Sharif Digital Repository

Dynamic compaction is a widely used soil deep improvement method in dry and/or saturated soils. Despite its vast application, numerical and /or experimental modeling studies of dynamic compaction due to impact are little. In order to clarify the ambiguities in process and to present a comprehensive design approach, numerical modeling of dynamic compaction in dry soils with PISA (A fully coupled dynamic finite element code: Program for Incremental Stress Analysis) has been done. Because the geometry and loading configuration are symmetric around the falling tamper (load centerline), a two-dimensional axisymmetric simulation has been used. Here for sake of simplicity, initial velocity of... 

Mechanical properties such as Young's and bulk modulus and strength of material is improved by adding Nano fillers to polymer substrates. Hence by adding Nano fillers such as graphene and carbon nanotubes to polymer substrates it is possible to achieve better properties in resultant nano composites. The aim of this study is to investigate the improvement in polymer-based composites properties by adding graphene Nano fillers for shock absorption. In this study, molecular dynamics method is used to model the molecular behavior of the material. First, a sample cell that have the properties of the whole material, is modeled, then by applying impact loading in modeling software, the response of... 

In most of the engineering applications, the mechanical behavior of materials in high strain rate deformations differs from their behavior in quasi-static deformations. In some engineering problems like impact loading on structures, metal forming and explosive forming, the range of strain rate is about . Taylor impact test is one of the experiments used for characterizing the dynamic behavior of materials in high strain rate deformations. In the Taylor impact test a rigid cylindrical projectile is impacted normally onto a hard and massive surface (anvil), the projectile deforms by mushrooming at the impact end. With plastic wave propagation analysis, the plastic deformation of projectile is... 

Given the increasing development of exploitation of deepwater oil and gas resources, access to realistic solutions for analyzing and designing offshore platforms is a major factor in facilitating the exploitation of oil and gas resources in these areas. There is a huge amount of oil reservoirs in deep water beds, and Tension leg platform (TLP), as a compliant structure, are suitable for oil extraction in deep water.The advantage of using these platforms is the ability to rotate and move at a rate of rotational and transient freedom. Surge motion The TLP is a 120-second long period; In high-amplitude and low period waves, the platform faces a tendon rupture due to high waves forces and bad... 

In this thesis, experimental and numerical investigations are performed on dynamic behavior of fiber reinforced concrete (FRC) by split Hopkinson pressure bar (SHPB) and penetration tests. In the experimental part, effects of parameters such as quasi-static compressive strength of matrix (36 and 48 MPa), strain rate (3*10-5 up to 100 s-1), type of fibers (crimped steel, hooked-end steel, micro polypropylene and micro polypropylene) and volume fraction of the fibers (0%, 1% and 2%) are studied by employing SHPB apparatus on testing more than 150 specimens. Also, different types of FRC panels with 5 cm thickness were casted to perform 20 penetration tests with compressed gas gun apparatus. The... 

Reinforced concrete shells are widely used to cover the small to large area with more aesthetics at minimum cost. Shell structures carries load through their shape rather than material strength. Funicular shells are special type of shells that their shape is obtained so that stresses be compressive under a special load (for shell, this load is its dead weight). This study deals with forced vibration of funicular shells on a rectangular ground plan under impulse loads using shallow shells theory. Two boundary conditions, simply supported and clamped, are considered. Displacement components are product of position and time functions. The analysis is based on the expansion of displacement... 

The investigation of non-prestressed concrete components subjected to impact loadings has been reported in the literature. However, the knowledge on the impact-resistant capacity of pre-stressed concrete components is very limited. In this study, behavior of pre-stressed concrete slabs strengthened by FRP sheets is investigated. The behavior of strengthened pre-stressed concrete slabs under impact load is analyzed using finite elements method. The effects of FRP strengthening of pre-stressed concrete slabs to resist impact loads have been studied using ANSYS software. Pre-stressed concrete slabs have been modeled without/with different FRP strengthening measures. Pre-stressed concrete slab... 

Precise numerical models to predict responses and damage of FRP strengthened RC slabs to impact loads are limited in the literature. The behavior of (RC) slabs strengthened by FRP sheets is investigated. The behavior of strengthened RC slabs under impact load is analyzed using finite elements method. In this study, the effects of FRP strengthening of RC slabs to resist impact loads have been performed using ANSYS software. RC slabs without/with different FRP strengthening measures have been simulated in this study. RC slab without strengthening and RC slab strengthened with FRP sheets applied to the tension face of the slab have been included in the model. Each slab is subjected to repeated... 

In the experimental approach, graphene and Graphene Oxide (GO) were synthesized through a chemical method. In order to study the quality of GO, characterization tests were performed. Then, reinforced polymer with GO and graphene was made. Moreover, tension, compression and Split- Hopkinson pressure bar tests were performed on standard samples of reinforced polymer nanocomposite. The experimental data show that nanoparticles have a destructive effect in very low and high percentages for extension test as well as in high percentages for compression test. On the other hand, graphene is more effective than GO on improving material properties. Furthermore, comparison of compression results in...