جستجوی مقالات مرتبط با کلیدواژه « منحنی های شکنندگی » در نشریات گروه « عمران »

Due to the increase in the age of bridges, the explanation and use of effective methods for detecting partial damage with the help of health monitoring systems are crucial since they provide the conditions for repairing the damage before the damage increases. One of the primary goals of this article is to provide an effective and efficient method for health monitoring and detect partial damage in the pier of a straight bridge using fragility curves of harmonic forces, and provide a criterion to show the correlation of fragility curves in healthy and damaged states. To achieve these goals, a complete model of a straight bridge that includes 8 piers, each 10 meters high and its deck includes 5 openings, the length of each is 15 meters, and the total length of the deck of 75 meters was modeled in the CSI Bridge software, and then, was validated. To detect the most vulnerable column for damage modeling for health monitoring operations, three earthquake records corresponding to the soil of the construction site were successively applied to the model. By examining the decrease in the slope of the moment-rotation graphs, the level of damage that occurred at the bottom of the column was detected. Finally, it was found that the middle piers were more prone to seismic damage and health monitoring operations were performed on one of the middle columns. To draw the fragility curves of harmonic forces, harmonic forces were first applied to the top of the column, and then, the rotations created at the bottom of the column were measured. Based on the obtained data and using the relevant relations, the fragility curves were drawn. The index of the maximum intensity of force, the index of rotation damage that occurred at the bottom of the column, and the defined performance level of exceedance from the linear state are the characteristics of these fragility curves. To draw the fragility curve in the damaged state, the desired earthquake (seismic) force was first applied to the bridge, and then, harmonic forces were applied to the top of the desired column. The results of this study revealed that the fragility curves of harmonic forces have been drawn well in healthy and partially damaged states according to the defined characteristics, and partial damages with different intensities have been correctly detected. To examine the correlation of the fragility curves of harmonic forces in both damaged and healthy states, two new criteria PCOMAC and PDI were introduced. The results of this article indicate that the PCOMAC criterion is very suitable for examining the correlation of fragility curves of harmonic forces.

In this research, the seismic behavior of the back-to-back MSE walls has been assessed in a probabilistic approach using the fragility curves and the effect of the overlapping length of the metal strips on the vulnerability of this type of walls has been investigated. To this end, the back-to-back MSE walls are simulated using FLAC2D finite difference program, and validated with a shaking table physical model test. So, using the results of nonlinear incremental analysis, fragility curves are analytically extracted based on PGA and PGV intensity measures under far-field and near-fault earthquakes. The obtained results, in addition to providing the possibility of predicting the vulnerability of the wall in different seismic intensities, indicate that increasing the length of the metal strips from 0.65 to 0.85 of the wall height (increasing the overlapping length from 0.3 to 0.7wall height), reduces the probability of seismic damage up to 35% in the far-field and by about 50% in the near-fault earthquakes, respectively.

Reduction and management of risk of industrial plant especially energy is an important concern. Probabilistic and reliability method are used in risk and cost estimations. Oil, Gas and Petrochemical plant are the most energy producer plants that are in focus of cost, life and operation. These plants consist of several units, parts and equipment’s. In order to study the risk of plants, it is needed to study the equipment’s. The main goal of this research is probabilistic seismic assessment of fixed horizontal vessels. In this paper, finite element model of designed and constructed vessels in a real project is prepared and incremental dynamic analysis (IDA) is performed. Response of vessels components including the vessel body stress, piping stress, flange and elbow deformations, anchor bolt stress are extracted and their related limit state are defined. Finally the fragility curve of vessels components is prepared. The result shows that flange connection is the components that are potential for starting the damage of vessels.

The main purpose of this study was to evaluate the vulnerability of steel shear walls using brittleness curves. To achieve this goal, the amount of ductility and damage index of several sample frames reinforced by steel shear wall are evaluated by modeling and performing nonlinear static and dynamic nonlinear analyzes, and damage index control based on ductility is introduced as a performance acceptance criterion. Seismic performance was evaluated using IDA incremental dynamic analysis and fragility curves were obtained using displacement and ductility index. According to the results, a relationship between performance levels and damage index is presented, which indicates the probability of passing performance levels in each of the structures. Damage index for each model was calculated by extracting increasing curves, as a result of which other structural characteristics such as stiffness, ductility and yield point of the structure can be obtained. The advantage of this method and the introduction of fragility curves based on damage index is determining the ductility parameter based on the structural criteria of the structure. Based on this, the strength of each structure can be calculated according to the yield displacement of the structure.

