Nonlinear Time History Analysis Research Articles

Machine learning prediction models for ground motion parameters and seismic damage assessment of buildings at a regional scale

This study examines the feasibility of using a machine learning approach for rapid damage assessment of reinforced concrete (RC) buildings after the earthquake. Since the real-world damaged datasets are lacking, have limited access, or are imbalanced, a simulation dataset is prepared by conducting a nonlinear time history analysis. Different machine learning (ML) models are trained considering the structural parameters and ground motion characteristics to predict the RC building damage into five categories: null, slight, moderate, heavy, and collapse. The random forest classifier (RFC) has achieved a higher prediction accuracy on testing and real-world damaged datasets. The structural parameters can be extracted using different means such as Google Earth, Open Street Map, unmanned aerial vehicles, etc. However, recording the ground motion at a closer distance requires the installation of a dense array of sensors which requires a higher cost. For places with no earthquake recording station/device, it is difficult to have ground motion characteristics. For that different ML-based regressor models are developed utilizing past-earthquake information to predict ground motion parameters such as peak ground acceleration and peak ground velocity. The random forest regressor (RFR) achieved better results than other regression models on testing and validation datasets. Furthermore, compared with the results of similar research works, a better result is obtained using RFC and RFR on validation datasets. In the end, these models are utilized to predict the damage categories of RC buildings at Saitama University and Okubo Danchi, Saitama, Japan after an earthquake. This damage information is crucial for government agencies or decision-makers to respond systematically in post-disaster situations.

Structures incorporating damping devices: Are we correct in our design thinking?

The use of discrete damping devices in New Zealand buildings is increasing as designers seek to limit damage to both architectural and structural building elements in moderate earthquakes. The overall damping of the structure becomes a combination of inherent material damping, hysteretic damping from yielding of building elements at specific locations and damping from discrete devices. For over 60 years, engineers have used simplified analysis procedures (e.g., modal response spectrum analysis) to predict building response under seismic actions. The design of structures incorporating viscous dampers requires a paradigm shift in approach as the force each damper resists is a function of the relative velocity between its ends. Popular pseudo-static design methodologies promote the use of a viscous strut in the analysis model to represent them. However, it is incorrect to use elastic, mode-based analysis for a structure incorporating damping devices and relying on significant inelastic behaviour. This paper elucidates the complex mechanics of damper-structure interaction by reviewing some of the established classical, modal‑based, simplified analysis techniques used in seismic design. A series of numerical investigations demonstrate how these techniques are usually invalid for structures that incorporate viscous dampers because they violate the laws of physics. The reason why mode-based techniques are invalid is explored with reference to the imaginary components of the natural modes of vibration and the effect on them of significant inelasticity within the structure. The dynamic characteristics of viscous dampers challenge conventional design approaches such as displacement-based design. This paper establishes that nonlinear time-history analysis is the only meaningful way of predicting the dynamic response of a structure incorporating viscous dampers when significant inelastic behaviour of the structure is expected.

A new performance‐based seismic design method using endurance time analysis for linked column frame system and a comparison of structural systems and seismic analysis methods

SummaryThis paper presents a new performance‐based seismic design method for the design of repairable linked column frame (LCF) and linked column system (LCS). Currently, the biggest problem of these systems is the lack of a simple and practical design method that leads to the design of optimal models with sufficient seismic capacity. The interaction of the primary and secondary systems, changing the lateral load pattern during an earthquake, and the implementation of the target performance objectives have complicated the design of these systems. The evaluations carried out in this research show that the rotation of link beams must be controlled in the design. Therefore, the ultimate plastic rotation of links is determined to be 0.01 rad for the seismic intensity of design base earthquake and 0.015 rad for maximum considered earthquake. The results show that the models designed using the presented method are optimal, have sufficient seismic capacity, and achieve the target performance objectives. In addition, although previous researches have shown that these systems have a suitable seismic behavior, their seismic behavior have not been compared with other structural systems. Comparing can show the behavioral characteristics of a new structural system; hence, the elastic and plastic behavior of the LCF and LCS models have been compared with other common steel structural systems using all analysis methods. Moreover, in the presented method for the design of LCF and LCS systems, nonlinear time history analysis using the endurance time method (ETM) is used, and due to the newness of the endurance time method, its results are compared with the median results of nonlinear time history analysis at different seismic hazard levels and incremental dynamic analysis (IDA), in 45 samples. The results show that the endurance time analysis is a reasonable and efficient method, and in this comparison, the difference between the results of ETM and IDA methods is 6% on average.

