Sharif Digital Repository

Grillage structures are used at roofs of some buildings and community halls and shopping centers and airports, or structures that used as bowers. The grillages is constructed with steel or concrete beams. In most of the carried out Researchs the twisting effect on these structures has been ignored. In this research the behavior of such structures with considering regulation and softwares limits by some simple programable assumptions is simulated. So with using MATLAB software a program extracted for grillages nonlinear analysis and its results was compared with common engineering software. In This approach in addition to pure bending, bending – torsion interaction is considered too and I... 

Nowadays in high-tech industries there is a serious demand for using advanced materials. Functionally graded materials (FGMs) are in the last generations of these group of materials. FGMs have shown good behavior in special conditions. According to sensitive applications of FGMs , there is a large amount of effort to understand it’s behavior in the presence of crack. Finite element method and other numerical methods, in recent years are widely used in modeling fracture problems.Remeshing requirements and mesh sensitivity are among the disadvantages of analyzing crack growth using the conventional FEM. Recent finite element methods such as extended finite element method, are proposed to model... 

These days steel frames are among the most widespread structural systems, and apart from this, tendency for using slender members in these frames, shows the need for study of effects of axial force and in other words stability of the structure and its members. When secondary effects due to axial gravity forces which results in lateral displacement of the structure come in action, they will reduce strength significantly; as a consequent ductility demand with raise. If this decreased strength exceeds the existing redundant strength, displacements will increase significantly and cause instability of the structure and its collapse. AISC 360-10 has introduced 3 methods for analyzing stability of... 

Fiber Reinforced Polymer (FRP) tendons are suitable to be used in concrete beams exposed to aggressive environments. This study proceeds the design and it presents the flexural capacity (in relation to the moment-curvature) for composite sections (reinforced with steel bars and pre-stressed FRP) rectangular, T-section which has been bent and broken. The failure is in attending with strain softening, stress hardening of fiber reinforced concrete (FRC) and reinforcing with steel bars and polymer. Using the predicted moment-curvature relationship, a numerical method is used to estimate the load deflection response at sample beams under concentrated and uniform loads. A parametric study will be... 

Blind source separation methods such as independent component analysis (ICA) and second order blind identification (SOBI) have shown considerable potential in the area of ambient vibration system identification. The objective of these methods is to separate the modal responses, or sources, from the measured output responses, without the knowledge of excitation. Several frequency domain and time domain methods have been proposed and successfully implemented in the literature. Whereas frequency-domain methods pose several challenges typical of dealing with signals in the frequency-domain, popular time domain methods such as NExT/ERA and SSI pose limitations in dealing with noise, low sensor... 

Computational Nano Mechanics growth has led researchers towards the development of new multi-scale models. Accordingly, in this dissertation, a step was taken towards introduction, presentation and creation of a new concurrent multi-scale by studying the feasibility of coupling of molecular dynamics methods and temperature related Cauchy-born.To do so, firstly, the above mentioned methods have been studied and then in order to perform molecular dynamics simulations, a program written in C++ language has been used. The accuracy of the written code has been confirmed through studying intuitive phenomenon of gas perfect particle exit from cylinder with an open end. The interpretation of out put... 

Nowadays, regarding to knowledge progresses in various fields,advanced materials for which have acceptable performance in sensitive and special conditions must be used. Functionally graded materials are advanced multiphase composite materials that are characterized by continues spatial variations in mechanical and thermal properties. Clearly, studying on fracture mechanics of FGMs is important because they are used in igh-tech and sensitive applications.In this research, numerical modeling of fracture mechanics in isotropic/orthotropic/ transversely isotropic FGMs via interaction integral method is performed. Both incompatible and non-equilibrium formulations of interaction integral are... 

Including control systems structures against lateral forces such as dynamic loads, earthquakes etc. are viscoelastic damper, that their use in recent years on the structure had positive results. Although the use of dampers improve certain behavioral characteristics, such as relative displacement, but can increase the structural acceleration and energy absorption structures. Passive damper performance depends on several factors such as temperature, time, frequency, stiffness of bracing and structures, type of loading that should any of these uncertain in the optimal design of controlled structures taken into account. Common method of achieve proper placement pattern of passive dampers, which... 

Because of mistakes in the design and calculation, incoherence between construction and design, structural changes, changes in loads and also damages caused by the passage of the time, concrete structures need to be improved and strengthened. Polymeric sheets reinforced by fibers (FRP), according to their appropriate characteristic, are more efficient for strengthening concrete structures. Most studies on confined columns refers to confined RC columns with FRP and less mentioned about prestressed columns. In this study, the behavior of prestressed columns is analyzed by modeling a case of prestressed column in a nonlinear analysis software. Samples of confined concrete columns with CFRP and... 

Prestressed concrete structures are used all around the world widely; especially for elements which are under the effects of bending like prestressed concrete slabs. In these sorts of elements the aim of designing is to control the tensional stresses and the cracks delivering higher strength. This can improve the capabilities of the structure, architecturally and economically. Seismic design of structures is based on horizontal component of ground motions. In recent years, it has been observed that the vertical component of ground motion could be stronger than horizontal one especially for those which have happened in near field sources. In these kinds of earthquakes the importance of... 

