Scientia Iranica
Volume:22 Issue: 1, 2015

In this paper, scour profiles downstream of adverse stilling basins due to the submerged jet issuing from a sluice gate, were investigated. Experiments were conducted in a wide range of sediment sizes, incoming flow Froude numbers, tailwater depths, length and slope of stilling basin. The results showed that the scour profiles at any bed slope are similar in shape. However, the longitude evolution of scour profiles and the volume of eroded materials were increasing in accordance with slope of basin. It was observed that the maximum depth of scour hole occur at the vicinity of side walls and slightly decrease towards the centerline. A polynomial equation was derived to describe the nondimensional scour profiles at different slopes. Based on experimental data, the scour characteristics have been correlated with the time of equilibrium stage by developing some empirical relationships. Finally, a power-law equation was derived and fully defined to include the dimensions of scour hole time scale and geometry of sluice gate.

The Endurance Time (ET) method is a time-history based dynamic pushover procedure. In this method, the structures are subjected to gradually intensifying acceleration called an acceleration function. Then, their performances are assessed from linear to collapse level based on the interval time through which they can satisfy the required objectives. ET Acceleration Functions (ETAFs) are calibrated upon actual earthquake spectra compatible with the Iranian National Building Code (standard no. 2800). In this code, there is no distinction between far and near fault regions. ETAFs scale based spectrum increases uniformly at all periods as the time passes which is why this uniform increment is not desirable in near fault earthquakes. As the rupture propagation is oriented towards a site, near fault earthquakes have further spectral acceleration in the period over 0.6 sec compared to far fault earthquakes. The shape of the spectrum becomes richer over long periods as its level increases. In this research, ETAFs are presented for near fault target spectra, provided by Abrahamson-Silva attenuation relations. These relations have been modi ed by Somerville near fault correction coecients. According to the results obtained in this research, while the new acceleration function can model directivity eff ects at higher periods, it also satis es endurance time concepts.

Urmia Lake, the second largest hyper-saline lake in the world, has experienced a significant drop in water level during the last decade. This study was designed to examine the water quality of Urmia Lake and to characterize the spatial heterogeneity and temporal changes of the physico-chemical parameters between October 2009 and July 2010. Two spatial interpolation methods, Inverse Distance Weighting (IDW) and Ordinary Kriging (OK), were used and compared with each other to derive the spatial distribution of ionic constituents as well as TDS and density along the lake. Results showed that the main dominant cations and anions in Urmia Lake were Na+, Mg++, K+, Ca++, Cl-, SO4--, and HCO3-, respectively. Although water quality of the lake is homogeneous with depth, it differs between the northern and southern parts. Water quality also varies seasonally, determined by river inflows and the lake bathymetry. Moreover, with the present salinity level, salt precipitation is likely in Urmia Lake and is becoming one of the principal factors determining the distribution of solutes within the lake. This study shows that the combined use of temporal and spatial water quality data improves our understanding of complex, large aquatic systems like Urmia Lake.

In this paper, the recently developed meta-heuristic algorithm, named Ray Optimization (RO), was applied to optimize the thickness of granular layers in railwaytracks. RO is a multi-agent algorithm, each agent of which is modeled as a ray of light that moves in the search space in order to nd global or near-global optimum solutions. To utilize RO, considering structural and serviceability constraints, rst, hypothetical values of three thicknesses were assigned to the layers. Then, stresses under the sleeper and on the subgrade layer were compared with the allowable values. The total minimum thickness of the layers was also compared with possible minimum thickness (serviceability constraint) and then minimum thickness values were selected. Optimization results showed that the moment of inertia of the rail had no signi cant impact on the minimum total thickness of the ballast and sub-ballast layers. On the other hand, train speed and axle load were the parameters that had a considerable e ect on the minimum total thickness of granular layers in the railway track.

