Identification of the modal parameters of the DAMAGEd structure by signal processing of vibration based on changes in dynamic properties such as frequency, stiffness, and mode shape of structures. Some of these approaches fail when applied to civill engineering structures, the main reasons are the low sensitivity of the structural response to the DAMAGE location, or the low accuracy of structural response obtained by installed sensors. However, due to the rigorous evaluation and low cost of signal processing methods, this method has made a great progress. Signal processing methods have been extensively employed to examine the measured system responses and determine system variations. These methods include Fourier analysis, wavelet transform and Hilbert-Huang transform. During the last decades, the number of vibration-based DAMAGE detection methods has been greatly developed and has influenced much of the research. The purpose of these methods is to determine the resulting changes in the modal characteristics of the structure including its natural frequency, mode shape, and damping ratio. For example, the basis of the Fourier transform method is to determine the structural modal parameters from the random vibration data in the frequency range. However, time-frequency analysis is introduced to overcome the limitations of the Fourier method, the most important of which is not providing a frequency-time range of a signal. The first case of frequency-time analysis was the short-time Fourier transform method based on the Fourier transform of the data divided by the time window function. According to this method, the interaction between time and frequency is difficult due to the existence of the time window function. If the windows are smaller in the time segment, its accuracy increases, and in the frequency domain it becomes less accurate. Several DAMAGE detection methods have been proposed based on the vibration signal of structures. In most of them, a DAMAGE INDEX has been described as the difference between DAMAGE and unDAMAGEd structure. This paper intends to propose a DAMAGE detection method based on the amplitude coefficient correlation of DAMAGEd and unDAMAGEd responses of structures, while a signal decomposes to IMFs and the changes appear in the first IMF. Therefore, every change on the original signal can be revealed on IMFs, since the original signal depends on IMFs. Also, these changes have an effect on the analytical signal and the Hilbert transform. The instantaneous frequency is measured joints on the structure is calculated by the Hilbert transform of the first IMF of response. Then, by introducing the instantaneous frequency energy (EDI), the location of DAMAGEs are detected. To assess the feasibility and reliability of the proposed method, the ASCE benchmark problem has been used. To consider the robustness of the proposed method, contamination of signals during the data acquisition process is investigated. The ASCE benchmark study is carried out by the International Association (IASC) ASCE Structural Health Monitoring Task Group. The dynamic responses of the structure have been obtained by numerical analysis under random vibration loading. To evaluate the HHT method, it is required to attain the DAMAGEd responses of the ASCE benchmark. The first five DAMAGE patterns of the ASCE benchmark building is used. Then the DAMAGE on the structure is detected with a comparison of DAMAGE and unDAMAGEd dynamic responses. According to the measured noise levels, dynamic responses to noise values have been contaminated and the results have been evaluated. According to the results, this method can trace the location of the DAMAGE by the energy of instantaneous frequency. Therefore, the locations of DAMAGEs in different scenarios were located with the EDI INDEX and velocity vector. The results show that the proposed method determined the location of DAMAGE with the acceptable accuracy for low and moderate DAMAGE in DAMAGE scenarios.

By identifying the DAMAGE INDEX of a structure, in addition to a correct understanding from real behavior of the structure, the required criterion for strengthening would be given. Researchers have given many relations for determination of DAMAGE INDEX but such relations have been based upon laboratory methods which challenge their usage in a broad term. In this paper two new methods are given for calculation of DAMAGE INDEX. Surveying the first crack limit and total structure failure is based upon the formation of plastic joints in the first column and basic floor columns. To give a qualitative simple and functional DAMAGE INDEX, the functional method was given in the form of a qualitative method with statistical analysis and collection of different views. Using this method is very simple and meantime offers suitable accuracy. With a numerical study on three models it was made clear that the difference of new method with amended method of Papadopolos in approximate 3%. This shows that given qualitative method is suitable to be used in a broad terms.

The ability of a structure that has experienced an earthquake to withstand the next earthquake is estimated by DAMAGE INDEX. There are several DAMAGE indices that have been proposed by researchers to quantify the amount of DAMAGE to the structure. These are generally defined based on dynamic response of structure and its hysteretic characteristics. Due to time consuming and complicated process of nonlinear dynamic analysis and calculation of DAMAGE INDEX via these methods, in this paper using a pushover analysis and employing the stiffness DAMAGE INDEX, the deterioration of the stiffness of the structure in various performance levels is evaluated. The obtained results are compared to that of qualitative definitions of FEMA. For this purpose a computer program has been prepared that considering earthquake specifications and characteristics of any structure, automatically evaluates the DAMAGE in RCMRF in various performance levels. Eight samples of RCMRF that had been designed based on ABA and Iranian Standard No. 2800 and one sample that was designed based on FEMA for four performance levels were evaluated for DAMAGE and discussed on. The results of evaluations show that the proposed DAMAGE INDEX can be a proper criterion for seismic performance evaluation of RCMRF. According to the results it seems that the criterion of drift in, FEMA and ATC, alone cannot be a correct and perfect criterion for performance and DAMAGE of structure.

In recent years, in order to have a comprehensive evaluation of structural DAMAGEs, quantitative methods are developed. In this regard, several research works have been done. The DAMAGE indices are based on structural drift regarding the importance and vast application of performance-based design. In this paper, the relationship between the performance levels and DAMAGE indices are studied. Several models of RC moment resisting frames were selected and analyzed using dynamic and pushover methods. Furthermore, various DAMAGE indices i. e.; Park-Ang INDEX, stiffness INDEX, drift INDEX, and maximum softening and Plastic softening INDEX for different models were estimated. Finally, the relationship between the values of these indices and the performance levels of frames is discussed in accordance with FEMA-356.

