Sharif Digital Repository

The purposeof this study isto findthe propertiesof an equivalent linear Multiple Degrees of Freedom (MDOF) system, or so-called substitute structure, that its response is an approximation ofthe target actualnonlinearMDOF structure’s response (Shodja, 2013). In that regard,thestiffness anddampingmatricesofthe substitutestructure are considered as functions ofthe stiffnessand dampingmatrices ofthe actualnonlinear structure. Inthisway,the substitute structurescan be constructedthroughtrial and errorfor structures with different fundamentalperiods, damping ratios and number of floors.Inthat regard, a number of multi-story steel moment resisting frames are considered. The ductilities of these... 

In this study, seismic performance of steel diagrid structures is investigated using far-field earthquake records and their seismic performance factors, such as overstrength factor (Ω_0), ductility ratio (µ_T) and response modification coefficient (R) are evaluated according to the FEMA P695. To meet this objective, 12 archetype 3-D models of diagrid structure with two different height of 8 and 12 stories and three different diagonal angles of 45, 63.4 and 71.5 degrees are designed according to the ASCE 7-10 and using response modification factor R=3.6. With regard to the main horizontal beam connections with the diagrid system, equal number of models with pin and rigid type of connections... 

Reducing the seismic response of structures under dynamic loads has been highly considered by many researchers in the past few decades. Among them, Tuned Mass Dampers (TMD) have been studied extensively and used as a mean to control the response of structures under earthquake and wind loadings. In the majority of these studies, it is assumed that the structural models are located on rigid base and only their linear response has been considered. Soil-Structure Interaction (SSI) and nonlinear response of structures could have significant effect on the dynamic characteristics of structures that could results in detuning of TMDs. In this study, a number of 3-D nonlinear steel structural models... 

In this study, the change in friction damper’s optimal slip load in 3-D structures due to soil-structure interaction was evaluated. Using AISC-LRFD code, an 8 story shear building has been designed considering gravitational and equivalent static lateral loads. Then, the changes in friction damper’s optimal slip load due to PGA and soil type variation were studied. In this part two PGAs and two soil types were considered. Seven strong ground motions, recorded on soil types E and D was used for each of the two soil types. After normalizing the PGAs of selected records, these records were used for dynamic time history analyses. In the next step, the soil-structure interaction effect has been... 

Viscoelastic(VE) dampers are among the most practical passive control devices that are used to reduce the seismic-induced response of the structures. In this regard, extensive parametric studies have been conducted so far to investigate the performance of these dampers in reducing the seismic response of the structures under various types of ground motions and site soils. In most of these researches, the effect of soil-structure interaction (SSI) is neglected which is acceptable only for the structures located on stiff soils. In present research, the effect of the soil-structure interaction on the performance of VE dampers in reducing the seismic structural response is investigated. Also,... 

In the present study, the performance of Viscoelastic Dampers in reducing the seismic response of the structures was investigated. For this purpose, first the effect of added damping to the system was studied. Number of 3-D steel structural models, with and without eccentricity which are designed with the 2800 code (first edition) and 519 code provisions that is not satisfied the provisions of the code-2800(third edition) is considered. It is assume that this system is located on a relatively stiff soil (soil type II based on Iranian Seismic Standard Code - 2800), a number of compatible earthquake records also considered to be used in the parametric studies. The results indicate that in... 

Tuned Mass Dampers(TMD) are among the most studied passive or active control devices that have been used around the world to control the lateral vibration of different building structures. On the other hand, since 2-D structural models are not appropriate for estimating the true response of the eccentric structures, application of 3-D models have been considered for determining their seismic-induced coupled lateral-torsional behavior. In this research, the performance of the Active Tuned Mass Dampers (ATMD) in controlling the seismic response of 3-D structural models was investigated. Three structural models with 4, 8 and 15 number of stories and 3 different eccentricities (0, 10% and 15%)... 

In recent years there has been a huge amount of attention in the application of the base isolation system as a passive procedure to limit seismic response of structures. A number of international codes including UBC97, ASCE07-2005, and ASCE-2010 have devoted a special part for the Seismic analysis and design of base-isolated structures. The present work investigates the vertical distribution of the lateral seismic force, for base-isolated structures suggested by the ASCE07_05 code under near field earthquakes. Near field earthquakes have attracted so much interest among the researchers and engineers due to their disastrous effects on structures. According to the recorded data, it is... 

In existing societies, transportation of water, oil, gas and other liquids in great amounts between distant locations is economically feasible only through pipelines. Design of buried pipelines against static loads is an established and straight forward process. On the other hand, because of difficulties in predicting the behavior of buried pipelines under seismic loads and also lack of sufficient studies in this field, there is no specific code oriented approach for performance analysis of buried pipelines under seismic loads. Due to insufficient three dimensional numerical analyses on the behavior of buried pipelines crossing active normal and normal-oblique faults for different dip angles... 

