AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2010 | Volume:42 | Issue:1|Papers Count:16

It is widely known that the bearing capacity of a shallow foundation is reduced when the foundation is subjected to rocking moment and horizontal loads during an earthquake event. This paper discusses a series of numerical solution carried out in FLAC that calibrate with results of experimental testing on small scale reinforced foundation in order to measure the bearing capacity of a reinforced shallow foundation due to horizontal cyclic loading. In this study, the horizontal bearing capacity ratio (HBCR) was compared with vertical bearing capacity ratio (BCR) and the effect of such parameters as number of cycles and loading magnitude on the dynamic bearing capacity of reinforced soil was discussed.

Seepage under coastal structures including coastal dikes is one of the major issues for controlling stalinization of coastal lands and stability of the related structures. So far, for analysis of seepage under hydraulic structures much research works have been conducted in the form of numerical models. However, less field and laboratory works have been done for evaluating of the numerical models. In the present research, a laboratory model was made to simulate seepage and its controlling measures under coastal dikes. The model consists of a flume 8m long, 1m deep and 1m wide, in which horizontal blanket and vertical cut off were provided by Perspex sheets. The flume was made of steel frame and Perspex as well as thick glass sheets. The foundation material was made of clean fine sand, compacted to a uniform density and covered the bottom 50cm of flume. Perspex sheets were employed as blanket and cut off variable length. The piezometric heads at the downstream side of dike were measured using small diameter clear plastic tubes. The results of the test showed that the optimum ratio of blanket length and cut off depth to the depth of water and the thickness of foundation at the upstream side of dike for minimum seepage loss and control of piping was 8 and 0.8 respectively.

Plate in steel plate shear walls has high capability for earthquake energy damping. The Experimental investigations show that the plate zipping in corner and edge of plate is the cause of damage and failure in steel plate shear walls. For prevention of zipping the first, classic theory is investigated using finite element and then a steel plate shear wall specimen was tested experimentally with using four stiffeners in the edges. The results show that the plate zipping doesn't occur when the stiffeners are used in the edges of plate. In the specimen, tearing was started from the stiffener corner and then extended up to the triangular area which is closed between stiffener and fish plate edges. Finally the tearing speard smoothly to the edge of fish plate in the out of aforesaid triangular area. Also the stiffeners are capable to create a post buckling field after tearing of plate.

Fluid hyper-element is usually utilized to model semi-infinite region in dynamic analysis of concrete gravity dams. This part of water domain is assumed to have constant depth that extends to infinity in the upstream direction. The accurate dynamic analysis of concrete gravity dam is obtained by employing two dimensional semi-infinite fluid element.The usual method for calculating the impedance matrix of fluid hyper-element is dependent on the solution of a complex eigen-value problem for each frequency. In the present study, an efficient technique is proposed which simplifies this procedure significantly, and results in great computational time savings. The accuracy of this method is tested under various conditions thoroughly and concluded that efficient technique is accurate under all practical conditions.

ABA design code increases the reliability of a structure by means of multiplying the partial safety factors by load and resistant. In this paper, the reliability index of code-based designed structures are calculated and investigated. Also it is shown that the different values of reliability index are calculated for the different values of the coefficient of variation. This result expresses the importance of the code design collection on basis of reliability theory. In other words, the partial safety factors of design parameters for ABA must be calculated on basis of the local statistical data (in favor of Iran) of the parameters.

Uniform hazard spectrum is a modern and effective method in achieving the design spectra that provide a uniform desirable safety level in performance of structures with different periods. In this study uniform hazard spectrum is determined for Tehran region considering the area and line seismic sources in the design area using the probabilistic analysis of seismic hazard and spectral attenuation relations. As the ground motions in nearby fault regions cause large damage, in this research the effects of site closeness to the seismic sources is taken into account considering near source spectral attenuation relations besides the far field attenuation ones.The results gained by this method are presented in the form of uniform hazard spectrum, peak ground acceleration and spectral acceleration maps in different periods. Uniform hazard spectrum is obtained by applying approximate method using average values of spectral acceleration in two or three controlling periods and it is compared to the spectra suggested by UBC97 and Iranian 2800-84 codes.