Seismic performance of rocking braced frames with double base plate connections

This paper presents a rocking system for concentrically braced frames (CBFs) to mitigate the seismic demands induced by seismic motions. The proposed system incorporates double base plate connections (DBPCs) at the base of the braced-bay columns, enabling them to uplift and initiate a rocking motion. The DBPC comprised two base plates: the upper one is thin, connected to the column and designed to yield under uplift loading, while the lower one primarily distributes compressive loads to the foundation. The DBPC was modeled using a combination of spring and gap elements in SAP2000 software. A comparative study was performed to investigate the seismic performance of the proposed rocking system against a conventional CBF system. Key parameters such as the thickness of the upper base plate and the arrangement of anchor rods were considered. Four prototype frames of different heights (3, 6, 9, and 12 stories) were investigated under the Sylmar-x record using the nonlinear time history analysis. The results demonstrated that utilizing rocking braced frames with double base plate connections can remarkably mitigate the base shear force by softening the structural response, decreasing the seismic damage experienced by the structure. The upper base plate acted similarly to a footing damper, absorbing a substantial amount of energy by yielding. Importantly, the residual drifts caused by the plastic deformations of the upper base plate remained within the acceptable performance limits for self-centering systems. Moreover, the self-centering mechanism was achieved solely through the structure’s self-weight, eliminating the need for additional re-centering devices.

Sensitivity of human-induced vibrations and comfort analysis to partially rigid STS joints in timber-to-timber composite floors

The study of floors vibration serviceability represents a well-known challenging task and has a critical role in comfort analysis, assessment and optimization of pedestrian systems in general. To this aim, several consolidated and/or simplified tools are available in the literature to address the most important aspects. In practice, however, most of assumptions for the analysis and verification are based on the use of rough mechanical models of joints and connections, which have indeed a primary role especially for composite floors. In this paper, the attention is given to timber-to-timber floors with inclined self-tapping screws (STS). A parametric Finite-Element (FE) numerical investigation is carried out by taking into account conventional walking features and a case-study timber-to-timber composite beam, well representative of a one-way wooden floor. A major advantage for structural and pedestrian modelling stages is taken from previous literature efforts, while large attention is spent for structural analysis and vibration serviceability assessment tasks, as a function of the STS mechanical parameters (first of all the secant stiffness). Comparative linear modal and non-linear time history analyses are carried out and addressed towards limit mechanical configurations for STS joints, in terms of vibration frequency considerations, as well as structural response and comfort assessment, based on classical performance indicators. The parametric numerical results are further discussed based on simplified methods provided by selected design standards. A critical analysis of major effects due to partial joint rigidity and floor performance classification is presented, both in terms of expected structural safety and comfort levels for similar systems.

Time history nonlinear analysis for 2D modelization of an existing building using flexibility and displacement-based formulation

The object of the research is the response of a structure in time between formulations, namely force-based (flexibility-based) and displacement-based. An existing two-story reinforced concrete structure subjected to three earthquakes separately is presented in order to carry out a comparative study in terms of time history structure response between the two formulations cited above namely force based (flexibility based) and displacement based. This research aimed to compare between two formulations namely displacement based and force-based (flexibility-based), in order to show the accuracy and the reliability of the second one. In the case of nonlinear time history response of a residential two-storey reinforced concrete building, which is representative of typical residential building construction in Italy in the 1970’s and 1980’s with the aim of taking advantages of flexibility-based formulation if the comparison proves conclusive. In the course of the research, the former approach is a classical two-node, displacement-based, Euler-Bernoulli frame element with the disadvantage of discretizing the structure thus increasing the number of degrees of freedom and equation, in order to achieve the required precision. The latter is a two-node, force-based, Euler Bernoulli frame element. The main advantage of the second element is that it is «exact» within the relevant frame element theory. This implies that one element per frame member (beam or column) is used in preparing the frame mesh, thus leading to a reduction of the global number of degrees of freedom. Therefore, a reduction in number of equations to solve, resulting in a saving of time with increased precision. An existing two-story reinforced concrete structure subjected to three earthquakes separately is presented in order to carry out a comparative study in terms of time history structure response between the two formulations cited above namely force based (flexibility-based) and displacement-based. As a result of the research, it is shown that with flexibility-based approach no discretization error occurs and all governing equations are satisfied exactly, making a possibility of simpler and faster numerical modeling. In the proposed approach will be of great use in the field of numerical modeling due to its ease and accuracy. This elegant formulation is promising for future work thanks to its advantages.

