نشریه مهندسی عمران فردوسی
سال بیست و چهارم شماره 1 (پاییز و زمستان 1391)

Dynamic analysis of two-dimensional elasticity problems using the Isogeometric analysis method and its comparison with the finite element method is the subject of this research. For this purpose، formulation of the governing differential equation is obtained by using the B-spline basis functions. Some numerical examples employing consistent and lumped mass matrices are presented in order to compare the results of Isogeometric analysis and finite elements. The effect of increasing the number of control points and the degree of B-spline basis functions on the accuracy of the solution are also investigated. Furthermore، since the Newmark method is employed for transient dynamic analysis، the effects of parameters α and β on the solution accuracy are investigated. The obtained results demonstrate higher accuracy of the isogeometric analysis method in comparison with the FEM، despite employing fewer numbers of degrees of freedom and consequently reduction in the dimensions of system of equations and computational effort.

The central panel in steel plate shear walls (SPSWs) with two openings is considered as an I-shaped beam extending the height of the opening. Based on its «height to width» ratio، the dominant behavior can be due to shear or flexure or a combination of the two. The double stiffeners on the vertical sides of the central panel act as columns، comparable to columns of a typical SPSW system. Care is taken to keep the sectional area of the stiffeners above a minimum specified value in order to ensure that shear yielding of the central panel''s plate precedes flexural yielding of the stiffeners. The leading dimensions of central panel directly govern the behavior of the panel in shear and flexure. In this paper، central panel has been modeled as an I-shaped beam and equations have been derived for panel aspect ratio and cross sectional area of double stiffeners for different modes of behavior. Theoretical results are then compared with results of finite element analysis using ABAQUS Finite Element software. Based on this comparison، it can be concluded that in SPSWs with two openings، selection of a reasonable aspect ratio for central panel can cause shear dominant behavior in central panel.

In this article، a transversely isotropic linear elastic half-space with depth wise isotropy axis of material containing a cylindrical cavity of finite length is considered to be under the effect of an arbitrary torsion force applied on the wall of the cavity. To this end، the equation of equilibrium has been written in a cylindrical coordinate system، by dividing the involved domain to two regions and considering the equation of equilibrium in each region and by means of Fourier cosine integral transforms، the non-zero displacement component is obtained in the transformed domain. With the aid of the inversion theorem of the Fourier cosine integral transform، the displacements are determined in the real domain. By writing boundary and continuity conditions، a governing generalized Cauchy singular integral equation is obtained. By solving the governing integral equation، the shear stress and the torsional displacement are obtained for any point. The degenerated results for isotropic media are compared with existing results reported in the literature، where there exists an excellent agreement. The results of the paper may be used as the benchmark for the related research in the transversely isotropic media.

The conventional Intervening Opportunity Model which is potentially a powerful analytical and probabilistic model، has been used in transportation planning to model trip distribution pattern. This model is basically suffering from two main limitations. These limitations are the assumptions that trip makers are fully aware of all available opportunities in the area and their trip lengths to all possible destinations and that they evaluate all the destinations during their decision making process. This paper has attempted to extend conventional intervening opportunity، omit the limitations inherent in it and maximize its compatibility with the common destination choice pattern of home-based shopping trips. The overall idea is that for the main parameters of the intervening opportunity model (i. e. the opportunity and destination ranking variables) some coefficients and weights may be considered in order to calibrate the model once these weights and coefficients are calculated and included. These weights have been considered as modification factors according to the knowledge of the trip makers about the opportunities at destinations and also the knowledge on the accessibility of the shopping destinations. In this paper، the proposed structure of Extended Intervening Opportunity Model (EIOM) has been calibrated for a case study in Qazvin city. So، the effectiveness of conventional intervening opportunity model and extended intervening opportunity model has been measured and compared. In addition to results of calibrations and validations for both models، relative improvement of proposed model in comparing to conventional intervening opportunity model has been shown

Local scour around the abutment is of utmost importance in bridge failures. Numerous methods such as riprap have been proposed to reduce the destructive effects of scouring; one of the ways to harness and reduce the local scour depth is installed protective collars around the abutment. In this paper effect of collar elevation (upper level، bed level and lower level)، collar geometry and its size as a multiplier of the length of the abutment () have been experimentally investigated. All experiments were performed at the threshold of bed material motion under clear-water conditions and uniform-sized bed material. In this study the full-collar and partial collar performance as a bed protective on the two types of abutments; vertical wall and 45˚ wing wall abutment were investigated. The abutment considered in all experiments was short (ratio of abutment length to approach flow depth less than unity). Results from the experiments indicate that by increasing the collar width the local scour reduced and the collar width is utmost importance parameter in scour depth reduction. The Experimental results presented show in the best case، percentage of scour depth reduction that around the vertical wall (collar at lower bed elevation) and wing wall abutment (collar at streambed elevation) which is 2. 25 times wider than the abutment width، was obtained 87. 8 and 67. 8.

Bearing capacity prediction of axially loaded piles is one of the most important problems in geotechnical engineering practices، with a wide variety range of methods which have been introduced to forecast it accurately. Machine learning methods have been reported by many contemporary researches with some degree of success in modeling geotechnical phenomena. In this study، a fairly new machine learning method known as Support Vector Machine (SVM) has been used to develop a model to approximate the ultimate bearing capacity of axially loaded piles، based on Cone Penetration Test (CPT) data. The utilized dataset obtained from published literature contains full scale static load test and CPT results and pile geometry for each sample. Aditionally، sensitivity analysis of the model respect to each input parameter has been investigated. Finally، a comparison between actual values and predicted bearing capacity confirms efficiency of the developed model.

Steel structures are usually built with some defects. According to the standard building codes، the central axes of the bracing members should go through the beam-column joints، However، in most of the braced steel structures، bracing members are unintentionally connected eccentrically. This paper presents a numerical investigation on performance analysis of CBFs (Concentrically Braced Frames) having unwanted in-plane eccentricities at the connection of their braces. Nonlinear behavior analyses are taken as numerical examples. Finite element modeling of the whole members is conducted using ANSYS analyzing program. Numerical results show that in-plane eccentricities in beams can be acceptable within a safe region (max. 10cm for this specific case). However، no safe region is found for in-plane eccentricity in columns since the strength loss may be significant. Finally، some suggestions are made for decreasing constructional shortcomings of eccentric connections.