Damage sustained of electrical transformers in past strong earthquakes led to irrecoverable and severe economic losses of them. The seismic performance evaluation is associated with the loss of proper functioning of the transformer. This study deals with modeling existing isolated electrical transformer structures to evaluate the effects of variables that may affect the seismic performance and dynamic characteristics. The results probabilistically determine the seismic performance acceptability of study isolated electrical transformer structures based on the impact of key structural response parameters on the seismic performance of the transformer. Analyses of systems for a wide range of parameters are performed. The effects of horizontal and vertical near-fault pulse-like ground motions, the displacement capacity of the seismic isolation system, limit states of electrical bushings, and details of the isolation system design are considered. Also, the probability of failure of the transformer under the near-fault excitations with pulse-like characteristics is investigated. The results of this study demonstrate that three-dimensional seismic isolation systems can improve the seismic performance for a wide range of parameters and can be further effective compared with only horizontal seismic isolation and offer the lowest probabilities of failure for all cases of transformer and isolation system parameters.

The vulnerability of industrial plants to natural hazards has made world worries because of countries general disability about the prediction of the level of effects and preparedness for the consequences of these types of events. For this purpose, seismic assessment of plant equipment is a strategic issue. One of the most equipment that is used in most oil & gas plants is stack flares. Stack flares are a type of stacks that are used for burning additional flammable gases before causing any other problem for other plant facilities. Proper seismic assessment of this type of equipment has been missed in the past and its exact performance evaluation can be effective in determining probable damages in future earthquakes and distinguishing the weakness of components of this type of structure. In this study probabilistic seismic behavior of two designed and constructed stack flares are investigated and using incremental dynamic analysis their fragility curve and behavior factor are calculated. Results show that in ordinary intensities, the seismic demand of these structures is not considerable but in range of rare intensities, extreme damages are probable. Also, in the above case studies, the performance of 4 side stack with respect to 3 side stack was more proper, and seems more assessment is needed on the suggested behavior factor by codes.

Evaluation of the damages caused by past earthquakes confirms that the infilled-frame buildings, which were built on soft soil, can be damaged more than expected values in design performance level. In-fact the lack of attention to the effects of infilled-frames on the behavior of the structure despite the recommendation of seismic regulations is a very important subject. However, according to the observed damages, the improvement of these regulations is undeniable. Therefore, in this study, to investigate the effect of the presence or absence of infill panels on the behavior of steel moment frames, by considering the effects of soil-structure interaction is examined. In this regard, incremental nonlinear dynamic analyzes were performed on two-dimensional frames with three, six, nine, twelve, fifteen and twenty floors. For this purpose, 21 far field ground motion accelerations were selected according to the FEMA-P695. Nonlinear time histoy analyses were performed in SeismoStruct software. Then, using statistical relationships, the seismic fragility curves of the studied models were extracted and compared for three performance levels, ie, IO, LS and CP. It should be noted that the seismic demand parameter was selected in the form of maximum relative displacement. The results show that with increasing the number of floors, the presence of infill reduces the vulnerability of the structure and vice versa, considering the effect of soil-structure interaction increases the vulnerability of the structure.

Bridges are a critical part of the urban and suburban transportation network, so they are supposed to be designed to sustain earthquake induced damages to be utilized after earthquake. Various parameters can affect the behavior and probability of failure of a bridge and the present work aims to evaluate the effects of changes in structural parameters on the probability of failure in isolated concrete bridges OpenSees software is used for simulating and analyzing 16 different bridge models. Incremental dynamic analysis is conducted using this software and IDA and fragility curves of models are derived and presented. The results show that the probability of failure decreases with the increase of the pier diameter, concrete compressive strength, yield strength of longitudinal rebars and diameter of longitudinal bars. Also increasing the stiffness of elastic isolator and decreasing confined diameter of pier results in increasing the probability of failure. Furthermore, results show that, the probability of failure is more sensitive on the variation of pier confined diameter, yield strength of longitudinal rebars, diameter of longitudinal bars and the stiffness of elastic isolators in comparison with the variation of concrete compressive strength.