A Comparative Study of Seismic Performance Evaluation of Reinforced Concrete Frame Structures Using Chinese and African Seismic Codes

The evaluation of various earthquake codes, it is one of the significant challenges in the study area of earthquake engineering. However, according to the literature review, most research works have not addressed comparing Chinese and African seismic codes. Therefore, the purpose of this study is to identify each code’s advantages by comparing assessment of the seismic efficacy of moment resistance frame reinforced concrete (MRF-RC) frames using four different codes: the Ethiopian Building Code Standard (EBCS-8), the Egyptian Code for Design and Construction of Reinforced Concrete Structures (ECP-201), the Algerian Seismic Regulations (RPA-99), and the Chinese Code for Seismic Design of Buildings (GB-50011), the first three are the major codes used in Africa. The seismic provisions of these codes are compared and evaluated using nonlinear time-history analysis (NL-THA) and nonlinear static pushover to validate the results. These analyses are performed on four MRF-RC frame models with different heights. The results include various parameters that reflect the seismic performance of the structures. The study revealed that the Chinese code is more conservative and overestimates seismic performance compared with African codes. However, the Chinese code can be applied in African projects considering the African soil classifications, and seismic weight are adjusted to meet the African design criteria.

Constant damage inelastic permanent period shift ratios spectra

The phenomenon of elongation of the structural period after earthquake excitation has been widely observed, and elongated period obtained after earthquake excitations can be used for post-earthquake assessment. The inelastic permanent period shift ratio, an indicator representing the degree of stiffness degradation and closely relating to the damage state, is defined as the ratio of the elongated period Tin of single-degree-of-freedom (SDOF) systems after earthquake excitations to the initial period Tel. The objective of this paper is to investigate the inelastic permanent period shift ratios under constant damage performances through nonlinear time-history analysis of SDOF systems, and the modified Park-Ang damage index is employed to characterize the structural damage. Inelastic permanent period shift ratio spectra are statistically constructed considering both the ground motion characteristics (such as site conditions, velocity pulse, magnitude, closet distance, directivity effects, significant duration and frequency contents) and structural parameters (including damage states, hysteretic models, ultimate deformation capacity, energy dissipation factor and postyield ratio). The results showed that the permanent period shift ratio is a reliable damage indicator for assessment of global damage states. The influence caused by ground motions on the estimation of the mean of the permanent period elongation ratio under constant damage performances is limited, while the effects caused by different structural damage and deformation capacity can reach up to approximately 70% and 33%, respectively. An expression for the relationship between the damage index and the permanent period shift ratio is established. Ignoring the differences of structural performances, using the period shift ratios to directly assess the global damage states will lead to erroneous results.

Seismic improvement of structures using hybrid self-centring dampers and rocking core

Extensive research on seismic-resistant systems aims to lower earthquake repair costs and downtime. This article presents a novel low-damage self-centring system that aims to improve the seismic resilience of buildings by enabling controlled rocking motion while reducing the risk of overturning. Significantly, the rotational movement can be entirely restored. This system combines a rocking core with damping devices, including disc springs and peripheral slit dampers. In this hybrid system, two damping devices are mounted to both first-floor columns of the rocking bays and the rigid movement of the rocking core triggers the dampers. Firstly, a comparative investigation was conducted to assess the efficacy of the endorsed hybrid system. The cyclic pushover results showed that the hybrid system is superior to other typical bracing systems in energy dissipation, with a five times higher margin. In addition, by employing the suggested system, the frame's drift ratio profile under nonlinear time history analysis (NTH) remained consistent throughout the structure, indicating its ability to withstand the soft storey mechanism. Secondly, a comprehensive assessment was conducted on the proposed system's collapse using incremental dynamic analysis (IDA) took into account various seismic intensities and engineering demand parameters for buildings with different bay lengths and included low, medium, and high-rise structures. The system's flag-shaped behavior and self-centring capability were confirmed by the average residual drift ratio of approximately 0.03% (almost zero) for all examined structures. Also, the collapse performance of the system exhibited a safety margin against collapse, with an average of 1.9 across all buildings and seismic intensities.

