Sharif Digital Repository

Carbon nanotubes (CNTs) are promising candidates for high-resolution mass nanosensors owing to their unique vibrational behavior. The structural characteristic (e.g. defect type and density) and working temperature have a significant effect on the natural frequency of CNT-based sensors. Herein, a stochastic approach based on novel finite element and molecular mechanics simulations is implemented to model the effect of temperature and structural characteristics of single-wall CNTs including defects (vacancy defect with different densities) and chirality (zigzag and armchair) on their vibrational behavior. The results show that the vacancy defects exert a significant deterioration of the... 

In this paper, the hybrid Delay-And-Sum (DAS) with Sparse Reconstruction (SR) method was further developed for damage location in composite plates. In composite materials, anisotropy leads to some challenges in using conventional damage location methods, which are developed for isotropic materials. In the hybrid DAS-SR method, the DAS and SR methods were combined as a complement of each other. To investigate the DAS-SR method for composite structures, the group velocity of the travelling wave for different directions was first measured experimentally via PZTs. The DAS and SR formulations were then modified to be compatible with the direction-dependent group velocities. The results show that... 

A procedure based on the linear amplitude sweep (LAS) test has been developed to determine the optimum rejuvenator content for restoring the properties of aged asphalt binders. The LAS test was employed to assess the damage tolerance, fatigue resistance, and fracture behavior of rejuvenated aged binders. In case of fracture analysis, a crack-based indicator to govern the stable crack propagation was defined to characterize fracture resistance of asphalt binders. While rejuvenators improved all of these properties, higher contents were required to restore the cracking behavior of the original binder. The linear relationship between the integrated damage-fatigue-fracture indicator and... 

To perform active structural health monitoring, guided Lamb waves for damage detection have recently gained extensive attention. Many algorithms are used for damage detection with guided waves and among them, the delay-and-sum method is the most commonly used algorithm because of its robustness and simplicity. However, delay-and-sum images tend to have poor accuracy with a large spot size and a high noise floor, especially in the presence of multiple damages. To overcome these problems, another method that is based on sparse reconstruction can be used. Although the images produced by the sparse reconstruction method are superior to the conventional delay-and-sum method, it has the challenges... 

Based on the code specifications, in moment-resisting frames the span-to-depth ratio has to be larger than a minimum value to make sure of adequate plastic hinging at beam-ends. This provision poses a restriction on the use of deep beams with short spans, especially for the framed-tube system in tall buildings. In this paper, a new energy dissipation method is introduced for moment-resisting frames by modifying the mid-span of the beam by two different methods, resulting in: (i) Perforated Shear Links (PSLs) and (ii) Slit Shear Links (SSLs). The links dissipate energy through shear yielding of the web, weakened by perforation or slitting, respectively. A thorough study is conducted on the... 

Crack detection by Piezoelectric Wafer Active Sensors (PWAS) is one of the emerging methods of Non-destructive Evaluation (NDE). These sensors can assess the health state of the structure in far filed through the analyzing the high frequency Lamb wave propagation. As PWAS is the essential part of this method, simulation and modeling of these sensors and their interaction with the host structure, strongly affect the accuracy of results. In this study, unlike the previous works, in which some certain areas of the host structure were considered as a sensor and actuator, the direct simulation of electro-mechanical interaction of the PWAS and the host structure is modeled among modeling the PWAS... 

Abstract: Using adhesively bonded composite patch repairs has been increased in various industries to improve the structural integrity of cracked metallic structures in recent decades. Monitoring of crack propagation and composite patch debonding, as two dominant failure mechanisms in this repair technique, plays a significant role in the integrity assessment of the component. This research conducts an experimental investigation on the simultaneous monitoring of these two failure mechanisms in a cracked metallic specimen repaired by a composite patch. For this purpose, the electromechanical impedance method was used to evaluate the feasibility of recognizing the type of damage at any phase... 

Estimation of damage to structures after severe earthquakes is important for loss estimation and is an essential step for rescue program. Using seismic or spectral parameters could be a quick method for this purpose. In this article damage estimation for some world's destructive earthquakes has been carried out. For this purpose some earthquake seismic parameters, response spectra and damage indices have been calculated and compared. Damage indices are calculated for three types of intermediate sway concrete frame buildings, i.e. low-rise, mid-rise and high-rise, designed according to Iranian Seismic Code and ACI 318-95. Finally the trend between earthquake seismic parameters, response... 

In this paper, a new sensitivity-based model updating method is presented based on the changes of principal components (PCs) of frequency response function (FRF). Structural damage estimation, identification of damage location and severity, is conducted by an innovative sensitivity relation. The sensitivity relation is derived by incorporating PC analysis (PCA) data obtained from the incomplete measured structural responses in a mathematical formulation and is then solved by the least square method. In order to demonstrate the performance of the proposed method, it is applied to a truss and a frame model. The results prove the ability of the method as a robust damage detection algorithm in... 

The purpose of this paper is to estimate the stiffness and strength of damaged rectangular reinforced concrete shear walls after an earthquake using surface crack patterns. Assessing the damage severity of buildings after an earthquake is an important part of the emergency inspection operation of buildings. Expert inspectors tag buildings into two categories of safe or unsafe that are usually affected by subjective decisions, which may result in catastrophic events reported in previous earthquakes. In this research, an extensive database on the images of damaged rectangular reinforced concrete shear walls (RCSWs) is collected and used to develop predictive equations for updated stiffness and... 

