Sharif Digital Repository

Near-Field earthquakes have gained so much attention through their catastrophic consequences on structures in the vicinity of seismic sources during recent events. Based on recorded data, it is understood that these kinds of phenomena are often accompanied with a large energy pulse at the first times of record whose impulsive characteristic is primarily caused by “forward directivity”. Incapability of response spectra for depicting great demand for energy dissipation disqualifies this method for utilization. Thus it seems inevitable to analyze the models prone to this kind of hazard using time-history based analysis. Being simple enough in time domain, raises hopes for finding a mathematical... 

The considerable structural damage caused by near field earthquakes has revealed the need for further research on their characteristics and their corresponding effects on structures. The short-duration, high- energy pulses present in these types of earthquakes impose high demands on the structures compared to far field ground motions. Thus, more research is needed to improve the current design methods, especially from a performance based point of view for the structures close to faults. This study is about damage assessment of steel moment resisting frame structures under near-field ground motions from a performance based design point of view. A number of 3 and 9-story, 3-D structural model... 

Researches carried out on the damages imparted to the building structures under severe earthquakes have shown the importance of asymmetry effects of the buildings on the level of these damages. In these cases, the structures enter into the nonlinear state of their behavior and the structural elements, as well as nonstructural ones undergo large deformations. Additional damping systems have been proposed in many studies to avoid enforcing such large forces on the structures. One example of these systems is viscous fluid damper. The effectiveness of this type of dampers in reduction of the forces has been shown in many previous works. In this research we look for a damping eccentricity which... 

The detuning of the structures equipped with Tuned Mass Dampers (TMDs) caused by their nonlinear behavior under strong ground motions is a real concern in their practical application. This thesis presents a feasibility study on the effectiveness of TMDs in reducing the seismic response and the resulting structural damage of reinforced concrete structures under intense ground motion. A number of 2-D concrete moment resisting frames with different numbers of stories are considered. TMDs are used as a mean to protect these structural models against ground excitation. The mass of TMDs are varied from 1% to 5% of the first effective modal mass of the structural models. IDARC 2-D program is used... 

The circular flexible cylindrical liquid tanks usually are made of steel or aluminum and in majority of cases are built on grade due to its economic advantages. The most important part of a safe design of a storage tanks is the accurate estimation of the seismically induced lateral forces that should be transferred to its base through the tank shell and its support. Seismic behavior of liquid storage tanks is quite different from regular buildings and industrial structures due to its nonlinear behavior caused by complex distribution of hydrodynamic pressure, buckling of its walls, etc.. Moreover, the effect of rocking motion caused by the under laying soft soil, on its response parameters... 

In the current design Codes, the estimation of maximum inelastic Single Degree Of Freedom (SDOF) displacements is done through simplified procedures by either applying modification factors on maximum SDOF elastic displacement demands or by considering equivalent SDOF systems with elongated fundamental period and increased damping ratio. Thus, the inherent uncertainty caused by approximating maximum inelastic displacements with maximum elastic displacements is neglected. On the other hand, in time history dynamic analysis of structures, the free field recorded ground motions are applied to the base of structures. Obviously, this procedure would be correct when the structure is built on firm... 

Buried pipes are among the most important urban infra-structures which are developed to distribute water, gas, oil, etc.. Researchers have already demonstrated that extreme failures which lead to total disruption of the pipelines, both mains and the distribution network, due to permanent ground displacement in fault zones. In order to avoid any disturbance in the regular performance of pipelines and prevention of environmental contamination, there is a need to investigate the vulnerability of pipelines and their seismic retrofitting, if necessary. In the presented study, the method of pipeline retrofitting by high strength CFRP composite is investigated. In that regard, using a 3D model of... 

This study evaluated post-tensioned system’s behavior in the steel structure. The post-tensioned system includes post-tensioned frame and gravity system (gravity frame and floor diaphragm) and considers the interaction of post-tensioned frame with gravity frame. Post-tensioned frame is the moment frame that has post-tensioned connections instead of ordinary connections. Bolted top and seat angles are used in the connection, along with post-tensioned high strength strands that run parallel to the beam. The strands compress the beam flanges against the column flange to develop a resisting moment and the friction between the beam and column and the two angles resist shear. Studies showed that... 

This study aims to identify the structural damage using deep learning. Damage to structures reduces their lifespan. Therefore, continuous monitoring of structures is necessary to detect any possible damages that occurred due to various causes. Structural health monitoring systems that use wired sensors to measure signals are costly and time-consuming to install. Whereas, wireless sensor-based damage detection systems are relatively cost-effective. However, one of the most important problems in using them is the loss or non-recording of some data, which severely affects the accuracy of a structural damage detection system. On the other hand, health monitoring using machine learning-based... 

Classic controllers are designed to control the structure response at the desired thresholds concerning the minimum applied force by control elements. In some cases, the minimum applied force does not lead to the minimum energy consumption of the controlling system. Especially, the consumption energy of the semi-active control system is not linearly related to their applied force and their energy consumption is a nonlinear function of system dynamic variables. On the other hand, classic control algorithms are not optimized in the time domain of earthquakes and those are sub-optimal algorithms based on the structure's inherent characteristics. Time domain optimized algorithm control is an... 

