AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2019 | Volume:51 | Issue:3 |Papers Count:18

Real-time hybrid simulation (RTHS) is a kind of simulation where an experimental component of a structure is tested within a numerical model describing the remainder of the system. In this paper, a multi-story structure is partitioned into numerical and experimental substructures, and vibration behavior of the experimental stories are evaluated within the real-time simulation of the rest of the system. An electro-hydraulic actuator is employed to apply static and inertial forces to the experimental structure due to the forces calculated by the numerical substructure. An actuator dynamic is approximated by a pure time-delay, and the time-delay in the closed loop of simulation may causes inaccuracy results or even instability. Thus, the approach of delay differential equation (DDE) modelling is used to determine the dependence of the critical delay on the parameters of the system. The results demonstrate the influence of non-dimensional parameters and partitioning effects in stability of the hybrid simulation.

One of the most important components of water supply systems is the liquid storage tanks. During an earthquake, the interaction of fluid and structure in the liquid storage tanks and the sloshing phenomenon has a significant effect on the response values of the structure. Regarding the importance of the effects of near-fault earthquakes and their effect on seismic behavior and structures loads, in this study, the sloshing height and vibration of 2D concrete rectangular tanks under near-and far-field earthquakes was investigated using numerical methods. The effect of tank's dimensions, depth of water and ground motion characteristics on the maximum sloshing height was taken into account. Therefore, 9 tank models and 10 near-and far-field ground motion records were considered. The results indicated that the median values of maximum sloshing height in the near-field records are significantly higher than those related to far-field records. The average of increase of sloshing heights in tanks with lengths 20, 40 and 60 meters is 65, 77 and 100 percentage respectively. Also, with increase of fluid depth and tank width, the median of the maximum sloshing height increases and decreases respectively. In tanks, subjected to far-and near-field earthquakes, sloshing height had the highest correlation with Arias Intensity and PGV respectively. According to the results of this research, correction coefficients for the relations presented in the codes can be proposed to consider the effects of near-field earthquakes in calculating the maximum sloshing height.

Any investigative approach towards rock behavior will necessitate inherent deficiencies such as pores and cracks to be taken into consideration. One of the methodologies employed to study cracked rock is to consider an equivalent continuum as for the domain with defects which will lend flexibility to experimental and numerical schemes due to its seamless effects on the constitutive relationships, hence reducing computational costs as well as experimental restraints in the laboratory. A case in point in such approach is the crack tensor model which is based upon the idea to represent cracks’ size, orientation, and number density as one single entity through which proper geometric characterization of the in situ rock is carried out. Following the introduction of crack tensor concept and its application in the technical literature, the current work focuses on the determination of second rank crack tensor using P-wave velocity measurements on damaged granite. The benefit of such approach is emphasized via its role in boosting the degree of accuracy of the numerical analysis code developed in Matlab that implements different compliance matrices for four different stages of loading. The calculation results showed promising trends in agreement with those of the experimental data. Apparently, more experimental procedure is required to improve results’ accuracy in projects for which fulfilling more stringent regulatory requirements is a must.

Moisture damage in asphalt mixtures is defined as loss in strength and durability in present of water. Lack of relationship between distress mechanism in the laboratory and field, lack of measurement of effective properties of materials and their role, lack of modification solution, and other deficiencies of these methods have motivated researchers to present more appropriate experimental methods based on the properties of materials and asphalt mixtures, which could have a determining role in the occurrence of moisture-induced distress. Thus, the present research tries to present a model for predicting moisture sensitivity of asphalt mixtures based on thermodynamic parameters and characteristics of mix design of asphalt mixtures, which could predict the performance of an asphalt mixture against moisture based on the mentioned parameters. Results of this study demonstrated that using antistripping additives can generally improve the performance of asphalt mixtures against moisture; but, type and percent of these additives must be determined considering type of aggregate, type of asphalt binder, and properties of asphalt binder-aggregate mixture. Moreover, based on the presented statistical analyses, the results represented that the parameters of cohesion free energy and adhesion free energy of aggregate-asphalt binder in dry conditions, wettability of aggregate by asphalt binder, specific surface area of aggregates, and apparent film thickness of asphalt binder on the aggregate surface as well as free energy of system during antistripping event and permeability of asphalt mixture considerably influenced the occurrence of moisture damage directly and reversely, respectively.

