Design Limits Research Articles

Optimizing composite floors for sustainability and efficiency: Cross laminated timber, concrete types, and ductile notch connectors with enhanced shape

Timber-concrete composite (TCC) structures allow designing efficient building floors in terms of lightness, slenderness, and acoustic insulation. The late development of ductile notch connectors has further advanced TCC structures. This work aims to further optimize the shape of ductile notch connections and to optimally design TCC floors with minimum embodied carbon, floor thickness, self-weight and cost.Firstly, an experimental campaign was carried out to characterize the shear behavior of ductile notch connectors with different shapes, which varied from rectangular to trapezoidal to avoid the use of screws, and concrete types, which varied from normal concrete to ultra-high performance fiber reinforced concrete. For the sake of comparison, a glued connection was also considered. Then, a multi-criteria optimization method was performed to optimally design TCC floor with the developed notch connectors and concrete types. The latest design recommendations for TCC floors developed in Canada were considered. A Non-Linear Finite Element Analysis (NLFEA) was carried out for validation. The presented results push the current design limits in terms of embodied carbon and volume of construction materials towards climate-positive floors.

A Contact Load Distribution Model to Capture the Influence of Structurally Compliant Rotating Ring Gear on the Dynamic Response of Epicyclic Gear Sets

AbstractEpicyclic gears, also commonly referred to as planetary gears, are power transfer components that are commonly used in several industrial applications. The structural compliance of thin-rimmed annular ring gear can significantly influence the performance of an epicyclic gear set. As powertrain components are continually being optimized to their design limits, this influence becomes prominent and can no longer be ignored. Therefore to capture the influence associated with ring gear flexibility, the current study will incorporate a finite element-based ring gear formulation into the three-dimensional planetary dynamic load distribution model (Ryali, and Talbot, 2021, “A Dynamic Load Distribution Model of Planetary Gear Sets,” Mech. Mach. Theory, 158, p. 104229). The proposed contact model employs a modified simplex algorithm to iteratively solve for the elastic gear mesh contacts in conjunction with a numerical integration scheme, which enables it to inherently capture the influence of several components and system-level design variations without the need for an empirical mesh stiffness formulation or transmission error excitation of the system. The developed formulation will be used to study the dynamic response of planetary gear sets where the ring gear is a rotating member. The discussed results demonstrate the fidelity of the developed model, thus making it an excellent tool for the design and analysis of planetary gears.

Relationship of Rainfall Intensity with Slope Stability

The impact of rainfall on landslides is not an uncommon issue worldwide, including in Malaysia. It is a major challenge for geotechnical engineers to ensure the constructed slope is safe and can sustain longer periods of time, including during heavy rainfall. Kota Belud, Sabah, has been selected as the study area to meet the study objectives. Heavy rainfall has been recorded every year within Kota Belud, which has caused a repetition of landslide occurrences within the hilly areas, especially during the monsoon season. Presently, there is no local procedure for determining the rainfall intensity value for slope stability analysis. This study utilized the rainfall intensity value from Hydrology Procedure 26. Seepage analysis conducted shows rainwater infiltration has caused the groundwater level to increase from rainfall starts until 0.5 m below ground level and decrease after rainfall stops, creating fluctuations in the groundwater level during the wet and dry conditions within the wetting front. The factor of safety of the slope shows a decreasing trend, with a reduction of around 27 to 33% after 24 hours of rainfall in conjunction with the changes in groundwater level. However, the factor of safety increased by around 3% from the initial condition after 48 hours. The objective of this study is to identify the factor of safety of a rainfall-induced slope within Kota Belud utilizing the rainfall intensity design limits from Hydrology Procedure 26. Doi: 10.28991/CEJ-SP2023-09-06 Full Text: PDF

Analysis of Modified Finite Length Journal Bearing under Position Perturbation

The performance of journal bearings is significantly affected by the presence of misalignment, which is usually an accompanying problem for this type of bearing. This includes exceeding the design limits for the maximum pressure and the minimum film thickness levels, which affect, in other words, the load-carrying capacity of the system. In addition, it raises the possibility of increasing the wear rate at the bearing edges and increases the friction coefficient at high levels of misalignment. This paper deals with the problem of finite-length misaligned journal bearings, considering a novel comparison between two cases of misalignments: the general 3D misalignment and the vertical misalignment problems for modified bearings. The effect of introducing a variable axial bearing profile on the bearing characteristics and the time responses of the rotor bearing system under position perturbation has also been investigated. The numerical solution of this hydrodynamic problem is based on the finite difference method using Reynolds boundary conditions method. Results show that using a variable bearing profile improves bearing characteristics, such as increasing the minimum film thickness significantly and reducing the pressure levels in addition to reducing the friction coefficient. Furthermore, the modification enhances the rotor-bearing stability under position perturbation, extending the speed range for a safe operation.