Assessing the significance of nonlinear rotational behavior in high damping rubber bearings for seismic performance of base‐isolated RC frame building

AbstractUtilizing high‐damping rubber bearings (HDRBs) for seismic isolation significantly enhances building seismic performance. However, previous studies have often neglected the nonlinear rotational behavior of these bearings when assessing base‐isolated systems using HDRBs. This study introduces two numerical models of the HDRBs, each comprising six springs. The first model, referred to as the BIL model, assumes linear behavior for the rotational degrees of freedom of the bearings. The second model, referred to as the BINL model, accounts for the nonlinear rotational behavior. The parameters of the bearing shear springs and the rotational springs of the two models are calibrated using experimental data. In order to investigate the influence of nonlinear rotational behavior of HDRBs on the seismic performance of base‐isolated buildings, nonlinear time history analysis is conducted on a six‐story base‐isolated RC frame building. Comparative analysis between the BIL model and the BINL model covers bearing behavior, superstructure response, and energy dissipation distribution. Results indicate a significant influence of considering nonlinear rotational behavior on column bending moments. These findings provide crucial insights for enhancing seismic design strategies for base‐isolated buildings.

Analysis of Key Influencing Factors of Track Dynamic Irregularity Induced by Earthquakes in the High-Speed Railway Track–Bridge System

Stiffness degradation of track–bridge systems under earthquake excitations can lead to track dynamic irregularity, impacting the safety of train operations post-earthquake. In this paper, the nonlinear time-history analysis of CRTS II track–bridge system model established by ANSYS finite element analysis software is carried out under the action of transverse random earthquake. The train–track–bridge system model considering the stiffness degradation caused by earthquake is established by MATLAB, and the earthquake-induced track dynamic irregularity sample library is constructed. The probability distribution mode of the power spectral density sample of the earthquake-induced track dynamic irregularity is explored and the calculation method based on the probability guarantee rate is proposed. The influence of structural damping ratio, train running speed and train type on the power spectral density curve of the earthquake-induced track dynamic irregularity is analyzed. The results show that the power spectrum samples of track dynamic irregularity conform to the hypothesis test of a normal distribution. The power spectral density of earthquake-induced dynamic irregularity primarily consists of medium and low-frequency components. When the structural damping ratio increases from 0.03 to 0.04, 0.04 to 0.05, 0.05 to 0.06, and 0.06 to 0.07, the variation gradients are 0.1701, 0.1240, 0.1034 and 0.0999, respectively, which indicates that the structural damping ratio has a significant effect on the power spectral density of earthquake-induced irregularity, and the impacts of train speed and train type on the power spectral density of near-fault earthquake-induced irregularity are minimal.

Comparison of Linear and Nonlinear Procedures for the Analysis of the Seismic Performance of Straight Multi-Span RC Bridges

Comparison of Linear and Nonlinear Procedures for the Analysis of the Seismic Performance of Straight Multi-Span RC Bridges

Optimized Gauss–Legendre–Hermite 2-point (O-GLH-2P) method for nonlinear time-history analysis of structures

Optimized Gauss–Legendre–Hermite 2-point (O-GLH-2P) method for nonlinear time-history analysis of structures

Effect of Ground Motion Time–Frequency Non-Stationarity on Seismic Response of High-Speed Railway Simply Supported Bridge Based on Wavelet Packet Transform

Time–frequency non-stationarity is a ground motion characteristic which is frequently neglected in current seismic design and research. This paper studies its impact on the seismic response of high-speed railway simply supported bridge (HSRSSB). A method for generating time–frequency stationary earthquakes (TFSEs) and time–frequency non-stationary earthquakes (TFNSEs) using wavelet packet transform is proposed. A finite element model of a three-span HSRSSB is established using OpenSees. The seismic response is obtained through non-linear dynamic time history analysis, and the fragility curves of bridge components and system are calculated through incremental dynamic analysis. Finally, the reasons for the differences are analyzed by comparing the differences in seismic response of bridge, component fragility and system fragility under two groups of ground motion. The results show that the time–frequency non-stationarity of ground motion has an effect on the bridge response and fragility under strong earthquakes. TFNSE will lead to larger ground motion response, and the damage probability of bridge components and systems is higher. The reason is related to the damage and period extension of bridges under ground motion. Structures with prolonged period anti-seismic measures need to pay attention to this effect.