Structural system identification from vibration data is one of the most interesting research topics in the structural health monitoring area. Recently, realization and detection of the effects of damage when a structure is subjected to strong ground motion has become a great concern in earthquake and structural engineering communities. Seismic signal processing is one of the most reliable methods of detecting the structural damage during earthquakes. The structural responses during earthquakes are nonstationary with respect to both amplitude and frequency. The state-of-the-art time-frequency distributions when applied to vibration records were studied. Different methods of analysis for... 

In some cases, because of the need for installations, creating cutouts in the existing RC slabs will be necessary whereas these cutouts can cause weakness in the strength and stiffness of the slabs. Nowadays, expanding the use of FRP materials can provide the possibility of easier strengthening of such slabs. There are various methods for strengthening with FRP including Externally Bonded FRP sheets, Near Surface Mounted FRP rebars, and Mechanically Fastened FRP sheets. To select the most appropriate techniques for strengthening RC slabs with cutouts, it is essential to know different structural performance of these strengthened slabs. This research tends to model one and two-way spanning RC... 

In many structures, using long span girders due to architectural reasons is evitable. Studies show that in this situations, using plate girders is not only a non-economical choice, but also it reduces the structure performance, because of plastic hinges which would be formed in columns instead of beams, due to higher stiffness of girders. To overcome this difficulties, Truss girders or open-web ones are good choices for substitution. Recently, a novel lateral loading system named “truss bending moment system” equipped with buckling restrained braces (BRB) is also proposed. In this research, some structures with usual configurations are designed with both mentioned systems. In each case,... 

Explosion as a physical phenomenon have various effects on the environment, including living organisms, surrounding buildings, equipment and infrastructure there. Due to such extreme loading conditions, efforts have been made during the past three decades to develop methods of structural analysis and design to resist blast loads. The analysis and design of structures subjected to blast loads require a detailed understanding of blast phenomena and the dynamic response of various structural elements. The most appropriate method for evaluating the behavior of structures under blast loading is performance approach which specifies the response of structures against explosion. It seems that... 

Shear band is more relevant in porous medias rather than continuum media. Shear band is a narrow region of solid experiencing intense shearing. After initiation of shear band, the sliding on two sides of the band occurs. The area inside the shear band undergoes extreme plastic deformation, while experiences elastic unloading outside of the band. In porous materials, the direction of slip and discontinuity in displacement field is not same, as a result of dilation. In fact dilation requires an increase in the volume of the shear band zone. The main difficulty in modeling the shear band is that the width of shear band in contrast to the dimension of the media, is too small. Consequently, the... 

Steel Concentrically Braced Frames are common lateral load resisting frames. Poor design of this system can lead it to premature failure of braces. This failure may be due to non-elastic buckling of brace members or their connections. Design Codes divide Concentrically Braced frames into two groups: Ordinary Concentrically Braced Frames and Special Concentrically Braced Frames and for each, specific limitations have been determined for width to thickness ration and slenderness. Many of these limitation have been obtained on the basis of experimental tests. In this thesis steel braces behavior under cyclic loading is studied. For parametric investigation, Finite Element Method is used. Abaqus... 

The purpose of this thesis is assessment of seismic performance of self-centering concentric braced frames (SC-CBF). In this structures, the column under tension can uplift from the foundation at a specified level of lateral loading and by using some methods such as post-tensioning (PT) bars or tendons, the structure is able to self-center after severe Earthquakes. In this systems, PT bars and energy dissipation elements resist column uplift. The effect of energy dissipation ratio and initial stress in PT bars was investigated in design and performance of four four-story analytical models. Nonlinear static and dynamic analyses were conducted to compare some parameters in these four models... 

Tests have shown that concrete post-tensioned slab under heat condition suffer a significant reduction in stiffness and strength. Design and implementation of post-tensioned concrete slabs with large spans of industrial structures exposed to extreme variation in temperature can be possible with detailed research on its behavior under heating condition. In this study numerical modelling of PT concrete slabs with unbonded tendons under heating condition was created based on available test results in the literature. A parametric study has been carried out and the results are presented for concrete coefficient thermal expansion, thermal contact conductance between the concrete and the cables,... 

Assessment of the probability of collapse or exceeding other limit states is one of the major goals of Performance-Based Earthquake Engineering. Moreover, other beneficial materials such as estimation of loss of money and downtime, which make it convenient for decision makers to judge the condition of a structure and take wise steps about it, can be drawn from the results of such an assessment.Current work investigates the probability of collapse and also immediate occupancy limit states at three discrete hazard levels of 50%, 10% and 2% in 50 years and also by utilizing mean annual frequency approach for three archetypes of steel special moment-resisting frames of 4, 8 and 12 stories.Ten... 

Many reinforced concrete frame buildings with masonry partitions have been built all around the world. Observations from past earthquakes show that the partitions can endanger the life of buildings occupants and lead to significant damage and loss. Failure of the partitions can be caused by dynamic vibrations and in-plane and out-of-plane loads/displacements. The interaction between in-plane and out-of-plan behaviors and location of partitions, nonlinearity and higher modes of the structures could affect the out-of- plane seismic demands on partitions. Therefore, there is a need for a comprehensive assessment in order to limit the loss in buildings with masonry partitions. This research...