جستجوی مقالات مرتبط با کلیدواژه "ارزیابی احتمالاتی" در نشریات گروه "عمران"

In this paper, a new and efficient performance-based method is introduced for the optimal design of the tuned mass damper (TMD) to control the response of nonlinear structures. In this method, the FEMA-P58 probabilistic evaluation framework is used in the design and evaluation of TMD performance in order to reduce the repair cost and time caused by structural and non-structural damages. For this purpose, an innovative objective function has been defined based on structural responses resulting from different earthquakes, which is compatible with the probability of the repair cost and time exceeding a certain value in the FEMA-P58 method. Uncertainties due to earthquake records are directly considered in the introduced objective function. The genetic algorithm is used for the optimal design of TMD based on the proposed objective function. Also, due to the fact that considering the uncertainties in the input earthquake records leads to increasing the calculation time, therefore the artificial neural network technique is used as a fast estimator of the nonlinear dynamic response of the structure to reduce the calculation time. The probabilistic evaluation of the performance of the structure equipped with the proposed TMD shows the efficiency and effectiveness of the proposed design procedure in reducing the expected repair cost and time. So that the expected repair cost and time in the structure equipped with the proposed TMD under the design earthquake have been reduced by about 29% compared to the uncontrolled structure.

Fragility curves are powerful tools to assess and control of possible damages to the existing structures and estimate the exceedance probability from the seismic behavior of the structures under the influence of different earthquake levels. these curves present the probability of damage as a function of the ground motion characteristics. The main goal of the current study is to examine the existing methods and the presentation of a suitable method for the production of analytical seismic fragility curves and propose appropriate relationships for the exceedance probability from different performance levels. For this purpose, three high-rise building with 20, 25, and 30 stories with a slimming ratio greater than π, according to the standard 2800 and the sixth issues and tenth issues of the national building regulations of Iran, were designed. Then after extracting the perimeter frame, by using appropriate software, their analytical model was defined and validated. To evaluate the seismic response demand of frames, incremental nonlinear dynamic analysis (IDA) was performed. For IDA analysis, the 22 recommended records in the FEMAP695 guideline and two earthquakes in Iran were used. Spectral acceleration of the first mode of the structure with damping of 5 Percentage (Sa (T1.5%)) was used to introduce the intensity of the earthquake (IM) and the inter story drift ratio was used to introduce the engineering demand parameter (EDP) Or damage measure (DM). To find the appropriate function of the exceedance probability from limit states and use them in the production of fragility curves, the results of IDA analysis and nineteen different probability functions using the suitable program were used. in order that the used distribution describes the sample data in the best manner, the goodness of fit tests was used. the results obtained from the goodness of fit tests show that The probability distribution rank used by researchers (log normal) versus other probability distribution functions varies in ranking the best fitted probability distribution. and selecting the appropriate probability distribution is effective in the conclusions and determining the probability exceedance of the structure from the desired limit states. Therefore, in order to reduce the uncertainty related to the mathematical model (epistemic uncertainty) in the template of a comprehensive view and according to accuracy and the required seismic target, a suitable method for developing fragility curves for types of structural systems with different heights here called “intelligent seismic fragility curve (ISFC)” is introduced and presented. Such that if among the probability functions examined in this paper, the use of only one distribution is desired to compare several options, including deciding how to reinforce or comparing the seismic performance of several structures with duel system of special steel moment resisting frames with eccentric lateral bracings to plot the fragility curve, it is recommended: to use the probability distribution "Generalized Extreme Value", due to the ability to fit better than the distribution "log normal", but for more sensitive structures, such as nuclear power plants and hospitals that are of great importance and require high precision or in order to achieve the most accurate fitted possible to decide on about the vulnerability estimation for types of structural systems with different heights, It is then recommended: to estimate the exceedance probability from performance levels at the structure, before fragility analysis, by probabilistic evaluation and using the goodness of fit tests on suitable probability functions, at first, a best fitted probability distribution should be selected at all performance levels and then the vulnerability of structures is estimated by fragility curves.

Evaluation of the life model of concrete structures has an effective role in determining maintenance programs as well as estimating the probability of failure of these structures. One of the most important factors that affect the durability and strength of concrete structures is the corrosion of rebars, which is generally caused by the penetration of chloride ions in concrete. Due to the corrosion of the rebar, the effective surface of the rebars is reduced and over time, by creating cracks in the concrete section, the effective concrete cross-section is also reduced. In this study, considering the inherent and statistical uncertainties of the parameters affecting corrosion, for different states of chloride ion penetration, the concrete beam life model has been evaluated. For this purpose, considering a concrete beam, different scenarios of chloride ion penetration from different directions of the beam cross-section is considered, and based on each scenario, the corrosion initiation time of rebars, cracks, and scaling of concrete are calculated and the effect of each event on The flexural strength of the beam is evaluated. The results show that considering the effect of concrete scaling causes a difference of up to 20% in the predicted values for the flexural strength of concrete beams and a more realistic assessment of the remaining life of the structure will be obtained. Also, the states that cause the compressive cross-section of the concrete to peel are more critical in the concrete beam life model due to the reduction of the effective depth.

