Civil Engineering Infrastructures Journal
Year:2010 | Volume:44 | Issue:2|Papers Count:15

In this paper, seepage analysis in isotropic environment is presented by discrete singular convolution (DSC) method. This method has been used for solving numerical problems since 1999. The theoretical basis of the method is distribution and wavelet theory. DSC exhibits accuracy for integration of global methods and flexibility for handling complex geometries and boundary conditions of local methods. At first, a simple case governed by Laplace equation and regularized Shannon’s kernel is considered to show the accuracy and efficiency of DSC method through L? and L2 errors. Seepage under concrete dam with or without sheet-pile is then solved through two different case studies. The results of this method against finite difference results are considered. The results show that this method is more accurate than finite difference method with reception of more operation value and optimization of R parameter.

Analysis of flow through rockfill materials is usually carried out by solving the differential equation which is a combination of nonlinear [i=mvn] and continuity equations. However, solving this differential equation either by means of finite difference method or similar procedures is relatively time consuming, and with uncertainty involved in water surface profile this becomes even more difficult. To analyze flow through rockfill materials an alternative method which is based on gradually varied flow theory may be applied that is comparatively simpler and less time consuming. To apply this alternative method it is necessary to examine the validity of assumptions on which gradually varied flow method are based. Moreover, the involved parameters in gradually varied flow equation should be reverted to porous media condition. In this research by conducting a vast number of experiments on various types of materials the acceptability of assumptions of gradually varied flow method for analysis of flow through coarse porous media is investigated and the effect of physical characters of porous medium such as void ratio, uniformity coefficient Cu, gradation coefficient Cc and viscosity of fluid as well as certain features of flow such as velocity and hydraulic gradient are also examined. Findings indicate that: 1). by accepting some degrees of discrepancies, one may use the gradually varied flow method for analysis of flow through coarse porous media. 2). the permeability parameters of coarse porous media may be successfully related to the physical characters of granular materials. 3). A Comparison between observed and computed flow profiles through media indicates accuracy and applicability of equations that are derived by authors of this paper.

Dynamic effects of high speed trains on railway bridges have been analyzed in many research works. Two major approaches have been used widely: in the first approach represented by a constant load that crosses the bridges and thus dynamic properties of the vehicle itself are ignored. There are also more complex methods that incorporate dynamic properties of both the structure and the vehicle. In these models primary and secondary suspension systems the bogie and the wheels are incorporated into the model by their individual & commercial ad mechanical properties. In this paper, two and three dimensional finite element models of a high speed trains crossing bridges susceptible to resonance effects are developed. In order to model dynamic interaction of the vehicle and the bridge, differential equation of second order is solved for both the vehicle and the bridge. The equating differential equations of the 2 systems are coupled by forces exerted on the vehicle and on the structure in rail wheel contacts. An explicit time advancement scheme is used to drive the model in time. It was necessary to regenerate reprehensive matrixes of the system in each time step, resulting it considerable computational cost.Using the developed numerical model, a parametric study is done, revealing importance of damping and stiffness of primary suspension system, damping and stiffness of secondary suspension systems, damping and stiffness of ballast, interaction effects of vehicle and bridge simultaneously on dynamic behavior of bridge-vehicle system for high speed trains. The range of parameters for which a full dynamic model of the vehicle would be necessary is derived on the parametric study.

The cyclic behavior of saturated sand is studied in this paper using Firouzkooh sand. In order to evaluate the effect of induced anisotropy total number of 30 cyclic triaxial tests were programmed such that in addition to the occurrence of different types of liquefaction, investigation of the anisotropy effect after consolidation and stress reversal could be studied. Induced anisotropy extent is analysed by its effect on the liquefaction potential using Cyclic Stress method. The results show that the sand exhibits much more softening behavior in extensional mode which shows the importance of this phenomenon in the liquefaction susceptibility assessment of saturated sands. Finally, the reversal coeffitient index (rc) is introduced in this paper which indicates that in addition to anisotropy, the deviator stress reversal affects the soil behavior.

