Severe Damage State Research Articles

Fragility functions for structural-architectural shear walls with interlocking modules

ABSTRACT Tessellated structural-architectural (TeSA) shear walls, consisting of interlocking tiles, enable repairability because of modularization, and can satisfy both structural and architectural demands. This paper characterizes the behavior of TeSA walls made of 1-D interlocking reinforced concrete tiles using fragility functions. Two TeSA walls with varying tile patterns are analyzed under lateral loading. The modeling approach is validated using test results under quasi-static cyclic lateral loading. Damage states at tile and wall levels are defined, and a framework for generating fragility functions for TeSA walls is proposed considering uncertainties in the applied axial loading, tile-interface properties, modeling approach, and material properties of concrete. The results show that TeSA wall fragility functions are sensitive to tile shapes and patterns, particularly for the severe damage state. The onset of moderate and severe damage for TeSA walls is at 1% and beyond 2% drift ratios, respectively, showing high resistance of TeSA walls to damage.

Experimental investigation of retrofitting seismically damaged reinforced-concrete frames using steel jacketing

Retrofitting seismically damaged structures provides significant economic and social benefits. To investigate the rationality of using steel jacketing to retrofit seismically damaged reinforced concrete (RC) structures, we initially tested a half-scale single-span two-story frame structure under pseudo-static loads to achieve a severe damage state. Subsequently, the structure was retrofitted using steel jacketing and tested under another round of pseudo-static loads. The seismic performances of the original and retrofitted structures were compared. The test results indicated that both the original and retrofitted specimens sequentially developed plastic hinges at the beam ends and the bottom of the columns, indicating a generally similar damage evolution mode. Comparing to the original structure, the retrofitted specimen exhibited an increase of 33% and 78.5% in initial stiffness and strength, respectively. Although the ductility ratio of the retrofitted specimen was reduced by about 14%, the ultimate drift ratios of both specimens exceeded the threshold value (1/50), indicating an adequate deformation capacity. The retrofitted specimen exhibited a certain degree of pinching behavior on the hysteretic curve because of the presence of extensive inclined shear cracks at the mid span of the beams and the progressive failure of the anchoring of the strengthening steel angle at the beam ends and column base. Consequently, the energy-dissipation coefficients of the retrofitted specimen were lower than those of the original specimen. Based on the test, the finite element analysis modeling method for RC frame structures retrofitted using steel jacketing was also studied. By comparing the numerical simulation analysis results with the experimental ones, the reliability of the proposed numerical simulation method was verified. This study can serve as a foundation for the practical application of steel jacketing to retrofit seismically damaged RC structures.

Damage localisation using disparate damage states via domain adaptation

Abstract A significant challenge of structural health monitoring (SHM) is the lack of labeled data collected from damage states. Consequently, the collected data can be incomplete, making it difficult to undertake machine learning tasks, to detect or predict the full range of damage states a structure may experience. Transfer learning is a helpful solution, where data from (source) structures containing damage labels can be used to transfer knowledge to (target) structures, for which damage labels do not exist. Machine learning models are then developed that generalize to the target structure. In practical applications, it is unlikely that the source and the target structures contain the same damage states or experience the same environmental and operational conditions, which can significantly impact the collected data. This is the first study to explore the possibility of transfer learning for damage localisation in SHM when the damage states and the environmental variations in the source and target datasets are disparate. Specifically, using several domain adaptation methods, this article localizes severe damage states at a target structure, using labeled information from minor damage states at a source structure. By minimizing the distance between the marginal and conditional distributions between the source and the target structures, this article successfully localizes damage states of disparate severities, under varying environmental and operational conditions. The effect of partial and universal domain adaptation—where the number of damage states in the source and target datasets differ—is also explored in order to mimic realistic industrial applications of these methods.