Proposed Enhancements to the Risk-Informed and Performance-Based Regulatory Framework for Seismic Hazard Design at NRC-Regulated Nuclear Power Plants

The commercial nuclear power plant industry initiated the licensing modernization project (LMP) to enhance the risk-informed and performance-based (RIPB) regulatory basis for advanced nuclear power reactors. The LMP framework relies heavily on RIPB concepts and approaches that together integrate the defense-in-depth philosophy. One example approach for seismic design is to align the LMP concepts with the performance targets described in the American Society of Civil Engineers (ASCE) standard, ASCE 43-19. The underlying strategy of this approach is to consider the performance of individual structures, systems, and components (SSCs) in seismic design, as well as the role they play in an accident event sequence. This approach contrasts with current regulations, in which every individual safety-related SSC is designed to the same seismic criteria irrespective of the role the SSC plays in the overall system performance. This new philosophy envisions more flexible seismic design options for each SSC, such that the overall seismic design can meet system-level acceptability criteria as well as plant-level acceptability criteria. The objective of this paper is to illustrate the flexibility and benefits of this proposed approach to the seismic design of SSCs in terms of reduced SSC demands (by reducing the design ground motions for SSCs) and improved SSC capacities (by allowing for alternative damage state limits). A simple shear wall was designed using ASCE 43-19 for a hard rock site in the Central Eastern United States considering alternate seismic design category and limit state combinations to examine the physical designs and functional fragilities of these combinations and their impact on seismic performance. The flexibility of this proposed approach is illustrated by an example that shows reduced SSC demands, while the SSC capacities and margins remain consistent with the required safety performance without any loss in overall plant safety.

A performance‐based seismic loading protocol: The generated sequential ground motion

AbstractA realistic performance‐based seismic loading protocol called generated sequential ground motion (GSGM) has been developed in this paper. GSGM is a ground motion fabricated from segments of real recorded ground motions that could enable the introduction of performance‐based seismic assessment and design to experimental testing in setups such as shaking table testing. It can also significantly reduce the number of nonlinear time history analyses required in performance‐based seismic design. The protocol optimizes the behavioral information output of an experimental test or numerical analysis by incorporating dynamic demands corresponding to design limit states with different probabilities of exceedance (i.e. 10%, 5%, and 2% in 50 years) in a single record. In addition, since the segments are matched to relevant target spectra, the number of ground motions required to estimate the mean response is reduced. This paper presents the algorithm developed to produce the GSGM. The capability of the GSGM to replicate the structural responses produced by code‐compliant suites, and a suite of 100 ground motions as a more robust estimation of the actual response is investigated. The results of the case study bridge pier show that the drift variation of the GSGMs compared to code‐compliant suites is within 10%. Compared to the estimate of the actual response, the drift variation of GSGMs and the code‐compliant suites is 20% and 15%, respectively, and the damage variation is 30% and 15%, respectively. Furthermore, considering other relevant intensity measures when producing GSGMs can reduce these variations. This study suggests that the GSGM can replicate structural responses of the current code procedures.

