AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2017 | Volume:49 | Issue:2 |Papers Count:19

In this study, the ductility reduction factor of Ordinary Concentrically Braced Frames (OCBFs) and special concentrically braced frames (SCBFs) which are braced concentrically in two end sides of frames, is evaluated. The results confirmed that, using SCBFs will reduce about 15 to 45 percent of total used material for one to 16 story frames respectively. In addition, for all of the 16 ordinary X-braced frames, which have 1 to 16 story height, calculated ductility reduction factor exceeds from ASCE7’s proposed one, except for 16 stories frame. For studied frames, which are braced in two end sides, using the X-bracing system, the results confirmed that ductility demand is achievable without any significant problem. In addition, results indicated that although the response modification factor which is proposed by Iranian seismic design code (2800 standard), is more logical than ASCE7’s one, for frames which are braced in the end sides, the response modification factor should be taken less than 5.5.

The first step in designing structures is choosing sufficient elements for the applied loads, including dead, live, wind and earthquake ones. Then, drifts of all stories are compared with allowable values and if required some structural elements are so resized to satisfy the drift criteria. The process of resizing is normally carried out by trial and error and relied mostly on engineering judgment. In other words, there are many approaches for satisfying the drift criteria, which some of them may lead to structures with poor seismic behavior. Moreover, based on Iranian Standard 2800, the designer is allowed to use analytical period of vibration in drift controlling process, instead on one calculated by the code proposed formula.In this study, a method is proposed to find the best elements for resizing and subsequently satisfying the drift controlling criteria in order to achieve a building with better seismic behavior. Furthermore, it is shown that applying the analytical period of vibration leads to structures with better seismic behavior. For the purposes, Endurance Time method is applied in which nonlinear behavior of slender special moment resisting frame steel structures and their damage indices are considered.

Many of changes in ground floor of buildings may result in elimination of braces. This phenomenan, which called “soft story”, decreases the stiffness of stories and leads to collapse of building under severe earthquakes. Study of last earthquakes such as Bam on December 26 ,2003 and Chichi-Thaiwan on September 20 ,1999 shows that many peaple missed their life because of soft stories created due to elimination of structural infills by changing residential buildings to commercial or architectural reasons. In this research, the soft story studied in short steel buildings with four stories by removing X-braces at first and second stories using non-linear static and dynamic analyses. After removing braces, the stiffness of soft story increased gradually by providing rigid connections and using moment resisting frame and the replacement of braces with equivalent moment frame (with different stiffnessess) studied. The seismic design parameters such as transient and inherent dissplacements, ductility and energy dissipation capacity calculated and compared in various diagrames. In addition, the sttiffness of X-braced and moment resisting frames calculated using classical relations of solid mechanics and discussed. According to obtained results, the replacement of X-braces by an equivalent moment frame in a building leads to excessive drifts and less energy dissipation capacity. In addition, the findings of this paper is coin with specification requirements to avoid soft stories in buildings by avoiding stories with stiffness of 70 percent relative to above story.

Reinforced concrete structures usually suffer from damage due to corrosion of the reinforced bars, which may be caused by carbonation and chloride ions ingress. So, predicting the onset of corrosion and the formation of cracks in the concrete cover is important. In this study experimental samples were carried out, cured and then exposed to the accelerated corrosion condition. The results were used to verify a numerical model. The effect of concrete properties such as compression strength, initial pressure and some other parameters investigated on concrete cracks. The results showed that the compressive strength and concrete cover are the main parameters at the start of cracking, and with increasing these two parameters the internal pressure, which is due to products, to start the cracking will increase.

The hydraulic jump in the stilling basin can be considered macroscopically as a time-averaged steady, abruptly varied flow characterized by a free surface discontinuity and the formation of strong vortex that generates macro turbulent fluctuations. This paper are discussed the characteristics of pressure fluctuations in spatial hydraulic jumps with sudden expansion stilling basin. The effects of the channel expansion ratio and inflow condition on the dimensionless standard deviation of pressure fluctuations (cp’) and extreme pressure fluctuations (Cp+, Cp-) in the hydraulic jump were examined. In this study many tests were conducted in a relatively large flume size of 0.8 meter wide and 12 meter length. data were presented for Froude numbers from 2.5 to 9.5 and channel expansions ratio (B1/B2) was 0.33, 0.5, 0.67 and 1. Pressure data were recorded by means of pressure transducers systems. A sampling frequency of 40 Hz was selected. The results show that the dimensionless standard deviation of pressure fluctuations and extreme pressure fluctuations of the hydraulic jump are dependent on the inflow Froude number and position from the toe of the jump. Fluctuating pressure at the position of about (10-30)Y1, can reach the maximal value. And indicates that the sudden expansion at the hydraulic jump decreases pressure fluctuations. The dimensionless standard deviation of pressure fluctuations (Cp’) decreases on the order 43%, 38% and 19% for expansions ratio 0.33, 0.5 and 0.7, respectively compared with classic jump.