Bridges are vital arteries of the transportation network of every country, whose collapse during a strong earthquake discontinues their performance in circumstances that they are required to provide emergency services and facilitate the evacuation of a damaged region. The implementation of base isolation bearings is one of the effective methods in the developed countries to retrofit bridges. In this study, stress-strain response of base column from five different models of a highway bridge seismically isolated with: (1) Single Friction Pendulum, (2) Triple Friction Pendulum, (3) High Damping Rubber and (4) Lead-Rubber seismic isolation bearing plus (5) a typical bridge model by assuming a rigid connection between the deck and bridge piers is calculated. Responses were calculated by performing nonlinear time history analyses by considering the main aspects of the simulation and by taking into account the nonlinear behavioral complexity of the base isolation bearing in OpenSees software. Results indicated that the frictional base isolations significantly reduce the stresses induced in the columns of the seismically isolated bridge in comparison with the typical bridge model, and improved the seismic performance of the bridge substantially. The percentage of reduction for triple frictional pendulum bearings reached 89%.

Project time and cost constraints are its key attributes. Earned Value Management (EVM) is a well-accepted methodology to combine time, cost and scope of the projects reported in terms of Cost Performance Index (CPI) and Schedule Performance Index (SPI). However, a deterministic EVM cannot consider uncertainties of time and cost of activities of project and the correlation structure amongst them which are inevitable and prevalent in any project. Therefore, an advanced probabilistic EVM is needed. In this study after defining the probability density functions of time and cost of every activity of project’ s scheduled plan and their correlation structure Monte Carlo Simulation (MCS) is used and in every iteration a time based cumulative cost of project, the so-called S-curve, is created and normalized to be the inputs for curve fitting into a four parameter Beta-S function. Hence for every iteration the corresponding values of these parameters can be calculated and the best performing marginal pdfs, be derived. In this paper in a novel approach copula functions are employed to bind together these marginal pdfs reliving the limitation of their belongingness to the same parametric group of marginal pdfs. The proposed model collates all propagated uncertainties of the project activities in a single probabilistic closed form function. This copula function can be used in estimation of the performance indices of a probabilistic EVM and more importantly fed into a Bayesian updating scheme to estimate the project future performance more accurately.

In this paper, the effect of parameters such as the distance, number of layers and cross-sectional area of FRP strips, the amount of longitudinal rebars, dimensions of beam and compressive strength of concrete on shear capacity of reinforced concrete beams with rectangular cross-section stiffened by FRP strips under symmetrical concentrated loads using the finite element method has been studied. The non-linear analysis of 101 reinforced beams has been performed for evaluation of the effect of the parameters on load capacity and mid-span deflection of the beams with and without strengthening. The samples are deivided into six groups, which ultimately have been compared and investigated for load capacity and displacement of the mid-span. Obtained results indicate that for a constant concrete compressive strength, increasing the width and the number of layers of FRP strips increases the load capacity by 26% and 23%, respectively, compared to the control beam. At same time, by increasing of these two parameters the increase of the load capacity decreases. By changing the layout of reinforcing strips with irregular intervals along the beam, the load capacity increase is about 6% to 35%. Also, the increase of the amount of longitudinal rebars from ∅ 10 to ∅ 14, increasing the compressive strength of the concrete from 30 MPa to 50 MPa, and increasing the cross-sectional area of the beam from 150 × 300 mm to 150 × 400 mm in unsitffened beams, increase the load capacity by 31%, 23% and 55%, respectively, and decrease the deflection of the mid-span.

The coastal structures such as wharves withstand severe operational conditions during their service life; hence, they are susceptible to damage and reduction in the stiffness of their elements. In this paper, the performance of a damage detection method based on power spectral density is numerically investigated on the dolphin platform of the oil wharf used for the unloading of crude oil to the refinery. This investigation is held numerically, and the damage is modeled as a percent reduction in stiffness of the elements. For this purpose, the finite-element model of the dolphin is made in the MATLAB software and the effect of surrounding water is considered as the added mass on the elements. To probe the performance of the method on the dolphin model, several assumed damage scenarios with different levels of damage in the structure, are considered. Furthermore, an approach for calculation of the spectral density of excitation using an approximate FRF is introduced. Results prove the success of the method in the identification of the parameters of a stiff coastal structure like a dolphin. Besides, the results from these investigations prove that the added mass significantly affects the damage detection results. The quality and accuracy of the numerical results prove the merits of damage detection by finite-element model updating in the frequency domain. The results of the present study urge the practical assessment of the performance of the method in the future.

Every year heavy rainfalls cause many slope failures. In these rainfalls, the groundwater table increases that cause in increasing of pore water pressure and reduction of slope stability. Using of horizontal drains is an effective and economic method to control the slope stability in this condition. The purpose of this study is to investigate the performance of horizontal drains in increasing slope stability. For this purpose, the SEEP/W and SLOPE/W (subgroups of Geo-Studio software) were implemented. Results showed that increasing in the length, thickness, and number of horizontal drains causes increasing in slope stability during the heavy rainfalls and keep the slope more stable. In addition, installation of drains in the down part of slope is more effective than in the middle or top part of the slope. Relative drain length equal to 0. 4 is proper for improving of slope stability. Increasing of drain thickness have more positive effect on slope stability than the drain length.

