Scientia Iranica
Volume:18 Issue: 4, 2011

A new exponential model to depict the moment–rotation (M–θ) relationship of Bolted Endplate Connections (BEC) is proposed. The proposed model represents an approach to the prediction of M–θ curves, taking into account the possible failure modes and the deformation characteristics of the connection elements. The presented model has three physical parameters, along with two curve-fitted factors. These physical parameters are generated from dimensional details of the connection, as well as the material properties. By employing simplified connection behavioral models to estimate the connection M–θ behavior, analytical expressions for evaluating major connection parameters, such as initial stiffness and ultimate moment, are derived. The M–θ curves obtained by the model are compared with published connection tests and 3D FEM research. The model yields acceptable results in good agreement with actual connection behavior. Besides, comparison between the presented model and other existing equations, in prediction of the derived BEC’s M–θ curve, shows the reasonably accurate results of the proposed model.

In this paper, a meshless method, namely, Discrete Least Squares Meshless (DLSM) method is used for the solution of shallow water problems. In this method, the computational domain is discretized by some nodes and then a set of simultaneous equations are built using Moving Least Squares (MLS) shape functions and the least squares technique. The proposed method does not need any background mesh and therefore is a truly meshless method. The stability and accuracy of the DLSM method is improved using some sampling points. Some 2D benchmark problems and a two dimensional flow over an ogee spillway are used to illustrate the performance of the present DLSM method. Numerical results are compared with experimental or analytical ones. Both regular and irregular meshes of nodes are used to show the potential of the DLSM method in solving problems with more complex domains.

In this paper, the isogeometric analysis method is utilized in the three-dimensional shape optimization of structures, instead of finite elements. The main obstacles in shape optimization problems are inherent in the currently practiced numerical analysis methods and their distinction from the geometry definition model. The newly developed isogeometrical analysis has the potential to be employed for this goal. The main advantage of this technique, besides being computationally less costly, and its ease and precision in defining boundaries, is that it does not require several remeshings in the process of optimization. In this research work, the domain of interest is defined by using Non-Uniform Rational B-Splines (NURBS). Also, a numerical analysis tool is developed, which uses the NURBS basis functions for approximation. The control points defining the design boundary surface are considered as the design variables of the shape optimization problem. To demonstrate the performance of the method, some examples of two and three dimensional problems are presented.

This paper presents a global algorithm for damage assessment of structures, based on a parameter estimation method, using the finite element and measured modal response of the structure. Damage is considered as a localized reduction in structural stiffness. Unmeasured parts of the mode shapes of a structure are characterized as a function of the structural parameter and measured parts of the mode shape. Elemental damage equations, which relate the partially measured mode shapes of a damaged structure to a change in structural parameters, are developed using incomplete measured mode shapes. These equations are solved to find the changes in structural parameters, utilizing an optimization method. Noise polluted data are used through Monte Carlo simulation to investigate the sensitivity of the proposed method to errors present in the measured modal data. The algorithm is verified in a numerical simulation environment using a planer truss and frame. Results show the good ability of this method to detect any damage of structures in the presence of errors in the acquired data.

This study pertains to the free vibration problem of beams on an elastic foundation of the Winkler type, which is distributed over a particular length of the beam. Closed form solutions are developed by solving the governing differential equations of beams. Moreover, an innovative mathematical approach is proposed to find the precise analytical solution of the free vibration of beams with mixed boundary conditions. Results are discussed in detail through verification studies. Ultimately, it was concluded that the proposed mathematical method could successfully obtain the exact solution to the free vibration problem of beams on partial elastic foundations under mixed boundary conditions.

In this paper, we solve the well-known conditional and unconditional p-center problem using a modified harmony search algorithm. This music inspired algorithm is a simple meta-heuristic that was proposed recently for solving combinatorial and large-scale engineering and optimization problems. This algorithm is applicable to both discrete and continuous search spaces. We have tested the present algorithm on ORLIB and TSP test problems and compared the results of the classic harmony search approach to those of the modified harmony search method. We also present some results for other meta-heuristic algorithms including the variable neighborhood search, the Tabu search, and the scatter search. Finally, we utilize this location model to locate bicycle stations in the historic city of Isfahan in Iran.