Sand and clay soils are the most usually common soils that constitute the subgrade of roads in northern parts of Iran. The clay soil has high plasticity index. Also they have high strength in dry condition, in saturated state, they lose most of strength and during this time, sustain much swelling which is dangerous for pavement. Sandy soils in coastal zones are termed Beach sand and have considerable strength in confined state. However In unconfined state, because of their uniform gradation and lack of cohesion, they will be washed out by water flow. In this research, the effects of Waterproof cement on engineering properties of these soils compared to Type 2 cement and Lime have been considered. In order to investigate the effects of the above materials on improving soil properties, Atterberg limit, Unconfined Compressive Strength and CBR tests have been carried out. It was found that the Waterproof cement has superior effect on strength properties of soils compared to the two other additives. The tests have also shown the average effect of this additive on the Plastic properties of soils.

fiber reinforced soil behaves as a composite material in which fibers of relatively high tensile strength are embedded in a matrix of soil. Shear stresses in the soil mobilize tensile resistance in the fibers, which in turn imparts greater strength to the soil. In this paper a study on the influence of synthetic fibrous materials in improving the dynamic strength characteristics of a fine sandy soil is reported. The study is aimed at converting fibrous carpet waste into a value-added product for soil reinforcement. A series of stress controlled cyclic triaxial tests were carried out on fine sand specimens reinforced with randomly distributed carpet strips. The dynamic deformation properties of the reinforced sand are defined in terms of shear modulus and damping ratio. The effects of parameters such as fiber content and aspect ratio, number of cyclic loading and the level of confining pressure on the aforesaid parameters were investigated. The results clearly indicate the increase of damping ratio of reinforced samples in different confining pressure. The increase is more pronounced in higher fiber contents and aspect ratios.

The vehicle load repetition on the pavements leads to further deflections due to the material softening and the reduction of pavement stiffness. In this research, the stiffness reduction studied using a back analysis of surface bowls under wheel load. In this back analysis the visco-elastoplastic model and the finite element method used. There seems to be no evidence of evaluating the stiffness reduction of pavements using visco-elastoplastic modeling of asphalt concrete behavior. The results indicated that this modeling approach provides a more accurate predication of performance and useful cycle life of asphalt mixtures when compared to the visco-elastic models.

Steel plate shear walls have been used in structures as a lateral load resisting system since 1970. Main advantage of thin steel plate shear wall is buckling of steel plate under tension field action. Generally, there are two methods to delay the steel plate buckling, using stiffeners or concrete cover which attached to the steel plate by shear connectors.In the present study, a numerical approach has been used to investigate the shear behavior of composite shear walls under lateral loading. Furthermore a geometrical optimization analysis was carried out by changing the concrete cover thickness and distance between shear connectors. The results of numerical analysis, show increasing concrete cover thickness will result decreasing stress concentration in steel plate and distributing them. Furthermore the result show that decreasing distance between shear connector will result increasing the strength and stiffness of shear panel. Finally studying the models deformation the optimum concrete cover thickness and distance between shear connectors are proposed.

As experiments show, there is nonlinear behavior of carbon nanotubes after exceeding a certain boundary surface while loading continues. Avoiding being involved in molecular dynamics methods and quantum mechanics approach, a continuum macro mechanics based method is employed to predict the nonlinear behavior of bonding forces in carbon nanotubes. Both analytical and numerical approaches, assuming elasto-plastic behavior of tubes are considered in this research. The presented results are well compared with the test as well as molecular dynamics results. Finally, the limitation and advantages of the proposed method are pointed out.

This research investigates the behavior of reinforced concrete columns subjected to eccentric loading (combination of axial loading and bending moment) with experimental and numerical methods. The columns are reinforced and confined with regular spiral and cross spiral to enhance their strength and ductility. Fourteen R/C circular columns subjected to different load eccentricity with two different grades of spirals steel are experimentally tested. The force, axial and lateral displacement and concrete strains in different locations are measured during the testing. The columns are 2000 mm long and 250 mm diameter. The results show that regular spirally circular columns have more strength as compared with the cross spirally circular columns but the ductility of cross spirally columns has increased with respect to the regular ones. It was also observed that the use of higher yield strength for transverse reinforcement caused considerable increased ductility with respect to lower yield strength reinforcements.

Basics of dynamic push-over analysis and static push-over are same. But in the dynamic case the wave or seismic loads are exerted to structure dynamically. With increasing intensity of dynamic loading in every step, structure would then be analyzed. Results of these two analyses are “push-over graphs” that show behavior of structure. Two platforms were selected for investigation. At first static push-over analysis and then dynamic push-over was performed for two platforms. Results of the two analyses were compared to each other. FEM based program “ABAQUS” was used for modeling. In this investigation, following results were found: Jackets behavior in both dynamic and static push-over analysis is same for linear range of jacket behavior, but in nonlinear range, results are different. In dynamic push-over analysis reserve strength of jacket structures was estimated to be higher than that of static push-over analysis. In dynamic push-over analysis ductility capacity was increased compared with static push-over and structure can bear more partial failure in comparison with static case.