Sharif Digital Repository

In this paper, proper and safe planning of excavation method and design of support system in very weak rocks with case study of control room of Silveh dam are discussed. Silveh earth-storage dam, with 102 m height; is under construction in North-West of Iran. Due to numerous and various tectonic occurrences, the area of dam site is known as a high activity zone of Iran. In purposed location of control room, bedrock contains mostly weathered and crushed Shale and Schist. 60 m overburden and finite aquifers are another specific concern of this project. In this paper by using 3D finite element modeling, different stages of excavation and support system installation have been analyzed for the... 

In this study the effect of stress field on delamination and fiber/ matrix debonding in laminated composite panels is investigated from the micro-mechanical point of view by means of 3-D Finite Element Models. Specifically, the behavior of two-layer cross-ply symmetric laminates made up of SCS-6/Ti-24Al-11Nb Intermetallic Matrix Composite (IMC) during cooling from the processing temperature is studied. The results show that large plastic strains occur at the fiber/ matrix interface at the fiber end on the laminate free edge which may eventually extend to the interface of the layers of the laminate inflicting delamination damage. This phenomenon is more serious at the corner areas of the... 

Thin-walled cylindrical steel silos are susceptible to instability under wind pressure when they are empty or only partially filled. This paper investigates numerically the wind buckling behavior of a real steel corrugated silo with 8.02 m diameter and 17.62 m height, strengthened by open-section vertical stiffeners. Accordingly, comprehensive 3D finite element models were used and detailed linear and non-linear buckling analyses were conducted. The effects of sinusoidal corrugated sheet profile dimensions on this issue were specially explored. Wind load vertical and circumferential distributions were adopted from Eurocode. Two proposed circumferential pressure distributions for an isolated... 

Thin-walled cylindrical steel silos are one of the key structures for storage of materials in many industries and agricultural sectors. They are susceptible to instability under wind pressure when they are empty or partially filled. This paper investigates numerically the wind buckling behavior of three sample steel silos with stepped walls composed of isotropic rolled shells. Wind load vertical and circumferential distributions were adopted from Eurocodes. Two proposed circumferential pressure distributions for an isolated silo and a silo in a group with a closed roof were taken into consideration. Moreover, the effect of additional inward pressure, proposed by Eurocode, on buckling... 

The aim of this research is to obtain the bending moment and shear live load distribution factors (LLDFs) for interior girders of simply supported slab-girder bridges subjected to continuous loading, such as military tanks. The effective parameters considered in calculating the live load distribution factor were: Girders’ number and spacing, span length, slab thickness and the longitudinal to transverse ratio of deck stiffness. Over fifty 3D finite element models were created based on the existing information of bridges in the USA. An equation was obtained for the distribution factor and its validity was assessed against the numerical results. The proposed equation was compared with the... 

This current work considers the utilization of the completely Lagrangian technique, smoothed particle hydrodynamics to improve the 3D finite element model for numerical analysis of the friction stir welding (FSW) in the air and underwater conditions. This technique was primarily applied to simulate fluid motion because of various advantages compared to conventionally grid-based methods. Newly, its usage has been developed to analyze the metal-forming analysis. The temperature history, strain and stress distributions during the FSW process in the air, as well as underwater, were considered. Besides the cooling influence, the effect of traveling speed, friction coefficient, mesh size and the... 

Laser shock peening (LSP) is one of the life enhancement processes by inducing compressive residual stresses into the material. The effects of repeating LSP pattern on the residual stress is investigated numerically in this study. A 3-D finite element model was developed to obtain residual stress field in the material. FEM results have shown that increasing the number of peening impacts increase the magnitude and depth of compressive residual stress. Also the average surface residual stress in the impact region increased from −291 after 1 impact to −326, −343 and −356 MPa after 2, 3 and 4 impacts respectively. Moreover, the effects of repeating LSP pattern on fatigue crack growth properties... 

A three-dimensional (3D) finite element model (FEM) is developed to predict the progressive fatigue damage with provision for stochastic distribution of material properties. Fatigue damage model for low and high cycle fatigue considering plastic deformation is implemented in the FEM and the results are presented for Al 6061-T6, Al 7075-T6, Ti 6Al-4V and SS 316. Comparisons of the numerical and experimental results of stress-life reveal the validity of the approach. Also presented is the result of an investigation showing the effect of element types, element size, variation of material properties, and initial flaws on the randomness of fatigue life. The present fatigue damage simulation... 

In this paper, a micro-polar continuum model is presented based on the Cosserat theory for 3D modeling of localization phenomena. Since the classical continuum model suffers from the pathological mesh-dependence in strain localization problem, the governing equations are regularized by adding the rotational degrees-of-freedom to conventional degrees-of-freedom. The fundamental relations in three-dimensional Cosserat continuum are presented and the internal length parameters are introduced in the elasto-plastic constitutive matrix to control the shear bandwidth. The mesh independency of Cosserat model in strain-softening problem is verified and the effect of internal parameters is... 

Abutments of concrete arch dams are usually crossed by several joints, which may create some rock wedges. Abutment stability analysis and controlling the probable wedge movements is one of the main concerns in the design procedure of arch dams that should be investigated. For decades, the quasi-static method, due to its simple approach, has been used by most of dam designers. In this study, the dynamic method is presented and the obtained time history of sliding safety factors is compared with the quasi-static results. For this purpose, all three components of Kobe (1979) and Imperial Valley (1940) earthquakes are applied to the wedge, simultaneously, and the magnitude and direction of wedge...