The main goal of the current building design codes is to protect life safety, and generally, they do not directly address other societal, economic, etc., concerns regarding earthquakes. However, recent earthquakes around the world have shown that the effects of earthquakes' damages and losses can go beyond life-safety concerns. This observation has led many renowned scholars, organizations, and agencies to state the need to change the current design codes. In this regard, this thesis investigates the basis of setting the seismic design requirements and suggests a method in this respect. The study consists of two main parts. Part I (theory and design methodology) discusses some theoretical... 

The main goal of this research is detection, localization, and determining the severity of structural damages. The importance of this objective is to prevent abrupt destruction and severe human and financial losses. Damage detection is divided into local and global detection, and global detection contains static and vibration-based methods. In this research, the vibration-based method is used. Due to the complexity of this method, accurate and powerful tools are required for detecting effective features in damages; Deep Learning (DL), which is part of a broader family of machine learning methods based on artificial neural networks (ANN), could be used. Accordingly, in this project, the... 

Conventional eccentric braced frames often sustain large residual deformations and significant damages after strong earthquakes which may lead to heavy damages or even destruction of the structure. Here, a self-centering, Y-inverted, eccentrically braced frame (SC-YEBF) is proposed which combines the lateral load resisting benefits of YEBF including strength, stiffness and energy dissipation capacity with the re-centering capacity of post-tensioned (PT) high strength steel strands used at beam-to-column connections. A design procedure is presented assuming that all the seismic input energy is dissipated through inherent damping and plastic deformations of the link-beams. Thus, in the... 

Assessing the seismic loss incurred by structures post-earthquake, or to evaluate structural performance vis-à-vis potential seismic events, constitutes an imperative and pivotal measure for informed decision-making geared towards enhancing community resilience. However, large-scale assessments targeting risk analysis at citywide levels necessitate significant temporal and computational resources. To expedite this process and mitigate associated costs, this study introduces a machine learning-based methodology for estimating seismic loss and repair time of special steel moment-resisting frames. Six distinct machine learning models were trained based on results derived from nonlinear time... 

The objective of this paper is to explore and characterize the effect of practical construction details on the dynamic and gravity load carrying capacity of cold-formed steel framed shear walls sheathed with Oriented Strand Board (OSB). In order to improve the lateral stiffness and shear strength of cold-formed steel (CFS) framing wall, an innovative CFS wall equipped with OSB and gypsum boards are experimentally studied in this thesis. For this purpose, six K-braced frames with and without sheathing boards are investigated experimentally under lateral cyclic loading and gravity forces. The failure modes, loaddisplacement responses, and energy absorption capacity of the specimens were... 

General strategies for seismic design of structure include increasing the rigidity and strength, increasing the energy absorption capacity by implementing energy dissipating devices and reducing the seismic demand by isolating the structure from its base. Isolation system provides the required ductility of the structural system by concentrating its displacements mainly on the isolator level, and separates the structure from the horizontal components of the ground motion. That would create a system whose its main frequency is much lower than the dominant frequency of the earthquake records and the natural frequency of the equivalent fixed-base structure. Because of growing tendency towards... 

Drift spectrum has recently been introduced as a new measure for estimating the inter-story drift demands in buildings under near field ground motions. This new spectrum is developed using a uniform-stiffness continuous beam model. Practical limitations in the procedures based on such beam models have caused structural engineers to pay little attention to drift spectra. This thesis uses a lumped mass, non-uniform beam model to calculate the linearly elastic and also nonlinear drift spectra. The proposed method is simple and can overcome many deficiencies of the previously introduced models. In contrast to the other available methods, it can take into account the very important effect of... 

The circular flexible cylindrical liquid tanks are usually made of steel or aluminum and in majority of cases are built on grade due to its economic advantages. The most important part of a safe design of storage tanks is the accurate estimation of the seismically induced lateral forces that should be transformed to its base through the tank shell and its support . seismic behavior of the liquid storage tank is quite different from regular buildings industrial structures due to its nonlinear behavior caused by complex distribution of hydrodynamic pressure, buckling of its wall, etc.. moreover, the effect of rocking motion caused by under laying soft soil, on its response parameter could be... 

The on grade flexible steel storage tanks are extensively used in oil refineries, petrochemical plants, power plants and many other municipal utilities. The increasing statistics of various incidents and attacks occurred to these facilities clearly indicates the vulnerability of these strategic installations under the effects of intentional (terrorist) blasts. Therefore, Given the strategic nature of the care and maintenance for these tanks, their damage assessment under the prescribed explosion is quite important. Due to flammable content of some of these tanks, it is necessary to speed up the process of their vulnerability assessment and making the appropriate decisions for any needed... 

A new structural system of diagonally arranged elements, the so called "diagrid", has been introduced in recent years in which the frames that are made up of intersected members surrounding the main structure. This type of system provides excellent shear rigidity and stiffness, in contrast to the similar tubular structures. The triangular configuration offers structural stability for gravity and lateral loads, and the removal of external columns gives the building a unique architectural beauty. The seismic performance factors (SPFs) for diagrid systems are not yet explicitly introduced in the existing building codes and few studies have been conducted on the assessment of this parameter. In...