Many researchers have studied building pounding to calculate the dissipated energy and the impact force between two buildings during earthquake. In this paper, a new equation is proposed to measure the impact force and energy dissipation. The results based on the proposed equation are compared with results of the available equations. Using a suggested link element, a new formula is presented to calculate the impact force and energy dissipation. In order to evaluate the results of dissipated energy, a new relation between CR and impact velocity is also suggested. Since there is a need to have a reference curve to select impact velocity based on coefficient of restitution, several impact velocities and CRs were evaluated. By using the latter curve, results could be evaluated. A new equation of motion is assumed to select the best impact velocity and coefficient of restitution. Finally, based on coefficient of restitution and by using a steady-state response of single degree of freedom system due to the external force, a new equation of motion is suggested to calculate impact damping ratio.

It is imperative that any soil improvement technique can considerably affect the soil media mechanical behavior. However, considering the recent researches, it can be concluded that a combined study on the effect of cement treatment on soil-geotextile interfacial shear strength parameters has almost been neglected. Thus, the main objective of this study is to fill this research gap with the main focus on a selected site in Shiraz city, Iran. In this regard, shear strength parameters of untreated and cement treated soil samples have been acquired by traditional and modified direct shear tests apparatuses. The results indicate that at high cement contents, the soil-geotextile interfacial shear strength increases with an observed behavior similar to over consolidated soils. While up to 1% of cement treatment did not improve the properties, adding 5% and 10% of cement increased both friction angle and cohesion of the soil considerably. Complementary microscopic evaluation of the interface indicated that the interfacial soil-geotextile shear strength is highly dependent upon the soil particles size distribution and specially its fines content. Finally, the numerical modeling of an illustrative reinforced soil structure revealed that knowing the state of stress is a prerequisite to any selection of the soil improvement zone.

In this study, improvement of granular pumice soils strength by injection method in Nevşehir City (Turkey) was investigated. In the first phase of the study, the geotechnical properties of granular pumice soils were investigated. The specific density, dry unit weight and water absorption value increased with the decrease of grain size. Thus, it can be seen that the bearing capacity of pumice varies depending on the grain size. In the second level, changes in strength of unconfined compression of injected pumice samples were analysed. The samples taken from the field were prepared to 35, 65 and 85 % density, relatively. Pressure of 100 kPa and water/cement ratio of 1.0 was applied to this test samples and the samples were allowed to cure for a period of 7 and 28 days. The results of the study showed that injected pumice soil reached its maximum strength value with 35% relative density and reached its minimum value with 85% relative density. At the end of 28 days curing period, injected pumice soils prepared with 85% relative density have an equivalent strength to C8 concrete class and grouted pumice soils prepared with 35% relative density have an equivalent strength to C12 concrete class.

Developing the concept of performance based analysis and design has made the nonlinear dynamic analysis an efficient method for quantification of the seismic response of structures. Generally, this analysis is done by utilizing accelerograms which are ground motions obtained from earthquakes. This research is focused on assessing the seismic structural response of a comprehensive set of reinforced concrete moment resisting frames under excitation of real accelerograms and ground motions which are spectrally matched to a target spectrum. Matching process is conducted in the time domain and ASCE 7-05 spectrum is used as the target spectrum. Comparisons are provided for a number of ground motion parameters and the effect of spectrum matching has been investigated. Additionally, variation of structural response and the degree of compatibility and conservation of real and spectrally matched ground motions has extensively discussed. It is shown that spectrum compatibilization effectively decreases the variation of structural response. However, the measure of observed bias is thoroughly depends on the height of the structure. Finally, fragility curves of structural performance are provided and it is indicated that considering modeling uncertainties result in obtaining a fragility curve with reasonable resemblance to that obtained from real ground motions.

The aim of this article is twofold: (1) to provide more insight into the pattern of changes in modal parameters, including natural frequencies and mode shapes, of beams and girders resulting from the increasing of damage level and (2) verification of numerical modelling of the problem using data from experiments on an Aluminum box beam. To this end, first an impact hammer test has been conducted on the 2.6 meter long single span aluminum beam while a progressive damage has been applied at several stages. The modal parameters of the undamaged and damaged beam at different intensities have been extracted and the trend of their changes with respect to the increase in damage level has been studied. Then this process has been simulated numerically by Dynamic Finite Elements Method (DFEM) and the modal parameters have been extracted from numerical simulation. Finally the similarity between the experimental and numerical results has been investigated. The results show that at low levels of damage the modal parameters change very slightly, especially when just a part of the flange has been damaged, but when the damage has been extended to penetrate the beam web, the modal parameters have shown considerable sensitivity to the damage. Also the sensitivity of the different modes to damage has not been the same though relatively good agreement has been observed between the trend of changes in the modal parameters obtained from experimental and numerical studies, except for a number of modal parameters at very extensive damage level.

