Computational Methods in Civil Engineering
Volume:1 Issue: 1, 2010

A new approach for analyzing cracked problems in 2D orthotropic materials using the well-known element free Galerkin method and orthotropic enrichment functions is proposed. The element free Galerkin method is a meshfree method which enables discontinuous problems to be modeled efficiently. In this study, element free Galerkin is extrinsically enriched by the recently developed crack-tip orthotropic enrichment functions. Also, a suitable way is applied to select support domains near a crack so that the discontinuity can be modeled without the Heaviside enrichment function. Crack-tip enrichment functions span the possible displacement space that may occur in the analytical solution. For evaluating the mixed-mode stress intensity factors, the interaction integral is applied. Some numerical examples are simulated to investigate the efficacy of the new approach by comparing with other numerical or (semi-) analytical methods.

A reliability analysis of suspension bridges against buffeting failure due to gustiness of wind velocity is carried out using the concept of PRA (probabilistic risk analysis) procedure. For this purpose, the bending stresses at the critical nodes of the bridge deck are obtained for buffeting forces using a spectral analysis technique and a finite element approach. For the purpose of reliability analysis, uncertainties are considered as those arising due to variation of stiffness and mass properties of the bridge, damping, mathematical modeling, flutter derivatives and due to ductility and damage concentration effects. These uncertainties are incorporated by a set of multiplying factors in the limit state function. All multiplying factors are assumed to be independent log-normally distributed random variables. An extensive parametric study is conducted to show the effect of some important parameters on the reliability estimate. The results of the study show that ductility of the system and the structural damping have a significant effect on the reliability against buffeting failure.

In shallow foundations, the third bearing capacity factor, N, has been found to show a decreasing tendency with increasing the foundation size. It is supported by experimental observations and related mainly to stress level dependent nature of the soil. On the other hand, the bearing capacity is often obtained theoretically without consideration of the foundation vertical displacements. In this study, a simple form of the stress level dependent hyperbolic soil model is presented and implemented in the Zero Extension Lines (ZEL) method to predict the bearing capacity and load-displacement behavior of shallow foundations. A computer code is developed for this study. A procedure to find the actual behavior of relatively large foundations based on laboratory and in situ small scale or plate load tests data is also presented. An existing experimental full scale load test is investigated and analyzed with the presented method to show the possibilities and advantages of the method in comparison with ordinary approaches. The results show that the presented method is applicable for practical problems to provide a more precise estimate of the bearing capacity of shallow foundations.

One of the main distinctions between geomaterials and other engineering materials is the spatial variation of their properties in different directions. This characteristic of geomaterials -so called heterogeneity- is studied herewith. Several spatial distributions are introduced to describe probabilistic variation of geotechnical properties of soils. Among all, the absolute normal distribution was adopted as appropriate distribution which best represents these properties in the horizontal direction.Variation of geotechnical parameters in the vertical direction is however conceived to follow a deterministic trend. With the aid of random field theory and local average subdivisions (LAS) formulation and using MATLAB Mathworks, virtual data with different correlations were produced and by employing the autocorrelation function, a trend for this function was invoked for different predetermined values of scales of fluctuation. It was found that the autocorrelation function has a deterministic trend as long as the scale of fluctuation is not exceeded. It is concluded that for distances further than the specified scale of fluctuation the behavior is chaotic and this can be an index to calculate the scale of fluctuation of the experimental data.

Three dimensioned finite element analysis were conducted on concrete block paving. In order to verify the calculated results, an experimental case study was analyzed. Good agreement was observed between the measured and the calculated results. Based on the finite element analysis results and available failure models, comprehensive design charts were developed for port and industrial pavement which can take into account; the sub grade and pavement layers properties as well as the tire pressure and the number of repetitive loads. In addition by using 3D finite element model mechanism of interlocking between pavers was discussed. Parametric study were conducted on 3D models and it was found that jointing width, shape, size and thickness of blocks have a significant influence on the behavior of block pavement.

In this paper the active vibration control of a four-story shear frame instrumented with piezoelectric actuators is presented. The piezoelectric actuators are hosted on the columns in two manners and the produced controlling forces by actuators are considered in the equation of motion. The smart structure modeling and control design is carried out using MATLAB software in state space form. Subsequent details of designing feedback control are addressed. Pole Placement Controller (PPC) and Linear Quadratic Regulator (LQR) are applied in control algorithms and their performances are discussed. The results of both methods are compared which show excellent agreement, demonstrating that piezoelectric based structural control is a proper approach for optimized smart structure design. Results also show that the location of the piezoelectric actuators significantly influences the efficiency of the control system.

Rough Sets theory is a mathematical approach for analysis of a vague description of objects presented by a well-known mathematician, Pawlak (1982, 1991). This paper explores the use of Rough Sets theory in site location investigation of buried concrete water reservoirs. Making an appropriate decision in site location can always avoid unnecessary expensive costs which is very important in construction projects such as water reservoirs. The proposed site location investigation approach is illustrated using a case study data of a semi-buried concrete reservoir with the capacity of 15000m3 which is under construction in the North of Iran (Guilan Province, Maklavan). In this approach, the decision rules are derived from conditional attributes in Rough Sets analysis, in accounting for data vagueness and uncertainty in potentially reducing data collection. The results of study indicate that using this method can reduce unnecessary costs in water reservoirs construction.