Scientia Iranica
Volume:16 Issue: 3, 2009

A nonlinear nite element method with an eight-noded isoparametric quadrilateral element is used for the prediction of load-deformation behavior including the bearing capacity of foundations. A Disturbed State Concept (DSC) with a Hierarchical Single-Surface (HISS) plasticity model with an associated ow rule, and a Generalized Plasticity Model (GPM) with a non-associated ow rule are used to characterize the constitutive behavior of soils. The DSC model, however, can allow for non-associative behavior through the use of disturbance. Both models are able to simulate load-deformation including softening behavior. However, the GPM is based on the continuum approach while the DSC can allow for discontinuity due to factors such as microcracking. Predictions by both models show good agreement with laboratory data. A comparison between the DSC/HISS and generalized plasticity model is presented and it is found that the DSC/HISS model has certain advantages over the generalized plasticity model. A modi ed Terzaghi theory is developed for the bearing capacity based on the dependence of material behavior and in-situ stress; it can be used to compute the bearing capacity a ected by in-situ stress. Keywords: Generalized plasticity; Hiss plasticity; Non-associated ow rule; Terzaghi theory.

The seismic behaviour of a 4-story building is investigated under horizontal excitation of simulated earthquakes. The model has been constructed with a 3D sandwich panel system without any conventional frame system in four storeys on a shaking table. The building has been modelled before construction. Due to the table limit, the scale factor of the model is chosen as 1:2.35 of a prototype. The shaking table test of the scaled model of the building is carried out under several ground motions to verify the safety of the system. The simulated motions were applied to the model in two-perpendicular directions, simultaneously. The failure mechanism and dynamic behaviour of the model, as a 3D-panel building, is investigated in this study. Also, the objective of the study is to obtain the seismic performances of the described structural system under dynamic loading such as linear and non-linear structural characteristics, hysteretic behaviour, deformability and failure mechanism. Using these shaking tests, structural responses such as seismic capacity and damage mechanics, the distribution of seismic forces and weak points in the structures are evaluated. In addition, the lateral deformations, e.g. storey drifts are measured experimentally in the time domain. Accelerometers are mounted to measure accelerations in both vertical and horizontal directions. The results indicate that the 3D-panel system, due to its being well-con ned and its integrity, can resist mainly in the linear domain and has an adequate load bearing potential against moderate-intense seismic excitation. Keywords: Shaking table test; Sandwich panels; 3D wall system; Dynamic analysis; Shotcrete; Seismic exitation.

The development of second-order displacement functions for a Three-Dimensional Discontinuous Deformation Analysis (3-D DDA) is made by incorporating the complete second order terms. Formulations of sti ness and force matrices in second-order due to elastic stress, initial stress, point load, body force, inertia force and xed point are derived. Two illustrative examples of 3-D beams subjected to various loads are used to validate the new formulations and code. By contrast, the results calculated for the same model by use of the original rst-order 3-D DDA are far from the theoretical solutions. Keywords: Numerical method; Three-Dimensional Discontinuous Deformation Analysis (3-D DDA); Second-order displacement functions; Rock mechanics.

In this research, a microscopic model is developed that combines car following and lane changing models, describing driver behavior as a utility maximization process of drivers for reducing crash risk and increasing speed. This model is simulated by a cellular automata simulator and compared with the real data. It is shown that there is no reason to consider the model invalid for driver behavior in basic segments of the freeways in Iran, under non-congested conditions. Considering that the uncertain position of vehicles is caused by their acceleration or deceleration, a probability function is calibrated for calculating the presence probability of vehicles in their feasible cells. By multiplying the presence probability and impact of a crash, the crash risk of cells is calculated. An idea for estimating the crash risk of vehicles is introduced, named total risk. Total risk is the sum of risks on the path of the considered vehicles. It is shown that, when the di erence between vehicle characteristics such as brake deceleration increases, crash risk also increases, and vice versa. Keywords: Microscopic trac simulation; Utility maximization; Cellular automata; Crash risk.

Tabriz has experienced several large destructive historical earthquakes in the past. Due to the absence of ground motion records in this area, a simulation of future events based on a regional seismicity information and ground motion model is necessary. Based on a maximum likelihood method, earthquake magnitude is estimated for a 10% probability of exceedance within 50 years (475-year return period) and its corresponding strong ground motions have been simulated using stochastic nite fault modeling. Using di erent stress parameters, suites of ground motions have been simulated for a return period of 475 years and their spectral accelerations have been compared with the corresponding uniform hazard spectrum. It is observed that the t between simulated spectra and its corresponding uniform hazard spectrum has been improved including the directivity e ect especially at high periods. Keywords: Seismic hazard deaggregation; Stochastic nite fault; Stress parameter; Tabriz.

Plates on elastic foundations have attracted the attention of many researchers. Some elementary models have been introduced to consider interactions between the plate and its foundation. Other improved models have been proposed to develop basic models. In this work, a model based on the Winkler-foundation theory is proposed, while the constant parameter of Winkler is assumed to be variable; such as non-uniform springs with the functionality of the domain position, along with the plate and beam span in order to consider the non-uniform behavior of the foundation. The governing equation on the system is solved by using the Galerkin method and e ects such as the presence of rigid points in the foundation are considered. Keywords: Plate theory; Kirchho plate; Winkler elastic foundation; Galerkin''s method.

A semi-active controller-based neural network for a 3 story nonlinear benchmark structure equipped with a Magneto Rheological (MR) damper is presented and evaluated. An inverse neural network model (NIMR) is constructed to replicate the inverse dynamics of the MR damper. A Linear Quadratic Gaussian (LQG) controller is also designed to produce the optimal control force. The LQG controller and the NIMR models are linked to control the structure. The e ectiveness of the NIMR is illustrated and veri ed using the simulated response of a full-scale, nonlinear, seismically excited, 3-story benchmark building excited by several historical earthquake records. The semi-active system using the NIMR model is compared to the performance of an active LQG and a Clipped Optimal Control (COC) system, which is based on the same nominal controller as used in the NIMR damper control algorithm. Two passive control systems are also considered and compared. The results demonstrate that by using the NIMR model, the MR damper force can be commanded to follow closely the desirable optimal control force. The results also show that the control system is e ective, and achieves better performance than active LQG and COC system. The optimal passive controller performs better than the NIMR. However, the performance of NIMR will be improved if a more e ective active controller is replaced by a LQG controller. Keywords: Structural control; Semi-active; Neural network; Nonlinear; MR damper.

Abstract. This paper presents the application of a compact Genetic Algorithm (cGA) to pipe network optimization problems. A compact genetic algorithm is proposed to reduce the storage and computational requirements of population-based genetic algorithms. A compact GA acts like a standard GA, with a binary chromosome and uniform crossover, but does not use a population. Instead, the cGA represents a virtual population for a binary GA by a vector of probabilities representing the chance that the optimal solution has a one at each bit position. The application of the cGA to pipe network optimization problems is considered in this paper and the results are presented for two benchmark examples and compared with existing solutions in the literature. The results show the ability of the cGA to locate the optimal solution of problems, considered with a computational e ort, comparable to improved population-based GAs and with much fewer storage requirements. Keywords: Pipe networks; Optimal design; Compact genetic algorithm.