Performance Assessment of Reinforced Concrete Bridges Under Coupled Horizontal and Vertical Ground Motions Using Fragility Surfaces

ABSTRACT The objective of this study is to explore the seismic fragility of reinforced concrete bridges, specifically in response to the vertical components of ground motions, utilizing fragility surfaces. The examination of bridge responses involves the application of optimally selected intensity measures through three-dimensional nonlinear time-history analyses, encompassing uncertainties in both superstructure materials and soil–structure interaction effects. In this investigation, an extended Probabilistic Seismic Demand Model (e-PSDM) is employed, leveraging fragility surfaces to concurrently consider vertical and horizontal excitations. The results obtained from this approach are compared with traditional fragility curves. This study emphasizes Pile-cap displacement and drift ratio as pivotal engineering damage parameters, acknowledging their sensitivity to the influences of both soil–structure interaction effects and vertical ground motion. The fragility surfaces derived from the study reveal a correlation between increased vertical spectral accelerations and elevated probabilities of surpassing both slight damage and collapse limit states. These observations underscore the critical significance and practical utility of fragility surfaces in the context of performance-based seismic assessment and design for reinforced concrete bridges. The findings from this research contribute valuable insights into the nuanced behaviour of reinforced concrete bridges under seismic conditions, emphasizing the relevance of incorporating vertical components in fragility assessments for a more comprehensive understanding of structural vulnerability.

Exploring the Effect of Near-Field Ground Motions on the Fragility Curves of Multi-Span Simply Supported Concrete Girder Bridges

Investigating the impact of near-field ground motions on the fragility curves of multi-span simply supported concrete girder bridges is the main goal of this paper. Fragility curves are valuable tools for evaluating seismic risks and vulnerabilities of bridges. Numerous studies have investigated the impact of ground motions on the fragility curves of bridges. Ground motions are commonly categorized into two sets, based on the distance of the recorded station from the seismic source: far-field and near-field. Studies examining the influence of near-field records on bridge fragility curves vary depending on the specific bridge type and type of fragility curve being analyzed. Due to the widespread use of multi-span simply supported concrete girder bridges in the Central and Southeastern United States, this study makes use of this bridge type. This research investigates the component fragility curves for column curvatures, bearing deformations, and abutment displacements by employing 3-D analytical models and conducting nonlinear time history analysis. These curves illustrate the impact of near-field ground motions on different components. The component fragility curves for two sets of records, 91 near-field ground motions and 78 far-field ground motions, were obtained and compared. These findings demonstrate that near-field ground motions have a greater damaging effect on columns and abutments than far-field earthquakes. When it comes to bearing deformations, the far-field earthquake impact is more severe at lower intensities, whereas the impact of the near-field ground motion is stronger at higher intensities.

Seismic pounding of adjacent buildings considering torsional effects

This study aims to evaluate pounding effects in fixed-base models by considering torsional irregularity. For this purpose, 8 different adjacent building combinations were created by using 3-dimensional 5- and 9-story building models. In adjacent building models, the most critical situation was determined by evaluating the gap distance, different sequences of the same building models and regular or irregular plan view and if the structures are irregular, their eccentricity cases relative to each other. Nonlinear behavior of structural elements was taken into account for examine the change in the seismic behavior of structural elements due to pounding and torsion effects. The nonlinear time history analysis of the adjacent models was performed for 11 pairs of spectrum compatible ground motion recordings in the SAP2000 program. The results of 176 different analyzes show that the displacement demand, interstory drift ratio, damage ratio and torsional irregularity coefficient values tend to increase in general with the combined effects of pounding and torsion. The absolute maximum and most critical values of the relevant parameters were calculated in irregular structures with pounding where the eccentricity of buildings is in the same direction and same side. In addition, the large standard deviation of the result values according to the ground motion records indicates that care should be taken in choosing the number of ground motion records.