Low temperature cracking is one of the main distresses observed in pavements made of hot mix asphalt mixtures. As a material property, the fracture toughness of asphalt pavements is a fundamental parameter for estimating the load bearing capacity and resistance of cracked pavements against crack growth. In this paper, the fracture toughness (KIc) of different andvarious compositions of asphalt mixtures is obtained experimentally and the effects of asphalt characteristic specifications and its composition are investigated on the value of KIc. Several asphalt mixtures were prepared with three aggregate sizes, two aggregate types (limestone and siliceous), different air void percentages ranging from 3.5 to 8% and two binders (60/70 and 85/100). Other similar works have only studied the influence of limited characteristic parameters on the low temperature fracture resistance of asphalt mixtures. Several semi-circular bend (SCB) specimens subjected to three point bend loading were manufactured with different compositions and then were tested at -15oC. The experimental results showed the noticeable influence of characteristic specifications of asphalt mixtures on the value of KIc. Generally, the value of KIc decreases for those mixtures containing smaller size of aggregates made of siliceous with higher percentages of air voids and softer binder types.

Seismic fragility analysis is one of the main steps of consequence based earthquake engineering process. Accurate uncertainties modeling involved in this methodology, affects the final results of seismic fragility analysis and hence assessment of decision variables which are the final products of performance-based seismic analysis. One aspect of such efforts is to incorporate the sources of uncertainties associated with various factors controlling seismic loads on the buildings as well as structural responses to such excitations. Probabilistic approach are usually used to model quantitative sources of such uncertainties, however, there are other factors with descriptive nature which probabilistic approach may not well incorporate them. In this paper a fuzzy randomness approach is used to model epistemic uncertainties as an alternative to the conventional probabilistic method. The approach is used to model those uncertainties which have not been addressed by the others, in particular the definition of the collapse limit state. To illustrate the efficiency of the proposed approach, fragility curves for a sample moment-resisting steel frame are developed.The results demonstrate the superiority of fuzzy solution in comparison with excising probabilistic methods to incorporate epistemic uncertainty in view of much less computational effort.

Shear wall has been widely used in RC structures due to its high initial stiffness and lateral load capacity. Hence, the behavior and effectiveness of retrofitting technique on shear wall are needed to be investigated widely. In this paper, a numerical analysis was performed using LS-DYNA finite element program to predict the behavior of squat RC shear wall strengthened by fiber reinforced polymer in flexure. The strengthening scheme was conducted by externally bonding vertical layers of FRP on each side of the wall and anchoring them at the wall base with a structural steel angle bolted to the support. Numerical results were validated against experimental data. Then, influence of number of FRP layers, anchorage system, percentage of horizontal web reinforcement, percentage of vertical web reinforcement and percentage of vertical reinforcement in the boundary element were investigated.The results showed that the scheme can significantly improve the behavior of the RC shear wall. In addition, the behavior of strengthened wall and strengthening scheme strongly depend on the amount of web reinforcement which can also change the failure mode.

Standard Penetration Test (SPT) is one of the most effective tests for quick and inexpensive evaluation of the mechanical properties of soil layers. Numerous studies have been conducted to evaluate correlations between SPT blow counts (NSPT) and the soil properties such as friction angle (). In this paper, the relation between and in situ parameters of soil including NSPT, effective stress and fine content is investigated for granular soils. In order to demonstrate the relevancy of and corrected SPT blow count (N60), a new polynomial model based on Group Method of Data Handling (GMDH) type neural networks (NN) was used based on a 195 data sets including three soil parameters. That has been recorded after two major earthquakes in Turkey and Taiwan in 1999. This study addresses the question of whether GMDH-type NN is capable to estimate based on specified variables. Results confirm that GMDH-type NN Provide an effective way to recognize data pattern and predict performance over granular soils accurately. Finally, the effect of fine content and effective overburden stress on the correlation of N60 and has been studied by sensitivity analysis.