In this paper, the seismic response of base-isolated and fixed-base concrete structures with soil-structure-interaction effect was investigated. The structures with 4, 8, and 12 stories with lead rubber bearing isolators on three types of soils including soft, medium, and firm soils as well as on rigid foundation modeled using OpenSees software v 2.5.0. The ACI 318-02 code was used to design of RC intermediate moment frames. The incremental dynamic analysis was performed to determine the structural response under six near field and six far-field earthquakes recorded with the same seismic parameters but with different stations. The inter-story drift ratio and failure probability for each level of damage (slight, moderate, extensive and complete) were calculated and the fragility curves for maximum inter-story drift in different levels of PGA were drawn. The results indicated that considering the soil-structure-interaction decreased the structural damage on both isolated and fixed base structures. Softening the soil under isolated structures resulted in increasing the median fragility acceleration in each level of damage. Furthermore, considering the soil-structure-interaction effect in the low-rise to medium-rise structures (4 and 8 story buildings) has a more significant effect on median fragility accelerations than high-rise buildings. While, the effect of the base shear on the 12-story frame was more considerable.

Concrete shear walls has improved stiffness and ductility of moment frame systems in tall buildings,but high weight acheaved system can produce foundation engineering problems in loos coastal soils;An appropriate choise is substituting this shear walls with buckling restrained braces (BRB),have less weight and provide appropriate ductility and stiffness.In seismic design of structures3 models of 15, 25 and 35 floors in two systems Special reinforced concrete momment frame and special reinforced concrete momment frame equipped with buckling restrained brace ,also has lighter sections,desinged In accordance with the norms of Iranian design codes. After the sections are finalized in etabs 2016,3d models has been dane in opensees And by choosing a number of appropriate accelerometers compatibled with the region incremental Nonlinear Dynamic Analysis done. most of the floors drift Was considered As a demand parameter. By selecting the HAZUS relative displacement capacity Quadruple seismic performance damage levels (slight, moderate, extensive and complete) fragility curves produced. In higher rise models Fragility is more evident and median fragility difference increases from 0 in slighe damage level up to 0.13g in complete damage level in 3 type of building models that shows better Seismic performance in special brb moment systems than ordinary special moment frame systems.

Recent Iranian earthquake damages like the damages caused by the Kermanshah earthquake, revealed that RC buildings having soft story irregularities experienced more seismic vulnerability. Moreover, earthquake aftershocks increased the seismic failures in past earthquake events. But RC buildings having soft story irregularities and effects of earthquake aftershocks are not included in recent seismic design codes. In this article, for assessing the effects of soft story irregularities and also the effects of earthquake aftershocks, three, five, and eight story RC building models having intermediate sway moment frames are designed and then modeled in OPENSEES software platform and then IDA analysis are performed in order to producing the seismic fragility curves consistent with HAZUS definitions. The analytical results of seismic fragility curves revealed that the influence of soft story irregularities and also main earthquake shock-aftershock sequences on the vulnerability of considered RC building models. By increasing the height of the RC building structures, the effects of soft story irregularities and the earthquake aftershocks decreased in seismic vulnerability of the considered RC buildings.

In this study, the effect of isolators positioning at three Levels and different arrangements on seismic response of RC buildings are investigated. For this purpose 18 RC building of 4, 8 and 12 story with and without lead rubber bearing (LRB) isolators were selected. The LRB isolators positioned at three Levels and five different arrangements were modeled in Opensees software. The near field and far fault earthquakes were added to the frames and incremental dynamic analysis was performed. The fragility curves base on inter-story drift ratio as well as the IDA curves base on maximum inter-story drift ratio, maximum base shear, maximum roof displacement and acceleration versus peak ground accelerations (PGA) were plotted and compared. The results showed that among the isolated structures, the isolator positioning at the level of below the first floor (type 1 and type 2) had the best performance in reducing responses. The positioning type 1 (MSI-1) resulted the best decreasing in inter-story drift ratio and base shear. In addition, this type of isolator had the best increasing the PGA according to median fragility between the different types of the positioning levels. The recommended type of isolator had the best performance, especially in high rise buildings in severe damage levels.