A Fault Diagnosis Method for Drilling Pump Fluid Ends Based on Time–Frequency Transforms

Drilling pumps are crucial for oil and gas operations. Timely diagnosis and troubleshooting of fluid end faults is crucial to ensure the safe and stable operation of drilling pumps and prevent further deterioration of faults. Hence, from a data-driven perspective, this study proposes a fault diagnosis method for the fluid end of drilling pumps based on the generalized S transform (GST) and convolutional neural networks (CNN), using the vibration signal of the fluid end. To address the issue of noise pollution in the vibration signal resulting in unclear feature information and difficult feature extraction, the vibration signal is transformed into a time–frequency diagram based on GST, which more accurately characterizes the fault characteristics of the vibration signal. An AlexNet model, improved by introducing batch normalization and optimizing the number of neurons in the fully connected layer, is used to analyze the recognition performance of the model for the normal, minor damage, and severe damage states of the fluid end of the drilling pump. Finally, the diagnosis results are compared to other methods, with the results showing that the proposed method has the highest fault diagnosis accuracy. With an average recognition rate of 99.21% for the nine types of fluid end, the method proposed in this study provides a way to accurately diagnose fluid end failures, thus supporting the safe and efficient operation of drilling pumps.

Influence of ground motion duration on seismic behavior of RC bridge piers: The role of low-cycle fatigue damage of reinforcing bars

This paper assesses the influence of ground motion duration on seismic behavior of reinforced concrete (RC) bridge piers using spectrally equivalent short- and long-duration ground motions. Special attention is paid to the role of low-cycle fatigue damage of reinforcing bars. To this end, an experimentally validated nonlinear fiber-based beam-column element considering buckling and low-cycle fatigue of longitudinal bars is adopted for nonlinear dynamic analyses and fragility modeling. An advanced material level damage index is used to account for both the maximum response (strain damage) and cumulative damage (low-cycle fatigue damage of longitudinal bars). The dynamic analysis results indicate that the strain damage is the major failure mechanism for RC bridge piers under short-duration ground motions. Under long-duration ground motions, by contrast, the strain damage is prominent at the early excitation stage, while the low-cycle fatigue damage may dominate the late excitation stage. In particular, the role of low-cycle fatigue is more prominent for RC bridges against long-duration ground motions with significant durations beyond 50 s and peak ground velocities over 30 cm/s. The fragility analysis demonstrates that, ignoring the low-cycle fatigue damage of longitudinal bars will obviously underestimate the seismic fragility of RC bridge piers under long-duration ground motion, and the influences is more significant at more severe damage states. Therefore, the low-cycle fatigue damage of reinforcing bars is one of the main failure modes of RC bridge piers under long-duration ground motion, and should be considered in the seismic design,

A novel framework for seismic fragility analysis with the combination of Box-Cox transformation and Bayesian inference

Fragility curves describe the conditional failure probability that the structural demand reaches or exceeds a limit state under a given intensity measure, which is extensively used in performance-based earthquake engineering. To improve the performance of current methodologies, a novel framework for seismic fragility analysis with the combination of Box-Cox transformation and Bayesian inference is proposed in the present study. A long-span cable-stayed bridge is taken as a case study, and the numerical model of the bridge is established within the OpenSees platform. The probabilistic seismic demand models are established with the Bayesian inference for the Box-Cox transformed data and developing the fragility models with binary Bayesian regression analysis. The numerical results reveal that the proposed framework can establish the nonlinear probabilistic seismic demand models and improve the performance of the classical methods. In addition, the binary Bayesian logistic regression-based fragility model eliminates the assumptions of the classical analytical approaches, and robust results can be obtained. Based on the derived fragility curves, the classical cloud method usually underestimates the failure probability of the components in severe damage states. In contrast, the proposed framework can accurately predict seismic demands at a large intensity level.

Buckling restrained braced frame seismic response for far-field, near-field, and long-duration earthquakes

This paper presents the structural response of prescriptively designed buckling restrained braced frame buildings to four ground motion sets with different fault characteristics. The four ground motion sets are characteristic of far field, near field with pulse, near field with no pulse, and subduction zone long duration earthquakes. Two prototype buildings of different heights were used for the analysis and designed for a site in Seattle, WA. The analysis was conducted using three-dimensional numerical models of the prototype buildings developed in OpenSeesPy. The simulated buckling restrained brace response was validated with three experimental tests from the literature. The analysis results were used to investigate the effect of ground motion type on the structural response parameters of inter story drift, peak floor velocity, peak floor acceleration, residual inter story drift, and cumulative ductility demand. Results show that the near field motions increase the inter story drift demand compared to far field and long duration motions. All motion sets were likely to cause some level of structural and non-structural damage to drift, velocity, and acceleration sensitive components at the DE and MCER hazard levels, but severe damage states may not be highly likely. The median residual inter story drift was less than 0.5% for all motion sets. The cumulative ductility demand of the subduction zone long duration motion set was 5 to 6 times greater than that of the far field or near field motion sets and exceeded the code-minimum cumulative ductility for prequalification for upwards of 60% of the analyses.