This study considered artificial neural network (ANN), multi-linear regression (MLR), Genetic Programming (GP) and wavelet analysis and ANN combination (WANN) models for monthly water biological oxygen demand (BOD) in station Karaj Dam outlet and investigates the effects of data preprocessing on model performance using discrete wavelet. For this purpose, in the first proposed model, observed time series of BOD were decomposed into several sub-time series at different scales by discrete wavelet transform. Then these sub-time series were imposed as inputs to the ANN method. In the second proposed model, observed time series of BOD were decomposed at ten scales by wavelet analysis. Then, total effective time series BOD were imposed as inputs to the neural network model for prediction of BOD in one month ahead. Results showed that the wavelet neural network models performance was better in prediction rather than the neural network and multi-linear regression models. The wavelet analysis model produced reasonable predictions for the extreme values. This model dropped the mean absolute percentage error for the MLR, GP, ANN and the first hybrid models from 1.87, 0.91, 0.65 and 0.46 respectively, to 0.44 and increased the Nash-Sutcliffe model efficiency coefficient from 0.23, 0.53, 0.73 and 0.81 to 0.83..

In this study, ground water level fluctuations and nitrate concentrations of kabudarahang aquifer were investigated with application of time series models for modeling of ground water quantity and quality parameters. For data regarding the status of groundwater level and nitrate concentration fluctuations in project area, time series models were used to forecast the groundwater level and nitrate concentration. Residual error analysis, comparison of observed and calculated ground water levels and nitrate concentrations performed and finally a prediction model for ground water conditions in Kabudarahang aquifer developed. Predicted values were calibrated by the Box-Jenkins, Holt Winters and extrapolation methods. A residual error analysis, based upon calculated and observed groundwater level and nitrate concentrations performed as a model verification tool and finally the Box Jenkins models were evaluated through Portmanteau method and Akaike information criterion. The model verification results showed that the SARIMA model is the optimum algorithm to simulate seasonal input data variables. Model results showed that the groundwater level in this aquifer will endure a 5 meter decline in three upcoming years and indicated that the maximum nitrate concentration would reach 50 mg/l in Bahman and Shahrivar of 1390.

Application of aggregate coarse rockfill in hydraulic structures is increasing due to their special properties and is imperative due to its importance and their specific characteristics. Accurate investigation of the flow properties through coarse materials in order to determine hydraulic parameters is one of the most important necessities considering high application of such media in civil works. On the other hands, there is less works about transitional flow through coarse materials. In order to study the flow behavior through granular materials, a packed column test was built. Some experiments have done on three samples of rounded particles with average size of 10.348, 12.127 and 17.785 mm and seepage flow and upstream and downstream heads were recorded in a certain intervals. By using some calculating and depicting some graphs, their behaviors have evaluated. Using the relationship of flow velocity-hydraulic gradient, it was fund that such relationship is non-linear and this is a strong criteria confirming non-Darcy flow. The evaluating of results of this study by statistical indexes and its comparison by Ergun (1952), Kovacs (1981) and Sidiropoulou et al (2007) relationships showed that the relation of Sidiropoulou et al (2007) is more accurate than the other equations. The result of Reynolds number-friction factor curves showed that with increasing the grain size diameter, friction factor is decreased and Reynolds number is increased

At the most of executive project in Iran, using Tetrabromomethane (CBR+4) ion stabilizer solution is a chemical ion-exchange experiments. The necessity of present study is the investigation about the characteristics of strength behavior of clayey soils with various plasticity index (PI) stabilized by this method. The performance of stabilized soil samples by CBR+4 ion-exchange solution in wetting-drying and freeze-thaw cycles also been studied for the first time in this study. Firstly, in soil stabilization with CBR+4 solution the required amount of the stabilizer is determined, according to the amount of soils ion exchange, which is determined by a laboratory chemical test. Then, the samples are built in their optimum moisture content and maximum dry densities and after curing the samples for two weeks, dry samples are tested. Soils samples are also tested in saturated condition after two weeks curing time. Saturated samples showed more increase in strength compared to dry samples. Stabilized soil sample are also tested under 1 to 4 freeze-thaw and wetting-drying cycles. Tests results showed that using CBR+4 stabilizer increase bearing capacity of clayey soils. This increase is higher in soils with lower PI. Although freeze-thaw and wetting-drying cycles reduce soils bearing capacity, their strength are significantly more than the un-stabilized samples and is acceptable.