Experimental Study and Seismic Response Evaluation of Chlorobutyl Rubber-Based Viscoelastic Dampers

Conventional viscoelastic devices often use high-damping elastomeric pads, typically made of patented formulations, that are bonded to steel plates. The response properties of these pads under cyclic shear deformations directly influence the load-deformation hysteretic response of the device. Chlorobutyl (CIIR) is a high-damping rubber commonly used in industrial applications. However, this study found that the damping properties of a typical CIIR rubber compound are insufficient for effective structural seismic mitigation at ambient temperatures above 0°C. The goal of this study was to develop a new composite of CIIR, referred to as modified CIIR, with improved damping properties and to compare its performance with that of the reference CIIR rubber. In the first phase of the experimental studies, the viscoelastic characteristics of the reference and modified CIIR rubber materials were evaluated using dynamic mechanical thermal analysis (DMTA) in tension mode. Prototype viscoelastic damper devices were then fabricated from both the reference and modified CIIR rubber materials and subjected to cyclic shear tests at room temperature and various loading frequencies. The results showed that the modified CIIR rubber exhibited significantly improved effective damping compared to the reference CIIR. The final component of this study involved investigating the seismic response of a 2D frame structure equipped with prototype dampers made from both reference and modified CIIR materials, using nonlinear time-history analyses. The analysis results indicated that the modified CIIR rubber can be effectively utilized in the seismic response mitigation of structures.

Enhancing Seismic Damage Detection and Assessment in Highway Bridge Systems: A Pattern Recognition Approach with Bayesian Optimization.

Highway bridges stand as paramount elements within transportation infrastructure systems. The ability to ensure swift recovery after extreme events, such as earthquakes, is a fundamental trait of resilient communities. Consequently, expediting the recovery process necessitates near real-time diagnosis of structural damage to provide dependable information. In this study, a data-driven approach for damage detection and assessment is investigated, focusing on bridge columns-the pivotal supporting elements of bridge systems-based on simulations derived from nonlinear time history analysis. This research introduces a set of cumulative intensity-based damage features, whose efficacy is demonstrated through unsupervised learning techniques. Leveraging the support vector machine, a prominent pattern recognition algorithm in supervised learning, alongside Bayesian optimization with a Gaussian process, seismic damage detection and assessment are explored. Encouragingly, the methodology yields high estimation accuracies for both binary outcomes (indicating the presence of damage or the occurrence of collapse) and multi-class classifications (indicating the severity of damage). This breakthrough opens avenues for the practical implementation of on-board sensor computing, enabling near real-time damage detection and assessment in bridge structures.

Seismic risk assessment of highway bridges in western Canada under crustal, subcrustal, and subduction earthquakes

This study conducts seismic risk assessment of highway bridges in western Canada. The performance-based earthquake engineering (PBEE) framework is enhanced to assess the expected annual repair cost ratio (ARCR) and annual restoration time (ART) of a benchmark bridge class under the region’s three types of earthquakes - shallow crustal earthquakes (CEs), deep subcrustal earthquakes (SCEs), and megathrust Cascadia subduction earthquakes (CSEs). First, event-specific seismic hazard models are considered, whereas event-consistent ground motions are selected for non-linear time history analyses. Compared with those from CEs and SCEs, CSE ground motions feature a much longer duration. This long-duration effect is captured by validating the numerical model of the bridge column against (1) a cyclic pushover test under standard versus long-duration loading protocols and (2) a shaking table test excited by six consecutive ground motions. Besides, the Park and Ang damage index is utilized as the column’s engineering demand parameter (EDP) and updated as a demand-capacity ratio model when reaching four different damage states. A comprehensive list of ground motion intensity measures (IMs) is considered where the spectra acceleration at one second, Sa(1.0), is chosen as the most suitable IM based on its performance in proficiency, efficiency, practicality, and EDP-IM correlation across all three earthquake events. Subsequently, component- and system-level fragility models are derived under each earthquake type using the cloud analysis that convolves the seismic demands with capacity models for multiple bridge components. To further quantify and propagate the epistemic uncertainty associated with the development of probabilistic seismic demand models (PSDMs), the bootstrap resampling technique is utilized to generate numerous seismic demand datasets and develop a stochastic set of seismic fragility curves. Finally, the bootstrapped, event-dependent fragility models are combined with the respective hazard models and probabilistic loss functions to assess the expected ARCR and ART for the benchmark bridge class. This study underscores the significantly higher seismic risk of highway bridges when facing CSEs, followed by CEs and SCEs.