The main goal of this study is to increase the software capabilities of Iran towards the development of a tsunami warning system for its southern coast bordering the Indian Ocean. The devastating tsunami of 26 December 2004 in the Indian Ocean region emphasized the necessity for development of tsunami warning systems for the world’s vulnerable coastlines, especially for those neighboring the Indian Ocean. Studies showed that there are two main tsunamigenic zones in the Indian Ocean region, namely the Sumatra subduction zone in the east and the Makran subduction zone at the northwest of this ocean. The Makran subduction zone is located offshore Iran and Pakistan and produced some destructive tsunamis in the past. The most recent tsunami in the Makran region occurred on 28 November 1945 which claimed more than 4000 lives along the coasts of Iran, Pakistan, Oman and India. As the southern coast of Iran is at risk of tsunami from the Makran subduction zone, Iran is committed to work towards the development of a tsunami warning system, and to cooperate with the countries in the region in this field. All activities towards the development of a tsunami warning system can be classified into two categories: 1) hardwares like tsunameters, tide gauges, seismic networks, and etc., and 2) softwares. Numerical modeling of tsunami is among the second group and is a vital part of any tsunami warning system. Here, we discuss the modeling of tsunami generation and propagation. At first, the algorithm for tsunami generation modeling is presented and then, the generation phase of a possible tsunami in the region was modeled. The results of generation modeling were compared with international experiences. In the next section, the propagation of tsunami was modeled using a well-validated international numerical model for long waves. Results of the tsunami generation modeling showed that in the case of an earthquake with a moment magnitude of 8, the maximum vertical uplift of the seafloor will be about 1.5 m, and an area with the dimensions of 150 and 250 km will be deformed due to the earthquake. Tsunami propagation modeling showed that the first tsunami waves will hit the nearest coastline within 15-20 min after the earthquake. The maximum tsunami wave height was estimated about 3 m. It is showed that how the results of the numerical modeling of tsunami can help to develop a tsunami warning system. Our preliminary investigation shows that at least 891 case-scenarios should be simulated to develop the tsunami warning system in the Makran region.

One of the most dangerous threats which embankment dams face with is hydraulic fracture. This phenomenon usually happens during first water impounding when the water pressure increases instantly in dam’s core. There are different methods to study hydraulic fracturing in embankment dams. In this paper Hyttejuvet Dam, a rock fill dam in Norway, which has been damaged by hydraulic fracture, is selected to evaluate the efficiency of these methods. Behavior of the dam during construction and first water impounding is modeled using finite element method. Afterwards using different methods, hydraulic fracturing is investigated for the Hyttejuvet Dam. In the next step using relations which correctly predicted fracturing in Hyttejuvet dam, the risk of this phenomenon is studied for Galabar Dam in Zanjan Province, Iran. Therefore coupled pore fluid-displacement analysis has been conducted for the dam during construction and first water impounding stage. These investigations showed that hydraulic fracture in the Hyttejuvet dam is correctly predicted by Komakpanah and Ghambari relations. Also hydraulic fracturing of Glabar Dam is judged unlikely.

In this paper, acceptance criteria of steel building code, comprehensive and quick evaluation procedures for X-bracing, are compared to each other parametrically and numerically. For this purpose, it is assumed first that the sample building is designed to meet steel building code and then by introducing transform parameters and using stress ratio of the designed components, acceptance of the designed building for life safety performance level is investigated. X-bracing acceptance criteria are studied using the new method and a list of differences for 2, 4, 6 & 8 story buildings is prepared in details. Results show that almost 5% of X-braced samples designed based on steel building code are rejected by comprehensive and quick seismic evaluation. On the other hand, some rejected components based on steel building code, meet comprehensive and quick evaluation procedures. Furthermore, by using a similar method and assuming that building components meet quick evaluation, their acceptance possibility by comprehensive evaluation is investigated. Based on acquired results, almost 50% of X-braces meeting quick evaluation, are rejected by comprehensive evaluation. In contrast, some rejected samples by quick evaluation meet comprehensive evaluation procedure.

