and could significantly improve the structural efficiency, resulting in material savings, while preserving the required level of structural reliability.

Reliability-based bottom-up manufacturing cost optimisation for composite aircraft structures

A novel methodology is presented for the reliability-based manufacturing cost optimisation of composite aircraft structures. A comprehensive bottom-up costing approach is employed, enabling precise manufacturing cost estimation in terms of material, machine, labour, tooling, and indirect costs. This approach splits the manufacturing process into many individual activities, which can be combined in many different ways, allowing the proposed optimisation methodology to be applied to a wide range of composite aircraft structures. A genetic algorithm (GA) is coupled with a deep neural network (DNN) to efficiently determine the optimal composite ply stacking sequence for every part of an assembled structure. A numerical example featuring a composite-stiffened aircraft fuselage panel is investigated. The reliability of the panel is measured in terms of its buckling resistance, and its manufacturing cost is estimated based on the individual costs of over 20 activities. The labour times for each activity were estimated based on data collected from an aerospace company specialising in the manufacture of advanced composite aircraft structures. Results indicate that material, machine, labour, and tool costs can vary significantly depending on the level of structural reliability required, demonstrating the importance of accounting for non-material costs when designing composite aircraft structures.

Prospects for low-carbon design theory of concrete structures

<p indent="0mm">Industrial civilization causes huge carbon emissions, accelerates climate change, and hinders the sustainable development of human society. The construction industry causes about 40% of annual global anthropogenic carbon emissions, within which the massive construction of concrete structures alone accounts for more than 10% of the global emissions. China’s national goals for carbon peaking, neutrality, and the low-carbon development consensus call for the low-carbon design theory of concrete structures in the construction industry. Starting from the scientific issues with the concrete structure-environment symbiotic system, this paper clarifies the indicators, design methods and tuning means of low-carbon structural design, aiming to lay a foundation and provide suggestions for the development of low-carbon design, and promote the sustainable development of concrete industry. By briefly reviewing the history of the concrete industry, we illustrate the trend of low-carbon transitions, for which it is urgently needed to shift the perspective of structural design from only centering on human needs to meeting the sustainable needs of the integrated system of concrete structures and environments. Based on the characteristics of carbon emissions and uptake of concrete structures, the significance of regulating concrete structures’ net embodied carbon emissions for climate change mitigation is clarified. Further, to cope with climate change, we put forward the scientific issues and design requirements for the concrete structure-environment symbiotic system. To facilitate the sustainable development of the concrete structure-environment symbiotic system, we focus the low-carbon design method on the quantitative characterization of structure-environment dynamic coupling. The structural sustainability indicator is established to simultaneously reflect the structural reliability and carbon emission level of concrete structures. Further, we sort out relevant evaluation and design methods into the evolution of low-carbon design from the structural reliability design considering sustainability to the sustainability design characterized by a bidirectional perspective, which means the design methodology has developed from the reliability guarantee of qualitative low-carbon strategies facing climate change to quantitative carbon emission target guarantee in the form of conditional probability control, which ensures both low-carbon emissions and reliable service performance during the life cycle of concrete structures under climate change. Further, in order to assist the low-carbon design regulation, we put forward the carbon emission-based 3R^+C principles, i.e., carbon reduction, carbon reuse, and carbon recycling, to construct a low-carbon design technology system with superimposable carbon emission reduction benefits among categories. Typical low-carbon technologies for concrete structures are classified following the three principles according to their main emission reduction advantages, i.e., embodied carbon reduction in material production, embodied carbon allocation by construction mode transition, and carbon uptake with a developed end-of-life management system, and their emission reduction potential and promotion prospects are explored. A lot of future work is needed for the innovative development and promotion of low-carbon design of concrete structures, which includes clarifying the carbon emission benchmarks and goals for the concrete industry, strengthening the identification and management of failure risks and possible failure consequences under climate change, enriching and improving available low-carbon design technologies, and developing codes and software for integrated low-carbon design.

Calibration of Undrained Shear Strength Partial Factor Using Probability Theory

Design in accordance with Eurocode 7 applies the partial factors of geotechnical parameters to take into account uncertainties of various sources. The prescribed values of partial factors are unique, even though the degree of uncertainty can vary significantly. This can lead to an unequal reliability level of structures designed using the same procedures and methods. This paper analyses the influence of undrained shear strength variability on the reliability index (β), using reliability theory and statistical methods. Analyses were performed in the case of a shallow footing designed in accordance with Eurocode 7, design approach 3. It is shown that reliability indexes of a shallow footing could be lower than the target values prescribed in Eurocode. To meet these values, additional elaboration and calibration of undrained shear strength partial factor (γcu) was proposed.