In this paper, the evolution of elastic–plastic damage in the composite laminates under fatigue conditions is modeled. Continuum damage mechanics (CDM) has been coupled with the bridge micromechanics model to estimate the fatigue damage and life for laminated composite structures. Based on the elastic–plastic bridging model, three damage variables are defined. These variables estimate the fiber, matrix, and fiber/matrix damage response at the ply scale. To model the beginning of plastic deformation, a yield function is utilized, and evolution equations of the damage variables are obtained. Then the developed deformation plastic model is calculated. The model parameters are calibrated by... 

Road roughness-induced vibrations are the main source of fatigue damage accumulation in vehicles. Hence, road surface profile modeling and simulation are of high importance when it comes to vehicle fatigue damage assessment. This research focuses on uncovering the statistical distributions that describe the characteristics of road loads that affect fatigue damage accumulation. Particle filtering is deployed to estimate the log-volatility of the road surface profile by assuming a random walk behavior for the hidden log-volatility. The skew-normal distribution with three parameters is fitted to the estimated log-volatility. The inferred parameters are used for synthesizing artificial road... 

Dynamic analyses are necessary problems in offshore jacket structures design and assessment. These analyses have various applications in recognition of dynamic behavior, fatigue analysis, damage detection, etc. Natural frequencies and mode shapes, as inherent vibrational features of a structure, are key parameters in referred analyses. These parameters are mainly affected by mass and stiffness matrices and slightly by damping. Therefore, it is more important to estimate the stiffness matrix of a structure accurately, especially in stiff structures such as offshore jacket platforms. In many cases, the stiffness of levels is required. For example, it can be useful in the construction of an... 

Dynamic analyses are necessary problems in offshore jacket structures design and assessment. These analyses have various applications in recognition of dynamic behavior, fatigue analysis, damage detection, etc. Natural frequencies and mode shapes, as inherent vibrational features of a structure, are key parameters in referred analyses. These parameters are mainly affected by mass and stiffness matrices and slightly by damping. Therefore, it is more important to estimate the stiffness matrix of a structure accurately, especially in stiff structures such as offshore jacket platforms. In many cases, the stiffness of levels is required. For example, it can be useful in the construction of an... 

Trapezoidal Cemented Sand and Gravel Dam, namely Trapezoid CSG, is a new type of dam. Due to lack of dynamic studies in the field of CSG dam, this research was performed to analyze Trapezoidal CSG dam using dynamic Finite element method with ABAQUS Software. To investigate possible earthquake-induced damages, fragility curves are plotted based on damage index, the length of the cracks created at the dam base and the area of cracked elements in the dam. The seismic analysis indicated that minimum and maximum tensions are generated in the heel and toe of the dam, respectively. According to the fragility curves, with increase in PGA, the possibility of the exceeding the defined limit state is... 

This paper develops the seismic damage models of brick masonry veneer attached to the masonry infill without metal ties and assesses the life cycle cost of veneers subjected to earthquake excitation. Even though anchoring veneers to the backup wall has been prescribed in recent building codes, most of the existing brick veneers in seismic prone areas around the world lack the anchoring details. Besides, the damage and consequence models of masonry façades have not been presented in the FEMA-P58 database restricting detailed performance evaluation of buildings with unanchored masonry veneers. This study develops detailed finite element models to simulate various failure modes of the masonry... 

A new concept to determine state of the damage in concrete gravity dams is introduced. The Pine Flat concrete gravity dam has been selected for the purpose of the analysis and its structural capacity, assuming no sliding plane and rigid foundation, has been estimated using the two well-known methods: nonlinear static pushover (SPO) and incremental dynamic analysis (IDA). With the use of these two methods, performance and various limit states of the dam have been determined, and three damage indexes have been proposed on the basis of the comparison of seismic demands and the dam's capacity. It is concluded that the SPO and IDA can be effectively used to develop indexes for seismic performance... 

In this paper a new approach to risk based seismic assessment of structures is proposed based on acceptable risk levels. In this approach, the probabilistic seismic vulnerability, predicted lifetime of structure, importance and knowledge factors are considered in the evaluation process. Park & Ang damage index is used to quantify damage states of structure. By performing several incremental dynamic analyses, all damage states of structure from minor to heavy and collapse are considered under all possible ground motions. The structural risk level and the necessity of seismic retrofit measures are specified by seismic risk index of structure. This probabilistic performance based method is... 

The Al-Askari shrine, located in Samarra, Iraq, is a remarkable example of a building with ancient Islamic architecture and construction that was heavily damaged by massive bombings. The bombings were carried out by two separate terrorist attacks in 2006 and 2007. This paper summarizes the important undertakings in the identification of shrine buildings in terms of structural and architectural background and characteristics, damage classification and monitoring, site conditions and material properties. Moreover, the shortcomings of a series of previously performed partial restorations are elaborated upon. The results and findings of this study can be utilized as database in other numerical... 

Structural health monitoring (SHM) has been adopted in the aircraft and civil industries over the last two decades. The ultrasonic guided wave propagation technique is a promising damage detection approach in airplane thin wall structures because of their long distance traveling ability and low attenuation. In fact, by efficiently designing the pattern of sensors one can effectively pick up the changes that happen in propagated signals due to presence of any kind of structural damage. This detection approach could be effectively assisted by numerical simulation techniques like finite-element modeling. To obtain a damage detection algorithm based on instantaneous baseline data, the...