Localized singularities caused by changes in the stiffness or mass of the damaged region cannot be simply visible through smooth mode shape curves. However, the wavelet transform of input signal can identify the location of defects by sudden changes in the spatial variation of transformed response. The aim of this study is to present a new method for damage detection in a squarely damaged plate with element of reduced thickness with damage ratio 3% and to decrease the possible random noises that are come from different sources such as numerical solutions or physical situation. In this approach, the value of each point of mode shape data is subtracted from or is added with its symmetric point with respect to the plate’ s point of symmetry (point O). The obtained value is located at its first point, again. The result of this process is a symmetrical mode shape matrix of the damaged plate, which is utilized as the input signal function in wavelet analysis. The results demonstrated that using reconstructed modal data is superior to the original modal data and they provide a better crack indicator than the result of the DWT of the original mode shape data. The effects of crack location and sampling interval are examined. The simulated results show that this approach is more effective in damage detection of plate-like structures, as the method requires the knowledge of only the response of the damaged plate as a baseline for crack detection.

The highest part of chemical ions present in the seawater is related to the chloride ion. In this research, the effect of chloride curing condition on the properties of concrete containing zeolite as a mineral admixture and micro-nano bubble water is evaluated. Based on the experiments including X-ray diffraction, compressive strength, water absorption, chloride permeability and electrical resistance, it was determined that the addition of zeolite and micro-nano bubble water to the mixture improved the properties of concrete in the chloride conditions. Also results show that the chloride curing condition causes an improvement in the properties of concrete at the age of 28 days because of the formation of Friedel salt. With increasing age of concrete up to 90 days and decomposition of Friedel salt composition in samples, the process of improvement is reduced. The highest effects on improving the mechanical properties and durability of concrete at the age of 28 days is related to the sample containing 15% zeolite and 100% micro-nano buble water under chloride curing conditions. Improvement contents in the mentioned situation are 47, 78, 254, 84 and 49 percent corresponds to the compressive strength, tensile strength, electrical resistance, chloride permeability and water absorption test respectively.

Feldspar as a low-cost mineral adsorbent based on silica was used to removal a cationic dye, C. I. Basic red 14 (Brilliant red 4G), from aqueous solution. The adsorbent was characterized using scanning electron microscopy (SEM), X-ray Fluorescence (XRF) and Fourier Transform Infra-Red spectroscopy (FTIR). The effect of some parameters such as the amount of adsorbent, contact time, the initial concentration of dye, initial pH and electrolyte on dye removal was investigated. Results showed that dye removal increased by increasing pH; contact time and adsorbent dosage, whereas decreased by increasing the dye concentration. Also, the addition of electrolyte caused a negligible decreasing in dye removal. It took about 1 hour to equilibrium the feldspar with C. I. Basic red 14 and dye removal efficiency was 96%. So, feldspar is a suitable and powerful absorbent for removal of cationic dye from aqueous solutions. Equilibrium isotherms were analyzed by Langmuir, Freundlich, Temkin, Redlich-Peterson, and Dubinin– Radushkevich adsorption models and found that the experimental data were correlated reasonably well with Freundlich isotherm. The adsorption kinetics was studied by using pseudo-first-order, pseudo-second-order, and intra-particle diffusion models and realized the adsorption of C. I. Basic red 14 on feldspar followed the pseudo-second-order equation which indicates to chemical sorption.

Polyethylene pipes are widely used in pressurized water systems. In the design and interpretation of the ram-trapped signal for diagnostic purposes, viscoelastic behavior of polyethylene tubes should be taken into account. The aim of this study is to detect leakage, and experimental and theoretical comparison of pressure wave velocity and over pressure of transient flow in polyethylene pipes with different Reynolds number. To achieve the objectives of this paper, a physical model was developed in laboratory of the Faculty of Water Sciences Engineering of Shahid Chamran University of Ahwaz and developed two different models of control and a leakage system was and were conducted a number of water-hammer tests. The leakage accuracy in this model increased with increase of Reynolds number. The highest and the lowest percent of the relative error for computational and experimental leakage were estimated 48. 8% and 2. 02 through a leak hole of 5 mm for experiments with Reynolds numbers of 1282. 76 and 12973. 55, respectively. Also, this inaccurate study shows the relationship between the theory of compressive velocity and overpressure in the polyethylene transfer pipes, so that the compressive velocity obtained from theoretical relationships is less than its actual value, as well as the relative error of the overpressure in leakage experiments Increasing the Reynolds number increases between the amount of the laboratory and the theory.

