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In this research, a seismic retrofitting method for chevron-braced frames (CBFs) is proposed. The key idea here is to prevent the buckling of the chevron braces via a conventional construction technique that involves a hysteretic energy-dissipating element installed between the braces and the connected beam. The energy-dissipating element is designed to yield prior to buckling of the braces, thereby preventing the lateral stiffness and strength degradation of the CBF caused by buckling, while effectively dissipating the earthquake input energy. Nonlinear static pushover, time history and damage analyses of the CBF and retrofitted CBF (RCBF) are conducted to assess the performance of the RCBF compared with that of the CBF. The results of the analyses reveal that the proposed retrofitting method can efficiently alleviate the detrimental effects of earthquakes on the CBF. The RCBF has a more stable lateral force–deformation behavior with enhanced energy dissipation capability than the CBF. For small-to-moderate intensity ground motions, the maximum interstory drift of the RCBF is close to that of the CBF. But, for high intensity ground motions, it is considerably smaller than that of the CBF. Compared with the CBF under medium-to-large intensity ground motions, the RCBF experiences significantly less damage due to prevention of buckling of the braces.

Heavy damages on structures caused by near field earthquakes in recent years has brought serious attention to this problem. An examination of previous records has shown significant differences for near field earthquakes, including a large energy pulse, unlike far field earthquakes. But as a general rule, the effects of near field earthquakes have been ignored in most building codes. The purpose of this paper is to investigate the effect of near field earthquakes on reinforced concrete (RC) moment frames. To achieve this goal, the Erduran damage index, an efficient way to calculate damage, was employed to analyze two 4- and 8-story RC moment frame buildings. The buildings with moderate and high ductility were designed by the strength criteria. Seven pairs of near field and far field earthquakes were scaled and used for dynamic nonlinear time history analysis. Using Erduran’s beam and column damage index, respectively, based on rotation and drift, the results from both near and far field earthquakes were compared. Moreover, for better assessment, 4-story buildings were evaluated from the performance based viewpoint of design. We observe from the results that most of the components of the structures under near field earthquakes sustained severe damages and in some cases even component failure. Components of the structures under near field earthquakes suffered from 30% more of damage, on average, than that under far field earthquakes.

An assessment of seismic vulnerability of concrete gravity dams based on the fragility curves needs a well-defined damage index (DI) to define different states of damage. The DI formulation for other types of structures is not applicable to concrete gravity dams due to the change in failure mechanism. In this study, a definition of DI based on the factor of safety against sliding is attempted and correlated with the DI formulation based on the natural period of the structure and the maximum crest displacement with cumulative energy dissipation. The proposed DI relies on the nonlinear behavior of the concrete gravity dam model under cyclic testing. The hysteresis behavior is also verified through the finite element analysis by considering the damaged plasticity behavior of concrete.

In this study, a promising pattern recognition based approach is introduced for structural damage identification using the measured dynamic data. The frequency response function (FRF) is preferably employed as the input of the proposed algorithm since it contains the most information of structural dynamic characteristics. The 2D principal component analysis (2D-PCA) is used to reduce the large size of FRFs data. The output data generated by the 2D-PCA are used to extract the damage indexes for each of the damage scenarios. A dataset of all probable damage indexes is provided; of which 30% are selected to form the train dataset and to be compared with the unknown damage index for an unidentified state of the structure. The sum of absolute errors (SAE) are calculated between the unknown damage index and the selected indexes from the dataset; of which the minimum refers to the most similar damage condition to the unknown one. The artificial neural networks (ANNs) are used to form a smooth function of the SAEs and the imperialist competitive algorithm (ICA) is utilized to minimize this function in order to find the location and severity of the damages of the unknown state of the structure. To validate the proposed method, the damage identification of a truss bridge structure and a two-story frame structure is conducted by considering all the single damage cases as well as multi damage scenarios. In addition, the robustness of the proposed method to measurement noise up to 20% is thoroughly investigated.

A pattern recognition-based damage detection method using a brand-new damage index (DI) obtained from the frequency response function (FRF) data is proposed in this paper. One major issue of using the FRF data is the large size of input variables. The proposed method reduces the dimension of the initial FRF data and transforms it into new damage indices by applying a data reduction technique called the two-dimensional principal component analysis (2D-PCA). The proposed damage indices can be used as the unique patterns. After introducing the damage indices, a dataset of damage scenarios and related patterns is composed. Pattern recognition techniques such as the artificial neural networks and look-up-table (LUT) method are employed to find the most similar known DI to the unknown DI obtained for the damaged structure. As the result of this procedure, the actual damage location and severity can be determined. In this paper, the 2D-PCA and LUT method for damage detection is introduced for the first time. The damage identification of a truss bridge and a two-story frame structure is performed for verification of the proposed method, considering all single damage cases as well as many multiple damage scenarios. In addition, the robustness of the proposed algorithm to measurement noise was investigated by polluting the FRF data with 5%, 10%, 15% and 20% noises.