The aim of this study is to investigate the effect of aleatory and epistemic uncertainties on seismic performance of an intermediate steel moment frame. For this reason, generalized incremental dynamic analysis is employed. To model record-to-record aleatory uncertainties, 40 far-field ground motion records are utilized. Also, to model important epistemic uncertainties, 5 parameters of plastic hinge behavior are uncertainly modeled and statistical parameters are considered for these models. Then, by using effective simplified models of random variable production, 50 combination of these 5 parameters are produced and for each one of these models a bin of IDA curves are extracted. Results show that parameters with epistemic uncertainty affect fragilities of IO limit state more than other limit states. In other words, for CP and GI limit states fragilities of mean of models yield acceptable results even when incremental dynamic analysis cannot be conducted for all the 50 models. However, For IO level, the effect of epistemic uncertainties cannot be neglected.

The fragility curves are used to indicate the probability of damage to buildings during the earthquakes with different intensities. The main objective of this study is to present a new design procedure for exploring the effectiveness of using viscous dampers in the seismic rehabilitation of steel structures using the seismic fragility analysis. In addition, a straightforward formula is presented to determine the effectiveness of seismic rehabilitation of steel structures with viscous dampers. The inter-story drift as one of the effective parameters for assessing the safety of buildings after an earthquake is used in this study as a damage index. To compare the damage probability of buildings with and without damper, three 3, 9 and 20-story benchmark buildings are used. Furthermore, the earthquake records corresponding to three levels of seismic hazard are used for the nonlinear dynamic analysis. Comparison of the fragility curves between the steel structures controlled and the buildings without the damper shows a significant decrease in the damage probability after the rehabilitation with the viscous dampers. The results of numerical analysis showed that although seismic rehabilitation in all benchmark buildings led to the improved seismic performance, the decrease in the response of the 9-story structure is higher compared to the other buildings.

Non-uniform mass distribution in elevation is one of the main sources of irregularity in buildings that could lead to concentration of nonlinear deformations followed by local or global damage to buildings during earthquake excitation. Considering lack of accurate information about behavior of tunnel form RC buildings in preceding earthquakes, it is required to evaluate vulnerability of such buildings with mass irregularity in elevation. In this research, seismic behavior of tunnel form RC buildings with heights of 5 and 10 stories, having different patterns of non-uniform mass distributions in elevation is studied in the nonlinear deformation range. For this purpose, seismic performance levels of understudied buildings under design earthquake are determined using time history analysis as well as pushover analysis. Fragility curves are developed by analytical approach for different hazard levels. The results show excellent performance of this structural system and placement in immediate occupancy performance level under maximum design earthquake Iranian seismic code (standard No. 2800). Moreover, modal vibration response of the system is not influenced by building height and height-wise mass distribution pattern. It seems that the provision No. 5 of regulations issued by Road, Housing & Urban Development Research Center of Iran pertaining to design and construction of tunnel form RC buildings, which stipulates that this type of buildings have to be regular in elevation, is so strict and conservative for the studied models with selected patterns of mass irregularities.

Recently, the Iranian code is established for the LRFD design of steel structures that consistent with the Iranian seismic design code (2800-4). This study is aimed to compare the performance of steel moment frames (SMF and IMF) in the Near-faults earthquakes designed with the Allowable Stress Design (ASD) and Load and Resistance Factor Design (LRFD) in a probabilistic framework. After the Static Push over (SPO), new Performance based earthquake engineering (PBEE) approach is incremental dynamic analysis (IDA) that can lead to the probabilistic judgment using fragility curves of the structure under the different types of ground motions at different levels of intensity. For the incremental dynamic analysis a large number of nonlinear time history analysis must be carried out. The evaluated steel moment frames are 4-story and 8-story frames. The nonlinear models of structures are constructed in the Perform-3D software to perform the nonlinear time history analysis. For the nonlinear modelling of beam element, the chord Rotation Model is used that proposed by FEMA and available in the Perform-3D software for the beam elements. This model predict the nonlinear behavior of element in the two end region that plastic hinge may be caused duo to the seismic load of earthquake. For the column elements, the fiber element method was employed. In this method, the cross-section of column element is subdivided into some spring elements. Each spring is subjected to axial load, given by the combination of axial force and bending moment acting on the section. This model sometimes is called multi-axial spring model (MS model). The fiber model represents a section at the structural member-end. This modelling can represent the axial-flexural interaction in the column element that their properties of nonlinear flexural bearing depends on its axial load in each time step. Near-field events due to their pulse-like effect are in the spotlight in the last decay. To evaluate their effects on the steel structures that located in the seismic areas of Iran, a number of near-field earthquakes are used in the probabilistic assessment. In the IDA curves, the roof drift is used as Damage Measure (DM) and the Spectral Pseudo-Acceleration of the first mode of the structure with 5% modal damping ( ) is used as Intensity Measure (IM). Also in the probabilistic fragility curves, the direct method is used. It means that the IM is used directly in the fragility curve. To predict the probabilistic function for the different level of performance of structures, the lognormal distribution was used. The study results show that the structures designed by the ASD method have a better seismic performance than the LRFD frames specially in the performance level of Life Safety (LS) and Collapse Prevention (CP). It can be concluded from comparison of the median of collapse functions. For example for the special moment frame (8-story structure), the use of ASD design (instead of LRFD design) leads to a 11% increase in the median of fragility function in the Life Safety (LS) level and 10% increase in the Collapse Prevention (CP) level.