Effect of antenatal corticosteroid administration-to-birth interval on maternal and newborn outcomes: a systematic review

Antenatal corticosteroids (ACS) are highly effective at improving outcomes for preterm newborns. Evidence suggests the benefits of ACS may vary with the time interval between administration-to-birth. However, the optimal ACS administration-to-birth interval is not yet known. In this systematic review, we synthesised available evidence on the relationship between ACS administration-to-birth interval and maternal and newborn outcomes. This review was registered with PROSPERO (CRD42021253379). We searched Medline, Embase, CINAHL, Cochrane Library, Global Index Medicus on 11 Nov 2022 with no date or language restrictions. Randomised and non-randomised studies of pregnant women receiving ACS for preterm birth where maternal and newborn outcomes were reported for different administration-to-birth intervals were eligible. Eligibility screening, data extraction and risk of bias assessment were performed by two authors independently. Fetal and neonatal outcomes included perinatal and neonatal mortality, preterm birth-related morbidity outcomes and mean birthweight. Maternal outcomes included chorioamnionitis, maternal mortality, endometritis, and maternal intensive care unit admission. Ten trials (4592 women; 5018 neonates), 45 cohort studies (at least 22,992 women; 30,974 neonates) and two case-control studies (355 women; 360 neonates) met the eligibility criteria. Across studies, 37 different time interval combinations were identified. There was considerable heterogeneity in included administration-to-birth intervals and populations. The odds of neonatal mortality, respiratory distress syndrome and intraventricular haemorrhage were associated with the ACS administration-to-birth interval. However, the interval associated with the greatest improvements in newborn outcomes was not consistent across studies. No reliable data were available for maternal outcomes, though odds of chorioamnionitis might be associated with longer intervals. An optimal ACS administration-to-birth interval likely exists, however variations in study design limit identification of this interval from available evidence. Future research should consider advanced analysis techniques such as individual patient data meta-analysis to identify which ACS administration-to-birth intervals are most beneficial, and how these benefits can be optimised for women and newborns. This study was conducted with funding support from the UNDP-UNFPA-UNICEF-WHO-World Bank Special Programme of Research, Development and Research Training in Human Reproduction (HRP), Department of Sexual and Reproductive Health and Research (SRH), a co-sponsored programme executed by the World Health Organization.

Global atlas of extreme significant wave heights and relative risk ratios

Interest in offshore wind, wave, and tidal energy power generation to supply electricity to the grid nearshore or power off-grid applications far offshore has motivated numerous studies of the ocean wave climate, including extreme wave conditions that characterize project risk and wave loads for design. The present study uses the 30′ resolution 31-year Global WAVEWATCH III® model hindcast, the 4′ resolution 31-year coastal US model hindcast, and the US NOAA buoy network to estimate and map the global distribution of the mean, 50-, 5- and 1-year significant wave heights and the relative-risk-ratios computed by non-dimensionalizing these n-year extreme wave heights with their mean values. A two-step linear correction method is applied to correct systematic underbias of model-derived extreme wave heights relative to the observation-derived values, resulting in a 20% or more increase in model-derived values compared to uncorrected ones. The corrected 30’ resolution extreme wave height and relative risk ratio atlas generated herein provides important metrics that support resource characterization and international standards development for the marine energy industry, including resource and site assessment, and the establishment of upper design limits for device type classification and certification to streamline product line development.

Energy-Based Fatigue Assessment of Defect-Afflicted Cast Steel Components by Means of a Linear-Elastic Approach

Cast steel components are affected by manufacturing process-based imperfections, which severely limit their fatigue strength. In this work, the linear-elastic strain energy density concept is applied to assess the fatigue behaviour of bulk defect-afflicted components made of high-strength cast steel alloy G12MnMo7-4+QT. Based on analytical calculations, an energy-based design limit curve is derived which merges experimental results of notched and unnotched small–scale specimens into a statistically proven scatter band. The stress ratio dependency is also investigated. Moreover, a numerical methodology is introduced, which facilitates the energy-based fatigue assessment of complex spatial imperfections on the basis of radiographs. Validation of the established framework utilizing experimental results of defect-afflicted large–scale specimens leads to sound accordance of numerically and experimentally derived fatigue strength values, showing an average deviation of about only eight percent.