Damage indices based on structural dynamic characteristics are often used to detect damage in the structures. In this study, a new index for identifying damages in base-isolated structures is proposed using the frequency response function (FRF). Since calculation of the FRF data is time- and memory-consuming for problems of large size, the two-dimensional principal component analysis technique is employed to decrease the data size. The damage indices calculated, representing the health state of the structure, are stored in a database, which are then used to detect the damage location and severity by utilizing the lookup table method. The proposed damage detection method is applied to four concrete frame models, one of which is fixed at the base and the others are isolated by elastomeric bearings. The FRF data are polluted with three different noise values (5%, 10% and 15%) in order to evaluate the uncertainty of measurements. The accuracy of the proposed indices is compared with each other for various parameters such as noise values, bearings characteristics, base conditions and different damage scenarios. The results show the precision of the proposed method.

For the seismic design of a mid-rise reinforced concrete (RC) building considering the damage control, the main purpose of this work is to propose a simplified method that can be used to estimate the damage index or damage state induced by the near-fault and far-fault earthquakes. In addition to the maximum deformation response, the hysteretic energy dissipation induced the earthquakes is also considered in the damage index quantification based on the modified equivalent linearization method (MELM). Based on the damage index model in terms of the maximum deformation response and hysteretic energy dissipation under an earthquake, this work provides a convenient method by which an engineer can determine the damage-controlling minimal ductility requirement to ensure that the damage index remains under a specified value. For a mid-rise RC building structure, an engineer can also apply the simplified formula proposed in this work to obtain the damage-controlling yielding strength for a specified ductility capacity.

Nonlinear characteristics in the dynamic behaviors of civil structures degrade the performance of damage detection of the linear theory based traditional time- and frequency-domain methods. To overcome this challenge, this paper proposes a damage detection approach for nonlinear structures based on Variational Mode Decomposition (VMD). In this approach, the measured dynamic responses from nonlinear structures under earthquake excitations are adaptively decomposed into a finite number of monocomponents by using VMD. Each decomposed mono-component represents an amplitude modulated and frequency modulated (AMFM) signal with a limited frequency bandwidth. Hilbert transform is then employed to identify the instantaneous modal parameters of the decomposed monomodes, including instantaneous frequencies and mode shapes. Based on the identified modal parameters from the decomposed structural dynamic responses, two damage indices are defined to identify the location and severity of structural damage, respectively. To validate the effectiveness and accuracy of the proposed approach, a nonlinear seven-storey shear building model with four different damage cases under earthquake excitations is used in the numerical studies. In experimental verifications, data from shake table tests on a 12-storey scaled reinforced concrete frame structure with different earthquake excitations are analyzed with the proposed approach. The results in both numerical studies and experimental validations demonstrate that the proposed approach can be successfully applied for nonlinear structural damage identification.

The identification of a breathing crack is a highly challenging inverse problem in structural health monitoring. A novel output-only diagnostic technique for breathing cracks is proposed in this paper based on the singular value decomposition (SVD). A new damage index based on the singular values of the harmonic time history response, related to the Fourier spectrum amplitude of the superharmonics, is presented for breathing crack localization. The robustness and effectiveness of the proposed SVD-based approach are verified through both numerical and experimental studies.

This paper deals with seismic performance and damage assessment of concrete grain silos. An existing large silo is taken as a case study to conduct the numerical analyses. A global damage index based on target displacement is proposed to quantify numerically different damage states of the structure. To this aim, the classical N2 method is extended to adaptive multimodal to evaluate seismic performance of the structure for increasing pic ground acceleration levels with taking into account degradation of stiffness and modification of modal characteristics. The seismic capacity of the silo is evaluated, as an averaged curve, by conducting pushover and several incremental dynamic analyses using artificial and recorded accelerograms. The seismic demand is derived from the design spectrum of the Algerian seismic code (RPA 2003). The target displacement is determined by taking into account both the participation of the dominant modes, and the degradation of the structure’s modal characteristics. The nonlinear behavior of the structure’s walls is modeled by using nonlinear multilayered shell elements. The effect of the stored granular material is included through distributed equivalent masses. It is found that when the structure modal characteristics are updated as its stiffness is degraded, the target displacement is correctly computed. Whereas, it wrongly grows indefinitely, with increasing PGA, when constant modal characteristics of the intact structure are assumed, as usually done. The proposed global damage index is compared to three existing reliable indices. It better reflects the different damage states of studied silo.

