Scientia Iranica
Volume:26 Issue: 2, Mar-Apr 2019

Binary Cement incorporating Supplementary Cementitious Material (SCM) is widely used in concrete to reduce the cement consumption in construction industry. Cement production is a major source for the emission of Green House Gases (GHG) and there is an increasing pressure to reduce its consumption to avoid further Global Warming and Climate changes etc.  In this research, Pulverised Fly Ash was used to partially replace cement in the concrete. Three levels of replacement of cement by PFA were selected and the specimens were cured under summer and winter environments. The strength development characteristics of the blended concrete were compared with the control mix without PFA.  The strength gain under winter curing condition was observed as slower.  At water cement ratio of 0.35, concrete with 30 % replacement of cement by PFA achieved high early age strength. PFA concrete gained more strength than the PC concrete after the age of 28 days. The 28 days compressive strengths of blended concrete for 30 % of cement replacement by PFA has been observed as nearly the same as that of control concrete mix.

One of the major problems in highway and railway bridges is the settlement of the bridge abutments, which its reduction has always been set as the research target. Two methods which have been widely used for controlling the settlement are either reinforcing the abutment subsoil with geogrid orconstructing the abutments on piles. This paper describes the application of a two-dimensional finite element method (FEM) by using Plaxis2D V8.5 for comparing the performance of these two methods. The effect of the geogrid normal stiffness, length and depth of reinforcement on the horizontal and vertical displacement of abutment is also investigated. Data from an instrumented bridge abutment has been used for the model verification. The reduction of the bridge abutment,the vertical settlement and the horizontal displacement by pile and geogrid have been analysed and compared.It is found that constructing the abutment on piles has a better performance in reducing the vertical settlement of the bridge abutment. However, lower lateral displacement can be obtained by using a geogrid with a higher normal stiffness. It is also found that, while the vertical settlement is not affected by the geogrid stiffness, the horizontal displacement of the abutment decreases with increasing the stiffness.

Shear behavior of reinforced concrete (RC) beams strengthened with fiber reinforced polymers (FRP) sheets is studied in this paper using modified compression field theory(MCFT). The beam is considered to be under the combined effects of shear force and bending moment. Equilibrium and compatibility equations, as well as stress-strain relationships are developed for an element in the strengthened beam. Due to the extensive computations, a computer program wasdeveloped to solve the governing equations. The accuracy of the presented method herewas verified by the experimental results of 84 strengthened RC beams reported in the literature. Comparison between the measured and predicted results shows that the method can predict the shear behavior of the beam throughout its entire range leading up to failure. The method can also incorporate the effect of debonding of the FRP sheets in the analysis. The results of a case study indicates that preventing thedebonding of theFRP sheets from the web of the beam adds significantly to  the shear capacity, and in certain cases changes the failure mode from brittle to ductile.

In an uncoupled analysis, blast loads can be evaluated by empirical models, and then applied to the structure in a separate response analysis. The literature includes a variety of empirical models. However, the potentials of these models may not be fully realized due to a wide variation that may exist in their outcomes, particularly at detonations with a relatively close standoff distances from the target. As such, the selection of an appropriate model should be made with special considerations. This paper investigates the efficiency of various empirical models in blast analysis of the RC-slabs that are subjected to near-field air-detonations. The blast loads resulted by the empirical models are employed in a set of nonlinear FEA-runs. Due to the proximity of detonations, the distribution of blast-overpressure across the concrete slab at any instant in time is nonuniform. A simplified approach that accounts for this nonuniform distribution has been developed and verified in this study. To examine the effectiveness of the empirical models, the FEA-results are compared with the observations made in a set of previous experimental studies. Based on this comparative study, the most effective empirical model is identified, and remarks are made on the performance of the other models.

