نشریه مهندسی عمران فردوسی
سال سی‌ام شماره 1 (پاییز 1396)

Labyrinth Spillways are one of the hydraulic structures to regulate and control the flow of water in canals, rivers and reservoirs. In some situations, there is no enough space for increasing the length of the weir to increase the discharge. Therefore, labyrinth spillways are one of the solutions for this problem. If the cycle of linear labyrinth spillway is located on the curve, then the crest length increases, and as a result the inlet flow condition is improved and the hydraulic coefficient increases. In this laboratory study, the discharge coefficient for different downstream wall slopes is studied. 2 different spillways with side-wall angle (6 and 11/25) and 4 downstream wall slope are studied. The results indicate that downstream wall sloping reduces the hydraulic coefficient. Discharge coefficient variations with downstream slope and flow height on spillway crest were studied. Different equations were presented to estimate the discharge coefficient of the spillway by considering the downstream slope.

In his paper, back-analysis using rsults from instrumentation by finite element software for design of preloading method by embankment with prefibricated vetical drains (PVDs) was used, and the results were compared with each other. Hence, the basic geotechnical parameters obtained by laboratory and field experiments have been modified using this method. In this regard, the Mahshahr oil storage project has been used as a case study. All of the methods that are used for improving soil must ultimately result in increased soil resistance parameters, reduced compressibility, and reduced soil permeability. The soil improvement technique using preloading was used in Mahshahr where there are soft soil layers beneath higher than sub-surface water. control performance of the embankments, some instruments such as Settlement Plates and Piezometers have been used. The results obtained from the analysis shows that settlement parameters obtained from the instruments data by back-analysis were less than primary consolidation settlement parameters based on laboratory tests. Finally, soil settlement estimation of the oil tank was compared before and after preloading, and it was found that using this method for soil improvement can be very efficient in the current project.

The performance of plates can be changed due to their uncertainties in applied loads, material properties, geometry and boundary conditions. In this paper, the failure probabilities of rectangular steel plates are evaluated using the displacement performance function using the first-order reliability method (FORM) – based on a novel finite-step length. The displacement limit state function of the isotropic plates for different boundary conditions is used for their reliability analysis based on the random variables such as material, plate dimensions and applied external load which have been simulated by use of Normal and Lognormal distribution functions. The finite-step length of FORM is developed based on Armijo line search that is simply computed and is improved the robustness and efficiency of FORM. The results demonstrate that by decreasing plate dimensions, the failure probabilities are decreased. The failure probabilities of plates with free boundary conditions are obtained to be more than the failure probabilities of plates with clamped boundary conditions. The minimum thicknesses of rectangular plates with simply supported conditions are found to be about (around plate)/300 to achieve a reliable performance.

Special prefabricated connections and pyramid-shaped column heads are important innovations in steel structural forms. These connections have been proposed for accurate assembly and prompt implementation. In this study, the interactions between the two parts of connections have been investigated. For this purpose, the pyramid-shaped part is modeled in the ABAQUS software with different dimensions and under cyclic loads according to ATC-24 code. For verification of the software outputs, the outputs of the software have been compared to the experimental results. The results show that all specimens can bear a 0.01 radian rotation in the linear region and at least 0.06 radian rotation without a reduction in the tolerated force. These results demonstrate that the connection has a high rotational capacity and may be classified in the special moment frames. Maximum energy absorption capacity occurs in the specimen whose pyramid-shaped part is placed on the flange of the lower column and a box section is also placed on the flange of the upper column. Beams without lateral support show 42 percent reduction in connection resistance compared with un-rotated beams due to rotation.

Many researchers have applied single-objective optimization algorithms for structural damage identification. Recently, multi-objective optimization algorithms have also been considered for this purpose. This article applies two recent multi-objective evolutionary optimization algorithms and modal shape and stiffness objective functions for structural damage detection in a simply supported beam and a two fixed-end moment beam. For the fixed supported beam, the results are compared with the experimental results from the literature. The results demonstrate the good performance of proposed approach in localization and quantification of damages.

In this research, the behavior of plastic concrete materials with a strain Hardening/Softening Elasto-Plastic constitutive model are investigated using FLAC software based on a series of drained triaxial test results. The constitutive model is based on the mobilized strength (friction and cohesion) and mobilized dilatation angle concepts. The results indicate that the assumed functions of modified mobilized friction angle and mobilized cohesion (The Yield function of the model) which are common for geotechnical materials, can predict stress-strain behavior with a sufficient accuracy. However, they cannot simulates the Volume changes due to dilation effects accurately, especially for plastic concrete with a relatively high stiffness and strength. Therefore, the potential function of the model is modified. The stress-strain and Volume strains that have been obtained from the modified model are in good agreement with the experimental data, especially for soft plastic concrete, as well as for hard plastic concrete in a low confining pressure.

Investigation of lateral bearing capacity of piles under lateral loading in the vicinity of soil slopes and level ground is one of the interesting issues in the engineering of the deep foundations in recent decades. In the meantime, the estimation of lateral stiffness of soil layers, coefficient of soil reaction, ks, is an old challenge on the basis of the creation of empirical (testing) and theoretical p-y curves. In this paper, we attempt to estimate lateral soil stiffness in the length of concrete piles in various depths in sloped ground and level ground and in the all type of soils, including cohesive soil, frictional (granular) soil and mixed soil, i.e. c-φ soil with the aid of numerical analysis in three dimensional finite difference software, Flac3D. For the purpose of estimating lateral soil stiffness, Ki, in different depths by means of this numerical method, the p-y curves have been derived in several depths in the length of concrete pile with circular section under static lateral loading up to the threshold of the yielding of soil materials. The empirical relationship established between soil lateral stiffness Ki and the effective dimensionless parameters on the Ki in general is calculated as a six order polynomial, and this six order polynomial reduces to a fourth order polynomial for the cohesion component of the soil. At the end of the paper, some well documented lateral loading tests by the present numerical method have been investigated for validation of the numerical method of derivation of the p-y curves and pile-head load deflection curves, H-y curves have been calculated and are compared with other results obtained by other researchers and methods. There are good agreements between test results and the results obtained from the numerical method presented in this paper.

This paper concentrates on the presentation of a closed form solution of dam-reservoir interaction considering reservoir viscosity and bottom absorption under harmonic excitations. For this purpose, the governing equations of dam-reservoir are solved in the frequency domain and using the obtained frequency response function, the effects of different parameters are considered on dam or hydrodynamic pressure response. The results show that consideration of reservoir viscosity creates an imaginary term and the responses depend on values of viscosity, bottom absorption, exited period and dam-reservoir period.