Buried pipelines are among the most important elements of lifelines that are used for distribution of water, gas, petroleum, etc. Previous studies indicate that the severe damages that resulted in complete disruption of pipelines, is mainly due to permanent ground displacement caused by faulting. Previous studies on this subject have mostly focused on strike-slip and normal faulting. Since it is reported that damages due to reverse faulting can be more severe than damages caused by normal faulting, a comprehensive study on the behavior of buried pipelines subjected to reverse faulting is needed. In this thesis, the effect of various parameters including burial depth, pipe diameter, pipe wall... 

Recent studies in the area of damage assessment of structures under severe earthquakes have shown that plan asymmetry of structures have considerable effects on the severity of the induced damages. In these cases, structure enters into its nonlinear behaviour, and both structural and nonstructural elements sustain large forces and deformations. Nowadays, due to the complication of nonlinear dynamic analyses in estimating these forces and deformations in case of seismic ground motion, the use of nonlinear static analysis methods has increased. These procedures expose the structures to monotonically increasing lateral forces with an invariant height-wise distribution until a predetermined... 

A large number of bridges in Iran are deteriorating under long and heavy traffic loadings, while getting closer to the end of their design life time. Therefore, many of them have been exhibiting various problems such as excessive vibration or large deflection under the normal service loadings. So, mitigating traffic-induced bridge vibration and damages is necessary to extend their efficient period of serviceability. On the other hand, application of active and passive control devices in structural retrofitting have absorbed the attention of many engineers and researchers. In this work, the performance of an active control system made of piezoelectric actuators is investigated in reducing the... 

Tuned Mass Damper (TMD) is one of the most popular device implemented in structures in order to control the motion induced by wind. The performance of TMD has correlation with its design, which is depending on the Structure dynamic properties as well as the specifications of lateral loading. During the earthquake since the both of the mentioned parameters will be uncertain, hence, the reduction of TMD’s sensitivity to its design parameters is vital. In this regard, in 2012, Maurizio De Angelis et al. tested the unconventional TMD – it has a large mass ratio – and corroborated its merit. The results were limited to short structures with linear behavior. This research not only verified... 

Structural response to near fault ground motions has received significant attention in recent years. Such ground motions are different from ordinary ones and are characterized by a large, long period, velocity pulse caused by the forward directivity. These velocity pulses could potentially impose sever demands on structures and increase their risk of seismic collapse. The situation could even be worse for tall buildings with fundamental periods close to the period of the velocity pulses, and requires special consideration in design process. Prediction of seismic-induced collapse potential of structures has been among the main concerns in Performance Based Earthquake Engineering (PBEE). The... 

Application of passive control systems in reducing the seismic induced forces on different structures has attracted the attention of many engineers and researchers during the last few decades. Various damping systems have been introduced in this regard, and many of them have practically been implemented in different buildings. Tuned Mass Dampers (TMD) are certain types of passive control systems that can effectively reduce the dynamic response of tall buildings under various types of dynamic forces. More specifically, extensive researches have been carried out on the application of TMDs on suppressing the seismic response of tall buildings in recent years. In this regard, the soil-structure... 

The parallel combination of friction damper with shape memory alloys has been proposed as a self-centering friction damper (SFDB) in the past. The aim of this study is to improve the performance of the SFDB as M-SFDB and investigate its effect on seismic responses of steel moment resisting structures. The basic idea used in the proposed M-SFDB damper is to create sloped surfaces and using SMA bolts to change the slip load of friction during the loading and unloading cycles. In order to evaluate the effect of the proposed mechanism, four types of 4, 8 and 12-story structures located on site classes B and D are designed using ASCE_7-10 and AISC_360-10 codes. These structural models include... 

The necessity of providing synthetic acceleration records suitable for seismic assessment of the structures in the regions whose seismological history has not enough instrumental recordings has become one of the main concerns of the earthquake engineers. Despite being accurate in estimating earthquake ground motion, physics-based methods involve complicated procedures and need the detailed information about source, path and the site conditions of the scenario event which is not available for lots of engineering problems. The main goal of this dissertation is to introduce a novel stochastic method for the simulation of the non-stationary earthquake acceleration records compatible enough with... 

Application of Shape Memory Alloys (SMAs) as a means for vibration suppression of structural systems has extensively been explored in recent years. Recovering the applied residual strain upon unloading (super-elasticity) or by heating (shape memory effect) at different temperature ranges are two inherent features of SMA materials that have gained most attention. In this work, the seismic behavior of a proposed beam-column semi-rigid end-plate connection that has been equipped with both steel and SMA studs in austenite phase is investigated. A number of 3-D steel MRF structural models with 6,9 and 12 number of stories are considered. These structural models are subjected to bi-directional... 

Cable stayed bridge are characterized by a long fundamental period, large flexibility, lightweight and low structural damping, which is vulnerable to large amplitude oscillations when excited by earthquake. So, it is important to study the seismic behavior of cable-stayed bridges. Spatial variation of seismic ground motions denotes the differences in amplitude and phase of seismic motions recorded over extended areas. The result of past analyzes indicate that the effect of the spatial variation on the response of bridges can be detrimental. On the other hand, tuned mass dampers (TMDs) or vibration absorbers are small mass-spring-dashpot units calibrated to be in resonance with a particular...