Scientia Iranica
Volume:24 Issue: 5, 2017

This article presents a new empirical equation for the estimation of horizontal strong ground motions caused by shallow crustal earthquakes. This model is developed empirically by regression of the database which is used by the NGA-West2 GMPE developers with a fault rupture distance less than 60 kilometers. The data set consisted of corrected and processed accelerograms of 1545 strong-motion records of earthquakes between Mw 5.2 and 7.9. Model is a function of earthquake magnitude, distance from source to site, local average shear wave velocity, nonlinear soil response, sediment depth, rupture dip, faulting mechanism and hanging wall effect.
This equation was derived by a stable algorithm for regression analysis called mixed effect model. The algorithm was used to develop PGA and PSA (T1) for periods from 0.01 to 10.0 seconds. Major differences between this model with recent developed attenuation relations for the world and Iran were observed for large-magnitude ground motions which were recorded at small-to-moderate distances from seismic source. The results showed that the near-field affected the predicted values especially in soil sites. Moreover, comparison with the attenuation relations developed by Iranian data set confirmed that the equation in this region is sensitive more to distance than to other parameters.

The prediction of material response is necessary for the analysis of structure under static or dynamic loading. Mathematical modeling of the nonlinear tri-dimensional mechanical behavior of quasi-brittle materials like concrete caused by damaging and plasticity effects are one of the most serious classical challenges we face in the engineering science. Among phenomena of different orientation, the micro-plane models, like multi-planes models which use a constitutive equation in a vectorial form rather than tensorial form by means of capturing interactions, can serve this goal adequately. This paper presents a simple realistic and robust damage based model in the multi-planes framework accomplished with a few parameters for calibration and suitable for engineering purposes without volumetric-deviatoric split of strain tensor and its problems. This damage formulation has been built on the basis of two types of fundamental damage, axial damage and shear damage, that essentially can be occurred on each micro-plane and based on this concept two new axial and shear damage functions are presented. By comparing between the results of the proposed model and experimental data, model verification has been examined under different loading/unloading/reloading stress/strain paths.

Dominant collapse mechanisms (DCMs) have been reported to play an important role in collapse capacity of structural systems and the seismic losses consequent to it. Therefore, DCMs of Reinforced Concrete (RC) frames have been studied, in this article, considering Record-to-Record (RTR) and modeling uncertainties. Two sets of RC frames have been designed, in this regard, that share the design assumptions but contain different levels of over-strength. Each set contains 26, 4- to 20-story nonlinearly modeled frames. Initially, Incremental Dynamic Analysis (IDA) was used to identify frames’ DCMs. The RTR variability reflected through IDA was next combined with spectral shape and pulse effects of the ground motion records. Modeling uncertainties were introduced finally to the study using a response surface based Monte Carlo method. The study results reveal that the degree to which DCMs are affected by the associated uncertainties is a function of the over-strength provided to the frames. This affection is found to be generally important and particularly remarkable for especially detailed ductile structures.

Construction of diagonal reinforcement in concrete coupling beam is difficult so its replacement is steel coupling beam. Literature shows that a few studies have been done on seismic behavior of RC coupled wall with steel coupling beam. In this paper, the influences of increase in building height on the seismic nonlinear behavior of dual structural systems in forms of RC frames accompanied with RC coupled shear walls once with concrete then with steel coupling beam have been investigated. Therefore the buildings with 7, 14 and 21 story and containing RC coupled wall systems with concrete and steel coupling beams used to perform the pushover analysis having different load patterns. Some seismic parameters such as ductility factor, response modification factor due to ductility, over-strength facto, response modification factor (R) and displacement amplification factor (Cd) have been studied. Regarding the results, the response modification factor for the mentioned structural system is higher than the values which are used in Codes of practice for seismic resistant design of buildings. Also, the displacement amplification factor and the response modification factor increased as the structure height decreased and the value of these factors at steel coupling beam structures are higher than concrete coupling beams.