Bridges are exposed to DAMAGE during their service life which can severely affect their safety. Thus, it is important to monitor bridges for existence of DAMAGE. A DAMAGE in a structure alters its dynamic characteristics. Changes in properties such as the flexibility or stiffness matrices derived from measured modal properties and changes in mode shape curvature have shown promise for locating structural DAMAGE. Since DAMAGE alters the dynamic characteristics of a structure, namely its eigenproperties (natural frequencies and modes of vibration), several techniques based on experimental modal analysis have been developed in recent years. Therefore vibration characteristics of a structure can be used as the basis for vibration based DAMAGE detection (VBDD) techniques. These techniques have been recently subjected to a considerable amount of attention for DAMAGE detection due to their relative simplicity and the moderate cost of dynamic measurements. DAMAGE detection methods based on the dynamic measurements of structures are one of the most important techniques for DAMAGE evaluation in bridges. VBDD methods use DAMAGE-induced changes to the dynamic properties of a structure to detect, locate, and sometimes quantify the extent of DAMAGE.VBDD methods are able to detect DAMAGE with information from the dynamic response of the bridge only. The performance of these methods for DAMAGE detection in bridges has not been fully proven so far and more research needs to be done in this direction. In this article a new method base on developing the Co-Ordinated Modal Assurance Criteria and DAMAGE Inedx (DI) is present. For applying these methods, mode shapes and natural frequencies that came from health bridges model and DAMAGE bridges model are used. The bridges that used are a two-span bridge and a five-span bridge that modeled and verified. To verifying the models, five natural frequencies of the models that created with software, copmared to natural frequencies of the original models. In this article just one element defined as DAMAGE location. The DAMAGE created by redusing stiffness in one element near the abutments. The four level DAMAGE that considered are 15%, 30%, 70% and 90% reduce in module of elasticity. At first the unability of COMAC and DI methods to detecting the DAMAGE near the abutment is shown. Then the new method base on these method is presented. This new method is use of mode shapes that obtained from several longitudinal section instead of one longitudinal section. Results confirmed that if mode shapes are just extract from one longitudinal section like before, methods can not always detecting the DAMAGEd cross section or DAMAGEd longitudinal section. But if mode shapes obtain from several longitudinal sections, these methods will be able to assessment the DAMAGEd cross section plus DAMAGEd longitudinal section. Although in the most of the times these methods detecting the elements at the abutment as DAMAGE location wrongly. So it is necessarily to eliminate the result of the element at the abutment and then decided for the DAMAGE location. Besides it is concluded that for detecting the DAMAGE near the abutment, COMAC method has better result than DI method.

Despite a significant progress in loading and design codes of seismic resistant structures and technology improvements in building structures, the field of civil engineering is still facing critical challenges. An example of those challenges is the assessment of the state of DAMAGE that has been imposed to a structure after earthquakes of different intensities. To determine the operability of a structure and its resistance to probable future earthquakes, quick assessment of DAMAGEs and determining the operability of a structure after an earthquake are crucial. Present methods to calculate DAMAGE to structures are time consuming and do not accurately provide the rate of DAMAGE. DAMAGE estimation is important task in the fields of structural health monitoring and decision-making. This study examines the relationship between period elongation and the Park-Ang DAMAGE INDEX. A dynamic non-linear analysis is employed with IDARC program to calculate the amount of DAMAGE and period of the current state. This new method is shown to be a quick and accurate technique for DAMAGE assessment. It is easy to calculate the period of an existing structure and changes in the period which reflects changes in the stiffness matrix.

Shear keys are bridge components that support the superstructure in transverse direction and may experience large displacements and extensive DAMAGEs during earthquakes. Shear keys are designed to limit DAMAGE to abutment walls and piles by restraining the transverse movements. The shear force transferred to the abutments is controlled by the design and detailing of the shear keys. DAMAGE to shear keys during earthquakes may affect significantly on seismic behavior of the abutments and consequently the bridge system. In this paper, a DAMAGE INDEX is proposed for DAMAGE assessment of the bridge shear keys. The proposed DAMAGE INDEX is defined based on the friction behavior and the ratio of the energy dissipation capacity to input energy. To evaluate the reliability of the DAMAGE INDEX in DAMAGE assessment of the shear keys, finite element models of shear keys units, previously tested under cyclic loadings are developed and the proposed DAMAGE INDEX is calculated. In addition, seismic response of shear key specimens are obtained under seven earthquake records using incremental dynamic analysis and the DAMAGE INDEX is calculated for the shear keys in different PGA values of earthquakes. The results indicate that the proposed DAMAGE INDEX can predict the DAMAGE progression in shear keys throughout loading histories and can provide reliable values for DAMAGE levels of shear keys with respect to the experiment observations.

Assessing the effects of near-field ground motions shows that the directivity effects in velocity histories of these ground motions leads to one or more impact pulses with large amplitudes that yield in increased ductility demand of rigid structures placed in near source areas. In this study, the cumulative Park-Ang DAMAGE INDEX has been used for comparing the DAMAGE potential brought about by the two acceleration components of ground motions that are normal to the fault direction or parallel to it. Two-dimensional steel moment frames with 4, 7, 10, 15 and 20 stories have been nonlinearly modeled and analyzed using the Opensees software. The investigations have been performed in different performance levels corresponding to target ductility values equal to 2, 3 and 4. The utilized ground motion records include 40 records divided equally to the normal and parallel sets regarding the fault direction. The scaling of the record sets have been performed so that the studied frames have met the considered target ductility values. The results show that the lower stories are more frequently affected by the normal records, therefore, more intense DAMAGEs are attributed to these records. That is while, the parallel records have been found to affect mostly intermediate and especially upper stories. The results also show that increasing the target ductility values leads to an increased DAMAGE potential for the studied structures.