Sharif Digital Repository

The continual deterioration and insufficient strength of reinforced concrete (RC) structures has been a vital problem in the field of civil engineering such an extent that traditional methods of strengthening found to be inconvenient. Nowadays by increasing demands for retrofitting of structures, it necessitates the application of efficient, inexpensive and unobtrusive methods of strengthening. Common way on retrofitting was to use of steel plates externally bonded to RC members. Although this technique has proven to be reasonably effective, it has several distinct disadvantages such as susceptibility of the steel plates to corrode and the excessive weight of steel plates when used in... 

In this research, solidification and microstructure of ductile cast iron was simulated using Fourier heat transfer equation. Using Fourier heat transfer equation, distribution of macroscopic temperature with heat transfer coefficient was obtained. The purpose of simulation, forecasting ductile iron microstructure, including grain size, number per unit volume of graphite (NC), microstructure including volume fractions of ferrite and pearlite and graphite phases. Knowing the phases of the microstructure and nodule count and the use of empirical relationships, we can estimate mechanical properties. In this regard, all transformations during cooling of molten ductile iron was simulated. Results... 

This thesis presents an extension of an analytical method previously introduced for evaluation of the deformation capacity of RC columns. The method utilizes fiber elements to arrive at nonlinear moment-curvature relationship for each segment. An existing stress-strain model has been modified and used in this study. This model considers the crushing failure of confined concrete, buckling of longitudinal reinforcements in compression, and their fracture in tension. It also accounts for the spiral fracture. This method was employed to determine the force-displacement diagrams for circular RC columns dominated by flexural mode of failure, and was calibrated against a number of relevant... 

After the 1994 Northridge earthquake when investigations show clear results for brittle failure near Beam-Column rigid Connections, research on these connections begun and various theories were suggested for better performance under cyclic loads. One of the appropriate ways is shifting yield beam location from beam-column connection to the beams only. Reducing the capacity of the beam through the beam flange or web far enough from the column, creating special ductile region in the beam. In this thesis, weakening is made by creating an elliptical opening in web beams. If the correct design criteria for this type of connection are suggested, it can satisfy the "weak beam - strong column" and... 

In recent decades, the soil-structure effect has been considered in seismic studies. Most of these researches are based on the premise that the foundation is bonded to the ground. However, several examples of structures that experienced uplift have been reported. Uplift affects the soil-structure contribution and nonlinear behavior of the structure. It seems that a parametric study should be done for the simultaneous effects of the soil-structure interaction, foundation uplift and inelastic behavior of the superstructure. Although the most accurate methods to estimate the behavior of structures is the nonlinear time history analysis, this analysis is very time consuming. The endurance time... 

It is well-known that the behavior of soil-structure systems can be well described using a limited number of non-dimensional parameters. This is the outcome of researches based on the premise that the foundation is bonded to the ground. Here, it is shown the concept can be extended to systems with foundation uplift. A set of non-dimensional parameters are introduced which controls the main features of uplifting systems. The super-structure is modeled as an equivalent single-degree of freedom system with elastic behavior mounted on a rigid foundation resting on distributed tensionless Winkler springs and dampers. The effect of foundation uplift on response of soil-structure systems are... 

Zipper frames were proposed to provide a solution of prevention of forming soft Story due to the existence of unbalanced vertical load in Chevron frames. In this study, at first, by performing a nonlinear pushover analysis on the 2D zipper frames with 3, 7 and 12 story and 3 span that the middle one are braced, a Response modification factor for zipper frames is proposed. Then, The seismic behavior of zipper frames is evaluated under far and near-fault earthquakes by nonlinear time history analysis and at the end of the research, the cyclic behavior and energy absorption capacity of these frames are compared with the 2-story-X chevron frames with 3 and 7 story. It is concluded that the... 

Recent studies on inelastic behavior of soil-structure systems indicate that seismic design codes provisions, which use the same response modification factor for fixed base structures and soil-structure systems, are not appropriate and could lead to an increase in ductility demand of structures (as a part of soil-structure system). As a result, to reduce design base shear and design forces with regards to collaboration of soil-structure interaction could be in non-conservative manner. In all of these studies, the ductility component of the response modification factor (i.e. Rµ ) has been the major concern and the overstrength component has been ignored. However, the existence of... 

In this research, the effect of nonlinear behavior of soil on the nonlinear responses of super-structure has been investigated. During the design process of practical buildings, engineers usually disregard the effect of soil-structure interaction. In some cases in which the effect of soil-structure interaction is considered, nonlinear behavior of soil usually is modeled through an equivalent linear method which is proposed by the most existing design codes. Past studies show that considering the effect of soil-structure interaction, could change the responses of super-structure in comparison with those whose base are fixed. In many of these studies, nonlinear behavior of beneath soil is... 

Regarding the numerous casualties and financial losses due to intense earthquakes, the ductility is considered of the main importance in addition to stability, stiffness, and strength criteria of the structure’s connections. In order to enhance the seismic behavior of the structures in such severe earthquakes, design codes for steel structures have suggested special types of connections. Among them, bolted end plate connection is considered a conventional type of connection used for creating ductile semi-rigid connection.In this study, in order to simulate the behavior of this joint, a 3-D finite element model is developed in Abaqus software, in which the inelastic behavior of the materials... 