Fragility assessment for new and deteriorated portal framed industrial buildings subjected to tropical cyclone winds

Low-rise portal framed industrial buildings are widely used as warehouses, workshops and storage facilities. Damage surveys following severe tropical cyclones have shown that both structural and non-structural damage can occur to these buildings. While non-structural damage to the building envelope of portal framed industrial buildings are considered by several existing fragility models, almost none exist that include structural failures in the wind fragility assessment. This study develops a fragility assessment method for portal framed industrial buildings that accounts for wind-induced damage to both structural (steel portal frame and end wall frame) and non-structural (metal cladding system and fenestration) building components. Fragility curves are developed for a prototype industrial building located on the cyclone-prone east coast of Australia considering four damage states with increasing damage severity. A Monte Carlo simulation incorporating probabilistic models of the spatio-temporal variable wind pressures, wind-induced demands and component capacities is employed to conduct the fragility assessment for both individual building components and the building system under critical failure modes. It was found that the fragility of structural framing is non-negligible when wind speed exceeds 80% of the design level. Structural framing failure is a major contributor to the most severe damage state and is a necessary inclusion in the fragility assessment for this type of building. A sensitivity analysis also showed that fastener corrosion can significantly increase the fragility of deteriorated buildings near to coastlines, particularly for low levels of damage.

Machine Learning for Enhanced Regional Seismic Risk Assessments

The ability to conduct accurate regional seismic risk assessments is key to informing a risk-reduction policy and fostering community resilience. This paper presents a machine learning-based framework to predict a building’s postearthquake damage state using structural properties and ground motion intensity measures as model inputs. The machine learning techniques assessed, namely, logistic regression, k-nearest neighbors, decision tree, random forest, AdaBoost, and gradient boosting, are trained using a dataset of nonlinear response history analysis results from 36 detailed structural models of modern reinforced concrete shear wall buildings ranging from four to 24 stories and subjected to approximately 500 ground motion records with a range of shaking intensities. The results indicate that the gradient boosting classifier is the most efficient algorithm by achieving a prediction success (F1-score) of 87%. The proposed framework also leverages synthetic data samples to support the prediction of severe damage state instances, that is, collapse. The percentage of observed collapse cases correctly classified by the gradient boosting algorithm is increased from 76% to 93% when synthetic data are also used for training. The framework is implemented in a portfolio of reinforced concrete shear wall buildings across the Metro Seattle region to quantify earthquake-induced damage and collapse risk. The framework shows great potential for enhancing regional seismic risk assessments by leveraging datasets of detailed nonlinear response history analysis results.

Numerical Simulation of Dynamic Response and Evaluation of Flexural Damage of RC Columns under Horizontal Impact Load

By using the ABAQUS finite element (FE) model, which has been verified by experiments, the deformation and internal force changes of RC columns during the impact process are investigated, and a parametric analysis is conducted under different impact kinetic energies Ek. According to the development path of the bottom bending moment-column top displacement curve under impact, the member is in a slight damage state when the curve rebounds before reaching the peak and in a moderate or severe damage state when the curve exceeds the peak, in which case the specific damage state of the member needs to be determined by examining whether there is a secondary descending stage in the curve. Accordingly, a qualitative method for evaluating the bending failure of RC column members under impact is obtained. In addition, the damage state of RC columns under impact can also be quantitatively evaluated by the ratio of the equivalent static load Feq and the ultimate static load-bearing capacity Fsu.

