Civil Engineering Infrastructures Journal
Volume:46 Issue: 2, Jun 2013

An infinitely long hollow cylinder containing isotropic linear elastic materials is considered to be under the effect of arbitrary boundary stress and thermal condition. The two-dimensional coupled thermoelastodynamic PDEs are specified based on motion and energy equations، which are uncoupled using Deresiewicz-Zorski potential functions. The Laplace integral transform and Bessel-Fourier series are used to derive solutions for the potential functions، then the displacements-، stresses- and temperature-potential relationships are used to determine displacements، stresses and temperature fields. It is shown that the formulation presented here is collapsed on the solution existed in the literature for a simpler case of axis-symmetric configuration. To solve the equation used and evaluate the displacements، stresses and temperature at any point and time، a numerical procedure is needed. In this case، the numerical inversion method proposed by Durbin is applied to evaluate the inverse Laplace transforms of different functions involved in this paper. For numerical inversion، there exist many difficulties such as singular points in the integrand functions، infinite limit of the integral and the time step of integration. Finally، the desired functions are numerically evaluated and the results show that the boundary conditions are accurately satisfied. The numerical evaluations are presented graphically to make engineering sense for the problem involved in this paper for different cases of boundary conditions. The results also indicate that although the thermal induced wave propagates with an infinite velocity، the time lag of receiving stress waves with significant amplitude is not zero. The effect of thermal boundary conditions are shown to be somehow oscillatory، which is due to reflective boundary conditions and may be used in designing of such an element.

Inspecting the behavior of the rockfill materials is of significant importance in analysis of rockfill dams. Since the dimensions of grains in such materials are greater than the conventional sizes suitable for soil mechanics tests، it is necessary to experimentally study them in specific large-scale apparatuses. In this research، the behavior of rockfill materials in two large rockfill dams constructed in northwest of Iran were studied using large-scale direct shear and triaxial tests. Various indices regarding the quantity of particle breakage in rockfill materials were assessed for both dams and an experimental correlation has been proposed between the Los Angeles Abrasion Value and internal friction angle of rockfill material. Also، the effect of surcharge intensity، grain size distribution and degree of compaction on the shear strength of rockfill material for both dams was studied. The findings indicate that increase in particle breakage leads to reduction of internal friction angle. Also، for a specific sample the particle breakage index increases with an increase in surcharge، percentage of gravel and degree of compaction.

This study aims to undertake a statistical study to evaluate the accuracy of nine models that have been previously proposed for estimating the ultimate resistance of plate girders subjected to patch loading. For each model، mean errors and standard errors، as well as the probability of underestimating or overestimating patch load resistance، are estimated and the resultant values are compared one to another. Prior to that، the models are initially calibrated in order to improve interaction formulae using an experimental data set collected from the literature. The models are then analyzed by computing design factors associated with a target risk level (probability of exceedance). These models are compared one to another considering uncertainties existed in material and geometrical properties. The Monte Carlo simulation method is used to generate random variables. The statistical parameters of the calibrated models are calculated for various coefficients of variations regardless of their correlation with the random resistance variables. These probabilistic results are very useful for evaluating the stochastic sensitivity of the calibrated models.

A water distribution network is subjected to various abnormal conditions such as pipe breaks، pump failures، excessive demands etc. in the design period. Under such conditions، the network may not be able to meet required demands at desired pressures، and becomes deficient. Traditional network analysis assumes nodal demands to be satisfied and available nodal pressures are calculated. However، assumption that demands are satisfied at all nodes is not true under deficient conditions. Therefore، under deficient conditions nodal demands and pressures are considered simultaneously through head-flow relationships to calculate available nodal flows. This type of analysis that determines available flows is termed as node flow analysis or pressure-driven or dependent wherein، outflows are considered as function of available pressure. Various node head-flow relationships (NHFR) have been suggested by researchers to correlate available flow and available pressure based on required flow and required pressure. Methods using these NHFRs have been classified herein as direct and indirect approaches. Applications of these approaches have been shown with two illustrative examples and results are compared.

Elevated tanks are important structures in storing vital products، such as petroleum products for cities and industrial facilities، as well as water storage. These structures have various types and are constructed in a way that a greater portion of their weight is concentrated at an elevation much about the base. Damage to these structures during strong ground motions may lead to fire or other hazardous events. In this research، a reinforced concrete elevated water tank، with 900 cubic meters capacity، exposed to three pairs of earthquake records was analyzed in time history using mechanical and finite-element modeling techniques. The liquid mass of the tank was modeled as lumped mass known as sloshing mass، or impulsive mass. The corresponding stiffness constants associated with the lumped mass were determined depending upon the properties of the tank wall and liquid mass. Tank responses including base shear، overturning moment، tank displacement، and sloshing displacement were also calculated. Obtained results revealed that the system responses are highly influenced by the structural parameters and the earthquake characteristics such as frequency content.