The goal of this paper is to develop a modified Bouc–Wen hysteretic model from cyclic loading test data for reinforced columns, including the behavior of stiffness degradation, strength deterioration, pinching and softening effects of RC members. Seismic demands on this inelastic single-degree-of-freedom system when subjected to both near-fault ground motion and far-field ground motion excitations were examined.

The cyclic loading test of reinforced concrete columns was experimentally observed and a system identification computer program was developed to solve each control parameter of the hysteretic model. A least-squared method for identifying parameters of the model is proposed in this paper. The hysteretic constitutive law produces a smoothly varying hysteresis such as the control-parameters for strength deterioration, stiffness degradation, pinching and softening effects. Two implementations of (1) flexure damage and (2) shear damage were conducted to provide better understanding of hysteretic behavior of RC structural members. A pseudo-dynamic experiment was also developed to verify the model parameters.

Based on the developed hysteretic model, the seismic demand of this inelastic model was investigated by using both near-fault ground motion data and far-field ground motion data as input motion. An R-μ-T inelastic response spectrum from different hysteretic models was generated.

The paper deals with the inelastic analysis of infilled frames. It aims to appraise the effectiveness of existing member-by-member models and damage indices in representing seismic response and sustained damage. Results from pseudo-dynamic and cyclic tests on one-storey one-bay half-size-scale specimens are the basis for this evaluation. The frame is modelled with linear beam elements and hysteretic end springs, and the infill with diagonal struts for which two inelastic behavioural laws are compared. Provided parameters are carefully calibrated, time-histories of the global response can be traced with an accuracy that depends on model refinement. Certain indices reflect the visible damage of structure and infill. Nevertheless, if the structure index is derived from the calculated local response, not even the major damage of the weak beam is captured.

The role of residual deformations when evaluating the performance of multi-storey frame structures subjected to ground motion is investigated in this paper. The limitations of damage indices available in the literature, either based on ductility, energy dissipation or a combination of both, in capturing such a significant aspect of the seismic response of frame structures are discussed. The concept of residual deformations as a critical complementary indicator to cumulative damage, introduced in a companion paper (Part I) for single-degree-of-freedom (SDOF) systems, is herein extended to multi-degree-of-freedom (MDOF) frame systems. The seismic performance of multi-storey frame structures, either representative of new designed or existing structures, is investigated, focusing on the response in terms of residual deformations. Residual deformations are shown to be sensitive to the hysteretic rule adopted, to the system inelastic mechanism as well as to the seismic intensity. The influence of higher modes and P-Δ effects on the final residual deformations is addressed. A combination of maximum drift and residual drift in the format of a performance matrix is used to define the system's global performance levels and is then extended to a framework for an alternative performance-based seismic design and assessment approach.

In this paper, the damage prediction of shear-dominated reinforced concrete (RC) elements subjected to reversed cyclic shear is presented using an existing damage model. The damage model is primarily based on the monotonic energy dissipating capacity of structural elements before and after the application of reversed cyclic loading. Therefore, it could be universally applicable to different types of structural members, including shear-dominated RC members. The applicability of the damage model to shear-dominated RC members is assessed using the results from reversed cyclic shear load tests conducted earlier on eleven RC panels. First, the monotonic energy dissipating capacities of the panels before and after the application of reversed cyclic loading are estimated and employed in the damage model. Next, a detailed comparison between the analytically predicted damage and the observed damage from the experimental tests of the panels is performed throughout the loading history. Subsequently, the effects of two important parameters, the orientation and the percentage of reinforcement, on the damage of such shear-dominated panels are studied. The research results demonstrated that the analytically predicted damage is in reasonably good agreement with the observed damage throughout the entire loading history. Furthermore, the orientation and percentage of reinforcement is found to have considerable effect on the extent of damage.