This article presents, for the first time, an investigation into the presence of rip currents along the southern coast of the Caspian Sea. The study site is selected at the Anzali port where 3 people were drowned in one day of summer 2007. Bathymetric surveys were obtained twice during the summers of 2008 and 2009 and rip currents were measured for two days in the summer of 2008 and the summer of 2009 with different wave conditions, using five GPS drifters. An RCM 9 current meter was installed in the rip channel for credibility of the drifter velocity. The cross-shore location of their velocity maxima and the distance they extend offshore are just two important unknowns. These questions were investigated using drifter trajectories. An oblique and a classic rip current were observed in two experiments. A field validation of the drifters shows that correspondence between the drifters and RCM 9 measurements is good.

In this article, construction of the most precise possible probabilistic model for the estimation of seismic demand in steel moment-resisting frames, with different heights, using the Bayesian Statistic, is attempted. In this study, after proving that the best form for defining the model is a linear combination of the logarithm of Intensity Measure (IM) parameter, the best IM was selected based on the practicality, efficiency and sufficiency of models. Some particular results show that the precision of models with one single IM depends on the number of stories in the structure, so no model including the current one, i.e. the one with spectral acceleration in the first period as IM can be introduced as the best model of all frames with whatever height. Since making use of a combined IM including two spectral values as a solution is not practical due to the extreme difficulty of producing a multiple parameter seismic hazard curve, in this study it was shown that the best possible method for construction of the model is the use of two single IMs, i.e. the best model to cover all structural heights is the one with a linear combination of the logarithm of spectral acceleration at the first and second periods.

This paper presents an updated study and numerical modelling of the Tabas, eastern Iran earthquake (Mw=7.4), which occurred on September 16, 1978, using new techniques recently proposed by various researchers. Firstly, the near-fault ground motions recorded at a station very close to the fault were examined based on the characteristics of the velocity pulses and the frequency content of the motions. Evidence of directivity effects in recorded, near-fault ground motion, has been investigated using various methods. In the second part of this paper, stochastic simulations of near-fault, strong ground motion, using finite-fault modelling, based on a dynamic corner frequency recently proposed by Motazedian and Atkinson [Motazedian, D. and Atkinson, G. “Stochastic finite-fault modelling based on a dynamic corner frequency”, Bull. Seismol. Soc. Amer., 95(2), pp. 995–1010 (2005)], have been presented. In order to model the impulsive behaviour of near-fault ground motion, the finite-fault model was combined with the mathematical expression of Mavroeidis and Papageorgiou [Mavroeidis, G.P. and Papageorgiou, A.S. “A mathematical representation of near-fault ground motions”, Bull. Seismol. Soc. Amer., 3, pp. 1099–1131 (2003)] for modelling pulse characteristics. A new set of modelling parameters has been recommended and good agreement has been found between the recorded and simulated response spectra. The velocity pulses observed in near-fault ground motion records could also be mimicked.

Metakaolin is a pozzolanic material obtained through thermal activation of kaolin. This research aims to investigate the effect of degree and duration of heating on the pozzolanic properties and reactivity of the produced material. Two types of Iranian mineral raw material, namely, K1 and K3, and one by-product of the domestic kaolin beneficiation process, K2, were activated by heating in a furnace chamber at temperatures 650–900 °C for 1 and 2 h. The changes in the crystalline structure of these materials were evaluated using X-Ray Diffraction (XRD), and also compressive strength tests were carried out on the mortars containing metakaolin to study the reactivity of the produced materials. The obtained results indicated that 1 h is sufficient for thermal activation of kaolin, and the optimal activation temperature is between 750 and 850 °C. Moreover, it was observed that activated metakaolin has an appreciable influence on the increase in compressive strength of the mortars.