ساسان معتقد

The panel zone is the central part of the beam and column joint in the frame. The purpose of this article is to investigate the effect of panel zone modeling on the behavior of concrete moment resistance frames. For this purpose, two 8- and 12-story concrete moment resistance frames are modeled using OpenSees software and the results of nonlinear cyclic static analysis, nonlinear dynamic analysis and nonlinear incremental dynamic analysis, with and without consideration of panel zones are compared to each other. In all cases, the degradation has been considered based on the Ibarra, Medina and Krawinkler model. The results show that the in the static analyses, the differences in the results of the models are very small. In the dynamic analyses, the effect of the panel zone is significant. The fragility curves of the structures indicate that the models with the panel zones reached the collapse threshold at lower intensity levels. Also, in the non-linear time history analysis of the structural response, it was observed that when the structures have linear behavior, the effects of modeling of the panel zones are insignificant, but when the structure enters the non-linear region, the displacements are greater in the presence of the panel zones.

Rice husk as an agricultural waste material has a large amount of amorphous silica, adding its ash to concrete increases the pozzolanic property of concrete and consequently increases the strength and durability of reinforced concrete structures. The quality and method of rice husk ash preparation greatly influence the final properties of the concrete prepared from it. In this article, rice husk ash has been burned in controlled, semi-controlled, and uncontrolled conditions in terms of temperature conditions, and the resulting ash has been used as a 10% substitute for cement in self-compacting concrete. Properties related to concrete performance and compressive strength of samples containing rice husk ash at different ages have been evaluated. The properties of rice husk ash powder have been determined through XRF, FESEM, and the determination of grain size range. The results show that in all cases the sum of SiO2, Al2O3 and Fe2O3 is higher than 70%; which indicates being within the standard range of pozzolanic cement materials. In the semi-controlled state, the amorphous silica is more than 8%. Based on the results, adding rice husk ash increases the long-term compressive strength (90 days) and decreases the short-term compressive strength of self-compacting concrete. The increase in long-term strength for samples with ash produced in controlled conditions was more and up to 18%. The reduction of short-term compressive strength for samples with uncontrolled ash has been obtained up to 25%.

Earthquake wave transmission from the source to the site is modeled by the ground motion prediction equations (GMPEs or attenuation equations). Considering the high contribution of these equations in the variability of the ground motion in the site, the selection of the appropriate relations for the region is of particular importance. The number of prediction equations is large, but there is no specific relationship for many areas, so it is necessary to use criteria to determine the best equations for probabilistic seismic hazard analysis(PSHA). In this paper, 62 relationships used by analysts in Iran and Tehran region are introduced to the three criteria of Rennie divergence, Euclidean distance and likelihood method, are ranked based on similarity with actual occurrence data, and the most suitable relationships for Tehran are introduced. The results show that the relationship of Zare and Sabze Ali (2006) in all three methods has a very good match with the Tehran region earthquakes. Also, some global relations have a better match than the regional relations obtained in Tehran. The results of the sensitivity analysis show a decrease in the effectiveness of the regional PSHA using the ranking. It also shows that relying on the opinion of experts brings more than 90% confidence in the selection of GMPEs, which seems sufficient in some cases. .If this level of accuracy is not sufficient, it is necessary to use the appropriate weighted equations in the analysis based on the physics-based ranking results. Otherwise, the results of the probabilistic seismic hazard analysis will fluctuate and may not have the sufficient reliability.

Soil deformation can have a major impact on the seismic design inputs of structures. In practice, the soil is always bounded by rocks. In this case, the phenomenon of resonance or beating due to the closeness of the frequency of the structure to the natural frequency of the soil can be very destructive. For this reason, the natural frequency of the soil is considered in the construction regulations in presenting the spectral shape. To determine the natural frequency of soil in Behbahan city, the H/V method based on non-destructive measurement of ambient noise, which is a inexpensive and successful method for evaluating soil properties, was used. After recording microtremor data in 69 stations, H/V analysis was done to estimate the resonance frequency at the points. Then, natural frequency maps of the soil were presented. The results showed that the natural frequency range of soil in Behbahan city is between 0.57 and 5.42 Hz. Therefore, this soil is included in soil types 2 and 3 (standard No. 2800). Moreover, based on the construction information, a resonance-prone areas map was provided. In the central areas, the soil type is mainly type 3. Most of the buildings in this area are low codes, so it requires more precision in future developments. In the northwest and southeast of the city, the period of soil resonance is more than one second; therefore, in the construction of tall buildings in these areas, more strict measures should be taken into account to control the structures.