During the recent two decades, many structures have become in need for seismic retrofit due to changes in either requirements of relevant seismic codes or the building usage. Viscous dampers are increasingly employed for seismically retrofitting various structures thanks to their easy installation and minimum intervention into the existing structure while significantly improving the seismic performance of the building. The main objective of this paper is to present a new design procedure for the evaluation of probabilistic seismicity of steel structures equipped with nonlinear viscous dampers. For this purpose, numerical investigation was conducted on, as benchmark structures, three steel-made moment-resistant frames with 3, 9, and 20 stories. Due to significant differences in their dynamic characteristics, these three structures represented low-rise, mid-rise, and high-rise buildings, respectively. Nonlinear time history analysis was performed using two near-field and two far-field accelerograms at various intensities (making up a total of 10 accelerograms). Moreover, nondimensional analysis was done to evaluate the uncertainties associated with velocity exponent of the nonlinear viscous dampers. Next, probabilistic estimation of damages occurred to the benchmark structures was performed and the effect of the uncertainty associated with the dimensionless power intensity of the damper on the seismic response of the structure. Investigating the results of the seismic analysis for viscous dampers at power intensities of 0.2, 0.3, and 0.4, it was found that although the seismic retrofit had significantly improved the seismic performance in all model structures but the proposed design procedure was more effective in the retrofitted high-rise structures at the power intensity of 0.4.

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.

Nowadays, there are various types of existing buildings with poor seismic detailing so they cannot cover the seismic code provisions. Accordingly, the seismic rehabilitation technics should be implemented for these structures. Eccentrically Braced Frame having vertical link is a new strategy for retrofitting of existing RC buildings. In this article, three types of reinforced concrete structures with the same architectural plan having 3, 5, and 8 stories are retrofitted with Eccentrically Braced Frames having vertical links and the seismic fragility curves are developed based on Incremental Dynamic Analysis (IDA) in OpenSEES. The demand statistics in terms of maximum inter-story drift ratio are obtained for 20 sets of ground motion records, the capacity is determined according to the HAZUS-MH limit states, and finally the corresponding seismic fragility curves are developed. The results represent the effect of the implemented retrofit strategy on the seismic vulnerability of this subclass of structures. The median seismic fragility for 3, 5, and 8 story models are increased 35%, 90% and 146 % accordingly, at the complete damage state.

Risk reduction and management of oil, gas, and petrochemical plants are important in terms of energy supply, financial implications, life loss, and repairs. Probabilistic analysis and reliability methods are effective approaches for calculating the risk and cost to such plants, which are composed of units with different types of equipment and structures that have different responses and consequences. One major piece of equipment in a plant that has been shut down is the flare. Depending on the height, the flares can be self-supported, guy-supported, or derrick-supported. The current study investigated the seismic probability behavior of a derrick-supported flare. An existing flare was investigated using the finite element method and incremental dynamic analysis as a case study. The different limit states of the structures were considered when calculating the fragility curves using the results of incremental dynamic analysis. The results showed that the seismic demand on the main structure of the flare stack in the ordinary seismic intensity range was not significant due to the flexible behavior of the structure.

Reinforcement corrosion due to chloride ingress into the reinforced concrete (RC) structures adjacent to the sea and bridge in the snow-prone areas caused compromising the operation of these RC structures over time. Thereby in some of these structures, corrosion initiation is used for operational limit-state. There are so many methods for calculation of corrosion initiation time. There are many uncertainties in these models and because of that some errors made in calculated corrosion initiation time. In this paper using structural safety calculations and Monte Carlo sampling method (MC), the probability of corrosion initiation is calculated. As a new approach, corrosion initiation time is calculated based on the level of structural performances with the probability of 25,50 and 75 percent for the occurrence of corrosion initiation. Concrete quality, as well as the severity of environmental factors, were used as other basic parameters in this study. The uncertainty in the calculated time to corrosion initiation is also evaluated based on the statistical properties of the effective parameters in the model. Based on the results obtained, increasing the quality of concrete by reducing permeability has a greater effect on increasing the time for the first inspection of concrete structures.