Bearing Capacity of concave slopes is such a three-dimensional problem that two-dimensional assumptions do not result in satisfactory and acceptable results. Presented in this article is an algorithm to calculate the bearing capacity of foundations located on such slopes based on the upper bound theorem of the limit analysis approach.Limit analysis method is based on the extensions of maximum work principle derived by Hill, and was given in the form of theorems by Drucker, Prager and Greenberg. Using this approach, the true solution from a lower bound to an upper bound would be bracketed. Applicability of this theorem requires that the soil’s behavior be perfectly plastic and the deformation be governed by the normality rule. Considering the theorem of kinematic approach (upper-bound), the rate of work done by traction and body forces would be less than or equal to the energy dissipation rate in any assumed kinematically admissible failure mechanism. In this algorithm, initially the collapse mechanism is assumed as a set of five or six-face rigid blocks slipping on each other with enrgy dissipation taking place along planar velocity discontinuities. and then, during an optimizing process the minimum result would be considered as the ultimate load of the slope. This approach can be considered as an extension of the procedure proposed by Farzaneh and Askari in 1999. The numerical results indicate that the bearing capacity of a shallow foundation on concave slope is more than that of the same foundation on linear slope and also fewer is the ratio of slope radius to its height, more would be the bearing capacity of the foundation located on it. In addition, unloaded slopes are more stable when they are concave comparing with linear slopes. In bearing capacity, the curvature effect in concave slopes is more considerable for frictional soils than cohesive ones. The results are presented in the form of applicable charts to evaluate the bearing capacity of a foundation located on a concave slope.

The wind pressure is one of the important loads on cooling towers which can be computed via numerical solution of the wind flow. In this paper, the effects of turbulent modeling on accurate computations of wind pressure on a cooling tower with base structure are investigated. For this propose, the results of a finite element flow solver using various commonly used turbulence models are compared with the reported laboratory measurements on a small scale physical. Having chosen the most suitable turbulence model, the effect of considering the geometrical features of the base structures supporting the louvers on formation of pressure fields over the external surface of a cooling tower in actual scale (designed for the KAZERUN combined cycle power plant) is investigated. The computed results of this case with and without base attachments are compared with the wind loads which are suggested by the VGB guidelines. The comparison of the results shows that, the pressure distribution trend (particularly in the rear side) slightly differs for various elevations. Furthermore, considering the effects of base structures of the cooling towers ends up with computed pressure distribution different from the pressure distribution suggested VGB guidelines, particularly in lower parts of the tower.

In this work, with the consideration of difficulties associated with the fabrication of boxed columns with internal continuity plates at the position of the beam to column connections, the behavior of connections with peripheral plates has been investigated with the aid of the finite element method. The following types of connections and suggested details have been studied: Model 1) beam to boxed column connection without any continuity plate, with direct welding to the column? Model 2) as above, with the column in-filled with concrete? Model 3) as the first model with added triangular horizontal plates to form a peripheral diaphragm in collaboration with the flanges of the beams? Model 4) same as the model 3 without welding at the juncture of the added plate to the corner of the column in order to reduce stress concentration? Model 5) same as the model 3 with the column in-filled with concrete? Model 6) same as the above with reduced weld at corners? Model 7) with the use of internal continuity plates? Model 8) same as the model 7 with the column in-filled with concrete? Model 9) same as the model 7 with beams of reduced flange sections (dog bone flanges), and Model 10) same as the model 3 with reduced flange sections (dog bone flanges). A comparison of the results indicates that the connections with the peripheral diaphragm plates, as suggested here, represent a desirable behavior/performance in terms of both strength and ductility. An increased ductility and reduced stress concentration may be achieved in the case of the use of the dog bone connections together with the peripheral triangular plates. In-¬filled concrete will also help to reduce the column plate deformations and increase the moment transfer capabilities of the beam to boxed column connections.

Prediction of scour due to outflows from hydraulic structures is an important field in hydraulic engineering. There have been many studies concerning this subject which have invocated field analyses or laboratory experiments. As scouring is a complex process and many parameters affect it, there is not any equation that contain all parameters and limited for predicting scour hole dimensions. One of an important parameter that affect the scour hole dimensions is sediment gradation. In the previous researches ,the sediment non-uniformity effects on the scour hole dimensions due to free falling jets ,did not study completely. In this paper the effect of this parameter is studied. The experiments were performed in the hydraulic laboratory of Tarbiat Modares University. The results show that by using d90 instead of d50 in the densimetric Froude number as a sediment size characteristic better correlation between the densimetric Froude number and scour hole dimensions can be obtained. The previous research data along the data that was obtained in this research were used for checking the accuracy of the previous equations and presenting new equations for predicting the scour hole dimensions. By using the Frd90 and omitting the (d50/Hc) and sediment non-uniformity coefficient, the accuracy of the equations do not changed significantly. The results show that the new equation predict the scour hole dimensions in the field more accurately in compare to the previous equations.