In the variability of earthquake hazard analysis results, ground motion prediction equations play an important role. Selection of appropriate prediction relationships for the region can lead to stability and accuracy of earthquake hazard analysis results. In this study, different prediction relationships were investigated and analyzed for earthquake hazard analysis in Ahvaz city. These relationships were ranked based on the criteria of logarithmic probability, Euclidean distance and deviation information in different periods. Then the most efficient relationships were selected by data envelopment analysis (DEA) method on the basis of differences in the obtained results. Out of 67 possible relationships, 5 were identified as suitable relationships for earthquake hazard analysis in the Ahvaz urban area. Then, a special efficiency criterion was used to determine the weight of these relationships. The results of this study can help to reduce to a large extent the uncertainties involved in analyzing the seismic hazard of the area studied.

There are several sources of uncertainty in the analysis and design of steel moment resisting frames, the random assumption of each of which can have a significant effect on the satisfiction of performance requirements of the structure. Among these factors, structural parameters can be mentioned, the most important of which are yield stress, modulus of elasticity, sections geometry and structural mass. Evaluating the impact of these factors depends on how the parameters are distributed and modeled. In this study, three common types of uniform, normal and log normal distributions for the parameters of mass structures, yield stress, modulus of elasticity and sections geometry that are random in nature are considered and using Monte Carlo method, the effect of uncertainty of these parameters is considered. The seismic performance of steel structures is investigated. Studies are performed on 4 structures of 3, 5, 10 and 15 floors of steel moment resisting frames with medium ductility, which are designed according to Iranian regulations. In order to model the structures and perform incremental dynamic analysis, Open Sees software was used .In order to evaluate the seismic performance of the structures, fragility curves were used. The results show that the type of distribution does not have a significant effect on the results of applying uncertainties. It is also observed that considering the mass uncertainty, increases the acceleration range in the Collapse Prevention (CP) and life safety (LS), which shows the significant effect of mass uncertainty compared to other parameters.

Reinforced concrete shear wall structures are an important part of the construction due to their ability to withstand in large earthquakes force and deformation demands. In some of these buildings, shear walls are implemented in successive bays to create more lateral resistance, to reduce drift or to satisfy architectural requirements, and adhered walls are appeared. In Open Sees, the MVLEM and SFI_MVLEM methods do not have the ability to model the common boundary element between two shear walls adhering to each other. So, modeling of these walls in Open Sees software is difficult. In this paper, we propose a method for modelling these walls, Multiple Vertical Columns (fiber) method, and modeling results are compared with experimental results and the results of other models. The ability of this method in the modeling of the adhered shear wall is measured via the actual building modelling. The results of static posh-over analysis and nonlinear dynamic analysis show that the proposed model has a good performance for the modeling of adhered walls. The main advantages of using Multiple Vertical Columns (fiber) method are the use of multiple fiber columns to model the geometry continuity of the wall in a horizontal direction (similar to the MVLEM) and the possibility of folding the vertical elements along their longitudinal axis and using horizontal joints in the mid-points to model The geometric continuity of the wall is vertical direction.

Pervious concrete with high cavity volume serves as pre-treatment of runoff, as well as groundwater feeder and runoff reducer. Generally, this concrete has low resistance. In this research, we have tried to improve the resistance properties of pervious concrete using magnetic water. To this end, four mixing designs were selected and, based on each mixing design, 28 samples were made with tap water and 28 samples with magnetic water; 14 cubic samples for 7 and28-day compressive strength test and 14 cylindrical specimens for 7 and 28-day tensile strength and permeability tests. The results show that the of the 7-day compressive strength has increased by 36 to 43% using magnetic water. However, 28 day compressive strengths increase only 9 to 16 percent. 7-day compressive strength tap water samples obtained about 44-48 percent of 28-day strength, while in samples made with magnetic water at 7-day compressive strength achieved 56-61% of their 28-day strength. Permeability of Magnetic water samples have been reduced by about 8-34 percent relative to those made with tap water. Samples made with magnetic water have a more uniform appearance and physical properties.