Comparing Hysteretic Energy and Ductility Uniform Annual Failure Rate Spectra for Traditional and a Spectral Shape-Based Intensity Measure

In this study, with the objective to develop a reliability-based seismic design tool, ductility and dissipated hysteretic energy uniform annual failure rate (UAFR) spectra are obtained and compared using the spectral acceleration at first mode of vibration of the structure Sa(T1) and the well-known spectral shape-based intensity measure INp. Notice that this is the first time in the literature that UAFR spectra are obtained for the advanced spectral shape intensity measure INp. For this aim, 110 simulated ground motions recorded from the soft soil of Mexico City were selected due to their large energy amount demanded to the structures; moreover, four elastoplastic hysteretic behavior models are considered for the dynamic analyses with post-yielding stiffness of 0, 3, 5, and 10%. It is observed that the use of elasto-perfectly plastic models provided similar UAFR spectra in comparison with hysteretic models with different post-yielding stiffness. This conclusion is valid for the two selected intensity measures. In addition, the lateral resistance required to achieve similar structural reliability levels is larger when the INp intensity measure is used, especially for buildings with vibration periods equal or larger than the soil period, in such a way that the traditional use of Sa(T1) could provide structures with less structural reliability levels.

EFFECT OF DOUBLE BOTTOM HEIGHT ON THE STRUCTURAL BEHAVIOUR OF BULK CARRIERS

This is the first of a series of companion papers that the authors propose to present on the effect that the new CSR Rules will have on the design of bulk carriers. Our initial focus will be on the new design framework established for the inner bottom height of such vessels, a parameter critical to their structural integrity. It examines the effect that double bottom height reduction has on the reliability of the bulk carrier structure, by applying a finite element 3D - 3 hold analysis of varying double bottom heights to a typical current Panamax bulk carrier design. The results are compared to pre and post IACS CSR[2] requirements. The conclusion reached is that the establishing of the double bottom height should not be left to direct calculations. A minimum acceptable height should be established in order to maintain a minimum level of structural reliability and safety.

Estimation of the current structural reliability level of existing railway bridges and viaducts

Problem starzenia sie mostow i wiaduktow kolejowych oraz ich degradacja stanowi wazne zagadnienie w wiekszości krajow europejskich. Prognozowanie przydatności do uzytkowania kolejowych obiektow inzynieryjnych, zaprojektowanych wedlug schematow obciązenia obowiązujących w czasie ich projektowania, a uzytkowanych obecnie w nowych warunkach eksploatacyjnych zwiekszonego nacisku osi (do 25 ton/oś) i predkości pociągow towarowych (do 120 km/h), jest istotne przy podejmowaniu decyzji eksploatacyjnych. Dlatego tez, niezwykle wazne jest opracowanie algorytmu określającego poziom niezawodności konstrukcji nośnej istniejących (starzejących sie) mostow oraz wiaduktow kolejowych w obecnych i w przyszlych warunkach eksploatacyjnych. Obecne procedury oceny mostow i wiaduktow kolejowych w zakresie dalszej ich eksploatacji nie uwzgledniają zmienności obciązen i parametrow nośności konstrukcji, co moze prowadzic do blednej oceny przydatności kolejowego obiektu inzynieryjnego do dalszego uzytkowania. Celem artykulu jest przedstawienie metody probabilistycznej do oceny istniejących mostow i wiaduktow kolejowych w aspekcie ich dalszej eksploatacji. To podejście określa prawdopodobienstwo wystąpienia awarii (bezpieczenstwo) oraz ryzyko konsekwencji związanych z awarią.

Fatigue resistance of steel ropes: failure criterion: Background to the verification in prEN 1993‐1‐11:2020

AbstractMany steel rope systems are subjected to fluctuating tensile loads and therefore can fail due to fatigue. Available fatigue test data indicate that rope diameter, mean stress, socket type, lay angle and rope length influence the fatigue resistance. Most of the tests were terminated before full failure of the ropes. This paper shows that the test termination criterion, such as fracture of the first wire, fracture of 5 % of the wires or full rope fracture, has a large influence on the resulting fatigue resistance. A probabilistic analysis is carried out for a rope system in a bridge, demonstrating that the required structural reliability levels are met when considering full failure as the end‐of‐life criterion for ropes.

Uncertainty in reliability of thick high strength pipelines with corrosion defects subjected to internal pressure

This paper assesses the uncertainties in the structural reliability levels of thick high strength pipelines with active corrosion defects subjected to internal pressure. A general burst strength model and other applicable to thick high strength pipes are adopted and their predictions uncertainty over a wide range of corrosion defect depths is assessed by Monte Carlo simulation. A 3-parameter lognormal probability model is adopted to describe the uncertainty in the burst pressure. Global and corrosion defect depth dependent model uncertainty factors are derived by comparing the predictions of the burst strength models with burst test data of corroded pipes. Burst failure limit states are formulated in terms of the burst strength models and corresponding model uncertainty factors. Linear and nonlinear corrosion models are adopted to describe the growth of corrosion defects. The uncertainty on the safety levels of pipelines due to the uncertainty on the corrosion defect, corrosion growth model and reliability algorithm is assessed. The results presented for the two strength models provide insights on the adequacy of a thick high strength burst model for probabilistic applications in comparison with a general burst strength model.

