نشریه مهندسی سازه و ساخت
سال دوم شماره 3 (پیاپی 4، پاییز 1394)

The goal of this research is to study the effect of the space between long and short piles beneath combined deep foundation caps on the forces acting on piles and the resulting summit, all done by considering variables such as; short pile length, soil pad stiffness (cushion), short pile stiffness and long pile stiffness, using a modeling and numerical analysis method. Modeling and numerical analysis are performed using the Abacus software, which results indicated that by increasing the space between short and long piles, the compressive axial tension acting on short piles rises and the compressive axial tension acting on long piles almost reduces, and also increasing the space between short and long piles will reduce the resulting summit and by rising the elastic modulus of short piles the summit reduces and increasing the elastic modulus of long and short piles results in reducing the summit.

Common methods analysis and design of structures are based according to elastic analysis and and reduction of earthquake forces. This reduction design load in the codes is done by the behavior factors. Applying the non-linear static analysis and make ideals pushover curves obtained from its, including conventional in determining behavior factor. The purpose of this study is evaluating the accuracy of nonlinear static analysis in determining behavior factor reinforced concrete moment-resisiting framesby performing nonlinear incremental dynamic analysis that is a more accurate analysisby considering the damping, dynamic nature of the load and higher modes effects. The response modification factors for reinforced concrete moment-resisiting framesobtained in this study by performing nonlinear incremental dynamic analysis are difference about %13 those obtained by pushover analyses analysis. The results of nonlinear incremental dynamic analysis are generally more than those obtained from pushover analysis.

Column-tree moment resisting frames, as the efficient shop-welded and field-bolted structural systems, are used in many countries. Very limited research has been carried out on such systems under fire conditions. This paper presents experimental investigations of the behavior of beam and bolted splice connections in steel column-tree moment resisting frames exposed to fire. Two full-scale steel sub-frames with different splice connections were tested under ISO 834 standard fire. The flange splice plates were configured as a single plate with single shear bolts in first specimen, and as double plates with double shear bolts in second specimen. The observation of thermal and structural fire behaviors including temperature histories, temperature-deflection of the beam, temperature-rotation of splice connections and failure modes were investigated. The temperature-deflection and temperature-rotation curves remained in the elastic range until about 600°C. Beyond 600°C, the behavior would be highly nonlinear plastic. The beam splice connection failed due to shear fracture of top bolts at temperatures beyond 750°C. Consequently, stub beam web failed at those temperatures because of block-shear. Using double plates with double shear bolts for flange splices would enhance the temperature resistance and rotational capacity of the beam splice connections. Both tests results confirmed that specimens retain the capacity to support the design load when the average beam temperature does not exceed 600°C. This temperature limit confirms the temperature criteria provided by ASTM E119 and ANSI/UL 263 for a restrained beam, and can be used to specify the minimum fire resistance criteria for beams in column-tree MRFs. The measured time-deflection curves showed that the restrained fire resistance rating for both unprotected specimens obtained about 15 minutes in both tests.

Concrete Filled Double Steel Tubes are mostly used in bridge piers, tall buildings, offshore and coastal structures and power transmission towers. Finite element analyses via ABAQUS software have been performed aiming to evaluate the strength, ductility and plastic deformation of CFDST columns with different hollow ration and stiffeners configurations. According to analyses results more strength and high ductility levels can be provided decreasing the composite section hollow and increasing stiffeners thickness. More stiffener plates with larger dimensions result in more strength and stiffness in composite columns due to increase in concrete confinement and adjoint interaction of steel and concrete. It also raises plastic deformation level of the columns and postpone the local buckling.

One of the biggest items in decision-making is selecting the best choices considering all their aspects. In the meantime, employing an instrument that can guide the choice in a structuralized way is very useful. In this research, value engineering along with hierarchical analytic processing method as instruments to select the best choice for the type of dam and the spillway are utilized. To do this, three categories of operational cost, time and performance as the main indicators of decision-making have been considered. The results revealed that the best choice is the roller compacted concrete dam with free spillway.

The use of numerical methods, particularly finite element methods in solving different problems are used in abundance. Because these methods are approximate, having a real understanding of the extent and distribution of the errors is extremely important. Studies show that the mesh used in the finite element method will be an essential error rate. So many different ways to find the optimal mesh and minimize the error of the proposed method. These methods are mainly aimed at reducing the error in the stress field have been obtained. Although one of the aims of reducing errors tension field finite element method is adaptive, but no guarantee is intended to achieve specific issues. These issues can be Craek to the issues noted in the analysis of the elastic parameters of the stress intensity factor will play a key role in determining the direction and Craek the design. The purpose of this study is to measure the stress intensity factor adaptive analysis on the parameter to be modified to accommodate ancillary parameters such as strain, stress intensity factor able to modify the target parameter.