Operational Modal Analysis and Non-Linear Dynamic Simulations of a Prototype Low-Rise Masonry Building

This paper focuses on the dynamic behaviour of a low-rise masonry building representing the Italian residential heritage through experimental and numerical analyses. The authors discuss an application of combined Operational Modal Analysis and Finite Element Model updating for indirect estimation of the structural parameters. Two ambient vibration tests were carried out to estimate the structure’s dynamic behaviour in operational conditions. The first experimental setup consisted of accelerometers gathered in a row along the first floor to characterize the local dynamic of the floor. Conversely, the second setup had the accelerometers placed at the building’s corners to characterize the global dynamics. The outcomes of the first setup were used to estimate the mechanical parameters of the floor, while the ones form the second were used to characterize the mechanical parameters of the masonry piers. Therefore, two finite element models were implemented: (i) a single beam with an equivalent section of the floor to grasp the local behaviour of the investigated horizontal structure; (ii) an equivalent frame model of the entire building to characterise the global dynamic behaviour. The model updating process was developed in two phases to seize local and global dynamic responses. The updated numerical model formed the basis for a sensitivity analysis using the modelling parameters. The authors chose to delve into the influence of the floor on the dynamic behaviour of low-rise masonry buildings. With this aim, non-linear dynamic analyses were carried out under different mechanical characteristics of floors, expressing the scatter for ordinary masonry buildings. The displacements’ trends along the height of the building evidenced the notable role of the floor’s stiffness in the non-linear dynamic behaviour of the building. Lastly, the authors derived the fragility curves predicting the seismic performance in failure probability under a highly severe damage state.

An integrated approach for the numerical modeling of severely damaged historic structures: Application to a masonry bridge

This paper presents an integrated approach that combines advanced survey procedures, such as close range photogrammetry based on high resolution images provided by Unmanned Aerial Vehicles, and Ambient Vibration Tests to develop accurate Finite Element models of severely damaged historic masonry structures. The proposed methodology is applied to a masonry arch bridge located in Todi, Central Italy, characterized by severe damage conditions involving diffuse material degradation and structural damages. Two numerical models are developed starting from the digital geometric survey: the first accurately describes the irregular actual geometry due to damage; the second regularizes the boundary surfaces as standard procedure in common practice when detailed survey is not available. The crucial role of the geometric irregularities given by the severe damage state on the dynamic properties of the masonry bridge is demonstrated by comparing the modal parameters of the two models. Furthermore, sensitivity analysis is carried out in order to assess the combined effect of different mechanical characteristics and geometric configurations on the modal properties and to select suitable updating parameters. The overall methodology is completed by a final model updating procedure targeting the experimental modal parameters estimated from Ambient Vibration Tests.

Vulnerability assessment of a high‐rise building subjected to mainshock–aftershock sequences

SummaryStrong aftershocks have the potential to further aggravate the damage state of structures, and much less attention has been given to the seismic vulnerability of high‐rise buildings than that of low‐ to medium‐rise buildings. This study assesses the seismic vulnerability of a 32‐storey frame–core tube building by performing the incremental dynamic analysis on the material‐based three‐dimensional numerical model. A storey damage model based on the material damage is developed using the weighted average method. Eighteen recorded mainshock–aftershock sequences, whose mainshock records match the target spectrum, are selected. The results indicate that the developed stroey damage model can effectively reflect the additional damage induced by aftershocks. Strong aftershocks have high potential to change the location of weak storeys. Notably, shifts of weak storeys are observed in more than 30% of aftershocks with relative spectral acceleration of 0.8. As the mainshock‐induced damage state becomes more severe, the mainshock‐damaged building becomes increasingly fragile to the aftershock excitation and more sensitive to aftershock intensities. The probability of exceeding severe damage state increases from 35.3% to 62.1% due to the effects of strong aftershocks. The results in this study can provide supports to the seismic resilience assessment of this high‐rise building.