In this paper, the Incompressible Smoothed Particle Hydrodynamics (ISPH) method is presented to simulate flood waves in uneven beds. The SPH method is a mesh free particle modeling approach that is capable of tracking the large deformation of free surfaces in an easy and accurate manner. Wave breaking is one of the phenomena that its free surface is complicated. Therefore, ISPH method is robust tool for the modeling of this kind of free surface. The basic equations are the incompressible mass conservation and Navier–Stokes equations that are solved using a two-step fractional method. In the first step, these equations are solved to compute velocity components by omitting the pressure term and in the absence of incompressible condition. In the second step, the continuity constraint is satisfied and the Poisson equation is solved to calculate pressure terms. In the present model, a new technique is applied to allocate density of the particles for the calculations. By employing this technique, ISPH method is stabled. The validation by comparison with laboratory data is conducted for bumpy channel with various boundary conditions. The numerical results showed good agreement with available experimental data. Also relative error is calculated for two numerical cases.

In this paper, an analytical solution for the axisymmetric interaction of a rigid disc inclusion embedded in bondedcontact with the surfaces of a penny-shaped crack and a transversely isotropic medium is investigated. By using amethod of potential functions and treating dual and triple integral equations, the mixed boundary value problem iswritten in the form of two coupled integral equations, which are amenable to numerical treatments. The axial stinessof the inclusion and the shearing stress intensity factor at the tip of the penny-shaped crack for dierent degrees ofmaterial anisotropy are illustrated graphically. Useful limiting cases such as a rigid disc inclusion in an uncrackedmedium and in a completely cracked solid are recovered

A normal way to dissipate energy of the dam released high velocity jets is to allow them to free-fall in to a plunge pool or impact a plane surface in case of dam site limitations. The water jets have an undisturbed core from nozzle outlet to a certain falling height, which has more impact force and less turbulent intensity than the developed part of the free jet. Experiments are conducted to determine core impact pressure coefficient of a vertical jet on smooth and rough plane surfaces. The experiment results for different jet diameters and falling heights showed considerable increase of the mean dynamic pressure coefficient with increase of the jet Froude number for both smooth surface and rough surface. A simple Froude based mathematical model is correlated for estimation of jet core impact force on the smooth and rough plane surfaces. In addition, a considerable increase of the jet core length was indicated with increase of the jet Froude number. Results also showed a strong correlation between turbulence intensity coefficient and the jet core length.

This paper reports the results of an experimental study where the axial capacity of fire-damaged specimens repaired by expansive cement concrete and CFRP wrap were investigated. Specimens were subjected to axial compressive loading and their resulting stress-strain curves were recorded. Since the flat sides of the square samples remained unconfined then the cross sections of the tested specimens largely remained unconfined. The FRP jacket was effective only along the two diagonals of the cross-section. Confinement is generally more effective in specimens with circular cross-section than those with square cross-section. The change in cross section for some of the specimens from square to circle was implemented. To modify the shape, expansive cement concrete has been utilized to fill the gap between the circular and the square cross sections. The test results indicated that heating up to 500 °C caused a severe decline in compressive strength and the elastic modulus of concrete.  Two layers of CFRP wrap around the concrete not only compensated the drop in compressive strength but furthermore it increased the strength beyond that of unheated specimen. However, the effect of wrapping alone on the stiffness and the elastic modulus is negligible. The heated square specimens that were first subjected to shape modification and then wrapped by CFRP sheet, experienced increase in the strength and the elastic modulus. Therefore, the stiffness and the compression strength of fire-damaged square concrete specimens could be compensated fully by the use of shape modification and CFRP wrapping of the cross section.

Shear failure of slender beams made of high strength concrete (HSC) is one of the most crucial failures in design of reinforced concrete members. The accuracy of the existing design codes for HSC unlike the normal strength concrete (NSC) beams seems to be limited in prediction of shear capacity. This paper proposes a new set of shear strength models for HSC slender beams without web reinforcement using conventional multiple linear regression, advanced machine learning methods of multivariate adaptive regression splines (MARS) and group method of data handling (GMDH) network. In order to achieve high-fidelity and robust regression models, this study employs a comprehensive database including 250 experimental tests. Various influencing parameters including the longitudinal steel ratio, shear span-to-depth ratio, compressive strength of concrete, size of the beam specimens, and size of coarse aggregate are considered. The results indicate that the MARS approach has the best estimation in terms of both accuracy and safety aspects in comparison with regression methods and GMDH approach. Moreover, the accuracy and safety of predictions of MARS model is also remarkably more than the most common design equations. Furthermore, the robustness of proposed models is confirmed through sensitivity and parametric analyses.