The intensity measures of ground motions are closely related to the damage of bridge structures. However, it is difficult for engineers to select these parameters to predict the potential damage of cable-stayed bridges under earthquakes. This paper investigated the correlation between the intensity measures of far-fault ground motions and the damage of cable-stayed bridges. 322 far-fault ground motions were selected, and 26 available intensity measures in the literatures were chosen to carry out comparative analysis on a cable-stayed bridge with a single pylon. The nonlinear finite element model of this bridge was built, considering the stiffness degradation of concrete and low-cycle fatigue effect of steel. It is concluded in this study that velocity spectral intensity (VSI) is the optimal intensity measure for seismic damage analysis of cable-stayed bridges subjected to far-fault ground motions, followed by spectral acceleration at fundamental period and Housner intensity. Five commonly used intensity measures, namely peak ground acceleration (PGA), the ratio of PGA to peak ground velocity (PGA/PGV), specific energy density (SED), predominant period (T_p) and mean period (T_m), demonstrate low correlations with the bridge damage. In particular, there is very weak correlation between the conventionally used PGA and the seismic damage of cable-stayed bridges.

The effects of geometric configuration on the seismic vulnerability of concrete gravity dam are discussed in the present study. The seismic vulnerability of concrete gravity dams has been represented through fragility curves obtained through incremental dynamic analyses by considering their nonlinear dynamic behavior. Five different geometries of concrete gravity dams are considered and fragility analyses are carried out on the basis of Incremental Dynamic Analyses. The effect of smoothening of re-entrant corners in the geometry of high concrete gravity dam is also presented as a possible solution.

Inelastic seismic responses of flexibly supported reinforced concrete (RC) moment-resisting frames representing short-to-tall structures stiffened with ductile RC structural walls were evaluated considering both far-field and near-field ground motions. A dual shear wall-frame resisting system with symmetric reference plan was created by adding shear walls into excitation direction of the three-dimensional frames developed by generic structure algorithm. The current study also aims to take into account soil–structure interaction effects in to damage assessment of multi-story RC buildings in terms of ductility demand, damage index, story shear force and overturning moment, as well as kinetic energy profile over the structure height. In doing so, the developed set of generic frames was considered accounting for different values of story strength, stiffness distribution and number of stories. A realistic modeling of nonlinear ductile behavior of RC elements was developed in combination with the sub-structuring method to consider the foundation flexibility in nonlinear seismic responses. Conducting a parametric study through nonlinear static analyses (pushover) as well as nonlinear response history analyses, the results indicated that the near-field ground motion presents much more damage than the far-field one. Inelastic dynamic responses to near-field records demonstrated that structures with a fundamental period greater than the pulse period respond differently from those that have shorter periods. The results were also presented as charts and tables that provide helpful information for engineering design purposes such as damage assessment of multi-story RC buildings with specific fundamental natural period and base shear strength.

This study presents an innovative and automated methodology for assessing damage levels in masonry structures following earthquakes, utilizing a deep learning-based segmentation approach. Central to this research is the use of a U-Net convolutional neural network (CNN) model, which facilitates automated damage detection with a focus on smartphone-enabled, real-time analysis. A key feature of this method is a novel damage index (DI), calculated by normalizing the surface area of detected damages against the total area of the structure, as viewed from the same perspective. The findings indicate a marked improvement in damage detection capabilities, with the U-Net model achieving a precision of approximately 92% and a recall of around 93%. These figures highlight the model’s proficiency in accurately identifying damaged areas and reducing false positives, an essential aspect of post-earthquake evaluations. While this methodology represents a significant step forward in enabling rapid and cost-effective post-earthquake inspections, it is accompanied by certain constraints, particularly in terms of dataset diversity and computational requirements. Despite these challenges, the high accuracy and effectiveness of the damage detection and indexing process demonstrate strong potential for future applications in structural health monitoring, especially in scenarios that demand prompt action and are limited by resources.

To examine the damages of structure in use is generally a challenging task., particularly when a fast inspection is required by using limited tools or even the bare eyes. The other challenge is how to evaluate the damage state after the fast safety examination. Most well know damage indexes for the structure are for the design purposes such as to estimate the possible damage state when structure is under extraordinary loading condition. The index must relate to the maximum force applied and maximum deflection or plastic deformation. To have structure's real response is generally impossible unless on-line monitoring is applied. Therefore, it is the interest of this study to find a means to evaluate the damage state through the limited data obtained by bare-eye examination or using limited tools. The evaluation was performed in the laboratory by testing the scaled down beam models and compared the data obtained by limited tools to the one obtained through data acquisition system. It was found that for the large scale, fast structure inspection this new developed simplified damage index may provide a convenient means for the damage evaluation of the structures.