Probabilistic seismic performance and loss evaluation of a multi-story steel building equipped with butterfly-shaped fuses

Shear fuses are structural elements that protect surrounding members from damages by undergoing substantial yielding, and then are easily replaced after a major earthquake event. Butterfly-shaped shear fuse is a promising type of structural system, which can effectively align member's flexural capacity to the imposed moment demand due to its unique geometry. Although recent studies suggest that butterfly-shaped fuses exhibit substantial ductility and energy dissipation, their impact on the global performance of multi-story buildings requires further investigation. This study presents a comprehensive risk-based evaluation of a six-story eccentrically braced steel frame retrofitted with butterfly-shaped fuses. Two nonlinear finite element models of the original prototype building and retrofitted building with butterfly-shaped fuses are developed in OpenSees and incremental dynamic analysis is conducted. The results are used to derive global and story-based fragility and seismic demand hazard curves. Furthermore, earthquake-induced losses associated with structural and non-structural assemblies are quantified and the impact of butterfly-shaped fuses on the distribution of story acceleration and drift demands are evaluated.The results show that butterfly-shaped fuses significantly improve the structure's performance in terms of all drift-related damage states and the improvement is more pronounced at severe damage states. In particular, the risk of exceeding complete damage state in the retrofitted building's lifetime is reduced to approximately one-fourth of the original building's values. Furthermore, shear fuses effectively mitigate weak story formation at lower stories due to their large energy dissipation and ductility. The improved drift-related performance reduces the drift-induced loss of structural and non-structural assemblies, resulting in 44.64% smaller total annual loss for the studied building. In addition, although butterfly-shaped fuses reduce the probability of exceeding slight damage state for the floor acceleration, their impact is negligible at higher acceleration-related damage states.

Crack length based healing characterisation of bitumen at different levels of cracking damage

This study aims to characterise the healing properties of asphalt binders at different damage levels. The healing and the damage levels were quantified by crack length (CL) in binder samples generated by rotational shear fatigue loads in strain-controlled dynamic shear rheometer (DSR) tests. For comparison, the healing was also characterised by the commonly used material parameters including pseudo shear stiffness (S) and dissipated pseudo strain energy (DPSE). A normalized healing index was formulated using the above three parameters, respectively. A healing test of polymer-modified bitumen was designed based on DSR including a strain-controlled time sweep test plus a rest duration and followed by another strain-controlled time sweep test. The healing tests were performed at different rest start times (5min, 10min and 20min), rest durations (5s, 10s, 0.5min, 1min, 2min, 5min, 10min, 20min, and 40min), and amplitudes of the shear strain (5%, 7%, and 10%) at 20 °C and 10 Hz. Results show that the CL-based healing index is a fundamental and accurate parameter to evaluate the healing rate and healing potential of the bitumen. DPSE-based healing index is applicable only when the energy is mainly dissipated to generate cracks. Healing is underestimated when characterised using S or DPSE-based healing indices. Healing index increases due to the advance of rest duration or the decrease of the damage level, and the healing rate can be essentially modelled by Ramberg-Osgood model. Higher damage levels (introduced by higher load levels or longer loading time) can effectively decrease the binders’ healing potentials when the binders are at the relatively low damaged levels. The healing potential becomes low when the material is at severe damage state, thus will remain at that low levels even though the damage level increases.

On the accuracy of UAV photogrammetric survey for the evaluation of historic masonry structural damages

Photogrammetric surveys via Unmanned Aerial Vehicles are nowadays a valuable tool for historic masonry structures inspection, surveillance, mapping and 3D modeling issues. When structural damage mapping and structural assessment are of interest obtaining accurate and reliable geometric models is a crucial issue. Therefore, the flight plan, the georeferencing and the data processing steps need to be properly designed.In this paper, a procedure for the photogrammetric survey via Unmanned Aerial Vehicles of a masonry structures is used in order to obtain effective visual inspections and a 3D model of a historic masonry arch bridge located along the ancient Via Amerina (Todi, Perugia, Italy). The photogrammetric survey provides a detailed representation of the actual geometry, including lack of volumes and significant cracks along the vault and the spandrel walls, outlining a severe damage state affecting all the structure. Finally, a Total Station and a Laser Scanner were used to compare the results obtained by photogrammetry, highlighting the advantages, the limits and the weaknesses offered by their use.