This study show the combination of computational fluid dynamics (CFD) and soft computing techniques to make viewpoint for two-phase flow modelling and accuracy evaluation of soft computing methods in the three-dimensional flow variables prediction in curved channels. Therefore, artificial neural network (ANN) and support vectors machines (SVM) models with CFD is designed to estimate velocity and flow depth variable in 60° sharp bend. Experimental results in 6 different flow discharges of 5, 7.8, 13.6, 19.1, 25.3 and 30.8 l/s to train and test, ANN and SVM models is used. The results of numerical models with experimental values are compared and the models accuracy is confirmed. The results evaluation show that all three models ANN, SVM and CFD perform well in flow velocity prediction, with correlation coefficient (R) of 0.952, o.806, and 0.680, and flow depth (R) of 0.999, 0.696, and 0.614 respectively. ANN model to predict both velocity and flow depth variables with mean absolute relative error (MARE) of 0.055 and 0.004 is the best model. Then SVM and CFD models with MARE of 0.069 and 0.089 in velocity prediction and in flow depth prediction CFD and SVM models with MARE of 0.007 and 0.011 are the best models, respectively.

Climate change can change the intensity-duration-frequency (IDF) curves. This research evaluates IDF curves changes of the Baghmalek climatic station in Iran's southwest. Developed integrated method extracts the IDF curves using of the Gumbel and log-Pearson III probability distributions and observed maximum annual precipitations. Durations of these precipitations are 15, 30, 45 minutes and 1,2,3,6 and 12 hours.    For this purpose, this method utilizes the recorded precipitation data of the Baghmalek climatic station in a 40-year period (1974-2013). Then mean square error method determines the probability distribution that has the best fitting with this data. The HadCM3 prepares precipitation data for a 30-year period (2021-2050) based on A1B, B1 and A2 scenarios. Also this method selects an optimum artificial neural network to extraction of maximum annual rainfall intensity for different durations and scenarios. Then selected network and the chosen probability distribution produce IDF curves for different return periods and scenarios. Produced IDF curves for different scenarios are compared to IDF curves of base time period. Because of increasing carbon dioxide and its greenhouse effects in these scenarios, rainfall intensity will increase for return periods less than 2.33 years while it will decrease for return periods more than 2.33 years.

Nowadays, the very low reliability of the project planning in certainty-based approaches, caused to use more intelligent methods for uncertainty management in construction projects. This systematic study aims to survey the methods which have been used to manage the uncertainties in time estimation of construction projects. A series of steps were undertaken during the review. The study was started with determining the purpose of the study, selecting appropriate keywords, and reducing the selected papers using some criteria. A deeper analysis was carried out on the final paper that meets the criteria for this review. The study is limited solely to papers referred in six top online databases. It aims to review how the papers have been distributed by a period of publishing and by country and the domains that these methods have been applied for. The result confirms that uncertainties which affect any project are based probability and possibility theories controlled by Risk Management and Fuzzy Logic. Finally, a hybrid method for uncertainty management in project scheduling is proposed. The result of the implementation of this method in the construction project of Iranian Gas Company shows that proposed method increases the accuracy of time estimation about 8 to 24 percent.

Evaluation of liquefaction is one of the most important issues in geotechnical engineering. Liquefaction prediction depends on many factors and the relationship between these factors is non-linear and complex. Different methods have been proposed by different authors for liquefaction prediction. These methods are mostly based on statistical approaches and neural network. In this paper a new approach based on Rough Set data mining procedure is presented for liquefaction prediction. The Rough set theory is a mathematical approach for analysis of imperfect knowledge or unclear description of objects. In this approach the decision rules are derived from conditional attributes in Rough Set analysis and the results are compared with actual field observations. The results of this study indicate that using this method can be helpful for liquefaction prediction and can reduce unnecessary costs in site investigation process.