International Journal of Civil Engineering
Volume:4 Issue: 3, Sep 2006

The main aim of this paper is to extend the recently developed methods for calculating the buckling loads of planar symmetric frames to include the effect of semi-rigidity of the joints. This is achieved by decomposing a symmetric model into two submodels and then healing them in such a manner that the union of the eigenvalues of the healed submodels result in the eigenvalues of the entire model. Thus the critical load of the frame is obtained using the eigenvalues of its submodels.

In this paper, a higher order continuum model is presented based on the Cosserat continuum theory in 3D numerical simulation of shear band localization. As the classical continuum models suffer from the pathological mesh-dependence in strain softening models, the governing equations are regularized by adding the rotational degrees-of-freedom to conventional degrees-of-freedom. The fundamental relations in three-dimensional Cosserat continuum are presented and the internal length parameters are introduced in the elasto-plastic constitutive matrix to control the shear bandwidth. Finally, the efficiency of proposed model and computational algorithm is demonstrated by a 3D strip in tensile. A comparison is performed between the classical and Cosserat theories and the effect of internal length parameter is demonstrated. Clearly, a finite shear bandwidth is achieved and the load-displacement curves are uniformly converged upon different mesh sizes.

Seismic behavior of a rockfill dam with asphalt-concrete core has been studied utilizing numerical models with material parameters determined by laboratory tests. The case study selected for these analyses, is the Meyjaran asphalt core dam, recently constructed in Northern Iran, with 60 m height and 180 m crest length. The numerical analyses have been peiformed using a nonlinear three dimensional finite difference software and various hazard levels of earthquakes. This study shows that due to the elasto-plastic characteristics of the asphalt concrete, rockfill dams with asphalt concrete core behave satisfactorily during earthquake loading. The induced shear strains in the asphalt core, for the case presented in this research, are less than 1% during an earthquake with amax=0.25g and the asphalt core remains watertight. Due to large shear deformations caused by a more severe earthquake with amax= 0.60g, some cracking may occur towards the top of the core (down to 5-6 m), and the core permeability may increase in the top part, but the dam is safe.

Pushover analysis is a simplified nonlinear analysis technique that can be used to estimate the dynamic demands imposed on a structure under earthquake excitations. One of the first steps taken in this approximate solution is to assess the maximum roof displacement, known as target displacement, using the base shear versus roof displacement diagram. That could be done by the so-called dynamic pushover analysis, i.e. a dynamic time history analysis of an equivalent single degree of freedom model of the original system, as well as other available approximate static methods. In this paper, a number of load patterns, including a new approach, are considered to construct the related pushover curves. In a so-called dynamic pushover analysis, the bi-linear and tri-linear approximations of these pushover curves were used to assess the target displacements by performing dynamic nonlinear time history analyses. The results obtained for five different special moment resisting steel frames, using five earthquake records were compared with those resulted from the time history analysis of the original system. It is shown that the dynamic pushover analysis approach, specially, with the tri-linear approximation of the pushover curves, proves to have a better accuracy in assessing the target displacements. On the other hand, when nonlinear static procedure seems adequate, no specific preference is observed in using more complicated static procedures (proposed by codes) compared to the simple first mode target displacement assessment.

This paper presents the results of a series of monotonic and post-cyclic triaxial tests carried out on a clay specimen and three types of clay-sand mixed specimens. The focus of the paper is on the post-cyclic mechanical behavior of the mixed specimens, as compared to their monotonic behavior. Analyses of the tests results show that cyclic loading degrade untrained shear strength and deformation modulus of the specimens during the post-cyclic monotonic loading. The degradation depends on the sand content, the cyclic strain level and to some degrees to the consolidation pressure.

Optimization is an important methodology for activities in planning and design. The transportation designers are able to introduce better projects when they can save time and cost of travel for project by optimization methods. Most of the optimization problems in engineering are more complicated than they can be solved by custom optimization methods. The most common and available methods are heuristic methods. In these methods, the answer will be close to the optimum answer but it isn''t the exact one. For achieving more accuracy, more time has been spent. In fact, the accuracy of response will vary based on the time spent. In this research, using the generic algorithms, one of the most effective heuristic algorithms, a method of optimization for urban streets direction will be introduced. Therefore model of decision making in considered one way - two way streets is developed. The efficiency of model in Qazvin network is shown and the results compared whit the current situation as case study. The objective function of the research is to minimize the total travel time for all users, which is one of the mostused in urban networks objectives.