The history of the human efforts for safety against earthquakes shows the catastrophic and harmful events, even nowadays. The majority of decisions in seismic safety policy are based on randomness assumption for earthquake time series. The accuracy of this assumption assessment, can accurate the strategies and resulted in more secure decisions. Also in structural control context, seismic time series prediction in the feedback systems, can reduces the time of control system reaction and in subsequent decreases structural damages. Recent studies have shown that dynamical structure of these complex time series can be better understand using nonlinear dynamics theory. In the present paper, we evaluate randomness and nonlinear characteristics of 9 earthquakes time series from metropolitan Tehran earthquake database using chaos theory conceptions. These earthquakes are Arjomand, Bumahen, Damavand, Eshtehard, Firuzkooh, Taleqan 1, Taleqan 2, Taleqan 3 and Tehran earthquake. To this end, we reconstruct phase space for delay time calculation using average mutual information function. Embedding dimension is calculated based on false nearest neighbors. Correlation dimension is used for earthquake chaotic behavior assessment and local prediction algorithm and artificial neural network are employed for earthquake prediction. Results illustrate nonrandom nature of evaluated earthquakes. These earthquakes have high dimension chaotic behavior. Earthquake prediction is good and acceptable accuracy using chaos theory and artificial neural network. The existence of the specific attractors in a part of 2D reconstructed phase space for the earthquakes show the presence of a nonlinear processes. This is an evidence for no stochastic behavior of the earthquakes. Also, reduction in the false neighbors with embedding dimension increases, shows no stochastic time series. Lyapanov exponent positive gradient displays a nondeterministic process, although it cannot warranty the chaotic behavior. Correlation exponents have high values for Taleqan1 and Tehran earthquakes. So these earthquakes saturate in large quantities. Bumahen and Damavand earthquakes correlation exponents have increasing trend and do not saturate. These observations prove the chaotic behavior of high dimension or random process with inconsiderable chaos. So these earthquakes cannot be predicted properly. Performing the local prediction based on the selected embedding dimensions and the neighbor’s number, showed that the predicted time series are relatively good for the earthquakes of Arjomand, Eshtehard, Firuzkooh, Taleqan 2 and Taleqan 3. Proper anticipated of trends, upward and downward branches as well as amplitudes illustrate the chaotic nature of the earthquakes. The correlation coefficient for Arjomand, Eshtehard, Firuzkooh, Taleqan 2 and Taleqan 3 are 0.9541, 0.4494, 0.5124, 0.6600 and 0.3697 respectively. In the case of Talegan1 and Tehran earthquakes, time series amplitudes and peaks do not predicted appropriately, but the prediction is acceptable. Correlation coefficient of Taleqan1 and Tehran are 0.2452 and 0.1760 respectively. Bumahen and Damavand earthquakes do not trace properly. It should be noted that for each earthquake, 20% of the endpoints of accelerations are used to evaluate the prediction process. According to the results of the analysis and earthquakes prediction in Tehran region, using phase reconstruction and artificial neural networks, we can say that the dynamics governing the earthquakes in this region are not random, but, chaos with high dimension. Earthquake prediction is good and acceptable accuracy using chaos theory and artificial neural network.

Self-compacting concrete (SCC). was developed about four decades before since that time it has been used very scarcely due to a number of problems including : separation, lack of flowability and filling ability, high cracking potential, and thereupon low compressive and tensile strength. In this study, properties of SCC containing viscosity modifying agent, steel and polypropylene fibers were investigated. polypropylene fibers with dosages of 0.1, 0.125, 0.20, 0.150, 0.185, 0.205, and hook end steel fibers with volume fractions of 0.5, 1, 1.5, 0.2 and 2.5 were employed; fresh and hardened SCC were examined. The results of the fresh concrete tests revealed that rise of the both fiber types reduces the slump flow and raises the T50 time. In the V-funnel test, the time shortened with polypropylene fibers up to dosage of 1.25%, and then soars. Growing steel fibers elongate the time of the V-funnel test. Adding both types of the fibers reduces the passing ability of concrete in the L box test. Hardened concrete tests indicated that the compressive strength is falling by rising the dosage of steel fibers. The compressive strength at the age of 7 and 28 days improves up to the polypropylene fiber dosage of 1.50% and then declines. At the age of 90 days, strength trend changes in dosage of 0.1. Tensile strength grows as the both fibers increase. The crack test results show that the length and width of the cracks lower with the growth of the fibers. Adding steel fibers boosts the number of cracks.