Reservoir operation plays an important role in economic development of a region. Hedging operations were used for municipal, industrial and irrigation water supplies from reservoirs in the past. However, hedging operation for hydropower reservoir operation is very rare. Practically simple and useful new form of Standard Operation Policy and new form of hedging rules for hydropower production are introduced in this paper and demonstrated with a case study for hydropower reservoir operation of Indirasagar reservoir system in India. The performances of optimal hedging rules were compared with that of a new standard operation policies and the superiority (reliability increases by about 10%) of the hedging rules are presented. When the number of decision variables is increased from 5 to 15, the energy production is increased by 0.7 %, the spill is reduced by 16.8 % while the reliablity is decreasing slightly by 2.1 %. A bi-level simulation-optimization algorithm was used for optimizing the hedging rules. For optimization, Genetic Algorithm, artificial bee colony algorithm and imperialistic competitive algorithms were attempted. The results indicate that all the three algorithms are competitive and artificial bee colony algorithm is marginally better than the other two.

An investigation into the causes of settlement and its control can place an obstacle to such hazards as derailing of a train due to the railway settlement. In this study, the effect of both geogrid and the geogrid anchor concerning the railway ballast layer settlement reduction has been taken into account. For this purpose, the ballast performance in the field conditions was simulated using a small-scale box test. In this experiment the static load was considered as the sum of the train and passenger weightand the dynamic load relating to the train vibration. Since this research aims at launching an investigation into the influence of utilizing geogrids in order to reduce the ballast settlement, this experiment has been carried out by considering the geogrid and geogrid anchor layer, the loading frequency variation, the amount of loading, the geogrid position, the number of geogrid layers and the related distances. Also, the results obtained from the empirical model have been analyzed and compared. A number of relations based upon the test results have been developed to estimate the permanent settlement relative to the dynamic load and the number of reinforcement layers.

In fluid mechanics applications, transport occurs through the combination of advection and diffusion. This paper presents a stochastic approach to describe uncertainty and its propagation based on Advection-Diffusion Equation. To assess the uncertainty in initial water depth, random initial condition is imposed on the framework of 1D open cannel flow. Karhunen–Loeve Expansion is adopted to decompose the uncertain parameter in terms of infinite series containing a set of orthogonal Gaussian random variables. Eigenstrucures of covariance function associated with the random parameter, which play a key role in computing coefficients of the series, are extracted from Fredhulm’s equation. The flow depth is also represented as an infinite series of its moments, obtained via polynomial expansion decomposition in terms of the products of random variables. Coefficients of these series are obtained by a set of recursive equations derived from the ADE. Results highlight the effect of various statistical properties of initial water depth. The mean value and variance for the flow depth are compared with Monte Carlo Simulation as a reliable stochastic approach. It was found that when higher-order approximations are used, KLE results would be as accurate as MCS, however, with much less computational time and effort.

In fi ll walls are not generally taken into account in structural analysis due to their complex behavior at seismic actions. As it is known, they increase the sti ness as well as the lateral load capacity of the system. Sometimes, in ll walls may have window and door openings in their planes. In the present study, behavior of Reinforced Concrete (RC) frames with in ll walls, which have openings, is investigated under cyclic lateral loadings. Location and size of the openings in the in ll wall are selected as investigation parameters.
Test specimens are constructed and experimentally analyzed. The in ll wall changes the behavior of the frames under cyclic lateral loads signi cantly. Location and size openings in the in ll wall are two main parameters that a ect the behavior of the in ll walls as well as the frame. The test results clearly show that the contribution of the in ll wall to the behavior of RC frame diminishes signi cantly when the opening ratio is larger than 9%.
Therefore, the e ect of the opening in the in ll wall must be taken into account in the
structural modeling when the opening ratio is larger than 9%.

One of the important steps in seismic collapse assessment of structures by using nonlinear dynamic analyses is the appropriate selection of ground motion records. Epsilon (εSa), eta (η), and gamma (γ) for long-period structures, are proxies that have been recently proposed for Ground Motion Record Selection (GMRS). In this study, two parameters, named γs, are proposed, which have considerable correlation with the collapse capacity of short-period structures having fundamental period less than 1 s. One of these parameters is a linear combination of εSa, epsilon of Pseudo Spectral Acceleration (PSA) at 1.5 times of the fundamental period of the structure (εSa(1.5T1)) and εPGV. The other one is a linear combination of εSa, εSa(1.5T1) and epsilon of spectrum intensity, εSI. To obtain and optimize γs, the Particle Swarm Optimization (PSO) algorithm is applied. Since the parameters proposed as γs have significant correlation with the collapse capacity of short-period structures, they can be used as efficient proxies for GMRS in seismic collapse assessment of short-period structures. The results show that GMRS using γs leads to reduction in the dispersion of structural collapse capacity in comparison with GMRS based on εSa or η.

