MODARES TECHNICAL AND ENGINEERING
Year:2005 | Volume:- | Issue:19|Papers Count:11

Design of pavements by mechanistic - empirical methodology involves use of different parameters such as contact pressure, vehicle speed and properties of the pavement materials. Therefore changes in the loading and environmental conditions and pavement structure brings about changes of design. The work presented here, is the results of extensive analysis performed by use of MFPDS and KENKLAYER software, pertaining to the design of pavements. Several variables such as surface thickness, surface and sub-grade strength, pavement temperature, contact pressure, loading speed and axle spacing were considered and taken into account. Critical strains and allowable number of load repetitions were determined and subsequently were used in the corresponding analysis. From this investigation analysis the results shown that, higher number of load repetition is attainable at a higher loading speed. This is true, specially for areas of moderate temperatures. The results also shown that the effects of variation in contact pressure are noticeable with thin pavement sections. Findings also showed single axles, are not necessarily more destructive than those of tandem.

Spatial distribution of the strength of interplate coupling between Philippine Sea (PHS) plate and continental plate in Tokai district (central Japan) is investigated in detail through inverse analysis of geodetic data. In this research, the major causes of crustal deformations are assigned to three main factors; namely, rate of tectonic forces, rate of fault deformations (sliding field of interface boundary), and far-field treatment. Using geodetic data concerning the Tokai zone, the inversion tool will compute driving tectonic forces and slippage vectors rates. Far-field boundary conditions are determined by means of minimization of residuals. These residuals are differences between the calculated and observed crustal movements. All peripheral boundaries of the model are covered by a set of springs whose stiffness coefficients are initially unknown. These stiffness coefficients are investigated in a manner that a plausible pattern of problem's components could be reproduced by the model. An assessment of coupled zone of the next coming Tokai earthquake could be considered as the main result of this research. Some evidences such as the seismicity patterns of Tokai district, play remarkable role to prove the validity of the proposed method.

Cavitation is a destructive phenomenon in flows with high velocity, and becomes more critical in curvatures. Therefore, adequate consideration in design of curvatures is a necessity. Furthermore, it has been suggested that aerators should not be used in the design of curvatures. Consequently suitable design of curvature without cavitation is very important. In this paper, various curvature profiles have been defined and compared with each other and the optimal profile has been selected. For this purpose, curvature profiles have been determined using different methods such as: "constant cavitation number profile", "controlled pressure profile", etc. In the design of flip bucket curvature, cavitction index in the upstream end of curvature is very important, which must be more than its critical value at the upstream end and along the curvature. Different curvature profiles have been evaluated for the flip bucket of Silve dam spillway. The best curvature profile considering economic and hydraulic parameters has been resulted from the controlled pressure profile method using cosine pressure distribution function. In this profile, the upstream end of profile is similar to the rotational assumption profile of constant cavitation number. In this case study, the length of curvature is 45.24 meters and maximum value of the cavitation index is 0.2648. Cavitation index values in the upstream and downstream end of curvature are equal to 0.2139 and 0.2248, respectively.

Modeling of the mechanical behavior of geomaterials such as rock is an important topic in the field of mechanics of materials. In this paper multi-plane framework has been implemented on a new multi-line model for softening behavior of rock. The general-applicability of this model has importance and is main characteristic of this model. Multi-plane frame work as a powerful method to handle anisotropy in material behavior is able to discretise the overall behavior onto multi-planes. According to multi-line model the stress-strain curve is rationalized and justified into multi-lines to be the capability of seeing softening/hardening etc. in material behavior. These capabilities are added to the multi-plane capabilities as predicting inherent/induced anisotropy and the rotation of principal stress/strain axes during non-linearity. The stated features make the model able of predicting behavior of rock upon any stress/strain paths. To verify the capability of the proposed model the behavior of a typical rock including softening are compared well wit the test results.

This research presents a numerical tool for estimation of subduction zones' behavior during interseismic periods. This approach is based on the least-squares method to derive slippage vectors at subduction fault. The spatial distribution of under ground coupling could be investigated in detail through inverse analysis of geodetic data. During an interseismic period, a region at an intermediate depth remains locked, while the shallower and deeper portions are decoupled, and a steady slip proceeds there. The steady slip could be detected by micro-earthquakes continuously occurring in these two portions. The standard equations of Inverse Problems offer a straightforward way for finding slippage vectors at the interface of two converging plates. One of the new aspects of the current study is evaluation of Green's function operator matrix by means of FEM. Green's function operators are functions of some fundamental parameters such as Tectonic Forces and Far-field Treatment, which are regarded in the present Inverse analysis. To implement fault sliding in a continuum-based FEM code, Split Node Technique as a simple and efficient method is applied. This method does not increase the number of degrees of freedom and no net forces or moments are induced on the finite element mesh. As other common Inverse problems, singularity of coefficient matrix is the main problem. This problem particularly emerges if the number of degrees of freedom is too large. The numerical procedure returns a set of slippage vectors that are not correct. Singular Value Decomposition (SVD) diagnoses precisely what the problem is. In some cases, SVD will not only diagnose the problem, it will also solve it.

In this paper a new time step will be formulated for Dynamic Relaxation method. For this purpose, residual force is minimized in each iteration. Calculation of the convergence rate shows the advantage of the recommended technique. For illustrating usability of this method, some plane and space trusses have been analyzed. In this paper, geometrical non-linearity is considered. Moreover, proposed method is widely examined by author's computer program and some examples will be given.

In this paper, the effects of connection stiffness on main period of vibration and behavior factor of moment resisting steel frames with semi-rigid connections are evaluated. For this purpose, behavior of different moment resisting steel frames with semi-rigid connections with 1,2, and 3 spans, and 1, 2, 4, 6 and 8 stories and with different connection stiff nesses are considered. Based on the results, new relationships for the main period and behavior factor of moment resisting still frames with semi rigid connections are purposed.

An efficient two-phase method for discrete optimization of pipe networks is presented in this paper. The method consists of two stages. In the first, the problem of pipe network optimization is formulated as an unconstrained optimization problem using an iterative penalty method, which is then solved by an all purpose optimization tool, DOT, to get the continuous solution for the pipe diameters. In the second stage, a second optimization tool, DOC, incorporating a branch and bound method is used to get the discrete solution starting from the already available continuous solution as a good initial guess. Two different strategies are used at the discrete solution stage. In the first, named as local here, the search space is restricted to the upper and lower diameter limits of the optimal continuous solution, while in the second strategy, so called as global, this restriction is relaxed. The method is shown to be capable of producing results comparable to the existing sophisticated algorithms with much less computational effort. The method is used to find the optimal solution to some of the benchmark pipe networks and the results are presented. The results obtained for the networks consisting of pipes are encouraging.