Scientia Iranica
Volume:21 Issue: 5, 2014

In this paper, the dynamic characteristics of skewed bridges are explored analytically. Closed form solutions for translational and torsional periods of free vibration and mode shapes are given for slab-girder skewed bridges. Moreover, the seismic displacement of the deck of skewed bridges is calculated using the response spectrum method and its skew term is compared with the requirement of AASHTO. The eff ects of seismic force resisting elements, such as elastomeric bearings and end diaphragms are included. It is shown that the skew term in AASHTO''s equation can underestimate the seat width requirement for some bridges. A new skew term for the bridge seat width requirement is suggested.

Application of an elastoplastic-viscoplastic constitutive model for tunnel safety evaluation is presented in this paper. For achieving this purpose, in the first step, through FLAC code, the model parameters were identified for a section of Tehran Towheed tunnel (as a case study) by a back analysis process. In the second step, with definition of two safety parameters related to short term (time-independent) and long term (time-dependent) behaviors, the safety of tunnel was assessed. For short term behavior which is related to excavation phase of tunnel, the elastoplastic part plays the essential role, so the safety parameter was defined based on hardening variable of constitutive model. But for long term behavior, time-dependent deformation will be generated during time, thus evaluation of safety was done by comparison of current shear strain and a defined limit shear strain based on experimental data. The results of back analysis showed a good capacity of model in reproduction of tunnel behavior. Application of defined safety parameters on Towheed tunnel indicates that stability of tunnel is guaranteed during construction stages and long term situation.

Ward’s, hierarchical clustering method, is applied to classify the annual floods and identify the hydrologic homogeneous regions in Turkey. For this aim, the annual flood data obtained at the 117 gauging stations having data records of 31 years operated by the General Directorate of Electrical Power Resources Survey and Development Administration (EIE) throughout Turkey are considered. Discordancy and regional homogeneity measures are applied to test homogeneity of regions identified by Ward’s cluster method. Flood frequency analyses for seven sub-groups defined by Ward’s clustering method are carried out using variousfrequency distributionsbased on index flood and L-moments approaches. The best fit distributions for all sub-regions are identified based on L-moments goodness of fit statistic. The accuracy of results of quantile estimates are evaluated by using relative RMSE % and relative BIAS % through the use of Monte Carlo simulation.

Sluice gates are widely used for flow control in open channels. Flow under a gate is complicated with a rapidly varying free surface and dynamic pressure distribution. Due to this complexity most of the studies to date are based on physical models. In the present study the flow under sluice gates on a flat plate is modeled numerically. Owing to the capabilities of SPH model in simulating rapidly varied free surface flows, this lagrangian method was applied in the present study. The SPH model was further developed by introducing IXSPH and an innovative method was proposed to simulate the constant inflow discharge. The present model results for free surface profile, as well as velocity and pressure field indicate good agreement with experimental and existing Eulerian numerical results. In the present work, the contraction and discharge coefficients were also captured for different opening ratios and gate inclinations. This study shows the ability of the developed SPH model as a useful tool in designing hydraulic structure.

Considering the need to invest on road safety programs, an efficiency analysis on the implemented countermeasures is required. The system presented in this study is designed to evaluate the efficiency related to the measures annually implemented throughout 30 provinces of Iran in two years 2008 and 2009. The model calculates a relative inefficiency index for each province and in each year, using Data Envelopment Analysis (DEA) method. Each province in each year is defined as a decision making unit (DMU) in DEA analysis. The inefficiency index is defined as the proportion of weighted sum of road fatality risk indices to the weighted sum of road safety performance indicators. The inefficiency rate for each DMU must be minimized by either decreased fatality indices and/or increased safety measures to an optimal extent. Using a dual model of the main DEA model for each DMU, a target setting task can be conducted by identifying the benchmarks as the leading entities. Moreover, some discussions are provided for the results concerning the efficient units and two-year comparison analyses.

Discrete Least Squares Meshless (DLSM) method has been used for the solution of different problems ranging from solid to fluid mechanics problems. In DLSM method the locations of discretizationpoints are random. Therefore, the error of the initial solution is rather high.In this paper, an adaptive node moving refinement in DLSM method is presented using the Charged System Search (CSS) for optimum analysis of elasticity problems. The CSS algorithm is effectively utilized to obtain suitable locations of the nodes. The CSS is a multi-agent optimization technique based on some principles of physics and mechanics. Each agent, called a Charged Particle (CP), is a sphere with uniform charge density that can attract other CPs by considering the fitness of the CP.To demonstrate the effectiveness of the proposed method, some benchmark examples with available analytical solutions are used. The results show an excellent performance of the CSS for adaptive refinement in meshless method.