This paper presents a novel Cellular Automata approach for solution of reliability-based reservoir hydropower operation problems. The method is based on the observation that a low value of the penalty parameter would lead to partial enforcement of the constraints. In this method, therefore, the constraints of the chance-constrained operation problem, namely operational and reliability constraint, are dealt differently. A high enough value of the penalty parameter is used for the first set while a lower than enough value is used for the second set leading to strong enforcement of the first set of the constraint and partial fulfillment of the second set. Since the proper value of the penalty parameter to be used for the reliability constraints is not known a priori, an adaptive method is, therefore, proposed to find the proper value. The proposed model is used for operation of Dez reservoir in Iran and the results are presented and compared with those of a Genetic algorithm. Hydropower operation is considered over short, medium and long term periods to demonstrate the efficiency and effectiveness of proposed method for problems of different scales. The proposed model is shown to produce superior results to the GA with much reduced computational effort.

A new family of one-step integration methods is presented herein. A free parameter is used to control the numerical properties and it can be considered as an indicator of numerical dissipation for the high frequency modes. This family method can have unconditional stability, explicit formulation and desired numerical damping, which implies that the low frequency modes can be accurately integrated while the spurious growth of high frequency modes can be suppressed or even eliminated. In addition, a zero damping ratio can be achieved. Since the unconditional stability and explicit formulation are integrated together for the proposed family method, it can drastically reduce the computational efforts when compared to the traditional integration methods.

This paper presents three dimensional (3D) and two dimensional (2D) axisymmetric finite element analyses of a corner of a tailings dam. The analyses were performed to: (i) locate tension and/or low compression zones and to evaluate slope stability during sequential raising of the dam corner, and (ii) find whether the results of 2D axisymmetric analyses can be reliable for the dam corner. The corner is a potentially weak section of the dam where tension and/or low compression zones may develop. Development of such zones inside the dam corner can lead to cracks and initiation of internal erosion. The results of both the 3D and 2D axisymmetric analyses indicated that (i) tension and/or low compression zones were located in vicinity of surface of the dam corner mainly above the phreatic level, and (ii) the dam corner is stable up to the planned height if it is gradually strengthened with rockfill berms on the downstream side. The results of 2D axisymmetric analyses showed a fairly good agreement with those of 3D analyses. It is concluded that 2D axisymmetric analyses are appropriate for this dam corner. This implies that significant computational time can be saved by utilizing 2D analyses instead of 3D analyses.

The slip line or Stress Characteristics Method (SCM) is used to analyze the active lateral earth pressure in the axisymmetric case. In this paper, in addition to the retaining walls in the axisymmetric and plane strain conditions that studied in the past, a new model of the retaining wall in the axial symmetry is considered, which widely used in the design of grain silos, buildings and road constructions. The effects of the various parameters, including cohesion and friction angle of the soil, wall and backfill slopes and soil-wall interface adhesion and friction angle on the lateral earth pressure have been evaluated for all cases of the retaining walls. Based on the proposed theory, a computer code has been developed for the plane strain and axisymmetric cases. Also, finite element modelling is used to verify the results of the SCM. Comparison of the results indicated the accuracy of the proposed method. Furthermore, the effect of the plastic critical or tension crack depth has been evaluated and indicated that neglecting the plastic critical depth is not conservative.

Fluid infiltration into unsaturated soil is of vital significance from many perspectives. Mathematically, such transient infiltrations are described by Richard's equation; a nonlinear parabolic Partial Differential Equation (PDE) with limited analytical solutions in the literature. The current study uses separation of variables and Fourier series expansion techniques and presents new analytical solutions to the equation in one, two, and three dimensions subject to various boundary and initial conditions. Solutions for 1-D horizontal and vertical water infiltration are derived and compared to numerical finite difference method solutions, whereby both solutions are shown to coincide well with one another. Solutions to 2- and 3-D vertical water infiltration are derived for constant, no-flow, and sinusoidal boundary and initial conditions. Presented analytical solutions are such that both steady and unsteady solutions may be obtained from a single closed form solution. The solutions may be utilized to test numerical models that use different computational techniques