Tunnel Boring Machines (TBM) is among the most important machines for tunnel excavation purposes. Evaluation of the performance of these machines for excavation is of special importance due to the high cost of these machines. Prediction of the penetration rate is one of the indicators in evaluation of TBMs. There are various methods and equations for predicting the penetration rate, which are based on parameters related to the rock mass and specifications of the machine, and each of them has its own particular characteristics. Multivariable linear regressions, artificial neural networks, and adaptive neuro-fuzzy inference systems are among the highly efficient modeling and data pattern recognition methods. In this research, some equations have been proposed for predicting the penetration rate in Zagros I Tunnel by employing multivariable linear regression method and by considering the key parameters of the rock mass and the specifications of the TBM; the best equation was selected according to the results of statistical analysis. For verifying the validity of this equation, the penetration rate was calculated at certain parts of Ghomrood Tunnel. In comparison with the real values and results of other models, the outcomes of calculations indicated that predicted values for the penetration rate are of acceptable accuracy.

Doing deep excavation in urban limited spaces, stabilization of massive soil slopes and construction of large coastal walls require using the new methods and accurate calculation and analysis. So, in this study the finite element method (FEM) with ABAQUS software was used to modeling of the retaining wall. To evaluation of wall and soil behavior accurately, solid element and non-linear behavior material was used to demonstrate more exactly responses of retaining wall. Also the structure response calculated for different parameters in concrete and soil. More than 50 analysis were used in this study. Sensitive analysis in interaction parameters and material behavior was considered to calculate the maximum displacement at the top and shear stress at button. It is shown that density changes are more important in the static and dynamic response of structures, “and in dynamic analysis, the sensitivity parameter will increase about 30 percent more comparing static analysis”

In this research the mechanical properties of structural lightweight concrete including compressive, tensile and flexural strengths and energy absorption using five types of fibres (industrial and scrap steel, glass, polypropylene and straw) in the form of single type of fibre or combination of two or three types of fibres have been studied. At the first stage, two reference samples of lightweight concrete and normal concrete without fibres are produced. At the second stage, samples of lightweight concrete with single type of fibres with volume percentages of 0.1, 0.25, 0.4, and 0.5 are made. At the third stage, samples of lightweight concrete containing twin combination forms of fibres with volume percentages of (0.1, 0.4), (0.4, 0.1) and (0.25, 0.25) are produced. At last stage, samples of lightweight concrete with triad combination forms of fibres with volume percentages of (0.1, 0.1, 0.3), (0.1,0.3,0.1) and (0.3, 0.1, 0.1) are produced. Obtained results indicated that samples with combination of two types of fibres had the best behaviour compared to other samples. The highest compressive strength have been resulted from the combination of industrial steel and polypropylene fibres and the highest tensile and flexural strengths have been obtained from the combination of glass and polypropylene fibres. The highest energy absorption is related to the combination of industrial steel and glass fibres.

In this paper, designing variable stiffness semi-active tuned mass damper (SATMD) for mitigating the responses of nonlinear structures under earthquake excitation has been studied. Two semi-active control algorithms based on instantaneous optimal control and clipping control concept as well as modified balance control have been developed to determine the optimal stiffness of SATMD for nonlinear structures in each time step. For determining optimal parameters of semi-active control system including the weighting matrices in performance index of control algorithm as well as the maximum and minimum values of SATMD stiffness, an optimization problem for minimization of structure maximum response has been defined where genetic algorithm (GA) has been used for optimization. For numerical simulations, an eight-story nonlinear shear building with bilinear hysteresis behavior has been subjected to a white noise excitation and optimal SATMDs have been designed. The results showed that optimal variable stiffness SATMD using both control algorithms has been effective in suppressing the seismic responses of nonlinear structure. Also, variable stiffness SATMD shows better performance than TMD and variable damping SATMD in structural response controlling. Comparing the performance of the variable stiffness SATMD under testing earthquakes which were different from design record, showed that the efficiency of SATMD depends on the characteristics of excitation, hence design record needs to be chosen properly.