Spur dike is a hydraulic structure used for protection of river banks. In the past few decades, the use of spur dikes for stability of the outer banks of rivers has attracted the attention of hydraulic engineers. Setting spur dikes in the flow’s direction leads to local scour around the spur dike and changes the topography of the bed. This study experimentally measures the flow field and scour around T-shaped spur dike install in 90 degree bend. The experiments were carried out in a channel with a 90 degrees bend and with a mild curvature. Uniform sediments having an average diameter of 1.28mm were used under clear water condition. The three-dimensional Acoustic Doppler Velocimeter (ADV) and point gage were used for measuring the flow field and bed topography. For this purpose, scour test was done at the beginning of the experiment and the topography of the bed with the scour hole around the sour dike installed at the 75 degree was measured. And the three-dimensional time-averaged velocity was measured. Then the comparison of the three dimensional components of speed was made in different sections and the differences of the flow pattern along the bend was analyzed. The observations showed the effect of the spur dike and the bed’s topography in distorting the secondary flow pattern and in the formation of the subsequent secondary flow. In addition, the secondary flows are formed along the scour hole slope development. In the downstream sections of the spur dike, the power of the secondary flow increases. At the end of the bend, this changes the flow direction from the external bank towards the internal bank. In the plans, some horizontal vortices with a counter-clock-wise direction can also be observed in the upstream of the spur dike in different layers.

Rubber springs could perform the same function of the steel springs in railway vehicle suspension systems and they have benefits of having no wear and rust. They are now successfully being used in both primary and secondary suspension systems of passenger trains. Nonlinear vibration of rubber springs used in suspension systems of passenger trains is studied in this paper. The rubber spring model mainly aims at representing the mechanical behavior of rubber springs for the frequency range of 0±20 Hz. The model is one-dimensional with a relationship between force and motion based on a superposition of elastic, friction and Maxwell visco-elastic forces. Inclusion of a friction force means that increased stiffness at small displacement amplitudes as well as rate-independent damping (hysteresis) can be considered. The validity of the model experimentally has been verified in the literature. A parametric study shows that the rubber spring equivalent stiffness has softening behavior with respect to both amplitude and frequency and its equivalent damping has hardening behavior with respect to both amplitude and the excitation frequency. The nonlinear rubber model is used in a dynamic ride model consists of body, bogies and wheel sets. The excitation here is the surface roughness of the rail which arises from the rail corrugation. The rail roughness is generated randomly by its Power Spectral Density (PSD) for 5 classes of rails according to USA rail classification. Classes 1 to 5 are considered and a dynamic simulation is carried out in order to more identify the rubber spring behavior in suspension systems. The numerical simulation is carried out using MATLAB software and all nonlinearities are exactly modeled. The simulation output here is the level of comfort index obtained by Sperling Comfort Index. A comprehensive parametric study is carried out and the effects of train speed as well as the rubber mechanical properties and the rail class on the comfort indexes and also the equivalent stiffness and damping of the rubber elements are studied.A new linearization technique namely Weighted-Linearization Method (WLM) is proposed in this paper in order to simplify full-nonlinear model. In this method the behavior of nonlinear rubber spring is more magnified in vicinity of the frequency range of 4-6 Hz in which all filter gains are in their highest value (close to 1.0). The aim here is to enhance correlation between the linear and nonlinear model to get similar results for the Comfort Index. The weighting frequency function which is utilized in linearization procedure is the Sperling filter transfer function. Very good correlation is achieved between the results obtained for linear and nonlinear model. It is also found that the classical linearization procedure results in considerable error in calculating comfort indicators.

WAVEWATCH-III is a third generation spectral wave model, developed originally for deep water in Ocean Modeling Branch of NOAA. By adding nearshore processes and removing some restriction from its code, the model can be applied to a full range of water depths from offshore to coastal regions. Depth induced wave breaking, surf zone energy dissipation and Triad wave-wave interactions are the important physical processes considered in shallow waters. The restrictions on time steps and minimum water depth in the original code have been relaxed to make the model applicable to coastal areas with high spatial resolution. The simulation results of the modified model have been compared with another third generation and widely tested spectral model, SWAN, in addition to some laboratory and field data.