The ultimate goal of concrete as the most important and most used building material is the durable resistance properties. Self-compacting Concrete, as an option to solve the major problems of conventional concretes, has a higher cost due to the use of special additives and aggregates size. Also, the presence of fine grains increases the cracking potential of the concrete. The aim of this paper is to assess the effect of coarse aggregate ratio and steel fibers on the properties of self-compacting concrete (SCC). For this purpose, 27 SCC mixtures with C/T(coarse aggregates as a fraction of the total combined aggregate mass) for 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35% and 30% and 12 SCC mixtures containing hook end steel fibers with volume fractions of 0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5% were prepared. The effect of C/T ratio on the fresh properties and mechanical properties of SCC was studied. The test results indicated that aggregate with C/T ratio for 50% has the best fresh and hardened properties. With the change in fiber ratio from 0% to 2.5%, the slump flow, blocking and segregation ratio are increasing, while in the fiber ratio above 2%, the self-consolidation property is lost. Fibers increase the tensile strength above than 40 % and decrease shrinkage cracking more than 50%. Fiber has no positive effects on compressive strength. According to the results, the best percentage of hook end steel fibers which can be recommended for self-compacting concrete is 1.5%.

Uncertainty is the inseparable part of the engineering analysis. These uncertainties have different Distributions. Sobol decomposition method is one of the most well-known methods of sensitivity analysis. Sobol decomposition as a robust sensitivity analysis method can only be used for uniform distribution. In the present paper, we generalize Sobol sensitivity method for all continuous and discrete distributions. Hence it can be used for wide Varity models in engineering and science of different distributions. The capability of the generalized method for precise numerical values presentation, the results of the sensitivity analysis of the Tehran seismic hazard is given. Due to the variability of materials and earthquakes, Structural and geosciences are full of uncertainties. Calculating the role of the uncertainty of each parameter in the overall uncertainty can be to optimize the efforts and costs necessary for outputs precision, so, it is possible to provide a precise values of sensitivities. The results are satisfactory.

Summary
Seismic response of circular tunnels embedded in homogenous ground has been studied using the FEM code abaqus. Results show that the tunnel embedded in one layered ground has a completely different behavior in comparison with the same tunnel embedded in two( or more) layered ground.
In this study, the effect of ground stratification on the seismic response of circular tunnel''s lining is investigated, as most practice-oriented studies consider homogeneous ground. The above mentioned situation has been argued detailed in the coming content.
Methodology and Approaches
A finite element plain-strain model of a circular tunnel''s cross-section embedded in an one and two-layered ground is used to highlight the influence of stratification on the tunnel''s seismic response at the crown, springline and invert points. The finite-element mesh grid simulates a 30-meter soil mass in a plain-strain condition with amount of 31226, 4-node rectangular elements in a rugged limestone rock. Ground and tunnel both are simulated with Single-phase linear elastic materials and Wang’s closed form solution is used to predict the seismic response of tunnel’s cross section. The model only considers the vertical propagation of shear waves in the visco elastic layers on a hard rock bed. The degrees of freedom at the bottom of the floor are completely restrained, because displacements are calculated from the base.
Results and The main parameters govern the calculated loads derived from analytic solutions are the compactness C, the F flexibility ratios, and the maximum rate of free shear strain ɣ. Results prove that the conditions of the ground layers, specially the amount of layers, play an important role in the situation of seismic forces encountering the tunnel lining. The layers interface was placed at the crown, center and invert level. . Models clarify that when the tunnel is fully embedded in one of the two consecutive layers, the seismic forces created in lining may vary significantly in comparison with the case that we have only one layer for tunnel to be embedded in. Furthermore if the tunnel intercepts both layers, maximum lining forces aggravation occurs when the lower layer is very stiff. When the tunnel passes through both layers of soil, the values of R follow the single-layer lining response for , otherwise less R values are obtained. For the lower stiffness of the layers, the R values obtained are almost unaffected by the higher hardness values, EV.

Because of the many advantages, using of self competing concrete (SCC) in structures is increasing. Construction of precast-prefabricated components, with the use of concrete has also recently been considered. Concrete properties have significant role in precast-prefabricated girders behavior. Exact prediction of these properties is the base of members analysis and design. Determine the optimum composition is the mean to obtain the best set of useful concrete properties. In this paper, SCC mix design optimization method is presented based on multi-criteria optimization using particle swarm algorithm (PSO). The results show the Successful application of Pareto optimization method in the optimization of scc mix design used in bridge girders.