Ferdowsi Civil Engineering
Year:2010 | Volume:21 | Issue:2|Papers Count:9

To investigate the effect of isolation system on bridge response, two types of pier are studied. The bridge without isolator is designed based on AASHTO96 and then the system with and without isolator are modeled in DRAIN-2DX program. The nonlinear time history analyses are preformed on bridges subjected to different earthquake records.To study the effect of stiffness and yield strength of isolator on response of bridge with isolated pier, during the repetitive analyses, the isolator stiffness is varied from 20% to 100% of elastic pier stiffness in each step. The ratio of yield strength to pier tributary mass is varied from 5% to 20%.In each case, the maximum deck displacement, the isolator ductility demand the Pier Protection Index (PPI) and the deck residual displacement are computed and the results are presented in form of diagrams. Finally, based on results obtained from this research, the conclusion are made and the recommendations to design the isolated bridges are presented.

Excavation in urban plans influences the adjacent buildings and sometimes creates the irreparable damages. In this regard the effect of adjacent structure stiffness on the ground movement due to excavation is important. However, there are only a few studies in this area of research. In this paper, the interaction of excavation and its adjacent structure is studied using two famous finite elements codes (PLAXIS & SAP) and an elastoplastic constitutive model. For this purpose, the two excavation systems have been considered. The adjacent structure in the first system is a concrete bending frame. In the second system, instead of a real structure, an equivalent (in stiffness) elastic beam has been used. The achieved results indicate the considerable effect of adjacent structure on the ground movement due to excavation. In addition, the remarkable influence of excavation on internal forces of different members of structure is addressed. It is shown that the application of an equivalent elastic beam, which has the characteristic of simplicity and flexibility in consideration of different stiffness for a given building weight, can be used for evaluation of the interaction of excavation and its adjacent structure.

Steel columns filled with concrete, so called CFST columns are kind of mega composite columns that poses greater mechanical and daynamic behavior. In recent years, due to this enhanced behavior, more and more are being used specially in tall structures. They also result in more cost effective and easy to construct structures. In order to study these columns, an experimental program was lunched to provide detailed properties. In doing so, 12 specimens with different cross sectional geometry and D/t ratios with a 1/3 scale were constructed and tested. Testing was performed under cyclic dynamic manner using actuators.It was obseved that, both mechanical and cyclic behavior of CFST colums were enhanced while some cross sectional shapes behavied even better meaning acoordingly, circular, ortagonal and squared. Also, it was resulted that much ductility was introduced to the columns when they were used as CFST columns. The set up and experimental program as well as test results are provided in this paper. Conclusions and comparisons are also provided in this paper in the forms of cyclic graphs.

The formulation of simultaneous analysis of dynamic crack growth and contact of its faces in twodimensional domain is introduced. Displacement and traction boundary integral equations and additional contact equations are used simultaneously in one region in the time domain. The proposed method has the capability of automatic modelling of crack propagation and contact of crack faces in mixed mode fractures by adding only new elements in front of crack tips. This automatic capability of simultaneous analysis of dynamic discrete crack propagation and contact problem is not enhanced in any of available commercial softwares. In order to verify the proposed method and so as to show the versatile features and capabilities of the method, dynamic crack growth of edge cracks and contact of crack faces in a T shaped plate is analysed.

Large size direct shear tests (i.e.300´300mm) were conducted to investigate the interaction characteristics between clay-geogrid, sand-geogrid and clay-sand-geogrid. The lack of adequate frictional resistance between clay and reinforcing elements was compensated by using thin sand layers to encapsulate the geogrid. Results indicate that encapsulating geogrids in thin layers of sand is very effective in enhancing the strength and deformation behaviour of reinforced clay. Variations of bond coefficient indicate that the shear resistance between the geogrid and the soil can be larger than the shear resistance of the soil itself. The increase in the shear resistance is mainly due to the influence of the geogrid apertures providing some bearing resistance during shear. In order to investigate the effects of passive resistance provided by the transverse members of the geogrid, several tests were conducted with these members removed. Total shear resistance provided by the geogrids with transverse members removed was approximately 10% lower than shear resistance of geogrids with transverse members.

Historical researches concerning unit hydrograph (UH) demonstrate significant variation and presence of noise due to error in measurements and the assumption of linearity in rainfall–runoff relation. In this study, first, the UH is calculated for 16 storm events based on The least square method in a 449 hectare basin located in the vicinity of Riesel city, USA. In order to recognize noise frequencies, spectrums of the UHs are calculated for each UH by Fourier transformation. The results obtained from the spectral analysis are used for the noise reduction of the UH via a normal - weighted moving average method. From 16 smoothed UHs, one UH is selected as the representative UH of the basin by crossvalidation method. The results showed that the methods of the weighted moving average and cross– validation are suitable for obtaining a non – oscillatory and unique UH.

This paper deals with the results of experiments on strength of the secondary flow and vorticity in a channel bent with and wiuthout a spur dike located at section 75o of the bend. Experiments were conducted in a channel with a 90o bend. The results of experiments with spur dike for two cases of flat bed and scoured bed are compared. The three-dimensional Acoustic Doppler Velocimeter (ADV) was used for measuring the flow field. The comparison of three dimensional components of velocity was made in different sections and strength of the secondary flow and vorticity along the bend were analyzed.The results show that in the bend without the spur dike, The strength of the secondary flow and vorticity were maximum at about section 40 degree of the bend. While in the bend with the spur dike, maximum strength of the secondary flow and vorticity were maximum at about section 73.75 degree of the bend.The variations of secondary flow, vorticity and vortices in diiferent sections of the bend were also addressed in this paper.

Implementation of 3D Panel system in the constructional industry has increased over the last decades due to the advantages, such as lightness, simple installation and reduction in energy consumption.Thus, due to the fact that Iran is a country with high risk of earthquake, investigation of the seismic performance of this system and definition of its seismic parameters are necessary. Distribution of lateral load in pushover analysis is based on the first mode shape of the structure. However, nonlinear dynamic analysis is necessary to assess the maximum displacement and to specify the existent forces in the frame and the panel due to earthquake. This article begins by the modeling of the ‘1-story 1-bay steel structure sample’ that was tested experimentally. The derived results from the experiments applied to check the integrity of the model and to confirm the chosen elements. Then, frames with 3, 5 and 10 stories (filled in different bays by panel) are modeled and analyzed under Elcentro, Tabas and Naghan seismic records. Finally, it concludes that the reinforcement of one panel bay decreases the stresses in the major elements and provides a better seismic behavior in the structure.

The damaged concrete obtained from destruction of aged concrete buildings could be turned into crushed aggregates and reused for making concrete. By using recycled concrete, it can be eliminated the environmental problems of accumulation of unwanted concrete on the ground surface and also it will prevent the extraction of materials and stone from natural environments. In this research, the effect of microsilica and superplasticizer on the recycled concrete made of crushed aggregate has been investigated. some concrete with certain strength for recycling have been considered and also compressive, tensile strength and modulus of elasticity of recycled and normal concrete with and without microsilica and superplasticizer have been compared.102 specimens were cast with six different concrete mix designs of constant cement content (cement, microsilica), however, the type of aggregate, (natural, recycled, combination of both) and also the usage or the lack of the additive were different.The analysis of the results of tests show that in most of the concrete mix designs, by usage of microsilica and superplasticizer in recycled concrete it is possible to reach a concrete with higher compressive and tensile strength with compare to the normal concrete.