In view of potential vulnerability of even exciting buildings designed based on seismic design codes under consecutive strong earthquakes, paying attention to the use of a secure system, especially in earthquake-prone regions is revealed. Tunnel form system is a new industrial construction system in which only the slabs and walls are used as lateral load resisting elements (Balkaya and Kalkan, 2004). Naming this system as the tunnel form is due to the installation of formworks in box manner (Fig. 1) (Mirghaderi et al., 2009).
Previous earthquake experience and the results of laboratory and numerical studies of lateral resistance of tunnel form construction represent a very significant performance against strong earthquakes. So far no study has been conducted to assess the resistance of this construction system subjected to consecutive earthquakes. It seems that this structural system is able to retain safety against successive earthquakes. This study aims to quantify the post-earthquake capacity of the damaged tunnel form buildings after subjecting the main shock and also their performance assessment subjected to multiple earthquakes.

Fragility curves are usually used to determine the vulnerability of structures. But defining failure criteria is of great importance in seismic vulnerability which probability of exceeding from these failure criteria is considered as the basis of probabilistic analysis. In the present study, three types of 3D reinforced concrete buildings having 3, 5 and 8 floors with reinforced concrete moment resisting frame structural system having medium formability designed seismically according to Iranian guideline (seismic regulations of Iranian 2800 code and chapter 9 of National Building Regulations, last edition in 2013) with and without the effect of infill considering structural failure (including low-strength concrete) are analyzed using accelerogram (far source) using OpenSees (Open System for Earthquake Engineering Simulation). Finally, fragility curves of the above-mentioned structures calculated and drawn using Nonlinear Incremental Dynamic Analysis (IDA). The results showed that the infill has an effective role in decreasing lateral stiffness of buildings as much as 20 to 40 percent in proportion to building height

Fragility curves play an important role in damage assessment of buildings. Probability of damage induction to the structure against seismic events can be investigated upon generation of afore mentioned curves. In current research 360 time history analyses have been carried out on structures of 3, 10 and 20 story height and subsequently fragility curves have been adopted. The curves are developed based on two indices of inter story drifts and equivalent strip axial strains of the shear wall. Time history analysis is carried out in Perform 3d considering 10 far field seismograms and 10 near fields. Analysis of low height structures revealed that they are more vulnerable in accelerations lower than 0.8 g in near field earthquakes because of higher mode effects. Upon the generated fragility curves it was observed that middle and high structures have more acceptable performance and lower damage levels compared to low height structures in both near and far field seismic hazards.

Despite widespread construction of mass-production houses with tunnel form structural system across the world, unfortunately no special seismic code is published for design of this type of construction. Through a literature survey, only a few studies are about the seismic behavior of this type of structural system. Thus based on reasonable numerical results, the seismic performance of structures constructed with this technique considering the effective factors on structural behavior is highly noteworthy in a seismic code development process. In addition, due to newness of this system and observed damages in past earthquakes, and especially random nature of future earthquakes, the importance of probabilistic approach and necessity of developing fragility curves in a next generation Performance Based Earthquake Engineering (PBEE) frame work are important. In this study, the seismic behavior of 2, 5 and 10 story tunnel form structures with a regular plan is examined. First, the performance levels of these structures under the design earthquake (return period of 475 years) with time history analysis and pushover method are assessed, and then through incremental dynamic analysis, fragility curves are extracted for different levels of damage in walls and spandrels. The results indicated that the case study structures have high capacity and strength and show appropriate seismic performance. Moreover, all three structures subjected were in immediate occupancy performance level.