Seismic loads may damage municipal solid waste landfills (MSWLF) through the relative movements within the waste, bottom lining system, cover system, foundation, and interfaces. The smooth synthetic materials might be placed beneath the structures to provide seismic protection by absorbing the imparted energy of earthquakes through the sliding mechanism. In the present study, experimental investigations were conducted in order to evaluate role of in-soil base isolation on seismic response of the Kahrizak MSW landfill. Shaking table tests were conducted on the MSW embankment isolated by semi-elliptic shaped liners and subjected to harmonic sinusoidal base excitations. Furthermore, the shaking table model was simulated by numerical analysis. The results of the isolated and non-isolated cases are compared in terms of permanent displacement and seismic response. Subsequently, the behavior of the numerical model was evaluated for different parameters. A reasonable agreement was found between the results of the physical model and the numerical model in prototype scale. The efficiency of in-soil isolation increases with increasing the amplitude of input motion. The results show that increasing the shear modulus reduces the amount of spectral amplification and relative displacement. It was also observed that as the age of the MSW increases, base isolation increases the displacement and crack width. Moreover, employing flat liner facilitates the movement of the ridge to the sides; and the concave liner prevents the wedge to move and, hence the quantity of settlement is reduced.

Graphene oxide nano-sheets were synthesized using modified Hummer’ s method and characterized using SEM, XRD, and FTIR analyses. Response surface methodology (RSM) was used to optimize the effects of the effective factors including pH (4-9), adsorbent dosage (0. 05-0. 4 g/L), initial dye concentration (50-400 mg/L), and temperature (10-40 C° ) in batch adsorption reactor. The adsorption capacity of graphene oxide and removal percentage of crystal violet in the optimum condition (pH of 7. 4, the adsorbent dosage of 0. 19 g/L, the initial concentration of 100 mg/L, and temperature of 30. 4 C° ) were predicted by the polynomial regression model to be 474 mg/g and 90%, respectively. Dye initial concentration and the adsorbent dosage with 51. 6 and 41. 7% respectively, showed the most percentage of contribution among the effective factors. Adsorption kinetic was investigated using pseudo-first order, pseudo-second order, and intraparticle diffusion kinetic models. Adsorption isotherm also was studied using Freundlich and Langmuir isotherm models. Results demonstrated the high correlation of adsorption kinetic and isotherm with pseudo-second order and Langmuir models respectively. In addition, the thermodynamic study indicated the endothermic and spontaneous nature of adsorption.

A majority of Iranian residential buildings have RC frame structures with intermediate ductility. Recent earthquakes have revealed major seismic deficiencies in these buildings, some of which led to catastrophic collapses and significant death tolls. Causes for the unsatisfactory performance include the absence of special seismic detailing of key structural elements, inadequate material and construction quality. Based on an extensive field investigation done by the authors on the short, mid-rise and high-rise Northern Iranian as-built structures having RC frames, in this study, reduced strength of concrete and also insufficient overlap length of column’ s longitudinal bars are considered as common structural deficiencies and then by considering probable uncertainties such as material and earthquake uncertainty, the seismic performance of considered buildings are developed via fragility curves based on probabilistic method. For generation of seismic fragility curves for as built and also retrofitted models, 3 dimensional analytical models analyzed 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 and the capacity is determined according to the HAZUS-MH limit states and finally the corresponding fragility curves for four damage states are developed for as built and retrofitted models. The results represent the effect of the story numbers, structural deficiency and implemented retrofit strategy on the seismic vulnerability of this subclass of structures.

Green buildings are consistant objects which consider environment issues and natural resources throughout the life cycle. The risk of a green construction project reduces the accuracy of the estimation of the projects objectives and reduces the efficiency of green building projects. Therefore, identification and prioritization of risks can play a significant role in the success of green construction projects. In this research, we present a comprehensive model of all criteria and indicators of the risks of green construction projects; we have made the final ranking of green building construction risk indicators so that we can reduce the risk of green projects at run-time. For this purpose, at the first step, the identification and screening of indicators from the viewpoint of experts in green construction projects is considered by using the Fuzzy Delphi technique and then, the new method is used to combine the results of the network analysis process and the DEMATEL technique in fuzzy conditions to rank and evaluate the causal relationships between the factors and ultimately final prioritizing green building risk indicators have been done in terms of the results of the initial steps using the fuzzy Analysis Network Process (FANP) and DEMATEL technoique. The results of the research show that the risks associated with poor quality of materials and inappropriate equipment are very important and the lack of scale for the cost of activities has the least importance.