سال:1390 | دوره: | شماره: |تعداد مقالات:6

Post-failure analysis of massive structure infers that Soil-structure interaction (SSI) is a crucial phenomena influencing seismic response of massive structures. Cable-stayed bridge popularity and numbers are increasing nowadays because of economical longer span & aesthetic good look. The current paper examines the effect of depth of foundation on seismic response of cable-stayed bridges. In total 16 cases are solved with and without SSI by time-history analysis with Finite Element Program. Full 3D bridge model is developed and soil is modeled by assigning the spring and dashpots as Kelvin element to simulate SSI effects. The result yielded that SSI effects must be considered for soft soil conditions irrespective of the depth of foundation. The effects of SSI are site specific and cannot be generalized. However the fundamental time period is increasing as high as 28% due to SSI effects. The depth of foundation has also a great role in seismic response of the bridge; the medium depth foundation is proven critical compared to other cases.

In this paper, the results of an analytical investigation on the behavior of RC columns reinforced with fiber reinforced polymer bars FRP are presented and discussed. Nonlinear finite element analysis on 10-column specimens was achieved by using ANSYS software. The nonlinear finite element analysis program ANSYS is utilised owing to its capabilities to predict either the response of reinforced concrete columns in the post-elastic range or the ultimate strength of a reinforced concrete columns reinforced by FRP bars. An extensive set of parameters is investigated including different main reinforcement ratios, main reinforcement types (GFRP, Steel), the transverse reinforcement ratios, and the characteristic compressive strength of concrete. A comparison between the experimental results and those predicted by the existing models are presented. Results and conclusions may be useful for designers, have been raised, and represented.

Starting from two-dimensional (2D) equations of motion, discretized formulations for transient behavior of soil-structure interaction problems have been derived. Two different dynamic infinite elements taking into account single and two-wave types are presented in transformed space. By coupling the infinite elements with standard finite elements, an ordinary finite element procedure is used for simulation of wave propagation in an unbounded foundation due to external forces.

Records from near-fault earthquakes to close the distance where the wave propagation source is a special property that their behavior makes them different from other records. Mostly near-fault earthquakes have strong pulse velocity (pulsatile wave) with great period accompanied with permanent deformation of earth. Velocity pulse occurs in horizontal component perpendicular to the motion surface of fault which is resultant of directionality effect of fault rupture. The properties of pulse such as velocity record in near-fault earthquakes cause the response spectrum to show non-ordinary behavior in pulse period. Also, due to imposing much energy to structure in during short period by these pulses, most of earthquake energy is absorbed in first made hinges instead of extension of non-linear behavior and plastic hinges in height of structure and the extension of non-linear behavior is not observed. This absorption of energy causes large relative inter-story displacements. Considering today’s using energy dissipation systems is current due to reducing earthquake vibrations of structures, which one of these energy dissipation systems are passive viscoelastic dampers. In these dampers which their energy dissipation mechanism depends on velocity of motion or in other words, on loading frequency and to be active these dampers there is no need to determined level of external excitation and they act in every earthquake. For this purpose, a number of structural models have been modeled in 2D form in “OpenSees” software for different damping ratios due to the added viscoelastic damper, non-linear dynamic analysis has been done under acceleration of horizontal earthquake and the amount of reduction of displacement response and base shear have been studied.

Semiconducting carbon nanofibers (CNF) are prepared from three different sources, i.e., acetylene, ethanol, and cotton by the chemical vapor deposition (CVD) process. These fibers are having rich elastic, engineering and conductivity properties. Fresh self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact, without any segregation and blocking. To obtain maximum benefit from SCC, it has to be adopted in general concrete construction practice. Such practice requires inexpensive and medium strength concrete. This investigation aims to develop a medium strength carbon nanofiber self - compacting concrete (CNFSCC), which improves the fracture resistance characteristics of the concrete. In addition to that, the mechanical and structural properties of self-compacting concrete containing carbon nano-fiber with different concentration are experimentally studied by conducting suitable tests. The test results indicate that the presence of a reasonable concentration of CNF not only enhances mechanical performance, but also improves the structural characteristics of SCC.

This paper provides a comparison of the maximum inter-story drifts and tip acceleration of both a 16 and 30 stories building each with different structural systems; hybrid R.C moment frame with shear walls and hybrid steel frame with shear walls and X bracing which are equipped by passive dampers. Each of the building models were analyzed as fully non-linear structures for variety of dampers placements and subjected to a total of 4 different earthquake excitations. Three-dimensional (3D) finite-element models have been developed in the (FE) code LUSAS to predict the effects of passive damping on the vibrating structures. The manuscript tries to presents a rational comparison for determining dynamic response of seismic-excited high-rise buildings installed with friction and viscoelastic dampers in the cut outs of shear walls in order to capture their advantages in creating efficient damping systems. The results have shown that it is possible to achieve seismic mitigation, under all earthquake excitations, for all the structures considered in this study, by using appropriate damper types suitably located within the structure.