To investigate the accurate performance of a structure, the knowledge of the way its connections function, is of great importance. Moreover, cognition of the actual behavior of connections which is often semi-rigid can lead to better apprehension of the actual and more accurate behavior of structures, whilst it is often considered to be pinned or fully-rigid.Therefore, in this study a new semi-rigid steel connection of beam to column will be introduced, and its behavior will be investigated using commercial finite element packages along with mathematical approximate modeling methods. One of the features of this connection is that its behavior mainly depends uponfolding of top and bottom... 

A generic single-span frame has been used to represent a shear-flexural building and the degree of participation of overall shear and flexural behavior in mode shapes, is controlled by dimensionless parameters of α, δk and δp. By evaluation of modal analysis results, one may conclude the extent to which each parameter affects the dominancy of shear/flexural behavior. By understanding the relation between the abovementioned parameters and proportion of shear/flexural behavior of structures, effects of these parameters and consequently trend of modal shapes on the nonlinear analyses results would be investigated. According to nonlinear analyses results of the flexural structures, ductility... 

This study inspects the flexural response of RC beams at the presence of compressive GFRP bars as well as tensile bars. Total of 9 reinforced beams were investigated. Three values of tensile reinforcement percentage were considered. For each tensile reinforcement value, three types of compressive reinforcement were taken into account which are classified into zero compressive bars, less than tensile reinforcement value and similar to tensile reinforcement value. The concrete was used in this study is C45 and as a constant parameter.Specimens were tested with four-point bending method using the actuator equipped at the strong floor laboratory to attain maximum flexural strength and... 

It used to be widely accepted as a virtue in engineering society that, fibers are generally used as mechanism to resist cracking and increasing the strength of concrete in some cases. Since 1990, fibers are usually used in concrete to control cracking due to plastic shrinkage and to drying shrinkage. They also reduce the permeability and bleeding of concrete. Some types of fibers produce greater impact, abrasion and shatter-resistance in concrete. Studies turn this notion to cognition that among all types of existing fibers, Steel Fiber and Polypropylene Fiber resulted the highest improved behavior in concrete. The Ultra-High-Performance Concrete which heated the debate in recent papers... 

This paper aims at investigating the seismic behavior of strengthened reinforced concrete (RC) shear walls using a 3D finite element analysis. A series of four different configurations of carbon fiber reinforced polymer (CFRP) composites, four different schemes of steel elements and two different schemes of concrete jacket are utilized to compare the two methods of retrofitting RC shear walls with similar dimensions and reinforcement ratios. Nonlinear simulations of the RC shear walls are conducted under the action of lateral cyclic loading in ABAQUS Explicit software. In addition, the numerical modeling for RC walls strengthened by CFRP composites as well as steel elements are validated... 

Every year hundreds of thousands of lives are taken away worldwide by natural disasters such as earthquakes. Walls made of concrete blocks or bricks, are amongst the most vulnerable type of walls, which tend to collapse during an earthquake. Due to their good sound and thermal insulation properties, unreinforced masonry (URM) walls are widely used in partitioning many of the commercial and residential buildings worldwide. URM is considered one of the most common types of partition wall systems in many of the school and hospital buildings and commercial buildings.URM partition walls are known to have very low drift capacity in seismic events and the failure mechanisms are known to be mostly... 

Reduced beam section connection was one of the connections that were introduced and prequalified by SAC project to replace pre-northridge connections. This connection reduces both flanges of the beam at appropriate distances from beam to column connection to make a fuse protecting welds from brittle fracture. The RBS is prequalified in limited span-to-depth ratio, for designing this connection for short and deep beams may effect its performance. Since these limitations are based on limited experiments, forty three numerical models were analysed to recheck them in this study. These models are verified based on two published experiments and are capable of predicting all known yield mechanisms... 

Theory of Critical Distances (TCD) is one of the methods that has attracted the scientists in life estimation of fretting fatigue problems in recent years. Less difficulty and less time consuming features of this method in comparison with other methods like fracture mechanics are the attracting aspects of this theory. In this research, the capability of the Theory of Critical Distances in life estimation of combined bending and tensile loading modes in fretting fatigue for the pads with sharp edges has been evaluated. This included the evaluation of this method in lifetime estimation of 316L stainless steel for fretting fatigue in two different types of heat treatments and the evaluation of... 

Severe plastic deformation (SPD) processes, in addition to increasing the strength of alloys, reduce their ductility. Aluminum alloy 2024 in the initial annealing state (420°C, 150 minutes) is failed after 5 passes if subjected to the multi-directional forging (MDF) process at room temperature. Therefore, in this project, with initial effective strains of 1 and 2, intermediate annealing was used at temperatures of 150°C, 250°C and 350°C (20 minutes) between process passes. This not only maintains the major strength created in this alloy after the initial passes but also provides the capability of applying more passes in this process. After each step, the microstructural examination was... 

In this dissertation, using experimental and numerical methods, the effects of grain morphology on the formability of sheet metals are investigated. In this regard, in the first stage, by conducting heat treatment on two different sheet metals with bcc and fcc crystal structures, different grain sizes are produced. Using metallographic observations, these grain structures are examined and the grain sizes are measured. Tensile test and Nakazima formability test have been implemented on these specimen. The grains are also shaped in the rolling process and different grain morphologies are created. In the second stage, a software has been developed to generate various grain structures and...