Liver and cardiometabolic markers and conditions in a cross-sectional study of three Australian communities living with environmental per- and polyfluoroalkyl substances contamination

Background: Per- and polyfluoroalkyl substances (PFAS) have been associated with higher cholesterol and liver function markers in some studies, but the evidence for specific cardiometabolic conditions has been inconclusive.Objectives: We quantified the associations of single and combined PFAS with cardiometabolic markers and conditions in a cross-sectional study of three Australian communities with PFAS-contaminated water from the historical use of aqueous film-forming foam in firefighting activities, and three comparison communities.Methods: Participants gave blood samples for measurement of nine PFAS, four lipids, six liver function markers, and completed a survey on sociodemographic characteristics and eight cardiometabolic conditions. We estimated differences in mean biomarker concentrations per doubling in single PFAS concentrations (linear regression) and per interquartile range increase in the PFAS mixture (Bayesian kernel machine regression). We estimated prevalence ratios of biomarker concentrations outside reference limits and self-reported cardiometabolic conditions (Poisson regression).Results: We recruited 881 adults in exposed communities and 801 in comparison communities. We observed higher mean total cholesterol with higher single and mixture PFAS concentrations in blood serum (e.g., 0.18 mmol/L, 95% credible interval −0.06 to 0.42, higher total cholesterol concentrations with an interquartile range increase in all PFAS concentrations in Williamtown, New South Wales), with varying certainty across communities and PFAS. There was less consistency in direction of associations for liver function markers. Serum perfluorooctanoic acid (PFOA) concentrations were positively associated with the prevalence of self-reported hypercholesterolemia in one of three communities, but PFAS concentrations were not associated with self-reported type II diabetes, liver disease, or cardiovascular disease.Discussion: Our study is one of few that has simultaneously quantified the associations of blood PFAS concentrations with multiple biomarkers and cardiometabolic conditions in multiple communities. Our findings for total cholesterol were consistent with previous studies; however, substantial uncertainty in our estimates and the cross-sectional design limit causal inference.

Seismic performance of damaged frame retrofitted with self-centering and energy-dissipating rocking wall

This paper proposes the novel concept of retrofitting damaged reinforced concrete frame with self-centering and energy-dissipating rocking wall. Parametric studies were carried out base on pushover and time-history analysis. In both pushover and time-history analysis, the soft-story mechanism was effectively mitigated through the rocking wall retrofit of the damaged structures. The results demonstrated that the stiffness and bearing capacity of the retrofitted system were improved compare to its intact state. Additionally, the seismic response of the damaged frame retrofitted using rocking wall in combination with post-tension and shear-type damper fell within the relevant design limits. Pushover analysis of the rocking wall indicated that there is a linear relationship between the wall thickness and the initial stiffness of the retrofitted system. The addition of post-tension tendon to the rocking wall system enables the wall to self-center and increases lateral stiffness and bearing capacity of the retrofitted system. When the shear-type damper was installed, the energy dissipation of the system was increased, and the stiffness and bearing capacity of the retrofitted system were also improved. In the time-history analysis, it was found that the thickness of the rocking wall is directly related to the maximum inter-story drift and the distribution patterns of inter-story drift of the frame. As the post-tension was added to the system, the maximum inter-story drift under rare earthquake excitation improved significantly. With the addition of shear-type dampers, the overall drift magnitude of the retrofitted system was fundamentally decreased.

Domain-Specific Architectures: Research Problems and Promising Approaches

Process technology-driven performance and energy efficiency improvements have slowed down as we approach physical design limits. General-purpose manycore architectures attempt to circumvent this challenge, but they have a significant performance and energy-efficient gap compared to special-purpose solutions. Domain-specific architectures (DSAs), an instance of heterogeneous architectures, efficiently combine general-purpose cores and specialized hardware accelerators to boost energy efficiency and provide programming flexibility. Indeed, the hardware, software, and systems aspects in DSAs are highly tailored to maximize the energy efficiency of applications in a target domain. As DSAs and their conceptualization advance rapidly, there is a strong need to understand the research problems that need immediate attention. This article discusses the primary research directions in the design and runtime management of DSAs. Then, it surveys some promising approaches and highlights the outstanding research needs.

A Declarative Application Framework for Evaluating Advanced V2X-Based ADAS Solutions

Application of Vehicular Ad Hoc Networks (VANETs) aims to help in the solution of some problems that have arisen in road transportation systems via short-range, low-latency mobile communication. The application of V2X (Vehicle-to-Everything) communication technologies to the next generation of Advanced Driver Assistance Systems (ADAS) is essential to the extension of the operational design domain (ODD) of the systems to provide safe, secure, and efficient automated driving solutions. Due to the safety-critical nature of the problem, the large-scale testing of V2X enabled ADAS solutions to evaluate and measure the anticipated quality and functionality of the experimental system is of great significance. This article proposes a novel ADAS application prototyping framework, using declarative programming, built on top of the popular Artery/OMNeT++ simulator. The framework is capable of simulating V2X-enabled ADAS applications using accurate network simulation and realistic simulated traffic on real-world maps. The solution features XML descriptions for application specification. The sensor model of Artery is used to provide information to applications. By using the simulator, one can conclude the performance of the applications and discover locations, circumstances and design patterns, where design limits should apply.