In this article, the fragility curves of RC structures with 3, 5 and 8 stories in Iran have been studied. The structures which have been estimated in this article have the system of RC Intermediate Moment Frame which is designed in accordance with Standard No. 2800 (Third Edition). These models in order to make a non-linear analysis in 3D form, they were modeled in OpenSEES software. The structure analysis was selected of the type of increasing dynamic analysis. In selecting the records of the earthquakes, it was tried that the characteristics of the selected records to be close to the conditions of the construction as much as possible. For this reason, the far-from the fault records of the FEMA P695 Code was used. The selected records were scaled from 0.1g to 1.5g with 0.1g steps and in each step, the structure was analyzed. The IDA curves were drawn for three types of structures under consideration up to structural complete damage. Then using MATLAB software and considering the lognormal probability distribution, the failure probability for each performance level was calculated and the fragility curves for Max Inter Story Drift in different levels of PGA were drawn. The results indicate that in comparing the structure behavior with different heights, it can be said that with the increase of height, the structure reaches to non-linear zone sooner and the structure capacity decreases. In general, with the structure height increase, the structure vulnerability in four specified levels of damage (slight, moderate, extensive and complete) increases but the trend of the increase of damage probability decreases. For the low rise RC structures (Intermediate moment-resisting frame) which have been built in accordance with the Standard No. 2800 (Third Edition), the Probability of extensive and complete damage in earthquakes with PGA’s less than 0.4g and 1.0g accordingly is almost insignificant. For the mid and high rise buildings, the probability of extensive and complete damages in earthquakes with PGA’s less than 0.3g and 0.7g is almost insignificant.

F o r m a n y y e a r s، p r o v i d i n g s u f f i c i e n t s t r e n g t h f o r b u i l d i n g s، w h i l s t t r y i n g t o p r e v e n t c o l l a p s e، w a s t h e m o s t i m p o r t a n t p u r p o s e b e h i n d s e i s m i c c o d e s. A f t e rt h e N o r t h r i d g e e a r t h q u a k e (1994) a n d t h e a m o u n t o f d a m a g e d u e t o b r i t t l e b e h a v i o r i n s t e e l s t r u c t u r e c o n n e c t i o n s، m a n y s t u d i e s a b o u t d e g r a d i n g e f f e c t s h a v e b e e n u n d e r t a k e n. O n e o f t h e m o s t i m p o r t a n t d e g r a d i n g b e h a v i o r s w a s i n-c y c l e s t r e n g t h d e g r a d a t i o n. I n r e c e n t y e a r s، m a n y r e s e a r c h e r s h a v e f o c u s e d o n i n-c y c l e s t r e n g t h d e g r a d a t i o n i n h y s t e r e s i s c y c l e s. I n t h i s p h e n o m e n o n، d e g r a d a t i o n o c c u r s i n t h e s a m e c y c l e o f l o a d i n g. R e c e n t i n v e s t i g a t i o n s d o n e b y F E M A-P440A، h a v e s h o w n t h a t t h e e f f e c t s o f i n-c y c l e s t r e n g t h d e g r a d a t i o n c a n b e c r i t i c a l i n d e t e r m i n i n g t h e p o s s i b i l i t y o f l a t e r a l d y n a m i c i n s t a b i l i t y i n S i n g l e D e g r e e O f F r e e d o m (S D O F) s y s t e m s. M u l t i d e g r e e o f f r e e d o m (M D O F) s y s t e m s h a v e m o r e c o m p l i c a t e d b e h a v i o r t h a n S D O F s y s t e m s. I n t h i s r e s e a r c h، i n o r d e r t o s t u d y t h e e f f e c t s o f s u c h k i n d s o f d e g r a d a t i o n، 3، 5 a n d 7 s t o r y s t e e l m o m e n t f r a m e b u i l d i n g s w i t h t h r e e t y p e s o f c o n n e c t i o n (P r e-N o r t h r i d g e، P o s t-N o r t h r i d g e a n d E l a s t i c-P e r f e c t l y-P l a s t i c)، h a v e b e e n m o d e l e d. I n o r d e r t o h a v e a m o r e p r e c i s e s t u d y، a p r o b a b i l i s t i c s e i s m i c d e s i g n a p p r o a c h h a s b e e n u s e d a n d، t h e n، t h e r e l i a b i l i t y o f s t r u c t u r e s a t p r e-d e f i n e d c o n f i d e n c e l e v e l s h a v e b e e n c a l c u l a t e d، B y p e r f o r m i n g I n c r e m e n t a l D y n a m i c A n a l y s i s (I D A)، t h e r e q u i r e d p a r a m e t e r s i n t h e p r o b a b i l i s t i c a p p r o a c h، s u c h a s d e m a n d a n d c a p a c i t y، h a v e b e e n c a l c u l a t e d. R e s u l t s o f t h i s s t u d y h a v e s h o w n t h a t i n-c y c l e s t r e n g t h d e g r a d a t i o n c a n g r e a t l y i n c r e a s e t h e l i k e l i h o o d o f g l o b a l d y n a m i c i n s t a b i l i t y a n d d e c r e a s e t h e r e l i a b i l i t y o f m i d-r i s e s t e e l m o m e n t f r a m e s t r u c t u r e s.