Not only should dams be evaluated for seismic shaking, but their capability to survive potential fault displacements in their foundations should also be assessed. Safety reviews of existing dams suggest the geological-seismic evaluations of some dam sites had failed to recognize the existence of possibly active faults. In this study, nonlinear seismic behavior of concrete gravity dams due to relative fault dislocation occurring in foundation has been investigated. Two types of fault movements including normal-slip and reverse-slip have been considered. These two types, combining with location of fault line respect to toe, middle, and heel of the dam base, angle of the fault, and water elevation in reservoir which result in 36 types of models, have been considered to study their behaviors. Results shows that each type of fault can cause to propagate specific crack pattern; Angle and location of fault beneath the dam are very effective on amount of damage induced; Water pressure of the reservoir can also have increasing or even decreasing effects on the crack propagation rate. Existence of foundation fault movements beneath concrete gravity dams, depending on the conditions of problem, can cause rapid crack propagations in the dam body, jeopardize the stability, and significantly change dam''s dynamic response.

Determination of site liquefaction potential and taking deterrent action can prevent a significant damage to structures. In this way, a probabilistic liquefaction assessment can develop potential flexibility and risk management decisions. Based on the advantage of probabilistic assessment, considerable research has been carried out in the past few years on liquefaction potential. In this research,the jointly distributed random variables method is used as an analytical method for probabilistic analysis and reliability assessment of liquefactionpotential based on cone penetration test results.The selected stochastic parameters are corrected CPT tip resistance and stress reduction factor, which are modeled using a truncated normal probability density function and the peak horizontal earthquake acceleration ratio and earthquake magnitude, which are considered to have a truncated exponential probability density function. The depth of water table and fines content are regarded as constant parameters. The results are compared with those of the Monte Carlo simulation. Comparison of the results and parametric analysis indicates very good performance of the proposed approach in assessment of reliability. A sensitivity analysis shows that themoment magnitudeis the most effective parameter in soil liquefaction potential.

Soils have an anisotropic response and changing the inclination (α) and magnitude of the major principal stress will affect the collapse potential and brittleness as well as the shear strength and shear stiffness. In this paper the effect of stress path with changing in intermediate principal stress on the dynamic behavior of Babolsar sand is studied. A series of undrained monotonic and cyclic tests on loose sand with induced anisotropy were conducted using automatic hollow cylinder apparatus. Special attention was paid to the significant role of the intermediate principal stress parameter (b) in the deformation behavior of sand during cyclic loading. Results show that at constant α, confining stress and fabric; variation ofb has significant effect on the strain amplitudes but it would not change contractive or dilative behavior of specimens. The variation of b has high effect on liquefaction resistance but has no effect on the mobilized friction angle at steady state. It is shown that confining stress has significant effect on soil response (the strain development, excess pore water pressure generation and shear modulus and damping ratio). Moreover by increasing the confining stress, the effect of b value on cyclic behavior will be more pronounced.

Silica fume as new supplementary cements have several effects on initial mechanical characteristics and long term improvement. In this paper, the impact resistance and mechanical properties of concrete mixed with silica fume are statistically investigated with selecting 288 specimens in three mix designs. Zero,7% and 14% of Portland cement by weight was replaced by silica fume in silica-fume mixtures. Twenty 100×100×100mm cubic specimens, twenty100×200mm cylindrical specimens, twenty 60×80×320mm specimens and thirty-six 150×64-mm discs were cast from each batch to prepare specimens for different test purposes. Cubic and cylindrical specimens were used to determine the compressive strength and prismatic specimens were tested to obtain rupturing tensile. Also, cylindrical cutting specimens were subjected to the drop-weight test following the ACI committee 544 to determine impact strength of mixed concretes. Experimental data on the mechanical properties of the different mixes indicated that silica fume improves mechanical properties and impact resistance while statistical analysis done based on these experimental tests showed the reduction the coefficient of variation values. In other words, adding silica fume improves statistical dispersion of data.

In this study, a new hybrid method based on Firefly Algorithm (FA) and Harmony Search (HS) techniques, is presented for solving the least-cost design problem of water distribution systems (WDS). This algorithm is designed to improve the performance of the FA as a recently developed meta-heuristic that mimics the natural behaviour of fireflies. The use of such a nature–inspired optimization method to solve the optimal design problem of WDS needs particular modifications to produce high quality solutions. Therefore, a modification is proposed to the movement stage of artificial fireflies and based on the HS strategy a memory is utilized to save a number of the best solutions. Another improvement in this algorithm contains the addition of pitch adjustment operation in the FA as a mutation operator.The presented method is applied to optimal design of some well-known benchmark problems taken from literature, and the results confirm its validity. In addition, a sensitivity analysis is performed on the parameters of the algorithm.

In this paper, the seismic response of anchored cylindrical steel tanks with various dimensional parameters has been investigated by endurance time method considering fluid-structure interaction e ects. Various response quantities, such as stresses and displacements, have been evaluated by subjecting tanks to specially designed intensifying accelerograms and their performance is judged based on their response at prede ned level(s) of dynamic excitation. It is shown that ET analysis can reliably predict the result of ground motion time history analysis in all seven tank models studied. In four of the tanks in which height of the shell and the level of fluid is the same, the variation of signi cant parameters with height to diameter ratio is discussed. The reliability of the ET method in predicting the response of models considering nonlinear material and geometric nonlinearity is also investigated using a limited number of models. In general, results by endurance time method, while entailing highly reduced computational demand, appear to be reasonably consistent with those from ground motions in anchored steel tanks analysis considering fluid-structure interaction.