In order to decrease the destructions due to landslides, it’s important and unavoidable to recognize and to map the hazard zonations. For this, different mehods were utilized by researchers in other countries with specific conditions. In this paper, landslide inventory map has been prepared and then the effective parameters on the landslides in the study area have been investigated. Finally, some empirical methods such as Mora-Vahrson and Nilson methods with bivariate statistical and Artificial Neural Network (ANN) methods were selected by using comparison of various methods between original locations and this study area in Behesht Abad Dam reservoir. In consequence of landslide hazard zonation mapping by above mentioned methods, some relations including empirical Probability Factor (P), Landslide Index (Li) and Reciever Operating Characteristic (ROC) curves were used to evaluate the accuracy of each method. Finally, the results of ROC curve and calculation of Area Under ROC Curve (AUC) were based for evaluation of accuracy. Therefore, artificial neural network and statistical methods were selected to provide suitable maps in this area.

Re-generated silk fibroin (RSF) with various concentrations including 8, 10, 12.5 and 13% (w/w), was dissolved in N-methyl morpholine N-oxide (NMMO) to prepare spinning solutions. The effect of several coagulants such as methanol, ethanol and 1-propanol, and temperatures of spinning including 95, 110 and 120oC, on the wet spinnability of the silk fibroin solutions were investigated. Tenacity at break of undrawn fibers, which were produced by various concentrations and coagulants, were measured. Bead free fibers with high tenacity and elongation at break (1.6 cN/dtex and 34.25% respectively) were produced at concentration of 8% (w/w), temperature of 95oC and by presenting of methanol coagulant. Also by increasing of concentrations from 8% to 10, 12.5 and 13%, the tenacity was decreased to 0.81, 0.70 and 0.20 cN/dtex, respectively. Tenacity of fibers were obtained in 1-propanol (0.6 cN/dtex) was lower than those in ethanol and methanol coagulation bath, 0.8 and 1.6 cN/dtex, respectively. These results were shown that chemical structure type of coagulant strongly influenced the wet spinnability of undrawn regenerated silk fibers.

The friction of a pavement surface indicates safety of a pavement. Pavement friction properties depend on pavement surface’s micro-texture and macro-texture characteristics. Recently, considerable attention has been paid by researchers to find new methods and procedures for more accurate and quick measurement of the pavement skid resistance. Most of the proposed approaches in this regard have been in the range of non-contact methods, the use of laser and digital images. It has been found that image processing as a non-contact method with adequate precision and high speed can prove to be a promising and effective approach for further research on determining the pavement skid resistance. In this paper an intelligent system based on image processing was introduced which analyzes the texture of the pavement and presents a new index for pavement skid resistance by taking the effects of horizontal, vertical and diagonal components of its texture into consideration. By comparing the results of the proposed system and the corresponding British Pendulum Number (BPN) test results it can be said that, the proposed system through using the image processing technology and more accurate assessment of pavement textures is capable of better recognizing the pavement textures and can produce repeatable results associated with the pavement skid resistance.

Present study investigates an experimental performance of mud brick wall under static lateral load. The size of bricks was about 22×22×7 cm3 (face × bed × end). For wall specimens, two types mortar was used: a) non-reinforced mortar, b) reinforcement mortar. For reinforcement mortar many types such as: metal mesh (mesh size: 0.5 and 0.75 inches), polymeric mesh (mesh size: 10 and 25 mm) and palm fiber considered was used. First mechanical properties of each types of mortar have been determined. Then the 12 wall with dimensions of 120 × 120 × 22 cm3 are made with six different kinds of mortar. Walls are loaded under static lateral load in order to evaluate their cracks pattern, load capacities, deformability and energy absorption characteristics. Cracks in the specimens occurred between the first and the second row that caused the failure. The mortar was vulnerable part of conventional walls (unreinforced mortar). Ultimate strength of walls with mortar reinforced by polymer mesh (mesh size was 25 × 25 mm) increased the load and energy capacity to 83.04% and 158% respectively. The palm fibers increased the load carrying capacity about 82.14% and energy absorption capacity about 247%. Test result was shown that using palm fiber and polymer mesh with diameter of 25 mm in mortar can increase adobe wall performance.