Neutronics and thermal-hydraulics coupling analysis for a small lead-based fast reactor based on the discrete ordinate nodal and parallel channel method

The full-core neutronics/thermal-hydraulics (NE/TH) coupling analysis for a small lead-based fast reactor (SLFR) was presented. The NE-to-TH coupling occurs via power distribution, whereas the TH-to-NE coupling occurs via the material cross section, which is related to the temperature distribution. In the NE module, a discrete ordinate (SN) nodal solver is implemented based on the hexagonal prism mesh. In the TH module, a parallel channel model is implemented with each hexagonal fuel assembly as a channel. The mass flow of each channel is searched according to the same pressure drop, the temperature and density of the coolant within each channel is calculated with a one-dimensional axial heat convection model, and the temperature distribution along the fuel pin is calculated with a one-dimensional radial heat conduction model. In order to update the cross section, a temperature-dependent homogenized microscopic cross-section library is prepared in advance, and based on the temperature distribution obtained from the TH calculation, the cross-section data required by the NE calculation are obtained by interpolation. The results of the NE/TH coupling analysis for SLFR indicate that the TH parameters (the maximum temperature of the fuel, cladding, and coolant and the maximum velocity of the coolant) are all within the design limits, and the TH feedback provides negative reactivity feedback (about −200 pcm) and has a fairly small effect on the power distribution (<1.0%).

Shaking table test study on dynamic performance of a base-isolated frame structure under an isolation bearing removal scenario

Studies on the progressive collapse of structures have been at the forefront in structural engineering domain recently. The progressive collapse of isolated structures is quite different from that of conventional fixed-base structures. Once an initial failure occurs in the isolation layer which is the most vulnerable to accidental events due to the low horizontal stiffness, progressive failures at other locations may lead to a large-scale collapse of isolated structures. This paper presents a 1:4 scale model shaking table test of a three-story irregular plane reinforced concrete (RC) frame isolated structure to investigate the progressive collapse resistance of isolated structures. An edge bearing was removed quickly by an electromagnetic failure excitation device during the first seismic input case. The dynamic responses such as the macroscopic crack distribution, acceleration responses, displacement responses, internal forces of the isolation bearings, and concrete and reinforcement strains of the failure span beams were evaluated. The results show that the significant vertical deformation with dynamic impact response was produced at the failure point under multi-directional dynamic coupling excitation, i.e., the combined effect of the vertical unbalanced load caused by sudden failure of a bearing and horizontal earthquakes. This sudden failure of the isolation bearing not only had an impact on the internal forces of bearings adjacent to the failure bearing, but also on other non-adjacent bearings. As the tensile and compressive stress of adjacent bearings were more likely to exceed design limits under earthquakes, the risk of overturning collapse for isolated structures markedly increased following the failure of a few bearings. In addition, vertical and low-frequency components of earthquakes could have a significant influence on dynamic responses and damages of isolated structures, especially in the area of bearing failure. The experimental results obtained in this study act as important references for the progressive collapse design of isolated structures.

Influence of Recycling Waste Glass as Fine Aggregate on the Concrete Properties

Recent years have witnessed an increase in the quantity of waste glass (WG) across the globe. Replacing the fine aggregate with WG is one of the steps toward preserving the natural resources of the environment and creating low-cost concrete. The present study is concerned with replacing fine aggregates with glass powder (GP) at (0%, 15%, 30%, and 50%). It has studied the fresh and hardened properties (compressive strength, tensile strength, hardened density, and slump) for all the mentioned percent replacements. The findings have shown that all mixtures containing GP gave acceptable slump results within the design limits (2–5 cm) according to ACI standard 211.1. It has been observed that increasing the proportion of GP led to a decrease in the weight of concrete. Lastly, replacing GP with sand by 30% has led to an increase in the compressive strength by about 2.4% and 12.45%, and the tensile strength by about 2.5% and 26.54% at 7- and 28-d, respectively in comparison to normal concrete.