Impact of corrosion on risk assessment of shear-critical and short lap-spliced bridges

Increasing corrosion in aging reinforced concrete structures is increasing their vulnerability to failures. This is particularly true for bridges with low-ductility columns, including shear-critical columns and columns with short lap splices. This paper presents a methodology to assess the impact of corrosion on performance of these structures. The combined analytical and numerical modeling of shear-critical and lap-spliced columns is detailed, and outcomes are verified with previous experimental test data. Corrosion effects are accounted for through reduction of longitudinal and transverse reinforcement and bond deterioration between the steel and concrete through corrosion-induced cracking. The impact of corrosion on risk is assessed through conducting fragility analyses. Results quantify the increase in failure probabilities of these structures, measured by increasing probabilities of exceeding defined damage states, with increasing levels of corrosion. Corrosion is found to have a larger impact on increasing probabilities of exceeding more severe damage states. Twenty percent mass loss of reinforcement increases the probability of exceeding the complete damage state by up to 49% and 34% for a shear-critical and lap-spliced column, respectively. The effect is more pronounced at intermediate loading intensities, where there is uncertainty about the performance of the structure. Comparing between failure modes, bridges with columns of short lap splice are more vulnerable to collapse under the same degree of corrosion compared with shear-critical columns.

Evaluation of power substation equipment seismic vulnerability by multivariate fragility analysis: A case study on a 420 kV circuit breaker

Recent earthquakes have shown that Electrical Power Substations apparatuses are seismically vulnerable. This causes to disrupt the power supply in many cases, and therefore their seismic evaluation with high reliability is significantly important. Using fragility curves is a common practice for assessing seismic vulnerability. In general, fragility curves are based on only one intensity measure (IM), such as peak ground acceleration (PGA). This study has attempted to propose multivariate fragility analysis. One of the major advantages of this developed multivariate fragility analysis is to more reliably determine the seismic vulnerability of a region. A 420kV circuit breaker (CB) was modeled and analyzed by using finite element technique. The results show that by adding another IM as peak ground velocity (PGV) the dispersion of the created data decreases to a great extent and therefore, the developed fragility surfaces helps conducting the seismic risk evaluation of electric power system components with higher level of reliability. Based on the obtained numerical results it can be expressed that for moderate damage state the fragility values are not much dependent on the PGV variation, while for severe damage state the dependence of fragility values on PGV is noticeable, particularly for PGA values in range of 0.1–0.7g.

FRAGILITY CURVES: A POWERFUL TOOL FOR SEISMIC VULNERABILITY ASSESSMENT OF PILE-SUPPORTED WHARVES

Seismic vulnerability assessment of structures is usually illustrated in the form of fragility curves. These curves show the probability that a component, element or system will be damaged to a given or more severe damage state as a function of a single predictive demand parameter. In addition, these curves are useful for seismic risk assessment and performance based design engineering, as well as prioritization of retrofitting programs. This paper reviews recent works on the seismic vulnerability analysis of pile-supported wharf structures. Different aspects for each paper are reviewed in terms of characteristic of the selected pile-supported wharf structure, institution and procedure of numerical modeling, capabilities of numerical models, analysis method for seismic response evaluation, ground motion records, damage states, intensity measure and obtained results. This paper shows that very limited studies have been performed on the seismic vulnerability of pile-supported wharves indicating a clear need to the development and application of fragility analysis of pile-supported wharf structures.

Seismic Damage Evaluation of Gravity Load Designed Low Rise RC Building Using Non-linear Static Method

In India, the 2001 Bhuj earthquake has given a serious warning to many existing reinforced concrete (RC) buildings. However, a considerable portion of the building stock of India is reinforced concrete buildings which are generally designed mainly for gravity loads only. Therefore, potential seismic evaluation of these buildings, especially in high seismic region, is very essential in order to implement any kind of seismic hazard mitigation strategy. Hence, the present study aims to evaluate the seismic vulnerability of low rise RC frame building which is designed for gravity load according to the Indian code. The non-linear static analysis is performed using SAP2000 (v16) to find the capacity curve of the building. Fragility analysis is used to develop the fragility curve for different damage grade based on HAZUS methodology. Damage probability matrices (DPM) are formed for two different seismic hazard levels i.e. for maximum considered earthquake and design basis earthquake depending on the performance point to compare the damage state for each hazard level. The result shows that the damage of considered building is vary from moderate to severe damage state to the corresponding different seismic hazard level.