Current issues of improving the pricing system in construction in the transition period

Introduction. In the world practice, promotion of structural steel for execution of new effective projects for building and installation construction is linked with innovative introduction of new materials and technologies. This process is specified by the regulatory requirements for reliability of building facilities including indices of load capacity, serviceability and durability. At the same time, the priority is to prevent corrosion damages based on the analysis of the design consideration and assurance of quality of corrosion protection measures. However, for today the possibilities of the concept of limit states as the main instrument for eliminating uncertainty of corrosion protectability parameters are not fully unveiled. The aim of the study is to justify the technical and economic parameters of corrosion protectability in the course of structural steel designing taking into account the required level of structural steel reliability.&#x0D; Materials and methods. The regulatory requirements for means and methods of corrosion protection of structural steel are analyzed on the basis of limit state design principles. Considered are the features of the process approach for affirming compliance of corrosion protectability indices of structural steel. Established are the conditions that allow carrying out the static check and mathematical modeling of design criteria for load capacity, serviceability and durability. Determined are the nomenclature, indices and methods of offline and online monitoring of the constitutive parameters of corrosion state of structural elements.&#x0D; Results. The regulations in force based on the interval estimation of indices of corrosion resistance and life of protective coatings describe conditions of protective means designing as a state or case linked with corrosion hazard. Corrosion protectability defines conditions for designing the corrosion protection measures based on the specified design criteria for serviceability and durability. At that, design decisions of primary and secondary protection are justified by means of computational or computational-measuring verification of compliance of quality and reliability indices of protection means&#x0D; Conclusions. Design characteristics of corrosion resistance and durability obtained by offline and online monitoring of the constitutive parameters of corrosion state of structural elements provide engineering of corrosion protection quality. Management of quality and reliability indices based on corrosion protectability signs lays the groundwork for robust designing measures for the long-term technical and economic protection of building facilities

Consequence classes and associated models for predicting loss of life in collapse of building structures

Most building design codes distinguish structural reliability levels in terms of failure consequences, for which they normally define consequence classes based on building type and use. Although readily applicable in everyday practice, that approach may entail adopting inconsistent safety requirements. Such a significant drawback could be minimised by establishing separate reliability levels for key members on the grounds of the potential consequences of their collapse.Further to those concerns, this paper proposes a series of consequence classes determined in keeping with the number of persons at risk in a given collapse scenario and the extent of the respective damage. Consequence class-related models for predicting loss of life are derived from statistical assessments of data on over 150 collapsed buildings. The models developed estimate the number of fatalities and conditional probability of death of building users under given collapse circumstances. In addition to their utility in establishing target reliability values, these models can be applied in risk analysis of specific building structures, especially where the potential consequences of failure are high.

Design of stadium roofs with a given level of reliability

The article discusses method for the selecting cross-section of steel rod elements of the roof structure placed above the stands of stadiums. Particular attention is paid to ensuring a given level of structural reliability. An algorithm to determine the actual safety factors for the most critical elements in the roof structure is proposed. Snow load, cross-sectional area of the elements, ultimate stress of the material, settlement of the base, mounting imperfections and defects are considered as the stochastic parameters in calculation of the reliability indicators. All specifications of the distributions for these magnitudes are based on the real experimental data. Since the building regulations do not provide a clear algorithm for calculating the reliability indicators of unique (and any other) building structures, it is possible to apply the proposed methodology both to ensure the design reliability of the whole structure as well as the separate most critical structural elements. It also might be applied to other kinds of spatial steel rod structures whose elements work as trusses. The internal force factor in the elements of such structures is longitudinal force. The method has been tested on the stadium structures of FC Olympic in Donetsk city (Ukraine).

Safety level assessment of the fib model code 2010 shear design provisions for beams with stirrups using a mechanics-based probabilistic model

Stirrups are provided in reinforced concrete members to prevent sudden brittle shear failures. However, accurate prediction of the ultimate shear strength of stirrup reinforced concrete beams is still an involved process. Most of the available design codes of practice implements simplified ultimate strength methods for providing stirrups in design. The fib Model Code 2010 shear level of approximation III (MC-10 (III)) design procedure is based on the simplified codified version of the modified compression field theory (SMCFT). Previous studies pointed to the probable insufficient safety bias of MC-10 (III) shear capacity predictions for large beams. This trend of results for large beams leaves cause for concern. Adequate reliability performance of MC-10 (III) design model for large beams should be confirmed. Reliability evaluation informs on the level of safety of a structure. A practical reliability assessment of a shear design procedure for stirrup reinforced concrete beam requires the use of a suitable probabilistic model with corresponding model factor statistics. This contribution aimed at assessing the level of structural resistance reliability of the fib Model Code 2010 shear level of approximation III design provisions at parametric variations of beam depth. The reliability assessment was performed using the probabilistic representation of the mechanics-based compression chord capacity model (CCCM). The CCCM is shown to provide accurate estimates of shear capacity. Conclusions from the reliability investigation indicate that deep beams designed according to MC-10 (III) have consistently low reliabilities for the design range considered.