Monetary Policy Rules: Model Uncertainty Meets Design Limits

Monetary Policy Rules: Model Uncertainty Meets Design Limits

Improving Rock Pillar Stability Guidelines Through Detailed Numerical Investigation

Pillar stability guidelines have been presented by numerous authors in the past, based on a combination of empirical observations (mostly visual) from mining applications and simple numerical (elastic or simple continuum plasticity) models. In many cases, the resulting design limits for pillar dimensioning are presented as universal for all rockmass conditions and stress regimes. There have been numerous developments in the past decades in mechanistic classification (brittle spalling, effective continuum rockmass, structural control) and mechanism-appropriate modelling and design metrics. These new tools and paradigms for rockmass behaviour allow for a modelling-based revision of the empirical guidelines from the past century that still form the basis of many performance critical designs. This paper includes the consideration of rockmass deformation and yield (rockmass strength approach), brittle strength, and damage behaviour where appropriate. This paper presents correlations for residual GSI and the effects of Hoek-Brown dilation on pillar behaviour. The investigation includes generating 3D FEM synthetic pillar models with equivalent elastic and plastic continuum.

THERMAL-HYDRAULIC ANALYSIS OF A HIGH-TEMPERATURE HELIUM-GAS-COOLED REACTOR UNDER VARIOUS STEADY-STATE OPERATING CONDITIONS

This paper focuses on thermal-hydraulic analysis, which plays a critical role in system efficiency and the selection of the optimal design of nuclear reactors. The analysis is done based on a one-dimensional computer code called MIGHT that performs a subchannel thermal-hydraulic analysis of a typical gas-cooled fast breeder reactor (GCFBR) cooled by helium (He). In steady-state operation, two typical channels, the hot and average channels, with the same flow rate and pressure drop were tested. Temperature distribution profiles and the heat flux were computed and compared for different types of power distribution. The effects of coolant mass flow rate and power level on the thermal-hydraulic performance of the tested GCFBR were investigated for cosine power profile. The results demonstrate that the lowest flow rate for the tested reactor to continue operation in the safe mode at the nominal operating power (2530 MWt) is 80% of the nominal flow rate (10 × 10<sup>6</sup> kg/h). The maximum cladding temperature stays within the suggested design limit of GCFRs (700-750°C) when the power is increased by 10% and 15%. The results revealed that temperature is more sensitive to changes in power level than mass flow rate. Data of GCFBR typical reactor were used as input data and for code validation. Good agreement between tested reactor data and MIGHT code calculation concerning the reactor proves the reliability of the methodology of analysis from a thermal-hydraulic perspective. The minor discrepancies could be explained by differences in the relevant physical parameters used in each method of calculation.

Порівняльний метод кваліфікації систем безпеки ядерних енергоустановок з ВВЕР‑1000 та АР1000

A deterministic method of analyzing conditions for ensuring the safe operation of VVER-1000 and AP1000 nuclear power plants has been developed. The method is based on the comparison of the provision of the required safety functions by critical (minimum permissible) configurations of safety systems for accident management. During the analysis, the composition and information on the technical characteristics of the safety systems of the VVER-1000/320 and AP1000 reactor installations, which are designed to ensure the safety functions of feeding and cooling the reactor/PG, were considered. On the basis of the developed method, the relative criteria and safety conditions (for example — the criterion of safety — the maximum temperature of the heating element shell; the condition of safety is not to exceed the maximum design limit of damage to the twelfth (the temperature of the twelfth shell is 1,200 °C) for nuclear power plants with VVER-1000 and АР1000 reactors in terms of safety functions for emergency fueling and cooling of the reactor core and steam generators are determined. Preliminary estimates of the relative criteria and conditions for ensuring nuclear safety during accident management of natural circulation circuits of passive safety systems AP1000 obtained taking into account data on their composition and technical characteristics, the table showed that the required height of natural circulation circuits of passive safety systems should be several hundred meters. Based on the established relative criteria and safety conditions, the need for additional modernization of the АР1000 safety systems to successfully ensure the safety functions of emergency coolant/feedwater supply and core and steam generator cooling is preliminarily determined.