Wall-jet flow is an important flow field in hydraulic engineering، and itsapplications include flow from the bottom outlet of dams and sluice gates. In this paper، the plane turbulent wall jet in shallow tailwater is simulated by solving the Reynolds Averaged Navier-Stokes equations using the standard k  turbulence closure model. This study aims to explore the ability of a time splitting method on a non-staggered grid in curvilinear coordinates for simulation of two-dimensional (2D) plane turbulent wall jets with finite tailwater depth. In the developed model، the kinematic free-surface boundary condition is solved simultaneously with the momentum and continuity equations، so that the water surface elevation can be obtained along with the velocity and pressure fields as part of the solution. 2D simulations are carried out for plane turbulent wall jets free surface in shallow tailwater. The comparison undertaken between numerical results and experimental measurements show that the numerical model can capture the velocity field and the drop in the water surface elevation at the gate with reasonable accuracy.

Different construction materials with different roughness used to make circular weirs highly affect surface roughness and، in turn، flow hydraulics passing over these structures. In the present research، numerous experiments under different hydraulic conditions were performed on a physical model to study the effects of roughness on flow hydraulics over a circular weir. The flow hydraulics included velocity profile، discharge coefficient and longitudinal water surface profile. The actual water surface elevation and velocity profile at different cross sections were measured using a point gauge and micro current meter، respectively. About 200 experimental tests were performed on a circular weir made of polyethylene with 29. 5 cm height، 30cm wide، and 7. 5 cm radius. The results showed that for a constant discharge، as the weir surface roughness increases the upstream water level over the weir increases and the discharge coefficient reduces. The velocity profile at upstream sections of the weir crest is extremely different from that over the weir crest while the velocity profile at downstream sections of the weir crest follows the same pattern as those experienced at the weir crest. Also، the increased roughness makes the velocity profile over the weir more uniform، with a higher average velocity. Finally the effects of roughness on velocity values are less near weir in comparison with water surface.

Failure of the quay walls due to earthquakes results in severe economic loss. Because of hazards threatening such inexpensive nodes of national and international transportation networks، seismic design of quay walls is still an evolving topic in marine structural engineering. This study investigates the sensitivity of the gravity-type quay wall stability respect to uncertain soil and seismic properties using ultimate limit-sate pseudo-static design process. Stability is defined in terms of safety factor against sliding (sfs)، overturning (sfo) and exceeding bearing capacity (sfb). In order to assess the forces exerting on quay walls، to be more accurate، pore water pressure ratio، horizontal and vertical inertia forces، fluctuating and non-fluctuating components of hydraulic and soil pressure were considered. It was found that the increase of water depth in front of the quay، vertical and horizontal seismic coefficients، and pore water pressure ratio play important roles in reduction of all mentioned safety factors. Increase of specific weight of the rubble mound، backfill and foundation soil، friction angle of wall-foundation/seabed interface and wall back-face/backfill interface and friction angle of backfill soil، lead safety factors to magnify. A comprehensive sensitivity analysis was also performed using the tornado diagrams. Results of this study could give designers insights into the importance of uncertain soil and seismic factors، in order to choose geometry of the design in a way that its analysis and assessment is less relied on severely uncertain parameters and to introduce more reliable and economic quay walls.

Stress waves contain useful information about the properties of porous materials; they can be recovered through different non-destructive testing methods such as crosswell، vertical seismic profile، borehole logging as well as sonic tests. In all these methods، it is crucial to assess the effects of frequency on wave attributes including velocity and intrinsic attenuation. The dependency of permeability on frequency which is known as dynamic permeability and its effects on wave attributes of compressional waves are investigated in the present paper. Utilizing the dispersion relation derived for compressional waves، it is shown how the velocity and intrinsic attenuation of waves propagated in water saturated sand may be influenced by dynamic permeability. In low frequency range (viscous dominated flow regime)، the dynamic permeability behaves like Darcy steady-state permeability and its effects on wave attributes are negligible. However، deviations from Darcy permeability start to occur at higher frequencies. Therefore، it is important to know how dynamic permeability controls the behavior of wave velocity and intrinsic attenuation in relatively high frequencies. For example، it is demonstrated that neglecting dynamic permeability results in overestimation of velocities of fast and slow waves in high frequency ranges (inertia dominated flow regime).

Differences between stress-based and strain-based criteria are investigated in seismic performance evaluation of the arch dams in time domain. A numerical model of the coupled dam-reservoir-foundation system is prepared with the finite element technique. Reservoir is modeled using the Eulerian approach as a compressible domain، and the foundation rock is assumed to be massless. Dynamic equilibrium equations for the coupled system are solved using Newmark’s time integration algorithm. Seismic performance of the arch dam is evaluated according to parameters such as demand-capacity ratio، cumulative inelastic duration and overstressed (or overstrained) areas obtained from linear elastic analyses. The results show، although there are some similarities between stress-based and strain-based criteria، evaluation of the performance based on the strain gives different results which can be led to different decision making in dam safety related projects.